The Spatiotemporal Characteristics Of Temperature Lapse Rate In China

Tropospheric air TLR（Trop-ATLR）is an index to measure the atmospheric stability.The near-surface air TLR（SATLR）and the land-surface TLR（LTLR）can be considered as indirect indices for the atmospheric stability to a certain extent.In addition,SATLR and LTLR have their distinctive research values;for instance,they are important parameters in the hydrological and climate modeling,and regional climate downscaling,which affect the simulation results in the surface or surface air temperature.With complex topography and climatic conditions,the studies on climatological characteristics of temperature lapse rates（TLR）in China is of great significance.As the long-term change of SATLR are closely related to the elevation-dependent warming and the long-term change of Trop-ATLR can reflect the sensitivity of climate system,it is significant to study the long-term trend of these two kinds of TLR.Based on the data of surface meteorological stations,radiosonde stations,moderate-resolution imaging spectroradiometer（MODIS）,and digital elevation model（DEM）,the spatiotemporal characteristics including climatological characteristics and long-term trend of three kinds of TLR,i.e.LTLR,near-SATLR,and Trop-ATLR,were studied.On the aspect of climatological characteristics,the spatial distribution of annual mean and seasonal mean and annual variation of LTLR,SATLR,and Trop-ATLR,the diurnal variation of SATLR,and the temporal variation of average LTLR in seven geographical zones,were analyzed.In addition,the relationship between the LTLR and the surface temperature and elevation were studied,and the distance of values beween the three kinds of TLR were compared and discussed.On the aspect of long-term trend,those of SATLR and Trop-ATLR were calculated and the spatial distribution of long-term trend in China were discussed and analyzed.In order to do the above-mentioned studies,a novel methodology for the calculation of gridding TLR was developed,which was based the drived formula of TLR with temperature gradient field and elevation gradient field and was achieved in compute with image enhance technology.The improved fuzzy c-means（FCM）clustering method was utilized to distinguish the seasonal variation patterns of TLR.Due to the complex terrians and climate conditions in China,ecological sub-regions were attempted to divide whole research areas into different parts,and the linear mixed-effects（LME）model was used to calculate the average TLR in each region,based on the high-resolution automatic weather stations dataset.Moreover,the geographically weighted regression（GWR）model was applied to estimate the SATLR at the 2419 national meteorological stations.The climatological characteristics of LTLR were:（1）the annual mean LTLR mainly ranged from 4 to 7℃/km,and the average value was 4.6℃/km;（2）the seasonal variation pattern of steepest-in-summer（about 5.9℃/km）and shallowest-in-winter（about3.0℃/km）was the typical characteristics of annual variation;（3）the annual range of LTLR in the Southeast and Central China were relatively small;（4）the phenomenon of temperature inversion mainly occurred in the areas with lower elevation and lower land surface temperature.The climatological characteristics of SATLR were:（1）the annual mean SATLR mainly ranged from 4 to 7℃/km;（2）the annual range of SATLR were mostly less than4℃/km;（3）the monthly SATLR were uaually found steepest in summer,followed by winter and spring,less in autumn;（4）the nocturnal mean SATLR was usually shallower than the daytime mean SATLR by about 0 to 2℃/km;（5）the diurnal range of SATLR mainly ranged from 3 to 7℃/km;most of the steepest hourly mean SATLR in a day occurred between 7:00 and 9:00 in the eastern part of China;（6）for the 16 main mountainous areas,there might be quite different in different aspects of the same mountain,and the time that the hourly SATLR got the steepest or shallowest values was changeable with season.The long-term trend of SATLR were:（1）the regional average annual SATLR anomalies in mean temperature showed a significant decreasing trend of-0.023℃·km^-1·decade^-1 during the period of 1961-2018;（2）in the early period（1961-1998）,the regional average of SATLR anomalies in mean temperature showed significant decreasing trends in summer and autumn,however,those in recent two decades（1999-2018）did not undergo significant decrease in all seasons;（3）the spatial distribution of grids with significant positive trend and negative trend of annual SATLR anomalies in maximum temperature and in minimum temperature was different:the strong positive trend SATLR anomalies in maximum temperature were mainly distributed in Central China,and those in minimum temperature were in Southwest China,e.g.the eastern part of the Tibetan Plateau,the Hengduan Mountains;（4）the strong and widespread negative trends of SATLR anomalies were usually found in winter in minimum temperature,while the strong and widespread positive trends did in spring in maximum temperature.The climatological characteristics and long-term trend of Trop-ATLR were:（1）the annual mean Trop-ATLR was 6.1℃/km,which increased gradually from the southeastern part of China to the northwestern part;（2）the Trop-ATLR became the steepest in spring,with 6.4℃/km;（3）the common seasonal variation pattern of Trop-ATLR was the summer pattern,followed by the spring pattern and the winter pattern,and no autumn pattern was found;（4）though the areas was extensive that the Trop-ATLR became steep,it was not significant in statistics.On the whole,the relationship of the three kinds of TLR was Trop-ATLR>SATLR>LTLR,and the distances of values in winter were larger than those in summer.SATLR was steeper than LTLR in all months,and the difference between them was smaller in summer than that in winter;the difference between Trop-ATLR and SATLR was relatively small in the months of late spring and early summer,and relatively large in winter months.In addition,the spatiotemporal variation of TLR may be related to the variation of relative humidity,wind speed,aerosol,etc.