Relationships among monsoon-season circulation patterns, gulf surges, and rainfall within the Lower Colorado River Basin, USA

The purpose of this study is to assess the connections between the monsoon anticyclone, gulf surges, and rainfall within the Lower Colorado River Basin (LCRB) during North American monsoon seasons from 1988-2006. The methods involved calculating rainfall characteristics and near-surface humidity for 500-hPa circulation patterns, creating circulation and near-surface humidity composites for rainfall days, and creating near-surface humidity composites for rainfall days occurring under each circulation pattern. The circulation was dominated by the monsoon anticyclone being over or to the immediate east of the basin. The anticyclone was shifted to the northwest (east) of its seasonal mean position on rainfall days in the central portion of the basin (far eastern portion of the basin). Rainfall influenced by gulf surges was most likely when the monsoon anticyclone was shifted westward, especially northwestward, of its typical position. The central portion of the basin received substantially more surge-influenced rainfall than did the far eastern portion of the basin.     

Summer monsoon rainfall patterns over South Korea and associated circulation features

Summary Seasonal summer monsoon (June through August) rainfall patterns over South Korea are classified by an objective method using data for a 40-year period (1961–2000). The rainfall patterns are represented by the percentage departures from the normal rainfall of 12 stations spread uniformly over South Korea. The statistical technique employed is the k-means (KM) clustering method. The Euclidean distance has been used as a measure of similarity between the patterns. Four dominant types are obtained by this method. Intercorrelations among the types suggest that the dominant patterns are distinct. The summer monsoon rainfall shows an increasing trend. Investigation of the physical processes associated with these patterns using NCEP/NCAR Reanalysis data clearly reveals contrasting circulation features associated with the dominant types during the summer monsoon period. In particular, contrasting circulation features are related to the position, shape and strength of the North Pacific Subtropical High. Received October 30, 2000 Revised November 12, 2001     

Asymmetries in tropical rainfall and circulation patterns in idealised CO2 removal experiments

Atmospheric CO₂ removal is currently receiving serious consideration as a supplement or even alternative to emissions reduction. However the possible consequences of such a strategy for the climate system, and particularly for regional changes to the hydrological cycle, are not well understood. Two idealised general circulation model experiments are described, where CO₂ concentrations are steadily increased, then decreased along the same path. Global mean precipitation continues to increase for several decades after CO₂ begins to decrease. The mean tropical circulation shows associated changes due to the constraint on the global circulation imposed by precipitation and water vapour. The patterns of precipitation and circulation change also exhibit asymmetries with regard to changes in both CO₂ and global mean temperature, but while the lag in global precipitation can be ascribed to different levels of CO₂ at the same temperature state, the regional changes cannot. Instead, ocean memory and heat transfer are important here. In particular the equatorial East Pacific continues to warm relative to the West Pacific during CO₂ ramp-down, producing an anomalously large equatorial Pacific sea surface temperature gradient and associated rainfall anomalies. The mechanism is likely to be a lag in response to atmospheric forcing between mixed-layer water in the east Pacific and the sub-thermocline water below, due to transport through the ocean circulation. The implication of this study is that a CO₂ pathway of increasing then decreasing atmospheric CO₂ concentrations may lead us to climate states during CO₂ decrease that have not been experienced during the increase.     

Dry conditions over Argentina and the related monthly circulation patterns

Summary This paper presents an analysis of the frequency and spatial distribution of droughts in Argentina during the 20th century. Special attention is given to the mean monthly atmospheric circulation associated with dry conditions in the Pampas during the second half of the century. A reduction in the number of dry cases is found throughout the century, especially during the warm season (October to March). Droughts occurred more often in only one or two regions simultaneously and only a few covered a large territory. Many of the dry months in the Pampas occurred under, or were preceded by, neutral ENSO conditions. During the warm season the ENSO cold phase preceded some of the dry months. Circulation patterns at 1000 hPa and 500 hPa and their temporal evolution are determined using Principal Component Analysis. A coupled 1000-500 hPa level analysis is performed to study the vertical coherence associated with dry conditions. Different patterns related to the warm season are clearly identified using this methodology. The principal feature are positive anomalies over the continent (principally at low levels), high circulation index and an enhancement of the westerlies. Patterns related to the cold season reflect high pressure at the surface, but some differences pre- and post- 1970 have been observed. In this season, some dry cases were found to have high correlations with opposites modes of PC scores. In these cases, a water deficit acted as the principal causes of the dry conditions.     

