Extratropical cyclone variability in the Northern Hemisphere winter from the NCEP/NCAR reanalysis data |
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Authors: | S K Gulev O Zolina S Grigoriev |
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Institution: | (1) P.P. Shirshov Institute of Oceanology, RAS, 36 Nakhimovsky ave., 117218 Moscow, Russia E-mail: gul@gulev.sio.rssi.ru, RU |
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Abstract: | The winter climatology of Northern Hemisphere cyclone activity was derived from 6-hourly NCEP/NCAR reanalysis data for the
period from 1958 to 1999, using software which provides improved accuracy in cyclone identification in comparison to numerical
tracking schemes. Cyclone characteristics over the Kuroshio and Gulfstream are very different to those over continental North
America and the Arctic. Analysis of Northern Hemisphere cyclones shows secular and decadal-scale changes in cyclone frequency,
intensity, lifetime and deepening rates. The western Pacific and Atlantic are characterized by an increase in cyclone intensity
and deepening during the 42-year period, although the eastern Pacific and continental North America demonstrate opposite tendencies
in most cyclone characteristics. There is an increase of the number of cyclones in the Arctic and in the western Pacific and
a downward tendency over the Gulf Stream and subpolar Pacific. Decadal scale variability in cyclone activity over the Atlantic
and Pacific exhibits south-north dipole-like patterns. Atlantic and Pacific cyclone activity associated with the NAO and PNA
is analyzed. Atlantic cyclone frequency demonstrates a high correlation with NAO and reflects the NAO shift in the mid 1970s,
associated with considerable changes in European storm tracks. The PNA is largely linked to the eastern Pacific cyclone frequencies,
and controls cyclone activity over the Gulf region and the North American coast during the last two decades. Assessment of
the accuracy of the results and comparison with those derived using numerical algorithms, shows that biases inherent in numerical
procedures are not negligible.
Received: 7 July 2000 / Accepted: 30 November 2000 |
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