WP3a - WEATHER REGIMES

Impact on weather regimes and application to air pollution levels

WP coordination: Hungarian Meteorological Service (András Horányi)

Participating institutes: Hungarian Meteorological Service (OMSZ), Institute Pierre Simon Laplace (CNRS), Env-In-Cent Consulting Ltd. (EiC)

WP3a Overview

Objectives
The objective is to make a complete analysis of weather regimes for the region of Central and Eastern Europe for the present-day climate, to study the future changes of weather regimes and their implication to air pollution levels.

Description of work
Weather regimes provide a dynamical paradigm for characterizing the multi-modal statistics of the large-scale climate system, and thus provide a natural point of departure for a downscaling method to local climate (precipitation and temperature). It is well recognized that mid-latitude atmospheric circulation is characterized by certain large-scale flow patterns that appear repeatedly at fixed geographical locations, and persist beyond the life time of individual synoptic-scale events. The concept of weather regimes is particularly suitable to the geographic sector of Central and Eastern Europe. Weather regimes are believed to be a main factor in organizing the local weather and climate of this region, and to be associated with significant anomalies of temperature, precipitation and winds. Four main tasks are planned (the leading institute’s name is in the parenthesis):

Characterization of the present-day regional climate (OMSZ)
The main methodology of the work is based on a synoptic-climatological approach: present-day and recent-past climate data will be analyzed to characterize the behavior of the atmosphere with special diagnostics, such as weather patterns and different indices. The study will be carried out by OMSZ and CNRS for both hemispheric and local scales. The hemispheric data to be used are the ERA40 for the period of 1961-2000, available on a resolution of 125 km. The local data to be used are from the data archive of the Hungarian Meteorological Service, which contains meteorological-station data for the last 50 years or more. The data will be firstly homogenized and then interpolated into a 0.1 by 0.1 latitude-longitude grid. Analysis will be performed for a thirty years period (1971-2000). The following characteristics will be obtained for the synoptic (hemispheric) scale: (1) macro-circulation classification (so called Hess-Brezovsky types); (2) cyclone detection with the identification of cyclone centers (frequency, persistence); (3) different indices, gradients, anomalies (e.g. zonality indices, mean sea level pressure trends, temperature gradients). For the regional (local) scale the following parameters will be calculated: (1) daily mean of 10-meter wind; (2) daily maximum 10-meter wind gust; (3) cold air pad situations (a typical weather pattern over the Carpathian Basin, when in winter cold air accumulates in the Basin, causing low level cloudiness and temperature inversion, for the entire territory and for a long period). This task will last from M1 to M18.

Main statistics of weather regimes for climate scenarios (OMSZ)
Classification methods will be applied to the datasets obtained in WP1 to obtain a complete statistics of weather regimes in the region and their future evolution.

Composite meteorological datasets based on weather regimes (CNRS)
Once the weather regimes are established, we will then work in the "spectral domain" defined by these regimes, and study the impact of climate change on each of the weather regimes. Composite meteorological situations will be calculated by considering both the average for a climatology and high quantiles for extreme events.

Application to air quality modeling (CNRS, EiC)
Composite meteorological situations will be used in a regional-scale air pollution model (called CHIMERE) to evaluate the changes of air quality and the associated impacts on tourism when climate varies in the future.

Results of WP3a

Status of WP3a Tasks (internal)