中国冬半年极端低温事件的时空特征及其与东亚冬季风的关系

利用1961～2012年全国553站逐日最低气温资料,根据百分位值法,定义了不同台站的极端低温阈值,并统计分析了逐年逐站发生极端低温事件的频数,并且使用经验正交函数分解(EOF)的方法对其时空变化特征进行了研究。研究结果表明:近51年来,我国冬半年极端低温事件总体呈明显的减少趋势,但仍存在明显的时空差异。EOF分析结果显示我国极端低温事件发生频率主要存在3种空间模态,即空间一致型和南北振荡型以及东西振荡型。并且对PC1(第一主分量)时间序列作突变检验的结果表明,我国冬半年极端低温事件频数在1986年前后存在明显突变现象,这与1986年前后东亚冬季风发生年代际突变时间点一致。进一步相关回归分析结果表明,我国冬半年极端低温事件频数与东亚冬季风指数存在很好的相关性,这可能与西伯利亚高压的变化有显著的联系,即冬半年西伯利亚高压强时,极端低温事件发生较多,反之亦然。分析的结果表明,1986年前后,中国冬半年极端低温事件发生频次的突变可能与西伯利亚高压的南移并且减弱有关。     

河南省1961—2011年极端气温和极端气温事件的时空变化特征

根据1961-2011年河南省32个气象站逐日最高、最低气温资料,以百分位阈值方法定义极端气温事件的阈值,采用线性倾向估计及Mann-Kendall检验两种方法,对河南省极端气温和极端气温事件的时空变化特征进行了研究.结果表明:1)河南省极端最高气温以0.20℃/10a的速率呈显著降低趋势;极端最低气温以0.42℃/10a的速率呈显著升高趋势,其升高趋势比前者降低趋势更为显著.2)河南省极端高温事件频数与极端低温事件频数分别以2.04天/10a和3.13天/10a的速率显著减少,且后者比前者减少趋势更为显著.3)极端最高气温降低的突变年与极端高温事件频数减少的突变年一致,均为1969年;极端最低气温升高的突变年与极端低温事件频数减少的突变年一致,均为1985年.4)河南省极端最高(低)气温与极端高(低)温事件频数变化趋势呈现明显的季节差异和地区差异.     

1960—2015年中国冬半年极端降温过程事件的时空演变特征

利用1960-2015年中国2 474个站点的逐日最低气温资料,采用REOF方法将中国分为7个区域,通过对每个区域内所有站点降温阈值进行平均,得到了7个降温阈值。当某区域内测站单日降温幅度超过区域平均阈值时,认为该测站发生一次极端降温事件。7个区域降温平均阈值各异,总体呈北大南小特征,最大降温-10.6℃,最小-7.6℃。根据上述定义,研究了中国冬半年极端降温过程事件的时空演变特征。结果表明：极端降温事件发生频数呈北多南少的空间分布。北部地区存在多个频发中心,在42°N和35°N附近存在两个高频发生带。南部地区频数呈一定的带状分布,在25°N附近发生该事件的频率亦高于南部其他地区。近56 a来,极端降温事件频数变化总体呈减少趋势,前期较明显,中后期趋于稳定。各年代频数的空间分布基本一致,但前期总体表现为北部增多。而在1990s则转变为南负北正的空间分布,后期中部及沿海地区发生了趋势符号的年代际改变。进一步分析表明,各区域极端降温频数突变的年份均不一致且突变前后的频数存在较大差异。这些结果可为深刻认识极端低温事件的变化规律和气候预测提供线索。     

山东夏季极端热事件变化特征分析

利用山东88个气象站1961—2019年夏季6—8月逐日最高、最低气温观测数据,分析了山东各地极端热昼、极端热夜、极端高温日三个极端热事件的时空演变规律和突变特征。结果表明：1）山东夜间出现极端热事件及白天和夜间同时出现极端热事件的天数增多、强度增强、占比增加。历年极端热昼出现天数和占比均呈不同程度的减少趋势,平均强度呈减小趋势,其中占比减少最明显;极端热夜、极端高温日出现天数和占比均呈不同程度的增加趋势,平均强度呈增强趋势。2）山东内陆和沿海地区各极端热事件变化差异明显。内陆地区极端热昼各指标减少、减小趋势更显著,大部分地区变化趋势通过了0.05的显著性水平检验,半岛南部和东部部分区域则有增加、增强趋势;中西部地区极端热夜各指标增加、增强趋势更显著,大部分地区变化趋势通过了0.05的显著性水平检验;中东部区域尤其是半岛地区极端高温日各指标增加、增强趋势更显著,大部分地区变化趋势通过了0.05的显著性水平检验。3）各极端热事件不同指标的突变情况迥异。极端热昼历年出现天数没有发生突变,平均强度在1970年前后发生突变,突变发生后,平均强度明显减小;极端热夜出现天数和平均强度均在1994年前后发生突变,突变发生后,出现天数明显增加、平均强度明显增强;极端高温日出现天数和强度分别在1994年、1973年前后发生突变,突变发生后,出现天数明显增加。     

