Estimation of probable maximum precipitation for catchments in eastern India by a generalized method

Summary A generalized method to estimate the probable maximum precipitation (PMP) has been developed for catchments in eastern India (80° E, 18° N) by pooling together all the major rainstorms that have occurred in this area. The areal raindepths of these storms are normalized for factors such as storm dew point temperature, distance of the storm from the coast, topographic effects and any intervening mountain barriers between the storm area and the moisture source. The normalized values are then applied, with appropriate adjustment factors in estimating PMP raindepths, to the Subarnarekha river catchment (upto the Chandil dam site) with an area of 5663 km². The PMP rainfall for 1, 2 and 3 days were found to be roughly 53 cm, 78 cm and 98 cm, respectively. It is expected that the application of the generalized method proposed here will give more reliable estimates of PMP for different duration rainfall events.With 5 Figures     

Daily rainfall trend in the Valencia Region of Spain

Summary ?We have analyzed daily rainfall trends throughout the second half of the 20^th century in the western Mediterranean basin (Valencia Region, E of Spain). The area is characterized by high torrentiality, and during the second half of the 20^th century some of the highest daily rainfall values in the Mediterranean basin have been recorded. In this area, mean annual rainfall varies between 500 and 300 mm and is overwhelmingly dependent on just a few days of rain. Daily maximum rainfall varies on average from 120 mm day⁻¹ to 50 mm day⁻¹, and represents a mean of 17% (coastland) to 9% (inland) of annual rainfall. The 10 days in each year with the heaviest rainfall (called “higher events”) provide over 50% of the annual rainfall and can reach more than 400 mm on average. We compared the annual rainfall trend and the trend of higher and minor events defined by percentiles, both in volume and variability. We, therefore, tested whether annual rainfall changes depend on the trend of the higher (rainfall) events. To overlap spatial distribution of trends (i.e.: positive, no significant and negative trends) we have used cross-tab analysis. The results confirm the hypothesis that annual rainfall changes depend on changes found in just a few rainy events. Furthermore, in spite of their negative trend, higher events have increased their contribution to annual rainfall. As a consequence, although torrential events may have diminished in magnitude, future scenarios seem to be controlled by a limited number of rainy events which will become more and more variable year on year. The high spatial density of data used in this work, (97 observatories per 24.000 km², overall mean 1 observatory per 200 km²), suggests to us that extreme caution should be applied when analyzing regional and sub-regional changes in rainfall using GCM output, especially in areas of high torrentiality. Received August 1, 2002; revised November 11, 2002; accepted December 1, 2002 Published online May 19, 2003     

Squall lines and rainfall over Western Africa during summer 1986 and 87

Summary Using digitized IR images from the European satellite Meteosat, 153 squall lines (SLs) were observed over Western Africa during July, August and September 1986 and 87. The SL mean rainfall volume was computed using the daily rainfall amounts of more than 800 raingauges: 15 km³ in 1986 and 22.5 km³ in 1987. A mean amount of 15 mm was collected per rainy episode at a given station, however, as only about half of the stations situated under a SL experienced a rainy episode, the rainfall amount averaged along the total SL’s swath was 6.8 mm. With the help of the 8 daily Meteosat slots the SL’s area daily variation could be estimated: namely a minimum around noon and a maximum around midnight. Using the SLs displacements (east–west) one had access to the daily variation of the rainfall volume, a minimum in the morning and a maximum toward the end of the afternoon, as already found by several authors who used Meteosat images.     

