Influence of turbulence and dynamics on dust transport in Owens Valley

The dry lakebed of Owens Lake is considered the single largest PM10 (i.e., particulates with a diameter less than 10 microns) source in the contiguous US. During the field phase of the Terrain-induced Rotor Experiment (T-REX, March-April, 2006), a strong dust outbreak took place in Owens Valley on 25 March with the observed instaneous PM10 maximum up to 7000 ƒÝg/m3. This dust event has been simulated using the Navy mesoscale model, COAMPS, with five-level nested grids. The finest grid is centered at Owens Lake with a horizontal spacing of 500 m. The PM10 sizes are partitioned into four distinctive bins. The simulated winds, stability, and PM10 concentrations agree reasonably well with the radiosonde and surface station observations.

The emission, transportation, dispersion, deposition and sedimentation of PM10 in Owens Valley have been extensively examined using the COAMPS output. According to COAMPS and the surface station observations, the dust outbreak started in the afternoon when the strong westerlies above the mountaintop level penetrated into the valley. The PM10 emissions were rather sporadic and well-correlated to the surface wind speed over Owens Lake. The COAMPS simulation indicates that PM10 particles can be advected far north along the valley and eastward into Malpais Mesa Wildness and Death Valley National Park through a relative gap in the Inyo Mountains (i.e., between Keynot Peak and Silver Mountain Summit), associated with strong vertical directional wind shear. The characteristic PM10 transport distance is of the order of 100 km, due to both the suspended fine particles and the presence of a deep well-mixed layer in the valley. The dust emission generally decreased with time after the sunset, in accordance with the decrease of the surface wind speed and increase in the boundary layer stability.