２种统计方法对气象要素均一性的影响

在天气现象观测中,轻雾、霾、浮尘是较易混淆的天气现象,准确的判断和记录这些现象,需要从形成条件、天气背景、垂直能见度、相对湿度等方面进行分析,综合判断,本文对此作了一些分析和探讨。     

北京气候变暖与主要极端气温指数的归因分析

在对资料进行均一化处理的基础上,分析了北京1960—2008 年气候变暖及主要极端气温指数的统计特征,并应用格兰杰检验法对其进行归因分析。结果表明:(1) 近49 a 来北京年平均气温增速约为0.39 ℃/(10 a),气候增暖具有明显的非对称性。(2) 霜冻指数和气温年较差呈下降趋势,降幅为3.9 d/(10 a)和0.8 ℃/(10 a)。生长季指数、暖夜指数及热浪指数则呈上升趋势,增幅平均达3.0 d/(10 a)、0.75%/(10 a)和1.5 d/(10 a)。(3) 北京年平均气温是霜冻指数、生长季指数及暖夜指数发生变化的格兰杰原因。虽然年平均气温与热浪指数在不同滞后期均具强相关性,但是检验表明它们之间并无显著的因果关系,很可能是由于某种原因导致的一种统计上的伪相关现象。      

中国东部夏季极端降水时空分布及环流背景

基于中国测站的降水资料和NCEP/NCAR逐日再分析资料,取第95百分位数作为极端降水阈值,通过经验正交函数分解(EOF)方法将中国东部分为华南、长江中下游、华北和东北三个地区,定义极端降水事件,并对中国东部夏季极端降水时空分布及环流背景进行研究。结果表明,极端降水事件随日期的变化与中国东部夏季雨带的南北移动相吻合。近54年来,华南极端降水事件频数在1991年左右突增,长江中下游地区有两次突变,1991年左右突增,2000年左右突减。华北和东北地区在1999年左右突减。发生极端降水事件时,低层850 hPa出现局地异常气旋环流,位势高度异常降低,对应低空异常辐合;中层500 hPa,西太副高位置异常偏南有利于华南极端降水的发生,副高西伸有利于长江中下游的极端降水,位置偏北易造成华北和东北极端降水;高层200 hPa,发生极端事件时降水关键区位于西风急流轴右侧,对应异常反气旋环流,这种高层辐散低层辐合的环流配置为极端降水提供动力条件。极端降水的气候平均态水汽主要来源于南半球和西北太平洋。副高的位置异常影响我国东部水汽输送异常,造成不同地区的极端降水。      

The Long-term Variation of Extreme Heavy Precipitation and Its Link to Urbanization Effects in Shanghai during 1916–2014

Using the hourly precipitation records of meteorological stations in Shanghai, covering a period of almost a century(1916–2014), the long-term variation of extreme heavy precipitation in Shanghai on multiple spatial and temporal scales is analyzed, and the effects of urbanization on hourly rainstorms studied. Results show that:(1) Over the last century, extreme hourly precipitation events enhanced significantly. During the recent urbanization period from 1981 to 2014, the frequency of heavy precipitation increased significantly, with a distinct localized and abrupt characteristic.(2) The spatial distribution of long-term trends for the occurrence frequency and total precipitation intensity of hourly heavy precipitation in Shanghai shows a distinct urban rain-island feature; namely, heavy precipitation was increasingly focused in urban and suburban areas.Attribution analysis shows that urbanization in Shanghai contributed greatly to the increase in both frequency and intensity of heavy rainfall events in the city, thus leading to an increasing total precipitation amount of heavy rainfall events. In addition,the diurnal variation of rainfall intensity also shows distinctive urban–rural differences, especially during late afternoon and early nighttime in the city area.(3) Regional warming, with subsequent enhancement of water vapor content, convergence of moisture flux and atmospheric instability, provided favorable physical backgrounds for the formation of extreme precipitation.This accounts for the consistent increase in hourly heavy precipitation over the whole Shanghai area during recent times.     

Ranking Regional Drought Events in China for 1960--2009

The spatiotemporal variations of the site and regional droughts in China during 1960–2009 were analyzed by applying a daily composite-drought index (CDI) to 722 stations in mainland China. Droughts frequently happened in a zone extended from Southwest China to the Yellow River, North China, and the southwestern part of Northeast China, with two centers of high frequency in North China and Southwest China. In Southwest and South China, droughts tend to happen during the winter. In North China and along the Yellow River, droughts mainly occur during the winter and during May–June. During the past 50 years, the geographical distribution of site drought events showed high frequencies (0.9–1.3 times per year) in the upper Yellow River basin and North China, comparing with moderate frequencies (0.6–0.9 times per year) in Southwest China and the southwestern part of Northeast China and with lower frequencies over the middle and lower Yangtze River basin. And the frequencies increased over mainland China except for the upper reaches of the Yangtze River. A regional drought (RD) event is a widespread and persistent event that covers at least five adjacent sites and lasts for at least 10 days. There were 252 RD events in the past 50 years—five times per year. Most RD events lasted for <100 days and covered <100 stations, but the longest and largest RD event lasted for 307 days from 6 September 1998 to 9 July 1999 and covered 327 stations from North to Southwest China.     