中国冬半年最低气温概率分布特征

 根据1955-2005年中国160个站冬半年 (当年11月至翌年4月)平均最低气温资料,使用统计检验的方法,分析了近50 a中国冬半年最低气温的突变事实,在此基础上给出了气候变暖前后最低气温的概率分布,比较了变暖前后时段全国最低气温空间分布的差异。结果表明：1) 20世纪80年代末中国冬半年最低气温发生了显著突变,进入异常增暖时期,其增温程度比平均气温明显;2) 增暖后中国最低气温的概率分布发生了明显的变化,最低气温偏冷的概率显著减小,偏暖的概率明显增大;3)气候变暖后除西南地区最低气温上升幅度不显著外,其余地区均呈现显著增温趋势。     

中国冬半年最低气温概率分布特征

根据1955-2005年中国160个站冬半年 (当年11月至翌年4月)平均最低气温资料,使用统计检验的方法,分析了近50 a中国冬半年最低气温的突变事实,在此基础上给出了气候变暖前后最低气温的概率分布,比较了变暖前后时段全国最低气温空间分布的差异。结果表明：1) 20世纪80年代末中国冬半年最低气温发生了显著突变,进入异常增暖时期,其增温程度比平均气温明显;2) 增暖后中国最低气温的概率分布发生了明显的变化,最低气温偏冷的概率显著减小,偏暖的概率明显增大;3)气候变暖后除西南地区最低气温上升幅度不显著外,其余地区均呈现显著增温趋势。     

中国冬半年极端低温事件的时空特征及其与 东亚冬季风的关系

利用1961～2012年全国553站逐日最低气温资料,根据百分位值法,定义了不同台站的极端低温阈值,并统计分析了逐年逐站发生极端低温事件的频数,并且使用经验正交函数分解(EOF)的方法对其时空变化特征进行了研究.研究结果表明:近51年来,我国冬半年极端低温事件总体呈明显的减少趋势,但仍存在明显的时空差异.EOF分析结果...     

综合极端气候指数的定义和趋势分析

综合极端气候指数对于极端气候变化监测、整体认识区域极端气候变化趋势及其原因和影响,具有实际意义。根据中国常年极端气候特点和不同种类极端气候事件的经济社会影响,选取全国平均高温日数、低温日数、强降水日数、沙尘天气日数、大风日数、干旱面积百分率和登陆热带气旋频数等7种极端气候指标,定义两个综合极端气候指数,分别为7种极端气候指标简单(等值权重)合成的综合指数I和加权(差异权重)合成的综合指数II。综合指数II主要依据各种极端气候事件引发的灾害严重程度及其社会影响大小,分别确定其对应指标的相对重要性和权重系数。分析结果表明:1956～2008年,综合指数I序列表现出明显的下降趋势,说明中国地区常见的极端气候事件总体有不断减少、减弱的趋势;同期综合指数II序列没有表现出明显的升降趋势变化,说明对中国地区具有重大经济和社会影响的极端气候事件频率总体上没有发生明显变化。就各个单项极端气候指数变化来看,全国平均年高温日数、强降水日数和干旱面积百分率呈上升趋势,但除高温日数外,其他指数趋势变化均不显著;全国平均年低温日数、沙尘天气日数和大风日数呈下降趋势,且趋势性均很显著;登陆中国大陆的热带气旋频数有所减少,但趋势不很明显。因此,在全球气候显著变暖的半个多世纪内,中国地区多数常见的极端气候事件发生频率,或者显著减少,或者变化不明显;而对全国经济和社会具有重大影响的主要极端气候事件,其频率总体上未见明显趋势变化。     

1961～2016年中国春季极端低温事件的时空特征分析

利用1961～2016年中国529个台站逐日最低气温资料,研究了中国春季极端低温事件的时空变异特征。旋转经验正交分解结果显示,中国春季极端低温事件的频次在空间上可以分为5个区域,即东北—华北东部地区、江南地区、西北东部—华北西部地区、西南地区和新疆北部地区。小波分析表明,这5个区域春季极端低温事件的频次在年际尺度上呈现出2～4年的振荡周期,其中江南地区、西北东部—华北西部地区和新疆北部地区2～4年的振荡周期在整个研究时段都显著,但东北—华北东部地区和西南地区2～4年的显著周期分别出现在20世纪80年代之前和80年代到90年代中期。在长期变化上,这5个区域春季极端低温事件的频次总体均呈减少趋势,但突变年份具有明显差异。Mann-Kendall和滑动t检验结果表明,东北—华北东部地区春季极端低温事件频次的突变时间为1987/1988年、江南地区为1995/1996年、西北东部—华北西部地区为1990/1991年、西南地区为1987/1988年、新疆北部地区为1997/1998年。伴随着春季极端低温事件频次的降低,5个区域春季极端低温事件的强度在过去半个多世纪也呈现出显著的下降趋势。但近10年来,中国东部地区春季极端低温事件的频次和强度却有所增加,需要引起关注。     

