Spatio-temporal variability in sea surface wind stress near and off the east coast of Korea

Sea surface wind stress variabilities near and off the east coast of Korea, are examined using 7 kinds of wind datasets from measurements at 2 coastal (land) stations and 2 ocean buoys,satellite scatterometer (QuikSCAT), and global reanalyzed products (ECMWF,NOGAPS,and NCEP/NCAR). Temporal variabilities are analyzed at 3 frequency bands; synoptic (2-20 d), intra-seasonal (20-90 d),and seasonal (>90 d).Synoptic and intra-seasonal     

The influence of mountainous relief on the vertical gradient of precipitation and pluvial zoning in the central slope of the Gulf of Mexico

Although variation of air temperature with respect to terrain altitude is widely understood, less is known about the altitudinal behaviour of precipitation. The eastern slope of Mexico is the most contrasting physiographic province of the country due to its relief. This area is also one of the most important regions of Mexico and of the intertropical region of America because of its biodiversity. Due to the vital and ecosystemic value of precipitation, this work seeks to analyse the altitudinal distribution of precipitation as a function of the relief. Our main methodology consisted of analysing the climatological normal of 86 weather stations to determine accumulated precipitation during rainy, dry and annual periods. Precipitation was correlated with the altitude of the relief, which allowed the study area to be divided into groups relative to the degree of accumulated rainfall throughout the year, as well as by the gradient of variation according to the elevation of the terrain. The results indicated that during the year, precipitation was favoured by the humidity of the Gulf of Mexico and decreased at a rate of -3.7 mm/m in coastal areas. Subsequently, precipitation increased with the altitude of the relief at a rate of 0.7 mm/m, between ~700 and ~ 1500 masl, which is where the greatest accumulation of rainfall was concentrated. Thereafter, it decreased by -0.9 mm/m until it reached the highest volcanic watershed. Crossing this watershed, the foehn effect caused rainfall rates to be much lower than on the windward slope, where the central plateau of the country begins.     

Airborne measurements of the impact of ground-based glaciogenic cloud seeding on orographic precipitation

Data from in situ probes and a vertically-pointing mm-wave Doppler radar aboard a research aircraft are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. A previous study (Geerts et al., 2010) has shown that radar reflectivity tends to be higher during seeding periods in a shallow layer above the ground downwind of ground-based silver iodide (AgI) nuclei generators. This finding is based on seven flights, conducted over a mountain in Wyoming (the Unites States), each with a no-seeding period followed by a seeding period. In order to assess this impact, geographically fixed flight tracks were flown over a target mountain, both upwind and downwind of the AgI generators. This paper examines data from the same flights for further evidence of the cloud seeding impact. Composite radar data show that the low-level reflectivity increase is best defined upwind of the mountain crest and downwind of the point where the cloud base intersects the terrain. The main argument that this increase can be attributed to AgI seeding is that it is confined to a shallow layer near the ground where the flow is turbulent. Yet during two flights when clouds were cumuliform and coherent updrafts to flight level were recorded by the radar, the seeding impact was evident in the flight-level updrafts (about 610 m above the mountain peak) as a significant increase in the ice crystal concentration in all size bins. The seeding effect appears short-lived as it is not apparent just downwind of the crest.     

PMP and PMF estimations in sparsely-gauged Andean basins and climate change projections

Abstract

Mixed-regime Andean basins present a complex scenario for flood analysis. In this study, we propose a methodology for incorporating orographic effects influenced by mountainous barriers in the Probable Maximum Precipitation (PMP) estimation method in sparsely-gauged basins. The proposed methodology is applied to the Puclaro Reservoir basin in Chile, which is affected by the Andes. The PMP estimations were calculated by applying statistical and hydrometeorological approaches to the baseline (1960–1999) and climate change scenarios (2045–2065) determined from projections of the ECHAM5 general circulation model. Temperature projections for the 2040–2065 period show that there would be a rise in the catchment contributing area that would lead to an increase in the average liquid precipitation over the basin. Temperature projections would also affect the maximization factors in the calculation of the PMP, as precipitable water content, raising it to 126.6% and 62.5% under scenarios A2 and B1, respectively; the probable maximum flood (PMF) would increase to +175.5% under the A2 scenario. These projections would affect the safety of dam design and would be generalizable to zones with similar mixed hydrology and climate change projections. We propose that the methodology presented could be also applied to basins with similar characteristics.

