Rainfall estimation using raingages and radar — A Bayesian approach: 1. Derivation of estimators

Procedures for estimating rainfall from radar and raingage observations are constructed in a Bayesian framework. Given that the number of raingage measurements is typically very small, mean and variance of gage rainfall are treated as uncertain parameters. Under the assumption that log gage rainfall and log radar rainfall are jointly multivariate normal, the estimation problem is equivalent to lognormal co-kriging with uncertain mean and variance of the gage rainfall field.The posterior distribution is obtained under the assumption that the prior for the mean and inverse of the variance of log gage rainfall is normal-gamma 2. Estimate and estimation variance do not have closed-form expressions, but can be easily evaluated by numerically integrating two single integrals. To reduce computational burden associated with evaluating sufficient statistics for the likelihood function, an approximate form of parameter updating is given. Also, as a further approximation, the parameters are updated using raingage measurements only, yielding closed-form expressions for estimate and estimation variance in the Gaussian domain.With a reduction in the number of radar rainfall data in constructing covariance matrices, computational requirements for the estimation procedures are not significantly greater than those for simple co-kriging. Given their generality, the estimation procedures constructed in this work are considered to be applicable in various estimation problems involving an undersampled main variable and a densely sampled auxiliary variable.     

降雨入渗补给地下水数值模拟研究

针对在地下水资源评价中入渗补给量采用经验估算存在较大误差的问题,以神东矿区为例,在广泛调查矿区包气带岩性结构并结合野外取样、室内参数测定的基础上,采用数值模拟的方法建立包气带水分运移数值模拟模型,定量模拟矿区内不同地段降雨入渗强度,探讨影响降雨入渗强度的主要因素,计算得出研究区降雨入渗系数大致在0.18~0.27,分析认为影响降雨入渗强度的因素有降雨量、潜水埋深、包气带岩性等。其中在研究区广泛分布的风积沙对地下水资源起到了一定的保护作用。     

2011年长江中下游旱涝急转及汛期暴雨的对流条件研究

利用ERA-Interim及雨量和土壤水分观测资料,对比诊断了2011年5—6月长江中下游梅汛前极旱期急转为梅汛期洪涝的极端天气事件的对流条件(水汽、不稳定、抬升作用)差异及特征,并研究条件性湿位涡垂直通量(CMF)指数与暴雨之间的定量关系。结果表明:在极旱期,干冷的东北气流控制,西太平洋副热带高压偏东,低层水汽通量弱且以偏北风输送为主,中低层为下沉气流,无低空急流,等θse线稀疏,边界层抬升机制缺乏,是干旱加剧的主要因子;在梅汛期,西南气流增强,西太平洋副热带高压西伸,低层气流在长江地区辐合,低层水汽通量增加且转为西南和东南风输送为主,伴随高低空急流耦合和深厚的上升运动,等θse线密集形成梅雨锋,增强不稳定暖湿空气强迫抬升和垂直输送,造成暴雨频发,引起区域性洪涝。暴雨中心600 hPa以下为负湿位涡的不稳定层,对流不稳定与条件性对称不稳定共同作用是强降水发生的不稳定机制。CMF指数与旱涝变化、暴雨过程演变非常一致,在极旱(梅汛)期,CMF指数低(高),变化平缓(剧烈),CMF指数在暴雨开始时逐步剧增,结束时迅速减小。     

暴雨和中尺度气象学问题

利用中国大陆2 400多站日降水资料（08-08时）和常规天气图资料,以1981-2010年30 a平均降水量为气候态,统计2018年4-10月我国主要暴雨天气过程,概述各主要暴雨过程的重要影响系统、出现时段、范围及累积降水量。结果表明：2018年4-10月我国共出现178个暴雨日、31次主要暴雨过程。2018年总共有10个台风登陆我国,较常年平均偏多2.8个。台风总体强度偏弱,登陆位置总体偏北,三个台风在上海登陆。本年度最大日降水量达351.3 mm,8月18日出现在河南商丘,系1818号台风\     

岩石破裂中的光声效应

在实验室条件下研究了花岗岩样品受单轴压缩破裂过程中的光和声发射效应,所得可见光谱轮廓与空气分子的光谱相似,但具有能量高于紫光的成份。除在主破裂时有大的光脉冲和声发射外,在主破裂前也记录到弱的光脉冲,它们与大的声发射率有同步现象。     

