Abstract
The diurnal/seasonal structure of the boundary layer height (BLH) is investigated over East Asia by using the hourly synoptic monthly ERA5 reanalysis variables from 1979 to 2019. Sensible heat flux (SHF) is the major factor in the temporal and spatial variation of the BLH. Although BLH, in general, is positively correlated with SHF throughout the year, BLH-SHF relationship varies significantly based on the surface type, latitude and time of the year. Analysis also reveals that stability is an important parameter controlling the diurnal maximum BLH. The growth of BLH is strongly limited by the presence of a stable layer. On the other hand, BLH increases abruptly in the presence of a weakly stratified residual layer. In addition, regional warming tends to increase the BLH in the mid- to high-latitude continental area. In the low-latitude continental area, the sign of anomalous SHF varies seasonally and regionally. Stability plays only a minor role in the BLH change except over the Tibetan Plateau, where the increased stability at the top of boundary layer due to warming reduces BLH rather significantly.
Highlights
The planetary boundary layer (PBL) is the lower portion of the atmosphere in which the flow field is strongly influenced by direct interaction with the Earth’s surface
This study aims to complement the observational studies with somewhat localized scope in space and time by providing the full spatiotemporal structure of boundary layer height (BLH) variability throughout the year
We hope that this study serves as (1) useful guideline for improving the boundary layer physics in computer models, (2) basic information on the spatiotemporal structure of boundary layer in East Asia, and (3) a benchmark solution aiding more localized and detailed analysis of the BLH and its physics
Summary
The planetary boundary layer (PBL) is the lower portion of the atmosphere in which the flow field is strongly influenced by direct interaction with the Earth’s surface. The portion above the PBL is called the free atmosphere, and a clear difference between the two layers is the timescale of response to surface forcing [1,2,3]. The exchange of heat, momentum, water, and chemical constituents between the surface and the free atmosphere occurs in the PBL, and specific features of this exchange are highly dependent on the turbulent motions in the PBL [4]. In this respect, the dispersion of chemical contaminants produced by human activities is closely associated with the physics of the PBL
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