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Objective calculated monthly cyclonic tracks in the Mediterranean are presented. The intermonthly variations within each season are shown to be quite significant and an particularly notable for December-January, April-May and June-July. We suggest that composite seasonal pictures are not faithful representations of the cyclonic routes over a complex terrain region like the Mediterranean.

A four-dimensional computer-analysis program for visualizing atmospheric fields on a personal computer is presented. The Program can display, on screen, a fast-time animation of meteorological fields on various surfaces or cross sections. An example is given of the application of the program for a potential vorticity analysis in a deep polar air-mass intrusion in the Mediterranean. This example has been chosen for demonstration from several other previously investigated case studies. These studies involve a variety of standard, as well as nonstandard fields and have been used for teaching in the synoptic meteorology laboratory course at Tel Aviv University, and also for basic research.

A high-resolution meso-γ scale indexing of the orographic precipitation over the Judean Mountains in Israel suggests a positive urban precipitation anomaly in Jerusalem. The urban rainfall enhancement for three case studies is found to be 20–30 per cent as compared to only about 10% for the annual normals. The role of the urban ‘heat island’ and the larger supply of artificial nuclei is discussed. The method presented here is a primary attempt to separate quantitatively urban recipitation effects over highly complex terrain, by applying a physical model.

[1] Moderate Resolution Imaging Spectroradiometer (MODIS) global monthly data from the Terra satellite (MOD08_M3, Collection 4, from March 2000 to May 2006) indicated, with the exception of the tropics, declining trends in aerosol optical thickness (AOD) over much of the globe, in contrast to slightly increasing trends in cloud optical thickness (COT) at many latitudes. In the tropics, increasing AOD trends coincide with increasing COT trends. In the latitudinal distribution of COT, in the Northern Hemisphere, a transition from increasing to declining tendencies was observed between 40°N and 60°N. There is a pronounced hemispheric asymmetry in latitudinal variations of the averaged total AOD, in contrast to those of the averaged total COT.

In this study, forecast errors in dust vertical distributions were analyzed. This was carried out by using quantitative comparisons between dust vertical profiles retrieved from lidar measurements over Rome, Italy, and those predicted by models. Three models were used: the four-particle-size Dust Regional Atmospheric Model (DREAM), the older one-particle-size version of the SKIRON model from the University of Athens (UOA), and the pre-2006 one-particle-size Tel Aviv University (TAU) model. SKIRON and DREAM are initialized on a daily basis using the dust concentration from the previous forecast cycle, while the TAU model initialization is based on the Total Ozone Mapping Spectrometer aerosol index (TOMS AI). The quantitative comparison shows that (1) the use of four-particle-size bins in the dust modeling instead of only one-size bin improves dust forecasts, (2) cloud presence could contribute to additional dust forecast errors in SKIRON and DREAM, (3) as far as the TAU model is concerned, its forecast errors were mainly caused by technical problems with TOMS measurements from the Earth Probe satellite. As a result, dust forecast errors in the TAU model could be significant even under cloudless conditions.

Publisher Summary The Mediterranean climate is under the influence of both tropical and mid-latitude climate dynamics, being directly affected by continental and maritime air masses with significant origin differences. The peak of the winter season occurs between December and February, when the mid-latitude cyclone belt has usually reached its southernmost position. However, spring and autumn also contribute to a significant amount of precipitation. Being located at the southern limit of the North Atlantic storm tracks; the Mediterranean region is particularly sensitive to interannual shifts in the trajectories of mid-latitude cyclones that can lead to the remarkable anomalies of precipitation and, to a lesser extent, of temperature. Storm-track variability impacts primarily the western Mediterranean, but it hasa signature clearly detected in the eastern Mediterranean as well. The complex orography that characterizes most regions surrounding the Mediterranean basin can modulate and even distort climate anomaly patterns that otherwise would be geographically much more homogenous. Lack of water in winter and spring reflects in the crop yield. However, too much water in winter is harmful by drowning the seeds and retarding root development. The variability of precipitation plays a crucial role in the management of regional agriculture, in environment, in water resources and ecosystems, as well as social development and behavior.

Publisher Summary The Mediterranean Region has many morphologic, geographical, historical, and societal characteristics, which make its climate scientifically interesting. The concept of Mediterranean climate is characterized by mild wet winters and warm to hot, dry summers and occur on the west side of continents between about 30° and 40° latitude. However, the presence of a relatively large mass of water is unique to the actual Mediterranean region. The Mediterranean Sea is a marginal and semi-enclosed sea; it is located on the western side of a large continental area and is surrounded by Europe to the North, Africa to the South, and Asia to the East. The chapter discusses that the climate of the Mediterranean region is to a large extent forced by planetary scale patterns. The time and space behavior of the regional features associated with such large-scale forcing is complex. Orography and land–sea distribution play an important role establishing the climate at basin scale and its teleconnections with global patterns. Different levels of services of readiness to emergencies, technological, and economic resources are likely to result in very different adaptation capabilities to environmental changes and new problems. The different economic situations and demographic trends are likely to produce contrasts and conflicts in a condition of limited available resources and environmental stress.

