North Sea near-surface wind climate and its relation to the large-scale circulation patterns

The North Sea 10-m wind speed (WS10) climate is compared and related to circulation patterns based on the sea level pressure (SLP) extracted from three reanalysis and one high-resolution model dataset. The mean magnitude and the trends of WS10 depend considerably on the selected reanalysis. The variability of WS10 among the three reanalysis datasets is highly correlated in the recent period (1980–2000) but less so in the past period (1960–1980). The WS10 over the North Sea is well represented by the relatively low reanalysis resolution when compared to the high-resolution WS10 model data partially owing to the high spatial correlation of WS10. Exceptions are observed only at the coastal areas. The dominant mode of WS10 explains coherent variability of WS10 over the North Sea and is related to a SLP pattern similar to the North Atlantic oscillation (NAO). The increase of the magnitude of the dominant WS10 pattern is related to the increase of the magnitude of the NAO-like SLP pattern from 1960s to mid-1990s. The second dominant WS10 pattern—a dipole in WS10 to the north and south of Great Britain—is related to the differences in SLP between Scandinavia and Iceland. The relation between the second WS10 and SLP patterns is more prominent in the recent period. The extreme WS10 in the German Bight is related to the low SLP over Scandinavia. The extreme WS10 is strongly increasing from the early 1980s to the beginning of 1990s, which is not observed in the corresponding SLP time series over Scandinavia.     

Multi-scale variation of the meridional movement of the western Pacific warm pool and its associated large-scale climate features

In this study, we investigated variation of the meridional movement of the western Pacific warm pool (WPWP). The variation was measured by the central latitude (Clat) of the WPWP on various time scales. Its relationships with global sea surface temperature (SST), precipitation, and atmospheric circulation were examined by applying several advanced statistical methods. First, the techniques of wavelet analysis and least-square adjustment were used to depict the time-frequency features and the mean dominant oscillating time scales of the Clat. Then, a multi-stage filtering technique was applied to illustrate the related dominant oscillating signals. We also examined the time-frequency characteristics of the relationships between Clat and the leading modes of the Indo-Pacific oceans by employing a cross-covariance function analysis and a multiple moving-window method. The physical mechanisms for the relationships between Clat and the patterns of SST, precipitation, and atmospheric circulation were discussed. Results indicated that there is a weakening trend in the oscillation of Clat mainly because the quasi-annual oscillation of Clat increases in January–March and decreases in July–September. The semi-annual oscillation of Clat closely interacts with the westerly wind over the summer hemisphere of the tropical western Pacific Ocean and with the easterly wind over the winter hemisphere of the ocean. The interannual component of Clat corresponds to El Niño-Southern Oscillation and the Indian Ocean basin-wide warming or cooling with strengthened oscillations in the 1970s, and the lower-frequency component of Clat closely corresponds to the central Pacific type of El Niño from the 1990s.     

Precipitation climate of Central Asia and the large-scale atmospheric circulation

The precipitation climate in the larger Tian Shan region of Central Asia is described in terms of the climatological seasonal moisture fluxes and background circulation based on the ERA-40 reanalysis data and a precipitation reanalysis. The study area is partitioned into (1) the Tarim river basin, (2) bordering regions of China, Kyrgyzstan and Kazakhstan, and (3) Northwestern China. Moisture supply to these areas is primarily due to the midlatitude westerlies with contributions from higher latitudes. In addition, moisture from the Indian Ocean is notably imported into the Tarim drainage area. Monthly interannual precipitation variability relates to the variability of hemispheric circulation patterns. Extreme precipitation above and below normal in Western China and Central Asia is analyzed using the standardized precipitation index. Related circulation composites show that, despite regional and seasonal differences, episodes of extreme and severe dryness are dominated by various upstream standing wave patterns from the North Atlantic to Central Asia. These features extend further downstream to the North Pacific. Non-symmetry between wet and dry composites is noted upstream and in regional moisture flux composites.     

