| Atmospheric water vapor is the key of regional water cycle and the source of regional precipitation.To further study the changes of air water circulation and atmospheric circulation in Northwest China,and to verify the applicability of different atmospheric water vapor data in this area.In this paper,atmospheric water vapor data of 21 sounding stations in Northwest China from 1958 to2013 were selected as measured values.Combined with the ECMWF?European Centre for Medium-Range Weather Forecasting?monthly reanalysis of water vapor data,MODIS?Moderate Resolution Spectrometer?remote sensing retrieved atmospheric water vapor image data and precipitation data of 21 meteorological stations corresponding to the sounding stations in the same period,the accuracy of ECMWF and MODIS data was evaluated by using the linear regression model and Thiessen?polygon?method,and the error of two kinds of lattice data was corrected.The spatial and temporal variation characteristics and vertical layered distribution of atmospheric water vapor content in Northwest China during 1979-2016 were analyzed by means of unitary linear regression analysis,anomaly accumulation,Kriging and IDW?inverse distance weighting?.Meanwhile,the spatial variation of precipitation conversion rate in this region was analyzed by combining precipitation data.The interannual and seasonal variations of atmospheric water vapor transport flux synthesis field,zonal and longitudinal atmospheric water vapor transport field in Northwest China were analyzed by Grads.The"source"and"sink"of atmospheric water vapor in the past 38 years were studied by analyzing the interannual and seasonal distribution characteristics of atmospheric water vapor transport flux divergence field.Meanwhile,resample and linear regression analysis were used to calculate the net atmospheric water vapor budget in Northwest China.Finally,the correlation between air temperature and atmospheric water vapor was discussed by using the temperature data of the same period in this area.The main conclusions are as follows:?1?Compared with MODIS,ECMWF was more consistent with the measured values of sounding,and the overall correlation was high.Meanwhile,the correlation between the two sets of data and the measured values varied greatly in different regions.ECMWF was lower than the measured value,MODIS data was higher than the measured value,and the deviation between the two sets of data and the measured value was significant.ECMWF and MODIS data deviated greatly from the measured values,but ECMWF deviated less than MODIS.Both ECMWF and MODIS data were overestimated at 1 000 mm.The errors between the corrected ECMWF and MODIS and the measured values was significantly reduced,respectively.The correlation coefficients were as high as 0.98 and0.95,and passed 0.01 significance test.MODIS data had a larger correction range than ECMWF data,but there still were the circumstances of low overestimation and high underestimation.ECMWF and MODIS water vapor error area distribution trend was the opposite,the corrected ECMWF data had a higher spatial accuracy than MODIS data.The annual average error between ECMWF data and sounding data was-43.4 mm,and MODIS and sounding data was 25.79 mm.?2?The atmospheric water vapor content in each layer of barometric layer in Northwest China decreases with the increase of altitude.Meanwhile,the annual average atmospheric water vapor content in each layer and the annual water vapor concentration in each season are mainly below 5 000meters.During 1979-2016,the atmospheric water vapor content in Northwest China decreased at a rate of 3.6 mm/10 a,and the average annual water vapor content was 813.31 mm.The climate in Northwest China became cold dry during 1979-1986,Warm and wet during 1987-2006,and warm dry during 2007-2016.In the past 38 years,the spatial distribution of atmospheric water vapor content in this region has decreased from monsoon and westerly sub-regions to plateau sub-regions.And the monsoon sub-region is much larger than the plateau sub-region.The maximum value of atmospheric water vapor content was 1 727.72 mm?Hanzhong Station?,and the minimum was 465.14 mm?Golmud?.?3?The precipitation conversion rate in Northwest China increased from plateau sub-region to westerly sub-region and monsoon sub-region to plateau sub-region as a whole.The average precipitation conversion rate in mountainous areas was 25.95%,the maximum was 68.78%?cooperation?,and the minimum was only 3.58%?Ruoqiang?.Meanwhile,in the region where the atmosphere was stable all the year round,the development potential of airborne cloud water resources first decreased from west to east and then increased.?4?The annual average atmospheric water vapor transport synthetic field in Northwest China during 1979-2016 was mainly controlled by the westerly,northerly and monsoon water vapor fluxes.Among them,the northerly wind water vapor transport flux intensity was up to 850 kg m-1·s-1,followed by the monsoon,400-700 kg m-1·s-1,and the westerly wind transport intensity was the smallest,only 200-300 kg m-1·s-1.In each season,summer was the season with the highest atmospheric moisture transport intensity in this region,and it was mainly affected by the northerly wind and monsoon moisture transport flux,with the maximum up to 400 kg·m-1·s-1,and the minimum in winter,with the maximum moisture transport flux intensity less than 20 kg·m-1·s-1.In recent 38years,the average zonal atmospheric water vapor transport in Northwest China had a large influence on the water vapor carried by the westerly wind,but its intensity of water vapor transport was relatively small(0-400 kg m-1·s-1).The northerly monsoon and southeast monsoon carried less water vapor,but the intensity of transporting water vapor was larger(0-800 kg m-1·s-1).Except for the summer monsoon water vapor flux in the eastern part of the summer,the rest of the season was mainly affected by the westerly water vapor flux.In the past 38 years,the annual average water vapor transport in the central and western parts of the Northwest China has been mainly affected by the northerly wind water vapor flux.The water vapor transport intensity was 200-1 200 kg·m-1·s-1 and0-200 kg·m-1·s-1,respectively.The eastern region was affected by the southeast monsoon,and the water vapor transport intensity was 0-200 kg·m-1·s-1;among the meridional water vapor transport in each season,summer was the largest and its intensity was the largest,the maximum was up to 400kg.m-1·s-1.?5?In the past 38 years,water vapor convergence centers have been formed in Tianshan Mountains,Tarim Basin,central Gansu Province and eastern and western Qinghai Province.The convergence intensity is 0-0.004 kg m-2·s-1,which was the"sink"of water vapor in this area,while in other areas,the atmospheric vapor divergence intensity was 0.001 kg m-2·s-1,which was the"source"of water vapor in Northwest China.?6?During 1979-2016,the annual average atmospheric water vapor balance in the northwest region was surplus,but the surplus was reduced at a rate of 7.59×108 t·a-1.The net annual net atmospheric water budget was 2 786.83×108 t;The latitudinal atmospheric water vapor surplus decreased at a rate of 17.88×108 t·a-1,and the average annual net income was 3 541.04×108 t;The net loss of water vapor in meridional atmosphere decreases at the rate of 10.29×108 t·a-1,and the annual average net revenue and expenditure was-754.21×108 t.In the past 38 years,the annual average atmospheric water vapor balance in the northwestern region has been in a loss state in the middle east,but the loss has decreased at a rate of 6.21×108 t·a-1.The average annual atmospheric water vapor input was 728.68×108 t;The atmospheric water vapor surplus on the western boundary,but the surplus was reduced at a rate of 0.81×108 t·a-1,with an average annual average of 586.35×108 t;Atmospheric water vapor surplus on the southern and northern borders and the annual average net atmospheric water vapor budget is 250.80×108 t and 509.45×108 t respectively,and the net water vapor input increases at the rates of 10.13×108 t·a-1 and 12.73×108 t·a-1 respectively. |
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