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Many cyclone detection and tracking methods (CDTMs) have been developed in the past to study the climatology of extratropical cyclones. However, all CDTMs have different approaches in defining and tracking cyclone centers. This naturally leads to cyclone track climatologies of inconsistent physical characteristics. More than that, it is typical for CDTMs to produce a non-negligible amount of bogus tracks which can be perceived as “false positives”, or more generally as CDTM artifacts, i.e. tracks of weak atmospheric features that do not correspond to large or mesoscale vortices. Lack of consensus in CDTM outputs and the inclusion of significant amounts of bogus tracks therein, has long prohibited the production of a commonly accepted reference dataset of extratropical cyclone tracks. Such a dataset could allow comparable results on the analysis of storm track climatologies and could also contribute to the evaluation and improvement of CDTMs. To cover this gap, we present a new methodological approach that combines overlapping tracks from different CDTMs and produces composite tracks that concentrate the agreement of more than one CDTM. In this study we apply this methodology to the outputs of 10 well-established CDTMs which were originally applied to ERA5 reanalysis in the 42-year period of 1979–2020. We tested the sensitivity of our results to the spatio-temporal criteria that identify overlapping cyclone tracks, and for benchmarking reasons, we produced five reference datasets of subjectively tracked cyclones. Results show that climatological numbers of composite tracks are substantially lower than the ones of individual CDTM, while benchmarking scores remain high (i.e. counting the number of subjectively tracked cyclones captured by the composite tracks). This suggests that our method is able to filter out a large portion of bogus tracks. Indeed, our results show that composite tracks tend to describe more intense and longer-lasting cyclones with more distinguished early, mature and decay stages than the cyclone tracks produced by individual CDTMs. Ranking the composite tracks according to their confidence level (defined by the number of contributing CDTMs), it is shown that the higher the confidence level, the more intense and long-lasting cyclones are produced. Given the advantage of our methodology in producing cyclone tracks with physically meaningful, distinctive life stages and including a minimum number of bogus tracks, we propose composite tracks as reference datasets for climatological research in the Mediterranean. The supplementary material provides the composite Mediterranean tracks for all confidence levels and in the conclusion we discuss their adequate use for scientific research and applications.

The Mediterranean Basin has several features that enhance cyclonic activity, such as its complex topography and sharp land-sea temperature differences. However, some processes occurring outside the basin can influence its seasonal variability. In this work, we highlight the relationship between the North Atlantic Storm Track (NAST) and cyclones passing through the Eastern Mediterranean (EM). We use Empirical Orthogonal Function (EOF) analysis of upper-level meridional wind variance to inspect monthly NAST regimes and their influence on wintertime flow in the EM.We find that the higher functions (EOF4-5) show stronger links to the region and specifically, to anomalies in synoptic fields associated with cyclones (upper-level potential vorticity, sea level pressure) and in monthly precipitation. These functions manifest as a pair of orthogonal zonal waves, reminiscent of subseasonal teleconnections that were previously linked to seasonal precipitation extremes in the EM (the South Levant pattern). It is hypothesized that this connection is mainly brought about by large-scale adiabatic advection of PV in the upper levels. Meanwhile, the two leading NAST modes (“pulsing” and latitudinal “shifting”) were found to produce a comparatively smaller effect.On the daily scale, we investigate the NAST-EM connection through the lens of zonally propagating Rossby wave packets, in both reanalysis and CMIP6 models (which capture the patterns well).

The “Teleconnection” term in climate studies was defined primarily for widely separated regions. This stems from the basic idea that a physical process, such as an advection or a particular synoptic system, cannot simply explain a relation or a correlation in large distances. Also, in modern times, models more often fail in predicting these remote patterns, particularly with regional models, such as in the hurricane example and its effect on Mediterranean precipitation, explored here. Several teleconnection relations are reviewed, with particular focus on Mediterranean rainfall. It is argued that even with a clear physical process of advection and for a short horizontal scale, ‘teleconnection’ is often not well understood, if the physical mechanism involved is complex, such as in the sub-synoptic scales of aerosol-rainfall interaction or megacities and their potential effects on precipitation. Thus, a broader look at the horizontal scale of teleconnection is proposed where the word TELE is still representing the word ‘far’, as in its Greek origin, but it also includes our limitation in understanding of complex atmospheric relations in various distances.Furthermore, the hidden assumption that ancients were not able to observe teleconnections is contradicted by an example from ~1800 years ago. In this example, a claim was made in the Talmud that the Euphrates flow is strongly related to the rainfall over the greater Israel region, located at ~700-900 km westward. However, the understanding of this ancient teleconnection was only possible at the 2nd half of the 19th century when the role of synoptic systems in weather, has emerged. Keywords: Teleconnection, Rainfall, synoptic system, Euphrates discharge, Middle East, Levant, Talmud REFERENCE:P. Alpert and H. Saaroni, “Historical and New Insights into Atmospheric Teleconnection” Oxford Research Encyclopedia of Climate Science (eds von Storch, H. et al.) (Oxford Univ. Press, Oxford, 2021).(accepted Aug. 2021)

The potential benefits of public urban green spaces (UGS) are widely recognized and well documented, but the actual realization of these benefits depends on appropriate design and ongoing maintenance. To properly consider the needs and preferences of users, the professionals who plan and manage UGS should ideally be guided by the same perceptions that motivate the people who benefit from them. This exploratory international study was aimed at assessing the perceptions of urban residents and their level of satisfaction with specific aspects of UGS quality, and the extent to which these perceptions align with those of the professionals responsible for providing UGS-related services. The data collection was conducted in five European countries (Croatia, Israel, Italy, Lithuania, and Spain) in 2020–2021. The results show that UGS professionals generally underestimate the fears that are experienced by users at night, especially women, but correctly prioritize the importance of tangible solutions such as adequate lighting and cleanliness. Users in all countries emphasized “nature” and “quiet” as factors that improve their general sense of wellbeing in UGS, whereas these two aspects were largely overlooked by professionals in almost all countries. In addition, user satisfaction with specific UGS characteristics ranging from accessibility to park furniture was overestimated by professionals. These findings reinforce the concern that the benefits and services of green spaces can only be maximized if UGS professionals recognize the actual needs and desires of UGS users, from the phase of planning and landscape design to the everyday management and maintenance of these shared amenities.

