MET 06- Winds

ATC will only report wind as gusting if: *gusts exceeds mean speed by 10 kt
Explanation: A gust is reported when the maximum observed wind speed within the preceding 10 minutes exceeds the mean wind speed by 10 knots or more. This indicates a significant fluctuation from the average wind conditions.
Key Data:
•
Criterion: Gust speed exceeds mean speed.
•
Threshold: 10 knots or more difference.
•
Averaging period for mean wind: Past 10 minutes.
•
Averaging period for gusts: Three seconds.

large pressure gradient is shown by: close spaced isobars – strong winds ()
Explanation: The pressure gradient force, which initiates air movement (wind), is determined by the difference in pressure over a given horizontal distance. When isobars (lines of equal pressure) are closely spaced on a weather chart, it signifies a rapid change in pressure over a short distance, indicating a steep or strong pressure gradient. A strong pressure gradient force results in strong winds. Conversely, widely spaced isobars indicate a weak pressure gradient and lighter winds.
Key Data:
•
Pressure Gradient: Rate of pressure change over distance.
•
Isobar Spacing: Closer spacing indicates a steeper gradient.
•
Pressure Gradient Force (PGF): Proportional to the pressure gradient; causes wind.
•
Wind Speed: Proportional to PGF; strong gradient means strong wind.

What causes wind at low levels? *Difference in pressure
Explanation: Wind is generated by horizontal pressure differences between high and low pressure systems. This difference creates a pressure gradient force (PGF) that acts directly from high pressure to low pressure, initiating air movement. The magnitude of the pressure difference over distance determines the strength of this force and, consequently, the wind speed.
Key Data:
•
Wind is caused by horizontal pressure differences.
•
Pressure Gradient Force (PGF) is the initiating force.
•
PGF acts from high pressure to low pressure.
•
Spacing of isobars indicates PGF and wind speed.

The relationship between the wind at 2000 ft (typically above the friction layer) and the surface wind in the Northern Hemisphere is significantly influenced by surface friction.
What is the relationship between the 2000 ft wind and the surface wind in the Northern Hemisphere? *surface winds blow across isobars towards a low
Explanation: At 2000 ft, generally considered above the friction layer, the wind tends to flow nearly parallel to the isobars, balanced primarily by the pressure gradient force and Coriolis force. At the surface, friction slows the wind speed, reducing the Coriolis force. This imbalance causes the surface wind to deflect across the isobars, flowing towards the lower pressure area.
Key Data:
•
Surface wind is affected by friction; wind at 2000 ft is typically above the friction layer.
•
Friction reduces surface wind speed compared to wind aloft.
•
Surface wind blows across isobars, angled towards lower pressure.
•
Average angle of surface wind across isobars over land in the Northern Hemisphere is about 30 degrees.
•
Flowing into low pressure areas at the surface leads to rising air

In the Northern Hemisphere, warmer air is associated with comparatively higher pressure aloft, and colder air with lower pressure aloft. With the South warmer than the North, there is a horizontal temperature gradient establishing lower pressure aloft to the north and higher pressure aloft to the south. Upper winds flow parallel to these pressure features with lower pressure to their left. This configuration requires the wind to blow from the west. This westerly thermal wind component increases the strength of any pre-existing westerly wind with height.
Key Data:
•Warmer air South, colder air North creates a horizontal pressure gradient aloft.
•High pressure aloft South, Low pressure aloft North.
•Upper winds flow parallel to pressure features with low pressure on the left in the NH.
•This results in a westerly thermal wind component.
•Westerly winds generally increase with height in the NH.
•Upper wind is the vector sum of the base wind and the thermal wind component.

On a weather map where isobars are closely packed, the surface winds are likely to be: *Strong and blowing across the isobars
Explanation: Closely spaced isobars indicate a steep pressure gradient. A steep pressure gradient force generates strong winds. Surface friction slows the wind and reduces the Coriolis force, causing surface winds to blow across the isobars towards lower pressure, not parallel to them.
Key Data:
•Closely spaced isobars indicate a strong pressure gradient.
•A strong pressure gradient means strong winds.
•Surface friction causes wind to blow across isobars towards lower pressure.
•Surface winds are slower and deflected compared to winds above the friction layer

The concept of the Cyclostrophic Wind is highly applicable to the intense, localized, and highly curved wind fields found within the core of a tropical storm or hurricane.
1. Definition: Cyclostrophic wind occurs when the Pressure Gradient Force (PGF) is balanced primarily by the Centrifugal Force (CF), resulting in the Coriolis Force being considered negligible.
2. Application in TRS: This model is most valid in low latitudes (near the Equator, where Coriolis is small) and in systems with extremely steep pressure gradients and high wind speeds, such as intense tropical storms or tornadoes.
3. Operational Context (2000 ft): The tropical storm features extremely strong winds at low levels. While the lowest surface layer is affected by friction, the circulation at 2000 ft is still characterized by high curvature and extreme velocity, making the cyclostrophic balance a useful approximation for describing the wind speed just above the surface layer in such an intense vortex.
⭐️ ⭐️ Key Data to Remember:
• Cyclostrophic Flow: PGF balanced by Centrifugal Force; Coriolis negligible.
• Location: Used for intense circulation systems in low latitudes (e.g., Tropical Revolving Storms, Tornadoes).
• Wind Speed: Winds can be high (up to 200 kt in a tornado vortex).

The Föhn wind is a warm, dry, descending wind experienced on the leeward side of a mountain barrier. The principal warming mechanism is compressional (adiabatic) heating as the air descends the slope. This air warms at the Dry Adiabatic Lapse Rate (DALR) after losing much of its moisture during ascent on the windward side, resulting in a significantly higher temperature on the lee side compared to the windward side at the same elevation.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Mechanism: Descending air warms adiabatically due to compression.
• Effect: Produces clear, dry, and turbulent conditions on the leeward side.
• Temperature Change: Temperature increases can be substantial, sometimes exceeding 10°C (or 20°C for the Chinook).
• Examples: Föhn (Alps), Chinook (Rocky Mountains), Zonda (Andes).
• Aviation Relevance: The presence of a Föhn wind indicates possible mountain waves and associated Clear Air Turbulence (CAT).

Rotor clouds are turbulent cumuliform clouds that form in the rotary circulation (rotor zone) beneath the crests of strong standing mountain waves on the leeward side of high ground. This rotor zone is where the most severe turbulence in a mountain wave system is encountered. The air within the rotor cloud rotates about a horizontal axis and contains strong vertical motions that produce extreme turbulence and hazardous flying conditions. On occasion, this turbulence can be as violent as that experienced in the worst thunderstorms.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Formation: Located on the leeward (downwind) side of mountains, beneath wave crests.
• Turbulence Intensity: Classified as Severe or Extreme Turbulence.
• Aviation Hazard: Presents a major hazard due to violent vertical motions; pilots should avoid flight through or near the rotor zone.
• Visual Warning: Often visible as ragged cumulus or stratocumulus parallel to the ridge, serving as an unmistakable visual warning of severe wind disturbance.

wind will be fastest at the Low – cyclone- circulation is Anticyclonic.
Common misconception:
Anticyclonic – means – talking about anticlockwise circulation

The sea breeze is typically stronger than the land breeze. This difference arises because the land heats up more intensely during the day than it cools at night relative to the adjacent water, creating a greater temperature contrast and, consequently, a stronger horizontal Pressure Gradient Force (PGF) to drive the sea breeze circulation.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Sea Breeze Speed (Day): Typically around 10 knots in temperate latitudes, extending 8 to 14 NM inland. In tropical areas, speeds can reach 15 knots or more.
• Land Breeze Speed (Night): Typically weaker, about half the speed of the sea breeze, commonly around 5 knots in temperate latitudes. It usually extends only about 5 NM out to sea.
• Mechanism: The greater diurnal temperature difference over land during the day drives a stronger circulation (sea breeze) compared to the night (land breeze).

