A corona is a prismatically colored circle or arc of a circle around the sun or moon, resulting from the diffraction of light by tiny liquid cloud droplets of uniform size.
• Best Producers: The best corona producers are thin, recently formed clouds such as Altostratus (AS) and Altocumulus (AC).
• Composition and Location: Coronas are characteristic of clouds composed of water droplets, distinguishing them from the halo phenomenon (associated with ice crystals in Cirrostratus, CS). AS and AC are medium-level clouds (6,500 ft to 23,000 ft in mid-latitudes) that typically contain water droplets and ice crystals.
• Distinction: A corona is smaller and has the color arrangement (blue inside, red outside) opposite to that of a halo. Halos are produced by Cirrostratus (CS).

The optical phenomenon known as a Halo is produced by the refraction of sunlight or moonlight as it passes through ice crystals. The presence of a halo indicates that cirriform clouds are present.
• Cloud Type: Halos are characteristic of Cirrostratus (CS) clouds.
• Altitude: Cirrostratus is classified as a High Cloud, with bases typically ranging from 16,500 ft up to 45,000 ft in middle latitudes.
• Significance: Halos often serve as a pre-frontal sign, predicting rain or snow within 12 to 24 hours as they form ahead of an advancing mid-latitude cyclonic storm, such as a warm front.
Key Data to Remember:
• Process: Refraction of light.
• Composition: Ice crystals.
• Size: The most common type is the 22° halo ( small halo ).

A Superior Mirage is an atmospheric optical phenomenon where objects appear displaced upward from their true position. This phenomenon occurs in a marked Inversion.
• Required Condition: A superior mirage forms when the air temperature increases with height, a condition known as a temperature inversion. This often happens over a cold surface, such as snow or ice, where cold, dense air is trapped near the ground beneath warmer air aloft.
• Mechanism: Light rays from distant objects are bent (refracted) downward toward the colder, denser air near the surface, causing the observer to perceive the object as being shifted upward (superior).
Key Data to Remember:
• Structure: Cold air near the surface, warm air aloft (Inversion).
• Location Context: Common in polar regions or over cold sea surfaces where warm air rests above a cold surface.
• Effect: Distant objects appear shifted upward, or higher than they actually are.

The Aurora Borealis, commonly known as the Northern Lights, is the specific term used for the luminous, radiant atmospheric emission occurring in the Northern Hemisphere.
This phenomenon is predominantly observed in the high-latitude or polar regions around the Arctic. The Aurora Borealis occurs when energetic particles from the sun interact with the rarefied gases of the outer atmosphere, illuminating them.
Key Data to Remember:
• Location: Northern Hemisphere (high latitudes/polar regions).
• Cause: Charged particles (solar wind) from the sun interacting with the Earth’s magnetic field and atmospheric gases.
• Counterpart: In the Southern Hemisphere, this display is called the Aurora Australis (Southern Lights).
• Altitude Context: Takes place at high altitudes, well above the Earth’s surface, within the thermosphere.

The Bishop’s Ring is an optical phenomenon specifically caused by the diffraction of light through fine, solid particles suspended in the atmosphere.
• Mechanism: It is a bluish or red-brown ring around the Sun or Moon, classified as a type of corona caused by light diffraction.
• Causative Particles: These fine solid particles are typically dust particles, especially volcanic particles (aerosols or ash) emitted into the stratosphere during major volcanic eruptions (e.g., El Chichón).
Key Data to Remember:
• Process: Diffraction of light.
• Particles: Fine dust or volcanic particles.
• Appearance: Bluish or red-brown ring, typically observed after large volcanic eruptions.
• Radius: Approximately 22 radius.

A Halo is an optical phenomenon caused by the refraction and dispersion of sunlight or moonlight as it passes through hexagonal ice crystals (usually found in Cirriform clouds).
When white light is dispersed by these ice crystals, the light is split into colors because different wavelengths (colors) are bent differently (dispersion).
• Red light (longer wavelength) bends the least. Consequently, the inner edge (closest to the sun or moon) of the halo appears red.
• The colors progress outward to blue/violet, which bends the most, appearing on the outside of the ring.
Key Data to Remember:
• Process: Refraction/Dispersion.
• Composition: Ice crystals.
• Color Order (Halo): Red inside, Blue/Violet outside. (This is opposite to the color order of a Corona).

The optical phenomenon known as a Halo is produced by the refraction of sunlight or moonlight as it passes through ice crystals, typically found in Cirrostratus clouds.
There are two primary sizes of halos:
1. Small Halo: The most common type has a radius of 22
2. Large Halo: A less common halo, often referred to as the 46 halo, is also observed.

