Characteristics of Cirrus Clouds from Different Formation Mechanisms

Cirrus clouds, formed through various atmospheric processes, vary in distribution and microphysical properties, playing distinct roles in regulating Earth’s radiative balance. This study examined the characteristics of cirrus clouds formed through different mechanisms, using joint radar and lidar observations from the A-Train satellite and the cirrus classifications from the Identification and Classification of Cirrus system. It was found that orographic cirrus, commonly observed near major mountains, shows a slight seasonal variation, being more frequent during summer. Frontal cirrus, typically forming along storm tracks over oceans, exhibits a global occurrence frequency of approximately 6% and accounts for one-fifth of total cloud, with higher occurrences in winter. These clouds have a moderate to high ice water content (IWC) due to the uplift of liquid droplets by frontal systems. Convective cirrus, mainly forming in tropical regions, reaches the greatest heights and thickness among all cirrus types, with a global occurrence frequency of about 13%, contributing nearly half of the total cirrus. These clouds exhibit the highest IWC and largest ice crystal sizes (Rice) among all cirrus types. Jet-stream cirrus, occurring around 10 km in midlatitudes, exhibits limited IWC and lower Rice values due to its restricted ability to generate cirrus. Synoptic cirrus, prevalent in subtropical and polar regions, is widely distributed across altitudes but is generally thin, with a lower IWC and lower ice crystal concentrations (Nice) due to weaker vertical velocities. This study underscores the importance of formation mechanisms in determining the distribution and microphysical properties of cirrus clouds.