[1] It is shown that the daily course of the total amount of dust in the atmosphere, based on the TOMS aerosol index (AI), is highly correlated (0.98) with the integrated daily solar insolation over the Sahara region for spatially and temporally averaged data. Moreover, the annual maximum is even reached nearly at the same day, i.e., the 17th (18th) June for the surface (top of the atmosphere) solar insolation, as compared to 21st June for the date of maximum atmospheric dust loading. Other factors like cloudiness, rainfall soil moisture, and wind probably play a more dominant role in smaller areas. The fact that on a very large scale, like the whole of the Sahara, the solar insolation becomes the one single forcing directly correlated with the total amount of dust in the atmosphere is suggesting a simple climatic index for the total dust loading in the atmosphere. This index is shown for the Saharan region only, while more studies are needed for other regions. The 3–4 day time-lag between the maximum insolation and the maximum dust loading in the atmosphere is compared to about a one-month delay with the maximum ground or air temperatures and may serve as an estimate to the surface response to the major forcing of the Sun. The maximum ground temperature, delayed to the 17th July, can be explained by the delay in the lagged-heating of the deeper soil layers. The 3–4 day delay only with the Sun insolation is probably linked to the period in which the dust is maintained in the atmosphere until it is deposited. One application to the present finding may be for climate models, since such a high correlation for spatially and temporarily averaged data may be used as an integrated index for the total amount of Saharan dust and for potentially validating the complex model parameterizations in climate models.

Publisher Summary The Mediterranean climate is affected by several tropical and subtropical systems as illustrated by some evidence presented in this chapter. These factors range from the El Nino Southern Oscillation (ENSO) and tropical hurricanes to the South Asian Monsoon and Saharan dust. This leads to complex features in the Mediterranean climate variability. It reviews some tropical and subtropical teleconnections to the Mediterranean climate. It discusses the South Asian Monsoon (SAM), which is a key factor influencing the climate of the eastern and central Mediterranean. It causes high variability in sea level pressure (SLP) over Arabia and the Middle East with high pressures in winter and low pressures in summer. The adjustment to the SAM couples the falling pressure and land temperature over the Indian subcontinent/Asia Minor with rising pressure and temperature over the Persian Gulf and Iraq. Red Sea Trough intrusions into the Eastern Mediterranean and the Saharan dust are also discussed in the chapter.

[1] From the 1950s to the 1980s, a significant decrease of surface solar radiation has been observed at different locations throughout the world. Here we show that this phenomenon, widely termed global dimming, is dominated by the large urban sites. The global-scale analysis of year-to-year variations of solar radiation fluxes shows a decline of 0.41 W/m 2 /yr for highly populated sites compared to only 0.16 W/m 2 /yr for sparsely populated sites (

[1] Mineral dust particles loaded into the atmosphere from the Sahara desert represent one major factor affecting the Earth's radiative budget. Regular model-based forecasts of 3-D dust fields can be used in order to determine the dust radiative effect in climate models, in spite of the large gaps in observations of dust vertical profiles. In this study, dust forecasts by the Tel Aviv University (TAU) dust prediction system were compared to lidar observations to better evaluate the model's capabilities. The TAU dust model was initially developed at the University of Athens and later modified at Tel Aviv University. Dust forecasts are initialized with the aid of the Total Ozone Mapping Spectrometer aerosol index (TOMS AI) measurements. The lidar soundings employed were collected at the outskirts of Rome, Italy (41.84°N, 12.64°E) during the high–dust activity season from March to June of the years 2001, 2002, and 2003. The lidar vertical profiles collected in the presence of dust were used for obtaining statistically significant reference parameters of dust layers over Rome and for model versus lidar comparison. The Barnaba and Gobbi (2001) approach was used in the current study to derive height-resolved dust volumes from lidar measurements of backscatter. Close inspection of the juxtaposed vertical profiles, obtained from lidar and model data near Rome, indicates that the majority (67%) of the cases under investigation can be classified as good or acceptable forecasts of the dust vertical distribution. A more quantitative comparison shows that the model predictions are mainly accurate in the middle part of dust layers. This is supported by high correlation (0.85) between lidar and model data for forecast dust volumes greater than the threshold of 1 × 10−12 cm3/cm3. In general, however, the model tends to underestimate the lidar-derived dust volume profiles. The effect of clouds in the TOMS detection of AI is supposed to be the main factor responsible for this effect. Moreover, some model assumptions on dust sources and particle size and the accuracy of model-simulated meteorological parameters are also likely to affect the dust forecast quality.

