Desert Amplification and Its Diurnal Cycle

Recent studies found that land surface air temperature (LSAT) in mid- and low- latitudes is amplified in a warming climate over deserts such as the Sahara Desert and the Arabian Peninsula (SDAP). This amplification, referred to as desert amplification (DA), maximizes near the surface and decreases gradually with height, and enhances linearly with the global mean greenhouse gas (GHG) radiative forcing. These results suggest that DA, analogous to the well-known arctic amplification, may represent a fundamental pattern of global warming in low- and mid- latitudes and will intensify with increasing GHGs. However, the major processes and mechanisms of DA are largely unknown. This study focuses on the diurnal cycle of DA considering the unique features of desert surface and atmospheric boundary layer (ABL) conditions relative to their surroundings. Among various climate zones the SDAP is the driest due to limited moisture availability and has the deepest and well-mixed atmospheric boundary layer (ABL) at daytime but the shallowest and stratified ABL at nighttime. For a given forcing, the surface warming rate depends inversely on the ABL depth, and thus is expected to be largest at nighttime. Analyses of in situ, satellite, reanalysis data and multi-model climate simulations show consistently that DA has a distinct diurnal cycle and a very stronger day-night asymmetry. Key findings will be presented, and other key thermodynamic and dynamic mechanisms of DA will be discussed. Understanding the diurnal cycle of DA will help us to determine the contribution of local land surface and ABL conditions relative to other mechanisms to DA.