Previous observational analyses have shown a declining rainfall trend over Israel, mostly statistically insignificant. The current study, for the period 1975–2020, undermines these findings, and the alarming future projections, and elaborates other ingredients of the rain regime. No trend is found for the annual rainfall, reflecting a balance between a negative trend in the number of rainy days and a positive trend in the daily rainfall intensity, both on the order of 2.0%/decade. In the mid-winter, the rainfall and the daily intensity increased, while both declined in the autumn and spring, implying a contraction of the rainy season. The time span between accumulation of 10% and 90% of the annual rainfall, being 112 days on the average, shortened by 7 days during the study period. This is also expressed by an increase of the Seasonality Index, indicating that the regional climate is shifting from “markedly seasonal with a long dry season” to “most rain in ≤3 months.” The intra-seasonal course of the rainfall trend corresponds to that of the occurrence and intensity of the Cyprus Lows and the Mediterranean Oscillation. The contraction of the rainy season and the increase in the daily intensity have far-reaching environmental impacts in this vulnerable region.

The Mediterranean region is projected to be significantly affected by climate change through warming and drying. The Eastern Mediterranean (EM) is particularly vulnerable since the bulk of the prec ...

The Red-Sea Trough (RST) is a lower-level trough extending from the tropical low-pressure to the Levant. Its annual occurrence is 20%, between October and May, producing mostly dry weather, but occasionally active and causing local showers and floods. During winter the dominant synoptic system over the Levant is the Cyprus low (CL). Previous studies showed that some CLs form within pre-existing RSTs, through a tropical-extratropical interaction.This study is the first comprehensive climatological framework of such formation events, analyzing occurrence, seasonality and the resulting rainfall in Israel. The study looked at events of new CLs formed within the domain 31°-35°N, 30°-36°E while a RST was detected within 24 hours before the event. We used the 6-hourly ERA-Interim database, with 0.75°×0.75° resolution, during 1979-2017, and identified 104 formation events, which constitute 10% of the CLs. Most events occurred during fall and early winter, as the case for the RST. Eighty-four percent of them formed during the evening or the night, and almost two thirds of the CLs disappeared temporarily at noon and regenerated afterwards. This is attributed to the sea/land diurnal oscillation. Most of the CLs that formed were found shallow with little rain, but occasionally became major storms, like "Alexa", which caused extreme snowing in Jerusalem, in December 2013.The evolution scenarios leading to formation events were divided into four clusters, according to the synoptic situation at the 500-hPa geopotential height. The first one is characterized by a closed cyclone approaching from the southwest, often connected to active RSTs, such as the event that occurred in 2-4 November 1994. In the second, a trough is deepening from the northern sector, possibly a polar intrusion, like the "Alexa" storm. In the third, the most populated cluster, a trough is approaching from the west. A separate cluster contains four events with no upper-level support.

Previous observation analyses have shown a declining rainfall trend over Israel, mostly statistically insignificant. These findings support the projections of the climatic models for the 21th century. The current study, for the period 1975-2020, undermines these findings, and the alarming future projections, and elaborates changes in the distribution of the rain along the rainy season.The annual rainfall has a negligible trend, of +0.002%/decade, the number of rainy days has declined by -1.9%/decade and the average daily rainfall has increased by +2.1%/decade, all statistically insignificant. In the mid-winter both rainfall and daily rain intensity increased, while these variables have declined in the autumn and spring. The implied contraction of the rainy season is estimated by 2 measures. The 'effective length', which is determined by the time between accumulation of 10% and 90% of the annual rainfall, lasting 112 days on the average. This has been shortened by seven days during the study period. The other is the Seasonality Index (SI), reflecting the temporal concentration of the rainy season around its center. The trend found indicates that the regional climate is shifting from being between 'Markedly seasonal with a long dry season' and 'Most rain in ≤3 months', further toward the latter.The trend in Cyprus Low occurrence and in the Mediterranean Oscillation Index were found to explain the rainfall trends only partially. We suggest that the cause for the increase in the mid-winter rain intensity is the increase in sea-surface temperature, found over the east Mediterranean, and for the decline in the transition seasons, to the poleward expansion of the subtropical highs. The contraction of the rainy season on the one hand, and the increased daily rain intensity in the mid-winter on the other, have ecological and hydrological impacts in this vulnerable region.

Measures of potential sailing mobility are essential for understanding the functioning of ancient maritime links. This requires measuring potential sailing mobility of coastal sailing runs, as well as direct passages in the open sea. Quantitative works attempting to measure potential sailing mobility have shortcomings related to the use of averaged wind data, thereby losing knowledge of wind variability; non-inclusion of the human factors impacting mobility; and not using methods of measuring coastal sailing. The method presented here was developed to measure potential sailing mobility of coastal sailing runs, based on using the patterns of hourly wind direction and speed variability – and specifically the coastal breeze cycle. The effects of wind variability on sailing mobility are extracted from a large dataset of data at high spatiotemporal resolution, by employing millions of sailing simulations which enable developing meaningful information from big data. This method has demonstrated its applicability to measuring coastal sailing mobility in several developmental case studies in the eastern Mediterranean, introducing realistic measures of mobility that include coefficients of mobility and of time spent waiting for favourable winds. Complementing a previously developed method to measure potential sailing mobility on direct open-sea passages, this new method can now provide a comprehensive toolkit for mapping potential sailing mobility. Such mapping is a valuable input to research on maritime networks and maritime-related developments.

Highlights • We investigated the change in visitation of urban green spaces (UGS) during COVID-19 pandemic. • Social isolation reduced extent, type and distance of visited UGS on the basis of legal restrictions. • Reasons for visiting UGS changed from non-essential before the pandemic to essential during it. • Respondents missed visiting UGS regardless of the view of UGS from their window. • Respondents expressed the need for UGS integrated within the urban fabric., Urban green space (UGS) is an essential element in the urban environment, providing multiple ecosystem services as well as beneficial effects on physical and mental health. In a time of societal crisis these effects may be amplified, but ensuring that they are maintained requires effective planning and management – which is a complex challenge given the rapid changes in modern society and the need for continual adaptation. This study aims to identify the drivers that normally attract visitors to UGS, and to assess the effects of social isolation on the usage and perception of UGS during the COVID-19 pandemic. We conducted an online survey during the period in which restrictive measures were imposed in response to the pandemic (March-May 2020), in Croatia, Israel, Italy, Lithuania, Slovenia and Spain. Results showed that urban residents normally have a need for accessible UGS, mainly for physical exercise, relaxing and observing nature. The reduction in UGS visitation during the containment period was related to distinct changes in the motivations of those who did visit, with a relative increase in "necessary activities" such as taking the dog out, and a reduction in activities that could be considered non-essential or high-risk such as meeting people or observing nature. Behavioral changes related to proximity were also observed, with an increase in people walking to small urban gardens nearby (e.g. in Italy) or tree-lined streets (e.g. in Spain, Israel), and people traveling by car to green areas outside the city (e.g. in Lithuania). What the respondents missed the most about UGS during the pandemic was "spending time outdoors" and "meeting other people" – highlighting that during the COVID-19 isolation, UGS was important for providing places of solace and respite, and for allowing exercise and relaxation. Respondents expressed the need for urban greenery even when legally mandated access was limited – and many proposed concrete suggestions for improved urban planning that integrates green spaces of different sizes within the fabric of cities and neighborhoods, so that all residents have access to UGS.

