基于拉格朗日方法的鲁南一次回流大暴雪的水汽来源分析

利用拉格朗日轨迹模式HYSPLIT,结合E-P诊断法,以及区域源汇归因法,研究了2015年鲁南一次回流大暴雪的水汽来源及输送路径。结果表明,影响暴雪过程的水汽路径有3条:一条是回流路径,沿中低空的回流冷空气经渤海、黄海输送至鲁南;另一条是南支路径,沿槽前西南气流经华南、华中向北输送至鲁南;第三条是偏西路径,沿平直的西风气流从黄土高原东侧输送至鲁南。源汇区定量分析显示,回流暴雪的水汽源地有6个,分别是渤海黄海区域、华东中北部区域、中南区域、南海区域、亚洲大陆南部和北部。对比不同源地的水汽贡献发现,中南区域与渤海黄海区域对回流暴雪的贡献最大,这与两者初期较高的源区水汽摄取量密切相关。华东中北部区域虽然初期水汽摄取较少,但由于其沿途水汽损耗较低并且在目标区域降水转化率较高,因此最终的水汽贡献不容忽视。尽管亚洲大陆南部和北部区域初期水汽吸收量明显高于华东中北部区域的,但过高的沿途水汽损耗,最终导致它们的实际水汽贡献低于华东中北部区域的贡献率。中国南海区域的水汽贡献最小,一方面是由较高的水汽损耗所致,另一方面还与初期较低的水汽吸收量有关。

Pressure drop of the film-enlarged tube bundles in air-water two-phase cross flow in evaporative air cooler

An experiment was carried out to investigate the relation of the maximum velocity of air passing through narrowest passage, mass flux of spray water in one square meter in one hour and the pressure drop of tube bundles. Twelve equations were obtained for the relation. The results show that the pressure drop of the tube bundles increases with increase of the maximum velocity of air and the mass flux of spray water. Comparing the pressure drop of the bare tube bundles with that of the film-enhanced tube bundles, it is found that the pressure drop of the film-enhanced tube bundles is lower about 11% and the surface roughness of the film-enhanced plates is a main factor that influences the pressure drop. The data and method obtained in the paper can be used to compute the pressure drop of the film-enhanced tube bundles and is helpful for selection of fan.

Responses of terrestrial water cycle components to afforestation within and around the Yellow River basin

Reforestation has attracted worldwide attention because of its multiple environmental benefits,but its impact on water resources is complicated and still controversial. In this study, the authors conducted numerical experiments within and around the Yellow River basin under the Grain-forGreen project using the Weather Research and Forecasting model. The results showed that the terrestrial water cycle process was sensitive to land use/cover change in the study region. Under the increase of mixed forests within and below the basin, the basin-averaged precipitation and evaporation increased by 223.17 and 223.88 mm respectively, but the surface runoff decreased by 2.22 mm from 2006 to 2010. In other words, the forest-induced increase in evaporation exceeded that of precipitation along with decreased surface runoff. Importantly, the afforestation effects on water resources seemed to enhance with time, and the effects of the same vegetation change were different in dry and wet years with different precipitation amounts(i.e. different atmospheric circulation background). It should be noted that it is difficult to obtain one product that can explicitly reflect the spatial distribution of actual land cover change promoted by the Grain-for-Green project in the Yellow River basin, which is an important obstacle to clearly identify the reforestation impacts. A land cover dataset derived from advantages of multiple sets of data therefore needs to be proposed.

THE VARIATION OF EVAPORATION OVER SOUTH CHINA AND ITS RELATIONSHIPS TO PRECIPITATION

The evaporation rate over South China is estimated based on the Climate Prediction Center Merged Analysis of Precipitation(CMAP)data and the NCEP/DOE reanalysis II data from 1979 to 2007. The temporal variation of evaporation over South China and its relationship to precipitation are discussed. Climatologically,the evaporation rate over South China is the largest in July and smallest in March.In spring and summer,the evaporation rate is approximately one half of the precipitation rate.However,the evaporation rate is approximately equal to the precipitation rate in fall and winter.The year-to-year variation of the evaporation rate over South China is quite in phase with that of the precipitation rate in the period from February to May but out of phase with that of the precipitation rate in early winter.Over South China there is a pronounced decreasing trend in the evaporation in colder seasons and a positive correlation between the evaporation variation and the rainfall variation in spring.In summer,the abnormality of rainfall over South China is closely related to the anomalous evaporation over the northeastern part of the South China Sea and its eastern vicinity.In winter,the rainfall variation in South China has a close linkage with the evaporation variation in a belt area covering the eastern Arabian Sea,the Bay of Bengal,the southeastern periphery of the Plateau,the southern part of South China Sea and the central part of Indonesia.

Comparisons of Several Evaporation/Precipitation Datasets for the Bohai Sea Based on Salinity Simulation

Evaporation （E） rate and precipitation （P） rate are two significant meteorological elements required in the ocean baro- clinic modeling as external forcings. However, there are some uncertainties in the currently used E/P rates datasets, especially in terms of the data quality. In this study, we collected E/P rates data from ERA-40, NCEP/NCAR Reanalysis, HOAPS for the Bohai Sea and nine routine stations around Laizhou Bay, and made comparisons among them. It was found that the differences in E/P rates between land and sea are remarkable, which was due to the difference in underlying surfaces. Therefore, the traditional way of using E/P rates acquired on land directly at sea is not correct. Since no final conclusion has been reached concerning the net water transport between the Bohai Sea and the Yellow Sea, it is unfeasible to judge the adequacy of the four kinds of data by using the water budget equation. However, the E/P rates at ERA-40 sea points were considered to he the optimal in terms of temporal/spatial coverage and resolution for the hindcast of salinity variation in the Bohai Sea. Besides, using the 3-D hydrodynamic model HAMSOM （HAMburg Shelf Ocean Model）, we performed numerical experiments with different E/P datasets and found that the E/P rates at sea points from ERA-40 dataset are better than those from NCEP/NCAR Reanalysis dataset. If NCEP/NCAR Reanalysis E/P rates are to be used, they need to be adjusted and tested prior to simulation so that more close-to-reality salinity values can be reproduced.