title: Ubiquity and impact of thin mid-level clouds in the tropics.
abstract: Clouds are crucial for Earth's climate and radiation budget. Great attention has been paid to low, high and vertically thick tropospheric clouds such as stratus, cirrus and deep convective clouds. However, much less is known about tropospheric mid-level clouds as these clouds are challenging to observe in situ and difficult to detect by remote sensing techniques. Here we use Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite observations to show that thin mid-level clouds (TMLCs) are ubiquitous in the tropics. Supported by high-resolution regional model simulations, we find that TMLCs are formed by detrainment from convective clouds near the zero-degree isotherm. Calculations using a radiative transfer model indicate that tropical TMLCs have a cooling effect on climate that could be as large in magnitude as the warming effect of cirrus. We conclude that more effort has to be made to understand TMLCs, as their influence on cloud feedbacks, heat and moisture transport, and climate sensitivity could be substantial.
authors.affiliation: Department of Meteorology, Stockholm University, Stockholm 10691, Sweden.|Bolin Centre for Climate Research, Stockholm University, Stockholm 10691, Sweden.
authors.forename: Quentin
authors.initials: Q
authors.lastname: Bourgeois
authors.affiliation: Department of Meteorology, Stockholm University, Stockholm 10691, Sweden.|Bolin Centre for Climate Research, Stockholm University, Stockholm 10691, Sweden.
authors.forename: Annica M L
authors.initials: AM
authors.lastname: Ekman
authors.affiliation: Department of Atmospheric Sciences, University of Miami, Miami, Florida 33149, USA.
authors.forename: Matthew R
authors.identifier: 0000-0001-8916-544X
authors.initials: MR
authors.lastname: Igel
authors.affiliation: Bolin Centre for Climate Research, Stockholm University, Stockholm 10691, Sweden.|Department of Applied Environmental Science and Analytical Chemistry, Stockholm University, Stockholm 10691, Sweden.
authors.forename: Radovan
authors.initials: R
authors.lastname: Krejci