Extreme weather events have long been considered challenging to predict. It is likely that global warming will trigger extreme weather in many regions of the globe and especially over the Mediterranean ´hot spot´. Therefore, extreme weather events have been selected as one of the grand challenges of the World Climate Research Program.The intrinsic predictability of a weather system, or any dynamical system, depends on its persistence and its active number of degrees of freedom. Recent developments in dynamical systems theory allow to compute these metrics for atmospheric configurations (1). In most of the mid-latitudes, synoptic scale patterns exert a strong control on regional weather, thus, stimulating a broad interest, especially in weather forecasting. Recently, we have integrated the dynamical systems approach with a synoptic classification algorithm over the Eastern Mediterranean (2). It was shown that the dynamical systems perspective provides an extremely informative tool for evaluating the predictability of synoptic patterns and especially of weather extremes.The novel perspective, which leverages a dynamical systems approach to investigate the predictability of extreme weather events, outlines a new avenue of research that may be fruitfully applied at operational weather and climate forecasting services in the Mediterranean Region and around the globe.ReferencesFaranda D, Messori G, Yiou P. 2017. Dynamical Proxies of North Atlantic Predictability and Extremes. Scientific Reports 7, 412782017b. DOI: 10.1038/srep4127 Hochman A, Alpert P, Harpaz T, Saaroni H, Messori G. 2019. A New Dynamical Systems Perspective on Atmospheric Predictability; Eastern Mediterranean Weather Regimes as a Case Study. Science Advances 5. DOI: 10.1126/sciadv.aau0936

Certain metals can surprisingly build-up charge spontaneously, when exposed to high relative humidity (RH), although they need to be isolated from the ground. We have explored this phenomenon, building on former experimental knowledge and carrying out additional experiments, to identify the parameters that could enhance this charging. We used many types of metals with different characteristics under different RH and temperature conditions. While some metals were unaffected by high RH, others, like zinc and stainless steel, did acquire charge, when RH was >60%, and charged a capacitor to a voltage of 1 V. For the first time, we also performed outdoors experiments, showing this phenomenon is also valid under similar natural ambient humid conditions. If these results can be scaled up, it may lead to the development of practical applications for regions and times of high RH conditions.

Careful planning of the use of water resources is critical in the semi-arid eastern Mediterranean region. The relevant areas are characterized by complex terrain and coastlines, and exhibit large spatial variability in seasonal precipitation. Global climate models provide only partial information on local‐scale phenomenon, such as precipitation, primarily due to their coarse resolution. In this study, statistical downscaling algorithms, based on both synoptic scale past weather regimes and analogues and their associated observed precipitation at rain gauges, are operated for eighteen Israeli rain gauges in four hydrological basins with an altitude ranging between ‐200 and ~1000 m ASL. In order to project seasonal precipitation over Israel and its hydrologic basins, the algorithms are applied to six Coupled Model Inter‐comparison Project Phase 5 (CMIP5) models for the end of the 21st century, according to the RCP4.5 and RCP8.5 scenarios. The downscaled models are able to capture quite well the seasonal precipitation distribution. All models display a significant reduction of seasonal precipitation for the 21st century of up to ~50% with variations depending on the scenario, algorithm and hydrological basin. The reduction is less acute when applying the weather regimes algorithm as it relies on past daily mean precipitation values per regime, while the analogues downscaling algorithm relies on the daily precipitation of the individual past analogues and therefore better captures the tails of the distribution. Moreover, the analogues downscaling algorithm projects a significant increase of outliers in the right tale of the distribution i.e. increase in extreme precipitation events. The reduction in seasonal precipitaton is due to both decrease in the frequency of the synoptic systems responsible for precipitation as well as reduction in the daily precipitation amounts at the stations. While the percentage of reduction is quite similar among stations (same reduction in the precipitating synoptic systems that affect the whole area), the reduced amounts are different as they are characterized by different seasonal precipitation amounts. In some cases reductions in precipitation can lead to transition of some areas to semi-arid and arid climates. The statistical downscaling methods applied in this study can be easily transferred to other regions where long‐term datasets of observed precipitation are available.

The Levant region is dominated in the summer by the persistent Persian Trough. Thus, the current synoptic classifications lack the ability to reflect inter-diurnal variations in the local weather conditions. This study aims to overcome this weakness and has two objectives: to develop operative prediction equations for the local weather conditions based on synoptic-scale data, and to propose a new synoptic classification, based on the environment to climate approach, to better reflect the local climatic stress. Prediction equations were derived for the national heat-stress (NHS) and the height of the persistent marine inversion (inversion base, IB). The potential predictors are comprised of atmospheric variables found correlated with these weather attributes together with indices representing synoptic to large-scale features. The indices were derived through a composite maps analysis of days with extreme values of these attributes. The Climatic Stress Index (CSI) developed is a combination of the heat-stress and the inversion height, for which a separate prediction equation was derived. The spectrum of the calculated daily CSI values was divided into three parts of equal size, used as the basis of the new synoptic types, defined as: ‘comfort’, ‘medium’, and ‘discomfort’. The attribution of a certain day to one of these types is determined according to its calculated CSI. Our proposed classification was found to better delineate the NHS and the height of the IB in Israel. The downscaling schemes and the new synoptic classification are applicable for both operative weather prediction and climate prediction. The latter enables the assessment of future trends in the climatic stress, in general, and heat-stress, in particular. This is due to being compatible with the output of operative weather prediction models as well as for the format of the disseminated output of climate models.

On-going changes in drought, vegetation and wildfires in Israel provide a key example of possible future evolution in transition areas at the border between Mediterranean and arid climates. Here we present multiple lines of evidence suggesting that drought conditions in Israel, representing the eastern Mediterranean, have increased during the period 1980–2014. Drought conditions were calculated using the Standardized Precipitation Evapotranspiration Index (SPEI), the Standardized Precipitation Index (SPI) and the Standardized Soil Moisture Index (SSI). A 30-year series (1982–2011) of monthly Fraction of Photosynthetically Active Radiation absorbed by vegetation (FPAR) indicates generally positive trends in winter and spring and negative ones in summer and autumn, except in the transition zone between the southern Negev desert and the Mediterranean climate region, where a statistically significant negative trend in all seasons was found. Available ground observations suggest that fire activity has decreased during the period 1987–2011. Apparent year-to-year oscillations are superposed onto these long-term trends. We show that inter-annual variability of summer fires is related to antecedent wet conditions and to above normal vegetation conditions. These relationships suggest the summer fires in Israel are mainly limited by fuel availability rather than by fuel flammability. On the other hand, the year-to-year variations of spring and autumn fires are significantly related with drought indices. Thus, the increase of drought conditions together with climate projections for further warming and drying in this region, point at a potential increase of fire risk in the intermediate seasons.

