Long-term observations of upper-tropospheric cloud ice from the MLS

Upper tropospheric cloud ice varies across different timescales and plays an important role in regulating Earth’s climate, but knowledge of the abundances and the variability of cloud ice has been limited for decades. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) provides an unprecedented record of cloud ice measurements since its launch in April 2006. However, CALIPSO has left the A-Train in September 2018 and entered the C-Train orbit which follows a slightly different ground track with a different local crossing time. This orbit change challenges the continuation of a long-term record of cloud ice since ice is subject to stronger diurnal cycle. Fortunately, the Aura Microwave Limb Sounder (MLS), still as a member of the A-Train, has a consistent local crossing time and has measured high quality radiance since launch in 2004, and will probably continue beyond 2024. We present the use of MLS 640-GHz cloud-induced radiance (Tcir) to build a robust upper tropospheric partial ice water path (pIWP) product due to its high dynamical range to different sizes of ice particles. The MLS rebuilt pIWP, which extends nearly two decades, captures the spatial and temporal variabilities of upper tropospheric cloud ice that CALIOP is capable of measuring. This provides valuable alternative for studying the upper tropospheric cloud ice and possibly provides a more consistent input to climate studies.