应用泊松耿贝尔分布估算海上极端风速

采用泊松耿贝尔分布,基于中国气象局发布的《CMA-STI热带气旋最佳路径数据集》资料来估算海上极端风速,并以上川岛气象站多年实测资料通过概率评估来加以验证。结果表明,采用泊松耿贝尔分布可以得到较为保守的海上极值风速取值。对于海上的小面积区域的重现期风速估算,采用50 km半径区域进行评估,可以得到较为合理的估算结果,当评估区域较大时,则需考虑适当扩大评估半径。     

Estimating Potential Evaporation over a Hill

A simple analytical model of the effect of a hill on potential evaporation (i.e., evaporation from well-watered vegetation) is presented. It is shown to reproduce the results from a two-dimensional non-linear numerical model. The analytical model is used to demonstrate the sensitivity of the changes in evaporation to surface resistance, aerodynamic resistance, temperature, slope and sun angle. Methods used by MORECS (Meteorological Office Regional Evaporation Calculation System) to estimate the potential evaporation at high elevations, and by Numerical Weather Prediction models to represent sub-grid scale hills, take account of the change in altitude but neglect the slope effects. A slope of 20 degrees, which is typical of upland terrain in the U.K., increases the potential evaporation by about 5%.     

Wave trains over the sea due to sea breezes

Meteorological observation by a helicopter was carried out to investigate the structure of sea breezes over the coastal area of Tosa Bay in Shikoku island, Japan. Several groups of wave trains were found over the sea during a flight made on 25 November 1992. Not only the terrain barrier but the remaining cold air pools formed in valleys hindered further advance of the sea breeze inland, so that the presence of such wave trains may appear to be due to the effect of the secondary flow which supplies moister and cooler air from behind the sea breeze front.     

Evaporation over the Arabian Sea during two contrasting monsoons

Summary Monthly mean surface fields of different meteorological parameters and evaporation are studied for the 1979 (poor monsoon) and 1983 (good monsoon) monsoon seasons over the Arabian Sea, in order to understand the role of evaporation on the Indian monsoon rainfall. It is noticed that in general, the sea surface temperatures are higher in 1983 throughout the monsoon season than in 1979 in the Arabian Sea excepting western region. The mean rates of evaporation on a seasonal scale are found to be equal in both years (3.66×10¹⁰ and 3.59×10¹⁰ tons/day in 1979 and 1983, respectively). No coherence is observed between the evaporation and the west coast rainfall within a season. It is also noted that the pressure distribution over the Arabian Sea is even important to advect the moisture towards the west coast of India, through winds.With 10 Figures     

Atmospheric lee waves in the Aegean Sea and their possible influence on the sea surface

Unusual satellite images of the Aegean Sea, in both the visible and infrared ranges, are discussed. Alternating bright and dark features downwind of islands suggest the presence of atmospheric lee waves. However, close examination of these features indicates that the observed signal is likely the signature of the influence of the lee waves on the sea surface rather than the signature of the lee waves themselves through atmospheric effects.     

Evaporation from coastal and open waters of the central zone of the red sea

Abstract

Monthly evaporation was estimated from the coastal and open waters in the central region of the Red Sea between latitudes 21 and 22°N. A recent equation based on the bulk aerodynamic method was used to calculate the evaporation using two sets of observations collected over the coastal and open waters. The annual evaporation from coastal water was 194 cm with a maximum in May and a minimum in October; from open water, it was 144 cm with a maximum and a minimum in November and September, respectively. The application of Sverdrup's (1937) equation was attempted, first when the roughness parameter z₀ in his equation was set equal to 0.6 cm as he proposed, and when z₀ was set equal to the most acceptable value of 0.01 cm. Our study shows that the evaporation values obtained in the first case are closer to those obtained either from the recent equation or from direct measurements than those obtained in the second case.     

Problems in large-scale modeling of sea ice cover evolution

Results of large-scale mathematical modeling of sea ice cover evolution are analyzed. Special attention is given to formalization of the thermal effect of the atmosphere on ice cover evolution. A model of sea ice cover evolution is developed in which thermal effects of the environment on ice cover and aggregation, fragmentation, and hummocking of ice are taken into account. The model adequacy is estimated by sample distribution of area and thickness of ice cover in the Sea of Japan.     

基于海气通量算法的海上蒸发波导诊断模型

蒸发波导是海上普遍存在的海洋天气现象, 也是导致海上电磁波异常传播的重要因素, 严重影响了海上雷达、通信及电子设备的有效应用。而TOGA COARE (海洋-大气耦合响应试验) 通量算法为蒸发波导的精确诊断提供了条件, 因此, 该文建立了基于海气通量算法的海上蒸发波导诊断模型, 并利用福建海域铁塔观测资料以及海上雷达探测试验数据与美国业务运转的Paulus-Jeske诊断模型对比, 结果表明:通量蒸发波导诊断模型的各项对比结果均优于Paulus-Jeske模型。     

Thermals over the sea and gull flight behavior

The flight performance of Herring Gulls relative to specific atmosphere and ocean conditions over the western North Atlantic indicates that large groups of gulls are able, through cooperative flight maneuvers, to induce ascending convective flow (thermals) in which they make extended soaring flights. These group flights in gull-induced thermals are limited to winds of 0 to ~ 1 m s^?1 and to sea-minus-air temperature differences (δT) of ~3 to 6?C. As wind speed increases from ~ 2 to 5 m s^?1, thermals are naturally induced, and the minimum δT required for soaring is inversely related to wind speed. At higher winds (~5 to 13 ms^?1), the minimum positive δT and minimum wind speed required for thermal soaring are directly related, thus indicating an apparent maximum efficiency for the natural production of thermals at wind speeds of about 5 m s^?1 and δT of 1 to 2 ?C.     

