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1.
本文从大尺度大气环流和海温异常方面对2019年12月吉林省降水异常成因进行分析,并探究前期秋季日本附近关键区海温异常对吉林省12月降水异常的可能影响。结果表明：1981—2019年吉林省12月降水有明显增多的趋势,在降水年代际偏多的气候背景下,2019年12月吉林全省降水量为常年同期的227.5%,居1981年以来同期多雨雪第4位。前期秋季日本附近关键区海温异常偏暖是12月吉林省降水异常偏多的驱动条件之一,在前期海温异常偏暖年：鄂霍茨克海至日本上空为异常反气旋,阻塞高压活跃,贝加尔湖附近地区为负高度距平,东亚冬季风系统减弱,局地海温的异常升高使其上空的水汽含量增加,配合东亚冬季风异常为吉林省上空带来了充足的水汽;另一方面,由于中纬度45°N附近为西风距平,为东北地区带来冷空气,在槽前正涡度平流作用下,有上升运动,为降水提供了动力条件。在前期海温异常偏冷年：中国东北地区盛行西风,东亚冬季风偏强,中国东部沿海有北风异常,西伯利亚高压偏强,吉林省降水的水汽和动力条件不足,降水异常偏少。  相似文献   

2.
The Maritime Continent (MC) is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon (EASM) and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP–NCAR reanalysis and CMAP [Climate Prediction Center (CPC) Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the Indian Ocean Dipole (IOD). The most significant interannual variability of convective activity is found over 10°S–10°N, 95°–145°E, which can be roughly defined as the key area of the MC (hereafter, KMC). Outgoing longwave radiation anomaly (OLRA) exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia–Pacific/Pacific–Japan (EAP/PJ)-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.  相似文献   

3.
Interdecadal variability of temperature and precipitation in China since 1880   总被引：28，自引：0，他引：28  
Reconstruction of a homogeneous temperature and precipitation series for China is crucial for a proper understanding of climate change over China. The annual mean temperature anomaly series of ten regions are found from 1880 to 2002. Positive anomalies over China during the 1920s and 1940s are noticeable.The linear trend for the period of 1880-2002 is 0.58℃ (100a)^-1, which is a little less than the global mean (0.60℃ (100a)^-l). 1998 was the warmest year in China since 1880, which is in agreement with theestimation of the global mean temperature. The mean precipitation on a national scale depends mainly on the precipitation over East China. Variations of precipitation in West China show some characteristics which are independent of those in the east. However, the 1920s was the driest decade not only for the east, but also for eastern West China during the last 120 years. The most severe drought on a national scale occurred in 1928. Severe droughts also occurred in 1920, 1922, 1926, and 1929 in North China.It is noticeable that precipitation over East China was generally above normal in the 1950s and 1990s;severe floods along the Yangtze River in 1954, 1991, and 1998 only occurred in these two wet decades.An increasing trend in precipitation variations is observed during the second half of the 20th century in West China, but a similar trend is not found in East China, where the 20- to 40-year periodicities are predominant in the precipitation variations.  相似文献   

4.
Four regions are detected in northern Africa (20° W–40° E, 0–30° N) by applying the cluster analysis method on the annual rainfall anomalies of the period 1901–2000. The first region (R1), an arid land, covers essentially the north of 17.75° N from west to east of the study zone. The second region (R2), a semiarid land with a Sahelian climate, less warm than the dry climate of R1, is centred on Chad, with almost regular extension to the west towards Mauritania, and to the east, including the north of the Central African Republic and the Sudan. The region 3 (R3), a wet land, is centred on the Ivory Coast and covers totally Liberia, the south part of Ghana, Togo, Benin and the southwest of Nigeria. The fourth region (R4), corresponding to the wet equatorial forest, covers a part of Senegal, the Central Africa, the south of Sudan and a part of Ethiopia. An analysis of observed temperature and precipitation variability and trends throughout the twentieth century over these regions is presented. Summer, winter and annual data are examined using a range of variability measures. Statistically, significant warming trends are found over the majority of regions. The trends have a magnitude of up to 1.5 K per century. Only a few precipitation trends are statistically significant. Regional temperature and precipitation show pronounced variability at scales from interannual to multi-decadal. The interannual variability shows significant variations and trends throughout the century, the latter being mostly negative for precipitation and both positive and negative for temperature. Temperature and precipitation anomalies show a chaotic-type behaviour in which the regional conditions oscillate around the long-term mean trend and occasionally fall into long-lasting (up to 10 years or more) anomaly regimes. A generally modest temporal correlation is found between anomalies of different regions and between temperature and precipitation anomalies for the same region. This correlation is mostly positive for temperature in cases of adjacent regions. Several cases of negative interregional precipitation anomaly correlation are found. The El Niño Southern Oscillation significantly affects the anomaly variability patterns over a number of regions, mainly regions 3 (R3) and 4 (R4), while the North Atlantic Oscillation significantly affects the variability over arid and semiarid regions, R1 and R2.  相似文献   