A Study on Typhoon-Induced Rainfalls over Beijing: Statistics and Case Analysis

Based on the Shanghai Typhoon Institute (STI) Typhoon Year Book and typhoon precipitation data, Japan Meteorological Agency satellite TBB data, and National Centers for Environmental Prediction (NCEP) reanalysis data, the climatic characteristics of rainfalls in Beijing associated with typhoons were analyzed for the period 1949–2006, and two typhoon cases with remarkable differences in rainfall intensity over Beijing were compared and diagnosed. The 58-yr statistical results show that rainfall events associated with typhoons occurred in Beijing about once every three years during June–September. These typhoons were mainly active in the region 20?–50?N, 109?–128?E and most of them moved northwestward while the others turned to the northeast. The typhoon rainfall over Beijing in general sustained for 2–5 days. Typhoon centers were usually located in the areas from Jiangxi to Anhui, the Yellow Sea, or near Beijing, when rainstorms occurred over Beijing. Case study indicates that the 2-day torrential rainfall event that happened in Beijing in 1984 was due to the interaction between Typhoon Freda (8407) and a westerly trough, while only a medium-strength rainfall event occurred in Beijing in 2005 in spite of the dominating cyclonic circulation of Typhoon Matsa (0509) directly over Beijing. It is found that both Freda and Matsa underwent extratropical transition and possessed an asymmetric structure. The rainfall difference was caused by the fact that Beijing was located in different convective development areas of the two typhoons. On the other hand, the lifting conditions were different although plentiful atmospheric moisture and convective unstable energy existed over Beijing during both events. The ascending motion of warm southerly in Beijing was stronger and deeper and a larger vertical wind shear was associated with Typhoon Freda. However, the lifting of water vapor was restrained by the descending motion of northerly cold airflow in Beijing under the impact of Typhoon Matsa. Besides, it is also found that topography played an important role in the typhoon rainfall over Beijing.     

Evaluating spatial scales of climate variability in sub-Saharan Africa

Summary Spatial scales of variability in seasonal rainfall over Africa are investigated by means of statistical and numerical techniques. In the statistical analysis spatial structure is studied using gridded 0.5° resolution monthly data in the period 1948–1998. The de-seasonalized time series are subjected to successive principal component (PC) analysis, allowing the number of modes to vary from 10 to 24, producing cells of varying dimension. Then the original rainfall data within each cell are cross-correlated (internal), then averaged and compared with the adjacent cells (external) for each PC solution. By considering the ratio of internal to external correlation, the spatial scales of rainfall variability are evaluated and an optimum solution is found whose cell dimensions are approximately 10⁶ km². The aspect of scale is further studied for southern Africa by consideration of numerical model ensemble simulations over the period 1985–1999 forced with observed sea surface temperatures (SSTs). The hindcast products are compared with observed January to March (JFM) rainfall, based on a station-satellite merged analysis of precipitation (CMAP) data at 2.5° resolution. Validations for different sized areas indicate that cumulative standardized errors are greatest at the scale of a single grid cell (10⁴ km²) and decrease 20–30% by averaging over successively larger areas (10⁶ km²).     

Monitoring of Mesoscale Precipitation Systems in the Alps and the Northern Alpine Foreland by Radar and Rain Gauges

Summary.  Mesoscale convective precipitation systems in the Alpine region are studied by analyzing radar and rain gauge data. The data from weather radars in Austria, France, Germany, and Switzerland are combined into a composite. Availability of radar data restricts the study mainly to the northern part of the Alpine region. Mesoscale convective systems (MCS) occur often in this region and are comparable to large systems observed in the USA. Seven precipitation events lasting one to six days from the years 1992–1996 are examined in detail. They all moved west to east and showed no diurnal preference in formation or dissipation. They reach sizes of 2 − 6 · 10⁴ km². MCS with leading-line trailing-stratiform structure tended to be larger and more intense. A 25-year set of rain gauge data indicates that a giant MCS (covering more than 4 · 10⁴ km² with more than 30 mm/day) occurs every 6 years in the northern Alpine region. MCS occur more frequently in the southern Alpine region. Received February 25, 1999/Revised June 29, 1999     

Monthly and daily precipitation trends in the Mediterranean (1950–2000)

