Search

With two groups of numerical experiments with and without the cold-core eddy (CCE), the impacts of the CCE on the upper-ocean responses to Typhoon Trami (2018) were investigated using a coupled atmosphere–ocean model. It is commonly accepted that the CCE promotes the sea surface cooling (SSC) primally through the enhanced vertical mixing, while the contributions from the wind-driven advection and the near-inertial advection to the differences in the sea surface temperature (dSST) were underestimated. This study found that the presence of CCE contributed to the stronger along-track cold advection, which dominated the increase in the SSC near the radius of maximum wind (RMW) to the right of Trami’s track, and the stronger cross-track warm advection was acting to prevent the cooling induced by the vertical mixing. During the relaxation stage, the stronger near-inertial advection within the CCE accounted largely for the amplification and the redistribution of the dSST. As for the dynamic responses, the enhanced upwelling and downwelling within the CCE explained the larger cooling and warming in the subsurface temperature oscillations. The wind-driven acceleration of the currents in the mixing layer was larger during the typhoon–eddy interaction so that the CCE became an efficient mixer, thus contributing to the rapid surfacing of the cold water and the ensuing stronger wind-driven advection. These results highlight the importance of the advection processes in the modulating effect of the CCE. Therefore, 3D ocean models are needed to incorporate the mesoscale features of the oceanic eddies for realistically reproducing the upper-ocean responses to tropical cyclones (TCs).

The South China coast has a high incidence of warm-sector heavy rainfall (WSHR) events. The ageostrophic winds in the boundary layer in most of these events associated with the southwesterly boundary layer jets (BLJs) mainly exhibit strong convergence at rainfall area. In this paper, we analyze two cases of WSHR in May 2013 and May 2015, which occurred in similar synoptic environments but varied in intensity, extent, and duration of rainfall, where the ageostrophic winds are the confrontational confluence and asymptotic confluence pattern, respectively. ERA-5 reanalysis data and the diagnostic equation of ageostrophic wind are used to examine the factors affecting the ageostrophic winds in the northern land region and the southern offshore region of the rainfall. The results suggest that land-sea contrast leads to the convergence of ageostrophic winds in the rainfall area. Boundary layer friction dominates the northeasterly ageostrophic winds on land. The diurnal variation of BLJs dominates the ageostrophic winds and their diurnal variation at sea, contributing southwesterly or southeasterly ageostrophic winds, so the phase difference between the land and sea forms confrontational or asymptotic confluence, respectively. BLJs with different intensities, extents, and diurnal variations can lead to different ageostrophic wind patterns and their confluence modes. The land-sea thermal contrast can directly affect ageostrophic winds, and it can also affect the diurnal variation of BLJs, thus affecting the ageostrophic winds and their confluence mode. It is further verified that the BLJs and thermal forcing are important in warm-sector heavy rainfall processes in South China.

The classical maximum intensity theory of Emanuel suggests that the maximum azimuthal wind of tropical cyclones (TCs) depends linearly on the ratio of surface enthalpy and momentum exchange coefficients (Ck and Cd). In this study a series of sensitivity experiments are conducted using the three-dimensional Cloud Model 1 (CM1), by fixing the ratio of Ck/Cd but varying the specific values of Ck and Cd simultaneously. Results show significant variations of simulated maximum intensities by varying Ck and Cd, even if their ratio is fixed. Overall the maximum intensity increases steadily with increasing Ck and Cd when their value is smaller than 1.00×10-3, and then this increase trend slows down with further increasing the coefficients. Two previous theoretical frameworks, one based on gradient-wind balance and the other one incorporating the unbalanced terms, are applied to calculate the maximum potential intensity (PI). The calculated value of the former one shows little variation with varying the specific values of Ck and Cd, while the latter one shows larger value with increasing both Ck and Cd. A further examination suggests that the unbalanced effect have played a key role in contributing to the increasing intensity with increasing Ck and Cd.

