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Winter (October to April) rainfall in Israel is caused mostly by migrating Mediterranean cyclones but certain rain situations are accompanied by a low pressure trough extending northward from the southern Red Sea towards the Eastern Mediterranean (EM) and the Levant. This system, the Red Sea Trough (RST) is one of the most frequent surface atmospheric circulation patterns over the southeastern Mediterranean, but most of the RSTs are not accompanied by rain. This paper presents a synoptic climatological comparative analysis between rain situations associated with RSTs, and those not connected with RSTs (non-RST rain, NRR). The RST situations were identified objectively with the aid of a new algorithm applied to the GEOS-1 reanalysis gridded data set from NASA, for the period of March 1985-- November 1995. Results show that RST rain is accompanied by a relatively narrow 500-hPa trough, located west of the Israeli coast-line and characterized by a deep southward penetration, while Non-RST-associated rain (NRR) is accompanied by a wider upper trough, located over the Israeli coast-line with a shallower southward penetration. We found a south-southwesterly wind vector anomaly at 200 hPa over Israel during RST rains, while during NRRs a similar wind vector anomaly pattern is observed east of Israel. There is a divergence center over, or a few degrees east of Israel during RST rains, while NRR is associated with a divergence value of nearly zero over Israel and a maximum divergence center located east of Israel. The moisture flux during NRR at 700 and 900 hPa is from the Mediterranean, while during RST rain there is a south-westerly moisture flux at 700 hPa from equatorial Africa to Israel and vicinity. A steeper temperature lapse-rate between 950-500 hPa was found during RST rain compared with NRR, resulting from a combination of cooling aloft together with heating near the surface. [ABSTRACT FROM AUTHOR]

The intraseasonal oscillations (ISOs) in sea currents in the easternMediterranean Sea near the central coast of Israel were analyzed by examining the velocity components of the sea currents at different depths as measured by acoustic Doppler current profilers located at various depths between 0 and 675 m. The total period covered by the observations was from December 2016 toMay 2018. Prominent intraseasonal oscillations, much stronger than tidal velocity components, were observed in the upper part of the sea, at 30-70 m. The amplitudes of these oscillations are between 4 and 10 cm s-1 and their periods are 7, 11, 22, and 34-36 days. The strongest oscillations are found in the boreal winter. The ISOs in the sea currents were apparently induced by corresponding oscillations found in atmospheric wind velocity over the eastern Mediterranean at the surface and at 500 and 250 hPa, as suggested by the high correlations, 0.6-0.9, between the wind velocity components of the oscillatory modes in the atmosphere and the velocity component of the oscillatory modes in the sea currents with similar periods. We propose that the source of the ISOs in the atmosphere over the eastern Mediterranean is the South Asian jet wave train. The track of this wave train passes over the eastern Mediterranean, and the periods of the ISOs in the wave train are in the same band as the oscillations found here. The wave train is equivalently barotropic and strongest in the upper troposphere. This property of the wave train can explain the high correlation found between the oscillatory modes of wind velocity at 250 or 500 hPa and those in the sea currents. In all the cases besides the 7-day oscillatory mode, the significant oscillatory modes found at 250 or 500 hPa are also significant in the velocity components of the surface wind. [ABSTRACT FROM AUTHOR]

Abstract: The Arctic Oscillation (AO) has been found in previous studies to be a major synoptic factor affecting the climate of many regions in the high and mid-latitudes. This paper demonstrates the physical process by which the AO affects the climate of the Eastern Mediterranean basin, with a focus on precipitation in Israel as a case study. It is shown that a trend of increasing AO is associated with a substantial decrease of winter precipitation from the Iberian Peninsula, though Italy, Greece, Turkey and Cyprus, as well as Lebanon, Syria and also the northern parts of Israel. Winter rain is slightly increased in the southern coast of the eastern half of the Mediterranean Sea. The immediate meteorological causes are shown to be a larger northerly component of the flow over the Mediterranean Sea, associated with a decreasing relative humidity and stability, except over the southern coast, where the air mass has the longest track over the relatively warm water. We suggest here that the observed changes in air flow that drives the precipitation trends can be explained by shifts in the AO that can be partially explained by increasing greenhouses gases. Results from the IPCC multi climate models show that the AO will continue to increase during the 21st century. This increase may lead to a continuation of the trends discussed here. The importance of the analysis provided here is in pointing out the possibility that processes that have been predicted by global warming and changes in global circulation have already started to affect precipitation and major water resources in the Mediterranean basin. [Copyright &y& Elsevier]

The sea breeze (SB) is a thermally induced boundary layer phenomenon that occurs at coastal locations throughout the world. Previous satellite remote sensing studies used low-level clouds formed over the sea-breeze convergence zones to identify the SB. In this study continuous thermal infrared data from a geostationary satellite (Meteosat Second Generation) and concurrent field measurements were used to detect and characterize the SB in clear sky conditions during the summer. Surface data (wind speed and direction) from 11 sites over Israel for ten summer days in July 2010 for three different synoptic circulation categories were selected. In order to assess the impact of the synoptic induced flow on the SB, we looked for the best agreement between surface and satellite SB timing. An independent classification of synoptic categories performed for the ten summer days revealed two distinct patterns of the SB. During weak horizontal pressure gradient (Weak Persian Trough and High to the West), which enables full development of the SB, the timing of the SB from satellite and field measurements were well correlated (R² = 0.75), as compared to unfavorable atmospheric conditions (Deep Persian Trough) yielding lower value (R² = 0.5). The SB was identified by surface measurements in an earlier time of the day, with respect to the satellite column integrated measurements. Visualizing timing of the SB retrieved from satellite data enabled distinction of SB behavior under different synoptic categories. Over desert regions the strong thermal contrast enables detection of the SB even under suppressing synoptic conditions (Deep Persian Trough). This method enables detection and timing of the SB over desert regions where clouds and field measurements are scarce, and is applicable worldwide. [ABSTRACT FROM AUTHOR]