[1] The mean synoptic situation associated with dust outbreaks from the Sahara into the central Mediterranean was examined on a daily basis for the month of July from 1979 to 1992. Composite patterns of wind, geopotential heights, and temperature for dusty days versus those for all days were analyzed. Dusty days were defined as days with the Total Ozone Mapping Spectrometer Aerosol Index (TOMS-AI) in the area around the Apennine peninsula (36°N–46°N, 10°E–18°E) equal to or greater than their monthly average plus 1 standard deviation. It was found that the strength and position of two essential features of the circulation patterns, such as the trough emanating southward from the Icelandic low and the eastern cell of the subtropical high, are the governing factors in making suitable flows for the Saharan dust transportation toward Italy. The deep, well-developed trough near the Atlantic coasts of Europe and Africa, penetrating well to the south, and the strong eastern cell of the subtropical high situated to the northeast from North Africa near the Mediterranean coast, cause strong south-southwestern flows with the potential to carry dust northward into the Mediterranean. In extreme cases the dust can reach Europe north of the Alps and even northern Europe, reaching the shores of the Baltic. These warm flows, accompanied by high dust load, also cause considerable warming in the central Mediterranean region of the order of 6–8 K at 700 hPa. Alternatively, the weak western trough and the weak eastern subtropical cell cause westerlies, which are inconsistent with the Mediterranean dust intrusions. Analysis of the extreme intrusion cases in July 1988, based on TOMS-AI data, and several others in July 2001–2003, based on lidar measurements in Rome, demonstrates the synoptic situation that allows the Saharan dust to reach Italy.

[1] Here we show the potential for dense fog monitoring using existing measurements from wireless communication systems. Communication networks widely deploy commercial microwave links across the terrain at ground level. Operating at frequencies of tens of gigahertz, they are affected by fog and are, practically, an existing, sensor network, spatially distributed worldwide, which can provide crucial information about fog concentration and visibility. The goal of this paper is to show the feasibility for fog identification and intensity estimation. A method is proposed and is demonstrated by two cases of heavy fog that took place in Israel. During these events, fog covered wide areas (tens of kilometers) and caused severe decrease in visibility, dropping as low as several tens of meters. Liquid water content and visibility values were estimated using measurements from tens of microwave links deployed in the observed area for each event. Each of the links provided a single measurement which was taken simultaneously across all of the links in the system. The values were found to be in the range of 0.5–0.8 gr/m3, high concentration values that match the maximum value range observed in field measurements carried out for prior studies in different test areas in the world. The visibility ranges calculated, between 30 and 70 m, fit the visibility assessments from the specialized measuring equipment operating in the observed area at the same time. These results point to the strong potential of the proposed technique.

well as the difference between them (intrusion minus no intrusion), in the area (60� W– 25� E, 0� –60� N), were analyzed. For both intrusion and no-intrusion days a closed high pressure, centered at approximately (45� W, 32� N), was found, with a ridge northeastward. EastoftheridgewasatroughlocatedtothewestoftheEuropeanandthenorthAfricancoast. Further east was a closed high in the western Sahara with a ridge northeastward. Each of the maps presenting the difference between the two aforementioned variables shows two highs: one over western Europe and the other, quite strong, west of the African coast on the 24� N–25� N latitudes. Between them, centered about (15� W, 37� N), there is a low-pressure area. As a result of the higher pressure at the African anticyclone in the intrusion cases, an easterly-northeasterly flow dominates at the latitudes 18� N–22� N, which presumably causes the dust intrusion from the continent into the Atlantic. Correlation between the Total Ozone Mapping Spectrometer aerosol index on the one hand and the wind magnitude and theuandvcomponentsontheotherhandwasalsoanalyzedfortheentiredataset.Correlation coefficients of r = 0.52, r = � 0.46, and r = � 0.27 were found. Analysis of two extreme intrusion and no-intrusion cases inJuly 1983 demonstrates the synoptic situation that allows the Saharan dust to reach England and NW Europe. INDEX TERMS: 0305 Atmospheric CompositionandStructure:Aerosolsandparticles(0345,4801);3309MeteorologyandAtmosphericDynamics: Climatology (1620); 3364 Meteorology and Atmospheric Dynamics: Synoptic-scale meteorology; KEYWORDS: Sahara, dust transport, dust intrusion

There is an on-going debate in Israel on the current political background of the water crisis with Lebanon whether the water shortage in recent years in this region has to do with global warming On the face of it the analyses of temperature as well as rainfall trends are not in agreement with global warming trends. It is the purpose of this Note to show that the observed changes can indeed be linked directly to global warming predictions.