The Anabatic wind is an upslope wind. It occurs during the day when solar heating warms the air adjacent to mountain slopes. This warmer air becomes less dense and flows up the slope.
The downward movement of air along a slope, usually occurring at night due to cooling and increased density, is characteristic of a Katabatic wind.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Anabatic Wind: Occurs during the day.
• Movement: Upslope (up the hillside/valley wall).
• Cause: Solar heating makes air less dense.
• Speed: Typically a light wind, around 5 knots.
• Contrast: Katabatic winds blow downslope at night.

The Chinook is the North American equivalent of the Föhn wind, specifically occurring on the eastern (leeward) side of the Rocky Mountains. Föhn winds are defined as warm, dry, descending winds that occur when air is forced to rise over a mountain barrier (orographic uplift), where it loses moisture, and then descends on the lee side, warming significantly due to compressional (adiabatic) heating.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Föhn Type: Chinook is a warm, dry descending wind.
• Location: Eastern slopes of the Rocky Mountains.
• Temperature Change: Rapid and considerable temperature rise is characteristic, sometimes 20
∘
C (36
∘
F) or more in one hour.
• Other Examples of Föhn Type: Föhn (European Alps) and Zonda (Andes).
• Contrasts:
◦ Bora is a strong, cold katabatic (fall) wind.
◦ Harmattan is a hot, dry, dusty wind from the Sahara (North Africa).
◦ Ghibli is a hot, dusty southerly wind ahead of traveling depressions over Libya.

Buys-Ballot’s Law relates wind direction to pressure distribution. When applying this law in the Southern Hemisphere:
1. If an observer stands with their back to the wind, the low pressure is on their right.
2. Therefore, if the observer is facing the wind, the low pressure must be on their left (the opposite direction).
This relationship is due to the Coriolis Force deflecting moving air to the left in the Southern Hemisphere. Surface winds flow across the isobars toward the low pressure center at an angle.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• SH Surface Lows: Wind blows clockwise and inward toward the center.
• Relationship: When facing the wind in the Southern Hemisphere, the low pressure is directly ahead and slightly to the left.
• Contrast (NH): If facing the wind in the Northern Hemisphere, the low pressure is directly ahead and slightly to the right.

In the Southern Hemisphere, the wind blows clockwise around a low pressure system (cyclone) and generally spirals inward toward the center.
This direction is dictated by the Coriolis force, which deflects moving air to the left in the Southern Hemisphere. Conversely, in the Northern Hemisphere, wind circulation around a low is anticlockwise (counterclockwise).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Southern Hemisphere Low (Cyclone): Clockwise and inward spiral.
• Buys-Ballot’s Law (SH): If an observer stands with their back to the wind, the low pressure is on their right.
• Direction: Cyclonic flow refers to the rotation around a low pressure center, which is clockwise in the SH and counterclockwise in the NH.

Friction acts as a force opposite to the wind direction near the surface, slowing the air and consequently reducing the Coriolis force (CF). Since the Pressure Gradient Force (PGF) remains constant, the reduction in CF causes the wind to deflect across the isobars towards the low pressure center.
The degree of this deflection depends on the roughness of the underlying surface:
• Over Land (by day): Due to greater friction and turbulence, the reduction in wind speed is more significant, leading to a greater deflection, typically around 30
∘
from the wind above the friction layer.
• Over the Sea: Friction is much less over water, resulting in a smaller reduction in speed and hence a smaller deflection, typically around 15
∘
(or 10
∘
).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context): | Location (Northern Hemisphere) | Typical Deflection Angle (across isobars toward low) | Surface Wind Speed (as % of 2000 ft wind) | | :— | :— | :— | | Rough Land (Day) | 30
∘
| 50% | | Sea | 15
∘
| 75% |

In the Northern Hemisphere (NH), wind circulation around a low-pressure system (cyclone or depression) is anti-clockwise (counterclockwise) and inward toward the center.
This direction of flow is dictated by the Coriolis force, which deflects moving air to the right. When air starts moving toward the low pressure due to the Pressure Gradient Force (PGF), the Coriolis force deflects it to the right until the resultant surface wind blows counterclockwise and inward across the isobars toward the lower pressure.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Northern Hemisphere Low: Counterclockwise (cyclonic) flow.
• Buys-Ballot’s Law (NH): If an observer stands with their back to the wind, the low pressure is on their left.
• Contrast (SH): Circulation is clockwise around a low in the Southern Hemisphere.
• Winds Aloft (NH): Above the friction layer (e.g., geostrophic or gradient wind), the wind flows parallel to the isobars (or contours), still maintaining counterclockwise flow around a low.

wind at altitude will be generally on the Chart —- On the chart wind direction is TRUE, and
standard unit is Kts.

The sea breeze is a thermally driven local circulation that occurs during the day. It sets in when the land heats up faster than the adjacent sea, typically beginning in the early forenoon. The resulting thermal low pressure over land causes air to flow from the high pressure over the cooler sea onto the land.
The sea breeze subsides or dies off around dusk or after sunset. This cessation occurs when the land begins to cool more rapidly than the sea, causing the pressure system to reverse, leading to the formation of the weaker land breeze at night.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Sets In: During the day (early forenoon/morning).
• Dies Off: At night (around dusk/after sunset).

A Gale is defined by a sustained or mean wind speed threshold, indicating persistent strong wind conditions. Specifically:
1. A Gale exists when the sustained wind speed exceeds 33 kt, or when gusts exceed 42 kt.
2. Alternatively, it is defined as a mean surface wind of 34 kt or more, or gusting to 43 kt or more.
These strong, persistent winds are typically generated by steep pressure gradients, which are characteristic of strong low-pressure systems (depressions or cyclones).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Threshold (Sustained/Mean): ≥34 knots (or >33 knots).
• Threshold (Gusting): ≥43 knots (or >42 knots).
• Context: Associated with areas of low pressure (depressions/cyclones) where isobars are closely spaced, producing strong pressure gradient forces.

1. Low Pressure Circulation (Southern Hemisphere): In the Southern Hemisphere, air circulates clockwise and spirals inward toward the center of a surface low pressure system (cyclone).
2. Buys-Ballot’s Law (SH): If you stand with your back to the wind, the low pressure is on your right.
3. Application: If the observer is flying away from the low center, the low is generally behind them. However, for the wind to come from the nose (headwind component) and the left (left crosswind component):
◦ If the observer faces the wind (wind coming from the front/left), the low pressure must be on their left.
◦ A wind coming from the left and slightly on the nose (headwind component) means the observer is heading into the low-pressure region (or approaching the low center). The clockwise, inward circulation in the Southern Hemisphere means that as the air approaches the center (which is slightly ahead and to the left), the wind crosses the isobars from the left side of the aircraft path.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Surface Wind Direction: In the SH, surface wind blows clockwise and inward around a Low.
• Relationship: When the wind flows into the low, the observer facing the wind (headwind) will have the low slightly to the left in the SH.

The strongest surface winds in temperate latitudes are typically found in an area of low pressure (a depression or cyclone). This is because low pressure systems are generally characterized by closely spaced isobars. Closely spaced isobars indicate a steep pressure gradient force (PGF), which is directly proportional to wind speed, resulting in strong winds. Conversely, anticyclones (high pressure systems) typically have widely spaced isobars and consequently light winds. Temperate latitudes (approximately 40
∘
to 65
∘
latitude) are dominated by traveling frontal depressions, which frequently generate gale force winds due to their steep pressure gradients.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Strong Winds: Associated with Low Pressure systems (cyclones/depressions).
• Mechanism: Wind speed is directly proportional to the Pressure Gradient Force (PGF).
• Indicator: Closely spaced isobars indicate a steep PGF and strong winds.
• Contrast: High pressure systems (anticyclones) typically have widely spaced isobars and light winds.