中国北方暴雪的年代际变化及其与大气环流和北极海冰的联系

采用相关、回归等统计方法,对中国北方暴雪的年代际变化特征及其与大气环流和北极海冰的联系进行探讨。结果表明:中国北方冬季暴雪发生频次较高区域主要位于东北,在空间分布上呈现由西北向东南增加的态势,且存在明显的年代际变化特征:1965—1980年为东北暴雪少发期; 2002—2011年为东北暴雪多发期。分析表明:暴雪少发期,输送至东北的水汽较少;暴雪多发期,更多的水汽输送来自于西北太平洋,同时偏北气流引导的极地冷空气与偏南风引导的太平洋暖湿空气在东北地区汇合,提供暴雪频发的动力条件,造成东北暴雪出现年代际增多。此外,研究发现:前期秋季北极海冰的年代际减少与东北暴雪的年代际增加存在很好的相关性;秋季北极海冰异常偏少导致的大气环流异常主要表现为纬向西风减弱和NAO负位相,由此导致大气经向活动增强,利于极地冷空气向南入侵,且冷空气与暖湿空气在东北地区汇合,这是东北暴雪年代际增加的重要原因之一。     

帕米尔高原东部径流量变化及其对气候变化的响应

水资源是制约中国西北干旱区社会经济可持续发展和生态安全的关键因素.以发源于帕米尔高原东部的喀什噶尔河和叶尔羌河流域为研究区,基于该区6个气象站月平均气温和降水量观测资料,以及5条代表性河流的出山口水文站1950年代晚期以来的月径流量观测数据,分析了该区域气候和水文年际变化特征,以及气候变化背景下径流量的响应特征.结果发...     

Tidal mixing in the Indonesian Seas and its effect on the tropical climate system

The sensitivity of the tropical climate to tidal mixing in the Indonesian Archipelago (IA) is investigated using a coupled general circulation model. It is shown that the introduction of tidal mixing considerably improves water masses properties in the IA, generating fresh and cold anomalies in the thermocline and salty and cold anomalies at the surface. The subsurface fresh anomalies are advected in the Indian Ocean thermocline and ultimately surface to freshen the western part of the basin whereas surface salty anomalies are advected in the Leuwin current to salt waters along the Australian coast. The ~0.5°C surface cooling in the IA reduces by 20% the overlying deep convection. This improves both the amount and structure of the rainfall and weakens the wind convergence over the IA, relaxes the equatorial Pacific trade winds and strengthens the winds along Java coast. These wind changes causes the thermocline to be deeper in the eastern equatorial Pacific and shallower in the eastern Indian Ocean. The El Nino Southern Oscillation (ENSO) amplitude is therefore slightly reduced while the Indian Ocean Dipole/Zonal Mode (IODZM) variability increases. IODZM precursors, related to ENSO events the preceding winter in this model, are also shown to be more efficient in promoting an IODZM thanks to an enhanced wind/thermocline coupling. Changes in the coupled system in response tidal mixing are as large as those found when closing the Indonesian Throughflow, emphasizing the key role of IA on the Indo-Pacific climate.     

太平洋大尺度环流数值模拟 Ⅲ：季节变化

本文在年平均环流数值模拟基础上,用季节变化的大气强迫场又积分了12年,并对由模拟得到的太平洋海面起伏、洋流、温度、海表热通量和上层热储存率等的季节变化特征作了较为详细的阐述和与已有观测结果进行了比较,事实证明,模式基本上模拟出了观测到的太平洋大尺度环流基本特征及其季节变化,证实基于理论考虑设计的IAP OGCM模式具有较好的性能和对实际环流的模拟能力,有些结果并优于国外一些具有同等分辨率的海洋模式。     

Interannual variation of tropical night frequency in Beijing and associated large-scale circulation background

This study examined the variability in frequency of tropical night occurrence (i.e., minimum air tem- perature >25℃) in Beijing, using a homogenized daily temperature dataset during the period 1960-2008. Our results show that tropical nights occur most frequently in late July and early August, which is consis- tent with relatively high air humidity associated with the rainy season in Beijing. In addition, year-to-year variation of tropical night occurrence indicates that the tropical nights have appeared much more frequently since 1994, which can be illustrated by the yearly days of tropical nights averaged over two periods: 9.2 days of tropical nights per year during 1994-2008 versus 3.15 days during 1960-1993. These features of tropical night variations suggest a distinction between tropical nights and extreme heat in Beijing. We further investigated the large-scale circulations associated with the year-to-year variation of tropical night occurrence in July and August, when tropical nights appear most frequently and occupy 95% of the annual sum. After comparing the results in the two reanalysis datasets (NCEP/NCAR and ERA-40) and considering the possible effects of decadal change in the frequency of tropical nights that occurred around 1993/94, we conclude that on the interannual time scale, the cyclonic anomaly with a barotropic structure centered over Beijing is responsible for less frequent tropical nights, and the anticyclonic anomaly is responsible for more frequent occurrence of tropical nights over Beijing.     

