| Atmospheric aerosols have a significant impact on climate change.Dust aerosols,accounting for nearly half of the total atmospheric aerosols,can affect climate and ecosystem through their direct and indirect effects,and their total amount is the most important link affecting the global material cycle and climate change.Dust storm process has been considered as the most important source of dust aerosols.but another important source of dust aerosols-dust devil should not be ignored.Compared with the dust storm process,although the amount of dust aerosols in the atmosphere lifted by the dust devil is limited every day,the frequency of this small and medium-sized dust devil is very high,and its contribution may account for 30?65%of the total annual dust aerosol,and it is a very important source of dust aerosols.At present,there are few observations on this kind of small and medium-sized dust devil,and the research on its formation mechanism and spatial and temporal distribution characteristics is still very weak.Therefore,it is of great scientific significance and value to carry out the dust devil observation and fine-resolution simulation research.Based on many years' first-hand observation data in the southern margin of Tengger Desert near in northwest China's Gansu province,we analyzed features and their relationship with the related meteorological factors of dust devil.Surface temperature by means of satellite remote sensing data of downscale and the temperature interpolation processing,reduction of relations with the observed data in the desert area,A resolution of 1km ground-air temperature difference field in the study area was established to solve the problem of underestimation of ground-air temperature difference,which is the most important judgment condition for dust devil and simulation by model.The spatial distribution of sediment in the study area from June to August 2019 was carefully simulated by using the latest sediment parameterization scheme of dust devil and WRF/ Chem model coupling.The spatial-temporal variation characteristics were analyzed,and the relationship between wind-induced sediment intensity and related factors such as desert surface type in this area was discussed.Based on the observation of the early stage of the formation mechanism and the dust devil "heat convection bubble" theory,we developed "heat convection bubble-power" concept model and theory that can reasonably explain the characteristics of sediment by dust devil.The main conclusions of this study are as follows:(1)Through 2014 ? 2017 in southwest margin of Tengger desert dust devil observation of summary data analysis found that: the dust devil of diameter of less than 2m in the area of probability is larger than 2m diameter of more than 8 times,dust devil is Often appear in the daily 9:00-16:00,the peak is in commonly between 14:00 to 15:00,More than 70% of dust devils occured in June and August of each year.The meteorological conditions and thresholds of dust devil are as follows: when the air temperature is between 19??35? and the wind speed is between 1?5m/s,the frequency of clear sky or little cloud is much greater than that of cloudy or cloudy weather.In the case of precipitation,dust storm does not occurred.It is found by practical observation that the local small terrain in desert area has an important effect on the surface temperature.The analysis shows that the surface temperature on both sides of the dune varies from 5 ? to 10? at clear sky day.Before 14:00 to 15:00,the surface temperature of the sunny slope is higher than that of the shady slope,and after 15:00,the shady slope is higher than that of the sunny slope.The difference of surface temperature on both sides of a dune on a cloudy day is much smaller than that on a clear sky day,only about 2??The temperature difference between the two sides of the dune is small whether it is sunny or cloudy.(2)Taking NVDI(Normalized difference vegetation index)and NDBI(Normalized difference building index)as statistical correlation factors,the statistical regression method was used to carry out spatial scaling of surface temperature data obtained by satellite remote sensing.It was found by comparison that FY-2G surface temperature data had better adaptability to this method than EMCWF data.By comparison with the measured data,The absolute error between the corrected LST with a resolution of 1km and the measured LST is2.06? and a relative error of 5.58%,which was nearly 20?better than the original surface temperature field.The temperature product with ERA5 resolution of 0.1 deg was interpolated into a temperature field with resolution of 1km by using the local thin plate smooth spline model,and the interpolation temperature was very close to the observed value.The results show that the temperature difference between earth and air is much higher in desert than in green continent,and the daily change of temperature difference is highly correlated with the daily change of dust devil frequency,indicating that the greater the positive value of temperature difference between earth and air,the higher the frequency of dust devil occurred.At the same time,when the local temperature difference is less than 8K,there is little dust devil appear.(3)The WRF model and the dust devil induced sediment parameterization scheme were used to conduct a fine-scale simulation of dust devil sediment in the study area from June to August 2019,and the daily variation distribution and monthly distribution characteristics of the dust devil from June to August were analyzed.The simulation results showed that the diurnal variations of the dust devil were distributed in a single peak,which was consistent with the observation results of the frequency of the dust devil.The dust devil mainly appeared in desert regions and occasionally occurred in oases.The farther the distance from the oasis area,the greater the frequency of dust devil,the corresponding amount of sand;In desert areas,sand formation is greater in dunes covered by scattered vegetation and undulating dunes.At the same time,the amount of removal by dust devil is also related to the state of sand on the underlying surface,and the amount of sediment by dust devil is smaller and smaller on the flowing sand,semi-fixed sand and fixed sand.The results show that in addition to the threshold value of meteorological elements,surface type and soil type can all affect the occurrence of dust devil,and there are slight differences between sediment of dust devil in desert areas.(4)Based on observation facts and the "thermal convection bubble" theory of formation mechanism of dust devil,two conceptual models of "thermal convection bubble-dynamic" between flat desert with sandy vegetation and dune with uniform underlying surface conducive to dust devil formation were established,which made up for the deficiency of the theory of horizontal wind that makes hot convection bubbles rotate.It is a good explanation for the high occurrence of dust devil around flat deserts with sandy vegetation and between dunes with uniform underlying surface. |
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