The atmospheric circulation changes over the Northern Hemisphere during the 20th Century

0493334 - ÚFA 2019 DE eng A - Abstract
Pískala, V. - Huth, Radan
The atmospheric circulation changes over the Northern Hemisphere during the 20th Century.
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 : atmospheric circulation * teleconnections * reanalyses * principal component analysis (PCA) * north atlantic oscillation (NAO)
OECD category: Meteorology and atmospheric sciences
https://meetingorganizer.copernicus.org/EMS2018/EMS2018-752.pdf

The Northern Hemisphere circulation has changed during the past century as many studies proved before. Our aim
is to find out whether these changes are also evident in modes of low-frequency variability (i.e. teleconnections).
The long-term reanalyses: 20th Century and ERA-20C, are employed to identify circulation changes in a period
longer than 100 years according to reanalyses availability. Modes are detected by the varimax-rotated principle
component analysis (PCA) of winter monthly mean 500 hPa geopotential heights. We use the moving PCA of 40
years periods with two years step which allows us to get more precise information about a geographical shift of
modes. The number of leading modes were specified separately for each analysed period.
The intensity and even the position of all modes have been slightly changing during the 20th century. The
NAO mode was the first leading mode in the late 19th and the early 20th century period. However, the highest
differences occur mainly in changes of the PNA mode which is the first leading mode for the most part of the
20th century. In the early century period, the explained variance of this mode is significantly lower and centres are
weaker. This is probably caused by lack of observed data over North America or Siberia which were assimilated
to the reanalyses. The distribution of assimilated data in the early period of reanalyses can lead to preference of
European modes. We hypothesize that the main detected changes are given by the different quality of assimilated
data during each period.
Permanent Link: http://hdl.handle.net/11104/0286705