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Characteristics of the large‐scale circulation changes during the sudden onset of the fall transition season
Author(s) -
Keller Linda M.,
Houghton David D.
Publication year - 2000
Publication title -
international journal of climatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.58
H-Index - 166
eISSN - 1097-0088
pISSN - 0899-8418
DOI - 10.1002/(sici)1097-0088(20000330)20:4<397::aid-joc473>3.0.co;2-d
Subject(s) - climatology , extratropical cyclone , northern hemisphere , environmental science , atmospheric sciences , atmospheric circulation , magnitude (astronomy) , geology , physics , astronomy
Abstract The characteristics of large‐scale circulation changes manifest in the abrupt onset of the fall transition season are analysed for the Northern Hemisphere extratropical region. Ten years of daily observational data from the European Centre for Medium Range Weather Forecasts (ECMWF) global model initialization analyses are examined using the vertically integrated total kinetic energy (TKE) as the primary descriptor for circulation intensity. The time series data are bandpass filtered to examine subsets of frequencies representing specific atmospheric time scales, i.e. the low‐frequency tropical forced oscillations (29.9–59.9 days), the intermediate‐frequency oscillations related to non‐linear processes such as weather regimes (10.0–29.7 days) and the high‐frequency extratropical synoptic scale (2.5–6.5 days). Times when significant increases in kinetic energy (KE) variability occurred in the area‐weighted hemispheric‐mean time series for each bandpass were determined, and the onset date for each year and for each bandpass period was designated as the first significant increase in KE variability during the 1 August–30 November time period. Statistically significant abrupt onset events are found, with the majority occurring in August, September and October. The mean onset times vary from 3 October for the 29.9–59.9‐day bandpass period to 30 August for the 2.5–6.5‐day bandpass period. Composites with respect to the onset time show robust features of the abrupt onset event in both the hemispheric‐mean time series and the spatial patterns of KE variability. Centres of maximum change in the magnitude of KE variability are in the western and central Pacific and the Atlantic Ocean sectors coincident with the areas of jet stream maxima. Separate analyses for onset characteristics for area‐mean KE time series for the Pacific and Atlantic Ocean areas show that there is little correlation between Pacific and Atlantic onset times for the 29.9–59.9‐day bandpass period. However, for the 10.0–29.7‐day bandpass period the Atlantic onset times tend to lead the Pacific onset times, while for the 2.5–6.5‐day bandpass period the Pacific region onset times tend to occur prior to the Atlantic onset times. Copyright © 2000 Royal Meteorological Society