[1] The inter-annual variation of the 850 hPa temperatures over the Eastern Mediterranean (EM) for July–August was analyzed for 1948–2002, using NCEP/NCAR reanalysis data. The time series of seasonal averages and the distribution of ‘hot’ and ‘cool’ days indicate the existence of three distinct warm periods. The warmest began in the mid-1990s. A long-term warming trend of 0.013 Ky−1 was found. The warming trend in July was 7 times greater than that of August, and July replaced August as the warmest month of the year. A trend of increasing extremity was also found. This was manifested in increasing seasonal standard deviation of daily temperatures, at a rate of 11% over 55 years, and in an increase in the frequency of both ‘hot’ and ‘cool’ days. These trends are also reflected in an increase in the seasonal maximum temperatures, which is 3 times greater than the increase in minimum temperatures.

The rising need to control industrial emissions over urban areas in Israel and to monitor the dispersion of pollutants (Graber, 1981) has stimulated extensive experimental and simulation studies in this field (Graber et al., 1984). The dependence of the dispersion of pollutants on mesoscale meteorological conditions was investigated with the aid of a recently developed model of air pollution transport over Israel (Tokar et al., 1993) and a mesometeorological model based on the PSU/NCAR mesoscale numerical model known as MM4 (Anthes et al., 1987). This model is suitable for forecasting flows with characteristic wavelengths of 10 to 2500 km under a variety of meteorological conditions. The models were implemented over a 324×270 km region with the Hadera power plant -the largest in Israel - at its center. Topography was included in the model. The MM4 model with 15 height levels and 6 km horizontal resolution was adapted to fit the Israeli conditions. The pollution transport model was applied for a smaller domain of 108×90 km with 2 km of horizontal grid spacing. The transport model uses the MM4 calculations as its input data.

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.

The effects of sea-breeze interactions with synoptic forcing on the PBL height over complex terrain are investigated through the use of a 3-D mesoscale numerical model. Two of the results are as follows. First, steep PBL height gradients — order of 1500 m over a grid interval of 10 km — are associated with the sea-breeze front and are enhanced by the topography. Second, a significant horizontal shift in the maximum PBL height relative to the mountains, is induced by a corresponding displacement of the thermal ridge due to the mountains, in the presence of large scale flow.

In this paper we analyze spatial variations of the annual rainfall that have taken place in the non-arid regions of Israel (annual rainfall>200 mm) during the years 1952–2006, incorporating all available data. The results of the present study over the research area as a whole indicate that no significant temporal change of the annual rainfall occurred in any region of the study area. However, focusing on spatial rainfall fluctuations between sub-regions in the study area, a significant increase was observed between the stations located downwind and those upwind of the Greater Tel Aviv region. This increase supports previous reports showing that rainfall enhancement is observed downwind (and close) to urban centers. In contrast to a few previous reports, no decrease in the ratio between the mountain precipitation to that over the coastal region was found. Over the period of the present study, the rainfall ratio between the upwind slopes and the seashore remained unchanged, with a slight increase in the central part of the country. The only hilly place where a slight decrease in annual rainfall was observed is the lee side (eastern slopes) of the Galilee Mountains. This result is important because the eastern slopes of the Galilee Mountains have for years been part of the target area for Israeli artificial cloud seeding for rain enhancement. The results therefore suggest that unless there was a pronounced change in the synoptic conditions during rain spells, seeding in Israel had no positive effect on rainfall amounts.

water cycle We use CMIP3 multi-model simulations to show how individual hydroclimatic changes will concur to determine even greater alterations of 21st century Mediterranean water cycle characteristics, with contrasting behavior over land and sea. By 2070-2099, the average of the models predicts a 20% decrease in land surface water availability and a 24% increase in the loss of fresh water over the Mediterranean Sea due to precipitation reduction and warming-enhanced evaporation, with a remarkably high consensus among analyzed models. The projected decrease in river runoff from the surrounding land will further exacerbate the increase in Mediterranean Sea fresh water deficit. 20th century simulations indicate that the 'transition' toward drier conditions has already started to occur and has accelerated around the turn of the century towards the larger rates projected for the 21st century. These tendencies are supported by observational evidence of century-long negative trends in regionally averaged precipitation, PDSI and discharge from numerous rivers; and are consistent with reported increases in Mediterranean sea water salinity.

The asymmetry in calculating the Coriolis terms by Marchuk's splitting method is discussed. It was found that although some asymmetry is required for linear stability, this asymmetry should be kept to a minimum. Otherwise, for instance, if the diffusion terms are calculated in between the Coriolis terms in the u and v equations of motion, one gets cross-isobaric low-level winds, which are different depending on the geostrophic wind direction. This is the first study to show that the required asymmetry in the splitting can cause a considerable error in the boundary-layer winds of atmospheric models if not handled in a specific way.

