Characterization of the Variability of the South Pacific Convergence Zone Using Satellite and Reanalysis Wind Products

Abstract

The variability of the South Pacific convergence zone (SPCZ) is evaluated using ocean surface wind products derived from the atmospheric reanalysis ERA-Interim for the period of 1981–2014 and QuickSCAT for the period of 1999–2009. From these products, indices were developed to represent the SPCZ strength, area, and centroid location. Excellent agreement is found between the indices derived from the two wind products during the QuikSCAT period in terms of the spatiotemporal structures of the SPCZ. The longer ERA-Interim product is used to study the variations of SPCZ properties on intraseasonal, seasonal, interannual, and decadal time scales. The SPCZ strength, area, and centroid latitude have a dominant seasonal cycle. In contrast, the SPCZ centroid longitude is dominated by intraseasonal variability due to MJO influence. The SPCZ indices are all correlated with El Niño–Southern Oscillation indices. Interannual and intraseasonal variations of SPCZ strength during strong El Niño are approximately twice as large as the respective seasonal variations. SPCZ strength depends more on the intensity of El Niño rather than the central-Pacific versus eastern-Pacific type. The change from positive to negative Pacific decadal oscillation (PDO) around 1999 results in a westward shift of the SPCZ centroid longitude, a much smaller interannual swing in centroid latitude, and a decrease in SPCZ area. This study improves the understanding of the variations of the SPCZ on multiple time scales and reveals the variations of SPCZ strength not reported previously. The diagnostics analyses can be used to evaluate climate models to gauge their fidelity.

Review of Tropical‐Extratropical Teleconnections on Intraseasonal Time Scales

“…The Southern Hemisphere is characterized by two regions with quasi-persistent convection, the South Pacific Convergence Zone (SPCZ) and the SACZ. The SPCZ extends from the tropical West Pacific southeastward into the Central Pacific subtropics (Trenberth, 1976) and is characterized by variability from intraseasonal to decadal time scales (Kidwell et al, 2016). The convective heating in the SPCZ is a significant Rossby wave source (Meehl et al, 2001;Shimizu & de Albuquerque Cavalcati, 2011), affecting the mean Pacific flow (van der Wiel et al, 2016).…”

Using Atmospheric Energy Transport to Quantitatively Constrain South Pacific Convergence Zone Shifts during ENSO

“…In fact, the variability of SPCZ convection often reflects interactions across multiple time scales; for example, the phase of ENSO or the MJO may modify the behavior of synoptic-scale interactions with SPCZ convection (Matthews 2012). Kidwell et al (2016) examined various metrics for characterizing SPCZ variability (e.g., intensity, areal extent, centroid latitude) and found that these metrics behave differently depending on the time scale of the variability.…”

Tropical circulation and precipitation response to ozone depletion and recovery

“…Upon reaching the SPCZ region, wave activity converges due to the decrease in zonal wind speed (Widlansky et al 2011, Matthews 2012, van der Wiel et al 2015. While intraseasonal variability of the SPCZ is related to the Madden-Julian Oscillation, its interannual-to-decadal variability depends on El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (Kidwell et al 2016). Large decadal variations in the SPCZ position since 1600 have been suggested based on ocean salinity proxies (Linsley et al 2006).…”