H. Kutiel

CIRCULATION AND EXTREME RAINFALL CONDITIONS IN THE EASTERN MEDITERRANEAN DURING THE LAST CENTURY

Dry and wet years, seasons, and sequences at four eastern Mediterranean stations, Thessaloniki, Athens, Nicosia, and Jerusalem, were identified and compared for circulation types. The definition of dry/wet year or season was done by means of z scores. A year or a season was defined as dry when z≤− 0ċ5 and as extremely dry when z≤−1ċ5, similarly as wet when z≥ 0ċ5 and as extremely wet when z\≥1ċ5. Dry/wet sequences at each station were identified and their timings were compared. Circulation types were defined by means of zonal and meridional indices calculated independently in two regions. Region 1: ϕ=35° N and 55°N; λ=10°E and 30°E for Thessaloniki and Athens. Region 2: =30°N and 50°N; λ=20 deg;E and 40°E for Nicosia and Jerusalem. Time series of both indices in both regions were calculated and are discussed. Correlations between the z scores of the precipitation with both indices were calculated. Prevailing flows for dry and wet conditions for each of the stations were defined and are discussed.

Spatial and temporal variations in the temperature regime in the Mediterranean and their relationship with circulation during the last century

Temperatures in 22 grid boxes across the Mediterranean were subjected to principal component analysis (PCA). Four factors were retained, dividing the Mediterranean into four different subregions in each season (only three in spring). PC1 and PC2 defined the eastern and western Mediterranean, respectively, in all seasons. PC3 defined the central Mediterranean in summer and autumn, the Balkans in winter and a combination of both regions in spring. Finally, PC4 defined the Balkans in summer and autumn and the central Mediterranean in winter. Time series analysis of PC scores enabled the determination of discontinuity time points when abrupt temperature changes occurred. The pressure patterns associated with high temperatures in each region were defined over a major part of the northern hemisphere. The circulation associated with each factor in each season was determined from meridional (MI) and zonal (ZI) circulation indices. A seesaw-like oscillation, namely the Mediterranean Oscillation, was found between the eastern and western Mediterranean. Favourable circulation for high temperatures in one part of the Mediterranean is associated with unfavourable circulation in the other part and vice versa. Copyright

New Evidence for The Role of The North Sea — Caspian Pattern on The Temperature and Precipitation Regimes in Continental Central Turkey

Abstract Monthly mean temperatures and monthly precipitation totals at six stations from theCappadocian sub‐region in the continental Central Anatolia region of Turkey were analysed in order to detect the response of the variability in the Cappadocian climate to the variability of the North Sea ‐ Caspian Pattern Index (NCPI). Most of this region is classified as semi‐arid according to various climate classifications. Time series of the NCPI for the period 1958–1998, enabled each month from October toApril to be classified as belonging to the negative phase NCP(−), positive phase NCP(+) or neutral conditions. Monthly temperature and precipitation series for each station were analysed separately for both phases. Temperatures during NCP(−) were found to be considerably higher than during NCP(+). These results confirm previous results regarding the role of the NCP in controlling the temperature regime in that region. No significant differences were found in precipitation totals between the two phases, but major differences were identified in their spatial structure.

Circulation indices over the Mediterranean and Europe and their relationship with rainfall conditions across the Mediterranean

SummaryCirculation types were identified by means of zonal and meridional indices calculated separately over ten different regions of 20° × 20° over the Mediterranean and Europe. Seasonal and annual rainfall totals in four stations Lisbon, Luqa (Malta), Athens and Jerusalem, were compared with circulation types for the period 1873–1991. Correlation coefficients of circulation indices with precipitation, for each station in each season were calculated and mapped.An oscillation in the meridional index during the winter and the spring, between the western and eastern Mediterranean, was detected.Time series analysis of the circulation indices demonstrates a significant reduction in zonality and an increase in meridionality mainly in spring and in summer, over most of the study area.

The multimodality of the rainfall course in Israel, as reflected by the distribution of dry spells

SummaryAn attempt to find fluctuations in the annual course of the rainfall in Israel was done, based on the distribution of dry spells. A trimodal rainfall course was found, with three minima and two secondary maxima between them. Each minimum represents a rainier period, while a maximum means a drier period. Different timing in the occurrence of the minima and maxima in different parts of the country is related to the fact that each region is affected predominantly by different rainfall systems.ZusammenfassungEs wurde ein Versuch unternommen, Fluktuationen im Jahresgang des Niederschlags in Israel zu finden, der auf der Verteilung von Trockenperioden beruht. Es wurde eine trimodale Verteilung gefunden - mit drei Minima und zwei Maxima dazwischen. Jedes Minimum entspricht einer regnerischen Periode, jedes Maximum einer trockenen. Das zeitlich verschiedene Auftreten der Maxima und Minima in verschiedenen Landesteilen steht damit in Zusammenhang, daß jede Region von verschiedenen Niederschlagsregimen beeinflußt wird.