5.
This paper presents new high-resolution proxies and paleoclimatic reconstructions for studying climate changes in China for the past 2000 years. Multi-proxy synthesized reconstructions show that temperature variation in China has exhibited significant 50–70-yr, 100–120-yr, and 200–250-yr cycles. Results also show that the amplitudes of decadal and centennial temperature variation were 1.3℃ and 0.7℃, respectively, with the latter significantly correlated with long-term changes in solar radiation, especially cold periods, which correspond approximately to sunspot minima. The most rapid warming in China occurred over AD 1870–2000, at a rate of 0.56°± 0.42℃(100 yr)~(-1); however, temperatures recorded in the 20 th century may not be unprecedented for the last 2000 years, as data show records for the periods AD 981–1100 and AD1201–70 are comparable to the present. The ensemble means of dryness/wetness spatial patterns in eastern China across all centennial warm periods illustrate a tripole pattern: dry south of 25°N, wet from 25°–30°N, and dry to the north of 30°N. However, for all centennial cold periods, this spatial pattern also exhibits a meridional distribution. The increase in precipitation over the monsoonal regions of China associated with the 20 th century warming can primarily be attributed to a mega El Nino–Southern Oscillation and the Atlantic Multidecadal Oscillation. In addition, a significant association between increasing numbers of locusts and dry/cold conditions is found in eastern China. Plague intensity also generally increases in concert with wetness in northern China, while more precipitation is likely to have a negative effect in southern China.  相似文献   

6.
We investigated the regional-scale relationships between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the regional-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001–2008, the increase of almost 40–50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anticyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies in July over the period 2001–2008, we found negative correlations over the areas encompassed by 105–115°E and 30–35°N and by 120–140°E and 35–40°N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation.  相似文献   

7.
利用1981—2013年中国160站逐月降水资料、NCEP/NCAR逐月再分析资料及NOAA海表温度资料,研究了华南前汛期降水年代际异常的时空特征及其可能成因。结果表明:1)华南前汛期降水在1992前后发生由异常偏少转为偏多的显著年代际转折,最显著异常中心位于广西东北部和广东北部。2)1990年代初发生的对流层高层南冷北暖(40°N附近为界)、对流层下暖上冷的年代际转折,使得高低层环流场均出现了有利于北方干、湿冷空气和孟加拉湾、西太平洋暖湿水汽在华南区域交汇并辐合上升的形势,造成华南前汛期降水发生偏少转偏多的显著年代际转折。年代际转折的前后两个时段中,位于热带的孟加拉湾槽、东亚沿岸EAP遥相关型波列中的西太平洋副高、阿拉斯加湾附近的脊,以及中纬度贝加尔湖以西以南脊的强度或位置均具有显著差异,故这些环流系统的年代际异常是华南前汛期降水年代际异常的重要原因。3)南太平洋关键区海温在1990年代初开始呈现增暖趋势,在偏暖(偏冷)时期,华南低空受异常气旋(异常反气旋)环流控制,对流层上层西风急流偏弱偏南(偏强偏北),造成华南地区降水异常偏多(偏少)。  相似文献   

