Development of the On-Line MM5 Tracer Model and its Applications to Sahara Dust Transport

Dusts and aerosols can play an important role in the genesis and development of tropical cyclones. Previous studies showed that the development and life cycle of Tropical storm Chantal (2004) were influenced by Sahara dust. Instead of studying detailed interaction between dust and Chantal through cloud microphysics and radiation, the dust loading and its transport were investigated to show a potential link between Saharan dust and Chantal's activities in the eastern Atlantic Ocean basin. Based on the fifth-generation Penn State/NCAR Mesoscale model (MM5), an on-line tracer model (MM5T) was developed to investigate the dust transport of this event. In MM5T, the advection, boundary layer mixing, sub-grid cumulus convective mixing, and sedimentation of tracers were taken into account. The parameters controlling dust pumping were vegetation, soil type, soil moisture, and wind speed. In the model integration, different types of dust were simulated and monitored as different tracers so that the origins of the dust, which potentially interacted with Chantal, were identified. The simulated meteorological results from MM5T were first compared with observations and were quite reasonable. The characteristics of the Middle Level Easterly Jet (MLEJ) and the Saharan Air Layer (SAL), the easterly wave disturbance which became the storm Chantal, and the anticyclonic eddy to the north of the MLEJ off the African coast were well simulated. The simulated dust showed strong evidence that Chantal interacted with Saharan dust at the very early stage of the storm development after propagating into the eastern Atlantic Ocean. Furthermore, simulated results also showed that the mechanism of the dust pumping for this special event was quite different from those previously documented.