Recent numerical modeling studies demonstrate that dry tropical cyclones can be stably sustained via a supply of surface sensible heat flux. This raises questions of whether surface sensible heat flux (SHX) and latent heat flux (LHX) have the same effect on the intensity evolution of tropical cyclones. An estimation of equivalent potential temperature budget in the boundary layer shows that LHX leads to larger increase in equivalent potential temperature than SHX even when they possess the same magnitude. By formulating these two kinds of surface heat fluxes with the same mathematical framework, the simulated intensifications of moist and dry tropical cyclones are compared, with the former driven exclusively by LHX and the latter by SHX. Results show significantly larger intensification rates for the tropical cyclone driven by LHX than that by SHX, revealing low effectiveness of SHX in the intensification of tropical cyclones. The diabatic heating in the moist tropical cyclone occurs accompanying the convection, while it is merely pronounced near the surface in the dry tropical cyclone and is decoupled from the dry convection. A new surface pressure tendency equation is proposed, without incorporating the implicit pressure tendency term on the right-hand side. The budget analysis indicates that the SHX is less effective than LHX in lowering surface central pressure and therefore in tropical cyclone intensification. A series of sensitivity experiments suggest that the threshold of energy input required for spinning up a tropical cyclone is lower in the form of LHX than that of SHX.

As a typhoon approaches the continent, the position where anthropogenic aerosols penetrate, the convection competition between the eyewall and peripheral rainbands, and the separate contributions of direct aerosol-radiation interactions (ARI) and indirect aerosol-cloud interactions (ACI), yield uncertainties in the convection intensification area and hence the typhoon intensity. Typhoon Lupit (2009) was simulated using the Weather Research and Forecasting Model with Chemistry (WRF-Chem) to investigate and isolate the direct and indirect effects of aerosols on the intensity, convection, and precipitation of the typhoon. Three simulations (CTL, CLEAN, and CTLARIOFF) were designed, representing a polluted case (CTL, considering the ingestion of anthropogenic aerosols with ARI and ACI), a clean maritime case (CLEAN, mainly with sea salt aerosols), and a polluted case without aerosol radiative forcing (CTLARIOFF, as per CTL but without ARI) The results showed that anthropogenic aerosols could penetrate into both the peripheral rainbands and the eyewall when the typhoon was approaching the Asian continent Owing to the representation of the real aerosol scenario, the simulated typhoon intensity weakened and was closer to observed values in the CTL experiment. The ARI dominated over ACI with the opposite effects. Specifically, the ACI mainly enhanced the formation of ice-phase hydrometeors within the upper level of the eyewall with more freezing latent heat releases, leading to an invigoration of eyewall convection. These excess ice-phase particles melted after they descended into the warm layer below the 0°C level, which accelerated the accretion of cloud droplets by raindrops (Pcacr) and hence the mixed phase precipitation process in the eyewall. The dynamic feedback induced by the ACI enhanced the boundary layer inflow and the upper layer outflow, supporting the maintenance of strong eyewall convection and intensification of the typhoon. Inversely, the ARI heated the distant periphery low-level atmosphere at an altitude of 1–2 km by the absorbing polluted aerosols. The heated air, driven by the radial inflow, firstly went through the periphery rainbands of the typhoon and invigorated convection there due to the low-level warming. Then, the enhanced periphery convection inhibited the further transport of warm moist air into the eyewall, resulting in weakening of the eyewall convection and hence typhoon intensity. In sum, for the polluted scenario, as the typhoon approached the continent, ARI played a dominant role over ACI. The WRF-Chem model with full consideration of aerosol-cloud-radiation interactions is advantageous in terms of reliably simulating typhoon intensity and precipitation distribution.

This study investigates simulated fair weather shallow cumulus-topped boundary layer (SCTBL) on kilometer and sub-kilometer scale horizontal resolutions, also known as the numerical gray zone of boundary layer turbulence. Based on a priori analysis of a simulated classic SCTBL with large-eddy simulation, its gray zone scale is determined. The dominant length scale of the cloud layer (CL) is found to be the effective cloud diameter, while that of the underlying mixed layer (ML) is the size of organized convection. The two scales are linked by a simple geometric argument based on vertically coherent updrafts, and are quantified through spectral analysis. Comparison to a simulated dry convective boundary layer (CBL) further reveals that the ML gray zone scale does not differentiate between clear and cloudy conditions with the same bulk stability. A posteriori simulations are then performed over a range of resolutions to evaluate the performance of a recently developed scale-adaptive planetary boundary layer (PBL) scheme. Simulation results suggest indifferences to the scale-adaptive capability. Detailed analyses of flux partition reveal that, in the absence of a shallow cumulus scheme, overly-energetic resolved fluxes develop in the CL at gray zone and coarse resolutions, and are responsible for over-predicted resolved convection in the ML. These results suggest that modifications are needed for scale-adaptive PBL schemes under shallow cumulus-topped conditions.