8.
The synoptic-scale winter precipitation variations over southeastern China (22°–32°N, 105°–125°E) and their association with the North Atlantic Oscillation (NAO) during 1951–2007 are investigated in this paper. The variability of wintertime precipitation is characterized by meridional displacement of its maximum center. Two precipitation regimes, with maximum centers located over the Yangtze and Pearl River basins, are identified via cluster analysis. Time-lagged analyses suggest that the two precipitation regimes are connected with the decaying phases of positive NAO (NAO+) events of different amplitudes. A strong (medium) NAO+ event is defined as one when the maximum amplitude of the NAO index exceeds 1.0 (in the range of 0.7–1.0) for at least 4 consecutive days and drops to less than 0.3 within 7 days following the peak index. After the peak of a strong NAO+, southerly winds expand northward to the Yangtze River (about 30°N), a northeast–southwest-tilted trough migrates to east of Lake Baikal, and cold air intrudes into central eastern China; thus, precipitation is strengthened over the Yangtze River basin where warm and cold air masses converge. In comparison, during the decaying phase of medium NAO+ events, the southerly winds are relatively weak, and precipitation tends to be enhanced at lower latitudes (around 25°N). Further analysis indicates that downstream Rossby-wave propagation may account for the latitudinal expansion of the southerly wind anomalies over the eastern coastal area of China during the decaying phase of NAO+ events of different strengths.  相似文献   

9.
The present study reveals cross-season connections of rainfall variability in the South China Sea (SCS) region between winter and summer. Rainfall anomalies over northern South China Sea in boreal summer tend to be preceded by the same sign rainfall anomalies over southern South China Sea in boreal winter (denoted as in-phase relation) and succeeded by opposite sign rainfall anomalies over southern South China Sea in the following winter (denoted as out-of-phase relation). Analysis shows that the in-phase relation from winter to summer occurs more often in El Niño/La Niña decaying years and the out-of-phase relation from summer to winter appears more frequently in El Niño/La Niña developing years. In the summer during the El Niño/La Niña decaying years, cold/warm and warm/cold sea surface temperature (SST) anomalies develop in tropical central North Pacific and the North Indian Ocean, respectively, forming an east–west contrast pattern. The in-phase relation is associated with the influence of anomalous heating/cooling over the equatorial central Pacific during the mature phase of El Niño/La Niña events that suppresses/enhances precipitation over southern South China Sea and the impact of the above east–west SST anomaly pattern that reduces/increases precipitation over northern South China Sea during the following summer. The impact of the east–west contrast SST anomaly pattern is confirmed by numerical experiments with specified SST anomalies. In the El Niño/La Niña developing years, regional air-sea interactions induce cold/warm SST anomalies in the equatorial western North Pacific. The out-of-phase relation is associated with a Rossby wave type response to anomalous heating/cooling over the equatorial central Pacific during summer and the combined effect of warm/cold SST anomalies in the equatorial central Pacific and cold/warm SST anomalies in the western North Pacific during the mature phase of El Niño/La Niña events.  相似文献   

10.

The statistical change-point analysis demonstrates that there is a climate regime shift in the April mean precipitation in Korea in 1981. The April mean precipitation in the years post-1981 showed a distinct decrease compared to the years pre-1981. This phenomenon was also noticed in China and Japan, excluding south China. One of the major causes for this decrease in April mean precipitation was the increased snow depth in the mid-latitude regions of continental East Asia. This resulted in a strengthened cold and dry anticyclone anomaly over continental East Asia and a relatively weakened subtropical anticyclone anomaly over the western North Pacific, thus forcing a continuation of the typical winter pressure pattern of “high-West and low-East” in East Asia in April. The strengthened northerly anomaly from this zonal pressure pattern anomaly played a significant role in restricting the northern movement of the subtropical anticyclone and preventing the inflow of warm and humid air into Korea.

  相似文献   

11.
中国东部夏季降水与东亚垂直环流结构及其预测试验   总被引：2，自引：1，他引：1  
韩雪  魏凤英 《大气科学》2010,34(3):533-547
本文在分析中国东部夏季降水的时空分布特征基础上, 从东亚高、中、低层大尺度环流异常着手, 选取对中国东部夏季降水异常有显著影响的大气环流预报因子, 分别应用逐步回归和最优子集回归法两种统计降尺度方法, 以动力气候模式CAM3.1预报输出的大气环流预报因子为基础, 以中国东部夏季降水的典型空间分布型为预报对象, 建立动力与统计相结合的中国东部夏季降水预测模型, 并对1981～2000年的中国东部夏季降水进行回报试验。结果表明: 中国东部夏季降水具有4类典型的空间分布型式, 且具有显著的准2年和年代际尺度振荡周期; 东亚高、中、低层大气环流异常的特定配置, 对东部夏季降水的空间分布型有显著影响; 使用两种降尺度方案建立的动力与统计相结合的预测模型对中国东部夏季降水异常具有一定的预报技巧, 可以在一定程度上提高动力模式对中国东部夏季降水的预报效果。  相似文献   

