欧亚持续性阻塞对6月大兴安岭地区气温和降水的影响及气温的前兆信号研究

根据国际新开发的可识别持续闭合性阻塞和开放性高压脊事件的判别方法,讨论了欧亚地区不同区域500 hPa持续性高值事件(PMZ)的发生频率及其对中国大兴安岭地区夏季气温和降水的影响。结果表明：欧亚105°-125°E区域内PMZ事件与夏季尤其是6月大兴安岭地区气温关系最为紧密。105°-125°E地区PMZ事件频发时,贝加尔湖至中国东北地区异常高压引起的下沉增温及晴空辐射造成大兴安岭地区气温偏高,同时,该地区对流层低层相对湿度条件较差,配合对流层中低层异常反气旋性环流系统以及下沉运动,不利于大兴安岭地区出现明显降水。此外,5月中亚两河流域位势高度可作为6月大兴安岭地区气温的前期预报指标,当中亚两河流域5月位势高度场偏高(低)时,6月贝加尔湖以东地区位势高度偏高(低),对应大兴安岭地区同期气温偏高(低)。     

中国东部夏季风北界年际变化的东西差异及其影响因子

采用1958～2016年JRA-55（Japanese 55-year Reanalysis）月平均再分析资料,利用夏季平均的可降水量定义了东亚夏季风北界,通过谐波分解、回归分析、合成分析、波活动通量等分析方法,研究了东亚夏季风北界位置的年际变化特征和东西差异。根据各经度上夏季风活动北界位置年际变化的一致性可划分为华北区域（107.5°～115°E）和东北区域（122.5°～130°E）两个区域,两个区域夏季风北界位置的年际变化具有明显差别。两个区域的夏季风北界位置的异常偏北都与东侧的异常反气旋式水汽环流密切相关,与华北区域北界位置密切联系的异常反气旋式水汽环流位于黄海附近,与东北区域北界位置相关的异常反气旋式水汽环流则位于日本海北部。两个区域分别位于反气旋式环流西侧,受偏南风水汽输送影响,区域水汽输送以及辐合增强。影响华北区域的反气旋式异常与中高纬度波列的传播有关;影响东北区域夏季风北界位置偏南年与偏北年的反气旋式环流的可能成因存在非对称性,偏南年对应西北太平洋低纬度正异常高度场以及中纬度负异常高度场,可能受东亚—太平洋遥相关波列的影响;偏北年则对应着东北亚的正异常高度场,可能与局地增温有关。     

A STUDY ON THE RELATIONSHIP BETWEEN THE SUMMER PRECIPITATION IN NORTHEAST CHINA AND THE GLOBAL SEA SURFACE TEMPERATURE ANOMALY (SSTA) IN PRECEDING SEASONS

1 INTRODUCTION Chilling damage, flooding and drought in summer are the major climatic disasters inNortheast China. Before the 1980s chilling damage often occurred, and after 1990s flooding and drought disasters were more noticeable in this region. These c…     

中国东北地区春季透雨早晚与2～3月热带印度洋海温异常的联系

利用1961～2019年中国东北地区测站逐日降水资料、美国国家环境预报中心/大气研究中心的月平均再分析资料、NOAA重构的月平均海温和向外长波辐射资料,采用统计诊断方法,从年际时间尺度上分析了东北春季透雨早晚环流特征和前期海温,尤其是热带印度洋海温强迫的联系。结果表明:春季透雨日期与4月降水量的变化具有显著的一致性,典型透雨偏早年的开始时间集中在4月中下旬,偏晚年的开始时间集中在5月中下旬;4月东北亚上空500 hPa位势高度场上,若呈自西向东的“? +”异常环流分布,东北地区以偏南风和气旋性环流为主,有利于水汽输送,春季透雨开始偏早,反之,春季透雨开始偏晚;2～3月热带印度洋暖海温异常是中国东北地区春季透雨偏早的重要稳定影响源之一,其可能机制是,若热带印度洋全区一致海温模态呈正位相,有利于4月西北太平洋地区呈异常反气旋,东北亚地区500 hPa环流异常类似春季透雨偏早年形势,东北地区位于200 hPa西风急流出口区右侧,垂直上升运动增强,呈现出多雨形势。     

Winter AO/NAO modifies summer ocean heat content and monsoonal circulation over the western Indian Ocean

