The role of dew as a moisture source for sand microbiotic crusts in the Negev Desert, Israel   总被引：2，自引：0，他引：2  

Giora J. Kidron  Ilana Herrnstadt  Eldad Barzilay 《Journal of Arid Environments》2002,52(4):517

Dew and fog were measured periodically during the years 1992–1995 at the Hallamish dune field, western Negev Desert (average annual rain precipitation ca. 95 mm). A major portion of the dunes are covered by cyanobacterial and moss-dominated microbiotic crusts. Chlorophyll- a measurements and microscopic examination were carried out in order to detect the possible changes in crust biomass and phenological changes of the mosses following the occurrence of dew and fog. Dew and/or fog were present in over 50% of the late summer and fall mornings with an average yield of 0·1 mm on cloth attached to glass plates. This corresponds to ca. 0·03 mm for the upper 0·5 cm of the crust, and is less than the 0·1 mm threshold which implies liquid water and which was also found necessary for net photosynthesis of the cyanobacterial crust. This threshold was met only during heavy dew or fog events, during which 10–40% of the crust surface area was moistened. It was estimated that dew and fog could account for upto 3·2–9·4% of the total annual time of crust wetness and consequently activity due to liquid water. Nevertheless, microscopic examination of the dominant moss species at Nizzana, Bryum dunense, disclosed phenological changes, mainly resulting in growth of vegetative reproduction organs (bulbils), and sexual organs, gametangia (antheridia and archegonia). B.dunense may thus be adapted to the utilization of dew and fog precipitation for the production of nearly mature sexual organs. The moss may thus be capable of already utilizing the first winter rains for fertilization and sporophyte formation.  相似文献   

1989年东海陆架水团及高密水环流的季节变化   总被引：3，自引：1，他引：3  

黄树生  潘玉球 《海洋学研究》1997,15(2):46-57

本文利用１９８９年的观测资料，分析了水团及高密水环流的季节演变特征。结果表明：东海高密水在陆架上存在一个季节性的变化过程，核心区有一个气旋型的密度环流；这个环流秋、冬季较弱，春、夏季较强；在该环流的产生过程中，它可以影响邻近水团的分布；在春季，邻近水团在东海高密水周围形成一个环状分布  相似文献   

关于海雾生成的探讨   总被引：3，自引：0，他引：3  

陈绍鑫  常美桂  曲维政  徐静琦  胡基福  赵松鹤  张正 《中国海洋大学学报(自然科学版)》1994,(3)

分析海上雷达波的超折射现象，指出：海雾的出现总是在雷达波发生超折射之后，由此确定海雾形成时的大气结构特征，并对海雾的生成以及其出现时间有了新的了解。指出根据雷达波超折射现象可用来作海雾预报。  相似文献   

New Development of Eastern Mediterranean Circulation based on Hydrological Observations and Current Measurements   总被引：2，自引：0，他引：2  

Beniamino B. Manca  Laura Ursella  Paolo Scarazzato 《Marine Ecology》2002,23(S1):237-257

Abstract. A number of recent studies based on hydrographic observations and modelling simulations have dealt with the major climatic shift that occurred in the deep circulation of the Eastern Mediterranean. This work presents hydrographic observations and current measurements conducted from 1997 to 1999, which reveal strong modifications in the dynamics of the upper, intermediate and deep layers, as well as an evolution of the thermohaline characteristics of the deep Aegean outflow since 1995. The reversal of the circulation in the upper layer of the north/central Ionian is worthy of note. The observations indicate a reduction of Atlantic Water in the northern Ionian with an increase on the eastern side of the basin. In the intermediate layer, the dispersal path of the Levantine Intermediate Water (LIW) is altered. Highly saline (>39.0) and well-oxygenated intermediate waters were found near the Western Cretan Arc Straits. They flow out from the Aegean, thus interrupting the traditional path of the LIW, and spread prevalently northwards into the Adriatic Sea. In the deep layer, dense waters, exiting from the Adriatic (σ_ø−29.18 kg · m⁻³), flow against the western continental margin in the Ionian Sea at a depth of between 1000–1500 m. Dense waters of Aegean origin (> 29.20 kg · m⁻³), discharged into the central region of the Eastern Mediterranean during the early stages of the transient, propagate prevalently to the east in the Levantine basin and to the west in the northern Ionian Sea. Near-bottom current measurements conducted in the Ionian Sea reveal unforeseen aspects of deep dynamics, suggesting a new configuration of the internal thermohaline conveyor belt of the Eastern Mediterranean.  相似文献   

Climatological Tools for Low Visibility Forecasting     

Otto Hyvärinen  Jukka Julkunen  Vesa Nietosvaara 《Pure and Applied Geophysics》2007,164(6-7):1383-1396

