Evolution of geophysical parameters over the Indian Ocean region during contrasting monsoon years of 2002 and 2003 using TRMM/TMI data

Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal) were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea (EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003. The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm over EAS during entire July and hence less rainfall. The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence less rainfall compared to July 2003.     

Comparison of Daily Extreme Temperatures over Eastern China and South Korea between 1996–2005

This paper examined the decadal mean, seasonal cycle, and interannual variations of mean and extreme temperatures using daily temperature and relative humidity data from 589 stations over eastern China and South Korea between 1996–2005. The results show that the decadal mean Tm (mean daily mean temperature) and the TNn (minimum daily minimum temperature) increase from north to south; the opposite spatial gradient is found in the DTR (diurnal temperature range); the value of the DTR over South Korea is in- b...     

Albedo enhancement over land to counteract global warming: impacts on hydrological cycle

A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO₂ leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (?8.2?W?m^?2) to counter global mean radiative forcing from a doubling of CO₂ (3.3?W?m^?2) is approximately twice the forcing needed over the oceans (?4.2?W?m^?2). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification.     

东亚夏季风指数的年际变化与东亚大气环流

文中从夏季东亚热带、副热带环流系统特点出发 ,定义了能较好表征东亚夏季风环流年际变化的特征指数 ,并分析了东亚夏季风指数的年际变化与东亚大气环流及夏季中国东部降水的关系。文中定义的东亚夏季风指数既反映了夏季东亚大气环流风场的变化特征 ,也较好地反映了夏季中国东部降水的年际变化特征。此外 ,还探讨了东亚夏季风指数变化的先兆信号     

2015/2016超强El Nio对中国南方冬春季降水的影响分析

利用1981—2016年的中国160站降水资料、OISST海温资料和NCEP/NCAR大气环流资料,对比分析了中等强度El Nio和2015/2016超强El Nio对中国东南部、江淮流域和西南地区冬春季降水影响的异同。结果表明:在中等强度El Nio的冬季,偏暖的赤道中东太平洋海表面温度(Sea Surface Temperature,SST)所激发的西北太平洋和日本附近的异常反气旋环流,其异常的西南风会加强南海—西北太平洋的水汽向中国东部输送,造成中国东南部和江淮流域的降水一致偏多。2015/2016超强El Nio的冬季,赤道中东太平洋SST的强度异常偏强,中国东部异常偏冷的表面气温和对流层低层温度加强大陆冷高压,长江流域及其以北地区受异常强的北风控制,从而造成中国东南部降水增多、江淮流域降水减少。在2015/2016超强El Nio事件衰减位相的春季,中国东南部和西南部降水的增加主要归因于异常偏暖的西北印度洋和东南印度洋SST的作用。经CAM5模式试验证明,西北印度洋异常偏暖的SST引起了北印度洋的异常西南风,激发了孟加拉湾—西北太平洋的异常反气旋,加强了印度洋和南海—西北太平洋的水汽向中国西南和东南部输送。此外,东南印度洋异常偏暖的SST还会激发局地异常上升运动,通过经向垂直环流加强南海—西北太平洋异常下沉运动,诱使中国东南部的上升运动加强,导致降水增多。     

