Seminar: Sarosh Alam Ghausi
- Date: Oct 27, 2022
- Time: 02:00 PM - 03:00 PM (Local Time Germany)
- Speaker: Sarosh Alam Ghausi
- Kleidon Research Group
- Location: Max-Planck-Institut für Biogeochemie
- Room: Hörsaal (C0.001)
Land surface temperatures are closely coupled to the hydrologic cycle because the presence of water in the atmosphere (clouds) and at the surface (evaporation) strongly modulate temperatures across regions. While both, clouds and evaporation, affect each other, they have a very distinct effect on the surface energy budget which reflects the inherent complexity and strong coupling between land and atmosphere. We used a thermodynamic systems framework forced with observations and quantify the effect of clouds and evaporation on surface temperatures. We first show that the turbulent fluxes of sensible and latent heat are thermodynamically constrained by the local radiative conditions and the ability of surface heating to perform work to sustain vertical mixing within the convective boundary layer. This implies that reduced evaporative cooling in dry regions is then compensated for by an increased sensible heat flux and buoyancy, which is consistent in observations. We show that the temperature variation across dry and humid regions is mainly controlled by clouds that reduce surface heating by solar radiation. Using "clear-sky” and “all-sky” fluxes from the NASA-CERES radiation dataset together with our thermodynamically constrained surface energy balance, we show that clouds cool the land surface over humid regions by up to 7 K while in arid regions this effect remains absent due to the lack of clouds. We conclude that thermodynamics and radiation are the primary controls on land surface temperatures and turbulent flux exchange which leads to an emergent simplicity in the observed climatological patterns within the complex climate system.
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