Lidar ratio and depolarization ratio for cirrus clouds

Area of Science:

• Atmospheric Science
• Cloud Physics
• Remote Sensing

Background:

• Cirrus clouds significantly impact Earth's radiative balance.
• Understanding cirrus cloud properties is crucial for climate modeling.
• Previous studies using LITE and PROBE provided foundational data.

Purpose of the Study:

• To investigate lidar and depolarization ratios for cirrus clouds.
• To determine the relationship between optical depth, lidar ratio, and depolarization ratio with altitude and temperature.
• To infer cirrus cloud composition based on optical properties.

Main Methods:

• Utilized lidar measurements to derive optical depth and effective lidar ratio from cloud transmission.
• Compared backscattering signals at cloud base and top.
• Fitted lidar signals to atmospheric density profiles to ensure linear response.
• Analyzed height and temperature dependencies of key cloud parameters.

Main Results:

• An average lidar ratio of 29 ± 12 sr was determined for clouds in 1999-2000.
• Optically thick clouds were observed near 12 km altitude at approximately -55°C.
• Depolarization ratio generally increases with height from 11-15 km, and is <0.3 above 16 km.
• Multiple scattering effects were considered, reducing lidar ratios for optically thick clouds.

Conclusions:

• Cirrus clouds near the tropopause are typically optically thin and subvisual.
• Lidar and depolarization ratios provide insights into hexagonal ice crystal types.
• Cloud optical properties exhibit significant variations with altitude and temperature, impacting climate models.