冬季黑潮延伸体区域海表温度锋对北太平洋风暴轴的影响

利用NOAA最优插值逐日海表温度资料和NCEP/NCAR的逐日大气再分析资料,分析了冬季黑潮延伸体区域海表温度锋的变化及其对北太平洋风暴轴的影响。结果表明,冬季黑潮延伸体区域海表温度锋强度和纬度位置既存在年际变化,也存在年代际变化,且强度和位置的变化是相互独立的。冬季黑潮延伸体区域海表温度锋强度的年际变化对北太平洋风暴轴没有显著的影响,而其年代际变化则对北太平洋风暴轴具有非常显著的影响,当冬季海表温度锋偏强时,大气斜压性在鄂霍次克海及阿拉斯加附近区域上空增强,而在海表温度锋下游至东太平洋区域上空显著减弱,平均有效位能向涡动有效位能的斜压能量转换在45°N以北的太平洋区域上空有所增多,而在30°-45°N的太平洋区域上空有所减少,涡动有效位能向涡动动能的斜压能量转换在35°N以北的西太平洋区域以及45°N以北的东太平洋区域都显著增加,而仅在其南部边缘存在东西带状的减弱区域,导致40°N以北海区北太平洋风暴轴增强,40°N以南海区北太平洋风暴轴减弱,冬季海表温度锋偏弱时则有与之相反的结果。冬季黑潮延伸体区域海表温度锋纬度位置的变化对北太平洋风暴轴也存在较显著的影响,当海表温度锋位置偏北时,在其下游45°N以南的太平洋区域上空大气斜压性减弱,45°N以南的中东太平洋区域上空区域平均有效位能向涡动有效位能、以及涡动有效位能向涡动动能的斜压能量转换都减少;而在45°N以北的太平洋区域上空大气斜压性增强,在阿拉斯加湾附近上空尤其显著,在黑潮延伸体区域附近以及45°N以北的中东太平洋上空平均有效位能向涡动有效位能、以及涡动有效位能向涡动动能的斜压能量转换都显著增加,导致北太平洋风暴轴在其气候平均态轴线两侧呈现北正南负的偶极子形态;海表温度锋位置偏南时则有与之相反的结果。冬季黑潮延伸体区域海表温度锋强度和位置的变化均对北太平洋风暴轴具有显著的影响,其具体的物理机制还需要进一步的研究。      

Simulated Spatial Distribution and Seasonal Variation of Atmospheric Methane over China: Contributions from Key Sources简

We used the global atmospheric chemical transport model,GEOS-Chem,to simulate the spatial distribution and seasonal variation of surface-layer methane （CH4） in 2004,and quantify the impacts of individual domestic sources and foreign transport on CH4 concentrations over China.Simulated surface-layer CH4 concentrations over China exhibit maximum concentrations in summer and minimum concentrations in spring.The annual mean CH4 concentrations range from 1800 ppb over western China to 2300 ppb over the more populated eastern China.Foreign emissions were found to have large impacts on CH4 concentrations over China,contributing to about 85％ of the CH4 concentrations over western China and about 80％ of those over eastern China.The tagged simulation results showed that coal mining,livestock,and waste are the dominant domestic contributors to CH4 concentrations over China,accounting for 36％,18％,and 16％,respectively,of the annual and national mean increase in CH4 concentration from all domestic emissions.Emissions from rice cultivation were found to make the largest contributions to CH4 concentrations over China in the summer,which is the key factor that leads to the maximum seasonal mean CH4 concentrations in summer.     

SIMULATING THE RESPONSE OF NON-UNIFORMITY OF PRECIPITATION EXTREMES OVER CHINA TO CO2 INCREASING BY MIROC_HIRES MODEL

The response of non-uniformity of precipitation extremes over China to doubled CO2has been analyzed using the daily precipitation simulated by a coupled general circulation model,MIROC_Hires.The major conclusions are as follows:under the CO2increasing scenario(SRES A1B),the climatological precipitation extremes are concentrated over the southern China,while they are uniformly distributed over the northern China.For interannual variability,the concentration of precipitation extremes is small over the southern China,but it is opposite over the northern China.The warming effects on the horizontal and vertical scales are different over the northern and southern part of China.Furthermore,the atmospheric stability is also different between the two parts of China.The heterogeneous warming is one of the possible reasons for the changes in non-uniformity of precipitation extremes over China.     

人类活动排放的CO2及气溶胶对20世纪70年代末中国东部夏季降水年代际转折的影响

全球变暖背景下,中国东部夏季降水在20世纪70年代末开始较19世纪呈现东北及长江中、下游地区多雨,华北及华南少雨的特征。与此同时,人类活动排放的CO₂及气溶胶量也发生了明显的年代际变化。文中利用地球系统耦合模式（CESM）诊断了中国东部夏季的水分收支对人类活动排放的CO₂及气溶胶年代际变化的响应。发现CO₂排放量增加后,江淮流域的水汽辐合以及中国南方的水汽辐散主要是与质量辐散有关的动力项及与湿度梯度相关的热力项共同作用的结果,但动力作用更显著。气溶胶效应则主要通过动力作用使得江淮流域水汽辐合,而中国南方地区水汽辐散。虽然CO₂和气溶胶对辐射量及温度的影响差别很大,但通过改变温度梯度,热成风效应产生的动力作用都会导致江淮流域上升运动增强,降水增多;而中国南方下沉运动显著,降水减少,与观测结果一致,且CO₂相较于气溶胶的影响更为显著,证实了20世纪70年代末人类活动对中国东部夏季降水年代际转折的影响。      