Summary The aim of the paper lies in the identification of possible significant linear trends at monthly, seasonal and annual timescales in the Mediterranean during the second half of the 20th century. Monthly and daily records of 63 stations have been used to elaborate several precipitation indices: sum of daily precipitation (SDP) for rainfall >0.1 mm, >10 mm and >95^th percentile, of number of rainy days (RD) >0.1 mm and >10 mm and of mean daily precipitation (MDP) >0.1 mm and >10 mm. For each index the stations have been gathered together by Rotated Principal Component Analyses to determine 8 sub-areas which can be considered as identical for all the timescales at the spatial scale of the research. Trends have been estimated from the scores of each eigenvector retained in all RPCAs. They are mainly non existant or non significant decreasing, even if a few monthly trends appear to be significantly diminishing, primarily during winter months, March in the Atlantic region, October in the Mediterranean Spain, December in the Lions and Genoa Gulfs, January, winter and the year in Greece, winter and the year in Italy and winter in the Near East and increasing in April in the two gulfs. Correlation coefficients between SDP>0.1 mm and other indices have been computed: the significant trends seem mainly related to RD>10 mm, which represents a high percentage of the total rainfall amount. Greece is remarkable: SDP>0.1 mm and >10 mm decrease significantly during January, winter, the rainy season and the entire year whereas SDP>95^th percentile increases significantly, in accordance with the climatic change scenarios for the end of this century as does the decreasing of the total monthly and seasonal rainfall.     

Probable maximum precipitation for a 2-day duration over the Indian Peninsula

Summary For the purpose of providing information to hydrologists for designing costly and large hydraulic structures, estimates of probable maximum precipitation (PMP) for a 2-day duration for stations in the Indian Peninsula lying between 8° N to 20° N were calculated using the Hershfield statistical techniqe. Maximum annual 2-day rainfall data of 80 years from 1901 for 131 stations in the region were used. In order to obtain values of PMP, an enveloping frequency factor (k _m ) curve based on the actual rainfall data of stations in the region was developed. The enveloping curve was then utilised to estimate 2-day PMP values of all the 131 stations. Based on these PMP estimates, a generalised chart showing the spatial distribution of 2-day PMP was prepared. It was found that 2-day PMP estimates over the Indian peninsula varied from 40 to 95 cm and the average ratio of 2-day PMP to the highest observed 2-day rainfall was found to be 1.76.With 2 Figures     

中国台风降水的气候特征

对中国台风降水的时空分布特征进行研究,发现台风降水分布在中国中东部广大地区,台风降水量自东南沿海向西北内陆逐渐减少.台风降水最大值出现在台湾岛的中东部地区和海南岛的个别地区,年平均台风降水量大于700 mm,最小值出现在内蒙古、山西、陕西、四川的部分地区,年平均台风降水量不足10 mm.台风降水一般出现在4～12月,峰值出现在8月.1957～2004年期间台风降水呈下降趋势.台风降水的异常主要由于亚洲地区大气环流和赤道中东太平洋沃克环流的异常变化所引起.进一步分析发现,台风降水在中国大部分地区为减少趋势,且这种趋势在台湾岛、海南岛、东南沿海部分地区和东北南部较显著.台风暴雨是我国东南沿海及部分内陆地区的极端强降水事件之一,这些地区的暴雨和大暴雨很大程度上是台风带来的.     

