Cloud climatologies from the infrared sounders AIRS and IASI: strengths and applications

Abstract

Abstract. Global cloud climatologies have been built from 13 years of Atmospheric Infrared Sounder (AIRS) and 8 years of Infrared Atmospheric Sounding Interferometer (IASI) observations, using an updated Clouds from Infrared Sounders (CIRS) retrieval. The CIRS software can handle any infrared (IR) sounder data. Compared to the original retrieval, it uses improved radiative transfer modelling, accounts for atmospheric spectral transmissivity changes associated with CO 2 concentration and incorporates the latest ancillary data (atmospheric profiles, surface temperature and emissivities). The global cloud amount is estimated to be 0.67-0.70, for clouds with IR optical depth larger than about 0.1. The spread of 0.03 is associated with ancillary data. Cloud amount is partitioned into about 40 % high-level clouds, 40 % low-level clouds and 20 % mid-level clouds. The latter two categories are only detected in the absence of upper clouds. The A-Train active instruments, lidar and radar of the CALIPSO and CloudSat missions, provide a unique opportunity to evaluate the retrieved AIRS cloud properties. CIRS cloud height can be approximated either by the mean layer height (for optically thin clouds) or by the mean between cloud top and the height at which the cloud reaches opacity. This is valid for high-level as well as for low-level clouds identified by CIRS. IR sounders are particularly advantageous to retrieve upper-tropospheric cloud properties, with a reliable cirrus identification, day and night. These clouds are most abundant in the tropics, where high opaque clouds make up 7.5 %, thick cirrus 27.5 % and thin cirrus about 21.5 % of all clouds. The 5 % annual mean excess in high-level cloud amount in the Northern compared to the Southern Hemisphere has a pronounced seasonal cycle with a maximum of 25 % in boreal summer, in accordance with the moving of the ITCZ peak latitude, with annual mean of 4 • N, to a maximum of 12 • N. This suggests that this excess is mainly determined by the position of the ITCZ. Considering interannual variability, tropical cirrus are more frequent relative to all clouds when the global (or tropical) mean surface gets warmer. Changes in relative amount of tropical high opaque and thin cirrus with respect to mean surface temperature show different geographical patterns, suggesting that their response to climate change might differ.

Regional Intensification of the Tropical Hydrological Cycle During ENSO

“…When combined with CERES, these data provide the surface net heat flux. Hydrological variables include cloud properties, humidity, and precipitation. Studied anomalies include total cloud and high cloud amount (with pressure < 440 hPa) from Moderate Resolution Imaging Spectroradiometer (MODIS) cloud data (MOD35 and MYD35; Frey et al, ), ice cloud amount from the NASA Atmospheric Infrared Sounder (AIRS) cloud data (Kahn et al, ), and occurrence of upper tropospheric clouds (with pressure < 330 hPa), further divided into opaque (convective), cirrus, and thin cirrus cloud relative to total cloud occurrence from Laboratoire de Météorologie Dynamique‐AIRS cloud data (2003–2015; Stubenrauch et al, ), all on a regular 1° × 1° grid. Cloud liquid water path and column‐integrated water vapor are from the NASA MEaSUREs Multi‐Sensor Advanced Climatology of Liquid Water Path (MAC‐LWP) product (Elsaesser et al, ).…”

“…The method is that adopted in other cloud feedback and ENSO feedback studies (e.g., Li et al, ; Lloyd et al, ; Stubenrauch et al, ; Yue et al, ; Zhou et al, ). Monthly anomaly time series of each observational and model variable for each grid box are linearly regressed against regionally averaged SST anomalies.…”

New Cloud System Metrics to Assess Bulk Ice Cloud Schemes in a GCM

“…For the evaluation of the UT cloud properties predicted by the LMDZ GCM, we use satellite retrievals from the Atmospheric InfraRed Sounder (AIRS) and the IR Atmospheric Sounding Interferometer (IASI) measurements (Stubenrauch et al, ). These instruments are sensitive to cirrus down to an IR emissivity, ε cld , of 0.1, during daytime and nighttime.…”

Vertical Profiles of Ice Cloud Microphysical Properties and Their Impacts on Cloud Retrieval Using Thermal Infrared Measurements

“…It is worth mentioning that there are other approaches in the literature for handling cloud vertical inhomogeneity in cloud property retrieval. For example, the Clouds from Infrared Sounders retrieval algorithm (Feofilov & Stubenrauch, ; Stubenrauch et al, ) implemented empirical weighting functions to account for the contributions of vertical cloud layers. In other words, rather than vertical profiles of cloud properties, the radiative effects of vertical cloud layers were the ones being implemented in Clouds from Infrared Sounders.…”

“…The cloud coverage is around 70% of the Earth's surface when analyzing clouds with optical thickness greater than 0.1 (Stubenrauch et al, , ). Out of all detected clouds, the high‐level clouds can occupy about 40–50% on the global scale, when considering instruments deemed most sensitive to thin cirrus clouds (Stubenrauch et al, ).…”