Assessment of climate extremes in the Eastern Mediterranean

Summary Several seasonal and annual climate extreme indices have been calculated and their trends (over 1958 to 2000) analysed to identify possible changes in temperature- and precipitation-related climate extremes over the eastern Mediterranean region. The most significant temperature trends were revealed for summer, where both minimum and maximum temperature extremes show statistically significant warming trends. Increasing trends were also identified for an index of heatwave duration. Negative trends were found for the frequency of cold nights in winter and especially in summer. Precipitation indices highlighted more regional contrasts. The western part of the study region, which comprises the central Mediterranean and is represented by Italian stations, shows significant positive trends towards intense rainfall events and greater amounts of precipitation. In contrast, the eastern half showed negative trends in all precipitation indices indicating drier conditions in recent times. Significant positive trends were revealed for the index of maximum number of consecutive dry days, especially for stations in southern regions, particularly on the islands.Current affiliation: National Observatory of Athens, Athens, Greece.     

Fluctuations of surface air temperature in the Eastern Mediterranean

Summary  Changes in surface air temperature during the last century are widely discussed among researchers in the field of climatic change. Using various techniques, we investigate trends and periodicity of surface air temperature series from eight meteorological stations in the Eastern Mediterranean. For the analysis, we use the Mann-Kendall rank test, low-pass filtering, autocorrelation spectral analysis and maximum entropy spectral analysis. The latter two tests are compared. The study is based on series over one hundred years in length for four stations, and over fifty years in length for the other four. Increasing and decreasing surface temperature trends were found. These trends, however, are only significant for Malta, Jerusalem, and Tripoli at the 99% confidence level (positive trend) and for Amman at the 95% confidence level (negative trend). We also found inter-decadal variations in surface air temperature, including a fairly regular quasi 20-year oscillation, although its amplitude varied between different cycles. A period of warming began around 1910 at all stations. During the 1970s, the annual mean temperature series exhibit warming, but this warming was not uniform, continuous or of the same order at all the stations. The results of the Autocorrelation Spectral Analysis and the Maximum Entropy Spectral Analysis are similar, pointing to the reliability of the results. The quasi-biennial oscillation (QBO) exists at all stations during both increasing and decreasing trends. Similarly, a broad maximum from 3–8 years (related to El Ni?o) is found at Malta, Athens, Jerusalem, Beirut, and Latakia. An inverse relationship between El Ni?o and the North Atlantic Oscillation with surface air temperature over the Eastern Mediterranean is found at a highly significant confidence level. Received November 15, 1999 Revised August 29, 2000     

Climate change and impacts in the Eastern Mediterranean and the Middle East

The Eastern Mediterranean and the Middle East (EMME) are likely to be greatly affected by climate change, associated with increases in the frequency and intensity of droughts and hot weather conditions. Since the region is diverse and extreme climate conditions already common, the impacts will be disproportional. We have analyzed long-term meteorological datasets along with regional climate model projections for the 21st century, based on the intermediate IPCC SRES scenario A1B. This suggests a continual, gradual and relatively strong warming of about 3.5–7°C between the 1961–1990 reference period and the period 2070–2099. Daytime maximum temperatures appear to increase most rapidly in the northern part of the region, i.e. the Balkan Peninsula and Turkey. Hot summer conditions that rarely occurred in the reference period may become the norm by the middle and the end of the 21st century. Projected precipitation changes are quite variable. Annual precipitation is expected to decrease in the southern Europe – Turkey region and the Levant, whereas in the Arabian Gulf area it may increase. In the former region rainfall is actually expected to increase in winter, while decreasing in spring and summer, with a substantial increase of the number of days without rainfall. Anticipated regional impacts of climate change include heat stress, associated with poor air quality in the urban environment, and increasing scarcity of fresh water in the Levant.     

