Why the South Pacific Convergence Zone is diagonal

Van Der Wiel, Karin, Matthews, Adrian, Joshi, Manoj and Stevens, David (2016) Why the South Pacific Convergence Zone is diagonal. Climate Dynamics, 46 (5-6). pp. 1683-1698. ISSN 0930-7575

[img]
Preview
PDF (vanderwieletal2016_accepted) - Submitted Version
Download (2695kB) | Preview

    Abstract

    During austral summer, the majority of precipitation over the Pacific Ocean is concentrated in the South Pacific Convergence Zone (SPCZ). The surface boundary conditions required to support the diagonally (northwest-southeast) oriented SPCZ are determined through a series of experiments with an atmospheric general circulation model. Continental configuration and orography do not have a significant influence on SPCZ orientation and strength. The key necessary boundary condition is the zonally asymmetric component of the sea surface temperature (SST) distribution. This leads to a strong subtropical anticyclone over the southeast Pacific that, on its western flank, transports warm moist air from the equator into the SPCZ region. This moisture then intensifies (diagonal) bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in Rossby waves that are refracted toward the westerly duct over the equatorial Pacific. The climatological SPCZ is comprised of the superposition of these diagonal bands of convection. When the zonally asymmetric SST component is reduced or removed, the subtropical anticyclone and its associated moisture source is weakened. Despite the presence of Rossby waves, significant moist convection is no longer triggered; the SPCZ disappears. The diagonal SPCZ is robust to large changes (up to +/-6 degC) in absolute SST (i.e. where the SST asymmetry is preserved). Extreme cooling (change less than -6 degC) results in a weaker and more zonal SPCZ, due to decreasing atmospheric temperature, moisture content and convective available potential energy.

    Item Type: Article
    Uncontrolled Keywords: spcz,sst,igcm4,asymmetry,rossby waves,moisture transport
    Faculty \ School: Faculty of Science > School of Environmental Sciences
    Faculty of Science > School of Mathematics
    Depositing User: Pure Connector
    Date Deposited: 24 Jul 2015 23:40
    Last Modified: 11 Apr 2019 14:52
    URI: https://ueaeprints.uea.ac.uk/id/eprint/53641
    DOI: 10.1007/s00382-015-2668-0

    Actions (login required)

    View Item