Zonal Cloud Trends Observed by Passive MODIS and Active CALIOP and CPR Sensors

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Abstract Active sensors such as Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Cloud Profiling Radar (CPR) aboard CloudSat are known to have great advantages in examining cloud vertical structures. However, these sensors were designed for a relatively short lifespan (∼3 yr), and trends using a combination of CALIPSO and CloudSat (CALCS) have yet to be explored. When clouds detected by CALCS are filtered for known sensitivity differences, the trends from the merged CALCS agree well with Moderate Resolution Imaging Spectroradiometer (MODIS) cloud trends from 2008 to 2017. Both CALCS and MODIS capture common features, although there are differences in high-level cloud altitudes. These trends are decomposed into El Niño–Southern Oscillation (ENSO) and non-ENSO components using a regression model with the multivariate ENSO index (MEI). The non-ENSO component is related to the cloud amount increase over the Arctic and the upward shift of high clouds (i.e., rising high clouds) over 60°S–60°N. The rising high clouds are further verified using MODIS measurements for the extended period from 2005 to 2022. Even though altitudes of high clouds rose, their cloud temperatures remained similar, supporting the fixed anvil temperature (FAT) hypothesis. Significance Statement Zonal cloud trends obtained from two active sensors, CALIPSO and CloudSat (CALCS), are compared with those from the MODIS passive imager. Despite the differences in high-level cloud altitudes, CALCS and MODIS zonal cloud trends capture common features. When the cloud trends are decomposed into ENSO and non-ENSO components, the non-ENSO component is related to the Arctic cloud increase and rising high clouds. Although altitudes of high clouds rose, their cloud temperatures remained similar.

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