Abstract
Clouds in the tropics have an important role in the energy budget, atmospheric circulation, humidity, and composition of the tropical-to-global upper-troposphere–lower-stratosphere. Due to its non-sun-synchronous orbit, the Cloud–Aerosol Transport System (CATS) onboard the International Space Station (ISS) provided novel information on clouds from space in terms of overpass time in the period of 2015–2017. In this paper, we provide a seasonally resolved comparison of CATS characterization of high clouds (between 13 and 18 km altitude) in the tropics with well-established CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) data, both in terms of clouds’ occurrence and cloud optical properties (optical depth). Despite the fact that cloud statistics for CATS and CALIOP are generated using intrinsically different local overpass times, the characterization of high clouds occurrence and optical properties in the tropics with the two instruments is very similar. Observations from CATS underestimate clouds occurrence (up to 80%, at 18 km) and overestimate the occurrence of very thick clouds (up to 100% for optically very thick clouds, at 18 km) at higher altitudes. Thus, the description of stratospheric overshoots with CATS and CALIOP might be different. While this study hints at the consistency of CATS and CALIOP clouds characterizaton, the small differences highlighted in this work should be taken into account when using CATS for estimating cloud properties and their variability in the tropics.
Highlights
Clouds are a key factor in the Earth’s global radiation budget and on the Earth’s climate system [1]
Since January 2015, the Cloud–Aerosol Transport System (CATS) LiDAR system onboard the International Space Station has provided important information on clouds, including high clouds in the tropics, because of its non-sun-synchronous orbit which allows the vertical sampling of clouds and their properties at different overpass times
This contrasts with the well-established Cloud–Aerosol LIdar with Orthogonal Polarization (CALIOP) LiDAR that sounds the atmosphere at fixed overpass times, far from the convective strength peak of early afternoon, that drives the development of higher tropical clouds
Summary
Clouds are a key factor in the Earth’s global radiation budget and on the Earth’s climate system [1]. Since January 2015, the Cloud–Aerosol Transport System (CATS) flies onboard the International Space Station (ISS), in a non-sun-synchronous orbit. With this kind of orbit, different local overpass times are possible. CATS is expected to provide important complementary and new information on clouds, including high clouds in the tropics. The first studies using CATS have recently been realized, and provided new insights into the diurnally resolved cloud occurrence [10]; the interplay of humidity, convection, and clouds in the tropics [11]; and the occurrence and characteristics of stratospheric overshoot in the tropics [12]. We provide a detailed comparison of CATS characterization of high clouds in the tropics with CALIOP data.
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