The Role of Jet Adjustment Processes in Subtropical Dust Storms

Abstract

Meso‐α/β/γ scale atmospheric processes of jet dynamics responsible for generating Harmattan, Saudi Arabian, and Bodélé Depression dust storms are analyzed with observations and high‐resolution modeling. The analysis of the role of jet adjustment processes in each dust storm shows similarities as follows: (1) the presence of a well‐organized baroclinic synoptic scale system, (2) cross mountain flows that produced a leeside inversion layer prior to the large‐scale dust storm, (3) the presence of thermal wind imbalance in the exit region of the midtropospheric jet streak in the lee of the respective mountains shortly after the time of the inversion formation, (4) dust storm formation accompanied by large magnitude ageostrophic isallobaric low‐level winds as part of the meso‐β scale adjustment process, (5) substantial low‐level turbulence kinetic energy (TKE), and (6) emission and uplift of mineral dust in the lee of nearby mountains. The thermally forced meso‐γ scale adjustment processes, which occurred in the canyons/small valleys, may have been the cause of numerous observed dust streaks leading to the entry of the dust into the atmosphere due to the presence of significant vertical motion and TKE generation. This study points to the importance of meso‐β to meso‐γ scale adjustment processes at low atmospheric levels due to an imbalance within the exit region of an upper level jet streak for the formation of severe dust storms. The low level TKE, which is one of the prerequisites to deflate the dust from the surface, cannot be detected with the low resolution data sets; so our results show that a high spatial resolution is required for better representing TKE as a proxy for dust emission.

From Tropospheric Folding to Khamsin and Foehn Winds: How Atmospheric Dynamics Advanced a Record-Breaking Dust Episode in Crete

“…Regarding dust emissions, the key factor is the enforcement of the boundary layer turbulent kinetic energy (TKE) [68]. This is evident at the 925 hPa map at 0900 UTC (Figure 3b) where the highest TKE values (up to 2 m 2 s −2 ) are found at northeast Libya coinciding with the generation area of the dust storm in the model as shown in the following paragraphs.…”

Organization of dust storms and synoptic-scale transport of dust by Kelvin waves

“…For the study of synoptic to meso-scale observational atmospheric processes that organize conditions favorable for a Kelvin wave, surface pressure, geopotential height, air temperature, wind speed and direction, vertical motion, vertically integrated atmospheric mass tendency, and kinetic energy due to the pressure gradient force obtained from the Modern-Era Retrospective analysis for Research and Applications (MERRA) model (https://disc.sci.gsfc.nasa.gov/ mdisc/data-holdings/merra/merra_products_nonjs.shtml, last access: 8 November 2014; Rinecker et al, 2011) were analyzed. These data were used to create horizontal cross sections at different pressure levels, as well as vertical cross sections of u and v wind speed, and isentropic surfaces at a resolution of 0.50 • × 0.67 • .…”

“…Table 1. List of observational data sets and horizontal grid dimensions, integration times, and WRF model physics applied in all three dust storm cases (Pokharel, 2016;Pokharel et al, 2017b (1) Momentum and heat fluxes at the surface using an Eta surface layer scheme (Janjić, 1996(Janjić, , 2001) that follows depth by MODIS, surface data from Weather Underground, and MERRA 208 × 274 grid points (18 km grid spacing)…”

Dust Devils: Structural Features, Dynamics and Climate Impact

“…Despite the large and increasing number of studies on dust transport, its impact on the Earth system remains very uncertain (see e.g., [39,[75][76][77][78][79][80]). Dust redistributes energy by scattering and absorbing both solar and terrestrial radiation.…”