Radiative controls by clouds and thermodynamics shape surface temperatures and turbulent fluxes over land

Area of Science:

• Earth and Environmental Sciences
• Atmospheric Science
• Climate Science

Background:

• Land surface temperatures (LSTs) are influenced by radiation, turbulent fluxes, and hydrologic cycling.
• Water vapor, through clouds and evaporation, modulates regional temperatures.
• Understanding these interactions is key to comprehending climate dynamics.

Purpose of the Study:

• To investigate the primary drivers of climatological variations in LSTs across dry and humid regions.
• To determine the role of radiative effects versus turbulent and hydrologic processes in LST variations.
• To elucidate the thermodynamic constraints on heat and moisture fluxes.

Main Methods:

• Utilized a thermodynamic systems framework.
• Forced the framework with independent observational data.
• Analyzed satellite observations for both cloudy and clear-sky conditions.

Main Results:

• Climatological LST variations are mainly mediated by radiative effects.
• Turbulent fluxes (sensible and latent heat) are thermodynamically constrained by local radiative conditions.
• Clouds significantly cool humid land surfaces (up to 7 K), an effect absent in arid regions due to lack of cloud cover.
• Reduced evaporation in dry regions is compensated by increased sensible heat flux and buoyancy.

Conclusions:

• Radiation and thermodynamic limits are the primary controls on LSTs and turbulent flux exchange.
• Clouds play a crucial role in modulating LSTs, particularly in humid regions.
• Despite system complexity, observed climatological patterns exhibit emergent simplicity driven by these fundamental controls.