This paper analyzes the possible influence of boreal winter Arctic Oscillation/North Atlantic Oscillation (AO/ NAO) on the Indian Ocean upper ocean heat content in summer as well as the summer monsoonal circulation. The strong interannual co-variation between winter 1000-hPa geopotential height in the Northern Hemisphere and summer ocean heat content in the uppermost 120 m over the tropical Indian Ocean was investigated by a singular decomposition analysis for the period 1979–2014. The second paired-modes explain 23.8% of the squared covariance, and reveal an AO/NAO pattern over the North Atlantic and a warming upper ocean in the western tropical Indian Ocean. The positive upper ocean heat content enhances evaporation and convection, and results in an anomalous meridional circulation with ascending motion over 5°S–5°N and descending over 15°–25°N. Correspondingly, in the lower troposphere, significantly anomalous northerly winds appear over the western Indian Ocean north of the equator, implying a weaker summer monsoon circulation. The off-equator oceanic Rossby wave plays a key role in linking the AO/NAO and the summer heat content anomalies. In boreal winter, a positive AO/NAO triggers a down-welling Rossby wave in the central tropical Indian Ocean through the atmospheric teleconnection. As the Rossby wave arrives in the western Indian Ocean in summer, it results in anomalous upper ocean heating near the equator mainly through the meridional advection. The AO/NAO-forced Rossby wave and the resultant upper ocean warming are well reproduced by an ocean circulation model. The winter AO/NAO could be a potential season-lead driver of the summer atmospheric circulation over the northwestern Indian Ocean.     

Assessment of surface air warming in northeast China, with emphasis on the impacts of urbanization

Based on homogenized land surface air temperature (SAT) data (derived from China Homogenized Historical Temperature (CHHT) 1.0), the warming trends over Northeast China are detected in this paper, and the impacts of urban heat islands (UHIs) evaluated. Results show that this region is undergoing rapid warming: the trends of annual mean minimum temperature (MMIT), mean temperature (MT), and mean maximum temperature (MMAT) are 0.40 C decade^?1, 0.32 C decade^?1, and 0.23 C decade^?1, respectively. Regional average temperature series built with these networks including and excluding “typical urban stations” are compared for the periods of 1954–2005. Although impacts of UHIs on the absolute annual and seasonal temperature are identified, UHI contributions to the long-term trends are less than 10% of the regional total warming during the period. The large warming trend during the period is due to a regime shift in around 1988, which accounted for about 51% of the regional warming.     

Changes in Extreme Maximum Temperature Events and Population Exposure in China under Global Warming Scenarios of 1.5 and 2.0°C: Analysis Using the Regional Climate Model COSMO-CLM

We used daily maximum temperature data (1986–2100) from the COSMO-CLM (COnsortium for Small-scale MOdeling in CLimate Mode) regional climate model and the population statistics for China in 2010 to determine the frequency, intensity, coverage, and population exposure of extreme maximum temperature events (EMTEs) with the intensity–area–duration method. Between 1986 and 2005 (reference period), the frequency, intensity, and coverage of EMTEs are 1330–1680 times yr^–1, 31.4–33.3°C, and 1.76–3.88 million km², respectively. The center of the most severe EMTEs is located in central China and 179.5–392.8 million people are exposed to EMTEs annually. Relative to 1986–2005, the frequency, intensity, and coverage of EMTEs increase by 1.13–6.84, 0.32–1.50, and 15.98%–30.68%, respectively, under 1.5°C warming; under 2.0°C warming, the increases are 1.73–12.48, 0.64–2.76, and 31.96%–50.00%, respectively. It is possible that both the intensity and coverage of future EMTEs could exceed the most severe EMTEs currently observed. Two new centers of EMTEs are projected to develop under 1.5°C warming, one in North China and the other in Southwest China. Under 2.0°C warming, a fourth EMTE center is projected to develop in Northwest China. Under 1.5 and 2.0°C warming, population exposure is projected to increase by 23.2%–39.2% and 26.6%–48%, respectively. From a regional perspective, population exposure is expected to increase most rapidly in Southwest China. A greater proportion of the population in North, Northeast, and Northwest China will be exposed to EMTEs under 2.0°C warming. The results show that a warming world will lead to increases in the intensity, frequency, and coverage of EMTEs. Warming of 2.0°C will lead to both more severe EMTEs and the exposure of more people to EMTEs. Given the probability of the increased occurrence of more severe EMTEs than in the past, it is vitally important to China that the global temperature increase is limited within 1.5°C.     

