P. Maheras

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.

Monthly mean pressure reconstructions for Europe for the 1780–1995 period

Monthly grid-point pressure data are reconstructed from station records of pressure for Europe since 1780. The region encompasses 35-70°N to 30°W-40°E. The reconstructions are based on a principal components regression technique, which relates surface pressure patterns to those of the station pressure data. The relationships are derived over a calibration period (1936-1995) and the results tested with independent data (the verification period, 1881-1935). The reconstructions are of excellent quality, although this is slightly lower for regions with poor station coverage in the early years, particularly during the summer months. The reconstructions are compared with other monthly mean pressure maps produced by Lamb and Johnson (1966) for the years 1780-1872 and by Kington (1980, 1988) for 1781-1785. Both of these map series show systematic biases relative to the present reconstructions.

WARM AND COLD MONTHLY ANOMALIES ACROSS THE MEDITERRANEAN BASIN AND THEIR RELATIONSHIP WITH CIRCULATION; 1860-1990

Anomalously wet and dry months in the Mediterranean basin were identified during the period 1860–1990 from observations at five stations located along the west-east axis of the Mediterranean basin (Barcelona, Florence, Malta, Athens and Jerusalem), supplemented by data from Madrid and Lisbon. Wet and dry months were characterized by hydric indices (HI) based on values of the standardized precipitation anomalies. Different patterns of anomalously wet and dry months were qualitatively identified on the basis of the spatial distributions of the hydric indices. The standardized sea level pressure values at 56 grid points in the domain 35° N–65° N, 30° W–40° E, for each of the anomalously wet and dry months, were subjected to T-mode Principal Component Analysis.

Monthly mean pressure reconstruction for the Late Maunder Minimum Period (AD 1675–1715)

The Late Maunder Minimum (LMM; 1675-1715) delineates a period with marked climate variability within the Little Ice Age in Europe. Gridded monthly mean surface pressure fields were reconstructed for this period for the eastern North Atlantic-European region (25°W-30°E and 35-70°N). These were based on continuous information drawn from proxy and instrumental data taken from several European data sites. The data include indexed temperature and rainfall values, sea ice conditions from northern Iceland and the Western Baltic. In addition, limited instrumental data, such as air temperature from central England (CET) and Paris, reduced mean sea level pressure (SLP) at Paris, and monthly mean wind direction in the Oresund (Denmark) are used. The reconstructions are based on a canonical correlation analysis (CCA), with the standardized station data as predictors and the SLP pressure fields as predictand. The CCA-based model was performed using data from the twentieth century. The period 1901-1960 was used to calibrate the statistical model, and the remaining 30 years (1961-1990) for the validation of the reconstructed monthly pressure fields. Assuming stationarity of the statistical relationships, the calibrated CCA model was then used to predict the monthly LMM SLP fields. The verification results illustrated that the regression equations developed for the majority of grid points contain good predictive skill. Nevertheless, there are seasonal and geographical limitations for which valid spatial SLP patterns can be reconstructed. Backward elimination techniques indicated that Paris station air pressure and temperature, CET, and the wind direction in the Oresund are the most important predictors, together sharing more than 65% of the total variance. The reconstructions are compared with additional data and subjectively reconstructed monthly pressure charts for the years 1675-1704. It is shown that there are differences between the two approaches. However, for extreme years the reconstructions are in good agreement.

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.

Climate of the Mediterranean: synoptic patterns, temperature, precipitation, winds and their extremes

This chapter considers a set of issues related to the synoptic climatology of the Mediterranean region (MR). The main Northern Hemisphere teleconnections affecting the MR and their role on temperature, precipitation, and atmospheric cyclones are described. The characteristics of the cyclones in the MR are presented. The role of teleconnections and atmospheric regimes on temperature and precipitation is discussed. The content includes extremes of temperature, precipitation, wind, and storminess (considering also marine aspects such as waves and storm surges).