北京地区的台风降水特征研究

采用上海台风研究所1949-2006年台风降水和台风年鉴资料、中国FY-2卫星和日本气象厅TBB资料以及NCEP再分析资料,首先分析58年台风影响北京降水的气候特征,然后对8407号台风Freda和0509号台风Matsa影响下北京两次强度差异显著的降水过程进行对比研究.结果表明:(1)台风影响北京降水年均0.33次,出现在6-9月.降水过程多为大雨以上天气过程,持续时间一般2 d,最长可达5 d.(2)影响台风的活动范围大致为(20°-50°N,109°-128°E).路径主要包括西北行和转向东北行两类,并以前者居多.北京发生暴雨时,台风中心主要出现在江西-安徽-带、黄海或北京附近.(3)Freda对北京的影响发生在台风与西风槽相互作用过程中,而Matsa的影响表现为台风低压环流直接控制北京.两个台风均受冷空气影响而变性,具有明显的非对称结构,两次过程中北京位于台风不同的对流运动发展区域是造成降水强度差异的原因之一.(4)两次台风过程中北京均具有较好的水汽条件和对流不稳定层结,但动力抬升条件差异明显.Freda影响下北京具有较强的水平风垂直切变,偏南暖湿气流上升运动深厚.而Matsa影响下北京盛行偏北气流,中低层下沉运动显著,水汽抬升受到抑制.另外,北京西北高东南低的地形也是其台风降水产生差异的原因之一.在台风东侧,地形作为偏南气流的迎风坡可加强上升运动,而在台风西侧则作为偏北气流的背风坡增强下沉运动.     

Design storm studies for the Upper Krishna river catchment upstream of the Almatti dam site

Summary The Almatti dam is the major engineering feature in the development of water resources in the Upper Krishna river forming a storage reservoir of 6425 million m³ at spillway crest level. In this paper, the design storm rainfalls for different return periods and also the Probable Maximum Precipitation (PMP) for the catchment above Almatti dam have been estimated to review the adequacy of the flood spillway design for the dam. The design storm rainfalls of various return periods have been computed from a statistical analysis of point and areal time series of annual maximum rainfall. In evaluating the PMP, the maximum observed rainfall obtained by Depth Duration method were maximized as the orography of the Western Ghats plays profound influence over the catchment. It was found that (area 35925 km²) the highest areal rainfalls over the catchment were 14.0 cm, 21.5 cm and 24.6 cm in 1, 2 and 3-day durations, respectively. These are scaled up by a factor of 1.23 to obtain the PMP rainfalls. The areal PMP estimates for the upper Krishna River (UKR) catchment above Almatti dam have been found to be 18.0 cm, 27.0 cm and 31.0 cm, respectively.With 6 Figures     

The 2001 Mesoscale Convective Systems over Iberia and the Balearic Islands

Summary This paper characterizes Mesoscale Convective Systems (MCSs) during 2001 over Iberia and the Balearic Islands and their meteorological settings. Enhanced infrared Meteosat imagery has been used to detect their occurrence over the Western Mediterranean region between June and December 2001 according to satellite-defined criteria based on the MCS physical characteristics. Twelve MCSs have been identified. The results show that the occurrence of 2001 MCSs is limited to the August–October period, with September being the most active period. They tend to develop during the late afternoon or early night, with preferred eastern Iberian coast locations and eastward migrations. A cloud shield area of 50.000 km² is rarely exceeded. When our results are compared with previous studies, it is possible to assert that though 2001 MCS activity was moderate, the convective season was substantially less prolonged than usual, with shorter MCS life cycles and higher average speeds. The average MCS precipitation rate was 3.3 mm·h⁻¹ but a wide range of values varying from scarce precipitation to intense events of 130 mm·24 h⁻¹ (6 September) were collected. The results suggest that, during 2001, MCS rainfall was the principal source of precipitation in the Mediterranean region during the convective season, but its impact varied according to the location. Synoptic analysis based on NCEP/NCAR reanalysis show that several common precursors could be identified over the Western Mediterranean Sea when the 2001 MCSs occurred: a low-level tongue of moist air and precipitable water (PW) exceeding 25 mm through the southern portion of the Western Mediterranean area, low-level zonal warm advection over 2 °C·24 h⁻¹ towards eastern Iberia, a modest 1000–850 hPa equivalent potential temperature (θ_e) difference over 20 °C located close to the eastern Iberian coast, a mid level trough (sometimes a cut-off low) over Northern Africa or Southern Spain and high levels geostrophic vorticity advection exceeding 12·10⁻¹⁰ s⁻² over eastern Iberia and Northern Africa. Finally, the results suggest that synoptic, orographic and a warm-air advection were the most relevant forcing mechanisms during 2001.     