Spatial and temporal characteristics of minimum temperature in winter in China during 1961–2010 from NCEP/NCAR reanalysis

Based on the surface 2?m monthly minimum temperature from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis dataset, the spatial and temporal characteristics of winter minimum temperature during 1961–2010 have been analyzed in China. Results showed that the minimum temperature in China has a significant increasing rate of 0.25° per decade calculated by the Mann–Kendall statistical test, which is consistent with the global warming trend. Empirical orthogonal function (EOF) analysis reveals that there are three main patterns that can explain more than 57.6% of the total variance of the winter minimum temperature. The EOF1, EOF2, and EOF3 account for 34.8%, 13.5%, and 13.5% of the total inter-annual variance, respectively. The EOF1, EOF2, and EOF3 patterns are synchronous in northern China, central China, and on the Tibetan Plateau. There exist a decrease trend in the corresponding time coefficients of EOF1 and EOF2 and an increase trend in that of EOF3 since the 1960s. Both the corresponding time coefficients of EOF1 and EOF2 have significant positive correlations with the 500?hPa geopotential heights of the Arctic region and negative correlations in the regions lower than 40°N, while a significant positive correlation is found between the corresponding time coefficients of EOF3 and 500?hPa geopotential heights in the low latitudes. This suggests that rapid warming occurs in northern China and on the Tibetan Plateau, while the weakest trend locates in southeast China. Thus, warming in winter is more pronounced at higher altitudes and latitudes. These patterns are tightly connected with the atmospheric circulation.     

Regional-scale winter-spring temperature variability and chilling damage dynamics over the past two centuries in southeastern China

Winter-spring cold extreme is a kind of serious natural disaster for southeastern China. As such events are recorded in discrete documents, long and continuous records are required to understand their characteristics and driving forces. Here we report a regional-scale winter-spring (January–April) temperature reconstruction based on a tree-ring network of pine trees (Pinus massoniana) from five sampling sites over a large spatial scale (25–29°N, 111–115°E) in southeastern China. The regional tree-ring chronology explains 48.6% of the instrumental temperature variance during the period 1957–2008. The reconstruction shows six relatively warm intervals (i.e., ~1849–1855, ~1871–1888, ~1909–1920, ~1939–1944, ~1958–1968, 1997–2007) and five cold intervals (i.e., ~1860–1870, ~1893–1908, ~1925–1934, ~1945–1957, ~1982–1996) during 1849–2008. The last decade and the 1930s were the warmest and coldest decades, respectively, in the past 160 years. The composite analysis of 500-hPa geopotential height fields reveals that distinctly different circulation patterns occurred in the instrumental and pre-instrumental periods. The winter-spring cold extremes in southeastern China are associated with Ural-High ridge pattern for the instrumental period (1957–2008), whereas the cold extremes in pre-instrumental period (1871–1956) are associated with North circulation pattern.     

Soil moisture influence on summertime surface air temperature over East Asia

Soil moisture influence on surface air temperature in summer is statistically quantified across East Asia using the Global Land Data Assimilation System soil moisture and observational temperature. The analysis uses a soil moisture feedback parameter computed based on lagged covariance ratios. It is found that significant negative soil moisture feedbacks on temperature mainly appear over the transition zones between dry and wet climates of northern China and Mongolia. Over these areas, the feedbacks account for typically 5–20% of the total temperature variance, with the feedback parameter of ?0.2°C to ?0.5°C (standardized soil moisture)^?1. Meanwhile, positive feedbacks may exist over some areas of Northeast Asia but are much less significant. These findings emphasize the importance of soil moisture-temperature feedbacks in influencing summer climate variability and have implications for seasonal temperature forecasting.     

