The South Pacific Convergence Zone in three decades of satellite images

Abstract

Interannual variability, seasonal evolution, and intraseasonal variability of the South Pacific Convergence Zone (SPCZ) are quantified using a new data set of 3-hourly SPCZ labels, available from 1980 to 2012 Nov-Apr. The SPCZ label is a binary field indicating presence (1) or absence (0) of the SPCZ at each grid point (1/2° longitude by 1/2° latitude) as a function of time and is the output of a Bayesian spatiotemporal statistical model that takes in instantaneous data from geostationary satellites. The statistical model is designed to emulate the way human observers identify the SPCZ. Results show two distinct parts to the SPCZ: the western tropical part and the eastern subtropical part. At times, the two parts do not connect. When they do connect, they are oriented quite differently, such that the subtropical part has a steeper meridional slope. The SPCZ is present 50-70% of the time in the tropics from Jan to Mar and is usually anchored to the warm sea surface temperature (SST) distribution of the equatorial west Pacific. The subtropical part does not have the same sensitivity to the underlying SST distribution and is present more often in Nov-Dec and Apr than in Jan-Mar when the SST is highest. Interannual variability in SPCZ location is strongly associated with El Niño-Southern Oscillation (ENSO); however, no change in overall SPCZ area is detected in association with ENSO. On the intraseasonal time scale, composite analysis shows the distinct spatial patterns in SPCZ presence associated with each phase of the Madden Julian Oscillation. Key Points Developed a 30 year, 3-hourly data set of SPCZ location and extent Presents interannual and intraseasonal variability of SPCZ location Presents seasonal evolution of SPCZ location and extent ©2013. American Geophysical Union. All Rights Reserved.