SST variability in the South Indian Ocean and associated circulation and rainfall patterns over Southern Africa

Summary A general circulation model is used to study the response of the atmosphere to an idealised sea surface temperature (SST) anomaly pattern (warm throughout the southern midlatitudes, cool in the tropics) in the South Indian Ocean region. The anomaly imposed on monthly SST climatology captures the essence of patterns observed in the South Indian Ocean during both ENSO events and multidecadal epochs, and facilitates diagnosis of the model response. A previous study with this anomaly imposed in the model examined differences in the response between that on the seasonal scale (favours enhancement of the original SST anomaly) and that on the decadal scale (favours damping of the anomaly). The current study extends that work firstly by comparing the response on the intraseasonal, seasonal and interannual scales, and secondly, by assessing the changes in the circulation and rainfall over the adjoining African landmass.It is found that the atmospheric response is favourable for enhancement of the original SST anomaly on scales up to, and including, annual. However, as the scale becomes interannual (i.e., 15–21 months after imposition of the anomaly), the model response suggests that damping of the original SST anomaly becomes likely. Compared to the shorter scale response, the perturbation pressure and wind distribution on the interannual scale is shifted poleward, and is more reminiscent of the decadal response. Winds are now stronger over the warm anomaly in the southern midlatitudes suggesting enhanced surface fluxes, upper ocean mixing, and consequently, a damping of the anomaly.Examination of the circulation and rainfall patterns indicates that there are significant anomalies over large parts of southern Africa during the spring, summer and autumn seasons for both short (intraseasonal to interannual) and decadal scales. It appears that rainfall anomalies are associated with changes in the advection of moist tropical air from the Indian Ocean and its related convergence over southern Africa. Over eastern equatorial Africa, the austral autumn season (the main wet season) showed rainfall increases on all time scales, while parts of central to eastern subtropical southern Africa were dry. The signals during summer were more varied. Spring showed generally dry conditions over the eastern half of southern Africa on both short and decadal time scales, with wet areas confined to the west. In all cases, the magnitude of the rainfall anomalies accumulated over a 90 day season were of the order of 90–180 mm, and therefore represent a significant fraction of the annual total of many areas. It appears that relatively modest SST anomalies in the South Indian Ocean can lead to sizeable rainfall anomalies in the model. Although precipitation in general circulation models tends to be less accurately simulated than many other variables, the model results, together with previous observational work, emphasize the need for ongoing monitoring of SST in this region.With 14 Figures     

塔里木盆地夏季降水年代际的变化及联系的大尺度环流[*]

基于1961-2020年夏季塔里木盆地33站逐日降水数据和NCEP/NCAR大气环流再分析数据,分析了塔里木盆地夏季降水的年代际变化特征及影响环流。结果表明,塔里木盆地夏季降水在1986/1987年发生了由少到多的年代际突变,降水显著增加的区域主要位于盆地的西部和北部,主要由降水日数的增加贡献。不同年代际背景下,影响塔里木盆地夏季降水的环流配置存在一定差异。1961-1986年,影响盆地夏季降水的中亚副热带急流位置显著南移,中亚上空的异常气旋位于40°N附近,水汽源于阿拉伯海;1987-2020年,影响盆地夏季降水的中亚上空异常气旋位置位于40°N以南,水汽源于孟加拉湾和西北太平洋。东大西洋—西俄罗斯大气遥相关型在塔里木盆地夏季降水的年代际变化中扮演了重要角色。     

