Circulation Types and Their Influence on the
Interannual Variability and Precipitation Changes in
Greece
P. Maheras, C. Anagnostopoulou
Abstract
The data used in this study are daily precipitation amounts of 20 stations
equally distributed over Greece and daily (12 TU) 500hPa geopotential
heights, (20
0
to 65°N and 20
0
to 50
0
E) for the period 1958-1997. A decrease
of annual, winter and autumn precipitation over the whole country was
found, significant over several parts of Greece. An automatic classification
scheme of the atmospheric circulation affecting Greece, between 1958-1997,
is presented using spatial methods of topology and geometry. A short
description of the synoptic characteristics of the 14 classified circulation
types is given as well as the probability and the amount of precipitation
associated with each type. It is found that the six anticyclonic types
presented, during the rainy period (October to March), a cumulative
frequency equal to 39.2% and give a rather small ( 8.2%) contribution to the
"rainy" period precipitation amounts. On the other hand the four more
"rainy" circulation types, namely the C, C sw , C NW and C w together represent
37.8% of all the rainy period days and account more than 72% of the
observed daily precipitation. The results obtained accentuate the existence
of the strong links between the interannual variability of seasonal
precipitation and interannual variability of seasonal frequency of the
circulation types. The anomalous low or high precipitation amount during
the hydrological year show a strong relationship with the anomalous low or
high frequency of "rainy" circulation types. Multiple regression models
developed for the simulation of the annual cycle of rain days and the
corresponding precipitation, as well as selected extreme precipitation events
for Greece stations. It is concluded that there is an agreement between the
simulated annual cycle as well as the extreme rainfall events with the
observations, both in terms of rainy days and precipitation amounts. It
suggests that the precipitation regime in Greece including interannual
variability, trend and extremes can be explained in terms of variability of a
small number of circulation types patterns.
Interannual Variability and Precipitation Changes in
Greece
P. Maheras, C. Anagnostopoulou
Abstract
The data used in this study are daily precipitation amounts of 20 stations
equally distributed over Greece and daily (12 TU) 500hPa geopotential
heights, (20
0
to 65°N and 20
0
to 50
0
E) for the period 1958-1997. A decrease
of annual, winter and autumn precipitation over the whole country was
found, significant over several parts of Greece. An automatic classification
scheme of the atmospheric circulation affecting Greece, between 1958-1997,
is presented using spatial methods of topology and geometry. A short
description of the synoptic characteristics of the 14 classified circulation
types is given as well as the probability and the amount of precipitation
associated with each type. It is found that the six anticyclonic types
presented, during the rainy period (October to March), a cumulative
frequency equal to 39.2% and give a rather small ( 8.2%) contribution to the
"rainy" period precipitation amounts. On the other hand the four more
"rainy" circulation types, namely the C, C sw , C NW and C w together represent
37.8% of all the rainy period days and account more than 72% of the
observed daily precipitation. The results obtained accentuate the existence
of the strong links between the interannual variability of seasonal
precipitation and interannual variability of seasonal frequency of the
circulation types. The anomalous low or high precipitation amount during
the hydrological year show a strong relationship with the anomalous low or
high frequency of "rainy" circulation types. Multiple regression models
developed for the simulation of the annual cycle of rain days and the
corresponding precipitation, as well as selected extreme precipitation events
for Greece stations. It is concluded that there is an agreement between the
simulated annual cycle as well as the extreme rainfall events with the
observations, both in terms of rainy days and precipitation amounts. It
suggests that the precipitation regime in Greece including interannual
variability, trend and extremes can be explained in terms of variability of a
small number of circulation types patterns.