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1.
In the last decade pan evaporation measured at the Southern Dead Sea has significantly increased. Wind, temperature and humidity measurements at the Dead Sea starting in the 1930s as well as 3-D model simulations all seem to indicate a statistically significant change in the local climate of the Dead Sea region. The potential contribution to this climatic change through the weakening of the local land-sea breeze circulation caused by the reduction in the Dead Sea surface area in 1979–1981, is examined. It is suggested that since the breeze tempers the Dead Sea climate, its weakening has caused the air temperature to increase, the relative humidity to decrease and thus increased the pan evaporation. The climatic changes as implied by the MM4 Mesoscale PSU/NCAR model simulations, seem to fit the observed changes and to suggest a local tendency to the more arid climate that now prevails to the south of the study region. 相似文献
2.
An equation is derived for the components of the horizontal (turbulent) frictional force in the -coordinate system with special attention to mesometeorological flow models. The starting point is the horizontal equation of motion in its flux-form in the -system in which we replace (following Reynolds' procedure) the velocity components u,v and % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % aaaaa!37B8! \[ \dot \sigma \] aswell as other relevant quantities by terms of the form u = + u,..., = ± + % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % Gbauaaaaa!37C3! \[ \dot \sigma ' \] , etc. ( = time average of u; u = fluctuating part of u.) Next, the equation is averaged with respect to time and terms which we believe are small in mesometeorological flows, are neglected. On expressing by an appropriate expression that involves w, the result shows the appearance of two new terms which, have not been considered previously in the published literature. While the expression earlier used in the literature involved the -derivative of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG3bGbauaaaaaaaa!380B!\[\overline {u'w'} \] alone, the new terms add the -derivatives of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37EC!\[\overline {u'^2 } \] and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the x-component of the force, and the -derivatives of % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG2bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37ED!\[\overline {v'^2 } \]} and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the y-component, where and are the slopes of the -surfaces in the x- and y-directions, respectively. Further, a few numerical simulations of the sea-breeze over topography are carried out with and without the correction terms. It is shown that when corrections terms are not included the effective smoothing is stronger above the sloping regions and may amount to as high as 50 percent of the convergence with slopes of ~.04. The ìnclusìon of the new terms does not lead to any special computational difficulties and for that reason there is no compelling reason to neglect them, all the more so because, as is shown, the addition of the new terms results in a consistent apportioning of the degree of horizontal diffusion.On leave from CIMMS, Norman, OK.Now visiting Dept. of Met., Helsinki, Finland. 相似文献
3.
T. Ben-Gai A. Bitan A. Manes P. Alpert A. Israeli 《Theoretical and Applied Climatology》1998,61(3-4):207-215
Summary Recent studies imply that significant climatic changes over the central and southern coastal plain in Israel may be due to
changes in land usage, which have taken place since the National Water Carrier operation in the early 1960’s. Such changes
are reflected in the spatial distribution of the surface albedo pattern, obviously resulting in changes in the surface radiation
balance and, subsequently, modifying the surface heat fluxes and the stability conditions of the Planetary Boundary Layer
(PBL).
An Eppley PSP Pyranometer facing downward was mounted on a small Cessna aircraft and flown along the coastal plain from Tel
Aviv to the northern Negev south of Beer Sheva, at an altitude of approximately 500 feet, measuring surface reflection. The
incoming solar radiation was measured simultaneously, at several surface radiation stations of the Israel Meteorological Service,
along the flight path. The results show large differences in surface reflection distributions, between the cultivated areas
in southern Israel (as low as 0.15), and the adjacent arid regions (with values of up to 0.35). Historical albedo maps were
reconstructed according to land utilization maps of the 1930’s and the 1960’s. A comparison between recent albedo map and
the reconstructed maps, indicates temporal changes in the surface albedo pattern during the last decades.
Received January 15, 1998 Revised June 23, 1998 相似文献
4.