Capture of a strong elevated ducting event, especially its maintenance and sudden change, is of great value to airborne radar to achieve its beyond-the-line-of-sight detection. However, the knowledge is not easily accessible over the open ocean and hence very rare. During the Air–Sea Interaction Survey (ASIS) over the western North Pacific (WNP) in May 2016, a strong elevated ducting event with a long-life period and sudden change in its evolution was observed. Measurements from the ASIS, images from the Himawari-8 satellite, reanalysis data from the ECMWF, and Weather Research and Forecasting (WRF) model, were used to analyze the maintenance and sudden change of this strong ducting event, together with the model performance on simulating it. The results showed that the maintenance of strong elevated ducts, with their tops ranging from 750 to 1050 m and average strength of approximately 38 M units, was caused by a strong dry air mass capping over the wet marine atmospheric boundary layer (MABL), together with the subsidence inversion associated with high pressure. The WRF model performs well in simulating them. However, a sudden increase in duct height with a slight decrease of strength was recorded by the subsequent GPS radiosonde, which was finally contributed to the mechanical turbulent inversion and hydrolapse associated with the marine low-level jet (MLLJ). The height of the maximum horizontal wind speed (Umh) of the MLLJ corresponds well with the bottom of the trapping layer. However, these jet-relevant ducts are generally weak and it is difficult to accurately simulate them by using the mesoscale numerical model, since the wind-shear produced eddies are too small to be properly parameterized.

The duration of the eyewall replacement cycle (ERC) in typhoons is determined by the rate of dissipation of the inner eyewall and intensification of the outer eyewall, which is an important indicator for predicting changes in the intensity and structure of typhoons. Previous studies on ERCs have focused on the internal storm dynamics associated with the interactions between the concentric eyewalls (CEs), but the impacts of the sea surface cooling (SSC) on ERCs remain not adequately investigated. The slow movement of Typhoon Trami results in remarkable SSC. Using a coupled atmosphere-ocean model, the simulation for Trami generates an ERC that matches observations, whereas an unrealistic long-lived ERC is produced in the uncoupled simulation. Numerical simulations suggest that the typhoon-induced nonuniform SSC can not only weaken the typhoon, but can also modulate the duration of the ERCs. The SSC acts like a catalyst for triggering the negative feedback between the surface heat exchange and the circulations of Trami to reduce the energy supply to the inner eyewall more severely where the sea surface temperature (SST) dropped more sharply. The SSC works in concert with the interactions between the CEs to weaken the inner eyewall faster, thus terminating the ERC of Trami rapidly. The results indicate that a better understanding of the modulation effect of SSC is required for the accurate forecast of ERCs.

In Part II of this study, the influence of an oceanic cold-core eddy on the atmospheric boundary layer structures of Typhoon Francisco (2013) is investigated, as well as a comparison with the cold wake effect. Results show that the eddy induces shallower mixed-layer depth and forms stable boundary layer above and near it. The changes of these features shift from northwest to southeast across the storm eye, following the translation of Francisco over the eddy. Nonetheless, the decrease in mixed-layer depth and formation of stable boundary layer caused by the cold wake are located at right rear of the storm. The sensible heat fluxes at the lowest atmospheric model level are mostly downward over the sea surface cooling region. Due to their different relative locations with Francisco, the diabatic heating in the northwest quadrant of the storm can be more effectively inhibited by the cold-core eddy than by the cold wake. The asymmetric characteristics of surface tangential wind are less sensitive to sea surface cooling than those of surface radial wind, implying a change in surface inflow angle. Different from previous studies, the surface inflow angle is found to be reduced especially above the cold-core eddy and cold wake region. An analysis of radial wind tendency budget indicates that the decrease in radial pressure gradient is dominant in changing the acceleration rate of surface radial wind, rather than the decrease in the Coriolis and centrifugal forces, and therefore more outward surface flow is induced by both the cold-core eddy and cold wake.