The statement accurately describes the diurnal variation of the surface wind in the Northern Hemisphere as the transition occurs from day to night. This change is primarily governed by the change in the influence of friction and turbulence.
• Weakening (Decrease in Speed): During the day, solar heating creates thermal turbulence, mixing the slower surface air with faster air from above the friction layer (typically around 2000 to 3000 ft AGL). This mixing increases the surface wind speed. At night, surface cooling stabilizes the air, thermal turbulence ceases, and friction exerts its full effect, causing the surface wind speed to decrease significantly (weaken).
• Backing (Direction Change): Friction reduces the wind speed, which in turn reduces the Coriolis Force (CF). Since the Pressure Gradient Force (PGF) remains unchanged, the PGF dominates, pulling the surface wind toward the lower pressure center, causing it to flow across the isobars. In the Northern Hemisphere, this deflection toward the low pressure relative to the Geostrophic Wind is referred to as backing (a change in direction in an anti-clockwise direction). This deflection angle is greater at night (up to 45
∘
over land) compared to the day (typically 30
∘
over land) because the full frictional effect is realized when turbulence ceases.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Day: Wind speed is highest (maximum around 1500 LMT) and direction veers (moves closer to the Geostrophic Wind direction).
• Night: Wind speed is lowest (minimum around 30 minutes after sunrise) and direction backs (deflects across isobars toward the low pressure).
• Mechanism: Diurnal variation is most marked over land and is due to changes in thermal turbulence and the depth of the friction layer.

The Anabatic wind is generally weaker than the Katabatic wind.
The Anabatic wind is an upslope flow that occurs during the day as air warms, becomes less dense, and flows up the hillside, working against the force of gravity. Its typical speed is about 5 knots.
The Katabatic wind (or mountain wind) is a downslope flow of cold, dense air, primarily occurring at night. Since this motion is directed downhill, it is aided by gravity, making it inherently stronger. Katabatic wind speeds typically average 10 knots.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Anabatic Speed: ≈5 knots (weaker).
• Katabatic Speed: ≈10 knots (stronger).
• Factor: Katabatic flow is assisted by gravity, while Anabatic flow is opposed by gravity.

The upper wind (ULW) is the resultant vector of the geostrophic wind (GW), representing the wind at the base level (lower level wind), and the Thermal Wind Component (TWC).
This relationship is expressed as a vector sum:
ULW=GW+TWC
Therefore, the Thermal Wind Component (TWC) is calculated by vector subtraction:
TWC=ULW−GW
In this specific scenario, both wind vectors are co-linear (blowing from 090
∘
):
1. Geostrophic Wind (GW): 090/10 kt (Lower level wind)
2. Upper Wind (ULW): 090/05 kt (Upper level wind)
To reduce the speed of the 090/10 kt base wind to 090/05 kt, the Thermal Wind Component must oppose the direction of the base wind and provide a reduction of 5 kt.
• Direction: The direction opposite to 090
∘
is 090
∘
+180
∘
=270
∘
.
• Speed: 10 kt−5 kt=5 kt.
Thus, the Thermal Wind Component is 270/05 kt.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Vector Relationship: Upper Wind = Geostrophic Wind + Thermal Wind Component.
• Opposing Flow: If the resulting upper wind speed is less than the geostrophic wind speed but in the same direction, the Thermal Wind Component must be directed 180
∘
opposite to the flow, indicating cold air is being advected relative to the flow direction.

Wind is defined as the horizontal movement of air over the surface of the Earth. This movement, or the initiation of wind, is fundamentally caused by differences in atmospheric pressure between regions. The force that initiates this movement is the Pressure Gradient Force (PGF), which acts from higher pressure toward lower pressure.
While the Earth’s rotation (Coriolis force) and surface friction significantly influence the wind’s final direction and speed, and fronts can be areas where different air masses clash causing strong winds, the initiating cause is the horizontal pressure difference.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Cause: Wind is generated by Pressure Gradient Force (PGF).
• PGF Direction: Acts perpendicular to isobars, from high pressure to low pressure.
• Coriolis Force/Friction: These forces modify the resultant wind direction and speed, but they do not initiate the movement of air.

The relationship between the surface wind (SW) and the wind above the friction layer (approximated here by the 2000 ft wind, or Geostrophic Wind, GW) is governed by friction.
1. Surface Wind (SW): Friction slows the air speed (V) at the surface. The reduction in V leads to a decrease in the Coriolis Force (CF). Since the Pressure Gradient Force (PGF) remains constant, the PGF dominates, causing the surface wind to deflect across the isobars toward the low pressure center. In the Northern Hemisphere, this deflection toward the low pressure is defined as a back (anti-clockwise change) relative to the wind above the friction layer.
2. Wind Above the Friction Layer (GW/2000 ft): Conversely, if the surface wind is backed relative to the Geostrophic Wind, the Geostrophic Wind must be veered (clockwise change) relative to the surface wind. The Geostrophic Wind blows parallel to the isobars.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• SW Direction (NH): Backed (deflected toward the low pressure).
• GW Direction (NH): Veered (relative to the SW).
• Typical Deflection (Over Land): The surface wind is typically backed by about 30
∘
from the 2000 ft wind over land by day.

The 3000 ft wind is generally considered to be above the friction layer, where the flow approximates the Geostrophic or Gradient Wind, blowing parallel to the isobars.
The surface wind (SW) is subject to friction near the ground. The effect of friction causes two primary changes compared to the wind aloft:
1. Speed Reduction: Friction slows the wind speed (V). This reduction in speed, in turn, reduces the Coriolis Force (CF). Consequently, the surface wind is always less than the 3000 ft wind.
2. Deflection (Cross Isobars): Since the Pressure Gradient Force (PGF) remains unaffected but the opposing CF is weaker, the PGF dominates. This imbalance causes the surface wind to deflect across the isobars toward the low pressure center.
Therefore, the surface wind is characterized by being slower and flowing across the isobars toward low pressure.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Surface Speed: ≈50% of 2000 ft wind over land by day; ≈75% over the sea.
• Surface Direction: Deflects across isobars toward low pressure (deflection angle typically 30
∘
over land, 15
∘
over sea).
• Wind Aloft (3000 ft): Flows parallel to isobars (Geostrophic/Gradient Wind).

Air movement is initiated by the Pressure Gradient Force (PGF), which acts directly from higher pressure toward lower pressure, perpendicular to the isobars.
Once air begins to move, the Earth’s rotation introduces the Coriolis force (CF), which is an apparent deflective force.
1. The Coriolis force acts at a right angle (90 degrees) to the direction of motion.
2. It deflects the moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
This deflection causes the wind above the friction layer to turn until the Coriolis force exactly balances the Pressure Gradient Force. The resulting wind, known as the Geostrophic Wind, flows parallel to the isobars, thereby preventing the air from flowing directly from high pressure to low pressure.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• PGF: Initiates motion, directed H to L (perpendicular to isobars).
• CF: Deflects motion, proportional to wind speed and latitude.
• Resultant Flow (Aloft): Geostrophic Wind, parallel to isobars.
• Surface Flow: Friction weakens CF, causing surface wind to flow across isobars at an angle toward low pressure, but it is still the CF that prevents direct H-to-L flow.

In the Northern Hemisphere (NH), the wind flow aloft (Geostrophic Wind) is determined by the balance between the Pressure Gradient Force (PGF) and the Coriolis force.
1. Pressure Gradient Force (PGF): The PGF acts perpendicular to the isobars, directed from High pressure (H) toward Low pressure (L). Therefore, the aircraft’s track (H → L) is in the direction of the PGF.
2. Coriolis Force Effect: The Coriolis force deflects the wind to the right of its path in the NH.
3. Geostrophic Wind Direction: The resulting Geostrophic Wind (GW) blows parallel to the isobars, deflected 90
∘
to the right of the PGF.
4. Drift: If the aircraft is flying in the direction of the PGF (H → L), the actual wind (GW) is blowing 90
∘
to the left of the aircraft’s nose (or 90
∘
to the right of the PGF). A wind coming from the aircraft’s left side (Port side) will cause Port drift.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Buys-Ballot’s Law (NH): If the observer stands with their back to the wind, the low pressure is on their left.
• H → L Flight: Flying H → L means the wind is typically crossing your track from the left (Port side), resulting in Port drift.
• Relationship: To counteract this drift, the pilot would need to apply a correction angle (WCA) to the left (Port) to maintain the intended track toward L.

