2002 Annual

Thursday, 17 January 2002: 1:43 PM
Interdecadal variations in the Northern Hemisphere storm tracks
Edmund K. M. Chang, Florida State University, Tallahassee, FL
In this paper, interannual variations in the northern hemisphere winter storm tracks are examined based on 51 winters (December-January-February) of NCEP/NCAR reanalysis data. The leading EOF corresponds to the simultaneous strengthening/weakening of both the Pacific and Atlantic storm tracks. The principal component associated with this leading EOF exhibits pronounced inter-decadal variability. There appears to be a transition during the early 1970's -- from a weak storm track state prior to the early 1970's to a strong storm track state after that. Decadal mean storm track intensity during the 1990's is nearly 40% stronger than that during the late 1960's and early 1970's.

In order to show that the inter-decadal variations are not introduced into the reanalysis data by changes in the observational network, radiosonde observations along the storm track maxima are examined. The radiosonde observations are largely consistent with the reanalysis data, except for the suggestion that biases in the reanalysis data might have led to a slight overestimation of the magnitude of the variations.

Relationship between storm track variations and low frequency (seasonal mean) flow anomalies are examined. Relations to several other modes of interdecadal variability are also explored. It is shown that parts of the storm track variations could be related to the Arctic Oscillation and parts to the inter-decadal ENSO-like variability. However, even when storm track variations linearly congruent with these other modes are taken out, substantial inter-decadal variations still remain, suggesting that a large part of the storm track variability is unrelated to these other modes of variations.

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