中国东部夏季不同雨带类型的海洋和环流特征差异

利用1951-2009年NCEP/NCAR再分析资料、UKMO HADISST1全球月海表温度及中国东部地区120站的月降水量资料,首先定义出能够客观表征中国东部夏季3种雨带类型的指数,然后分析了3种雨带分布类型海洋和大气环流特征的主要差异,并进一步分析了前期海洋背景的差异特征对夏季东亚环流关键系统的预测蕴示.结果表明:(1)3种雨带类型对应的前期冬季海洋信号比当年夏季强,其差异主要表现在:多雨带出现在北方地区的Ⅰ型对应的是北太平洋海温呈显著的正距平、暖池及东澳暖流为负距平、南太平洋西风漂流区为正距平;多雨带出现在黄淮地区的Ⅱ型对应的海温分布则与Ⅰ型完全相反;多雨带出现在长江及其以南地区的Ⅲ型对应的海温分布在北太平洋海域与Ⅰ型基本一致;(2)3种雨带类型对应的环流及水汽输送特征的差异主要表现在:Ⅲ型与Ⅰ型具有几乎完全相反的环流及水汽输送特征,当出现Ⅲ型时,东亚中高纬度有强盛的阻塞形势发展和维持,中高纬度的经向环流异常加强,同时西太平洋副热带高压偏强,位置偏西、偏南,该地区呈反气旋性距平环流,西太平洋副热带纬向水汽输送加强,而出现Ⅰ型时则相反;Ⅱ型与Ⅰ型的环流及水汽输送特征更接近,两者的主要差异是:当出现Ⅱ型时,西太平洋副热带地区呈反气旋性距平环流,而出现Ⅰ型时该地区呈气旋性距平环流;(3)前期冬季赤道中东太平洋海温和南太平洋西风漂流区的海温异常变化可以作为夏季西太平洋副热带高压预报的重要前兆信号.     

北京地区短时强降水过程的多尺度环流特征

为了探讨不同天气尺度背景下,北京地区短时强降水过程的基本特征,利用2007-2014年6-8月北京地区自动气象站观测数据和ECMWF ERA-Interim（0.5°×0.5°）全球再分析数据,在对北京地区短时强降水日的大尺度环流特征进行分型的基础上,基于分型合成场和距平场分析了北京地区短时强降水天气过程的基本环流背景及相应的中尺度环流特征。结果表明：（1）造成北京地区出现短时强降水过程的天气系统,依据其出现的频次,大体可分为副热带高压（副高）与西来槽相互作用型、西风小槽型、东北冷涡型和黄淮低涡倒槽型等4类;从低层水汽来看,除东北冷涡型主要来自于渤海、黄海外,其他3型短时强降水过程的水汽主要来自中国南海或东海。（2）不同天气系统主导下的短时强降水时空分布存在较大差异：在空间分布上,黄淮低涡倒槽型短时强降水带分布从北京东南平原穿过城区至西北山前成东南-西北走向,其余3型大体上沿北京地形成西南-东北走向,其中,西南山前、城区和东北山前地区是3个短时强降水事件的多发中心;在时间分布上,东北低涡型造成的短时强降水过程主要发生在午后,副高与西来槽相互作用型主要集中在傍晚至前半夜,而西风小槽型和黄淮低涡倒槽型短时强降水表现出较强的夜雨特征。（3）从中尺度环流特征上看,副高与西来槽相互作用型短时强降水过程主要是低层冷空气从北京西部、北部进入,首先触发山区对流,与之对应的雷暴高压逐渐组织化,外侧辐散气流（冷池出流）和山前的偏南风暖湿气流辐合造成对流过程加强;西风小槽型主要是边界层内较强东南风在北京西北部山前受地形阻挡,向两边绕流,西南支气流在西部形成气旋性环流,造成城区西部的对流性天气,东北支气流在东北部山前形成地形辐合线,夜间随着东南气流中偏南分量显著加强,东北部山前地区的辐合上升运动加强,造成东北部山前对流性天气,因此在短时强降水落区上表现为两个分离的多发中心且具有夜发性;东北冷涡型主要是系统性的冷空气从北京北部或西部南下,在山前与低空偏东风形成辐合切变线,触发午后对流性天气;黄淮低涡倒槽型主要是黄淮低涡顶部的低层偏东气流在北京西部山前辐合抬升,触发对流,并逐步演变为中尺度气旋性环流,形成相对组织化的短时强降水。     

Interannual variability of summer rainfall over the northern part of China and the related circulation features