2007/2008和2008/2009冬季平流层强、弱极涡事件对应的行星波活动的对比分析

在对逐日气象资料进行纬向谐波分析的基础上, 对比和讨论了2007/2008年冬季强极涡期间和2008/2009冬季弱极涡期间平流层和对流层不同波数的行星波的变化特征, 特别关注强极涡或弱极涡发生之后, 500 hPa 沿60°N和30°N行星波1波和2波振幅和位相的差异, 以及相应的500 hPa位势场的差异, 进而讨论为什么不同的平流层极涡异常会对东亚有不同的影响, 特别讨论为什么同一种极涡异常, 对我国南北方近地面气温的影响会不同。结果表明:平流层极涡发生异常时, 平流层行星波活动有明显的异常。随着极涡异常的下传, 对流层行星波的振幅和位相也有明显的变化, 而且, 对于不同的纬度带, 其变化又有不同, 表现为:2008年1月强极涡发生之后, 500 hPa行星波1波和2波的扰动都向南伸, 而2009年1月的弱极涡(SSW)期间和之后, 1波和2波的扰动都偏北; 在对流层, 强极涡和弱极涡发生之后不但行星波1波和2波的振幅有所差异, 其位相也有明显的不同。特别是, 其位相的差异还随纬度而变化。就同一年(或者说对于同是强极涡或者同是弱极涡)而言, 无论是1波还是2波, 在60°N和30°N附近的扰动相比, 几乎反位相。这样就使得它们的500 hPa 位势场也有明显不同:在东半球, 主要表现为乌拉尔高压和东亚大槽的强度和位置不同。2008年1月强极涡发生之后, 乌拉尔高压和东亚大槽东移, 不利于冷空气向欧亚大陆北部(包括我国北方)的输送, 使这些地区的温度偏高;而2009年1月弱极涡之后, 东亚大槽西退, 利于冷空气向欧亚大陆北部输送, 导致这些地区较冷。对于同一种极涡异常(如2008强极涡或者2009弱极涡)由于南方和北方行星波扰动的位相不同, 对南方和北方冷暖空气的输送也就不一样。所以同一种极涡异常对(我国)南北地区的温度影响是不同的。     

Impact of the western North Pacific subtropical high on the East Asian monsoon precipitation and the Indian Ocean precipitation in the boreal summertime

The western North Pacific subtropical high (WNPSH) is a crucial component of the East Asian summer monsoon (EASM) system and significantly influences the precipitation in East Asia. In this study, distinguished role of WNPSH on the EASM and Indian Ocean monsoon (IOM) are investigated. Based on the boreal summer mean field of 850-hPa geopotential height and its interannual variability, the WNPSH index (WNPSHI) is defined by the areaaveraged geopotential height over the region [110°–150°E, 15°–30°N]. The WNPSHI is significantly related to the precipitation over the East Asian monsoon (EAM) region [105°–150°E, 30°–40°N] and IOM region [70°–105°E, 5°–15°N]. Rainfalls over these two regions have good correlation with WNPSH developments and the geopotential height fields at 850 hPa related to the EAM precipitation and IOM precipitation have remarkably different teleconnection patterns in boreal summer. These features exhibit that EAM and IOM precipitations have different type of development processes associated with different type of WNPSH each other. Focusing on the relationships among the EAM precipitation, IOM precipitation, and the WNPSH variabilities, we assume that WNPSH and EAM precipitation are usually fluctuated simultaneously through the sea surface temperature (SST)-subtropical ridge-monsoon rainfall feedback, whereas the IOM precipitation varies through the different process. To clarify the relationships among WNPSH, EAM, and IOM, two cases are selected. The first one is the case that all of WNPSH, EAM, and IOM are in phase (WE(+)I(+)), and the second one is the case that WNPSH and EAM are in phase and WNPSH/EAM and IOM is out of phase (WE(+)I(?)). These two cases are connected to the thermal forcing associated with SST anomalies over the eastern Pacific and Indian Ocean. This different thermal forcing induces the change in circulation fields, and then anomalous circulation fields influence the moisture convergence over Asian monsoon regions interactively. Therefore, the monsoon rainfall may be changed according to the thermal conditions over the tropics.     

东北冷涡强度定义及特征分析

利用NCEP 1°×1°格点再分析资料,根据东北冷涡温度场有冷中心及高度场是闭合环状环流的特征,同时选取位势高度差和温度差两个指标,制定东北冷涡逐日强度定义方法,并分析了按此定义划分的不同强度东北冷涡的变化特征。结果表明：中等强度冷涡的出现频次最多,占全年冷涡出现日数的50%以上,其次是弱冷涡,超强冷涡出现日数最少;弱冷涡生命史约为3 d左右;超强冷涡活动期间中心位移变化较大,且生命史长,影响范围更为广泛。     

Future trend of extreme value distributions of wintertime surface air temperatures over Korea and the associated physical changes