The Impact of the Eastern Mediterranean Teleconnection Pattern on the Mediterranean Climate

Abstract The objective of this study is to investigate the impact of the eastern Mediterranean teleconnection pattern (EMP) on the present and future climate of the eastern Mediterranean during winter. For the present climate, daily precipitation and maximum and minimum surface temperature station data are employed for the period of 1958–2003. For the future climate, datasets of the same parameters are derived from the Hadley Centre Regional Climatic Model (HadRM3P) for the period of 2070–2100, using two Intergovernmental Panel on Climate Change (IPCC) emission scenarios for the evolvement of the future atmospheric concentrations of greenhouse gases. The investigation of the impact was based on the regularized canonical correlation analysis (RCCA), while qualitative estimations were performed for each phase of the pattern. It was found that the pattern indeed affects the mean winter patterns of temperature, precipitation, and their extreme events with inverse impacts between the two phases. More specifica...

Precipitation in the Central Mediterranean during the last century

SummaryMonthly precipitation data from 10 stations (Patras, Corfu, Hvar, Trieste, Venice, Florence, Rome, Naples, Catania and Malta) in the Central Mediterranean area are used for a period of 95 years (1894–1988). The homogeneity of these precipitation time series is tested and their statistical characteristics are analysed. An abrupt climatic change is found at Naples and Rome. The application of Principal Component Analysis (PCA) has yielded three groups of stations where the precipitation data indicate similar fluctuations. Group A includes the stations situated along the coasts of the Ionian and Adriatic seas and the station Naples, while Group B includes the Northern Italian stations and Group C includes the stations at Catania and Malta. In all three groups maximum precipitation was observed during the 1930s. The periodicities of the scores of the significant components have been studied by spectral analysis and significant periodicities of 13.6, 3.5 and 2.2 years were found. Finally, a discussion of the relationships between these precipitation fluctuations and circulation types over the Mediterranean is presented.

Climatological aspects of extreme precipitation in Europe, related to mid-latitude cyclonic systems

Climatic aspects of extreme European precipitation are studied. Daily pluviometric data from 280 stations across Europe, covering the period from 1958 to 2000, are used. First, the criteria for extreme precipitation cases and episodes are communicated using threshold and spatial definitions. The cases and episodes meeting these criteria are grouped according to their area of appearance. Most of them are located in three major areas: Greece, the Alps, and the Iberian Peninsula. The existence of trends in the annual and seasonal time series of these extreme events is examined. Decreasing trends are found in most of the cases, for Greece, the Iberian Peninsula, and Europe, as a whole. The Alps present a different behavior, with no trend at all in the southern part, and a possible increasing trend in the northern part. Finally, the positive impact of altitude in the frequency of occurrence of extreme precipitation episodes in Europe is discussed.

A factorial analysis of Mediterranean precipitation

SummaryPrincipal Components Analysis of 80 stations dispersed all over the Mediterranean (coastal and of low altitude) and 12 mean monthly amounts of precipitation collected at these stations is discussed. A natural interpretation of the first 4 components is given, followed by an application of the technique of classification according to ascending hierarchy on the matrixA1 =I×J1 , whereJ1 = 4 (the first four components of the previous analysis). Homogeneous groups (classes) of stations are formed (4 classes and 8 sub-classes), which are also described. A discussion follows concerning the influence of atmospheric meridional circulation on the surface and the upper layers, as well as that of geographic factors on the distribution and annual variability of precipitation over the Mediterranean.ZusammenfassungEs wird eine Anwendung der Komponentenanalyse auf eine DatenmatrixA =I×J vor geschlagen, wobeiI über 80 Stationen verteilt im ganzen Mittelmeergebiet (Küsten stationen in geringer Seehöhe) varüert undJ die 12 mittleren monatlichen Niederschlagssummen dieser Stationen sind. Es wird eine natürliche Interpretation der ersten 4 Komponenten gegeben, gefolgt von einer Anwendung der Klassifikationstechnik der aufsteigenden Hierarchie auf die MatrixAI =I×J1 , woJ1 = 4 (die ersten 4 Komponenten der vorhergehenden Analyse). Homogene Gruppen (Klassen) von Stationen werden gebildet (4 Klassen und 8 Unterklassen) und beschrieben. Es folgt eine Diskussion des Einflusses der meridionalen atmosphärischen Zirkulation auf die Oberflächen- und darübergelegenen Schichten, sowie des Einflusses geographischer Faktoren auf die Verteilung und den Jahresgang des Niederschlags im Mittelmeergebiet.