High-resolution sea wind hindcasts over the Mediterranean area

The goal of this study is to develop a high-resolution atmospheric hindcast over the Mediterranean area using the WRF-ARW model, focusing on offshore surface wind fields. In order to choose the most adequate model configuration, the study provides details on the calibration of the experimental saet-up through a sensitivity test considering the October–December 2001 period (the 2001 super-storm event in the West Mediterranean). A daily forecast outperforms the spectral technique of previous products and the boundary data from ERA-Interim reanalysis produces the most accurate estimates in terms of wind variability and hour-to-hour correspondence. According to the sensitivity test, two data sets of wind hindcast are produced: the SeaWind I (30-km horizontal resolution for a period of 60 years) and the SeaWind II (15-km horizontal resolution for 20 years). The validation of the resulting surface winds is undertaken considering two offshore observational datasets. On the one hand, hourly surface buoy stations are used to validate wind time series at specific locations; on the other hand, wind altimeter satellite observations are considered for spatial validation in the whole Mediterranean Sea. The results obtained from this validation process show a very good agreement with observations for the southern Europe region. Finally, SeaWind I and II are used to characterize offshore wind fields in the Mediterranean Sea. The statistical structure of sea surface wind is analyzed and the agreement with Weibull probability distribution is discussed. In addition, wind persistence and extreme wind speed (50 year return period) are characterized and relevant areas of wind power generation are described by estimating wind energy quantities.     

大尺度海气相互作用和长期天气预报

在五十年代初,我国气象工作者就注意到西北太平洋特别是黑潮海域,海表温度的冷暖和我国东部地区讯期的旱涝有密切的关系。六十年代开始,大尺度海气相互作用的研究在国外普遍受到重视。解放以后在党的领导下,通过广大台站预报员和专业科研人员的努力,我国长期天气预报有较大的进展,但是,预报准确率和和预报时效仍不能满     

Measurements of the turbulent heat flux over the sea

The turbulent heat flux was measured with two instruments simultaneously over the Baltic Sea by means of the eddy-correlation method. In one observational period, a small but noticeable divergence in heat flux was found, which may be explained by the advection of colder air. The parameterization of heat flux by the bulk method leads to a value for C _Hof 1 × 10^–3.     

Double-layer structure in the boundary layer over the baltic sea

Double-layered structures found over the Baltic Sea are investigated using radiosoundings and lidar measurements. Situations with double-layer structures are also simulated with the regional model REMO in a realistic manner. The double layer consists of two adjacent well-mixed layers, with a sharp inversion in between.Results from radiosoundings show that the double-layer structure over the Baltic Sea mainly occurs during the autumn with thermally unstable stratification near the surface. The structure is present in about 50 % of the radiosoundings performed during autumn. The presence of the double-layer structure cannot be related to any specific wind direction, wind speed or sea surface temperature.The lidar measurements give a more continuous picture of the time evolution of the double-layer structure, and show that the top of the lower layer is not a rigid lid for vertical transport. Two possible explanations of the double-layer structure are given, (i) the structure is caused by `advection' of land boundary-layer air over the convective marine boundary layer or, (ii) by development of Sc clouds in weak frontal zones connected to low pressure systems. Also the forming of Cu clouds is found to be important for the development of a double-layer structure.     

阳江地区54年来降雨量和蒸发量的变化特征

根据阳江（1953～2007年）、阳春（1961—2007年）气象观测站的降雨量和蒸发量资料,采用统计学方法分析其变化特征。发现阳江地区降雨量年际变化趋势一致,都存在大汛后数年内降雨量减少的现象。20世纪60年代以后,阳江地区蒸发量不断减少;到90年代中,达到蒸发量波谷,之后又出现上升趋势,且山区的上升趋势大于沿海地区,各季蒸发变化量与年蒸发量变化趋势相符。当年降雨量与蒸发量之差〈800mm时,阳江地区会出现大面积农作物受干旱影响的情况,每年的2月底-3月为阳江地区最缺水时期,应提前做好抗旱的准备工作。     

On the conversion of Pasquill categories for use over sea

Pasquill stability categories or similar classifications can be used to estimate dispersion of airborne material. Such categories are defined in terms of synoptic surface-layer variables. In order to transpose experience gained over land to sea, the different boundary conditions over land and sea must be considered. Using the assumption that the turbulence intensity and hence diffusion will be the same over land and sea if the boundary conditions expressed by sensible heat flux and shear stress are equal, a conversion is derived. With a reasonable degree of accuracy, synoptic parameters, mean wind speed and air sea temperature difference can be used at sea to specify stability categories.During the course of this research, it was found that Golder's relation between stability categories and Monin-Obukhov length can not be used at sea, since this relationship must depend on the Bowen ratio and albedo.