On the association between synoptic circulation and wildfires in the Eastern Mediterranean

In the present paper cluster analysis of 2-month air mass back-trajectories for three contrasting fire and non-fire events is conducted (high, low, and zero burnt area). The large fire event displays an air mass history dissimilar to other events whereby a 39-day period of warm and dry chiefly northerly anticyclonic conditions is evident, before a week of warmer predominantly southwesterly cyclonic activity, immediately prior to ignition. The pressure level of these anticyclonic air masses is above 800 hPa for more than 75 % of the trajectory length; this region is above the principal moisture transport regime of 800 hPa altitude. Analysis of variance on the mean rate of change of potential temperature identified weak statistically significant differences between two air mass pairs regarding the large fire: anticyclonic and cyclonic air masses in both cases (p?=?0.038 and p?=?0.020). Such regularity of type and occurrence, approach pressure levels and statistically significant differences are not evident for the small and non-fire event air masses. Such understanding is expected to permit appropriate steps to be undertaken including superior prediction and improved suppression strategy.     

Rainfall, spring discharge and past human occupancy in the Eastern Mediterranean

In ancient times human activities were tightly related and sensitive to rainfall amounts and seasonal distribution. East Mediterranean settlements were concentrated around numerous small to large springs, such as the Judean Mountains area. The goals of this study were to determine (a) the sensitivity of total discharge, recession curve, and response time of such springs to annual precipitation patterns, and (b) how spring hydrology responds to series of drought or wet years and to transitions from drought to normal and/or wet episodes (and vice versa). These goals were achieved by setting a finite-element hydro-geological flow model for selected perched springs that characterize the numerous springs throughout the carbonate karst terrain in the Judean Mountains. In addition, we estimated the effect of proposed regional past climate changes on the springs; in so doing, we transfer climate change to community size, livelihood and economic strength that were highly dependent on agricultural productivity. The results of the hydro-geological model revealed that these mountainous communities had the potential to prosper during historically wetter episodes and were probably adapted to short-term variability in annual rainfall. However, moderate to extreme droughts lasting only a few years could have led to a partial or even total abandonment of the springs as focal sites of intensive agricultural production. Spring drying eliminated the primary cause for the location of settlement. This occurred simultaneously in numerous settlements around the mountains of the southern Levant and therefore, must have caused dramatic economic and societal changes in the entire region, perhaps even resonating afar.     

Sulfur budget above the Eastern Mediterranean: relative contribution of anthropogenic and biogenic sources

To access the relative contribution of anthropogenic and biogenic sulfur sources to the sulfur budget in the Eastern Mediterranean, an area characterized by very high nss-     levels, measurements of both wet and dry deposition of sulfur were performed at a remote area on the island of Crete (Finokalia) during a 3-yr period (1996–1999). The estimation of dry deposition is based on both gaseous sulfur dioxide (SO₂) and particulate phase non-sea-salt sulfate (nss-     ) and methane sulfonate (MSA) measurements. During the dry period, deposition of SO₂ from long-range transport is the main component of anthropogenic sulfur deposition in the area. The results of the wet and dry deposition obtained at Finokalia have been compared with DMS emission from seawater obtained during two yearly surveys (1997–1998) in the Cretan Sea. Our results indicate that the contribution from biogenic sources to the sulfur budget in the Eastern Mediterranean, although negligible during winter, can account for up to 26% during summer.     

Analyses of summer lightning activity and precipitation in the Central and Eastern Mediterranean

The lightning activity and precipitation in two 3-hour time intervals in the grid boxes of 0.25 × 0.25° over East and Central Mediterranean during the summer of 2005 and 2006 are analysed. The results show that the frequency distribution of the precipitation amount is shifted towards larger values for the cases with lightning as compared with the cases without lightning. It was found that the number of cases with 3-hour accumulated rainfall greater than 10 mm was bigger when lightning occurred (65%) than when it was absent (35%). Investigation of diurnal and spatial distributions of lightning shows that the afternoon flash density peak is associated mainly with lightning over the land, which is in accordance with the results of earlier works. The early morning flash density peak is associated mainly with flashes over the sea. High correlation coefficients (0.89 during the morning hours and 0.98 during afternoon) were found between rain rate (mm/h) and average flash density (fl/km²) when flash density is averaged in logarithmic intervals of rain rate.     

