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

Ashok Kumar Pokharel,Michael L Kaplan

doi:10.5194/esd-10-651-2019

Abstract

Abstract. Based on the large-scale transport of dust driven by the winds parallel to the mountains in the Harmattan, Saudi Arabian, and Bodélé Depression dust storm cases, a detailed study of the generation of Kelvin waves and its possible role in organizing these dust storms and large-scale dust transport was accomplished. For this study, observational and numerical model analyses were done in an in depth manner. For this, MERRA reanalysis data sets; WRF-simulated high-resolution variables; MODIS Aqua and Terra images; EUMETSAT images; NAAPS aerosol modeling plots; and MERRA-2 dust scattering aerosol optical depth (AOD) modeling plots, surface observations, and rawinsonde soundings were analyzed for each of these three case studies. We found that there were meso-β-scale (horizontal length scale of 20–200 km) adjustment processes resulting in Kelvin waves only in the Harmattan and the Bodélé Depression cases. The Kelvin wave preceded a cold pool accompanying the air behind the large-scale cold front instrumental in the major dust storm. We find that this Kelvin wave organized the major dust storm in a narrow zone parallel to the mountains before it expanded upscale (meso-α to synoptic).

Highlights

The Sahara is dominated most of the year by the northeasterly wind-driven dry and hot air originating from the anticyclonic system centered over the North Atlantic Ocean (Shao, 2000)
Since Bechar lies to the east of Atlas Mountains and is the nearest sounding station to the Atlas Mountains, it is logical to expect that the information regarding the vertical profiles of meteorological variables in the lee of the mountains could be well represented in the analysis of before and after the Kelvin wave formation
Besides the downslope wind effects and the jet adjustment processes which were responsible for these three dust storms (Pokharel et al, 2017a, b, 2016; Pokharel, 2016), we found that the organization of the dust storms and the synoptic-scale transport of dust from the Harmattan and Bodélé Depression dust storms were seen to be caused by the Kelvin waves

Summary

Introduction

The Sahara is dominated most of the year by the northeasterly wind-driven dry and hot air originating from the anticyclonic system centered over the North Atlantic Ocean (Shao, 2000). The emission of dust from the Bodélé Depression takes place throughout the year though the peak emission occurs in winter and spring (Washington and Todd, 2005; Washington et al, 2006). These facts indicate the importance of the study of the Harmattan and Bodélé Depression dust storms. Studies of these phenomena have been increasing since these two systems deliver a significant amount of dust equatorward, causing severe negative impacts on visibility, agriculture, and human health (e.g., causes meningitis) (Burton et al, 2013; Kalu, 1979; Pérez García-Pando et al, 2014)

Methods

Results

Conclusion