46(2008)Published online in J-STAGE (www.jstage.jst.go.jp/browse/HRL). DOI: 10.3178/HRL.2.46Ben-Zvi and Givati (2008 hereafter BZG) raised twopoints on model’s ability to reproduce current climato-logy and hydrology used in Kitoh et al. (2008 hereafterKYA): one is reproducibility of present-day precipita-tion amounts and its spatial distribution in the model,and the other is the streamflow that is highly affectedby human intervention in reality.Ability to reproduce current climate by global nu-merical models is steadily increasing in the past decade(IPCC 2007; Reichler and Kim 2008). BZG pointed outthat the area with simulated annual precipitation >1000 mm in KYA is much larger than the area observedand the area with simulated annual precipitation < 200mm is substantially larger than the area observed. Inthe previous global models, such as those that hadprovided climate projections in IPCC AR4 (Reichler andKim 2008), regional geographical details have not beenresolved due to their coarse resolution. Our 20-km meshglobal model, however, has for the first time the suffi-cient resolution to resolve orographic rainfall well.Exact contour lines of the model simulation in KYA donot fully match with the observations, but desertclimate where annual precipitation < 200 mm is ratherwell reproduced in the Middle East. This is in contrastto the other aforementioned climate projections withcoarser resolution.Another aspect is that, while the model resultscontain uncertainties, the observed climatology datasetused in KYA to validate the model is also subject to un-certainties. In general, rain-gauge observation is morereliable than that of satellite-derived precipitation esti-mates over the land. Hence, we used a gauge-based pre-cipitation climatology dataset, which was developedwith many more rain-gauge observations over this area(Turkey, Israel and Iran), and have compared to othermonthly precipitation products and satellite-based pre-cipitation data. See Yatagai et al. (2008) for details.However, the quality of rain-gauge-based precipitationdataset depends on the density and distribution of rain-gauge network. For example, the rain-gauge network isvery sparse over a part of the Fertile Crescent area, par-ticularly over the high mountains and vast unpopulateddesert areas. These limitations certainly caused uncer-tainties in this precipitation dataset, and then hadcreated a part of the differences between the modeledand observed precipitation presented in KYA.Second point is that in our model simulation we donot account for any human intervention such as reser-voir and groundwater use. In order to project actualstreamflow at each of the targeted basins, we need toknow about future change in anthropogenic water use,but this was not sought in KYA for the reasons statedbelow. There are some attempts in the modeling com-munity to incorporate anthropogenic water usage, suchas a reservoir operation scheme, in climate models to re-produce present streamflow. By doing that, currentstreamflow reproducibility should become better. Forthis purpose, however, scenarios for how this anthropo-genic water usage will change in the future are needed,which contains further uncertainties of societal nature.Therefore, in order to avoid further complexity, wefocused on the future change in natural climate systemand its effect on regional streamflow. The difference inthe simulated streamflow between the present-day andthe future climate can be interpreted as a first approxi-mation of the streamflow change caused by the globalwarming.In spite of all the shortcomings mentioned, our pro-jections are the first ever of naturally-driven streamflowchanges in the region, which may suffer a lot fromglobal warming as suggested by most (nearly all) ofrecent IPCC (2007) AR4 models. At the same time, this isan extremely sensitive area to lack of water. Some of thestruggles or even wars in the region had to do withproblems related to water. Hence, it is tremendously im-portant to start a serious scientific dialogue on globalwarming impacts on water in this region and we hopeour Letter served in this positive direction.

The global spread of wireless networks brings a great opportunity for their use in environmental studies. Weather, atmospheric conditions, and constituents cause propagation impairments on radio links. As such, while providing communication facilities, existing wireless communication systems can be used as a widely distributed, high-resolution atmospheric observation network, operating in real time with minimum supervision and without additional cost. Here we demonstrate how measurements of the received signal level, which are made in a cellular network, provide reliable measurements for surface rainfall. We compare the estimated rainfall intensity with radar and rain gauge measurements.

V VH V, = -2 (tan # + cot $1, r where VH is the horizontal divergence, V = (ug, ve) the geostrophic wind vector, r the distance from the earth’s centre and @ the latitude. Although the two terms on the right-hand side of (1) appear as a result of the earth’s sphericity, it is suggested from what follows that the tan@ term is superfluous and should be omitted. The horizontal wind divergence on a spherical surface was given by Pedlosky (1979) as I 1 a r c o s @ { i i a@ V H v = + -(v cos @)

[1] Presented herein is an analysis of an exceptionally intensive central and eastern Mediterranean dust intrusion of 15–16 March, 1998. The intrusion has been associated with development of an intense cyclone over Africa. The weather and dust development processes were simulated with the Eta weather and dust prediction model. Also presented is a comparison of the model results with the Total Ozone Mass Spectrometer Aerosol Index (TOMS AI) pictures as well as with those of the surface and weather observations. The roles of the main processes responsible for the dust plume development and associated dust intrusion to the eastern Mediterranean (EM) are studied. The observation data as well as the model-simulated parameters are jointly analyzed. The analysis also includes the data from the back-trajectory computations. With the aid of the model-produced dust profiles we studied the significant variation in the altitudes of the dust layers within the cyclone sectors. In the warm sector of the cyclone located over the Mediterranean Sea the dust layer extended up to 8–10 km. Relatively low dust concentration values were found here. In the area of the cold front over Africa the dust was restricted to the lower troposphere and the planetary boundary layer. Here the model simulated high values of the dust concentrations. The sharp TOMS AI increase over Israel and the eastern Mediterranean up to 5.0 units, further away from the dust sources, is explained by the strong winds, by the increased cyclone convergence, and the formation of a two-layer dust plume.

