HR: 0800h
AN: OS41B-0536    [Abstracts]
TI: Variability of the South Pacific Convergence Zone and its Influence on the General Atmospheric Circulation
AU: * Widlansky, M J
EM: matthew.widlansky@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, GA 30332, United States
AU: Webster, P J
EM: pjw@eas.gatech.edu
AF: School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, GA 30332, United States
AB: Intense atmospheric convection associated with the South Pacific Convergence Zone (SPCZ) significantly impacts basin-scale circulation patterns over the Pacific. We explore dynamical processes which foster changes in convection along the convergence zone. These forcings include strong moisture convergence and accumulation of wave energy in the boundary layer, as well as dynamical instability associated with moderate cross-equatorial wind bursts. Focus is applied to observing the dominant modes of variability on synoptic to intraseasonal timescales using a combination of satellite observations and NCEP reanalysis data. Accumulation of energy, due to negative stretching deformation, comes from both tropical and extratropical modes suggesting that the SPCZ is an artifact of wide ranging modes. Signals of the dominant modes (inferred from fields of outgoing longwave radiation: OLR) are isolated using bandpass filtering techniques which are then mapped in space and time using Principal Components from Empirical Orthogonal Function analyses. Variability of convective systems in the SPCZ is believed to be significantly correlated with changes in the regional Hadley Circulation and the Pacific Walker cell. This presents the possibility of important teleconnection routes between the tropical West and East Pacific, as well as with the mid-latitude regions of the Northern and Southern Hemispheres. We test these interaction hypotheses by developing composites of the circulation patterns using dates of maximum convection events (regions of minimum OLR) in the SPCZ. Intensities of the large-scale circulations are measured using observations of stream function mass fluxes. Results suggest that deep convection maximums (minimums) are associated with an increase (decrease) in the Walker Circulation. Additional research is presented showing how off-equatorial convection anomalies in the subtropical portion of the SPCZ may cause changes to the Hadley Circulation. Interactions with the zonal (Walker) and meridional (Hadley) circulations appear to have important consequences on the ability for wave energy to propagate through the tropical Pacific atmosphere. Examples include Northern Hemisphere cross-equatorial teleconnections through the Westerly Wind Duct in the upper branch of the Walker circulation and Rossby wave trains in the SPCZ, which may be partially governed by characteristics of the regional Hadley circulation.
DE: 3300 ATMOSPHERIC PROCESSES
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3319 General circulation (1223)
DE: 3364 Synoptic-scale meteorology
DE: 3374 Tropical meteorology
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting