74 research outputs found
Extreme precipitation related to circulation types for four case studies over the Eastern Mediterranean
International audienceThe analysis of the links between the extreme precipitation and the associated atmospheric conditions through an aloft circulation type approach at the 500-hPa geopotential level, for the time period of 1958?2000, is the main motivation for the present study. Four stations in the eastern Mediterranean (17.5° E to 37.5° E and 30° N to 40° N) were selected as separate case studies. The extreme precipitation conditions were defined by the two most widely used indices: the 90th and 95th percentiles. It was found that two cyclonic types (C ? with its centre over the station and Cwsw ? with its centre at the WSW of the station) were mainly associated with extreme rainfall conditions for all the selected stations. Generally, these circulation types are deepening during days with extreme precipitation in comparison to the general mean field of the type
Cyclones in the Mediterranean region: present and future climate scenarios derived from a general circulation model (HadAM3P)
International audienceIn this paper, an attempt is made to assess and evaluate the skill of the Hadley Center atmospheric General Circulation Model (HadAM3P) in generating successfully the frequency and intensity of severe cyclones (<1000 hPa) in the Mediterranean region. The cyclonic occurrence is studied in three regions of enhanced cyclonic activity: Gulf of Genoa, Southern Italy and Cyprus. It was found that the HadAM3P predicts a future decrease of the frequency of the severe cyclones at the SLP level, but the future cyclones will be more intense (deeper), especially at the 500 hPa level
Quantifying uncertainties in precipitation: a case study from Greece
The main objective of the present study was the examination and the quantification of the uncertainties in the precipitation time series over the Greek area, for a 42-year time period. The uncertainty index applied to the rainfall data is a combination (total) of the departures of the rainfall season length, of the median data of the accumulated percentages and of the total amounts of rainfall. Results of the study indicated that all the stations are characterized, on an average basis, by medium to high uncertainty. The stations that presented an increasing rainfall uncertainty were the ones located mainly to the continental parts of the study region. From the temporal analysis of the uncertainty index, it was demonstrated that the greatest percentage of the years, for all the stations time-series, was characterized by low to high uncertainty (intermediate categories of the index). Most of the results of the uncertainty index for the Greek region are similar to the corresponding results of various stations all over the European region
The anomalous high temperatures of November 2010 over Greece: meteorological and climatological aspects
This paper presents an analysis of the exceptionally high maximum (<i>T</i><sub>max</sub>) and minimum (<i>T</i><sub>min</sub>) temperatures which occurred during November 2010 and affected the entire Greek region. This severe "warm cold-season spell" was unusual because of its prolonged duration and intensity for the entire month and particularly the maximum temperature anomalies, which in comparison with the 1958–2000 climatological average, exceeded 5 °C at several stations. Comparing the observed record with future projections from three regional climate models revealed that <i>T</i><sub>max</sub> and <i>T</i><sub>min</sub>, on several days in November 2010, exceeded the 90th percentile of the simulated data. An examination of the atmospheric – synoptic conditions during this period showed that the anomalous high temperatures could probably be related to the negative phase of the Eastern Mediterranean Pattern (EMP), with an intense pole of negative anomalies located over the British Isles, and to the east, a second pole of positive anomalies, centred over the Caspian Sea. Finally, an attempt is made to further investigate the mechanisms responsible for this phenomenon, for example, the thermal forcing in the tropics (Niño 3 or Niño 3.4)
Cyclones in the Mediterranean region: Present and future climate scenarios derived from a general circulation model (HadAM3P)
In this paper, an attempt is made to assess and evaluate the skill of the Hadley Center atmospheric General Circulation Model (HadAM3P) in generating successfully the frequency and intensity of severe cyclones (<1000 hPa) in the Mediterranean region. The cyclonic occurrence is studied in three regions of enhanced cyclonic activity: Gulf of Genoa, Southern Italy and Cyprus. It was found that the HadAM3P predicts a future decrease of the frequency of the severe cyclones at the SLP level, but the future cyclones will be more intense (deeper), especially at the 500 hPa level
An evaluation of a general circulation model (GCM) and the NCEP-NCAR reanalysis data for winter precipitation in Greece
In this study, an attempt is made to evaluate winter precipitation data derived from the general circulation model (GCM) - HadAM3P (atmospherical circulation model - Hadley Center) and from the National Center for Environmental Prediction-National Center of Atmospheric Research (NCEP-NCAR) reanalysis project for the period 1960-1990. These data sets are compared on a seasonal basis (winter) with observational data derived from stations over Greece. More specifically, the suitability of their average distributions and their spatial and temporal variability is examined. The methods used are principal component analysis (PCA) and canonical correlation analysis (CCA). The connection between the precipitation data sets and five cyclonic circulation types, from a daily catalogue, is also studied. With respect to the spatial distribution of the mean precipitation amounts, NCEP data show better agreement with the observational data compared to the modeled data. However, both NCEP and HadAM3P values are generally underestimated. Moreover, it seems that the HadAM3P is able to capture and reproduce quite satisfactorily the relationship between the precipitation data and the circulation types, but inadequately simulates the impact of orography and the Aegean Sea. Finally, the links between the precipitation variability in Greece and the European 500 hPa variability given by CCA seem to be fairly well reproduced by the model. Copyright © 2006 Royal Meteorological Society
The anomalous low and high temperatures of 2012 over Greece – an explanation from a meteorological and climatological perspective
2012 was the hottest year in Greece on the basis of the available record
dating back to 1958, displaying at the same time the widest annual
temperature range. During the summer and autumn months, numerous regions in
the domain of study experienced record-breaking maximum and minimum
temperatures. Conversely, the winter period was particularly cold and January
one of the coldest months over the last 55 yr. The analysis of the cold
period indicates that the synoptic conditions resemble the positive phase of
the Eastern Mediterranean Pattern (EMP). The predominance of these cool
conditions seems to be related primarily to an intense NNW or NNE atmospheric
circulation, as a consequence of the positive EMP phase. Moreover, the
reduction in the floating sea ice emerges as a key driver of the formation of
a low-pressure pattern and the reinforcement of the trough south of
Scandinavia, which in turn strengthened the Siberia High east of the trough.
This reinforcement resulted in a blocking pattern and in favorable conditions
for the EMP formation. The atmospheric circulation during the prolonged
high-temperature period resembles, respectively, the negative phase of North
Sea–Caspian Pattern teleconnection. The observed positive pole, in
conjunction with the strong southwestern circulation, results in temperature
increases and in the development of a smooth pressure field that contributes
to the weakening of the Etesian winds and therefore to calm conditions over
the continental areas
Relationship between atmospheric circulation types over Greece and western-central Europe during the period 1958-97
An attempt is made to examine the relationship of the surface circulation prevailing over Europe with the corresponding surface and 500 hPa over Greece by correlating Lamb weather types for western Europe and Hess and Brezowsky (HB) types for central Europe with those derived from a new classification scheme for the Greek area. It was found that it was difficult to formulate rules controlling the frequency distributions of the circulation types over the Greek area in relation to the circulation over western and central Europe. However, statistically significant correlation was found between certain types with high frequency, which is greater between Lamb and HB types with the surface circulation types over the Greek area, compared with 500 hPa circulation types. For the most correlated pairs, seasonal composites of mean sea-level pressure and 500 hPa geopotential height anomalies demonstrated that the formation of the circulation types over the Greek area depends on the extent, intensity of the anticyclonic or cyclonic centres, air mass characteristics, and stability profile in the lower troposphere over the regions examined, but especially over the central and eastern Mediterranean. Copyright © 2004 Royal Meteorological Society
ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION BY OVER-THE-TOP REPAIR COMBINED WITH POPLITEUS TENDON PLASTY
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