Satellite altimetry data has been a backbone of global oceanography research since the early 1990s. Because a satellite altimeter measures sea surface height (SSH) at the nadir point, it produces a one-dimensional profile of SSH. Along the track, an altimeter provides SSH sampling at an interval of about 7 km. However, the distance between adjacent tracks is larger than 100 km, and satellites have repeat times of 10–30 d. These characteristics limit the usefulness of altimetry data from a single satellite for scientific analysis of the space-time structure of ocean circulation. During the past two decades, there have usually been three to four altimeters in orbit at any one time. Mapping along-track measurements from multiple altimeters onto a uniform grid has been a major research theme. A popular merged data product, known as AVISO, has been developed and extensively applied to a wide variety of ocean research. One of key properties of a merged data product is its effective resolution. The effective resolution represents the minimum spatial size of an eddy or other mesoscale circulation that the data product can resolve. The AVISO data product has an effective resolution of 300 km in equatorial regions to 100 km in high latitudes. Nowadays, there are more than five satellite altimeters in orbit, including the Chinese HY-2A that was launched in 2011, and thus the density of the tracks has been much improved. However, the effective resolution of the AVISO data product has not increased accordingly. Effective resolution of mapped data is closely related to the background error correlation coefficient scale in the mapping scheme. The effective resolution is no more than twice the correlation coefficient scale even when the amount of satellite altimeter is more than 5. As the background fields contains the correct large scale information, the meso-scale or small-scale information in the background error will play a dominant role and the background error correlation coefficient scale becomes even smaller. Therefore, The option of background determines the effective resolution of mapped data. The above theory is the basement of our new proposed mapping scheme, which effectively improved the effective resolution. Another key technique is how to deal with the observation errors: to reduce time-smoothing by introducing evolution errors in observation errors and effectively mapping multi-mission satellite altimeters from different times. In this study, a new mapping system has been developed, aiming to maximize the effective resolution of the mapped data product. The formulation is based on a variational method and optimal estimation theory. The system has been applied to the South China Sea region. The product uses a regular grid with spacing of 0.08°, in comparison to 0.25° for AVISO. The product merged data from five satellites, Sentinel-3A, Jason-3, Cryosat-2, Saral/AltiKa and HY-2A. Systematic evaluations show that this new product has an effective resolution of 125 km, whereas the AVISO data product an effective resolution of 240 km for the same region. The accuracy is also significantly improved. The new proposed mapping scheme is important in the application of satellite altimeters on the study of meso-scale ocean eddies. In addition, the option of background fields and the processing method of observation error are strictly general and can be used in other schemes of high-resolution data mapping.

Simulations using a convection-permitting numerical model (The Weather Research and Forecasting, WRF) are conducted to investigate the mechanisms responsible for the maintenance and organization of long-lived moist convection into a Mei-yu rainband (091800–101,800 UTC June 2008). This rainband was composed of multiple two-dimensional precipitation bandings, being elongated from the southwest to the northeast with the narrow width. In addition to establishment of the Mei-yu frontal zone, the northwesterly flow behind the mid-tropospheric trough also brought about upper-level dry air. The downward transport of the dry air had a high value of potential vorticity and just overrode the low-level moist southwesterly component, inducing the conditional instability (CI) and frontogenesis at the coherent regions. This behavior combined with the Mei-yu frontogenesis, leading to successive convection to maintain the rainband, whereas the latent heat was not directly linked to the rainband longevity. The releases of CI, conditionally symmetric and inertial instabilities were simultaneously present in the bandings, as an indication of the mechanisms for the formation of banded structures. Therefore, the mesoscale circulations in banded convection developed in the form of coexisted upward and slantwise motions. Our attempt to integrate the dry intrusion and multiple instabilities could be a vital significance in discussing the Mei-yu rainband development.

To explore the effects of air‐sea interaction on the eyewall replacement cycle (ERC) of tropical cyclones (TCs), an ERC of Typhoon Sinlaku (2008) was reproduced using the high‐resolution coupled ocean‐atmosphere‐wave‐sediment transport (COAWST) model. The numerical simulations were evaluated with a wide range of observational datasets. Moreover, the importance of the ocean to ERC is discussed by comparing six sensitive experiments, that is, three uncoupled experiments with different time‐invariant sea surface temperatures, an ocean‐atmosphere coupled experiment, an ocean‐wave coupled experiment, and an ocean‐atmosphere‐wave fully coupled experiment. The results show that Sinlaku simulated by the fully coupled experiment was highly consistent with the observations, and the evolution of ERC varies from those only simulated by the atmospheric models in previous studies. When the ocean and waves were both considered, the lifetime of the ERC was significantly prolonged, even though the simulated Sinlaku was weakened by the cooling of the sea; the asymmetric distribution of the concentric eyewalls (CEs) which caused by the non‐uniform energy exchanges was also prominent. By contrast, without ocean coupling, the simulated secondary eyewall, composed of axisymmetric convections, exhibited false enhancement and fake inward contraction, and the duration of the ERC was also shorter than that actually observed. In conclusion, the results highlight the significance of ocean coupling for the numerical simulation of the ERC of a TC, including survival time and asymmetric structure.