[1] Forward trajectories of the air masses from the Arabian Sea area were computed for each day from February 1 to April 10, 1999. This allowed the determination of the episodes characterized by the air mass transport to Africa and the Mediterranean region. Numerical simulation of one of such episodes, also characterized by intense cyclone and dust plume development, was performed using the Eta weather and dust predicting system. The simulation allowed an evaluation of the vertical distribution of the pollutants in the cyclone. Backward trajectories, ending in the area of the cyclone development point to the origin of a part of its air masses over the Arabian Sea. Potential role of the eastern Mediterranean weather systems in the transport to Europe of the polluted air masses from the INDOEX area is discussed.

The physical mechanisms of a shallow short-lived meso-b scale cyclone over the Gulf ofAntalya, eastern Mediterranean, are studied, with the PSU/NCAR MM4 and MM5 mesoscalemodels. Although the thin stratus clouds within this cyclone as observed from satellitesare not resolved even by the 3 km nesting, the dynamical evolution and the 3-D structureare well captured. The small cyclone or eddy develops before sunrise following convergenceof the strong katabatic winds from the nearby steep Anatolya mountains slopes with 2 kmpeaks. The eddy’s lifetime is of the order of 5–7 h and it quickly dissipates before noon.Based on the simulated vertical winds, vorticity, humidity as well as the IR top cloudtemperatures, the depth of the eddy is estimated to be 500–800 m. It is shown that thedivergence term in the vorticity equation is dominant during the eddy’s generation.Lagrangian analysis for the trajectories of several air-masses that were identified as crucialfor the eddy’s development, reveals a sharp increase both in the PV (by 7–8 units), and inthe specific humidity, 3.5 to 7 g/kg, as the air-parcels descend from about 840 to 980 hPa.This air-parcel analysis also shows that the diabatic contribution is quite important. Factorseparation experiments confirm that pure topography is the major factor and the synergisticeffect of sea-fluxes and topography contributes about 20% of the total vorticity. The Antalyacyclone is common during July to September morning hours and its frequency of occurrencewas estimated from satellite pictures to be about 20%. DOI: 10.1034/j.1600-0870.1999.t01-2-00006.x

A thoroughly objective method for the definition, selection and tracing of Mediterranean region cyclones is presented. The method is applied to the ECMWF 1982-1987 analyzed datasets to show monthly cyclone frequencies, cyclonic tracks and vertical variation of average relative vorticity. Day-to-night changes and vertical variation of cyclonic frequencies/vorticities indicate the importance of the sea thermal effect in the eastern Mediterranean. In the western Mediterranean and to a lesser extent in the Cyprus region, the lee cyclogenetic effect is very pronounced. Monthly cyclone tracks are presented and they clearly indicate the preferred routes of cyclonic movements. DOI: 10.1034/j.1600-0870.1990.00007.x

A one-level sigma-coordinate model originally developed by Danard and modified by Mass and Dempsey and Alpert et al., is applied to the study of surface flow over an averaged summer diurnal cycle in Israel. The detailed flow features are compared to three-dimensional modeling studies and to dense surface wind observations. The winds al a height of 10 m from the one-level model were found comparable to those obtained by three-dimensional simulations, and in some cases the one-level model predicted observed surface flow features that were not simulated by the three-dimensional simulations, probably because of the finer horizontal grid resolution in the one-level model. The two models had similar deficiencies in diagnosing observed flow features in many cases. A severe drawback of the one-level model is the inability to advance the sea-breeze front (SBF) over a ridge crest correctly. Based upon an earlier vertical cross-sectional study by Alpert et al., an explanation for this discrepancy is suggest...

An equation is derived for the components of the horizontal (turbulent) frictional force in the Σ-coordinate system with special attention to mesometeorological flow models. The starting point is the horizontal equation of motion in its “flux-form” in the Σ-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 = ū + u′,..., Σ = ±Σ + % MathType!MTEF!2!1!+- % feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbai % Gbauaaaaa!37C3! \[ \dot \sigma ' \] ′, etc. (ū = 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 Σ′ 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 Σ-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 Σ-derivatives of ρα % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37EC!\[\overline {u'^2 } \] and ρβ % 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 Σ-derivatives of ϱβ % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG2bGbauaadaahaaWcbeqaaiaaikdaaaaaaaaa!37ED!\[\overline {v'^2 } \]} and ϱα % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaace% WG1bGbauaaceWG2bGbauaaaaaaaa!380A!\[\overline {u'v'} \] for the y-component, where α and β are the slopes of the Σ-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 inclusion 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.