Decadal trends of main Eurasian oscillations and the Eastern Mediterranean precipitation

Summary ?The role of the two main European low-frequency oscillations – the East Atlantic/West Russian (EA/WR) and the North Atlantic Oscillation (NAO), in controlling the precipitation in the Eastern Mediterranean region is investigated based on the NCEP/NCAR reanalysis and the Israeli precipitation data for 1958–1998. The data on the EA/WR and NAO indices, received from the NCEP Climate Prediction Center, are also adapted. Composite mean sea level and precipitation anomaly patterns are constructed and analyzed. In addition to the widely investigated positive NAO trend, another, also positive EA/WR trend characterized atmospheric developments during the period. During NAO positive months, the EA/WR-associated positive SLP anomaly areas were shifted from the east Atlantic to southwest Europe. The areas were shifted to the north during the NAO-negative months and were located over central and northern Europe. This demonstrates that the use of fixed pressure NAO patterns may be not the optimum way to understand climate variability. Analysis of the NAO, EA/WR patterns, as well as that of their decadal trends, demonstrated a relationship between the main European oscillations and the EM precipitation. The results allow explanation of the observed reduction of the north Israeli precipitation by the EA/WR positive trend during the period. Received April 5, 2001; Revised February 14, 2002     

On the warming of intermediate and deep waters in the equatorial North Atlantic

In July 2000, a transatlantic hydrographic section was made on board the Russian R/V Akademik Ioffe in the northern equatorial region at ～6.5° N on the WOCE (World Ocean Circulation Experiment) A06 line. A significant warming in the layers of intermediate and deep waters in the interior eastern basin is determined from comparison of the section temperature data and those obtained on the WOCE A06 line in 1993. This result, together with the results of the previous studies, indicates a substantial warming of intermediate and upper deep waters above 2800–3000 m in the eastern equatorial North Atlantic during the second half of the 20th century. In the 1000–2000 m layer, temperature has increased by 0.13–0.14°C since 1957.     

Changes in Fire and Climate in the Eastern Iberian Peninsula (Mediterranean Basin)

Fire is a dominant ecological factor in Mediterranean ecosystems, and changes in the fire regime can have important consequences for the stability of our landscapes. In this framework I asked firstly, what is the trend in fire number and area burned in the eastern Iberian Peninsula, and then, to what extent is the inter-annual variability of fires determined by climatic factors. To answer these questions I analysed the meteorological data (temperature and precipitation) from 350 stations covering the eastern Iberian Peninsula (1950–2000), and the fire records for the same area (historical data, 1874–1968, and data from recent decades, 1968–2000). The results suggested a slight tendency towards decreasing summer rainfall and a clear pattern of increasing annual and summer temperatures (on average, annual temperatures increased 0.35 °C per decade from 1950 to 2000). The analysis of fire records suggested a clear increase in the annual number of fires and area burned during the last century; however, in the last three decades the number of fires also increased but the area burned did not show a clear trend. For this period the inter-annual variability in area burned was significantly related to the summer rainfall, that is, in wet summers the area burned was lower that in dry summers. Furthermore, summer rainfall was significantly cross-correlated with summer area burned for a time-lag of 2 years, suggesting that high rainfall may increase fuel loads that burn 2 years later.     

The role of the interaction between polar and subtropical jet in a case of depression rejuvenation over the Eastern Mediterranean

Summary In this paper, an attempt is made to investigate the synoptic-scale atmospheric conditions and dynamic processes leading to the rejuvenation of depressions or cyclogenesis over the Eastern Mediterranean during the cold period of the year. A case study analysis is carried out when the Polar Front Jet (PFJ) is positioned to the south of its normal seasonal position and interacts with the Subtropical Jet Stream (SJS), which is positioned to the north of its normal seasonal position. It was found that the vigorous rejuvenation of a northeastwards moving Atlas mountains depression on 15 March 1998 over Cyprus region is associated with an increase of the hydrodynamic instability due to the juxtaposition of a polar front jet streak to the subtropical jet stream. Furthermore, the rejuvenation is related to the combined effect of the direct and indirect cross vertical circulations appearing on the right side of the entrance of a polar jet streak and the left side of a subtropical jet streak exit, respectively.     