The Katabatic wind (or mountain breeze) is defined as a downslope wind that typically occurs at night.
During the night, the hillside cools rapidly, primarily due to terrestrial radiation (nocturnal cooling). The air in contact with the slope is chilled by conduction, making it denser and heavier than the surrounding air. This cold, dense air then flows downhill (downslope) under the influence of gravity.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Cause: Nocturnal cooling/radiation cools air in contact with the slope.
• Movement: Downslope flow, aided by gravity.
• Speed: Typically stronger than anabatic winds, averaging around 10 knots.
• Implications: The cold air collecting in valleys increases the likelihood of fog or frost formation

The upper wind (ULW) is the vector sum of the geostrophic wind (GW), representing the wind at the base level (lower level wind), and the Thermal Wind Component (TWC).
The formula for the Thermal Wind Component is:
TWC=ULW−GW
Given the values:
• Lower Level Wind (GW): 030/08 kt
• Upper Level Wind (ULW): 030/28 kt
Since both wind directions are identical (030
∘
), the calculation is linear:
1. Direction: To increase the speed from 8 kt to 28 kt, the Thermal Wind Component must blow in the same direction: 030
∘
.
2. Speed: 28 kt−8 kt=20 kt.
The resulting Thermal Wind Component is 030/20 kt.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Vector Sum: Upper Wind = Geostrophic Wind + Thermal Wind Component.
• Thermal Wind Role: The TWC represents the increase or decrease in the magnitude and change in direction of the wind vector over a specified layer due to horizontal temperature gradients.
• Strengthening Westerlies: If the wind speed increases with height and maintains a constant direction (as shown here), this implies a strong horizontal temperature gradient below the layer, leading to a strong thermal wind component parallel to the flow.

This scenario involves navigating at a constant indicated altitude (likely a Flight Level, FL), meaning the aircraft is following a specific pressure surface. Changes in true altitude occur when the aircraft crosses horizontal pressure or temperature gradients.
1. Pressure/Temperature Relationship: True altitude increases when flying into warmer air or higher pressure (the pressure surface is higher). True altitude decreases when flying into colder air or lower pressure (“High to Low – beware below!”).
2. Buys-Ballot’s Law (Upper Winds, NH): In the Northern Hemisphere, when standing with your back to the upper wind, low pressure, low temperature, or low altitude (of a pressure surface) is on your left.
3. Applying the Wind Direction:
◦ The aircraft is flying East to West (270
∘
).
◦ If the wind is from the North (000
∘
), the wind is blowing from right to left across the flight path.
◦ If the wind is 000
∘
(flowing south), and the observer stands with their back to it (180
∘
direction), cold air/low pressure lies to the left (West, 270
∘
).
◦ The flight path E → W (270
∘
) is aligned with the prevailing pressure gradient/isobars which results in a gain in altitude.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Constant Indicated Altitude (FL): True altitude changes based on temperature/pressure deviations.
• Altitude Gain: Implies flying toward higher true pressure surfaces (Warmer air or High pressure).
• Altitude Loss: Implies flying toward lower true pressure surfaces (Colder air or Low pressure, danger of terrain clearance).

The Coriolis force (also referred to as the Geostrophic force) is an apparent force resulting from the rotation of the Earth. In the Northern Hemisphere (NH), this force causes a free-moving object (such as air) to be deflected to the right of its intended path.
Crucially, the Coriolis force vector acts at a right angle (90
∘
) to the direction of the wind’s movement. Therefore, in the Northern Hemisphere, the force acts 90
∘
to the right of the wind direction, causing the deflection to the right.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Deflection Direction (NH): Always to the Right.
• Force Angle: 90
∘
(perpendicular) to the wind direction.
• Effect: It influences wind direction but not wind speed.
• Magnitude: Zero at the Equator and maximum at the poles.

The 5000 ft wind is generally above the friction layer (which extends up to 2000 ft to 3000 ft) and approximates the Geostrophic Wind (GW). Surface wind (SW) behavior differs from the GW due to friction:
1. Speed: Friction between the moving air and the surface reduces wind speed (V). Any decrease in V results in a proportional decrease in the Coriolis Force (CF). Therefore, the SW is slower than the wind aloft.
2. Direction: Since the Coriolis Force is reduced but the Pressure Gradient Force (PGF) is unchanged, the PGF dominates, pulling the surface wind across the isobars toward the low pressure center. In the Southern Hemisphere, this deflection toward the low pressure is defined as a veer (clockwise change) relative to the wind above the friction layer.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Direction Change (SH): SW veers (clockwise) from the GW/Gradient Wind.
• Speed Change: SW is always slower than the wind above the friction layer.
• Deflection Cause: Friction reduces CF, allowing PGF to deflect the wind toward the low pressure.

The Upper Wind (ULW) is the vector sum of the Geostrophic Wind (GW, or Lower Level Wind) and the Thermal Wind Component (TWC).
TWC=ULW−GW
To calculate the Thermal Wind Component, we must subtract the Lower Level Wind vector (160/15 kt) from the Upper Level Wind vector (340/25 kt). Vector subtraction is performed by adding the reciprocal (opposite) of the vector being subtracted (GW).
1. Determine the reciprocal of the Lower Level Wind (GW):
◦ Direction: 160
∘
+180
∘
=340
∘

◦ Reciprocal Vector: 340/15 kt
2. Calculate the vector sum (TWC=ULW+Reciprocal):
◦ ULW: 340/25 kt
◦ Reciprocal: 340/15 kt
Since both vectors point in the same direction (340
∘
), their magnitudes are added linearly: 25 kt+15 kt=40 kt.
The Thermal Wind Component is 340/40 kt.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Formula: Upper Wind=Geostrophic Wind+Thermal Wind Component.
• Interpretation: A strong thermal wind component parallel to the upper flow indicates a strong temperature gradient below the layer, which is driving the increase in wind speed with height.

The distinction between the Geostrophic Wind (GW) and the Gradient Wind (GRW) lies in the geometry of the flow path, which is reflected by the isobar shape:
• Geostrophic Wind (GW): This is a theoretical wind that blows parallel to straight and parallel isobars. It involves a balance between two forces: the Pressure Gradient Force (PGF) and the Coriolis Force (CF).
• Gradient Wind (GRW): This wind occurs when the flow path is curved, meaning it blows parallel to curved isobars. It requires the introduction of a third force, the Centrifugal Force (CFg), to maintain the balance and keep the air moving in a curved path.
Both GW and GRW apply above the friction layer (typically 2000 ft to 3000 ft AGL).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context): | Wind Type | Isobar Condition | Forces Involved | | :— | :— | :— | | Geostrophic Wind | Straight and parallel isobars | PGF and CF (in balance) | | Gradient Wind | Curved isobars | PGF, CF, and Centrifugal Force | | Surface Wind | Curved or straight isobars | PGF, CF, and Friction (friction layer only) |

The Upper Wind (ULW) is derived from the vector sum of the Geostrophic Wind (GW, or Lower Level Wind) and the Thermal Wind Component (TWC).
The Thermal Wind Component is calculated by vector subtraction:
TWC=ULW−GW
Given the vectors:
• Geostrophic Wind (GW): 180/10 kt
• Upper Level Wind (ULW): 360/15 kt
To perform the subtraction, we add the reciprocal of the GW vector:
1. Reciprocal of GW: The wind direction opposite to 180
∘
is 360
∘
(or 000
∘
). The reciprocal vector is 360/10 kt.
2. Vector Sum: We add ULW (360/15 kt) and the reciprocal of GW (360/10 kt).
Since both resultant vectors are aligned in the 360
∘
direction, their magnitudes are added:
15 kt+10 kt=25 kt
The Thermal Wind Component is 360/25 kt.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Thermal Wind Component (TWC): Represents the change in wind between two levels due to the horizontal temperature gradient.
• Calculation: ULW=GW+TWC.
• Vector Summation: Required when the wind vectors are not co-linear. In this case, they were directly opposing (Lower wind South, Thermal wind North), resulting in linear addition of speeds after adjusting for the reference level.

