Chr. Anagnostopoulou

Drought Index Over Greece as Simulated by a Statistical Downscaling Model

Drought is the least understood of all weather phenomena, since it differs from other natural hazards in several ways. The hazardous of drought can be better understood by analyzing drought indices. The Standardized Precipitation Index (SPI) has been one of the most widely used indices for drought studies, as it can provide satisfactorily results for the appearance, variability and intensity of drought. Moreover, SPI has been developed in order to quantify and record drought episodes on multiple time scales (3 months, 6 months, 1 year, 2 years). In the present study a statistical downscaling technique based on artificial neural network was employed for the estimation of SPI over Greece. The aim of the study is to evaluate the simulated SPI index against the observational one. The performance of the statistical downscaling model is assessed utilizing biases, standard deviation and correlation coefficient between observed and simulated indices. An overestimation of the simulated mean SPI indices accompanied by a decrease in standard deviation is evident for all stations and all time periods. The reproduction of SPI3 and SPI6 for winter, spring seasons display rather promising results.

ECHAM5/MPI General Circulation Model Simulations of Teleconnection Indices Over Europe

In this paper, a study of potential future changes of the atmospheric circulation over Europe is presented. Atmospheric circulation is studied through two teleconnection indices, the North Atlantic Oscillation (NAO) Index – which mostly affects the climate of western Europe – and the North Sea-Caspian Pattern (NCP) Index – mainly affecting eastern Mediterranean and the Balkan Peninsula. Firstly, the ECHAM5/MPI (Max Planck Institute) General Circulation Model’s (GCM’s) simulations for the two teleconnection indices are evaluated against NCEP/NCAR reanalysis data for the control run period 1971–2000, both in a temporal and a spatial scale. Secondly, the GCM’s future simulations are studied. The main goals of this study are to validate the ECHAM5 GCM regarding the two teleconnection indices under consideration, and consequently to examine whether the current dominant circulation patterns change or not throughout the twenty-first century.

An Objective Classification of Synoptic Types over Europe

A synoptic classification scheme is developed for Europe based on an automated two-step cluster analysis. It employs daily NCEP-NCAR reanalysis data over 62 years (1948–2009) in creating synoptic types from surface and upper air (1,000, 850, 700 and 500 hPa) temperature and humidity data as well as geopotential height and winds aloft. The synoptic types that have been created exhibit distinct seasonal preferences.