In this study, interannual variability of summer rainfall over the northern part of China (NPC) and associated circulation patterns were investigated by using long-term (1961–2013) observational and reanalysis data. Two important NPC rainfall modes were identified by empirical orthogonal function analysis: the first is characterized by an almost uniformly distributed rainfall anomaly over most parts of the NPC, while the second shows rainfall variability in Northeast China (NEC) and its out-of-phase relationship with that in North China (NC) and the northern part of Northwest China. The results also suggest that the NPC summer rainfall anomalies are also closely associated with those in some other parts of China.It is revealed that the circumglobal teleconnection pattern associated with the anomalous Indian summer monsoon (ISM) and the Polar/Eurasia (PEA) pattern work in concert to constitute the typical circulation pattern of the first rainfall mode. The cooperative engagement of the anomalous ISM circulation and the PEA pattern is fundamental in transporting water vapor to the NPC. The study emphasizes that the PEA pattern is essential for the water vapor transport to the NPC through the anomalous midlatitude westerly.In the second NPC rainfall mode, the typical circulation pattern is characterized by the anomalous surface Okhotsk high and the attendant lower tropospheric circulation anomaly over NEC. The circulation anomaly over NEC leads to a redistribution of water vapor fluxes over the NPC and constitutes an out-of-phase relationship between the rainfall anomalies over NEC and NC.     

Intraseasonal variations of the Yangtze rainfall and its related atmospheric circulation features during the 1991 summer

The intraseasonal variations of the Yangtze rainfall over eastern China and its related atmospheric circulation characteristics during the 1991 summer are examined based on the gauge-observed rainfall and the NCEP/NCAR reanalysis data. Wavelet analysis shows that during the 1991 summer, the active and break sequences of rainfall over the middle and lower Yangtze Basin are mainly regulated by an oscillatory mode with a period of 15–35 days. An investigation of the circulation features suggests that the 15–35-day oscillation is associated with an anomalous low-level cyclone (anticyclone) appearing alternatively over the northern South China Sea (SCS) and the Philippine Sea, and related to a northeastward (southwestward) shift of the western Pacific subtropical anticyclone over the SCS, leading to a lower tropospheric divergence (convergence) over the Yangtze Basin. In the upper troposphere, the 15–35-day oscillation exhibits a dipole anomaly characterized by an anomalous cyclone (anticyclone) over eastern China and an anomalous anticyclone (cyclone) over the northern Tibetan Plateau, resulting in a southwestward shrinking (northeastward extending) of the South Asian anticyclone, and forming a convergence (divergence) over eastern China. Such a coupled anomalous flow pattern between the lower and upper troposphere favors large-scale descending (ascending) motion, and hence reduced (enhanced) rainfall over the Yangtze Basin. Dynamically, the intraseasonal variations in the Yangtze rainfall are mainly determined by the coupling between the low-level relative vorticity and the upper-level divergence. In the middle troposphere, the 15–35-day oscillation of the subtropical high is originated over the central North Pacific north of Hawaii, then propagates westward to the SCS-Philippine Sea, and finally modulates the intraseasonal variations of the Yangtze rainfall.     

Large-scale Circulation Anomalies Associated with Interannual Variation in Monthly Rainfall over South China from May to August简

Interannual variation in summer rainfall over South China （SC） was investigated on the monthly timescale.It was found that monthly rainfall from May to August exhibits different features of variation,and the amounts are basically independent of each other.There is a significant negative correlation,however,between May and July SC rainfall,which is partially related to the developing phases of ENSO events.It was also found that stronger （weaker） lower-tropospheric winds over SC and the upstream parts are responsible for more （less） SC rainfall in every month from May to August.Despite this monthly consistent enhancement of horizontal winds,the wind anomalies exhibit distinct differences between May-June and July-August,due to the remarkable change in climatological winds between these two periods.More SC rainfall is associated with a lower-tropospheric anticyclonic anomaly over the SCS and the Philippine Sea in May and June,but with a cyclonic anomaly centered over SC in July and August.     

Moisture source for the Amazon Basin: a study of contrasting years

The regions where the divergence of vertically integrated water vapor flux, averaged over a season or a year, is positive (negative) are sources (sinks) of moisture for the atmosphere. An aerial river is defined as a stream of strong water vapor flux connecting a source and a sink. Moisture flux, its divergence, and sources and sinks over the tropics of South and Central America and the adjoining Atlantic Ocean are obtained for dry years and for wet years in the Amazon Basin. Results show that the Amazon Basin is a sink region for atmospheric moisture in all seasons and that there are two source regions for the moisture in the basin, one situated in the South Atlantic and the other in the North Atlantic, both located equator-ward of the respective subtropical high-pressure centers. The convergence of moisture increases over the Amazon Basin in austral summer, and at the same time it decreases in the Pacific and Atlantic ITCZs. Box model calculations reveal that the wet years, on the average, present about 55 % more moisture convergence than the dry years in the Amazon Basin. A reduction in the moisture inflow across the eastern and northern boundaries of the basin (at 45°W and at the Equator, respectively) and an increase in the outflow across the southern boundary (at 15°S) lead to dry conditions. The annual mean contribution of moisture convergence to the precipitation over the Amazon Basin is estimated to be 70 %. In the dry years, it lowers to around 50 %. The net convergence of water vapor flux over the basin is a good indicator of the wet or dry condition.     