A deep polar air-mass penetration to the eastern Mediterranean in November 1982 is described. The unusual weather and, in particular, the rain pattern is discussed. This event contributes to heavy rain in the inland stations, of particular importance in the semiarid zone. The stability characteristics of the polar air mall on its way to the eastern Mediterranean are investigated and compared to a similar case in the western Mediterranean. It is suggested that the land-sea distribution along the path of the penetrating polar air mass is responsible for the significant differences that were found.

Following the theory of Kusuda and Alpert (Part I), expressions for the eccentricity and tilt angle of the surface-wind hodograph at different latitudes are derived as functions of the amplitude and phase shift of the horizontal thermal force and also of some reasonable frictional parameter. Further, analyses of 47 hodographs in Washington, Oregon and California give the observed tilt angles, eccentricities and senses of rotation. The tilt angle is nearly linearly dependent on latitude. Eccentricities are in general high (0.9–1) and higher friction leads usually to higher eccentricity. However, eccentricity may sometimes be very small giving a circular hodograph) even with high friction and also very high with low friction; the latter case is primarily due to a phase shift between the horizontal thermal forces. It is shown that although in general the frequency of ACR (anticlockwise rotation) hodographs decrease northward in the Northern Hemisphere, lower friction may lead to a minimum in ACR fre...

The diurnal and interdiural wind variabilities are defined in terms of the “relative gustiness” −σν/V. The proportion α between the diurnal and the interdiurnal variabilities thus defined is suggested as a useful index in mesoscale studies. The α index is calculated in more than 30 stations in the Israel area during summer and winter, and is shown as a simple tool for the identification of climatic-geographic regions in which: The variability due to the changes of the large-scale pressure gradients may or may not be ignored in mesoscale models. An α index larger than 1 indicates the dominance of the diurnal processes over the interdiumal processes in producing wind variability, in which case large-scale effects are relatively small. Hodograph representation for the average diurnal wind variation is or is not a faithful picture of the actual wind observations on a particular day. An α index larger than 1 suggests a more faithful representation of the wind hodograph. As expected, the α index is la...

A physical model for high-resolution (Δ x = 1–2 km) rainfall over complex terrain that was recently verified against radar-derived observations is shown to be capable of complementing rainfall normals in Israel. Two examples illustrate that even high resolution rain-gauge networks may miss important small-scale rainfall features over highly complec terrain, which are effectively detected by a simplified linear and adiabatic model.

A simple analytical expression for indexing the orographic precipitation rate over high mountains is presented. The formula is based upon the assumption that the moisture convergence in the mountainous boundary layer approximately equals the precipitation. Realistic precipitation distributions are obtained when numerical advection is permitted for the Himalayas, Equadorian Andes and the Sierra Nevada Mountains in California. In the latter case the simulated distributions compete well with a fully two-dimensional precipitation model for some unusual stormy events. Following the model results over high mountains, it is suggested that for the distribution of precipitation, particularly over the high mountains, the detailed microphysical processes may play a lesser essential role than that for small to medium size mountains. The elevation of maximum orographic precipitation zm, is investigated and an analytical expression for zm is derived for a bell-shaped mountain. This expression predicts zm value...

In a first theoretical study, the reasons for anti-clockwise rotation (clockwise rotation in the Southern Hemisphere) of the wind hodograph in the boundary layer are investigated. As observations of wind hodographs show two different kinds of anti-clockwise rotation (ACR), one frequently observed, which is highly irregular with partly ACR and the other with clear ACR, two methods have been applied. At first a two-dimensional nonlinear model which includes sea-land breezes as well as a mountain reveal partly ACR at the lee of the mountain. By analyzing the different terms in the equation for the wind vector rotation, it is shown that the pressure-gradient term is usually the leading one, and the advection term is very small. But the latter becomes important in cases of ACR. Second, a linear model is solved analytically showing that inclusion of a rotating thermal force in the ACR sense generates clear ACR. It is shown that a critical value for the phase shift between the thermal forces in the hori...

A model is described for the representation and study of air flow from the eastern Mediterranean (on the west side of the model's domain) past Lake Kinneret in the Jordan Valley (about 210 m below MSL) and beyond to the east (on the east side of the model) in the summer months. The primary purpose of the model is to improve our understanding of two striking features of the meteorology of the lake area in summer: 1) the almost daily development of strong winds and an associated storm on the lake in the afternoon, and 2) a nearly 50% drop in wind speed across the lake, from the western to the eastern shore, over a distance of only 10 km, again in the afternoon. The model is two-dimensional. It uses the sigma coordinate system and is thus hydrostatic. The horizontal grid distance is 4 km. It has 10 levels in the vertical, between the surface and the top at 750 mb. The first level in the vertical is 10 m above the surface and each of the higher levels is at an attitude that is approximately twice the...