12.
The regional characteristics of precipitation anomalies of total summer precipitation of June,July and August and individual monthly precipitation are analyzed by using the method of Varimax EOF and correlation analysis.The data set used is the precipitation of a 5°Lat.×5°Long.spatial uniform network over China in the period of 1959 to 1994.The analysis of total summer precipitation shows that the most significant regional characteristic is the existence of negative correlation in precipitation anomalies between the lower reaches of the Changjiang River and the Huaihe River Valley(the LRCH region) and the middle reaches of the Huanghe River Valley(the MRH region),and between the LRCH region and South China.The precipitation anomaly over the Sichuan Basin is negatively correlated with that over eastern part of Qinghai-Xizang Plateau and that over the LRCH region.The regional characteristics of summer precipitation anomalies in western China are that there exists negative correlation between the summer precipitation anomalies over the southern part of the central and eastern Qinghai-Xizang Plateau and that over its northern part.There also exists positive correlation between the southern part of the central and eastern Qinghai-Xizang Plateau and the eastern part of North China and the southern part of Northeast China.The above spatial correlation modes have significant periods of about 3 years and ten years.The analysis of the monthly precipitation shows that in June there exists positive correlation among the precipitation anomalies over the LRCH region,the eastern part of North China and Northeast China.In July,the precipitations in the MRH region and the LRCH region are negatively correlated.The regional characteristic of precipitation anomalies in August is very similar to that of the total summer precipitation anomalies.  相似文献   

13.
利用NCAR/NCEP-1再分析资料、NOAA的OLR资料以及GPCP降水资料等,通过功率谱分析、超前滞后回归等方法,对夏季南海周边105 °E、125 °E以及150 °E三支越赤道气流进行了多尺度特征分析,重点探讨三支越赤道气流季节内振荡与热带大气环流异常及南海周边降水的联系。结果表明,在季节内时间尺度上,105 °E与125 °E越赤道气流均具有10~20 d以及30~60 d低频振荡显著周期,而150 °E越赤道气流则以10~20 d周期为主。在年际尺度上,105 °E、125 °E、150 °E越赤道气流分别具有2~4年、2~3年、2~6年振荡周期。无论是季内还是年际变化,皆以105 °E与125 °E这两支越赤道气流之间关系较密切。南亚-南海-西太平洋地区对流层低层10~20 d振荡的气旋(对流加强)和反气旋(对流减弱)的环流活动变化,决定着105 °E及125 °E越赤道气流的10~20 d振荡的演变。这两支越赤道气流之30~60 d振荡所伴随的异常变化与热带夏季季节内振荡(BSISO)的演变过程非常相似,而150 °E越赤道气流之30~60 d振荡所伴随的异常低频环流则与南半球热带辐合带关系密切。105 °E及125 °E越赤道气流的季节内振荡及年际异常均与南海周边降水异常密切相关。   相似文献   

