Areal analysis of oscillations in 500‐hPa temperature field: a pseudo‐2D wavelet transform approach

This article introduces areal analysis of regular changes in 500‐hPa temperature fields with pseudo‐2D wavelet transform (p2D‐WT). p2D‐WT is a new technique, a practical approach based on the 1D continuous wavelet transform (CWT), designed to describe frequency characteristics of studied datasets in terms of their evolution in both time and space. The algorithm transforms datasets defined in a grid into a multidimensional object, which is subsequently interpreted by time and frequency slices. In this study, we describe the transformation fundamentals and application of the transform on the 500‐hPa temperature field. Two types of reanalysis data are studied: time series from the European Centre for Medium‐Range Weather Forecasts (denoted as ERA‐40) and datasets from National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR). The analysis of the climatological data shows the presence of various periodicities among which the most distinct are the annual cycle (AC), semi‐annual cycle, quasi‐quadrennial oscillation (QQO) and quasi‐decadal oscillation (QDO). The article also provides a comparison of frequency characteristics of the NCEP/NCAR and ERA‐40 reanalysis datasets; it shows that the frequency patterns found in the particular reanalysis datasets differ only in limited areas. Copyright © 2010 Royal Meteorological Society