Empirical Orthogonal Function Analysis of Daily Rainfall in the Upper Reaches of the Huai River Basin, China

Summary  The design and operation of hydro-structures for flood control and water conservation bring a need for improved characterization of precipitation patterns. A 73 000 km² study area in East Central China is situated in the East Asian monsoon region and experiences a strong seasonality in the rainfall regime. The characteristics of daily rainfall from 230 gauges during 1967–1986 were investigated for four periods in the summer monsoon season using empirical orthogonal function analysis (EOF) and extended empirical orthogonal function analysis (EEOF). The EOF analysis showed that for all four periods most of the variance was explained by an elongated spatial rainfall pattern. The pattern varied in direction, from roughly west-east to southwest-northeast, in the different periods. The zonally oriented patterns were interpreted as being caused by the stationary Mei-Yu front and the southwest-northeast patterns interpreted as cold fronts in cyclones that were developing over the study area. The latitude of the rain belt described by the first mode moved slightly northward with the advance of the East Asian monsoon from the first period, 9–22 June, to the third period, 23 July–5 August, and then withdrew southward again in accordance with the known seasonal movement of the Mei-Yu front. The EEOF analysis was used to show the development of the rainfall area over sequences of three days. During all four periods rainfall intensified on the second day, compared to the first and third days. During the first and last periods, 9–22 June and 5 August–30 September, respectively, there appeared to be little movement in the rainfall. During the second and third periods, the patterns were interpreted as a cold front in a developing cyclone. The results show the connection between the temporal variation in rainfall intensity and the temporal succession of spatial patterns over three day periods and should be used in the construction of design rainfalls for the study area. Received February 10, 1998 Revised June 23, 1998     

两次秋季北上台风引发东北地区暴雨的水汽特征

利用ERA5 0.25°×0.25°高分辨率再分析资料、实况融合降水资料、台风最佳路径数据集、HYSPLIT(Hybrid Single-Particle Lagrangian Integrated Trajectory model)后向轨迹追踪模型等资料,对2019年13号台风"玲玲"和2012年15号台风"布拉万"引发东北地区暴雨的水汽特征进行分析。研究表明:两次台风最大湿层厚度达200 hPa附近,700 hPa以下比湿大于10 g·kg^-1,高比湿主要集中在850 hPa以下的低层,台风的水汽分布具有明显的非对称结构特征。整层积分水汽通量散度与暴雨落区有一定的对应关系,尤其和降水强度对应。东北地区周边海域的水汽对东北暴雨的水汽供应很关键,源在日本群岛东部的西北太平洋的东南水汽通道是最重要的水汽通道。西南太平洋或阿拉伯海,包括欧拉方法研究发现的孟加拉湾较远距离的水汽输送存在,但是并非是东北台风暴雨的主要贡献者。     

利用多普勒雷达数据分析中国华东地区登陆台风轴对称降水特征

利用中国新一代多普勒雷达网温州雷达和台湾气象局五分山雷达资料、地面自动站降水资料,分析2004-2007年登陆中国华东地区的6个台风从登陆前18小时至登陆后6小时的降水结构时空变化特征.环状平均回波分析显示,在台风离陆地较远时,轴对称降水径向廓线呈双峰结构,最大降水位于台风眼墙处,降水次大值位于台风外围雨带处.台风强度越强,最大降水越强,且离台风中心的距离也越近.当台风接近登陆时,其内核区降水有增强的趋势,从登陆前6小时至登陆时,各台风内核区平均降水率的增强倍率在1.3-3.2,且外围降水随时间向台风中心收缩,内缩速率随台风强度增强而减慢.台风登陆后,台风眼被降水填塞,强度快速减弱,同时降水持续内缩,内核区总降水逐渐衰减.此外本文还建立了一个登陆前台风轴对称降水径向廓线模型,该模型能定量地描述降水廓线的双峰结构,模拟结果与实际雷达观测降水廓线的的均方根误差最小为0.46 mm/h,最大为5.3 mm/h.     