2006年夏季川渝地区伏旱与低频大气热源的关系

利用NCEP/NCAR再分析资料和中国地面观测站的逐日降水资料,研究了2006年夏季中国川渝地区的伏旱与亚洲地区大气低频振荡的联系.结果表明,2006年夏季中国川渝地区降水低频振荡的主要周期约为60 d;在川渝严重干旱期的7月下旬至8月上旬,经向上由于川渝地区上空低频热汇、广西和海南及其以西地区上空低频热源的影响,在1...     

Boundary-layer modification in wintertime cold-air outbreaks from the Arctic sea ice

During the field experiment ARKTIS 1993 ten cases of boundary-layer modification in wintertime cold-air outbreaks from the Arctic sea ice in the Spitsbergen region were observed by aircraft over a distance ranging from about 50 km over the ice to about 300 km over the water. The modification depends decisively on the initial conditions over the ice, the boundary conditions at the bottom and top of the boundary layer and on the conditions of the large-scale flow. The modification of the bulk boundary-layer characteristics in relation to these conditions is presented.Besides the air-sea temperature contrast, the most important role for the boundary-layer modification is played by the stability on top of the boundary layer and by the divergence of the large-scale flow. According to the high variability of these conditions the observed boundary-layer modifications were very variable ranging from 100 to 300 m thick boundary layers with air temperatures between -32 and -22 °C over the ice to thicknesses between 900 and 2200 m and air temperatures between -15 and -5 °C after 300 km fetch over the open water. In most cases the large-scale flow was anticyclonic and divergent over the ice and changed to cyclonic and convergent over the water and an ice-sea breeze was superimposed on it.The sensible and latent heat fluxes are the dominant terms in the surface energy budget over the open water and ranged between 200 and 700 W m^-2 whereas the net longwave radiation is the dominating term over the ice with the heat fluxes only about 10 W m^-2.     

Zonal circulation indices, 500 hPa April ridge position along 75° E and Indian summer monsoon rainfall: Statistical relationships

Summary This paper presents an examination of the statistical relationship between summer monsoon rainfall over all India, and two sub-regions (north west India and peninsular India) and the indices of mid-latitude (35° to 70° N) zonal circulation at 500 hPa level, over different sectors of the hemisphere, based on 19 years (1971–1989) data. The results indicate that summer monsoon rainfall (June–September) over India shows; (i) a significant and direct relationship with the strength of the zonal circulation index during concurrent July over the sector 90° E to 160° E. (ii) a significant inverse relationship with the strength of the zonal index during the previous April over the sector 160° E to 45° W and a similar relationship with the whole northern hemisphere and (iii) a significant and direct relationship with the frequency of the zonal index during the previous January over the sector 45° W to 90° E.Significant relationships are also observed between the zonal circulation indices of the above mentioned months and sectors with the 500 hPa ridge location in April at 75° E over India.With 4 Figures     

中国东部夏季降水80年振荡与东亚夏季风的关系

利用中国东部1470－1999年夏季降水级别资料和1951－1999年夏季降水观测资料，以及1871－2000年北半球海平面气压资料研究了中国东部夏季降水与东亚夏季风的关系。研究表明华北及东北南部、长江中下游地区和华南夏季降水存在明显的80年振荡，华北夏季降水的80年振荡与华南同位相，与长江中下游反位相。华北夏季降水与海平面气压在120°－130°E，20°－25°N区域内呈负相关，在121°－130°E，20°－25°N区域内呈正相关，并达到 95％信度。因此，利用这两个区域平均海平面气压差定义了一个表征夏季西南风强度的东亚夏季风指数。当东亚夏季风强时，华北夏季降水偏多，同时长江中下游少雨；当东亚夏季风接近正常时，华北干旱，长江中下游多雨。最后，利用530年的华北夏季降水长序列资料研究了东亚夏季风的年代际变率。     