济宁地区极端气温时空变化特征分析

选用1970—2014年济宁市11个国家气象站逐月极端最高气温、极端最低气温和年高温、低温日数资料,采用线性倾向估计、累积距平、M-K突变检验和滑动t检验方法,分析了济宁市极端气温时空变化特征,得出极端最高和最低气温均呈上升趋势,且最低气温上升趋势较最高气温更加显著,各区域变化与全市情况基本一致,但也因地域差异而有所不同。其中,全市年极端最高气温总体呈弱上升趋势,西北部平原地区年极端最高气温平均值较东部山区和南部湖区偏高,高温日数以1.077d/10a的速率显著上升;季节变化不显著;在呈现上升趋势的月份中,仅3月和7月通过了α=0.05的显著性检验。全市年极端最低气温呈极显著上升趋势,南部湖区、东部山区和济宁城区上升较快,西北部平原年极端最低气温平均值较南部湖区偏低,最高与最低相差2.7℃,1986年存在一个由冷变暖的突变,年低温日数以-1.682d/10a的速率极显著下降,1987年存在由多到少的突变;夏、秋、冬季极端最低气温呈极显著上升趋势,以南部湖区、东部山区和济宁城区上升尤为显著,而春季不明显,西北部的梁山县四季变化均不明显;各月极端最低气温均呈上升趋势,但3月和8月不显著。     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

IMPACT OF ATMOSPHERIC LOW-FREQUENCY OSCILLATION ON THE IMMIGRATION OF NILAPARVATA LUGENS(STL) IN HUNAN AND JIANGXI PROVINCES

Various features of the atmospheric environment affect the number of migratory insects, besides their initial population. However, little is known about the impact of atmospheric low-frequency oscillation(10 to 90 days) on insect migration. A case study was conducted to ascertain the influence of low-frequency atmospheric oscillation on the immigration of brown planthopper, Nilaparvata lugens(Stl), in Hunan and Jiangxi provinces. The results showed the following:(1) The number of immigrating N. lugens from April to June of 2007 through 2016 mainly exhibited a periodic oscillation of 10 to 20 days.(2) The 10-20 d low-frequency number of immigrating N. lugens was significantly correlated with a low-frequency wind field and a geopotential height field at 850 h Pa.(3) During the peak phase of immigration, southwest or south winds served as a driving force and carried N. lugens populations northward, and when in the back of the trough and the front of the ridge, the downward airflow created a favorable condition for N. lugens to land in the study area. In conclusion, the northward migration of N. lugens was influenced by a low-frequency atmospheric circulation based on the analysis of dynamics. This study was the first research connecting atmospheric low-frequency oscillation to insect migration.     

A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIO EVENTS

The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

VARIABILITY OF INTER-ANNUAL RELATIONSHIP BETWEEN INDIAN OCEAN DIPOLE AND HUAXI REGION’S AUTUMN PRECIPITATION

The moving-window correlation analysis was applied to investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the synchronous autumn precipitation in Huaxi region, based on the daily precipitation, sea surface temperature (SST) and atmospheric circulation data from 1960 to 2012. The correlation curves of IOD and the early modulation of Huaxi region’s autumn precipitation indicated a mutational site appeared in the 1970s. During 1960 to 1979, when the IOD was in positive phase in autumn, the circulations changed from a “W” shape to an ”M” shape at 500 hPa in Asia middle-high latitude region. Cold flux got into the Sichuan province with Northwest flow, the positive anomaly of the water vapor flux transported from Western Pacific to Huaxi region strengthened, caused precipitation increase in east Huaxi region. During 1980 to 1999, when the IOD in autumn was positive phase, the atmospheric circulation presented a “W” shape at 500 hPa, the positive anomaly of the water vapor flux transported from Bay of Bengal to Huaxi region strengthened, caused precipitation ascend in west Huaxi region. In summary, the Indian Ocean changed from cold phase to warm phase since the 1970s, caused the instability of the inter-annual relationship between the IOD and the autumn rainfall in Huaxi region.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on