While the standard meteorological value for the large halo is 46∘, the option ∗42∘ represents the large, distinct halo type which is significantly greater than the common 22∘ halo.

Key Data to Remember:
• Process: Refraction of light.
• Composition: Ice crystals.
• Common Size (Small Halo): 22∘radius.
• Large Size (Large Halo): 46∘ radius (rare). (Note: The inner edge of the halo is pure red).

A Halo is a ring of light encircling the sun or moon. It is exclusively caused by the refraction (bending) of sunlight or moonlight as it passes through tiny ice crystals.
• Cloud Association: Halos are characteristic of cirriform clouds, specifically Cirrostratus (CS), which are high clouds composed entirely of ice crystals.
• Significance: Halos indicate the presence of high-level ice crystal clouds, often signaling the approach of a warm front and possible subsequent widespread precipitation.
Key Data to Remember (FAA/ICAO Context):
• Process: Refraction of light.
• Composition: Ice crystals.
• Cloud Type: Cirrostratus (CS) (High Cloud).
• Size: Most common is the 22° halo; less common is the 46° halo.

A Corona is an atmospheric optical phenomenon caused by the diffraction of light as it passes around tiny particles. For a corona to occur, the light must pass through a layer of small, spherical particles of uniform size.
These required particles can exist in several atmospheric states:
1. Small Water or Ice Particles: The general mechanism requires tiny liquid cloud droplets. The phenomenon is caused by diffraction through small water droplets or ice crystals.
2. Clouds: Coronas are characteristic of clouds composed of water droplets, such as thin Altostratus (medium-level clouds).
3. Mist/Fog: Since mist (visibility 1000m to 5000m) and fog (visibility less than 1000m) are composed of minute water droplets or ice crystals suspended near the surface, light passing through them can also produce a corona.
Because the effect can be produced when light passes through any medium containing small, uniform water droplets or ice crystals (including mist, fog, and clouds like Altostratus), the mechanism relies on the consistent presence of these small particles found within all the listed options.
Key Data to Remember:
• Process: Diffraction of light.
• Required Particles: Tiny, uniform water droplets, ice crystals, or fine solid particles (e.g., volcanic ash).
• Appearance: Colored circle/ring, with colors opposite to a halo (blue inside, red outside).

The Aurora Australis, also known as the Southern Lights, is the luminous, radiant emission observed primarily in the high-latitude regions of the Southern Hemisphere. This optical phenomenon occurs when charged particles originating from the sun (solar wind) interacting with the Earth’s magnetic field lines and the rarefied gases of the upper atmosphere, causing them to emit light.

Key Data to Remember (ICAO Context):
• Location: Southern Hemisphere (centered over the Earth’s magnetic poles).
• Cause: Charged particles from the sun.
• Counterpart: Aurora Borealis (Northern Lights) occurs in the Northern Hemisphere.
• Altitude: Takes place at high altitudes in the outer atmosphere.

The most common and frequently observed atmospheric optical phenomenon, known as the Halo, has a standard angular radius of 22∘ from the sun or moon.

This primary halo is produced when sunlight or moonlight is refracted as it passes through tiny, randomly oriented ice crystals (hexagonal columns) found in high-level Cirrostratus (Cs) clouds.

Key Data to Remember (ICAO Context):
• Common Halo Size: 22∘ radius.
• Larger Halo Size: 46 ∘ radius (less common).
• Mechanism: Refraction of light.
• Composition: Ice crystals (Cirriform clouds).
• Appearance: Red light is dispersed to the inside edge of the halo.

A Corona is an atmospheric optical phenomenon caused by the diffraction of light. Diffraction is the bending of light waves as they pass around small objects.
• Mechanism: The corona appears as colored rings surrounding the sun or moon when light passes around tiny atmospheric particles, typically small liquid cloud droplets or ice crystals.
• Requirement: The phenomenon requires the cloud droplets or particles (which may include volcanic ash) to be of uniform size for the colors to appear.
• Cloud Type: Coronas are characteristic of clouds composed of water droplets, such as thin Altostratus (medium cloud).

Key Data to Remember:
• Process: Diffraction of light.
• Particles: Tiny, uniform water droplets.
• Color Order: Blue light appears on the inside of the ring, and red light appears on the outside. (This color progression is opposite to that of a Halo, which is caused by refraction).

The Aurora Australis is the name specifically given to the luminous, radiant atmospheric phenomenon that occurs in the Southern Hemisphere. It is popularly known as the Southern Lights.
This display is caused by charged particles originating from the sun (solar wind) interacting with the Earth’s magnetic field lines and the rarefied gases of the upper atmosphere.