东亚区域对流层臭氧及其前体物的季节性关联

利用2010—2012年对流层臭氧（O₃）及其多种前体物的卫星遥感资料和全球水汽再分析资料,研究东亚区域O₃及其前体物的时空分布,以及在中国东部（分为南、北两部分）相关性的季节变化。结果表明:东亚区域NO₂与CO的对流层柱含量均表现为冬季高、夏季低的时空变化形式。O₃对流层柱含量夏季达到峰值,冬季为谷值。中国东部的北部与南部地区O₃与NO₂均在夏秋季呈正相关,冬春季呈负相关。夏季大部分地区NO_x的光化学循环反应对O₃生成有积极的促进作用,冬季大部分地区O₃的光化学循环生成受到抑制。O₃与CO在北部地区夏秋季和南部地区夏季正相关性最大,无论是在北部还是南部地区,O₃与CO的相关性在轻污染情况下最大,而在重污染和背景情况下较小,表明重污染气团向下风方的输送更有利于O₃的光化学生成。O₃与水汽在北部和南部地区的多数时间均呈较显著的正相关性,而在南部地区夏季和北部地区冬季具有较大的负相关性,反映出不同的环流形式、气团来源及伴随的天气条件变化对O₃分布的影响。     

Competing impact of anthropogenic emissions and meteorology on the distribution of trace gases over Indian region

The spatial distribution of trace gases exhibit large spatial heterogeneity over the Indian region with an elevated pollution loading over densely populated Gangetic Plains (IGP). The contending role and importance of anthropogenic emissions and meteorology in deciding the trace gases level and distribution over Indian region, however, is poorly investigated. In this paper, we use an online regional chemistry transport model (WRF/Chem) to simulate the spatial distribution of trace gases over Indian region during one representative month of only three meteorological seasons namely winter, spring/summer and monsoon. The base simulation, using anthropogenic emissions from SEAC⁴RS inventory, is used to simulate the general meteorological conditions and the realistic spatial distribution of trace gases. A sensitivity simulation is conducted after removing the spatial heterogeneity in the anthropogenic emissions, i.e., with spatially uniform emissions to decouple the role of anthropogenic emissions and meteorology and their role in controlling the distribution of trace gases over India. The concentration levels of Ozone, CO, SO₂ and NO₂ were found to be lower over IGP when the emissions are uniform over India. A comparison of the base run with the sensitivity run highlights that meteorology plays a dominant role in controlling the spatial distribution of relatively longer-lived species like CO and secondary species like Ozone while short-lived species like NO_X and SO₂ are predominantly controlled by the spatial variability in anthropogenic emissions over the Indian region.     

Analyzing snowfall variability over two locations in Kashmir,India in the context of warming climate

Present study focuses on examination snowfall variability over Gulmarg and Pahalgam of Kashmir Valley in India during past 31 years (1980–2010). Trends in temperature over the study area is also explored. Minimum and maximum temperature shows increasing trends which is consistent with increase in black carbon column mass density. Increase in black carbon mass density is attributed to urbanization over study area. Trends of minimum temperature is statistically significant. It is reported that snowfall over the Pahalgam shows decreasing trend except for the month of February and January. Pahalgam shows a significant decreasing trend in snowfall of about 48 mm per decade during March. Pahalgam and Gulmarg show seasonal decreasing trends of snowfall of about 15 mm and 1.8 mm per decade, respectively. These decreasing trends in snowfall are consistent with decadal increasing trends of about 1.2 °C and 0.8 °C in minimum temperature over Pahalgam and Gulmarg, respectively. Seasonal snowfall over both the regions shows decreasing trend (insignificant). Results reported in this study show a decrease of about 24.16% ± 9.86% per degree increase in minimum temperature over Pahalgam. Changing characteristics of snowfall in the context of anthropogenic warming present major challenges to the tourism and socioeconomic aspects over the Valley.     

