Diurnal asymmetry of desert amplification and its possible connections to planetary boundary layer height: a case study for the Arabian Peninsula

Recent studies using observations, reanalysis data and climate model simulations documented that 2 m surface air temperature (T2m) has been amplified over the world's hottest and driest Sahara Desert and the Arabian Peninsula, referred to as desert amplification (DA). This study presents a comprehensive analysis of hourly surface observations, radiosonde measurements, and two latest state-of-the-art reanalysis products for the period 1979-2018 to examine the diurnal and vertical variations of DA and their connections with planetary boundary layer height (PBLH). It focuses on the Arabian Peninsula (AP), where observations are relatively abundant compared to the data scarce Sahara regions. Both observational and reanalysis data show that the diurnal cycle of surface warming rate depends, to some extent, inversely on the magnitude of climatological PBLH, and so DA has a distinct diurnal asymmetry with a stronger warming for a shallower PBLH. Results of upper air profiles reveal that DA is a bottom-heavy warming profile, which maximizes near the surface, decreases quickly with height, and is limited to the lower troposphere (> 700 hPa) and surface. The major PBLH biases could explain, at least partially, some of the diurnal and vertical warming/cooling biases in the reanalyses. These results suggest that besides the surface radiative forcing, the PBLH may play an important role in modulating the diurnal and vertical structure of DA over the AP through heat redistributing via turbulent mixing.

Automated summary

This study investigated the diurnal and vertical variations of desert amplification (DA) over the Arabian Peninsula, finding that the surface warming rate is inversely related to the magnitude of planetary boundary layer height (PBLH) and DA exhibits a distinct diurnal asymmetry with stronger warming for shallower PBLH. Results indicate that PBLH biases may explain some of the diurnal and vertical warming/cooling biases in reanalysis data, suggesting the importance of PBLH in modulating the structure of DA through heat redistribution via turbulent mixing.