On the assumption that moisture convergence due to mechanical uplifting approximately equals the orographic precipitation, the mesoγ-scale rainfall distributions over mountainous regions in Israel are investigated. The simulated distributions are compared to rainfall observations both from raingages and from radar reflectivities. The mean error in the predicted rainfall on scale of 2 km was ±8.4% for mean annual normals and 15%–20% for three case studies. It is suggest that orographic rainfall on the small mesoscale is highly predictable with the adiabatic assumption that the uplifting is determined by V·ΔZs, where V is the horizontal wind encountering the mountain and Zs, is the topographic elevation. It is also illustrated that the climatological observed rainfall distribution could be complemented by the model at locations where sufficient observations were not available. By comparison of the model simulation with the radar-derived rainfall, the considerable effect that a change in the wind di...

Three approaches for estimating meso-β (Δx=5–10 km) surface winds over complex terrain are applied to obtain best estimates of typical summertime surface flow in Israel, based on a detailed 3-D model, a one-level sigma model and a dense network of surface wind observations. A scheme for combining the three approaches is outlined and illustrated through two examples showing how the approaches complement each other. It is suggested that such a man-machine combination is best for estimation of surface winds over complex terrain.

It is shown that the normalized diurnal and interdiurnal surface wind variabilities have a clear decreasing trend in central-southern Israel for the last three decades. This trend is found in the surface data of the independent time series of three meteorological stations in this area. It is suggested that this change indicates a mesoscale modification of climate which is induced by the agricultural development and settlement of the central to southern part of Israel in the recent decades. The decreasing trend becomes particularly strong during the 1960s and this is correlated to the enhanced irrigational effects due to the starting-up of the National Water System in 1964. It is proposed that the region may have gone through a similar but reversed mechanism to that of the desertification process (reversed desertification!?) that was largely investigated in association with the Sahel zone drought.

The extinction efficiency is calculated for a volume containing randomly oriented long circular cylinders. The results are compared with the extinction efficiency of spheres with the same refractive index and are shown to be almost identical. Special attention is given to a corrected definition of the extinction efficiency for obliquely oriented cylinders with respect to the incident radiation direction. The corrected definition presented here is justified by use of the physical concept of the extinction efficiency as used in the case of other scatterers such as spheres. Calculations are presented for a polarized incident light (normal to the incident plane) when discussing the definition of the extinction efficiency. For the randomly oriented particles the incident light is assumed to be unpolarized.

In a first theoretical study, the reasons for anticlockwise rotation (clockwise rotation in the southern hemisphere) of the wind hodograph in the boundary layer are investigated. As observations of wind hodographs show two kinds of anti-clockwise rotation (ACR, in brevity) one frequently observed, which is highly irregular with partly ACR and the other with clear ACR, two methods have been applied. At first two-dimensional nonlinear model (described by Alpert et al., 1982) including sea-land breeze as well as a mountain reveal at the lee of the mountain partly ACR. By analyzing the different terms in the equation for the wind vector rotation (see Neumann, 1977) it is shown that usually the pressure-gradient term is the leading one and the advection term is very small. But the latter becomes important in case of ACR. Secondly, a linear model is solved analytically showing that inclusion of a rotating heating forcing in the ACR sense generates clear ACR.

Three major modifications to the treatment of land surface processes in the Pennsylvania State University‐ National Center for Atmospheric Research mesoscale model MM5, are tested in a matrix of eight model experiments. Paired together in each dimension of the matrix are versions of the code with and without one of the changes. The three changes involve 1) a sophisticated land surface model [the Parameterization for Land‐ Atmosphere Convective Exchange (PLACE)], 2) the soil moisture and temperature initial conditions derived from running PLACE offline, and 3) a 1.5-order turbulent kinetic energy (TKE) turbulence boundary layer. The code without changes, defined as the control code, uses the most widely applied land surface, soil initialization, and boundary layer options found in the current MM5 community code. As an initial test of these modifications, a case was chosen in which they should have their greatest effect: conditions where heterogeneous surface forcing dominates over dynamic processes. The case chosen is one with widespread summertime moist convection, during the Convection and Precipitation Electrification Experiment (CaPE) in the middle of the Florida peninsula. Of the eight runs, the code with all three changes (labeled TKE-PLACE) demonstrates the best overall skill in terms of biases of the surface variables, rainfall, and percent and root-mean-square error of cloud cover fraction for this case. An early, isolated convective storm that formed near the east coast, at the downwind edge of a region of anomalous wet soil, and within the dense cluster of CaPE mesoscale observation stations, is correctly simulated only by TKE-PLACE. It does not develop in any of the other seven runs. A factor separation analysis shows that a successful simulation requires the inclusion of the more sophisticated land surface model, realistic initial soil moisture and temperature, and the higher-order closure of the planetary boundary layer (PBL) in order to better represent the effect of joint and synergistic (nonlinear) contributions from the land surface and PBL on the moist convection.