Temperature Profiles and Lapse Rate Climatology in Altostratus and Nimbostratus Clouds

Global COSMIC Radio Occultation (RO) profiles in altostratus and nimbostratus clouds are firstly identified based on collocated CloudSat data from 2007 to 2010. Most of collocated cloudy GPS ROs are located in high latitudes. Temperature profiles in altostratus and nimbostratus clouds are then derived from GPS RO refractivity profiles using a physical retrieval method (Tcloud). The derived temperature profiles are compared with the standard GPS RO wet retrieval using a 1D-Var approach without recognizing the cloudiness of these profiles (Twet). Impacts of cloud liquid water content and ice water content on retrieval accuracy are also assessed. On average, Tcloud is about 0.5-1.0 K larger than Twet except for low latitude clouds within 1.5-km altitude range from the cloud base. The lapse rate with the nimbostratus cloud systems is smallest in winter and largest in summer, reaching an averaged maximum of about 7.0oC/km in winter and 7.5oC/km in summer at about 0.6 km below the cloud top. The colder temperatures at higher altitudes within the nimbostratus clouds result in a significant increase of lapse rate with altitude 0.7 km below cloud top, from 1-2oC/km near the cloud base to 7.0-7.5oC/km 0.7 km below the cloud top. Within altostratus clouds, the lapse rate in low latitudes is significantly larger than in high latitudes (~7.0oC/km) below the cloud top due to higher altitudes the tropical altostratus clouds reach.