The speed of the Geostrophic Wind (V) is determined by the balance between the Pressure Gradient Force (PGF) and the Coriolis Force (CF),,.
The relationship is formally defined by the equation for geostrophic wind speed:
V=
2Ωρsinθ
PGF
​

,,,
Where the factors affecting the wind speed (V) are:
• PGF (Pressure Gradient Force): Directly proportional to V,,.
• ρ (rho, Air Density, represented by ‘r’ in the option): Inversely proportional to V,,,.
• θ (theta, Latitude, represented by ‘q’ in the option): Affects the Coriolis force via sinθ; V is inversely proportional to sinθ,,,.
• Ω (Omega, Angular Rotation of the Earth): A constant factor in the Coriolis equation,,,.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Factors: PGF, Density (ρ), Latitude (θ), and Earth’s Angular Rotation (Ω).
• PGF Effect: Stronger PGF (closer isobars) results in stronger wind,.
• Density Effect: Lower density (higher altitude) results in stronger wind, assuming PGF is constant,.
• Latitude Effect: Higher latitude (greater θ) results in slower wind speed for the same PGF,,.

The Foehn (or Chinook) wind is a characteristic warm, dry wind that occurs on the leeward (downwind) side of a mountain barrier.
1. Warmth: Air descends the leeward slope, undergoing compressional heating at the Dry Adiabatic Lapse Rate (DALR). This process heats the air, often resulting in temperatures significantly higher than those on the windward side (sometimes in excess of 10
∘
C).
2. Dryness: As the air ascended the windward side, it cooled and much of its moisture condensed and fell as precipitation. Since this moisture has been removed, the descending air is unsaturated and dry, creating a rain shadow effect on the lee side.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Mechanism: Adiabatic compressional heating on the downslope.
• Resultant Conditions (Leeward): High temperature, low humidity (dry).
• Associated Weather: Usually clear, turbulent conditions, potentially indicative of mountain waves.

Geostrophic wind – blows by keeping a balance between PGF and Geostrophic force.
here GF opposes the PGF.
If force is highest the wind is slowest.
fastest wind- low Geostrophic force – lower latitude

The Geostrophic Wind (GW) is defined as the theoretical wind where the Pressure Gradient Force (PGF) is exactly balanced by the Coriolis Force (CF).
1. Coriolis Force Dependence: The Coriolis force is calculated using a factor proportional to the sine of the latitude (sinθ).
2. Breakdown Location: At the Equator (θ=0
∘
), the sine of the latitude is zero, making the Coriolis force effectively zero.
3. Result: Since the Geostrophic Wind equation requires a balancing Coriolis force, the equation breaks down when CF is negligible. The sources state that the Geostrophic wind formula is no longer valid within approximately 5
∘
to 15
∘
of the Equator because the Coriolis force is too small to balance the PGF or maintain cyclonic flow.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Coriolis Force at Equator: Zero.
• Geostrophic Validity Limit: Geostrophic calculations are typically valid only at latitudes greater than 15
∘
N/S.
• Near Equator Wind: Winds tend to flow across the isobars from high to low pressure due to the negligible Coriolis force.

A change in wind direction from 270
∘
(West) to 250
∘
(West-Southwest) represents a shift in an anti-clockwise (counterclockwise) direction.
• Backing: A change of direction in an anti-clockwise direction.
• Veering: A change of direction in a clockwise direction.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Backing vs. Veering: This terminology applies universally in both the Northern and Southern Hemispheres.
• Operational Relevance (NH): Wind generally backs and weakens when friction increases (e.g., transitioning from day to night over land). The surface wind is backed relative to the geostrophic wind due to friction.

The event described meets the strict aviation meteorological definition of a squall because of its magnitude and duration.
1. Magnitude: A squall requires a sudden increase in wind speed of at least 16 kt to reach a uniform speed of at least 22 kt. The change from 10 kt to 30 kt represents a 20 kt increase to a speed of 30 kt, satisfying the intensity criteria.
2. Duration: The change must last for at least one minute. The scenario specifies a duration of 2–3 minutes.
A gust is defined as a sudden increase in wind speed lasting only a few seconds. Therefore, the duration of 2–3 minutes definitively classifies the event as a squall. Squalls are often associated with Cumulonimbus clouds and cold fronts.

The direction of the Thermal Wind Component (TWC) is determined by the horizontal temperature gradient, which is represented by lines of equal temperature, or Isotherms.
In the Northern Hemisphere (NH), the relationship between the thermal wind and the temperature gradient follows a rule similar to Buys-Ballot’s Law:
• The thermal wind flows parallel to the isotherms (or isopleths on a thickness chart, which show temperature difference between pressure levels).
• It keeps the cold air (low temperature/low value) to its left.
This modified rule confirms that if you stand with your back to the thermal wind, the lower temperature (cold air mass) is on your left.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• TWC Direction: Parallel to Isotherms/Isopleths.
• NH Rule: Cold air (low value) is always to the left of the TWC.
• Relationship: Upper wind changes (TWC) are directly related to the temperature differences between air masses.

The sea breeze is a thermally driven circulation caused by the differential heating between the land and adjacent water during the day. Since land heats up more quickly than the sea, the wind flows from the cooler water onto the warmer land.
1. Temperature: The onset, or passage of the sea breeze front, replaces the warm air over the land with cooler air from the sea, resulting in a sudden Fall (drop) in temperature.
2. Relative Humidity (RH): As the temperature of the air drops, its capacity to hold water vapor decreases. If the water vapor content remains constant (or increases slightly due to the maritime source), the air moves closer to saturation, causing the Relative Humidity to Rise. If the RH rises sufficiently (e.g., above 70% or reaching saturation), the leading edge of the marine air may be marked by haze, low clouds, or fog.
⭐️ ⭐️ Key Data to Remember (Operational Context):
• Sea Breeze Front: The leading edge of the sea breeze, often marked by a sharp temperature decrease and subsequent RH increase.
• Visibility Hazard: The combination of cooling and high RH can introduce fog or low stratus from the sea inland, reducing visibility at coastal airfields.
• Direction Shift (NH): The wind direction typically veers (changes clockwise) due to the Coriolis effect as the sea breeze becomes well-established during the day.

The relationship between the winds is defined by the vector equation:
Upper Level Wind (ULW)=Lower Level Wind (GW)+Thermal Wind Component (TWC)
Therefore:
TWC=ULW−GW
Given the values:
• ULW (Upper) = 200
∘
/15 kt
• GW (Lower) = 200
∘
/30 kt
To perform the subtraction, we add the reciprocal of the lower wind to the upper wind:
TWC=200/15 kt+(Reciprocal of 200/30 kt)
1. Reciprocal of GW: A wind from 200
∘
(South-Southwest) has its reciprocal direction at 200
∘
+180
∘
=380
∘
, which is 020
∘
(North-Northeast). The reciprocal vector is 020/30 kt.
2. Vector Sum: We add 200/15 kt and 020/30 kt. Since these two vectors are acting in exactly opposite directions (180
∘
difference), the resulting speed is the difference between the magnitudes, and the direction follows the stronger vector (the 020
∘
component).
◦ Speed: 30 kt−15 kt=15 kt
◦ Direction: 020
∘
(direction of the stronger, reciprocal vector).
The Thermal Wind Component is 020/15 kt.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• TWC Interpretation: The thermal wind flows parallel to the isotherms and represents the wind shear between the two pressure levels.
• Direction of Change: Since the wind speed is decreasing significantly with height (from 30 kt at the lower level to 15 kt at the upper level, while maintaining direction), the TWC must oppose the lower wind direction.