Dynamical systems metrics provide an informative qualitative estimate of eastern Mediterranean weather regimes predictability., The atmosphere is a chaotic system displaying recurrent large-scale configurations. Recent developments in dynamical systems theory allow us to describe these configurations in terms of the local dimension—a proxy for the active number of degrees of freedom—and persistence in phase space, which can be interpreted as persistence in time. These properties provide information on the intrinsic predictability of an atmospheric state. Here, this technique is applied to atmospheric configurations in the eastern Mediterranean, grouped into synoptic classifications (SCs). It is shown that local dimension and persistence, derived from reanalysis and CMIP5 models’ daily sea-level pressure fields, can serve as an extremely informative qualitative method for evaluating the predictability of the different SCs. These metrics, combined with the SC transitional probability approach, may be a valuable complement to operational weather forecasts and effective tools for climate model evaluation. This new perspective can be extended to other geographical regions.

The use of detailed meteorological data with sailing software, in conjunction with sailing the Ma'agan Mikhael II replica ship, has engendered the development of a method for examining maritime mobility of single-masted square sail Mediterranean merchantmen in the Graeco-Roman period, with the initial objective of mapping direct, open sea, return sailing routes from the Levant that a priori lie contrary to the prevailing wind. Many quantitative works have used averaged winds as input, and evaluated sailing passages based on climatological averages, losing information on the intra- and inter-diurnal variability of the winds. Thus their sole measure of mobility has been a representation of sailing speed on direct crossings. Moreover, these studies have not considered the difference between physical and practical mobility, the latter driven by human factors. For instance, the choice of whether to sail, or wait for better conditions. The proposed method uses climatological resources at high spatial and temporal resolutions, with the premise that using high-resolution data reveals the recurring wind variabilities and patterns that are key to mobility, especially on routes lying contrary to the prevailing winds. The method generated a large set of over 5400 simulated sailing outcomes for each route segment, permitting well-established statistical analysis. Inclusion of criteria-based human factors of the mariners of the period provides a measure of mobility, representing not only sailing speed, but also waiting time, and the probability of conducting a feasible passage at a given time of the year. This new method provides deeper insight into maritime mobility and the understanding of seafaring in the Mediterranean, and is applicable to numerous scenarios, providing a practical and improved measure of maritime mobility.

This article presents a semi-objective methodology to classify formation scenarios of a new ‘daughter’ cyclone (DC), based on the thermal field characteristics of the parent cyclone (PC). An automated algorithm assigns a DC to one of seven formation types, according to the following considerations: Whether the DC is formed on a front belonging to the parent's frontal system or to a different frontal system, and whether this frontal system is cold, warm or quasi-stationary. An additional type contains DCs formed within the warm sector of the parent. The algorithm uses measures derived from wind and temperature fields at 850-hPa: the temperature gradient, the temperature advection and the temperature Laplacian, each computed at the formation location of the DC, and also the temperature difference between the DC and the PC. The classification method was applied to 4303 Mediterranean DCs which were observed during 33 winters. Totally 85% of the DCs were identified as belonging to one of the seven predefined types, implying that the formation of the remaining 15% was not related to baroclinic or thermal factors. Among the successfully classified DCs, over half were formed on the frontal system of the parent, a third of the DCs on a separate frontal system and only 13% were formed within the warm sector. Most of the ‘cold front’ cyclones were formed at the major Mountain Lee locations, whereas those formed on warm fronts were generated mostly over the Adriatic, Ligurian and Aegean Seas. Inspection of composite maps of distinct formation types in various regions revealed unique formation scenarios, like DCs forming over western Morocco but belonging to third generation Genoa Lows. Other reflects discontinuous movement of cyclones, resulting from encounter with topographical obstacles, found mostly on PCs' warm fronts, or from the attraction of cyclogenetic areas left behind, mostly on PCs' cold fronts.

Relatively high concentrations of particulate matter (PM) are characteristic to Israel and the Middle East. This is mostly attributed to natural dust storms and partly to anthropogenic sources, local, or remote. The research deals with relations between concentrations of PM10 and PM2.5, and between synoptic conditions and regional climatic stress. Our particular focus is the summer, a season with no dust outbreaks when mostly one synoptic system, the Persian Trough prevails over the region, with associated northwesterly Etesian winds. Therefore, the “climate to environment” approach to distinguishing among PM concentrations by classes of synoptic systems is not very successful in the summer. In contrast, the climatic stress index (CSI), representing the “environment to climate” approach, was found positively correlated with PM concentrations in Haifa, Israel, and more effective in explaining inter-diurnal variations of PM pollution. Synoptic analysis performed through composite anomaly maps for days with higher and lower PM concentration, indicates a weakening of the Etesian winds in days with high CSI. On the one hand, the weaker winds reduce imported PM, but, on the other hand, the lower marine inversion in days with high CSI enhances PM pollution from local sources, by weakening the dispersion mechanisms, both vertical and horizontal. The higher level of PM pollution in days with high CSI indicates dominance of the local PM sources. The positive correlation between climatic stress and PM pollution, and increased climatic stress associated with global and regional warming, necessitate further tightening of control on anthropogenic pollution sources.

The Mediterranean is one of the most cyclogenetic regions in the world. The cyclones are concentrated along its northern coasts and their tracks are oriented more or less west-east, with several secondary tracks connecting them to Europe and to North Africa. The aim of this study is to examine scenarios in the development of Mediterranean cyclones, based on five selected winter seasons (October–March). We detected the cyclones subjectively using 6-hourly Sea-Level Pressure maps, based on the NCAR/NCEP reanalysis archive. HMSO (1962) has shown that most Mediterranean cyclones (58%) enter the Mediterranean from the Atlantic Ocean (through Biscay and Gibraltar), and from the south-west, the Sahara Desert, while the rest are formed in the Mediterranean Basin itself. Our study revealed that only 13% of the cyclones entered the Mediterranean, while 87% were generated in the Mediterranean Basin. The entering cyclones originate in three different regions: the Sahara Desert (6%), the Atlantic Ocean (4%), and Western Europe (3%). The cyclones formed within the Mediterranean Basin were found to generate under the influence of external cyclonic systems, i.e. as "daughter cyclones" to "parent cyclones" or troughs. These parent systems are located in three regions: Europe (61%), North Africa and the Red Sea (34.5%) and the Mediterranean Basin itself (4.5%). The study presents scenarios in the development of Mediterranean cyclones during the winter season, emphasizing the cyclogenesis under the influence of various external forcing. The large difference with respect to the findings of HMSO (1962) is partly explained by the dominance of spring cyclones generating in the Sahara Desert, especially in April and May that were not included in our study period.

