Formation of a low‐level barrier jet and its modulation by dust radiative forcing over the Hexi Corridor in Central China on March 17, 2010

Abstract

AbstractA low‐level barrier jet (LLBJ) formed along the northeast slope of the Tibetan Plateau on March 17, 2010. The LLBJ was accompanied by a major dust event. Numerical simulations conducted with the Weather Research and Forecasting dust (WRF‐dust) model show that the formation of the LLBJ was primarily due to mid‐level, southeastward descent of high momentum air, which impinged on the north slope of the Tibetan Plateau, resulting in ageostrophic flow acceleration under geostrophic adjustment. The LLBJ was reinforced by the Bernoulli effect, where the physical barrier associated with the Tibetan Plateau to the southwest and the virtual barrier associated with sloped, packed isentropic surfaces to the northeast combined to constrict the air flow, thus augmenting the acceleration of the air as it entered the Hexi Corridor. The simulations show that the LLBJ, which stayed close to the western entrance of the Hexi Corridor, gradually descended during the daytime until early evening. During this period, the core of the LLBJ stayed directly above the 302‐K isentropic surface. The LLBJ, which was located to the south of the main dust plume, was modulated by dust radiative heating and cooling. Over the main dust plume, as well as in the LLBJ region, radiative heating of the dust warmed the upper part of the boundary layer and cooled it below, which stabilized the boundary layer, decreased the boundary layer depth, and reduced the vertical mixing, causing the surface winds to weaken. As a consequence of the feedback between the circulation and the dust radiative forcing, the total dust emission was reduced by ∼9.7–11% and peaked 1–2 hr earlier than without dust radiative effects, while the LLBJ's intensity, which was 1–2 m·s−1 stronger, was better maintained within the boundary layer during the daytime until early evening.