气候变暖背景下西太平洋副热带高压体形态变异及热力原因

采用美国NCEP/NCAR再分析资料,利用相关、合成分析、大气热源的计算等方法,研究了气候变暖背景下西太平洋副热带高压（副高）空间形态的变异及热力原因。结果表明,气候变暖前、后各层副高形态特征有很大的差异,副高体的空间形态从850—700 hPa开始显著西伸南扩,到500 hPa最为明显。各层副高在冷、暖期的形态差异与其周围大气热源和涡度的变化相对应。随着气候变暖,副高西侧和南侧的大气热源在850—700 hPa上开始有明显的加强,500 hPa热源加强最明显,且副高体南侧热源中心有所南移;同时,其西侧和南侧从对流层低层至中高层有反气旋涡度的增大,西侧的反气旋涡度在850—700 hPa增大最明显,南侧的反气旋涡度在500 hPa增大最明显,且反气旋中心整体南移。表明气候变暖后,副高体西侧和南侧大气热源的加强,导致相应区域反气旋涡度增大,副高体向反气旋涡度增大的方向发展,从而使副高西脊点西伸,南边界南扩,整体南移。      

Influence of the oceanic biology on the tropical Pacific climate in a coupled general circulation model

The influence of chlorophyll spatial patterns and variability on the tropical Pacific climate is investigated by using a fully coupled general circulation model (HadOPA) coupled to a state-of-the-art biogeochemical model (PISCES). The simulated chlorophyll concentrations can feedback onto the ocean by modifying the vertical distribution of radiant heating. This fully interactive biological-ocean-atmosphere experiment is compared to a reference experiment that uses a constant chlorophyll concentration (0.06 mg m⁻³). It is shown that introducing an interactive biology acts to warm the surface eastern equatorial Pacific by about 0.5°C. Two competing processes are involved in generating this warming: (a) a direct 1-D biological warming process in the top layers (0–30 m) resulting from strong chlorophyll concentrations in the upwelling region and enhanced by positive dynamical feedbacks (weaker trade winds, surface currents and upwelling) and (b) a 2-D meridional cooling process which brings cold off-equatorial anomalies from the subsurface into the equatorial mixed layer through the meridional cells. Sensitivity experiments show that the climatological horizontal structure of the chlorophyll field in the upper layers is crucial to maintain the eastern Pacific warming. Concerning the variability, introducing an interactive biology slightly reduces the strength of the seasonal cycle, with stronger SST warming and chlorophyll concentrations during the upwelling season. In addition, ENSO amplitude is slightly increased. Similar experiments performed with another coupled general circulation model (IPSL-CM4) exhibit the same behaviour as in HadOPA, hence showing the robustness of the results.     

呼伦贝尔市NPP时空变化及其对气候的响应

利用2000—2015年MOD17A3数据和气象站点资料,分析呼伦贝尔市NPP的时空变化特征及其对气候变化的响应情况。研究表明,呼伦贝尔市平均植被NPP为261.02 gC/(m~2·a),总体呈自西向东依次递增的分布格局。NPP的年际变化呈波动增长趋势,平均变化率为5.51gC/(m~2·a),线性增长达到显著的区域主要位于呼伦贝尔草原、大兴安岭南部林地和大兴安岭与松嫩平原过渡的耕地。16个气象站周边的NPP与各站年降水量均呈正相关,且除莫力达瓦达斡尔族自治旗(简称莫旗)外均通过了0.01水平的显著性检验,NPP与年平均气温均呈负相关,但除海拉尔区外均未通过显著性检验,NPP与日照时数正、负相关的台站同时存在。由此可知,降水是影响呼伦贝尔市NPP变化的主要因素。     

平流层大气环流的典型系统及变化特征综述

随着大气探测技术以及计算机性能的不断提高,近年来平流层探测数据日渐丰富,中层大气模式也得到了快速发展,平流层中一些重要的物理、化学以及动力过程得以深入研究,对平流层大气环流的认识也进一步加深。本文分析了平流层准2 a振荡（Quasi-Biennial Oscillation,QBO）、平流层残余（Brewer-Dobson,BD）环流和平流层极地环流等主要的平流层大气环流系统和信号的气候态特征、形成机制、年际变率以及长期趋势等,阐述了它们的主要影响因子和过程,讨论并展望了与平流层环流有关的一些主要科学问题。     