Interdecadal variability and trends of rainfall across the Amazon basin

Summary An analysis of decadal and long-term patterns of rainfall has been carried out using a combination of raingauge and gridded rainfall datasets, for the entire Amazon basin and for its northern and southern sub-basins. The study covers the period 1929–98. Rainfall variability and variations in circulation and sea surface temperature fields have been analysed in more detail for the period 1950–98. Negative rainfall trends were identified for the entire Amazon basin, while at the regional level there is a negative trend in northern Amazonia and positive trend in southern Amazonia. Decadal time scale variations in rainfall have been discovered, with periods of relatively drier and wetter conditions, with different behaviour in northern and southern Amazonia. Spectral analyses show decadal time scale variations in southern Amazonia, while northern Amazonia exhibits both interannual and decadal scale variations. Shifts in the rainfall regime in both sections of the Amazon basin were identified as occurring in the mid-1940s and 1970s. After 1975–76, northern Amazonia received less rainfall than before 1975. Changes in the circulation and oceanic fields after 1975 suggest an important role of the warming of the tropical central and eastern Pacific on the decreasing rainfall in northern Amazonia, due to more frequent and intense El Niño events during the relatively dry period 1975–98.     

Inter-annual temperature and precipitation variations over the Litani Basin in response to atmospheric circulation patterns

This study examines the sensitivity of a mid-size basin’s temperature and precipitation response to different global and regional climate circulation patterns. The implication of the North Atlantic Oscillation (NAO), El Ni?o Southern Oscillation (ENSO), Indian Monsoon and ten other teleconnection patterns of the Northern Hemisphere are investigated. A methodology to generate a basin-scale, long-term monthly surface temperature and precipitation time series has been established using different statistical tests. The Litani River Basin is the focus of this study. It is located in Lebanon, east of the Mediterranean Basin, which is known to have diverse geophysical and environmental characteristics. It was selected to explore the influence of the diverse physical and topographical features on its hydroclimatological response to global and regional climate patterns. We also examine the opportunity of conducting related studies in areas with limited long-term measured climate and/or hydrological data. Litani's monthly precipitation and temperature data have been collected and statistically extrapolated using remotely sensed data products from satellites and as well as in situ gauges. Correlations between 13 different teleconnection indices and the basin’s precipitation and temperature series are investigated. The study shows that some of the annual and seasonal temperature and precipitation variance can be partially associated with many atmospheric circulation patterns. This would give the opportunity to relate the natural climate variability with the watershed’s hydroclimatology performance and thus differentiate it from other anthropogenic induced climate change outcomes.     

Predicting Indian monsoon rainfall: a neural network approach

The summer monsoon rainfall over India is predicted by using neural networks. These computational structures are used as a nonlinear method to correlate preseason predictors to rainfall data, and as an algorithm for reconstruction of the rainfall time-series intrinsic dynamics. A combined approach is developed which captures the information built into both the stochastic approach based on suitable predictors and the deterministic dynamical model of the time series. The hierarchical network so obtained has forecasting capabilities remarkably improved with respect to conventional methods.     