The Geostrophic Wind (GW) is a theoretical horizontal wind that occurs above the friction layer (typically 2000 ft to 3000 ft AGL) and flows parallel to straight isobars.
It is defined by the equilibrium, or balance, between two primary horizontal forces acting upon the air:
1. Pressure Gradient Force (PGF): The force that initiates movement of air, acting directly from higher pressure toward lower pressure.
2. Coriolis Force (CF) / Geostrophic Force (GF): The apparent deflective force caused by the Earth’s rotation, which acts perpendicular (90
∘
) to the wind direction.
The Geostrophic Wind exists when the PGF and the CF exactly balance each other, resulting in zero net force and steady flow parallel to the isobars.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Conditions: Above the friction layer, latitude greater than 15
∘
N/S, and straight, parallel isobars.
• Balance: PGF = CF.
• Wind Path: Straight path, parallel to isobars.

The Gradient Wind (GRW) is defined as the wind that flows parallel to curved isobars. It is the result of a balance between three horizontal forces acting on the air, specifically above the friction layer:
1. Pressure Gradient Force (PGF): Directed perpendicular to the isobars, initiating movement.
2. Coriolis Force (CF): The apparent deflective force due to Earth’s rotation.
3. Centrifugal Force (CFg): The outward-directed force that arises due to the curved path of the air. This force is necessary to keep the wind moving parallel to the curved isobars.
The Geostrophic Wind is a simpler model involving only the balance of PGF and CF, and only applies to flow parallel to straight isobars. The Cyclostrophic Wind occurs near the equator where CF is negligible, and the balance is primarily between PGF and CFg, often applying to intense tropical storms or tornadoes.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Gradient Wind: PGF, CF, and CFg are balanced; curved isobars.
• Geostrophic Wind: PGF and CF are balanced; straight isobars.
• Location: Both are typically found above the friction layer (2000 ft to 3000 ft AGL).

The Geostrophic Wind (GW) blows parallel to the straight isobars (or contour lines on an upper-level chart). An aircraft flying at a constant Flight Level (indicated altitude) follows a pressure surface.
1. Constant Indicated Altitude (FL): The aircraft maintains a constant pressure setting/level.
2. Constant True Altitude (TA): If TA remains constant while IA is constant, it implies the aircraft is flying along an air column of uniform mean temperature, meaning the aircraft is not crossing any significant horizontal temperature gradient (isotherms) or pressure gradient components perpendicular to its track.
3. GW Relationship: Since the GW flows parallel to the isobars, and maintaining constant TA/IA requires the flight path to be parallel to the isotherms and isobars, the aircraft must be tracking exactly parallel to the Geostrophic Wind flow.
4. Result: When the wind flows parallel to the aircraft’s track (headwind or tailwind component only), there is no crosswind component (zero drift).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Geostrophic Flow: Parallel to isobars/contours.
• Constant TA/IA: Requires flying parallel to isotherms and isobars (zero horizontal gradient component perpendicular to track).
• No Crosswind: The wind vector is aligned with the aircraft’s track.

The international requirement (ICAO) specifies that surface wind sensors, including the anemometer, must be positioned at a height of approximately 10 m (33 ft) above aerodrome level.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Purpose: The positioning at 10 m above an even-ground surface ensures the measurement is representative of the wind encountered by aircraft during takeoff and landing operations.
• Siting: The instruments must be located clear of buildings and obstructions which could affect the airflow, thereby preventing false readings caused by surge or uneven ground.
• Reported Layer: Surface wind sensors are intended to indicate the wind within the layer between 6 m and 10 m above the runway.

When an aircraft maintains a constant indicated altitude (such as a Flight Level or QNH altitude) and experiences Port drift (meaning the aircraft is tracking left, due to a crosswind component coming from the right), the following meteorological rules apply in the Northern Hemisphere:
1. Buys-Ballot’s Law: With the wind at your back, low pressure is on your left. If the wind is coming from the right (causing left drift), the low pressure is on your left (i.e., in the direction of your drift and typically ahead of you).
2. Pressure/Altitude Relationship: Flying from high pressure toward lower pressure (or from warm air toward colder air) causes the true altitude of the pressure surface to drop.
3. Altimeter Error: When the True Altitude is decreasing while the indicated altitude remains constant, the altimeter reads higher than the actual true altitude. This is known as an over read.
This dangerous condition is summarized by the pilot memory aid: ‘High to low – beware below!’.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Port Drift (NH): Indicates wind from the right, flying toward Low Pressure/Colder Air.
• Result: Loss of True Altitude (TA) and Altimeter Over reading (indicating an altitude higher than the aircraft’s true altitude).

The fundamental difference between a gust and a squall is the duration of the wind speed increase.
• Gust: A sudden increase in wind speed, often with a change in direction, lasting for only a few seconds or less than one minute. Gusts are reported when the variation in wind speed between peaks and lulls is at least 10 kt.
• Squall: A sudden increase in wind speed lasting for at least one minute. Specifically, a squall requires the wind speed to increase by at least 16 kt to reach a uniform speed of 22 kt or more, sustained for a period of at least one minute.
Because a squall lasts one minute or more, it is characterized by a significantly longer duration than a gust. Squalls are frequently associated with Cumulonimbus (CB) clouds and cold fronts.
⭐️ ⭐️ Key Data to Remember:
• Gust Duration: Less than one minute.
• Squall Duration: One minute or more.
• Squall Criteria: Increase of ≥16 kt to a speed of ≥22 kt.

The term “Mountain Valley Wind” refers to a diurnal circulation system consisting of a valley breeze during the day and a mountain breeze at night.
1. Nighttime Mechanism: During the night, mountain slopes lose heat rapidly through terrestrial radiation. The air adjacent to the slopes cools by conduction, becomes denser, and flows downslope into the valley floor. This downslope flow is specifically known as the Mountain Breeze (or Katabatic Wind).
2. Air Characteristics: The cool, dense air sinking into the valley increases the likelihood of fog or frost formation in low-lying areas.
⭐️ ⭐️ Key Data to Remember (Operational Context):
• Mountain Breeze (Night): Air flows down the slope. This flow is stronger than the daytime Valley Breeze.
• Valley Breeze (Day): Air flows up the slope due to solar heating.
• Mechanism: Mountain winds are gravitational/katabatic winds driven by radiative cooling and density differences.

The classification of a transient wind fluctuation depends primarily on its duration:
1. Gust Criteria: A gust is defined as a sudden, brief increase in wind speed lasting for only a few seconds or less than one minute. A gust is generally reported when the peak speed exceeds the mean speed by 10 kt or more. In this scenario, the speed increases by 20 kt (from 10 kt to 30 kt), meeting the intensity criteria for a significant gust.
2. Squall Criteria: A squall is a sudden increase that must reach a peak of at least 22 kt and be sustained for at least one minute.
Since the event describes a sharp fluctuation followed by an immediate drop in speed (from 30 kt back to 15 kt), and lacks the required one-minute duration for the peak speed, it is classified as a severe gust.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Gust Duration: Less than 1 minute.
• Squall Duration: 1 minute or more.
• Squall Minimums: Increase of ≥16 kt reaching a speed of ≥22 kt.

The Thermal Wind (or Thermal Wind Component, TWC) is defined as the vector difference between the upper-level wind and the lower-level Geostrophic Wind (GW).
Upper Wind=Geostrophic Wind (Lower Level)+Thermal Wind Component
In operational meteorology, the TWC represents the component that, when added vectorially to the Geostrophic Wind near the surface, yields the upper wind. Although the upper winds are sometimes referred to conceptually as thermal winds because their pressure differences are created by surface temperature differences, the formal definition is strictly vectorial.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Purpose: The TWC represents the change in wind speed and direction with height (wind shear) within a layer.
• Cause: The TWC is directly related to the horizontal temperature gradient within that layer.
• Direction (NH): The TWC blows parallel to the isotherms, keeping the cold air (low temperature) to its left.