Estimation of rainfall fields using commercial microwave communication networks of variable density 总被引:1,自引:0,他引:1
The use of commercial microwave radio networks which are a part of cellular communication infrastructure for mapping of the near-the-ground rainfall is challenging for many reasons: the network geometry in space is irregular, the distribution of links by frequencies and polarizations is inhomogeneous, and measurements of rain-induced attenuation are distorted by quantization. A non-linear tomographic model over a variable density grid is formulated, and its applicability and performance limits are studied by means of a simulated experiment using a model of a real microwave network. It is shown that the proposed technique is capable to accurately measure integrated near-the-ground rainfall amounts over the area of 3200 km2 with a bias smaller than 10%. In urban area, where the density of microwave links is high, the average correlation in space between the simulated model and reconstructed rainfall fields reaches 0.89 over the variable density grid with average cell size of 5.7 km2 and 0.74 when interpolated into the rectangular grid with pixel size 0.775 × 0.775 km2, for the quantization interval of 0.1 dB. 相似文献
5.
Summary An investigation of the main features of large-scale synoptic patterns over Europe and the adjacent areas for extreme winter
periods during 1980–1995 over the Eastern Mediterranean (EM) is performed. The NASA reanalysis data set is used to investigate
composite sea level pressure (SLP), geopotential height of the 500 hPa surface (H-500) and precipitation–wet, normal and dry
patterns for each month during the period October–March. It is found that the wet and dry cool seasons in the EM are associated
with distinct SLP and H-500 anomaly patterns over Europe and the adjacent regions. During the dry spells large-scale positive
SLP/H-500 anomaly areas prevail over Eastern Europe. A negative SLP anomaly is normally found during these periods over southwestern
and Western Europe. During the wet cool seasons in the EM there are mainly negative SLP/H-500 anomaly areas over Eastern Europe
to the north east of the EM. Positive SLP/H-500 anomalies are found over Western Europe.
During wet months a trough zone between the Siberian and the Azorean Highs is positioned over the eastern part of the Mediterranean.
During dry months the Siberian anticyclone is more intensive and the zone with low surface pressure is displaced to the central
part of the northern Mediterranean.
Received May 26, 1999 Revised August 26, 1999 相似文献
6.
Numerical simulation of seasonal distribution of precipitation over the eastern Mediterranean with a RCM 总被引:1,自引:1,他引:0
Regional climate model (RCM) RegCM3 with 50 km horizontal resolution driven from the lateral boundaries by the data from NCEP/NCAR
re-analysis is used in a series of ten climate downscaling experiments over the eastern Mediterranean (EM) region. Results
of the experiments are characterized by seasonal precipitation patterns with notable offshore precipitation zones positioned
~50 km westward of a less intense precipitation zone over the coastal area. Atmospheric processes determining the distribution
of seasonal precipitation patterns in the EM are analyzed based on results of the RCM experiments performed. Level of success
of the model representation of the actual precipitation over the ECM appears to be depending on that of precipitation balance
over different parts of the domain. Excessive moisture convergence over a sub-area usually takes place at the expense of moisture
divergence from neighboring areas. Synoptic mechanism causing formation of the precipitation zone in the offshore zone appears
to be associated with the role of meridionally oriented atmospheric trough systems extending from Scandinavia or Siberia to
the EM during the period with rainy events. In such situations, air flows with strong northern components lead to intense
transport of cold air masses to the EM. Meeting of the cold air masses the warm and humid air over the sea surface in the
offshore zone causes formation of persistent squall lines and heavy rains there. Such processes may continue quite long as
long as the troughs are stationary. 相似文献
7.
A model was developed for pollutant dispersion from a point source simulating the Hadera (Israel) power plant stack. The model is based on the NCAR mesoscale meteorological MM4 model that provides the wind fields and coefficients of turbulent diffusion. The model was implemented using an implicit numerical scheme with changing directions. A comparison between the model calculations and an analytical solution for the advection-diffusion equation shows good agreement. Relatively low numerical diffusion of the adopted advection scheme was noted. Results for the hilly region of central Israel are presented for a summer case. 相似文献
8.