全球气候变暖对长江三角洲极端高温事件概率的影响

研究了全球气候变暖对长江三角洲极端高温事件（ＥＨＴＥ）概率的影响。结果表明,全球增暖将使ＥＨＴＥ发生的概率增大。当夏季逐日平均最高气温在现有的基础上升高３．０℃后,ＥＨＴＥ发生的概率将由现在的０．１３增加到０．２～０．３,即夏季出现级端最高气温≥３５℃的天数将由现在的１２ｄ左右增加到２０～３０d。     

我国极端气温指数的时空变化与分区研究

利用1961-2000年全国550个台站的逐日最高气温、最低气温资料计算出热浪指数和暖夜指数并对两个指数分别进行时空变化分析,结果表明极端气温指数的前2种模态基本代表了该指数的空间分布特征.热浪指数和暖夜指数的第一特征向量的荷栽场空间分布基本一致,全区为一致的增加和减少趋势,并且在时间变化上存在着明显年际和年代际变化特征.利用REOF和CAST聚类分析相结合的方法对热浪指数和暖夜指数进行分区,将全国热浪指数和暖夜指数分剐分成11个和10个变化区.经过验证发现该方法既克服了前者确定荷载值界限的主观性,又避免了后者选择气候中心的不确定性,使区划结果更具有客观性.     

近40 a青海湖流域逐日降水和气温变化特征

利用青海湖流域内刚察气象站1958～2001年的逐日降水和气温资料,分析了流域内的气候变化特征.结果表明,日降水量P≤5 mm的降水总量以9 mm/10 a的速率显著减少,已从1960s的130.8 mm/a减少为1990s的116.2 mm/a,而P≥20 mm的降水总量以9 mm/10 a的速率显著增加,已从29.7 mm/a增加为36.9 mm/a;连续无降水最长天数由1960s的32 d/a增加为1990s的45 d/a,至少10 d连续无降水总天数由103 d/a增加为145 d/a.逐年平均温度40 a来明显升高,已从1960s的-0.7℃升至1990s的0.1℃,且与逐年极端低温升高有较好相关性.1990s与1960s的同日平均气温相比,已有261 d变暖(占年天数的71.2%),且主要发生在冬季.这种气候变化特征对流域内的青海湖水位和河川径流有重要影响.     

Trends in Extreme Precipitation Events in the Indus River Basin and Flooding in Pakistan

In the absence of a sufficiently dense network of climate stations covering all topographic regions of the Indus River basin and delivering high quality data over the last 30 years or more, daily precipitation data were obtained from the National Centers for Environmental Prediction-Department of the Enviornment (NCEP-DOE) Reanalysis 2 dataset for the period 1979 to 2011. The daily precipitation data were transformed into time series of frequency of extreme precipitation events of 1-day and 10-day durations defined in terms of 90th and 99th percentile threshold exceedances. The non-parametric Mann-Kendall trend test was applied to determine whether statistically significant changes in precipitation extremes occurred over time, in due consideration of autocorrelation in the data.

Extreme precipitation showed a high spatial variability, with the highest daily and 10-day precipitation totals, and thus highest 90th and 99th percentiles, in the southeastern lowlands at the foot of the Himalayas and the lowest in the Karakorum. Significantly decreasing trends in extreme precipitation were observed in the western part of the Indus River basin; significantly increasing trends were mainly detected in the very high mountainous regions in the east (Transhimalaya and Himalayas) and in the north (Hindu Kush and Karakorum) of the Indus basin. High precipitation rates are not common in the arid climate of these high mountainous regions. Future flood management plans need to consider the increasing trends in extreme precipitation events in these areas.     

利用ECMWF产品对庆阳极端气温释用效果分析

利用CMSVM的回归方法,用2003～2007年的欧洲数值预报格点资料和庆阳市8个自动站极端气温资料建立最高最低气温预报模型.2008年业务运行效果检验评估表明:5 d最高、最低气温综合平均预报准确率达到64%和71%,对实时业务有较好的指导作用.最高、最低气温准确率随着预报时效的延长效果降低,最低比最高气温的预报准确率高.最低气温预报效果春夏季好于秋冬季,最高气温相反.最高、最低气温绝对误差和平均误差都随预报时效的延长增大,最高比最低气温平均绝对误差大,二者的平均误差接近,均为正值,预报值具有偏高的倾向.对9月明显变化过程的评估表明,最高最低气温预报与实况演变的趋势相似.