| Characteristics of snow are sensitive and active,which can reveal the change of climate system.The low thermal conductivity and high reflectivity of snow has impact on balance of energy,radiance and human activities on a regional spatial scale,even the global level.In the context of global warming,spatial and temporal changes of snow cover have become the hot issue of the scientific community.According to the IPCC fifth assessment report on global climate change,the global snow cover will keep reducing.The 24th Olympic Winter Games will be held in the Beijing-Zhangjiakou region.Monitoring and analyzing the characteristics of local snow cover,as well as temporal-spatial distribution and variation will play a significant role in learning about the local natural conditions and making preparations for the Olympic Winter Games.Remote sensing and meteorological observation data are the main sources of snow monitoring in general,by looking into which we'll be capable of monitoring and analyzing temporal-spatial variation and features of snow cover from different perspectives.Meteorological observation data and multi-source remote sensing data(NOAA-AVHRR,MODIS snow products and snow depth retrieved from brightness temperature of SMMR/SSMI/SSMIS)were selected to study the temporal-spatial variation and features of snow cover in Beijing and Zhangjiakou Region.The main analysis based on the remote sensing data includes:(1)Seasonal and monthly temporal-spatial variation of snow cover and depth area in winter(1980-2014);(2)Intra-annual variance of snow cover ratio and temporal-spatial variation of snow cover frequency in winter(2001-2014).The main research content based on records of meteorological stations(1962-2014)includes:(1)annual variation of the days with snow cover,lasting days with snow cover,snow cover period,the first and final days with snow cover;(2)temporal-spatial variation of the days with snow cover,lasting days with snow cover,snow cover period,the first and final days with snow cover and the snow coverage rate in snow accumulation period of meteorological stations,and the Mann-Kendall trend of listed items except the snow coverage rate in snow accumulation period;(3)the correlativity between temperature,precipitation,.the polar vortex area index and the snow cover days of meteorological stations respectively.Besides,the RegCM 4 Model was performed to stimulate seasonal and monthly temperature and precipitation in winter.Combined with historical data and prediction data,the abundance and stability of snow in Beijing and Zhangjiakou Region and its impact on Winter Olympic Games was concluded.The research results:(1)the area and depth of snow in winter showed an upward trend(1980-2014).The area and depth increased in December and January,which decreased in February.Intra-annual variance of depth was inverted U shaped.Speaking of spatial distribution,average depth of winter snow was between 0 and 2 cm,and high values existed in northern region of study area.During 2001 and 2014,intra-annual variance of snow cover ratio rose,similar to snow depth.Snow cover frequency kept a low rate,and the overall change showed a slight trend of increase.The spatial distribution of snow cover frequency was not uniform,and the high value area was corresponding to that of snow depth.(2)Trend of snow parameter changes increased in winter(December and January),and snow was most abundant and stable in January.The winter snow can be divided into three stages:Snow accumulation period(December and early January),Snow maintenance period(middle and late January),and Snow melt period(February).The snow resource in Zhangjiakou was better than that in Beijing.(3)The days with snow cover showed an increasing trend,which was similiar in December and January,opposite in February.The lasting days with snow cover showed a downward trend slightly.The first days with snow cover were advanced,and the final were advanced signifcantly.Snow cover period tended to shrink,which reflecte the decrease of snow stability.According to the records of meteorological stations,68%of meteorological stations showed an upward trend of the days with snow cover.Most stations showed an upward trend of the lasting days with snow cover,which was not significant,but the absolute value of the decline was greater than that of the rise.The number of the station whose first day with snow cover advanced was basically the same as the delayed.84%of the meteorological stations who's the final days with snow cover were advanced,84%of the stations had shorter snow cover period.The spatial distribution of snow cover indexes could meet the trend of "ladder shaped" in Northwest and southeast of the study area,except the snow cover ratio in snow cover period.(4)There was a negative correlation between the mean temperature during snow cover period and the snow cover days in most meteorological stations.There were significant positive correlations between the days with snow cover and the days whose temperature was below zero,the number of snow days and the snowfall rates in all stations.There was a negative correlation between the polar vortex area index and winter mean temperature,and no significant correlation between the polar vortex area index and the days with snow cover.(5)According to simulation results,compared with the winter during 2012-2017,the temperature and precipitation would increase during 2017-2022 in the study area.6)Snow resources in the study area tend to be abundant in winter,but the value is in a low state actually,and the trend in February is opposite to that in winter.The stability of snow in winter is likely to decrease,and the downward trend is obvious in February.Therefore,it is necessary to prepare artificial snow. |
PDF Full Text Request