Forecasters need climatological forecasting tools because of limitations of numerical weather prediction models. In this article, using Finnish SYNOP observations and ERA-40 model reanalysis data, low visibility cases are studied using subjective and objective analysis techniques. For the objective analysis, we used an AutoClass clustering algorithm, concentrating on three Finnish airports, namely, the Rovaniemi in northern Finland, Kauhava in western Finland, and Maarianhamina in southwest Finland. These airports represent different climatological conditions. Results suggested that combining of subjective analysis with an objective analysis, e.g., clustering algorithms such as the AutoClass method, can be used to construct climatological guides for forecasters. Some higher level subjective “meta-clustering” was used to make the results physically more reasonable and easier to interpret by the forecasters.  相似文献   

华北平原一次大雾天气过程的数值模拟   总被引：3，自引：0，他引：3  

李江波  沈桐立  侯瑞钦  孔凡超  王山旗 《南京气象学院学报》2007,30(6):819-827

应用非静力平衡中尺度模式MM5V3,模拟分析了2005年11月19-21日发生在华北平原的一次大雾天气过程.结果表明,本次大雾是发生在相对稳定的大气环流背景下的辐射雾.模拟的天气形势与实况基本一致,模拟雾在范围、强度、生消时间等方面基本反映了实际大雾的生消变化规律.近地层逆温的维持和充沛的水汽条件对雾层长时间维持起着重要作用.诊断分析表明,大雾维持期间,雾区近地面层处在弱的水汽辐合区;900 hPa以上为辐散区和负涡度区,整层大气中下沉运动占主导,大规模的下沉辐散运动有利于中低层大气增温,与近地层的辐射降温相配合,有助于边界层内形成逆温;冷暖平流的作用也有助于逆温形成;地面和大气的长波辐射冷却,是最主要的降温因子;太阳短波辐射是导致大雾减轻及日变化的主要原因.  相似文献   

A THREE-DIMENSIONAL NUMERICAL STUDY ON DENSE FOG OVER MOUNTAINOUS AREAS     

史月琴  邓雪娇  胡志晋  吴兑 《热带气象学报(英文版)》2007,13(1):17-20

Using the non-hydrostatic meso-scale model MM5v3, dense fog that occurred from March 7 to March 8, 2001 over the Mts. Nanling area was studied. With integrated field experiments and observations, the occurrence, development and lift mechanism of fog were analyzed. The results indicate that before the coming of stratiform clouds, southerly warm and wet air ascended along mountainside and cooling condensation formed mountain fog. Then fog was formed by the stratiform on cloud-contacting mountaintop. A front inversion layer accelerated the development and extended the duration of the lower cloud and fog. The intensity, occurrence time, mass content and the variation of temperature and relative humidity of the fog agreed with those of the observation. It showed that the meso-scale model has the potential to forecast mountain fog.  相似文献   

AMDAR资料在天气预报中的应用   总被引：2，自引：0，他引：2  

黄卓  李延香  王慧  李伟华 《气象》2006,32(9):42-48

使用国内的AMDAR资料对几次重大天气过程进行了动力和热力学分析研究。结果表明：飞机在航站上起降时探测的高时空分辨率的AMDAR资料与其它资料结合能够较连续地监视机场附近气象要素的时空变化特征，进而捕捉到一些常规观测资料难于发现的引发冰雹等强对流天气的中尺度天气系统。该资料对稳定性天气大雾的定点分析和预报，较之常规观测资料有更好的业务使用价值。该资料不仅可为制作定点的临近和短时预报提供精细的预报依据，而且可在一定程度上增强对灾害性天气的认知和预见性。  相似文献   

基于MODIS多通道资料的白天雾监测   总被引：3，自引：1，他引：3  

邓军 白洁刘健文  王新炜石红艳 《气象科技》2006,34(2):188-193

根据云雾微物理性质的差别,用SBDART辐射传输模式模拟了MODIS通道1、6、20、31的云雾光谱辐射特性。模拟结果表明,这4个通道的辐射值中都包含有云雾的信息,能体现出云雾的微物理性质差异,可以用来区分中高云、雾和无云地表,从而实现白天雾的监测。在模拟分析的基础上提出一种白天雾监测的方案,并进行了实例分析。实例分析结果表明,这种多通道雾监测方法提高了白天卫星识别低云和大雾的能力。  相似文献   

温泉县一次持续性大雾天气成因分析     

王静娟  王美玉 《沙漠与绿洲气象(新疆气象)》2006,29(6):6-8

通过分析2005年初春新疆温泉县出现的一次较罕见的持续性大雾天气发现:由于气温迅速回升、冬季偏厚的积雪迅速融化,在特定的天气形势及本地特殊的地形地貌影响下,水汽长时间达到饱和是此次大雾天气持续存在的主要原因。  相似文献