In operational data assimilation systems, observation-error covariance matrices are commonly assumed to be diagonal. However, inter-channel and spatial observation-error correlations are inevitable for satellite radiances. The observation errors of the Microwave Temperature Sounder (MWTS) and Microwave Humidity Sounder (MWHS) onboard the FengYun-3A (FY-3A) and FY-3B satellites are empirically assigned and considered to be uncorrelated when they are assimilated into the WRF model’s Community Variational Data Assimilation System (WRFDA). To assimilate MWTS and MWHS measurements optimally, a good characterization of their observation errors is necessary. In this study, background and analysis residuals were used to diagnose the correlated observation-error characteristics of the MWTS and MWHS. It was found that the error standard deviations of the MWTS and MWHS were less than the values used in the WRFDA. MWTS had small inter-channel errors, while MWHS had significant inter-channel errors. The horizontal correlation length scales of MWTS and MWHS were about 120 and 60 km, respectively. A comparison between the diagnosis for instruments onboard the two satellites showed that the observation-error characteristics of the MWTS or MWHS were different when they were onboard different satellites. In addition, it was found that the error statistics were dependent on latitude and scan positions. The forecast experiments showed that using a modified thinning scheme based on diagnosed statistics can improve forecast accuracy.

This paper presents an evaluation of the observational impacts on blended sea surface winds from a two-dimensional variational data assimilation (2D-Var) scheme. We begin by briefly introducing the analysis sensitivity with respect to observations in variational data assimilation systems and its relationship with the degrees of freedom for signal (DFS), and then the DFS concept is applied to the 2D-Var sea surface wind blending scheme. Two methods, a priori and a posteriori, are used to estimate the DFS of the zonal (u) and meridional (v) components of winds in the 2D-Var blending scheme. The a posteriori method can obtain almost the same results as the a priori method. Because only by-products of the blending scheme are used for the a posteriori method, the computation time is reduced significantly. The magnitude of the DFS is critically related to the observational and background error statistics. Changing the observational and background error variances can affect the DFS value. Because the observation error variances are assumed to be uniform, the observational influence at each observational location is related to the background error variance, and the observations located at the place where there are larger background error variances have larger influences. The average observational influence of u and v with respect to the analysis is about 40%, implying that the background influence with respect to the analysis is about 60%.

Ocean waves generally mix with wind waves and swell, of which only wind waves depend on the local wind field. Using 15 years of hourly observational wind-wave data from eight buoys off the northwest coast of the United States (US), the authors develop a new significant wave height (Hs) and dominant wave period (Tp) scheme (termed as WHP) for open oceans. This scheme relies only on the properties that a single atmospheric model can provide: H s = 0.0143 U 10 2 + 0.9626 , H * = 0.0628 T * 3 / 2 where U10 is the wind speed at a reference height of 10 m, H* is the dimensionless wave height, and T* is the dimensionless wave period. This relation is fitted to U10 values between 4 and 25 m s−1. Comparison results show that the WHP scheme gives an almost best performance in predicting Hs and Tp for the open oceans across different regions. In addition to wind speed, considering the influence of wind direction and stability of the air/sea boundary layer is necessary for wind-wave prediction in coastal areas. Data from the Coupled Boundary Layers and Air–Sea Transfer experiment in LOW winds (CBLAST-LOW) and coastal buoys demonstrate that the effects of the wind direction and stability on Hs and Tp are significant for shallow water; with an increase in water depth, such impacts gradually decrease. Parameterizations for coastal wind waves are also investigated in this paper in Eqs. (19) , (20) , (21) , (22) , (23) , (24) , (25) , (26) , (27) , (28) , (29) , (30) , (31) .