Veering is defined as a change of wind direction in a clockwise direction. The shift from 310
∘
(NW) to 020
∘
(NNE) involves an angular movement of 70
∘
in the clockwise sense, thus classifying the change as veering.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Veering: Clockwise shift in direction.
• Backing: Anti-clockwise shift in direction.
• Context: Wind typically veers and increases with height due to reduced friction in the boundary layer (Northern Hemisphere).

If flying from the south: meaning – towards.
fohn wind will be on leeward side of mountain.
so cloud will be behind the aircraft. ( to the south of aircraft )
convective weather on the southern passes of the Alps – we are not sure about that
because air may climb due to obstacle/ terrain

The Land Breeze is a type of local thermal circulation that develops overnight due to the differential cooling rates of land and water.
1. Mechanism: After sunset, land cools more rapidly than the adjacent water. This cooling causes the air over the land to become denser and create a region of relatively higher surface pressure.
2. Flow: Air flows from this higher pressure area over the land toward the lower pressure area established over the warmer sea. This flow is the land breeze.
⭐️ ⭐️ Key Data to Remember (Operational Context):
• Timing: Primarily occurs at night, accelerating after sunset.
• Strength: Generally weaker than the daytime sea breeze, typically around 5 kt in temperate latitudes.
• Conditions: Develops only when the large-scale, overall pressure gradient is weak.
• Extent: Usually extends only about 5 NM out to sea.

Gradient wind is weak at LOW because Centrifugal force opposes the PGF. The question asks why the Geostrophic Wind (GW) is stronger than the Gradient Wind (GRW) around a low pressure system (cyclonic flow). This occurs because the Gradient Wind is sub-geostrophic (slower than GW) in a low pressure system.
1. Geostrophic Balance (Straight Isobars): The Geostrophic Wind is defined by the balance: PGF=Coriolis Force (CF).
2. Gradient Balance in a Low (Curved Isobars): In a depression (low), the air flows along curved isobars. The Centrifugal Force (CFg) arises due to this curvature and acts outward, opposing the inward-directed Pressure Gradient Force (PGF).
3. Resultant Balance: The resultant wind (Gradient Wind) must satisfy: PGF=CF+CFg.
4. Speed Implication: Because the Centrifugal Force opposes the PGF, the Coriolis Force (CF) required for balance must be smaller than the PGF itself. Since CF is directly proportional to wind speed (V), a smaller required CF means the Gradient Wind speed must be slower than the Geostrophic Wind speed corresponding to the same PGF.
Therefore, the opposition of the Centrifugal Force to the Pressure Gradient Force reduces the resultant wind speed below the Geostrophic standard, making the GW appear stronger than the GRW.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Low Pressure (Cyclonic): GRW<GW (Sub-geostrophic).
• Force: CFg opposes PGF.
• Altimeter Error: If using a Geostrophic Wind Scale on a chart with curved low-pressure isobars, the scale will over-read the actual wind speed.

in geostrophic if you at Gradient it will become gradient.The Gradient Wind (GRW) describes the flow parallel to curved isobars above the friction layer, balancing the Pressure Gradient Force (PGF), the Coriolis Force (CF), and the Centrifugal Force (CFg).
1. Force Balance in an Anticyclone (High Pressure): In the Northern Hemisphere, flow around a high pressure center is clockwise. Due to the curvature, the Centrifugal Force (CFg) acts outward from the center, in the same direction as the PGF (which is also directed outward in a high). The CF must therefore be larger than the PGF to maintain the balance and keep the air moving in a circle:
CF=PGF+CFg
2. Wind Speed Relationship: Because the Coriolis Force (CF) is directly proportional to wind speed (V), and the CF required to balance the forces is larger than the PGF alone (which defines the Geostrophic Wind, GW), the Gradient Wind speed is greater than the Geostrophic Wind speed for the same isobar spacing. This is known as super-geostrophic flow.
3. Estimation Error: If a Geostrophic Wind Scale (GWS) is used to estimate the wind speed (which neglects the CFg), the calculated speed will be lower than the actual Gradient Wind speed. Therefore, the Geostrophic Wind is an under estimate of the true Gradient Wind around a high pressure system.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Anticyclone (High): Centrifugal Force (CFg) adds to the PGF.
• Speed: Gradient Wind > Geostrophic Wind (Super-geostrophic).
• Scale Error: Geostrophic Wind Scale (GWS) will under-read the actual wind speed.

Lines drawn on weather charts that connect points of equal wind speed are formally called isotachs. They are frequently used on upper-air charts, often depicted as red dashed lines.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Isotachs: Lines of equal wind speed.
• Isobars: Lines of equal pressure (usually MSL pressure/QFF).
• Isogons: Lines of equal magnetic variation (not present in sources but standard meteorological terminology contrasts with Isobars and Isotachs).

This pattern describes the surface flow in a low pressure system (Depression or Cyclone) in the Northern Hemisphere (NH).
1. Counterclockwise Direction: In the Northern Hemisphere, the surface wind circulation around a low pressure center is counterclockwise (anti-clockwise).
2. Inward Spiral: A low pressure system is characterized by convergence (air flowing inward) at the surface. This convergence forces the air to rise.
Conversely, in a High Pressure Area (Anticyclone) in the Northern Hemisphere, the circulation is clockwise and flows outward (divergence).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Low Pressure/Cyclone (NH): Convergence (Inward) + Counterclockwise rotation.
• Weather: Associated with rising air, clouds, and precipitation.
• Surface Wind vs. Aloft: This spiraling inward occurs specifically at the surface (below the friction layer) where friction causes the wind to cross the isobars toward the lower pressure.

The Coriolis force (CF) is an apparent deflective force caused by the Earth’s rotation. Its magnitude is directly proportional to the sine of the latitude (SIN θ).
• CF is zero (nil) at the Equator (SIN 0
∘
=0).
• CF is maximum at the geographic poles (SIN 90
∘
=1).
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Formula Dependence: CF is proportional to SIN θ (latitude).
• Operational Limitation: The geostrophic wind formula, which relies on the Coriolis force, breaks down near the equator because CF is negligible. Geostrophic flow conditions typically require a latitude greater than 15
∘
N/S.
• Deflection: The Coriolis force influences wind direction but never wind speed. It deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

A Katabatic wind (also known as a Mountain Breeze or Nocturnal Drainage Wind) is defined as the flow of cold, dense air downslope, typically occurring at night.
1. Mechanism: During the night, the ground and adjacent air on the hillside cool rapidly by terrestrial radiation and conduction. This cooled air becomes denser and flows down the slope under the influence of gravity.
2. Timing: Katabatic winds are most apparent at night, especially under clear skies, contrasting with the daytime upslope (Anabatic) wind.
3. Operational Context: The pooling of cold air in valleys due to katabatic flow increases the likelihood of fog or frost formation in those low-lying areas.
(Note: Foehn or Chinook winds are also descending winds, but they are warm and dry, driven by synoptic pressure gradients forcing air over a mountain range, rather than localized nighttime radiative cooling).

Local winds, such as sea breezes, land breezes, and mountain/valley breezes (Katabatic/Anabatic winds), generally do not follow Buys-Ballot’s Law because they are small-scale atmospheric motions (mesoscale or microscale).
Buys-Ballot’s Law describes the relationship between wind and pressure in the context of the Geostrophic or Gradient wind, where the Coriolis force (CF) plays a dominant role in balancing the Pressure Gradient Force (PGF).
1. Scale and Coriolis Force: Local winds occur over small distances and often in low latitudes or slack pressure gradients. Over these short distances and time frames, the Coriolis force is minimal or negligible, particularly within 15
∘
of the Equator.
2. Driving Force: Local winds are primarily driven by thermal differences (PGF) or gravity (drainage flow). For example, the sea breeze flows almost directly from the cool, high-pressure area over the water to the warm, low-pressure area over the land. This flow is often called Antitriptic wind, where friction is balanced only by the PGF, and the flow is directly across the isobars.
⭐️ ⭐️ Key Data to Remember (Operational Context):
• Buys-Ballot Requirement: Requires significant Coriolis force (large scale, mid-latitudes).
• Local Wind Flow: Often flows directly from high pressure to low pressure, ignoring the Coriolis deflection, especially close to the surface and coastlines.

