Explicit simulations of convective-scale transport of mineral dust in severe convective weather

Severe duststorms observed in the arid and semiarid regions of East Asia in spring are sometimes caused during the episodes of severe convective weather under the development of synoptic-scale mid-latitude cyclones. Convective processes such as strong updrafts and downdrafts would play an important role in raising mineral dust particles from the surface and transporting them from the planetary boundary layer into the free troposphere, and thus these convective-scale transports of mineral dust are critical in predicting and evaluating the amount of long-range transport of Asian dust (so-called 'yellow sand' phenomena). However, previous numerical studies on the dust transport have been focused on the regional-scale long-range transport, and hence the convective-scale processes have been somehow parameterized or modeled in their simulations. In this study, convective-scale processes such as updrafts, downdrafts, and cold pools are explicitly simulated in order to investigate the convective transport of mineral dust. For this purpose, we perform a high-resolution (i.e., horizontal grid-resolution of 2 km) cloud-resolving simulation that includes a bulk-type cloud-microphysical parameterization as well as wet scavenging and re-evaporation processes of dust. Surface dust fluxes are calculated in proportion to the fourth power of the friction velocity. A linearly-organized convective band whose environmental condition is taken from the study of Takemi (1999) and Takemi and Satomura (2000) is simulated, and the dust transport associated with this convective band is computed coupled with the cloud model. Results indicate that the surface dust is raised into the air by the fast movement of a well-developed surface cold-air pool and a large amount of the dust raised in the air is circulated within the cold pool. Only a small portion of the raised dust, but a significant amount for the free troposphere (i.e., hundreds of micro-grams per cubic meters), is transported upward with convective-scale updrafts at the interface of cold pool and updraft. The dust transported into the upper layer of troposphere is horizontally advected, which can be called as Asian dust.