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An analysis of New Zealand synoptic types and their use in defining weather regimes
Author(s) -
Kidson John W.
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(20000315)20:3<299::aid-joc474>3.0.co;2-b
Subject(s) - climatology , trough (economics) , precipitation , environmental science , synoptic scale meteorology , zonal flow (plasma) , el niño southern oscillation , geography , meteorology , geology , physics , plasma , quantum mechanics , economics , tokamak , macroeconomics
A new set of 12 daily weather types for the New Zealand region has been derived from the 40‐year NCEP/NCAR reanalysis dataset. Cluster analysis of the monthly frequencies of these patterns has led to the definition of three ‘regimes’, characterized by (i) frequent troughs crossing the country, (ii) highs to the north with strong zonal flow to the south of the New Zealand, and (iii) blocking patterns with highs more prominent in the south. Blocking regimes are more frequent in summer and autumn and are associated with above‐normal temperatures, less precipitation in the southwest of the country and more precipitation in the northeast. The Zonal regime, which brings below‐normal precipitation to the northeast and milder conditions in the south, is less common in summer. The Trough regime is less frequent in autumn and is linked to cooler temperatures in the west and above‐normal precipitation over the entire country. The monthly frequencies of individual synoptic types are only weakly related to the Southern Oscillation Index (SOI) and other indices of the hemispheric‐scale flow, with variance reductions from regression equations ranging from between 3 and 33%. Similar predictions of weighted combinations of the synoptic types corresponding to each regime gave mean variance reductions 70–80% higher. The correct regime could be specified from the hemispheric indices by the use of discriminant analysis for 56% of the 474 months in the dependent dataset. The monthly frequency of synoptic types was also tested as an alternative to monthly mean 1000 hPa patterns in the selection of analogues over the New Zealand region. The success of the selection process was measured by the variance of temperature and rainfall patterns over homogeneous regions for sets of two, four and eight analogues. The mean 1000 hPa patterns scored better in nearly all cases, but gave variance reductions of only 13–19% over randomly chosen analogues. Copyright © 2000 Royal Meteorological Society