Editor Z.W. Kundzewicz; Associate editor A. Porporato     

祁连山云特征参数及人工增雨研究进展与展望

综述了祁连山区云特征参数及人工增雨方面的主要研究成果,内容涉及祁连山区空中水汽特征、云量分布、不同云系分布特征、云光学特征、云降水机制、降水分布、人工增雨有利天气系统、催化机制以及人工增雨综合效益,有助于全面、深入了解祁连山区云降水物理和人工增雨机制。进一步对祁连山区综合应用多种观测资料,结合云数值模式,深入研究地形云结构及降水机制、定量化的人工增雨作业科学指标、播云优化技术、地形与垂直气流相互作用对天气系统影响等方面存在的问题进行了展望。     

太行山东麓一次强对流降雹过程中的地形强迫

利用WRF模式对2011年5月26日发生在太行山东麓的一次强对流降雹过程进行数值模拟,探讨了太行山及周边地形在本次强对流过程的作用。结果表明,控制华北平原的偏东暖湿气流受太行山阻挡并与切变线东南侧的西南暖湿气流汇合,在太行山东侧形成水汽高值区。太行山东坡下垫面向上热通量明显高于华北平原,午后850hPa高度山坡与平原的假相当位温梯度达到0.2 K·km~(-1),850~600 hPa假相当位温垂直梯度达4 K·km~(-1),对应上坡风的垂直速度大于1 m·s~(-1),热力环流为太行山东麓对流的发生提供了动力条件。太行山东侧暖湿气层之上为偏西干冷气流,由此形成的强热力不稳定与水汽高值区、上坡风共同造成太行山东麓强对流过程的发生。局地小尺度地形抬升与重力波共同促使太原盆地有对流单体生成,该单体移经太行山西侧迎风坡受阻挡抬升而增强,越过山顶后与维持在太行山东侧的对流单体发生合并,从而导致对流云的强烈发展。     

台风“桑美”的数值模拟和地形敏感性试验

用WRF模式对0608号台风“桑美”进行了数值模拟研究,较为成功地模拟出了台风路径和降水,但模拟的台风中心气压远高于实况。为研究“桑美”登陆期间地形的抬升作用对其降水及结构的影响,通过改变特定区域内的地形高度设计了一组敏感性试验。结果表明,台风登陆过程中地形抬升作用对台风降雨量有显著的增幅作用;台风中心位势涡度、气流垂直上升速度、水平水汽通量散度明显增大;地形抬升机制在台风登陆时刻达到最强。     

Low-Level Westerly Winds,Topography, and Tropical Cyclogenesis of Arlene (2005): Observations and Model Simulations

The evolution process of the low-level westerly winds over the eastern North Pacific is investigated to understand the tropical cyclogenesis (TCG) of Tropical Storm Arlene (2005) over the Intra-Americas Sea (IAS). Also considered are the influences of the topography of the Central American mountain region interacting with the low-level westerly winds on Arlene's TCG by comparing results from a modified-topography simulation of Arlene's TCG with those from a simulation with the original topography in the Weather Research and Forecast (WRF) model. Interactions among large-scale circulations associated with subtropical highs in both hemispheres and an anticyclone over the warm eastern North Pacific produced low-level westerly winds into the IAS. WRF model experiments with a virtually elevated terrain filling in mountain passes in Central America resulted in the delayed and suppressed development of the incipient storm. The model experiments suggest that the low-level winds and moisture fluxes from the eastern North Pacific passing through the low-level mountain passes in Central America could play a critical role in the TCG process and perhaps also sustenance of storms over the western Caribbean.     

近10年中国地区地形对降水影响研究进展

地形是影响降水的重要因子,其复杂性为研究降水的分布、强度等增加了难度,全面透彻地理解地形对降水的影响机制,有助于预警预报水平的提高。因此,地形对降水的影响研究受到广大气象学者的关注。本文通过回顾近10年来中国地区有关地形对降水的影响研究进展,简要概述了地形动、热力效应与云微物理过程对降水的影响机制,以数值模拟研究为主线,系统分析了中国各个地区关于地形作用的研究成果,重点讨论地形对局地中小尺度降水、锋面降水以及台风降水方面的影响,最后总结了目前的研究现状并提出一些需要深入研究的问题。