Monthly Synoptic Patterns Associated with Wet/Dry Conditions in the Eastern Mediterranean

Summary An investigation of the main features of large-scale synoptic patterns over Europe and the adjacent areas for extreme winter periods during 1980–1995 over the Eastern Mediterranean (EM) is performed. The NASA reanalysis data set is used to investigate composite sea level pressure (SLP), geopotential height of the 500 hPa surface (H-500) and precipitation–wet, normal and dry patterns for each month during the period October–March. It is found that the wet and dry cool seasons in the EM are associated with distinct SLP and H-500 anomaly patterns over Europe and the adjacent regions. During the dry spells large-scale positive SLP/H-500 anomaly areas prevail over Eastern Europe. A negative SLP anomaly is normally found during these periods over southwestern and Western Europe. During the wet cool seasons in the EM there are mainly negative SLP/H-500 anomaly areas over Eastern Europe to the north east of the EM. Positive SLP/H-500 anomalies are found over Western Europe. During wet months a trough zone between the Siberian and the Azorean Highs is positioned over the eastern part of the Mediterranean. During dry months the Siberian anticyclone is more intensive and the zone with low surface pressure is displaced to the central part of the northern Mediterranean. Received May 26, 1999 Revised August 26, 1999     

Origin and source regions of PM10 in the Eastern Mediterranean atmosphere

A set of daily PM₁₀ (n = 281) samples collected from April 2001 to April 2002 at a rural site (Erdemli), located on the coast of the Eastern Mediterranean, were analyzed applying Mass Closure (MC), absolute principal factor analysis (APFA) and Positive Matrix Factorization (PMF) to determine source contributions. The results from the three techniques were compared to identify the similarities and differences in the sources and source contributions. Source apportionment analysis indicated that PM₁₀ were mainly originated from natural sources (sea salt + crustal ≈ 60%) whilst secondary aerosols and residual oil burning accounted for approximately 20% and 10% of the total PM₁₀ mass, respectively. Calculations for sulfate showed that on average 8% and 12% of its total concentration were originated from sea salt and biogenic emissions, respectively. However, the contribution by biogenic emissions may reach up to a maximum of ~ 40% in the summer. Potential Source Contribution Function (PSCF) analysis for identification of source regions showed that the Saharan desert was the main source area for crustal components. For secondary aerosol components the analysis revealed one source region, (i.e. the south-Eastern Black Sea), whereas for residual oil, Western Europe and the western Balkans areas were found to be the main source regions.     

Intraurban variability of PM10 and PM2.5 in an Eastern Mediterranean city

The results of the first large scale chemical characterization of PM10 and PM2.5 at three different sites in the urban city of Beirut, Lebanon, are presented. Between May 2009 and April 2010 a total of 304 PM10 and PM2.5 samples were collected by sampling every sixth day at three different sites in Beirut. Observed mass concentrations varied between 19.7 and 521.2 μg m^? 3 for PM10 and between 8.4 and 72.2 μg m^? 3 for PM2.5, respectively. Inorganic concentrations accounted for 29.7–35.6 μg m^? 3 and 46.0–53.5 μg m^? 3 of the total mass of PM10 and PM2.5, respectively. Intra-city temporal and spatial variations were assessed based on the study of three factors: correlation coefficients (R) for PM and chemical components, coefficient of divergence (CODs), and source apportionment using positive matrix factorization (PMF). Based on R and COD of PM concentrations, the three sites appear homogeneous. However, when individual elements were compared, heterogeneity among sites was found. This latter was attributed to the variability in the percent contribution of biogenic and local anthropogenic source factors such as traffic related sources and dust resuspension. Other factors included the proximity to the Mediterranean sea, the population density and the topographical structure of the city. Hence, despite its small size (20.8 km²), one PM monitoring site does not reflect an accurate PM level in Beirut.     