南方涛动年际变化与夏季亚澳季风环流及海洋性大陆区域气候异常的联系

利用美国NOAA卫星观测的SOI(Southern Oscillation Index,南方涛动指数)资料以及NCEP/NCAR、CMAP月平均资料,采用相关分析等方法,研究了南方涛动年际变化与夏季亚澳季风环流及海洋性大陆区域气候异常的联系。结果表明:南方涛动具有显著的年际变化特征,这种年际变化对夏季亚澳季风区及海洋性大陆区域的环流、降水及温度异常有重要影响。当SOI正位相时,赤道以南的澳大利亚东部地区以及西北太平洋海域高层为气旋,低层为反气旋,赤道地区的东部太平洋低层为辐散中心,高层为辐合中心,有利于下沉运动维持;加里曼丹岛附近低层辐合,高层辐散,有利于上升运动维持;海洋性大陆地区降水为显著的正异常,东亚地区降水存在较弱的正异常;海洋性大陆地区以及我国青藏高原到东海一带温度为正异常,孟加拉湾及印度半岛区域温度为负异常。     

Streamflow trends and climate linkages in the Zagros Mountains,Iran

This paper examines trends in streamflow and their links with local climate in the Karkheh River and its major tributaries, which originate from the Zagros Mountains, Iran. Streamflow records from five mainstream stations for the period 1961–2001 were used to examine trends in a number of streamflow variables. The studied variables were mean annual and monthly flows, 1 and 7 days maximum and minimum flows, timing of the 1-day maxima and minima, and the number and duration of high and low flow pulses. Similarly, the precipitation and temperature data from seven climate stations for the period from 1950s to 2003 were used to examine trends in climatic variables and their correlation with the streamflow. The Spearman Rank test was used for the detection of trends and the correlation analysis was based on the Pearson method. The results reveal a number of significant trends in streamflow variables both increasing (e.g. December flows) and decreasing (e.g. May flows) for all stations. However, some trends were not spatially uniform. For example, decline in low flow characteristics were more significant in the upper parts of the basin, whereas increasing trends in floods and winter flows were noteworthy in the middle parts of the basin. Most of these trends could be attributed to precipitation changes. The results show that the decline in April and May precipitation causes the decline in the low flows while the increase in winter (particularly March) precipitation coupled with temperature changes lead to increase in the flood regime. The observed trends at the Jelogir station on the Karkheh River reflect the combined effect of the upstream catchments. The significant trends observed in a number of streamflow variables at Jelogir, 1-day maximum, December flow and low pulse count and duration, point to the changes in hydrological regime of the entire Karkheh River system and are attributed to the changes in climatic variables.     

Future climate in the Pacific Northwest

Climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) on the whole reproduce the observed seasonal cycle and twentieth century warming trend of 0.8°C (1.5°F) in the Pacific Northwest, and point to much greater warming for the next century. These models project increases in annual temperature of, on average, 1.1°C (2.0°F) by the 2020s, 1.8°C (3.2°F) by the 2040s, and 3.0°C (5.3°F) by the 2080s, compared with the average from 1970 to 1999, averaged across all climate models. Rates of warming range from 0.1°C to 0.6°C (0.2°F to 1.0°F) per decade. Projected changes in annual precipitation, averaged over all models, are small (+1% to +2%), but some models project an enhanced seasonal cycle with changes toward wetter autumns and winters and drier summers. Changes in nearshore sea surface temperatures, though smaller than on land, are likely to substantially exceed interannual variability, but coastal upwelling changes little. Rates of twenty-first century sea level rise will depend on poorly known factors like ice sheet instability in Greenland and Antarctica, and could be as low as twentieth century values (20 cm, 8^″) or as large as 1.3 m (50^″).     

中国东南部冬季降水变化及其环流特征

利用1951-2011年中国160站降水资料及NCEP/NCAR再分析资料,分析了中国东南部冬季降水的年际变化及与之相关的环流和水汽输送特征。结果表明:中国东南部冬季降水年际差异较明显,当降水异常偏多(少)时,蒙古高压及中国广大南方地区海平面气压异常偏低(高),而亚洲附近的洋面上则异常偏高(低);500 hPa上,巴尔喀什湖附近的高压脊和东亚大槽均偏弱(强);高层东亚西风急流异常偏弱(强),中东地区急流异常偏强(弱);中国东部20~30°N出现显著异常上升(下沉)运动,低纬度地区出现异常下沉(上升)运动。影响中国东南部冬季降水的水汽输送主要有两支:来自西风带绕高原的南支气流,经过阿拉伯海和孟加拉湾向华南的输送水汽;来自低纬西太平洋,经南海向中国西南的水汽输送。此外,东亚冬季风与中国东南部冬季降水关系密切。