基于FLAC3D不同降雨速率下土洞致塌规律研究

针对桂林市临桂区岩溶塌陷易发区域,采用FLAC3D模拟不同降雨速率下的强降雨入渗过程,探究不同直径土洞在强降雨作用下的致塌规律,结果表明：（1）强降雨条件下,不同直径土洞最大位移均出现在洞顶部。降雨速率相同,洞顶竖向位移增长速率随土洞直径的增加呈整体加快的特点;加快降雨速率,竖向位移增长明显,竖向位移与土洞大小呈正相关。（2）相同降雨速率下,土洞直径增大会引起土洞底部剪切破坏区域进一步扩展。上覆土层在强降雨初期主要受到潜蚀作用,加快降雨速率,土洞底部水位剧烈波动对上覆土体产生的水击气爆成为主导作用,剪切破坏速率加快,洞趾剪切应变明显增加,当土洞直径达到3 m时,水位波动愈加剧烈,加速上覆土层破坏。（3）降雨速率的变化对土洞塑性区拓展范围具有不同程度的影响,较大直径的土洞在加快降雨速率时塑性区拓展范围明显扩大,即土洞大小、降雨速率对上覆土层稳定性具有较大的影响。研究结果为定量研究强降雨与上覆土层塌陷的关系提供了依据,对有效、合理地预警岩溶塌陷具有一定的意义。     

Causes of rockfalls in Al-Huwayshah area, Yemen

According to topography of Yemen, most areas and villages are located at obligated crest, toe of mountain and under cliffs. Therefore Al-Huwayshah consisting of Tawilah sandstone group is characterized by steep slope reach to 90° in some areas. This area is affected by strong tectonic movements and faults that occurred during the geological epochs. This effect enhances to find out fractures and joints as well as the rocks become brittle and ready to slide depending on the position of area. And there are some fractures and joints on the surface of the areas due to tectonic movement associated with opening the Red Sea and Gulf of Aden. The rainfalls, fractures, joints, earthquakes, gravity, vegetations, temperatures and human activities play a big role in the processes of rockfalls and landslides in this area. All those factors are considered as the basic causes and catalyzed factors for occurrence of rockfall in the studide area. In addition, the authors carried out laboratory test for many rock samples to get the physical properties of the rocks.     

西北区东部“1998年8月19~20日”暴雨诊断分析

１９９８年８月１９～２０日,在西太平洋副热带高压东退退北跳的背景下,受５００ｈＰａ青藏高原中尺度低涡和７００ｈＰａ东西向切变线影响,甘肃、平西两省南部出现区域性暴雨,物理量诊断分析结果表明,暴雨区７００～１００ｈＰａ是一致上升运动,最大中心在７００ｈＰａ,７００～３００ｈＰａ为正涡度,正Ｑ矢量涡度中心在５００ｈＰａ,Ｑ矢量散度自地面到２００ｈＰａ为副合上升区,中心在５００ｈＰａ,水汽通量散度的辐合区来自两个地方,主要部分位于青藏高原,其次是来自东侧８５０～７００ｈＰａ。     

Seasonal dynamics of light absorption by chromophoric dissolved organic matter (CDOM) in the NW Mediterranean Sea (BOUSSOLE site)

We analyze a two-year time-series of chromophoric dissolved organic matter (CDOM) light absorption measurements in the upper 400 m of the water column at the BOUSSOLE site in the NW Mediterranean Sea. The seasonal dynamics of the CDOM light absorption coefficients at 440 nm (a_cdom(440)) is essentially characterized by (i) subsurface maxima forming in spring and progressively reinforcing throughout summer, (ii) impoverishment in the surface layer throughout summer and (iii) vertical homogeneity in winter. Seasonal variations of the spectral dependence of CDOM absorption, as described by the exponential slope value (S_cdom), are characterized by highest values in summer and autumn at the surface and low values at the depths of a_cdom(440) subsurface maxima or just below them. Variations of a_cdom(440) are likely controlled by microbial digestion of phytoplankton cells, which leads to CDOM production, and by photochemical destruction (photobleaching), which leads to CDOM degradation. Photobleaching is also the main driver of S_cdom variations. Consistently with previous observations, a_cdom(440) for a given chlorophyll a concentration is higher than expected from Case I waters bio-optical models. The total non-water light absorption budget shows that surface waters at the BOUSSOLE site are largely dominated by CDOM during all seasons but the algal bloom in March and April. These results improve the knowledge of CDOM absorption dynamics in the Mediterranean Sea, which is scarcely documented. In addition, they open the way to improved algorithms for the retrieval of CDOM absorption from field or satellite radiometric measurements.