Corona-producing cirrus cloud properties derived from polarization lidar and photographic analyses

Area of Science:

• Atmospheric optics
• Cloud physics
• Remote sensing

Background:

• Clouds composed of hexagonal ice crystals are known to produce optical phenomena like coronas.
• The specific conditions under which these coronas form in cirrus clouds are not fully understood.

Purpose of the Study:

• To demonstrate that hexagonal ice crystal clouds can generate multiple-ringed colored coronas.
• To identify the unusual cloud conditions associated with these displays.

Main Methods:

• Analysis of polarization lidar data from Project FIRE.
• Measurement of cloud top altitudes and temperatures.
• Analysis of color photographs of corona ring angles.
• Estimation of cloud optical thicknesses.

Main Results:

• Polarization lidar data confirmed hexagonal ice crystal clouds generate multiple-ringed coronas.
• Coronas were associated with high-altitude cirrus clouds (average 12.7 km) at -60 to -70°C.
• High laser backscattering and depolarization ratios (0.5-0.7) were observed.
• Crystal sizes ranged from 12 to 30 micrometers.
• Cloud types included thin cirrostratus and fibrous cirrus with optical thicknesses from 0.001 to 0.2.

Conclusions:

• Specific atmospheric conditions, including elevated tropopauses and specific ice crystal characteristics, are conducive to corona formation.
• Polarization lidar is effective in identifying these conditions and the resulting optical phenomena.
• Further research into these unusual cloud formations can enhance our understanding of atmospheric optics.