LAUSR

Abstract This study investigates the diurnal variations of the planetary boundary layer (PBL) properties during heat waves (HWs) based on a decade-long data record of hourly profiles from the Aircraft Meteorological Data Reports (AMDAR) at 54 major airports over the Continental United States. The results are also corroborated by surface observations from weather stations. HWs are defined as periods of at least two consecutive days with daily mean temperature higher than the 95th percentile of the warm season (May to September) climatology. Temperature differences between HW and non-HW periods show strong vertical variations throughout the PBL. Under HWs, the daytime convective PBL is deeper while the nocturnal residual layer is excessively hotter. The difference between HWs and non-HWs in the PBL wind and humidity are not uniform, with clear diurnal and vertical variations at some sites. HW-related changes in PBL wind components are strongly associated with changes in atmospheric circulation patterns, especially in the northeastern region. The specific humidity in the PBL shows increases in humid regions but decreases in arid regions under HWs. Moisture transport and surface evaporation are found to play an important role in modulating the changes in PBL humidity. This study highlights that HW-related changes in the PBL structure are not uniform and are affected by both synoptic and local factors.