Observations and cloud-resolving modeling of haboob dust storms over the Arabian Peninsula

Strong mesoscale haboob dust storms in April 2007 in the central Arabian Peninsula were studied using the cloud-resolving Weather Research and Forecasting-Chemistry (WRF-Chem) modeling system and observations collected during an intensive atmospheric field campaign. The field campaign provided the valuable aircraft and Doppler weather radar measurements. Active convection persisted for several days during the study period. Dust generation was caused by both strong large-scale winds and locally produced density currents. Because of insufficient spatial resolution, the event was not resolved accurately by the conventional reanalyses. However, the WRF-Chem model did successfully capture the primary features of the convection, its location, and precipitation patterns. Although the amount of rainfall in the model was slightly underestimated compared to the satellite measurements, it was approximately double the rainfall in the reanalysis. The convection-associated dust outbreaks were simulated well, with the aerosols optical depth magnitude and the temporal variability being in good agreement with both the ground-based and satellite aerosol retrievals. The model captured the major dust generation patterns, transport pathways, and several of the largest haboobs identified from the satellite observations. About 25 Tg of dust was emitted in the Arabian Peninsula during the 10-day period. Approximately 40% of the locally deposited dust was subject to wet removal processes. During periods of high local dust production, the WRF-Chem model underestimated the PM10 mass concentration (associated mostly with dust particles larger than 3 mu m in diameter) by nearly a factor of 2. This suggests that the current dust parameterizations, which prescribe the size distribution of the emitted dust, underestimate the number of large particles that increases at strong wind conditions.