The combined trends of urban heat island intensification and global warming are focusing attention on greening of cities as a tool for urban heat mitigation. Our study examines the range of research approaches and findings regarding the role of urban green infrastructure (UGI) in mitigating urban heat and enhancing human comfort. It provides an overview based on 89 studies, carried out in a range of geographic and climatic regions. We surveyed the distribution of methodologies employed, spatio-temporal scales considered, type and extent of UGI, climatic variables studied and contribution of UGI to ambient air cooling and enhancement of human comfort. It was found that neither the differences in geographic location or in climate conditions had a significant impact on the choice of research approach. The studies, mostly done on limited spatio-temporal scales, have focused on the rate of air cooling by UGI, and to a lesser extent on its impact on thermal comfort. Maximum observed intensities of park cool island (PCI) effects typically ranged between 1.5 °C–3.5 °C, with no apparent correlation to climatic region. However, there is a tendency seen for larger green sites to induce a stronger PCI, whereas well-shading street trees also have a significant cooling and relieving effect.

This study is the first one to objectively identify ‘parent–daughter’ relationships between cyclones and to apply it to Mediterranean cyclones (MCs). The methodology includes cyclone detection, tracking and mapping the area of influence of a cyclone; here daughter cyclones are expected to be found. Cyclone detection and tracking is based on standard algorithms, which were modified to cope with irregularities in intensity and trajectory shapes of MCs. We have developed our own algorithm for mapping cyclones' area of influence. Application of our methodology to the ERA-Interim data for 33 mid-winter seasons identified parents for 97.5% of the MCs. While previous studies claimed that most MC parents are situated over Europe, this study found the majority of MCs' parents (56%) positioned over the Mediterranean itself. This disagreement stems from the fine spatial resolution used here (0.75° × 0.75°), which enabled uncovering smaller cyclones than noticed previously, thus revealing earlier stages of cyclogenesis. The parenthood analysis identified two main types of cyclogenesis within the Mediterranean; one driven by parent MCs, the other driven by Atlantic or European cyclones. The latter is manifested either by directly generating a new MC or by intensifying existing weak MCs. Cyclone generations were explored through backtracking chains of parents down to the ninth generation, the longest chain found. The results indicate that the primary source of MCs is the Atlantic (2/3 of the MCs) and then Equatorial Africa and the Red Sea (1/3). The results also imply that although native MCs owe their existence to the Atlantic-European cyclone track, regional cyclogenetic effects, such as topographic, thermal and baroclinic, are even more influential. The innovative methodology for objective identification of cyclone parents can be used to characterize cyclogenetic scenarios, in particular away from main storm tracks and over complex terrain.

As the majority of people living in cities around the world continues to grow, the challenges connected with life in densely populated urban areas are growing as well. One of the most prominent environmental features of urbanization is the tendency of temperatures in cities to gradually rise in comparison to their rural surroundings, in a localized climatic phenomenon known as the Urban Heat Island (UHI ) effect. Especially during periods of heat stress in warm-weather cities, the UHI may have a debilitating effect on the health and activity of the urban population. Urban green infrastructure in general, and urban trees and forests in particular, hold an unmatched potential as a means for mitigating the UHI effect and enhancing the thermal comfort of people in cities.

Prolonged dry spells (PDSs) during the rainy season have severe environmental implications, including water shortage, damage to agriculture and increased potential for forest fires. This holds in particular for vulnerable regions, such as the Levant, already subjected to decrease in rainfall and lengthening of dry spells, in agreement with predictions of climatic models for the coming decades. This is the first comprehensive study which identifies atmospheric patterns responsible for PDS occurrence on thousands of kilometres scale. A total of 178 PDSs, of >7 days, were found within the 62 seasons studied. A subjective inspection of upper-level geopotential height (GPH), sea-level pressure (SLP) and lower-level temperature anomalies point at three types, each associated with a definite climatic regime. The ‘subtropical’ type is associated with an expansion of the subtropical high over the majority of the Mediterranean, accompanied by northward migration of the Mediterranean cyclone track. The ‘baroclinic’, the most frequent type, is induced by a pronounced stagnant ridge over the eastern Mediterranean, being a part of Rossby wave, accompanied by a pronounced trough/cut-off low over the western Mediterranean. The ‘polar’ type results from intrusion of lower-level continental polar air associated with upper-level trough east of the Levant and blocking high over central Europe. Quantitative indices were derived for objective classification of the types, based on the climatic regimes defined subjectively, and the centers of action representing each. Composite maps for each type indicate substantial differences in the synoptic configuration and the factors explaining absence of rain. For the subtropical type, the dynamic factor of subsidence is dominant. For the polar, the thermodynamic factor of continental dry advection is dominant and for the baroclinic, both dynamic and thermodynamic factors are important. Classification of PDSs according to synoptic scenarios enables analysis of future changes in the occurrence and duration pattern of PDSs, using output of climate models.

Cloud-to-ground lightning flashes usually consist of one or several strokes coming in very short temporal succession and close spatial proximity. The common method for converting stroke data into flashes is using the National Lightning Detection Network (NALDN) thresholds of maximum temporal separation of 0.5 s and maximum lateral distance of 10 km radius between successive strokes. In the present study, we tested a location-based algorithm with several spatial and temporal ranges, and analyzed stroke data obtained by the Israel Lightning Location System (ILLS) during one year (1 August 2009–31 July 2010). We computed the multiplicity, the percentage of single stroke flashes and the geographical distribution of single vs. multiple-stroke flashes for thunderstorms in the Eastern Mediterranean region. Results show that for the NALDN thresholds, the percentage of single stroke flashes in Israel was 37% and the average multiplicity was 1.7. We re-analyzed the data with a spatial range that equals twice the ILLS location error and shorter times. For the new thresholds of maximum distance of 2.5 km and maximum allowed temporal separation of 0.2 s we find that the mean multiplicity of negative CGs is lowered to 1.4 and find a percentage of 58% of single stroke flashes. A unique severe storm from 30 October 2009 is analyzed and compared to the annual average of 2009/10, showing that large deviations from the mean values can occur in specific events.