Daily winter temperatures in Korea have been analyzed via CSEOF analysis. Then, each PC time series was detrended and was fitted to an AR (autoregressive) model. Based on the identified AR model, an artificial time series of arbitrary length can be generated by using an arbitrary white-noise time series. In this way, one hundred new sets of PC time series were generated over the period of 1973–2058. Then, the trend for each PC time series was added back to the artificial PC time series extending the trend until 2058. Ultimately, artificial daily winter temperatures in Korea have been constructed by using the artificial PC time series and the original loading vectors derived from the observational data. The 100 new data sets have been investigated in order to understand the winter temperature variability 50 years into the future. Regression analysis in CSEOF space shows that temperature increase in Korea is associated with increased 850-hPa air temperature over most of the Asian domain (97°-153°E × 22°-73°N) and increased 850-hPa geopotential height in the southern part of the domain. As a result, southerly and southeasterly wind anomalies develop carrying positive temperature anomalies northward and northwestward. Both the 200-hPa air temperature and geopotential height changes indicate that there will be fairly significant northward shift of the jet stream in future. The standard deviation of the 200-hPa potential vorticity increases implying that shortwave trough and henceforth baroclinic instability will increase in future. Finally, GEV (Generalized Extreme Value) distribution and GPD (Generalized Pareto distribution) distribution have been compared between the observational records and the future records of the same length. The extreme value distributions based on the synthetic datasets show that warm extreme events will be more extreme in future and cold extreme events, on the other hand, will be less extreme. This study provides an estimate of future temperatures based on the observational data and serves as an independent baseline solution for comparisons with numerical model solutions.     

2018年夏季东北极端高温事件物理机制分析

基于观测资料和再分析资料,研究分析了2018年夏季中国东北地区持续多日出现高温异常事件的形成机理。首先分析了整个夏季该地区观测台站逐日的温度资料,计算了观测台站的超热因子（Excess Heat Factor,EHF）指数,发现东北地区出现高温异常的时段主要是7月和8月,异常高温的发生区域集中在东北南部。在此期间,东亚大气环流形势的异常主要表现为南亚高压和西太平洋副热带高压强度异常增强,作用相互重叠和位置持续偏北。进一步的分析可以注意到,二者的重叠造成研究区域内有负涡度异常增强,使得南亚高压和西太平洋副热带高压在北推的过程中不断带动东北南部上空负涡度异常增强,并伴随有异常下沉气流,下沉绝热增温与晴空辐射增温,这可能是东北南部地表增温的一个重要原因。相关分析证实,在整个夏季东北南部地表气温与其上空300 hPa至500 hPa涡度异常都有显著的负相关关系。因此,南亚高压和西太平洋副热带高压之间的相互叠加组合是导致东北南部在2018年夏季7、8月份出现高温异常的主要原因。进一步的研究发现,夏季副热带西风急流中准定常Rossby波能量的传播与南亚高压和西太平洋副热带高压异常增强有密切联系,同时夏季西太平洋暖池的显著增暖导致了菲律宾地区异常旺盛的对流活动,进而在500 hPa高度场上激发出PJ（太平洋—日本涛动）波列,从另一个路径上促进了西太平洋副热带高压偏强偏北。     

Adaptation of agriculture to warming in Northeast China

Northeast China comprises Heilongjiang, Jilin and Liaoning Provinces, with a total area of 790,000 km² and a population of about 107 million. Northeast China, located at relatively high latitudes, (from about 39 to 53°N), is one of the coolest regions in China with long and cold winters, a short growth season and frequent cold extreme events, which are adverse to agricultural production. However, since the 1980s, Northeast China has experienced significant warming with annual mean temperature rising by 1.0–2.5°C. The increase of accumulated temperature, the extension of the growth period and the recession of summer cool disasters all contributed to improved conditions for crop growth and led to a northward movement of the agricultural climate zone. In addition, the adaptation to warming including the adjustment of crop composition and structure as well as the adoption of advanced technologies greatly facilitated agricultural development. As a result, total grain production in the region increased rapidly. This paper describes in detail climate change, adaptation measures and final agricultural outcomes, alongside with economic and political factors and the role of different political actors in Northeast China.     

Vertical characteristics of cyclonic tracks over the eastern Mediterranean during the cold period of the year

The vertical structure of surface cyclonic tracks affecting the eastern Mediterranean region is studied on a climatological basis for the cold period of the year. The dataset used is the 1°?×?1° ERA-40 Reanalysis for a 40-year period (1962–2001). The vertical tracking of surface cyclonic tracks was performed with the aid of the Melbourne University Vertical Tracking Algorithm. It was found that about 83 % of the cyclones were extended up to the 500-hPa level and almost 65 % up to 200-hPa level, implying that the cyclones are in general well organized. The surface tracks that originate within the examined area exhibit the smallest vertical extension, intensity, radius, and depth compared to the cyclones originating in the other sectors. Moreover, the 500-hPa counterparts for the said cyclones are mainly located to the north-west or south-west of the surface cyclone position, consistent with the baroclinic character of the Mediterranean cyclones. The zonal (eastward) component of motion predominates both at the surface and at 500 hPa.     

