The Dynamics of an Orographically Forced Dust Storm in a Closed Basin

Abstract:

The Salton basin, located in southeast California and at the western edge of the Sonoran Desert, is a sub sea level basin bounded to the west by the Peninsular Mountain Ranges, and to the north and east by the Transverse Ranges, with varied land surface types, some of which are emissive, as well as the Salton Sea. Because of the extreme aridity and regular high wind speeds, dust storms are a common feature of this basin, so much so that the region is one of the dustiest in the Western US. However, despite the regularity of dust storms in this region, very little is known about the dynamics of these events, especially from direct measurements. Here we describe a new research site at the western edge of the Salton Sea, and use measurements from this site, which include surface observations, radiosondes, and remotely sensed data from a sun photometer and ceilometer, to describe a particularly interesting dust storm from 22 February 2020.

The synoptic forcing for this dust outbreak is characterized by cold frontal passage in the early morning hours, and strong westerly flow across the area of interest. The interaction of this flow with the north-south oriented Peninsular Range resulted in trapped lee waves and rotor clouds throughout the morning hours, as well as highly variable yet moderate dust concentrations in the well-mixed boundary layer. Later in the day, spillover precipitation from a cyclonic eddy embedded in the post frontal flow, and a subsequent convective downdraft in the lee of the Peninsular range initiated a shallow density current, with wind speeds greater than 15 m/s in the lower 500 m of the atmosphere. This density current propagated westward and over the desert surface, lofting dust throughout the boundary layer with the highest concentrations confined within the body of the cold jet. Following the passage of the density current, trapped lee waves and surface rotors were again apparent throughout the remainder of the day.