华东地区6-7月锋生的气候学特征及环流结构

利用中国华东地区212个站点2000-2010年6-7月逐日降水资料和NCEP/NACR再分析资料,运用运动学锋生函数公式,分析了华东地区6-7月锋生、锋面及其环流结构的气候学特征。结果表明,锋生函数值在华东区域呈现不均匀分布,且不同性质的运动学锋生具有不同的锋生强度和分布。其中,江淮地区是6-7月综合锋生最强的区域。根据风场在850 hPa强锋生带的切变及辐合情况,将6-7月的锋生类型分成4个大类,即暖切变型锋生、冷切变型锋生、西风辐合型锋生、东风辐合型锋生,其中,冷切变型锋生又分为两个亚类。不同类型的锋生个例数不同,江淮地区最多的是暖切变型锋生。不同锋面的水平结构与垂直结构存在显著差异,但对于强锋生过程,340 K假相当位温等值线与锋区平行且穿过锋区,其对判断强锋生过程和锋区位置具有指示意义。强锋生事件的出现有其大尺度环流背景,而不同类型的强锋生事件的环流背景差异较大:背景气旋或反气旋环流的中心位置、强度、辐散辐合场的分布、垂直环流结构等方面有不同程度的差异。降水与锋生强度紧密相关。锋生较强时,降水较多。暖切变型锋生日降水量最大,降水发生在锋区内部,与强锋生带走向一致;冷切变型次,两种类型的降水均发生在锋区的南侧,呈东北—西南走向;西风辐合再次之,降水发生在锋区内部偏南一侧。     

Summer circulation patterns related to the upper tropospheric vortices over the Tropical South Atlantic

Summary Daily 200-hPa relative vorticity data have been used to study the dominant patterns related to the cyclonic vortices over the South Atlantic Ocean in the vicinities of northeast Brazil, during the 1980–1989 period. Reference modes were obtained through empirical orthogonal function (EOF) analysis of the 200-hPa filtered vorticity anomalies over northeast Brazil, considering all the southern hemisphere (SH) summers within the study period. The amplitude time series of the first reference mode, separately for each SH summer, was correlated with the corresponding filtered vorticity anomalies in a larger area extending from 20°N to 40°S and between 120°W and 20°W. The correlation patterns feature a wave-like structure along eastern South America, with three main centers: the first one, over the South Atlantic off the northeast Brazil coast, is associated with the cyclonic vortices; the second one, over eastern Brazil, represents the corresponding anomalously amplified ridges; and the third one, over southern Brazil/Uruguay, is related to the equatorward incursions of midlatitude upper level troughs. This wave-like pattern is consistent with the vortex formation mechanism suggested in previous works. Another wave-like pattern southwest-northeast oriented is evident over the tropical southeastern Pacific, for some years. The internannual variability of these patterns is discussed in this paper.With 9 Figures     

Links between rainfall variability on intraseasonal and interannual scales over western Tanzania and regional circulation and SST patterns

Summary This study investigates the circulation anomalies associated with the intraseasonal evolution of wet and dry years over western Tanzania (29–37° E, 11.5–4.75° S) and how the onset and withdrawal of the rainy season as well as its wet spell characteristics are modified. It is found that for wet years, the rains begin earlier and end later, with strong wet spells occurring during the season, and there tend to be a greater number of moderate wet spells (although not necessarily more intense wet spells) than in dry years. In dry years, late onset and early cessation of the rainy season occur, often with an extended dry spell soon after the onset, and there tend to be a greater number of dry spells within the season. Large negative outgoing long wave radiation (OLR) anomaly values tend to be located between 20° and 40° E with anomalous westerly flow at 850 hPa occurring across the continent from 10° E to the tropical western Indian Ocean during wet spells in the anomalously wet seasons. Anomalously dry seasons are characterised by large positive OLR anomalies over 30–50° E as well as easterly anomalies at 850 hPa and westerly anomalies at 200 hPa. Eastward propagating intraseasonal anomalies are slower during the wet years implying that the convection remains over Tanzania longer. On the intraseasonal scale, Hovmoeller analyses of OLR and 850 and 200 hPa zonal wind indicate that convection over western Tanzania may be associated with a flux of moisture from the tropical southeast Atlantic and Congo basin followed by weak easterlies from the tropical western Indian Ocean.On interannual scales, wet (dry) years are characterized over the Indian Ocean by weaker (stronger) equatorial westerlies and weaker (stronger) trades that lead to less (more) export of equatorial moisture away from East Africa and increased (decreased) low-level moisture flux convergence over southern Tanzania, respectively. These anomalies arise from an anticyclonic (cyclonic) anomaly over the tropical western Indian Ocean during wet (dry) austral summers that may be related to cool (warm) SST anomalies there. Large scale modulation of the Indian Ocean Walker cell is also evident in both cases, but particularly for the dry years.Current affiliation: Tanzania Meteorological Agency, P.O. Box 3056, Dar es Salaam, Tanzania