Abrupt summer warming and changes in temperature extremes over Northeast Asia since the mid-1990s: Drivers and physical processes

This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990 s. Observations indicate an abrupt increase in summer mean surface air temperature(SAT) over Northeast Asia since the mid-1990 s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature(Tmax), daily minimum temperature(Tmin), annual hottest day temperature(TXx), and annual warmest night temperature(TNx) were observed. There were also increases in the frequency of summer days(SU) and tropical nights(TR).Atmospheric general circulation model experiments forced by changes in sea surface temperature(SST)/ sea ice extent(SIE),anthropogenic greenhouse gas(GHG) concentrations, and anthropogenic aerosol(AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes,although the abrupt decrease in precipitation since the mid-1990 s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA(through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990 s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease.     

MJO change with A1B global warming estimated by the 40-km ECHAM5

This study estimates MJO change under the A1B greenhouse gas emission scenario using the ECHAM5 AGCM whose coupled version (ECHAM5/MPI-OM) has simulated best MJO variance among fourteen CGCMs. The model has a horizontal resolution at T319 (about 40 km) and is forced by the monthly evolving SST derived from the ECHAM5/MPI-OM at a lower resolution of T63 (about 200 km). Two runs are carried out covering the last 21 years of the twentieth and twenty-first centuries. The NCEP/NCAR Reanalysis products and observed precipitation are used to validate the simulated MJO during the twentieth century, based on which the twenty-first century MJO change is compared and predicted. The validation indicates that the previously reported MJO variances in the T63 coupled version are reproduced by the 40-km ECHAM5. More aspects of MJO, such as the eastward propagation, structure, and dominant frequency and zonal wavenumber in power spectrum, are simulated reasonably well. The magnitude in power, however, is still low so that the signal is marginally detectable and embedded in the over-reddened background. Under the A1B scenario, the T63 ECHAM5/MPI-OM projected an over 3 K warmer tropical sea surface that forces the 40-km ECHAM to produce wetter tropics. The enhanced precipitation variance shows more spectral enhancement in background than in most wavebands. The zonal winds associated with MJO, however, are strengthened in the lower troposphere but weakened in the upper. On the one hand, the 850-hPa zonal wind has power nearly doubled in 30–60-days bands, demonstrating relatively clearer enhancement than the precipitation in MJO with the warming. A 1-tailed Student’s t test suggests that most of the MJO changes in variance and power spectra are statically significant. Subject to a 20–100-days band-pass filtering of that wind, an EOF analysis indicates that the two leading components in the twentieth-century run have a close structure to but smaller percentage of explained-to-total variance than those in observations; the A1B warming slightly increases the explained percentage and alters the structure. An MJO index formed by the two leading principal components discloses nearly doubling in the number of prominent MJO events with a peak phase occurring in February and March. A composite MJO life cycle of these events favors the frictional moisture convergence mechanism in maintaining the MJO and the nonlinear wind-induced surface heat exchange (WISHE) mechanism also appears in the A1B warming case. On the other hand, the Slingo index based on the 300-hPa zonal wind discloses that the upper-level MJO tends to be suppressed by the A1B warming, although the loose relationship with ENSO remains unchanged. Possible cause for the different change of MJO in the lower and upper troposphere is discussed.     

Impact of Heating Anomalies Associated with Rainfall Variations over the Indo-Western Pacific on Asian Atmospheric Circulation in Winter

Observational data show that the dominant mode of the boreal winter rainfall anomalies in the tropical Indo-Western Pacific (IWP) is a west-east dipolar pattern, which is called the Indo-Western Pacific Dipole (IWPD) mode and is related to El Niño-Southern Oscillation. It is found that corresponded to the IWPD mode is a new atmospheric teleconnection pattern—a wave train pattern emitted from the IWP toward Asia and the northwest Pacific in winter. During the positive (negative) phase of the IWPD, the teleconnection pattern features the negative (positive) anomalies of 200-hPa geopotential height (H200) centered at 30°N, 110°E and the positive (negative) anomalies of H200 centered at 45°N, 140°E. The teleconnection pattern represents the dominant mode of the boreal winter H200 anomaly over Asia. A series of simple atmospheric model experiments are performed to confirm that this winter teleconnection pattern is induced by the heating anomalies associated with the IWPD, and the heating anomalies over the equatorial central Pacific are not important to this teleconnection pattern from the IWP toward Asia and the northeast Pacific. The IWPD is strengthened after the climate regime shift of the 1970s, which leads to a stronger teleconnection pattern.