ECMWF极端降水预报指数在华东台风暴雨中的应用研究

台风强降水易引发极端天气事件,预报的难度和不确定性都很大。选取2013—2017年影响华东的13个台风个例,研究ECMWF集合预报降水极端天气预报指数(extreme forecast index,EFI)与台风暴雨的统计关系。研究结果表明:EFI降水指数对台风暴雨的预报具有一定的指示意义,对不同时效选取不同的EFI阈值可以作为暴雨落区预报的参考依据。总体来看:EFI增大,发生强降水的可能性增大;随着预报时效的增加,EFI阈值逐渐减小。以TS评分最大为标准,分别确立了不同时效、不同等级暴雨在华东区域的预报阈值。对于24、48、72、96 h时效的暴雨预报,EFI阈值分别取0.7/0.8、0.7、0.6、0.5可以获得较高的TS评分及合理的预报偏差,因此可将它们作为不同时效暴雨预报的参考阈值。EFI与降水的气候百分位有较好的相关关系,EFI值越大,降水气候百分位值也越大。当EFI值较大时,可参考相对应气候百分位的实况降水量来估测台风降水。极端天气预报指数对极端降水天气具有较好的识别能力,可提前3～5 d提供极端降水信息。     

Seasonal carbon dioxide balance and respiration of a high-arctic fen ecosystem in NE-Greenland

Summary  Turbulent fluxes of CO₂ were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment at Zackenberg (74°28′12″N, 20°34′23″W) in NE-Greenland. The measurements started on 1 June, when there was still a 1–2 m cover of dry snow, and ended 26 August at a time that corresponds to late autumn at this high-arctic site. During the 20-day period with snow cover, fluxes of CO₂ to the atmosphere were small, typically 0.005 mg CO₂ m⁻² s⁻¹ (0.41 g CO₂ m⁻² d⁻¹), wheres during the thawed period, the fluxes displayed a clear diurnal variation. During the snow-free period, before the onset of vegetation growth, fluxes of CO₂ to the atmosphere were typically 0.1 mg CO₂ m⁻² s⁻¹ in the afternoon, and daily sums reached values up to almost 9 g CO₂ m⁻² d⁻¹. After 4 July, downward fluxes of CO₂ increased, and on sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values of about −0.23 mg m⁻² s⁻¹ at midday and max values of daily sums of −12 g CO₂ m⁻² d⁻¹. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO₂ m⁻². Modelling the ecosystem respiration during the season corresponded well with eddy correlation and chamber measurements. On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO₂ balance the calender year 1997 was calculated to be a net-sink of 20 g CO₂ m⁻² yr⁻¹. Received October 6, 1999 Revised May 2, 2000     

Testing a GCM land surface scheme against catchment-scale runoff data

A GCM land surface scheme was used, in off-line mode, to simulate the runoff, latent and sensible heat fluxes for two distinct Australian catchments using observed atmospheric forcing. The tropical Jardine River catchment is 2500 km² and has an annual rainfall of 1700 mm y^–1 while the Canning River catchment is 540 km², has a Mediterranean climate (annual rainfall of 800 mm y^–1) and is ephemeral for half the year. It was found that the standard version of a land surface scheme developed for a GCM, and initialised as for incorporation into a GCM, simulated similar latent and sensible heat fluxes compared to a basin-scale hydrological model (MODHYDROLOG) which was calibrated for each catchment. However, the standard version of the land surface scheme grossly overestimated the observed peak runoff in the wet Jardine River catchment at the expense of runoff later in the season. Increasing the soil water storage permitted the land surface scheme to simulate observed runoff quite well, but led to a different simulation of latent and sensible heat compared to MODHYDROLOG. It is concluded that this 2-layer land surface scheme was unable to simulate both catchments realistically. The land surface scheme was then extended to a three-layer model. In terms of runoff, the resulting control simulations with soil depths chosen as for the GCM were better than the best simulations obtained with the two-layer model. The three-layer model simulated similar latent and sensible heat for both catchments compared to MODHYDROLOG. Unfortunately, for the ephemeral Canning River catchment, the land surface scheme was unable to time the observed runoff peak correctly. A tentative conclusion would be that this GCM land surface scheme may be able to simulate the present day state of some larger and wetter catchments but not catchments with peaky hydrographs and zero flows for part of the year. This conclusion requires examination with a range of GCM land surface schemes against a range of catchments. Received: 9 June 1995 / Accepted: 4 April 1996     