Key Data to Remember:
• Designation: Southern Lights.
• Location: High latitudes/Polar Regions of the Southern Hemisphere.
• Cause: Solar wind particles interacting with atmospheric gases.
• Northern Counterpart: Aurora Borealis (Northern Lights).

The optical phenomenon known as a Halo is characteristically produced by light interaction within Cirrostratus (CS) clouds.
• Mechanism: Halos are caused by the refraction of sunlight or moonlight.
• Composition: CS clouds are high-level clouds (cirriform) composed almost entirely of ice crystals, which act as prisms to bend the light.

The presence of a halo indicates that cirriform clouds are present, often heralding the approach of a warm front and suggesting possible rain or snow within 12 to 24 hours.

Key Data to Remember (Halo):
• Cloud Type: Cirrostratus (CS).
• Altitude: High cloud family (16,500 ft to 45,000 ft in middle latitudes).
• Process: Refraction.
• Composition: Ice crystals.
• Common Size: 22 degree radius.
• Color Order: Red light is dispersed least, appearing on the inside closest to the sun or moon.

The Inferior Mirage (or lower mirage) occurs when light rays are bent or refracted upward as they travel through air layers of significantly different densities. This requires the air near the ground to be much warmer and less dense than the air above it.

• Atmospheric Condition: This temperature profile—where temperature decreases rapidly with height—is known as a steep lapse rate.

• Mechanism: The hot surface, such as hot desert sand or asphalt, heats the adjacent air by conduction. This creates a layer of hot, less-dense air near the ground. Light rays passing from the cooler, denser air aloft into this hot, less-dense layer are bent upward (refracted), causing distant objects to appear displaced downward or inverted.

Inferior mirages are associated with warm surfaces and steep lapse rates. This effect often gives the illusion of water (blue skylight refracting upward) on roads or in hot deserts.

Key Data to Remember:
• Inferior Mirage: Steep Lapse Rate (Warm surface air, cooler air above).
• Superior Mirage: Inversion (Cold surface air, warmer air above).

The optical phenomenon known as a Halo is produced when sunlight or moonlight is refracted (bent) as it passes through ice crystals.
• Cloud Type: Halos are characteristic of Cirrostratus (CS) clouds, which belong to the High Cloud family.
• Composition: High clouds (Cirrus, Cirrostratus, Cirrocumulus) are composed almost exclusively or entirely of ice crystals. The presence of a halo indicates this specific composition.
• Contrast: Supercooled water droplets are generally not present in cirriform clouds but are characteristic of icing hazards in middle and low clouds.

The Bishop’s Ring is an atmospheric optical phenomenon caused by the diffraction of light as it passes through fine dust particles, commonly volcanic aerosols injected into the stratosphere. This diffraction produces a bluish or red-brown ring around the sun or moon.

Key Data to Remember:
• Radius: The radius of the Bishop’s Ring is approximately 22 degree
• Cause: Diffraction of light.
• Particles: Fine dust particles, often volcanic in origin.
• Context: It is considered a type of corona caused by these solid particles.

The Aurora Borealis is the technical term for the luminous atmospheric display commonly referred to as the Northern Lights.
This phenomenon is predominantly seen in high-latitude regions around the Arctic.

It is caused by energetic, charged particles (solar wind) from the sun interacting with eath’s magnetic field and the gases of the upper atmosphere, illuminating them.

Key Data to Remember:
• Location: Northern Hemisphere.
• Common Name: Northern Lights.
• Southern Counterpart: Aurora Australis (Southern Lights).

A Halo is a luminous ring or arc encircling the sun or moon. It is produced by the refraction (bending) of sunlight or moonlight as it passes through minute hexagonal ice crystals. This process splits the white light into a spectrum, an action known as dispersion.
• Cloud Type: Halos are characteristic of Cirrostratus (CS) clouds, which are thin, high-level clouds composed of ice crystals.
• Color Order: Due to dispersion, red light bends the least, appearing on the inside of the halo, closest to the sun or moon.
• Standard Size: The most common halo observed has an angular diameter of 22 degree

The optical phenomenon known as a Halo is produced by the refraction of light through ice crystals. Halos are characteristic of Cirrostratus (CS) clouds, which belong to the High Cloud family.
• Composition: Cirriform clouds (including CS) are composed almost exclusively of ice crystals.
• Icing Hazard: Since hazardous airframe icing relies on the presence of supercooled water droplets (SWD), and SWDs do not occur in cirriform clouds, the chance of ice accretion in CS clouds is considered Nil or Trace.

Key Data to Remember:
• Cloud Type: Cirrostratus (CS).
• Composition: Ice crystals.
• Icing Risk: Nil/Negligible.