The Weather Research and Forecasting model with chemistry (WRF‐Chem) is used to investigate an intense dust storm event during 26 to 30 July 2006 that originated over the Taklimakan Desert (TD) and transported to the northern slope of Tibetan Plateau (TP). The dust storm is initiated by the approach of a strong cold frontal system over the TD. In summer, the meridional transport of TD dust to the TP is favored by the thermal effect of the TP and the weakening of the East Asian westerly winds. During this dust storm, the transport of TD dust over the TP is further enhanced by the passage of the cold front. As a result, TD dust breaks through the planetary boundary layer and extends to the upper troposphere over the northern TP. TD dust flux arrived at the TP with a value of 6.6 Gg/day in this 5 day event but decays quickly during the southward migration over the TP due to dry deposition. The simulations show that TD dust cools the atmosphere near the surface and heats the atmosphere above with a maximum heating rate of 0.11 K day−1 at ~7 km over the TP. The event‐averaged net radiative forcings of TD dust over the TP are −3.97, 1.61, and −5.58 W m−2 at the top of the atmosphere (TOA), in the atmosphere, and at the surface, respectively. The promising performance of WRF‐Chem in simulating dust and its radiative forcing provides confidence for use in further investigation of climatic impact of TD dust over the TP.

Abstract. This study examines the uncertainties in simulating mass balance and radiative forcing of mineral dust due to biases in the dust size parameterization. Simulations are conducted quasi-globally (180 • W-180 • E and 60 • S-70 • N) using the WRF-Chem model with three different approaches to represent dust size distribution (8-bin, 4-bin, and 3-mode). The biases in the 3-mode or 4-bin approaches against a relatively more accurate 8-bin approach in simulating dust mass balance and radiative forcing are identified. Compared to the 8-bin approach, the 4-bin approach simulates similar but coarser size distributions of dust particles in the atmosphere, while the 3-mode approach retains more fine dust particles but fewer coarse dust particles due to its prescribed σ g of each mode. Although the 3-mode approach yields up to 10 days of longer dust mass lifetime over the remote oceanic regions than the 8-bin approach, the three size approaches produce a similar dust mass lifetime (3.2 days to 3.5 days) on quasi-global average, reflecting that the global dust mass lifetime is mainly determined by the dust mass lifetime near the dust source regions.With the same global dust emission (∼4600 Tg yr −1 ), the 8-bin approach produces a dust mass loading of 39 Tg, while the 4-bin and 3-mode approaches produce 3 % (40.2 Tg) and 25 % (49.1 Tg) higher dust mass loading, respectively. The difference in dust mass loading between the 8-bin approach and the 4-bin or 3-mode approaches has large spatial variations, with generally smaller relative difference (< 10 %) near the surface over the dust source regions. The three size approaches also result in significantly different dry and wet deposition fluxes and number concentrations of dust. The difference in dust aerosol optical depth (AOD) (a factor of 3) among the three size approaches is much larger than their difference (25 %) in dust mass loading. Compared to the 8-bin approach, the 4-bin approach yields stronger dust absorptivity, while the 3-mode approach yields weaker dust absorptivity. Overall, on quasi-global average, the three size parameterizations result in a significant difference of a factor of 2∼3 in dust surface cooling (−1.02∼ −2.87 W m −2 ) and atmospheric warming (0.39∼0.96 W m −2 ) and in a tremendous difference of a factor of ∼10 in dust TOA (top of atmosphere) cooling (−0.24∼ −2.20 W m −2 ). The impact of different size representations on dust radiative forcing efficiency is smaller. An uncertainty of a factor of 2 is quantified in dust emission estimation due to the different size parameterizations. This study also highlights the uncertainties in modeling dust mass and number loading, deposition fluxes, and radiative forcing resulting from different size parameterizations, and motivates further investigation of the impact of size parameterizations on modeling dust impacts on air quality, climate, and ecosystems.

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