This study illustrates the utility of empirical and digital methodologies in examining the question to which degree an architect who lives and builds in one distinctive geographic and climatic region adapts his sacred architecture design to a different climatic region. Specifically, we analysed the thermal comfort in a Synagogue in Tel Aviv, Israel, designed by a renowned Swiss architect in 1996. The morphological analyses, actual measurements, and computerized energy simulations show that the synagogue exhibits high thermal discomfort during the hot-humid summers in Tel Aviv. The results of morphological analyses and simulations also show thermal discomfort in the synagogue during Tel Aviv's mild winters. When simulating the synagogue as if built in Switzerland, the results also show high thermal discomfort. Thus, the design of this synagogue did not necessarily consider climate conditions. However, the design does exhibit attentiveness and sensitivity to symbols and faith requirements.

This research analyses the scenarios that break the monotonic summer regime over the East Mediterranean (EM). The study compares the five upper, median and lower percentiles of the 850-hPa temperature for July–August 1975–2005. The temperature differences were found to be confined to the lower 4 km. They are controlled by the intensity of the negative temperature advection, but not by the prevailing subsidence. Air trajectory analysis shows that the regional prevailing northwest winds are the strongest prior to cool events and the weakest, or nonexistent, prior to hot events. An index representing the location of the air source is proposed as an effective predictor for the temperature. The hot and the cool days were subdivided according to their evolution scenarios. All the cool days were associated with deepening of upper troughs over the EM. Different scenarios were found to generate hot days; ‘tropical’, associated with intrusion of tropical-like air, ‘subtropical’, resulting from an expansion of the subtropical high from North Africa towards the EM, and ‘baroclinic’, associated with a pronounced upper-level ridge, part of a Rossby wave over the Mediterranean Basin. The ‘tropical’ scenario was well identified through the mid-level relative humidity. An alternative classification approach, the objective K-Means clustering method, was applied to the air back-trajectories reaching the EM. They isolated successfully only the ‘tropical’ type. Back-tracking of temperature anomalies indicate two different evolutions for the hot days; one is associated with propagation from the west sector and other is quasi-stationary, associated with intrusion of tropical air. The cool events are all propagating from northwest. This indicates that extreme summer events over the EM are mostly regulated by mid-latitudes disturbances travelling eastward rather than by the Asian Monsoon.

Variations and trends in the rain regime of Israel are analyzed for 1975–2010, when persistent global warming has been observed. Negative trend is observed over the majority of Israel, statistically significant only in the super-arid region. The decrease is significant over the majority of Israel only in the spring, reflecting a shortening of the rainy season, >3 days/decade. The dry spells are becoming longer, significantly in most of the stations. The factors affecting these variations, synoptic systems, large-scale oscillations and global temperature, were studied for extended period, 1953–2010. A simple multiple stepwise regression model applied for the inter-annual rainfall variations indicates that the occurrence of Cyprus lows is the dominant factor and the Mediterranean oscillation index, MOI2, is also a significant factor. In order to reduce the inter-annual noise and reveal inter-decadal variations, the time-series of the rainfall and its potential predictors were smoothed by 11-year window, showing an increase toward the 1990s, followed by a decrease, at a higher rate, onward. Correspondingly, the aridity lines propagated southward till the mid-1990s and then withdrew back, at a larger rate. The large-scale oscillations and the global temperature explain 83 % of the variance on the inter-decadal time-scale, half of it explained by the global temperature alone. The findings of this study support the expected poleward expansion of the Hadley cell due to global warming.

This work presents a statistical reconstruction of average mid-winter (DJF) temperature in Jerusalem since 1750. It is a first comprehensive attempt to reconstruct the temperature in Jerusalem, as a good representation of the Eastern Mediterranean (EM) climate. This representativeness is verified here. The data has been reconstructed by using a statistical model based on Principal Component Regression (PCR), using both instrumental data and high temporal resolution records of proxy data, including tree ring chronologies from Jordan, and records of DJF precipitation and Sea Level Pressure from central and Western Europe. A split validation procedure has resulted in a 0.73 correlation between observed and reconstructed temperature. The warming trend of last decades is well noted in the reconstruction and is in line with other studies. Winters which were cold/warm were historically documented as wet/dry, respectively, consistent with earlier studies pointing a strong relationship between Jerusalem temperatures and precipitation. It is shown here for the first time that the 'First Aliyah' (immigration) to Israel during 1882-1904 initiated during favouring climate conditions (cool and wet) to establish an agricultural community in the region. These conditions were found to be exceptional compared to other periods since 1750.

Though widely acknowledged, climate change and global warming considerations are poorly integrated in landscape planning practices. Exploring this matter, the paper analyses the design of a contemporary urban park in Jaffa, Israel, investigating why climate considerations are so poorly addressed. The analysis focuses on the various competing parameters such as social use, design, political considerations and community desires that influence the planning process as well as the park experience. Results confirm a paradox. Though climate conditions are highly acknowledged, and aggravation in heat stress and discomfort conditions are well known in this region, planners and users alike prefer to suspend them in favour of image and aesthetics. Responding to these results, the paper discusses possible venues for further integrating climate considerations into landscape planning.

The spatio-temporal distribution of lightning flashes over Israel and the neighboring area and its relation to the regional synoptic systems has been studied, based on data obtained from the Israel Lightning Location System (ILLS) operated by the Israel Electric Corporation (IEC). The system detects cloud-to-ground lightning discharges in a range of ~500 km around central Israel (32.5° N, 35° E). The study period was defined for annual activity from August through July, for 5 seasons in the period 2004–2010. The spatial distribution of lightning flash density indicates the highest concentration over the Mediterranean Sea, attributed to the contribution of moisture as well as sensible and latent heat fluxes from the sea surface. Other centers of high density appear along the coastal plain, orographic barriers, especially in northern Israel, and downwind from the metropolitan area of Tel Aviv, Israel. The intra-annual distribution shows an absence of lightning during the summer months (JJA) due to the persistent subsidence over the region. The vast majority of lightning activity occurs during 7 months, October to April. Although over 65 % of the rainfall in Israel is obtained during the winter months (DJF), only 35 % of lightning flashes occur in these months. October is the richest month, with 40 % of total annual flashes. This is attributed both to tropical intrusions, i.e., Red Sea Troughs (RST), which are characterized by intense static instability and convection, and to Cyprus Lows (CLs) arriving from the west. Based on daily study of the spatial distribution of lightning, three patterns have been defined; "land", "maritime" and "hybrid". CLs cause high flash density over the Mediterranean Sea, whereas some of the RST days are typified by flashes over land. The pattern defined "hybrid" is a combination of the other 2 patterns. On CL days, only the maritime pattern was noted, whereas in RST days all 3 patterns were found, including the maritime pattern. It is suggested that atmospheric processes associated with RST produce the land pattern. Hence, the occurrence of a maritime pattern in days identified as RST reflects an "apparent RST". The hybrid pattern was associated with an RST located east of Israel. This synoptic type produced the typical flash maximum over the land, but the upper-level trough together with the onshore winds it induced over the eastern coast of the Mediterranean resulted in lightning activity over the sea as well, similar to that of CLs. It is suggested that the spatial distribution patterns of lightning may better identify the synoptic system responsible, a CL, an "active RST" or an "apparent RST". The electrical activity thus serves as a "fingerprint" for the synoptic situation responsible for its generation.