Mesoscale Convective System over the Yellow Sea – A Numerical Case Study

Summary  A mesoscale convective system (MCS) case that developed over the Yellow Sea (12–13 July 1993) is studied by using a 23-level, 30 km-mesh Penn State/NCAR mesoscale model MM5. This MCS was generated in northern China, south of the Changma front, in a convectively unstable environment, under the influence of a short-wave trough accompanied by a marked cold vortex aloft. The model with all model physics (refereed to as CNTL) captured the major features of this MCS. A mesoscale low-level jet (mLLJ), with a horizontal scale of a few hundred km, developed within the MCS. Available wind data support the realism of this mLLJ. This mLLJ not only transports convectively unstable air directly toward the MCS but is also responsible for a strong low-level convergence in the MCS. At 200 hPa, an anticyclonic northwesterly flow with a relatively high wind speed core on the east of MCS was simulated. This relatively high-speed flow can be regarded as a mesoscale upper level jet (mULJ), acted as an upper outflow over the MCS. Low-level convergence on the left-front of the mLLJ and upper divergence in the right-rear of the mULJ creates a strong upward motion (≅ 40 cm s⁻¹) in the MCS. Heavy precipitation up to 45 mm between 1800–2100 UTC was observed after this MCS landed on the southern Korean Peninsula. The CNTL run captured this heavy rainfall event. A maximum rainfall of 50 mm 3 h⁻¹ was simulated. In another experiment, with surface sensible and moisture fluxes withheld (NOSF), the 3-h simulated rainfall was decreased to 30 mm. Less latent heat released in the NOSF led to a weaker MCS and mLLJ. The concurrent surface fluxes sustained a high low-level moisture field over the Yellow Sea, which helped the development of the MCS and enhanced its precipitation in this case. Received January 8, 1999     

The LITFASS project of DWD and the LITFASS-98 experiment: The project strategy and the experimental setup

Summary ?The LITFASS project (‘Lindenberg Inhomogeneous Terrain – Fluxes between Atmosphere and Surface: a Long-term Study’) of the Deutscher Wetterdienst (DWD, German Meteorological Service) aims to develop and to test a strategy for the determination and parameterisation of the area-averaged turbulent fluxes of heat, momentum, and water vapour over a heterogeneous land surface. These fluxes will be representative for an area of about 10 * 10 km² (while the typical patch size is between 10⁻¹ to 10⁰ km²) corresponding to the size of a grid cell in the present operational numerical weather prediction model of the DWD. LITFASS consists of three components: – the development of a non-hydrostatic micro-α-scale model (the LITFASS local model – LLM) with a grid-size of about 100 * 100 m², – experimental investigations of land surface – atmosphere exchange processes and boundary layer structure within a 20 * 20 km² area around the Meteorological Observatory Lindenberg, – the assimilation of a data base as an interface between measurements and modelling activities. The overall project strategy was tested over a three-week period in June 1998 during the LITFASS-98 field experiment. This paper gives an overview on the LITFASS project, on the design and measurement program of the LITFASS-98 experiment, and on the weather conditions during the period of the experiment. Conclusions are formulated for the operational realisation of the LITFASS measurement concept and for future field experiments aimed at studying the land surface – atmosphere interaction in the Lindenberg area. Selected results from both experimental and modelling activities are presented in a series of companion papers completing this special issue of the journal. Received June 18, 2001; revised March 18, 2002; accepted April 2, 2002