Summary A comprehensive study of long-term changes in October rainfall patterns in southern Israel, a semi-arid fringe zone between the Mediterranean coastal plain and the Negev Desert, was carried out. It was earlier postulated that the observed positive trend in October rainfall amounts may result from land-use changes in the area following the installation of the National Water Carrier (NWC) in the early 1960s. The purpose of the present study is to delineate the anticipated local effects, as well as their spatial extent, in order to investigate the possibility of climatic change over a larger synoptic scale.In the study region, a total number of 51 rainfall stations with long-term records up to 55 years, were analyzed, along with six control stations in other parts of the country. All stations were analyzed for trends in early seasonal rainfall, spatial variability during the two reference periods before and after the 60s, and for the ratio between rain per day (RPD) and number of rain days (NRD) during the two periods.The results of the analyses point to a well defined localized climatic change in October rainfall patterns within the study area, that is traceable to intensive and extensive land-use changes following the installation of the NWC.With 5 Figures 相似文献
9.
Summary Continental wind storms are common along the Mediterranean coast. Along the northern coast they are mostly cold, similar
to the Bora or the Mistral, and along the southern coast they are mostly warm, e.g., the Ghibli or the Shirocco. At the eastern
Mediterranean basin and the Levant region, these storms are intermittently warm and cold during the same season and often
even during the same event. Quasi-stationary systems, as well as moving disturbances, are the cause of such wind storms. Accordingly,
the resulting weather conditions may be extremely converse due to the characteristics of the advected airmass. Specific regions
in Israel, sensitive to easterly storms, are influenced by these wind storms for about 10% of the year (e.g., the westerly
slopes of the mountains and valleys with west-east orientation). The frequency, however, of widespread storms covering the
entire region is only approximately 1.4% of the entire year. These wind storms are therefore classified in the present study
according to their climatological and synoptic characteristics; indicating that the dominant synoptic situation is the Red-Sea
trough and the warm advections. These storms appear only from October-May and are most frequent during the cold season. The
diurnal course is characterized by a strengthening in the morning hours and a weakening at noon and in the afternoon hours,
due to the opposing effect of the westerly sea breeze, suppressing the easterly winds and the effect of katabatic winds. Nevertheless,
synoptic conditions may contribute to this tendency as well. Accordingly, a significant increase in the frequencies of easterly
storms, in relation to distance from the seashore has been identified. Although most of the stormy days are with westerly
winds, the easterly wind storms has vast environmental implications, creating damage especially to agriculture and occasionally
also to property and life; coastal flooding, potential air pollution, intensifying of forest fires and occasionally dust and
sand storms.
Received September 9, 1996 Revised March 6, 1997 相似文献
10.
T. Ben-Gai A. Bitan A. Manes P. Alpert S. Rubin 《Theoretical and Applied Climatology》1998,61(3-4):177-190
Summary Annual and monthly rainfall totals in Israel were analyzed to reveal any long term changes in their temporal and spatial
distribution patterns, since the 1930s. The data consists of 60 rainfall stations, spread all over Israel from the far North to the Negev desert in the South, with long-term records of rainfall
covering two normal periods. A gamma distribution function was fitted to the annual rainfall at each station for the two normal
periods, and the shape and scale parameters of the distribution, as well as their percentage changes during the last normal
period with respect to the first one, were analyzed.
The analysis of the annual distribution function parameters reveals some appreciable changes, that are statistically significant,
in the spatial rainfall distribution patterns in the southern, northern and central parts of the country. The most striking
feature is revealed in the South, where a more than 60 percent increase in the shape parameter occurs, and a similar rate
of re-scaling, i.e. a decrease of about 40 percent in the scale parameter. Analysis of the monthly distributions revealed
considerable changes in October and November, at the beginning of the rainfall season, and an appreciable change in March,
at the end of the rainfall season.
Received December 10, 1997 Revised June 24, 1998 相似文献