This study proposes a method for estimating the canopy-layer net urban heat island (UHI) in regions with complex terrain that lack preurban observations. The approach is based on a linear relationship between the urban–rural temperature difference (ΔTu−r), measured via screen-level air temperature, and the population of the city, which was found to have the highest correlation with observations. The linear relation is extrapolated to zero population to yield the desired preurban value. The difference between the zero population ΔTu−r and the current one is proposed to represent the net UHI. Given the uncertainties of the population method, the relatively short time period of the temperature record, and possible inhomogeneity in the data, the results should be regarded as a first-order approximation of the net UHI contribution. The UHI was evaluated for an arid city, Beer Sheba, Israel, for the minimum and maximum air temperatures for the summer and the winter. The study region resembles the combined effect of complex terrain (i.e., the concave topography of the city in contrast with the plateau landscape surrounding it), the UHI, and the regional warming trend. The study assumes that the regional warming does not affect the ΔTu−r. The concave topography of the city dominates over the UHI contribution during nighttime, resulting in an average lower minimum temperature in the city relative to the rural area. This difference has decreased considerably during the study period and has even reversed for the summer nights toward the end of the period. The estimated net UHI contribution in Beer Sheba varies between +0.8° and +3.1°C, with the highest values during the night hours. The high positive UHI during the night is in line with previous studies. The positive UHI in the summer implies further aggravation of heat stress beyond that occurring, and that predicted to increase, over the region.

This study examines the ability of the interannual variability in the occurrence of synoptic types, intensity of large-scale circulations and global temperature to explain that of the 850 hPa temperature in Israel for the summer and the winter. The synoptic factor was represented by 19 types defined by Alpert et al(2004b). For the summer, the deep and the weak Persian Trough explained 35% of the interannual temperature variance. For the winter, the lows to the east and to the north explained 44% of the interannual temperature variance. Two additional factors were incorporated: large-scale circulations, the North Atlantic Oscillation for the summer and the Arctic Oscillation for the winter; and global radiative forcing, represented by the global temperature. Both of them were found to be significant, and the variance explained by all of them is 56% for the summer and 64% for the winter. In the summer the variation is dominated by warm and cool types whereas in the winter the cold systems dominate. The individual contribution of each factor to the long-term temperature trend was estimated. While the global radiative forcing contribution was positive and large in both seasons, the synoptic contribution was positive, four times larger in the summer. The large-scale contribution was negative, three times larger in the winter. The considerable warming in the summer results from a rapid increase in the occurrence of the weak Persian Trough, which is a warm type. The study approach may be useful for predicting future temperature regimes, based on predicted synoptic features in climatic models. Copyright © 2010 Royal Meteorological Society

Background: Previous studies provide increasing support for the impact of environmental factors on disease incidence and activity in multiple sclerosis (MS). Objectives: The purpose of this research was to assess the relationship between the incidence of MS relapses and weather conditions in Israel. Methods: Clinical data, including occurrence of relapses in 235 patients, during 3 consecutive years (2001–2003) were assessed against the general daily meteorological variables. Initially, the relationship between the relapses and their mode of distribution was evaluated. Second, the relationship between the number of relapses on a specific date and the meteorological variables was assessed. Third, the tendency to seasonality in the occurrence of relapses was examined. Results: No significant correlation was found between the number of relapses and a specific season, month or day. Moreover, no clear relationship was found between certain meteorological variables or a combination of variables and the frequency of the relapses. Conclusion: The meteorological parameters studied were not found to have a significant impact on the occurrence of relapses in this group of patients. These findings raise questions regarding the clinical significance of the impact of weather conditions, at least in the context of the Mediterranean climate, on the disease course of patients with MS.

This study deals with potential changes in the relative humidity associated with global warming and their implications on heat stress along the coastal region of the Mediterranean in the summer season. It is based on the assumption that the regional warming will enhance the lower-level stability due to the thermal inertia of the sea with respect to its overlying air. The enhanced stability implies more effective trapping of the near surface moisture, and as a result—further increase of the relative humidity. The marine boundary layer over the Mediterranean is modeled. The central feature of the model is the marine inversion capping the marine moist air, which intensity is positively correlated with the stability. Simple calculations indicate that if the temperature increases, while the stability remains unchanged, the near-surface relative humidity would not be affected. But, an increase in the stability would result in an increase in the near-surface relative humidity. This prediction is validated through observed trends of the respective fields, using the NCEP/NCAR reanalysis data and soundings from the eastern Mediterranean. The results are consistent in indicating an increase in the near-surface temperature, the lower-level stability and the relative humidity over the eastern part of the Mediterranean, but not in its western part. The results for the eastern Mediterranean support the expectation for an aggravation of heat stress beyond that imparted by the temperature rise.