Future changes in cyclone climatology over Europe as inferred from a regional climate simulation

This study analyzes the cyclone climatology in regional climate model simulations of present day (1961–1990) and future (2071–2100, A2 and B2 emission scenarios) european climate conditions. The model domain covers the area from Scandinavia to Northern Africa and from the Eastern Atlantic to Russia at a horizontal grid spacing of 50 km. Compared to present day, in the A2 and B2 scenario conditions the annual average storm track intensity increases over the North-East Atlantic and decreases over Russia and the Eastern Mediterranean region. This overall change pattern is larger in the A2 than in the B2 simulations. However, the cyclone climatology change signal shows a large intermonthly variability and important differences across European regions. The largest changes are found over the North-East Atlantic, where the storm track intensity increases in winter and decreases in summer. A significant reduction of storm track intensity is found during late summer and autumn over the Mediterranean region, and from October to January over Russia. The number of cyclones decreases in future conditions throughout Europe, except over the Central Europe and Mediterranean regions in summer (where it increases). The frequency of intense cyclones and the depth of extreme cyclones increase over the North-East Atlantic, decrease over Russia and show an irregular response over the rest of the domain.

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Study on Ozone Change over the Tibetan Plateau

This paper reviewed the main results with respect to the discovery of low center of total column ozone (TCO) over the Tibetan Plateau (TP) in summer, and its formation mechanism. Some important advances are summarized as follows: The fact is discovered that there is a TCO low center over the TP in summer, and the features of the background circulation over the TP are analyzed; it is confirmed that the TP is a pathway of mass exchange between the troposphere and stratosphere, and it influences the TCO low center over the TP in summer; models reproduce the TCO low center over the TP in summer, and the formation mechanism is explored; in addition, the analyses and diagnoses of the observation data indicate that not only there is the TCO low center over the TP in summer, but also TCO decrease trend over the TP is one of the strong centers of TCO decrease trend in the same latitude; finally, the model predicts the future TCO change over the TP.     

中国干旱半干旱区洪涝灾害的初步分析

中国干旱半干旱区的洪涝灾害是一个尚未引起人们重视的重大科学问题,这主要是因为干旱半干旱区对洪涝灾害的防范意识比较薄弱。而极端降水事件的次数、强度和持续时间与干旱半干旱区的洪涝灾害有密切联系,直接影响该区域洪涝灾害及其次生地质灾害的次数与严重程度。以干旱半干旱区的极端降水事件为切入点,分析了中国干旱半干旱区的极端降水事件次数和极端降水量的变化特征,旨在为干旱半干旱区的洪涝灾害研究提供科学依据。结果表明,进入21世纪以来,中国110°E以西的干旱半干旱区极端降水事件的日数有所增多,而110°E以东的区域日数都有所减少。干旱半干旱区极端降水量的变化也呈现出西增东减的分布,大部分干旱半干旱区的极端降水量变化占总降水量变化的40%以上,一部分地区能达到50%,甚至100%-200%。从季节变化来看,春季天山以北、新疆南部、甘肃敦煌和内蒙古包头以北地区极端降水量增加较多,夏季110°E以西的干旱半干旱区极端降水量均增大明显,秋季陕西榆林、内蒙古鄂尔多斯、包头和呼和浩特等地极端降水量增大较明显。     

Monthly Synoptic Patterns Associated with Wet/Dry Conditions in the Eastern Mediterranean

Summary An investigation of the main features of large-scale synoptic patterns over Europe and the adjacent areas for extreme winter periods during 1980–1995 over the Eastern Mediterranean (EM) is performed. The NASA reanalysis data set is used to investigate composite sea level pressure (SLP), geopotential height of the 500 hPa surface (H-500) and precipitation–wet, normal and dry patterns for each month during the period October–March. It is found that the wet and dry cool seasons in the EM are associated with distinct SLP and H-500 anomaly patterns over Europe and the adjacent regions. During the dry spells large-scale positive SLP/H-500 anomaly areas prevail over Eastern Europe. A negative SLP anomaly is normally found during these periods over southwestern and Western Europe. During the wet cool seasons in the EM there are mainly negative SLP/H-500 anomaly areas over Eastern Europe to the north east of the EM. Positive SLP/H-500 anomalies are found over Western Europe. During wet months a trough zone between the Siberian and the Azorean Highs is positioned over the eastern part of the Mediterranean. During dry months the Siberian anticyclone is more intensive and the zone with low surface pressure is displaced to the central part of the northern Mediterranean. Received May 26, 1999 Revised August 26, 1999