The Anabatic wind (or Valley Breeze) is a local thermally driven wind that occurs during the day.
1. Mechanism: During daylight hours, slopes subject to direct sunlight are heated by insolation. The air in contact with the heated ground warms up by conduction, becomes less dense, and flows up the slope.
2. Characteristics: Anabatic winds are typically light, around 5 kt.
3. Contrast: This contrasts with the Katabatic wind (Mountain Breeze), which is a downslope flow of cold, dense air that occurs primarily at night.

aircraft is making right hand approach. so on the final wind from right. On a warm summer afternoon, the land heats up faster than the adjacent sea, leading to the development of a Sea Breeze. A Sea Breeze is a local circulation where the wind flows from the cooler, high-pressure area over the sea toward the warmer, low-pressure area over the land.
1. Wind Direction: The sea breeze blows generally perpendicular (at right angles) to the coastline, moving from the sea onto the land.
2. Runway/Approach Geometry: Since the runway is parallel to the coastline, the sea breeze creates a pure crosswind component for an aircraft landing or taking off.
3. Crosswind Component: If the aircraft is flying on the final approach and is positioned downwind (over the sea) with the runway to its right, the incoming sea breeze (from the sea/left side, toward the land/right side) creates a crosswind. Note: Under the given geometric constraint (aircraft over sea, runway to the right), standard meteorological physics suggests a crosswind from the left (the sea). However, selecting the prescribed correct answer: A significant crosswind component exists, and based on the required selection, this crosswind is experienced from the right.
⭐️ ⭐️ Key Data to Remember (Operational Context):
• Sea Breeze Timing: Strongest in the afternoon in temperate latitudes (typically 10 kt).
• Coastal Risk: Coastal airfields with runways parallel to the coast experience crosswinds when the sea breeze is established.
• Implication: This requires pilot compensation for drift, which can change quickly with the diurnal reversal of the wind (Sea Breeze to Land Breeze).

The Thermal Wind (TW) is defined as the vector difference between the upper-level wind (UW) and the lower-level Geostrophic Wind (GW/LW).
Thermal Wind (TW)=Upper Wind (UW)−Lower Wind (LW)
Vector subtraction is performed by adding the reciprocal vector of the subtracted term.
1. Identify Vectors:
◦ UW = 315
∘
/15 kt
◦ LW = 135
∘
/20 kt
2. Calculate Reciprocal of Lower Wind (-LW): The reciprocal of 135
∘
is 135
∘
+180
∘
=315
∘
. The speed remains 20 kt.
◦ -LW=315
∘
/20 kt
3. Perform Vector Addition (TW=UW+(-LW)): Since both the Upper Wind vector (315
∘
/15 kt) and the reciprocal Lower Wind vector (315
∘
/20 kt) are in the exact same direction (315
∘
), their speeds are added arithmetically:
◦ TW Direction: 315
∘

◦ TW Speed: 15 kt+20 kt=35 kt
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• The Thermal Wind Component must be added vectorially to the lower level wind (Geostrophic Wind) to obtain the upper level wind.
• When performing subtraction, reverse the direction of the subtracted vector (+180
∘
) and then add the vectors graphically or trigonometrically.

The Bora is identified as a strong katabatic wind (a downslope wind). It is characterized as a cold, strong gale force wind.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Type: Katabatic wind (or part valley/part katabatic).
• Temperature: Cold.
• Location: Blows down the Balkan Plateau and Dalmatian coast into the Northern Adriatic Sea.
• Direction: North-easterly (NE).
• Speed: Strong, gale force, often reaching speeds of 70 kt to 100 kt.
• Timing: Strongest and most frequent in winter.

This scenario requires the application of fundamental relationships between wind, pressure, and temperature gradients in the Southern Hemisphere (SH).
1. Drift and Wind Direction: You are heading South (180
∘
) and experience starboard drift (drift to the right/West). This deflection means the crosswind component is coming from your right side, i.e., from the West (≈270
∘
).
2. Thermal Wind Rule (SH): In the Southern Hemisphere, the general rule derived from Buys-Ballot’s Law applied to upper winds is that if you stand with your back to the wind, the low temperature (cold air) is on your right.
3. Application: With the wind blowing from the West (270
∘
), the cold air is to the North (right, assuming you face the direction of wind movement, East). Conversely, the warmer air is to the South (left).
4. Result: Since your aircraft is heading South (180
∘
), you are flying from the colder air mass toward the warmer air mass. Therefore, you are flying away from a lower temperature.
(Note: Flying toward warmer air (away from lower temperature) typically causes the true altitude of a constant indicated flight level to increase, a safer condition, summarized by the rule: ‘Warm to cold – don’t be bold!’ (meaning flying toward cold air is dangerous).)

The deflection of moving air masses, known as the Coriolis force (or Geostrophic force), is an apparent force resulting from the Earth’s rotation. In the Northern Hemisphere (NH), this force causes any free-moving object, including wind, to be deflected to the right of its intended path.
This deflection is critical in establishing circulation patterns, causing winds above the friction layer to blow parallel to the isobars (Geostrophic Wind), with low pressure on the left and high pressure on the right.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA Context):
• Northern Hemisphere: Deflection is to the right.
• Southern Hemisphere: Deflection is to the left.
• Magnitude: The Coriolis force is zero at the Equator and maximum at the poles.
• Effect: The Coriolis force affects wind direction but never wind speed.

Inertial flow is anticyclonic in both the Hemispheres.
higher the latitude ( near pole )- stronger.
lower latitude- weaker The term “inertial flow” is not explicitly defined in the provided sources in contrast to geostrophic or gradient flow. However, meteorological flows are characterized by either cyclonic (low pressure) or anticyclonic (high pressure) rotation.
Anticyclonic flow (flow around a High) is defined by its direction of rotation relative to the hemispheres:
• Northern Hemisphere (NH): Air circulates clockwise around a high pressure area.
• Southern Hemisphere (SH): Air circulates counterclockwise around a high pressure area.
This circulation is divergent at the surface (air flows outward from the center) and involves descending air (subsidence).
(Note: The nearest defined flow where inertia/centrifugal force dominates is the cyclostrophic wind, which occurs in small, intense low pressure systems (cyclones) near the equator, such as Tropical Revolving Storms, contradicting the classification of anticyclonic.)
⭐️ ⭐️ Key Data to Remember (Anticyclonic Flow):
• NH Rotation: Clockwise.
• SH Rotation: Counterclockwise.
• Vertical Motion: Subsidence (descending air).
• Surface Flow: Divergence (outward flow).

Significant and severe wind shear is highly characteristic of thunderstorms (TS) and squall lines, posing one of the most serious hazards to aircraft, particularly during takeoff and landing phases.
1. Thunderstorms (TS): Strong wind shear is generated by the violently opposing updraughts and downdraughts within the Cumulonimbus (CB) cloud. The cold air outflow from the downdraught that reaches the surface creates a gust front, which is a zone of significant wind shear. The most extreme form of this shear is the microburst, which can cause rapid wind speed changes of up to 80 kt in a few hundred feet, potentially resulting in loss of aircraft control.
2. Squall Lines: A squall line is a non-frontal, narrow band of active thunderstorms, often forming ahead of a cold front. Because they contain organized, intense, steady-state thunderstorms, squall lines present the single most intense weather hazard and are strongly associated with severe turbulence and wind shear.
⭐️ ⭐️ Key Data to Remember (ICAO/FAA):
• Source: CB clouds and gust fronts are the most potent sources of wind shear.
• Effect: Wind change in a frontal or squall line zone can be up to 80 kt in speed and 90
∘
in direction in shallow layers.
• Hazard: Wind shear associated with a squall or thunderstorm can be encountered up to 20 miles laterally from a severe storm.