Official forecasts of tropical cyclone (TC) tracks issued by the China Meteorological Administration (CMA); the Regional Specialized Meteorological Centre in Tokyo, Japan; and the Joint Typhoon Warning Center (JTWC) were used to evaluate the accuracies, biases, and trends of TC track forecasts during 2005–14 over the western North Pacific. Overall, the JTWC demonstrated the best forecasting performance. However, the CMA showed the most significant rate of improvement. Two main zones were discovered in the regional distribution of forecast errors: a low-latitude zone that comprises the South China Sea and the sea region east of the Philippines, and a midlatitude zone comprising the southern Sea of Japan and the sea region east of Japan. When TCs moved into the former zone, there were both translational speed and direction biases in the forecast tracks, whereas slow biases were predominated in the latter zone. Twelve synoptic flow patterns of TCs with the largest error have been identified based on the steering flow theory. Among them, the most two common pattern are the pattern with the combination of cyclonic circulations, subtropical ridges, and midlatitude troughs (CRT, 26 TCs), and the pattern of the TCs’ track that cannot be explained by steering flow (NSF, 6 TCs). In the CRT pattern, TCs move northwestward forced by the cyclonic circulations and the subtropical ridges and then turn poleward and eastward under the influence of the midlatitude troughs. In the NSF pattern, storms embedded in the southwest flow by the cyclonic circulation and the steering flow suggest TCs should turn to the right and move northeastward but instead TCs persisted in moving northwestward.

The impact of mesoscale ocean eddies on tropical cyclone intensities is investigated based on a combination of observations and atmosphere–ocean coupling simulations. A statistical analysis reveals that the tropical cyclone–eddy interactions occur at very high frequencies; over 90% of the recorded tropical cyclones over the western North Pacific have encountered ocean eddies from 2002 to 2011. The chances of confronting a cold core eddy (CCE) are slightly larger than confronting a warm core eddy (WCE). The observational sea surface temperature data have statistically evidenced that CCEs tend to promote the sea surface temperature decrease caused by tropical cyclones while WCEs tend to restrain such ocean responses. The roles of CCEs are statistically more significant than those of WCEs in modulating the sea surface temperature response. It is therefore proposed that CCEs should be paid no less attention than WCEs during the TC–ocean interaction process. The CCE-induced changes in sea surface temperature decreases are observed to be more remarkable for more intense and slower-moving tropical cyclones and for thinner depth of mixed layers. A set of numerical experiments reveal that the effects of ocean eddies are positively related to their strengths and storm intensities, and the eddy feedback is less pronounced when the eddy is located at one side of storm tracks than right below the tropical cyclone center. The eddy-induced moisture disequilibrium sooner vanishes after the departure of tropical cyclones. The intensity recoveries last for 1–2 days because of the dependence of surface enthalpy fluxes on surface winds.

An observational study focusing on the locations of tropical cyclogenesis induced by tropical cyclone energy dispersion (TCED) in the western North Pacific is conducted. Statistical results indicate that the cyclogenesis cases associated with TCED widely occur around preexisting tropical cyclones (TCs). In addition to the typical scenario of cyclogenesis to the southeast of a preexisting TC, new TCs can even form in the east or southwest directions at distances ranging from 1000 km to 3500 km. Further analyses reveal that the locations of cyclogenesis are mainly governed by large-scale environments via regulating the patterns of Rossby wave trains. The observational relationships between wave train regimes and the structures of environmental flows are revealed, which are broadly consistent with previous idealized numerical simulations. The results in this study provide a valuable reference for the prediction of cyclogenesis considering the TCED mechanism.

Dust particles in the atmosphere play an important role in air pollution, climate change, and biogeochemical cycles. Some of the dominant sources of dust in mid-latitude regions are in Asia. An intense dust storm engulfed Northern China at the beginning of May 2017, and PM10 mass concentrations of 1500&ndash, 2000 &mu, g m&minus, 3 were measured near the dust source region. We combined numerical simulations, air quality monitoring data, and satellite retrievals to investigate dust emission and transport during this event. We found that the event was closely related to cold front activity, characterized by increased wind speed, which increased dust emission. We improved the dust scheme using a local dust size distribution to better simulate the dust emission flux. We found that accurate parametrization of the dust size distribution was important to effectively simulate both dust emission and ambient particle concentration. We showed that using a local dust size distribution substantially improved the accuracy of the simulation, allowing both the spatial distribution of pollution caused by the dust storm and temporal variability in the pollution to be captured.