14.
The aim of this research is to study the spatial and temporal variability of aridity in Iran, through analysis of temperature and precipitation trends during the 48-year period of 1961–2008. In this study, four different aridity criteria have been used to investigate the aridity situation. These aridity indexes included Lang’s index or rain factor, Budyko index or radiational index of dryness, UNEP aridity index, and Thornthwaite moisture index. The results of the analysis indicated that the highest and lowest mean temperatures occurred in July and January respectively in all locations. Among the study locations, Ahvaz with 37.1 °C and Kermanshah with 20.2 °C has the highest and lowest in July. For January, the highest was 12.4 °C for Ahvaz and the lowest was ?4.5 °C for Hamedan and Kermanshah together. The range of monthly mean temperature of study locations indicated that the maximum and minimum difference between day and night temperatures, almost in all study locations, occurred in September and January, respectively, and the highest and lowest fluctuation of temperature was observed in Kerman and Tehran. The temperature anomalies showed that the most significant increasing temperature occurred at the beginning of twenty-first century (2000–2008) in all locations. The long-term mean of monthly rainfall showed that, in most study locations, the maximum and minimum of mean precipitation occurred in winter and summer, respectively. Rasht with 1,355 mm had the highest and Yazd with 55 mm had the lowest of total precipitation compared with other locations. According to precipitation anomalies, all locations experienced dry and wet periods, but generally dry periods occurred more often especially in the beginning of twenty-first century. According to applied different aridity indexes, all the study locations often experienced semi-arid to arid climate, severe water deficit to desert climate, arid to hyperarid climate, and semi-arid climate during the study period.  相似文献   

15.
Dryness and wetness variations in east China were analyzed using the standardized precipitation index (SPI) based on monthly precipitation data for 1961?C2005. A drying trend over North China was observed, which can be attributed to decreasing precipitation since the late 1970s. Moreover, NCAR/NCEP reanalysis dataset was used to investigate causes behind the drying trend in North China. The moisture flux on the regional boundaries of East China was calculated and a higher wavelet power spectrum for low-latitude boundaries (based on 20 and 25°N) occurred with significant periods in a 1-year band during 1961?C2005; however, since 1977, a significant 1-year period can no longer be detected on the northern boundary of South China (based on 35°N). The summer moisture flux during 1961?C1977, when compared to the same during 1978?C2005, has increased in East China. Good matches are found between moisture alterations and precipitation changes, and are also confirmed by the periods of moisture transport along different latitudes. The significant 1-year periods of moisture transport along the mid-latitude boundary (based on 35°N) have disappeared since 1977, which could be the causes behind the drought in North China. The disappearance of the significant 1-year band of moisture transport along the mid-latitude boundary (based on 35°N) in the late 1970s could be a result of the significantly decreased moisture transport in North China in summer. When southerly winds are weakened in East Asia, the southwesterly winds can only reach the south of the lower Yangtze River, which is the major cause behind the frequent summer droughts in North China in the recent years.  相似文献   

16.
利用空间均匀网格对中国夏季降水异常区域特性的初步分析   总被引：24，自引：1，他引：24  
王晓春  吴国雄 《气象学报》1996,54(3):324-332
用方差极大正交转动ＥＯＦ（Ｖａｒｉｍａｘ　ＥＯＦ）及点相关图法分析了夏季总降水（６、７、８月降水之和）及逐月降水的区域特性。使用的资料为全国范围４７个５°×５°经纬度网格上的降水资料，分析时段为１９５９—１９９４年。分析结果表明，由于采用了空间均匀的格同资料，本分析除进一步证实了中国东部地区降水异常的区域特性外，也揭示了西部地区降水异常的区域特性及沿长江流域东西方向上降水异常的相互关系。夏季总降水异常最显著的区域特性是江淮流域与河套及华南反相关。另外沿长江流域，四川盆地的降水异常与青藏高原东部及江淮流域的降水异常也存在着反相关联系。西部地区的区域特性为青藏高原中东部南北两侧为负相关，并且青藏高原中东部南侧的降水异常与华北东部及东北南部为正相关。上述的空间模都有准２—３ａ及１０ａ左右的周期。逐月降水的分析表明，６月份，江淮流域、华北东部及东北大部分地区为正相关。７月，河套地区与江淮流域的降水异常呈现一定的负相关联系，８月份降水异常的区域特性与夏季总降水异常的区域特性极其一致。  相似文献   

