The South Pacific Convergence Zone in three decades of satellite images

Colene Haffke,Gudrun Magnusdottir

doi:10.1002/jgrd.50838

Abstract

AbstractInterannual 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 (½° longitude by ½° 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.

Highlights

South Pacific Convergence Zone (SPCZ) activity decreases to the east and south and is present less than 30% of the time in the subtropics
Our results suggest that two main axis lines describe the orientation of the SPCZ, one representing the more subtropical part in the southeast and another representing the tropical part in the northwest
Studies that only consider the height of the SPCZ active season, which is typically defined as Dec–Feb, miss this activity in the subtropics in their analysis

Summary

The South Pacific Convergence Zone in three decades of satellite images

Received 1 April 2013; revised 28 August 2013; accepted 13 September 2013; published 4 October 2013. [1] 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. Results show two distinct parts to the SPCZ: the western tropical part and the eastern subtropical part. 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. On the intraseasonal time scale, composite analysis shows the distinct spatial patterns in SPCZ presence associated with each phase of the Madden Julian Oscillation

Introduction

Longitude of Segmentation

Power Power