A LATE QUATERNARY PALEOENVIRONMENTAL SEQUENCE FROM DOR, CARMEL COASTAL PLAIN, ISRAEL

Abstract The 10.5 m deep “D-Dor” core was taken at Dor (Tantura Lagoon), on the Carmel coastal plain, Israel. The established chrono-stratigraphic sequence (based on x-ray radiographs, and both luminescence and radiocarbon dating) covers the last about 26,000 years. It provides the paleoenvironmental framework for the transition from hunter–gathering to agriculture in the Levant. Three clay units were identified, overlying kurkar (calcareous sandstone) and covered by 6.3 m of sand. The bottom clay unit is a paleosol. Pollen was not preserved in this unit. Gray clay (the top of which was dated to about 12,000 cal. YBP) was deposited, overlying the paleosol, in a wetland environment. Pollen was preserved only in the upper part of this unit. It indicates a slightly drier climate than todays, probably correlative with the Younger Dryas. At the beginning of the Holocene, between 10,300 and 9,550 cal. YBP, a new marsh originated, depositing dark clay. High concentrations of well-preserved pollen allowed the reconstruction of several fluctuations in humidity. When the marsh was first formed, precipitation was higher than today, and oak maquis was more extensive in the area. The date of the earliest submerged Pre-Pottery Neolithic settlement embedded in its upper part indicates that the marsh dried out no later than 9,400–8,550 cal. YBP. Around 5,000 years ago, long after the Early Holocene marsh had dried up, sand began to accumulate in the region as a consequence of the Holocene sea level rise, covering several submerged Neolithic settlements off the Carmel coast.

Recent variations in 700 hPa geopotential heights in summer over Europe and the Middle East, and their influence on other meteorological factors

SummaryRecent variations in atmospheric circulation in the eastern Mediterranean are analyzed and discussed. Interdecadal differences in mean monthly 700 hPa geopotential heights for June, July, and August in the period 1951–1980 show a trend of decreasing pressure of the subtropical high pressure belt over the Sahara Desert. The decrease is observed in the magnitude of the high pressure, in its areal extent, and in its northward position. Broader variations in other meteorological variables, such as rainfall regimes, temperature fields, wind variability, and evapotranspiration rates, are discussed in relation to variations in pressure fields and in indices of circulation such as the North Atlantic Oscillation. The trend from the 1950s through the 1970s was towards more temperate summer climate in the region.

Recent spatial and temporal variations in mean sea level pressure over Europe and the Middle East, and their influence on the rainfall regime in the Galilee, Israel

SummaryA comparison of maps of mean sea level pressure (MSLP) for two normal peridos enabled the detection of variations in MSLP over Europe and the Middle East. Even though a general pattern is evident on the maps for each month in both periods, differences in the magnitude of the values were detected. Plotting these differences permitted the identification of regions with the greatest variations and determination of the anomaly flow between the two periods. A polynomial curve fitted to the seasonal record of the MSLP at 35 selected points for each period allowed identification of temporal variations in MSLP. The main temporal change between the period 1931–60 and the period 1951–80 was a delay in the development of a high pressure over Siberia in the latter period. Changes in horizontal pressure differences (CHPD) between Byelorussia in the Soviet Union and the Sahara Desert related previously described rainfall variations to those pressure variations.

The distribution of Autumnal Easterly Wind Spells Favoring Rapid spread of forest wildfires on Mount Carmel, Israel

Wildfires became a severeecological and financial problem in Israel during the last few years. A significant increase in the incidence of severe wildfires in natural shrublands and planted forests as arson was observed. On 19–20. 9. 89 a large wildfire ignited as an act of terrorism, devastated large parts of Mt. Carmel forests.Weather conditions during a wildfire have an important role in the determination of the rate of spread of the fire. This depends mainly on the availability of dry matter and the wind speed. Two factors that reach their optimum at the end of the summer in September and October during Sharav episodes. The distribution of easterly wind spells associated with Sharav events is considered. The results show that there is no climatic limitation to a spread of a wildfire of the same order of magnitude as the last one, every year.

Spatial coherence of monthly rainfall in Israel

SummaryCorrelations of monthly totals from different stations were used to identify coherent regions in terms of parallel fluctuations of rainfall amounts from year to year. One coherent region was found during the fall, three during the winter and two during the spring. An attempt to explain the existence of those coherent regions with different known features of the rainfall regime and to relate them to different synoptic systems, was done.ZusammenfassungZur Feststellung von hinsichtlich paralleler Schwankungen der Niederschlagsmengen von Jahr zu Jahr zusammenhängender Gebiete werden Korrelationen zwischen monatlichen Mengen verschiedener Stationen verwendet. Von solchen zusammenhängenden Gebieten wurden eines im Herbst, drei im Winter und zwei im Frühling festgestellt. Die Erklärung der Existenz solcher zusammenhängender Gebiete wurde mit Unterschieden charakteristischer Merkmale von Niederschlagsregimes und mit Beziehungen zu verschiedenen synoptischen Systemen versucht.