17.
This paper assesses future climate changes over East and South Asia using a regional climate model (RegCM4) with a 50?km spatial resolution. To evaluate the model performance, RegCM4 is driven with ??perfect boundary forcing?? from the reanalysis data during 1970?C1999 to simulate the present day climate. The model performs well in reproducing not only the mean climate and seasonality but also most of the chosen indicators of climate extremes. Future climate changes are evaluated based on two experiments driven with boundary forcing from the European-Hamburg general climate model (ECHAM5), one for the present (1970?C1999) and one for the SRES A1B future scenario (2070?C2099). The model predicts an annual temperature increase of about 3°?C5° (smaller over the ocean and larger over the land), and an increase of annual precipitation over most of China north of 30°N and a decrease or little change in the rest of China, India and Indochina. For temperature-related extreme indicators in the future, the model predicts a generally longer growing season, more hot days in summer, and less frost days in winter. For precipitation-related extremes, the number of days with more than 10?mm of rainfall is predicted to increase north of 30°N and decrease in the south, and the maximum five-day rainfall amount and daily intensity will increase across the whole model domain. In addition, the maximum number of consecutive dry days is predicted to increase over most of the model domain, south of 40°N. Most of the Yangtze River Basin in China stands out as ??hotspots?? of extreme precipitation changes, with the strongest increases of daily rain intensity, maximum five-day rain amount, and the number of consecutive dry days, suggesting increased risks of both floods and droughts.  相似文献   

18.
This paper investigates monthly and seasonal precipitation–temperature relationships (PTRs) over Northeast China using a method proposed in this study. The PTRs are influenced by clouds, latent and sensible heat conversion, precipitation type, etc. In summer, the influences of these factors on temperature decrease are different for various altitudes, latitudes, longitudes, and climate types. Stronger negative PTRs ranging from ?0.049 to ?0.075 °C/mm mostly occur in the semi-arid region, where the cold frontal-type precipitation dominates. In contrast, weaker negative PTRs ranging from ?0.004 to ?0.014 °C/mm mainly distribute in Liaoning Province, where rain is mainly orographic rain controlled by the warm and humid air of East Asian summer monsoon. In winter, surface temperature increases owing to the release of latent heat and sensible heat when precipitation occurs. The stronger positive PTRs ranging from 0.963 to 3.786 °C/mm mostly occur at high altitudes and latitudes due to more release of sensible heat. The enhanced atmospheric counter radiation by clouds is the major factor affecting increases of surface temperature in winter and decreases of surface temperature in summer when precipitation occurs.  相似文献   

19.
Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of ?0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. Reconstructed geopotential height at 1,000 hPa (z1000) suggests enhanced southwesterly flow across New Zealand occurred during the LIA to generate the terrestrial temperature anomalies. The mean atmospheric circulation pattern for summer resulted from a crucial reduction of the ‘HSE’-blocking synoptic type (highs over and to the west of NZ; largely settled conditions) and increases in both the ‘T’- and ‘SW’-trough synoptic types (lows passing over NZ; enhanced southerly and southwesterly flow) relative to normal. Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Niño-Modoki in the tropical Pacific and negative Southern Annular Mode activity.  相似文献   

20.
Summary  Anomalously wet and dry months in the Mediterranean basin were identified during the period 1860–1990 from observations at five stations located along the west-east axis of the Mediterranean basin (Barcelona, Florence, Malta, Athens and Jerusalem), supplemented by data from Madrid and Lisbon. Wet and dry months were characterized by hydric indices (HI) based on values of the standardized precipitation anomalies. Different patterns of anomalously wet and dry months were qualitatively identified on the basis of the spatial distributions of the hydric indices. The standardized sea level pressure values at 56 grid points in the domain 35° N–65° N, 30° W–40° E, for each of the anomalously wet and dry months, were subjected to T-mode Principal Component Analysis. The mean hydric indices associated with each principal component in each season are arranged in four distinct different spatial distributions for wet months and in three for dry months as following: (a) Mediterranean wide distribution of positive/negative anomalies; (b1) Strong positive anomalies to the west, but weaker to eastern Mediterranean; (b2) Strong negative anomalies to the west, but weaker or normal to the east; (c1) Strong positive anomalies to the west and to the east and weaker ones to the central Mediterranean; (c2) Negative anomalies to the west and east, but weaker, or normal, or positive to the central Mediterranean; (d) Relatively strong positive anomalies to the east and weaker ones to the western Mediterranean. Finally, monthly mean charts of standardized anomaly and mean sea level pressure are presented for each principalcomponent in each season. These charts are used to interpret the spatial distribution of the positive and negative precipitation anomalies in terms of mean circulation over the domain. Received December 10, 1998 Revised June 14, 1999  相似文献   

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