An annual cycle of the circulation variability modes dominating over the Euro-atlantic sector

0493421 - ÚFA 2019 DE eng A - Abstract
Pokorná, Lucie - Beranová, Romana - Huth, Radan
An annual cycle of the circulation variability modes dominating over the Euro-atlantic sector.
EMS Annual Meeting Abstracts, Vol. 15. Berlín: European Meteorological Society, 2018.
[EMS Annual Meeting: European Conference for Applied Meteorology and Climatology 2018. 03.09.2018-07.09.2018, Budapest]
Institutional support: RVO:68378289
Keywords : circulation modes * atmospheric circulation * surface climate * principal component analysis (PCA)
OECD category: Meteorology and atmospheric sciences
https://meetingorganizer.copernicus.org/EMS2018/EMS2018-771.pdf

Modes of circulation variability in 500 hPa fields were recognized to be the main drivers of surface climate
variability on monthly and seasonal scale. It is widely assumed that the circulation modes occur in all seasons with
only slight changes of their character. They have been used in several ways including a validation of circulation in
global climate models, an explanation relationships between atmospheric circulation and surface climatic elements
and recently also as a support tool for the seasonal forecast.
In this research, the circulation modes over East-Atlanic sector were detected using Northern Hemisphere
extratropics in NCEP/NCAR reanalysis period 1948-2016. Instead of common monthly means, the modes were
detected using the method of sliding months of the 31-day length shifting within the calendar year with a
ten-day step. In case of substantial changes in position or intensity of action centres the step was modified to 5
days. Means of sliding months were reduced by mean standard deviation to include the disparity in winter and
summer circulation variability. Principal component analysis (PCA) was applied to mean 500 hPa heights of
sliding months; from 8 to 11 components were rotated in individual seasons. Annual cycles of the North Atlantic
Oscillation (NAO), Euroatlantic mode (EA), Scandinavian mode (SCAN) and Euro-Asian mode 2 (EU2, named
also East Atlantic-West Russia mode) are displayed.
The results show that the zonal modes (the NAO and EA) can be easily detected within the year even though the
position and intensity of their centres change from winter to spring and summer. Two main meridional modes
(SCAN and EA2) change its shape considerably and their existence in summer is debatable.
Permanent Link: http://hdl.handle.net/11104/0286791