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Lanzhou University (2016)

Dust Aerosol And Its Effects on The Meterological Fields in Northwest China

周旭

Titre : Dust Aerosol And Its Effects on The Meterological Fields in Northwest China

Auteur : 周旭

Grade : Doctoral Dissertation 2016

Université : Lanzhou University

Résumé
In this paper, we use ground observations and WRF/Chem model which coupled the dust emission module developed by Shao to analysis the sensitive factors during dust storm. The sensitive factors in dust emission parameterization scheme are fixed to suit Northwest China. Strong dust storm break out in Northwest China is simulated by the dust forecast system. The radiative forcing of dust aerosol and its effect to boundary layer is analyzed.Accurate forecasting dust storms can provide services for disaster prevention and mitigation. However, there is always some uncertainty to dust storm forecast. The dust emission parameterization schemes play an import role on dust storm forecast quality. Dust emission parameterization scheme developed by Shao Yaping combine with WRF/Chem be used in this article. The characteristic of dust emission, deposition, transport and vertical distribution of PM10 during dust storm is simulated. The applicability of the model in China also tested. The result show that model can simulate the process of dust storm process in northwest China, and the simulated concentration values and range of PM10 range of analog values is good agreement with observations. Soil plastic pressure P and emission factor cy in Shao’s dust emission parameterization scheme is take into sensitivity test and the influence to horizontal and vertical dust flux is analyzed. The uncertain to dust storm simulation of soil plastic pressure P and emission factor cy are surveyed during dust storm take place in Northwest China. The values of these two parameters are conformed to suit for simulation dust storm break out in Northwest China.The simulation of strong sandstorm process shows that the dust emission region is concentrated at Zhangye-Wuwei-Minqin region, maximum emission exceed 55000 mg/m2. PM10 is quickly settlement in the dust emission region. Minqin area where dry deposition accounted for about 5% of dust emissions, Yinchuan dry deposition accounted for 72% of dust emissions. Dust emission and deposition in Dunhuang area is very small, dust emission is only 4.01mg/m2, dry deposition amount is 6.23 mg/m2, but Minqin is 5040.79 mg/m2, Xi’an only have dry deposition for 63.62 mg/m2. During the black storm the dust emission of Minqin is 5.04 t/km2. The vertical distribution of the PM10 concentration in different regions is provided. We found that PM10 are mainly grouped distributed in the atmosphere under 3000 m, and only a less can diffuse to more than 3000 m for long-distance transmission. The PM10 that diffused to upper air can be transmitted to the thousands of kilometers away.The impact of dust aerosols to boundary layer meteorology fields is analyzed. The results show that the effects of dust aerosol to surface temperature have a certain relationship with dust layer height, concentration and time. At night, high concentrations of dust aerosols can be heating the lower atmosphere, which can increase the lower atmosphere temperature higher than 1 ℃. This “heating” characteristic is associated with the surface albedo,lager albedo greater “heating” effect. The dust aerosols can reduce temperature above the middle and upper of dust aerosols layer. Dust aerosols have a cooling effect on the lower atmospheric, leading to the surface temperature is decrease up to 3 ℃, during daytime. The variety of dust aerosol concentration with height lead to different effect on the atmosphere in different heights, the ‘heating’ effect is strongly at region of high concentration of dust aerosol at neight. Dust aerosol concentration is decrease with the reduced of height, the ability of ‘heating’ atmosphere effect is weakening. In addition, the ‘heating’ effect of dust aerosol reduce atmospheric stability can make boundary layer height raise, about 400 m, averaged. Cooling effect enables enhanced atmospheric stability, resulting in reduced boundary layer, maximum about 700 m during daytime. Dust aerosols lead to increased horizontal wind speed, the value is about 1m/s. Dust aerosol also can increase vertical wind velocity blow dust aerosols layer, maximum 0.22 m/s.In contrast with different simulation experiment, the influence of dust aerosol to downward long wave flux at ground surface(GLW), downward short wave flux at ground surface(SWDOWN) and top of atmospheric outgoing long wave(OLR) is analyzed. Found that the impact of dust aerosol to downward short wave flux at ground surface is very significant and can lead to its decreases 42.51%. In the region that dust aerosol concentration is high, downward short wave flux at ground surface decreases about 300 W/m2, and the region that dust aerosol concentration is smaller, d downward short wave flux at ground surface decreases about 100W/m2. Downward long wave flux at ground surface is associated with dust aerosol. Dust aerosol transport from upstream, can increased downward long wave radiation flux at ground surface, playing a role in reducing the surface temperature. While dust aerosol that emissions from local due to wind erosion, can decreased downward long wave radiation flux at ground surface, playing a " thermal insulation " effect, which can be increased surface temperature in the region at night. Dust aerosols can be increased the top of atmospheric outgoing long wave flux by in the atmosphere by its scattering, thus decrease the temperature of atmosphere, which resulted mechanism that in the cooling in middle of the dust aerosol, while the warming in the upper layer of dust aerosols. Analysis of changes in radiation flux in different locations, found that dust aerosols enhances downward long wave flux at ground surface, with hourly average ranging from 17.49 to 50.49 W/m2. Downward short wave radiation flux at ground surface is reduced by an average of 42.51%, with hourly average ranging from-3.30 to-49.46 W/m2. The affect to top of the atmosphere outgoing long wave radiation flux ranges from-25.29 W/m2 to +28.83 W/m2.

Mots clés : dust emission parameterization scheme; dust aerosol; boundary layer; meteorology field; radiative forcing;

Présentation (CNKI)

Page publiée le 28 janvier 2017, mise à jour le 11 septembre 2017