The study focuses on long-term trends of daily rainfall in Israel as a function of their intensity in order to identify potential trends in rainfall extremity. The study period is the rainy season, October-May between 1950/1 and 2003/4. For the total rainfall, an increased trend is shown across Israel, especially for the central and southern regions, though non-significant. Daily rainfall intensity showed non-significant trends of increase in the heavy rainfall at the center and south and decrease at the north. The light to moderate rainfall trends increased in the north while they decreased at the center and south. Trends are significantly correlated with known teleconnection patterns, especially the East Atlantic- Western Russia and the North Sea-Caspian Sea patterns. Positive trends toward heavier rainfall are noted in Israel, which are significant in several specific locations. This finding has to be carefully followed since the region is a climatic border subjected to severe water shortage and is predicted to dry-up in most global warming scenarios. During the last decades there is an increasing evidence for more extreme rainfall at different places around the globe. Global warming was suggested to be linked with an increase in heavy rainfall due to an increase in atmospheric vapor and the warmer air. This trend is shown in the 4 th Assessment Report of the IPCC (1). In general, the Mediterranean Basin shows decreasing trends in the precipitation amount (2-4). The EM shows mixed rainfall trends but almost all stations show a decreasing trend in the precipitation which is especially large and significant during winter in the Greek, Cypriot and Turkish stations (5). Precipitation reduction over most Greek stations, combined with enhanced anticyclonic activity over almost the whole Mediterranean was found during the late 1980s and the early 1990s, a period characterized by high North Atlantic oscillation index values (6). Time series of extreme precipitation cases in Greece for the period 1970-2002, did not reveal significant positive or negative trend (7). Alpert et al. (8) showed the paradoxical increase of Mediterranean extreme daily rainfall in spite of the decrease in the total rainfall. They showed an increase in the torrential rainfall in Italy and Spain, heavy rainfall in Israel and heavy- torrential rainfall over Cyprus for the period 1951-1995. These trends were significant only in Italy and Spain. Kostopoulou and Jones (5) analyzed seasonal and annual trends over the central and Eastern Mediterranean (EM, 1958-2000). They showed statistically significant positive trends toward intense rainfall events and greater amount of precipitation for stations around the Italian Peninsula. For the EM, i.e., the Balkan Peninsula, western Turkey and

This study examines the synoptic conditions controlling NOx pollution in the metropolitan area of Tel Aviv, using a semi-objective synoptic classification for the eastern Mediterranean. A day in which NOx concentration exceeded the Israeli standard in ≥1 of the seven monitoring stations was defined an “exceeding day” and in ≥5 as an “extensive exceeding day”. For 1998–2004, 19% and 3% of the days were found exceeding and extensive exceeding days, respectively, over 85% of them in the winter months, November–March. The inter-annual variation in the occurrence of the synoptic types was found to explain 72% of the variations in the number of exceeding days. A significant negative trend in the occurrence of types with high pollution potential explained the decrease of 10% per year in the number of exceeding days during 1998–2004. The Red Sea Trough, though being cyclonic system, contributed 51% of the exceeding days, while highs, though being more frequent, contributed only 35%. The “pollution potential” of a synoptic type was defined as the percentage of exceeding days belonging to this type. The majority of synoptic types with the highest pollution potential were cyclonic, most being the Red Sea Trough with western axis, with 82% potential. Our findings indicate that the identity of the synoptic system as cyclonic or anticyclonic is not the key factor for the pollution potential in the study region, but rather, the ambient atmospheric conditions they induce, i.e., high temperatures, static stability, and weak easterly offshore flow. Local processes are the direct cause of the pollution and that the role of the synoptic conditions is to enable, or even to reinforce, the supportive meso-scale processes. This study is a first step in downscaling synoptic features to local NOx pollution potential, constituting a basis for alarming against pollution events, based on the predicted synoptic conditions.

The relevance of the midlatitude conveyor belt model to Mediterranean cyclones (MCs) is examined using data from two winters. Eight MCs, which exhibit typical midlatitude cyclone structure, were scrutinized and their conveyor belts were examined. The analysis was based on satellite imagery, isentropic wind maps, vertical cross-sections of potential and equivalent potential temperatures, and air back-trajectories. The conveyor belts found in the studied MCs were similar to the common features of midlatitude cyclones, except for three aspects. First, the warm conveyor belt was not associated with massive organized cloudiness in five of the eight cyclones since it consisted of dry air originated from the Saharan desert. Second, the anticyclonic branch of the cold conveyor belt was not found in half of the MCs. Third, the dry air intrusion originated north of the cyclone and extended southward around it, unlike its common midlatitudinal northwest–southeast orientation. This is consistent with the relatively small baroclinic vertical-westward tilt of the cyclones analyzed.

The interannual variations and the spatial distribution of rainfall in the Mediterranean and semi-arid regions of Israel are analysed with respect to variations in the occurrence of the typical synoptic systems of the Eastern Mediterranean. The synoptic analysis is based on a daily, semi-objective synoptic classification (Alpert et al., 2004a). The study covers the months November–March, in which 90% of the annual rainfall is obtained, mostly resulting from Cyprus lows. The interannual variations of the rainfall are well explained by the synoptic types, and the occurrences of Cyprus lows are highly correlated with the rainfall. It was found that the daily and seasonal rainfall are highly dependent on the depth of the cyclone. Moreover, deep lows are more effective for the mountainous regions, due both to the enhanced orographic effect and to the fact that stronger winds, associated with deep lows, are more efficient in transporting rain-producing clouds from the Mediterranean Sea inland. The location of the cyclone determines the spatial distribution of the rain it produces over Israel. The cyclones located east of Cyprus were found productive mainly for the southern parts of the study region, while those located to the west and north of Israel were found productive for the north of the country. The high sensitivity of the rainfall to the location of the surface cyclones emphasizes the major role that lower level moisture transport plays in rain formation. Copyright © 2009 Royal Meteorological Society

The factors controlling lightning activity over central Israel and the adjacent Mediterranean Sea were studied. Potential predictors were correlated at 12-h intervals with total number of flashes. Since during the winter season lightning is generated in this region by Cyprus Lows, the data includes 283 observations on days in which this system prevailed for December to February, which covered four winters. The average lightning rate was 26.8 h-1, with a high standard deviation of 55.2 h-1. The total number of flashes at night exceeded the daytime number by 35%, in agreement with previous studies. The CAPE values were on the order of hundreds of J kg-1. A statistical linear multi-regression model was developed for the number of lightning flashes based on 35 atmospheric variables. The correlation between the modeled and the observed number of lightning flashes was 0.67, and 0.81 for the logarithm of the number of lightning flashes (log-lightning). This suggests that the lightning intensity responds exponentially to its governing factors. A linear multi-regression stepwise model for the log-lightning selected seven predictors as significant and yielded a correlation of 0.74. This model was validated by three holdout and three leave-one-out validation experiments. The composition and hierarchy of the significant predictors reflect the dominance of the thermodynamic factors, in particular instability, in determining lightning activity. Though thunderstorms are local or meso-scale phenomena, the synoptic-scale atmospheric variables were found to be powerful predictors for their intensity.

Some strong natural fluctuations of climate in the Eastern Mediterranean (EM) region are shown to be connected to the major tropical systems. Potential relations between EM rainfall extremes to tropical systems, e.g. El Niño, Indian Monsoon and hurricanes, are demonstrated. For a specific event, high resolution modelling of the severe flood on 3-5 December 2001 in Israel suggests a relation to hurricane Olga. In order to understand the factors governing the EM climate variability in the summer season, the relationship between extreme summer temperatures and the Indian Monsoon was examined. Other tropical factors like the Red-Sea Trough system and the Saharan dust are also likely to contribute to the EM climate variability.