ENSO-independent contemporaneous variations of anomalous circulations in the Northern and Southern Hemispheres: The polar-tropical seesaw mode

Using the NCEP/NCAR reanalysis and the ENSO indices from the Climate Prediction Center over the period 1978–2014, we have investigated the contemporaneous circulation variations in the Northern and Southern Hemispheres by performing the singular value decomposition analysis of sea level pressure anomalies (SLPA) after the ENSO signal is regressed out. It is found that there exists a polar-tropical seesaw mode (PTSM) that characterizes with the out of phase fluctuations of SLPA between the polar and tropical regions in the Northern and Southern Hemispheres in boreal winter. This PTSM explains 47.74% of the total covariance of SLPA and is almost independent of ENSO. It demonstrates a long-term trend and oscillation cycles of 2–3 and 4–6 yr. The long-term trend in PTSM indicates that the sea level pressure gradually decreases in the tropics and increases in the polar region with time. This PTSM looks roughly symmetric about the equator besides the seesaw pattern of SLPA between the tropics and polar region in each hemisphere. The disturbances in the geopotential height field in association with the PTSM shows baroclinic features in the tropics whereas equivalent barotropic features in the mid and high latitudes in the troposphere. The anomalous thermal forcing in the tropical region is possibly one of the factors facilitating the formation of this PTSM. Significant global precipitation and temperature anomalies related to the PTSM are observed. In the positive PTSM phase, precipitation and temperature are higher than normal in southern Europe and the Mediterranean and surrounding areas, but lower than normal in northern Europe and Siberia. Precipitation is higher than normal while temperature is lower than normal in Northeast Asia. Significant temperature and precipitation anomalies possibly occur in the regions of western China, northern India, parts of North America, parts of subtropical Africa, Maritime Continent, and Antarctic. These results are helpful for better understanding of the circulation variations and the mechanisms behind the interactions between the Northern and Southern Hemispheres and the related winter climate anomalies over globe.     

Global photosynthetically active radiation and its relationship with global solar radiation in the Eastern Mediterranean basin

Summary ?The relationship between global photosynthetically active radiation (PAR) and global solar radiation is studied with a 2-year data archive of hourly values H_PAR and H_SW of these irradiances obtained at Athalassa, Cyprus. These data are used to determine the temporal variability of H_PAR and its dependence on sky conditions. The seasonal variation of the ratio H_PAR/H_SW obtained from daily data ranges from 0.456 (during summer) to 0.451 (during winter) with an annual mean value of 0.454. The ratio increases from 0.454 to 0.467 (daily values) or from 0.460 to 0.501 (hourly values), as sky conditions change from clear to overcast. Finally, the effect of aerosol content on the H_PAR/H_SW ratio is found to incur substantial changes in the PAR fraction. Received June 27, 2001; revised April 17, 2002; accepted May 18, 2002     

A Comparison of Model Predictions to Observations of Seasonal Variability and Circulation in the Eastern Mediterranean

Expendable Bathythermograph (XBT) observations collected along a transect across the Eastern Mediterranean are compared with the respective predictions of thermocline structure and variability produced by the POSEIDON system's ocean circulation model. The observations, obtained in the framework of the Mediterranean Forecasting System project, cover a complete annual cycle, at a repetition rate of 1-2 transects per month, thus providing an excellent data set for estimating the model's skill to forecast seasonal variability and mesoscale circulation in the upper 450 m of the ocean. The comparison has revealed that the model adequately predicts the seasonal cycle of the evolution of the thermocline but tends to generate less steep thermoclines than observed. Furthermore, the mesoscale circulation is not accurately predicted. For the latter, data assimilation is considered a necessary step towards the improvement of the system.     

Impact of data assimilation of glider observations in the Ionian Sea (Eastern Mediterranean)

Glider observations of temperature, salinity and vertically averaged velocity in the Ionian Sea (Eastern Mediterranean Sea), made in the period October 2004–December 2004, were assimilated into an operational forecasting model together with other in situ and satellite observations. The study area has a high spatial and temporal variability of near surface dynamics, characterized by the entrance of the Atlantic Ionian Stream (AIS) into the Northern Ionian Sea. The impact of glider observations on the estimation of the circulation is studied, and it is found that their assimilation locally improves the prediction of temperature, salinity, velocity and surface elevation fields. However, only the assimilation of temperature and salinity together with the vertically averaged velocity improves the forecast of all observed parameters. It is also found that glider observations rapidly impact the analyses even remotely, and the remote impacts on the analyses remain several months after the presence of the glider. The study emphasizes the importance of assimilating as much as possible all available information from gliders, especially in dynamically complex areas.