13B.3 Thunderstorm Outflow Dust Lofting and Resulting Impacts on Convection

Thursday, 27 January 2011: 11:30 AM
615-617 (Washington State Convention Center)
Robert B. Seigel, Colorado State University, Fort Collins, CO; and S. C. van den Heever

Dust lofting via outflow from mesoscale convective cold pools is a common occurrence that, once lofted, alters both the microstructure of clouds and the radiative budget. On a global scale, dust directly impacts the radiative budget through the absorption and scattering of both shortwave and longwave radiation. Additionally dust can indirectly affect the climate through microphysical processes by acting as effective aerosols that alter cloud properties and cloud radiative feedback effects. On the mesoscale, lofted dust modifies precipitation processes within convection by acting as IN, CCN, and GCCN. In extreme cases, strong outflow lofts high concentrations of dust such that visibility is dramatically reduced and air quality is degraded, which becomes a danger to the public, air travel, and military forces.

Numerically modeling this phenomenon is a difficult task due to the resolution required to accurately resolve the small-scale eddies responsible for lofting combined with an effective dust scheme. As such, a three-step approach using the Regional Atmospheric Modeling System (RAMS) with an on-line dust scheme will be utilized to accurately simulate: 1) how convective outflow boundaries loft mineral dust particles from the surface, 2) how the lofted dust becomes entrained into the parent convection, and 3) the resultant feedback of the ingested dust has on the parent convection and associated cold pool. Results presented are with respect to the first portion of the study.

Using RAMS with a very high-resolution domain (100m and 25m horizontal and vertical grid-spacing, respectively), an idealized downdraft generates the surface cold pool and outflow boundary responsible for dust lofting. Sensitivity experiments are conducted by systematically altering soil moisture, soil type, and low-level wind shear to develop a diagnostic parameterization of dust lofting potential as a function of surface soil conditions and cold pool strength. The parameterization will be useful for both operational forecasting to indicate dust storm potential and numerical modeling as an internal lofted dust concentration parameter. Future simulations will use idealized squall lines and supercells to better understand the pathway of dust ingestion and the impacts on the parent convection.

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