基于极端气温指数的青藏高原年际升温及不对称特征研究

Characterizing the Inter-annual Warming and Asymmetry Condition on Tibetan Plateau Using the Extreme Temperature Indices

基于青藏高原地区98个气象观测站点53年(1960-2012)的气温实测记录,计算了年度昼夜极端温度指数、温度极值和日均温差,并利用趋势分析、变化点检测与分段拟合方法分析了各指数反映的年际变化趋势及空间差异特征。结果表明:青藏高原整体区域各极端温度指数均表现出上升特征,昼夜升温和冷暖升温的不对称性特点显著,夜间冷、暖指数变化速率均快于白天;而在同等昼夜条件下,冷指数下降速率则高于暖指数上升速率,日均温差以-0.18℃/10a的速率小幅降低,温度极值普遍表现为升温现象,近53年来最低气温的极小值上升幅度为4℃左右,明显高于其他极值指数的上升速率,其中最高温度的极大值上升速率最慢,也证实了青藏高原地区温度上升的冷暖不对称性。空间分布上,青藏高原各气温极端指数年际变化速率存在区域差异性,其中西藏的南部及青海的西北部冷昼指数、冷夜指数和暖夜指数变化最为显著;青海、四川及西藏东北部的暖昼指数增长速率稳定。日均温差的变化点大多发生在20世纪80年代初期,多数站点的冷昼指数在90年代中后期发生变化,其余温度指数的变化点集中于90年代初期及中期,时间变化点分布表明研究期间青藏高原温度突变主要集中在20世纪后期。

Based on daily temperature records from 98 meteorological stations on Tibetan Plateau for 53 years（1960-2012）,this paper calculated the annual diurnal extreme temperature indices,temperature extreme indices and diurnal temperature range（DTR）.Among these indices,the first type of indice is a relative indice,and the latter two are absolute indices.The long term trend and spatial variation reflected by these extreme temperature indices were analyzed in this paper,combining the methods of trend analysis,change point detection and piecewise regression methods.Firstly,the general trend of extreme temperature indices in the near 53 years of the Tibetan Plateau was fitted by using the linear regression model.Then,the univariate linear regression method was used to fit the variation segmentally based on Pettitt nonparametric mutation test results.Finally,the inter-annual variation of extreme temperature indices from the site unit was calculated,and regional differences of that were analyzed.The results show that there is a significant warming trend derived from the extreme temperature indices over the whole Tibetan Plateau.The cold and warm indices are becoming warmer in a significant asymmetrical condition,thus both of them in night become warming faster than daytime.While in the same diurnal conditions,the decline rate of cold index is faster than the rising rate of warm index.Furthermore,DTR is also slightly decreased at a rate of-0.18℃/10 a.At the same time,the extreme value of temperature is generally rising.The minimum daily minimum temperature（TNn）index rises about 4℃ in the past 53 years,which is higher than that of other extreme indices.The maximum daily maximum temperature（TXx）index indicates the slowest increase trend,which confirms the asymmetry of the temperature warming on Tibetan Plateau.From the spatial distribution,there are regional differences in the inter-annual variability of extreme temperature index.The occurrences for cold days（TX10 p）,cold nights（TN10 p）and warm nights（TN90 p）in the southern of the Tibet Autonomous Region and Qinghai Province demonstrate a significantly changing condition.There is a stable long term growth trend of warm days（TX90 p）for the regions in Qinghai,Sichuan and the north-eastern part of the Tibet Autonomous.The change points of DTR index occur mostly in the early 1980 s,while the cold day index of most stations changed in the middle and late 1990 s.The change points of the other temperature indices are concentrated in the early and middle period of the 1990 s,which indicates that the temperature change over the Tibetan Plateau is mainly concentrated in the late twentieth century during the study period.