Poleward propagation of boreal summer intraseasonal oscillations in a coupled model

Role of internal processes

Ajaya Ravindran, H. Annamalai, Jing Jia Luo, Jan Hafner, Toshio Yamagata

    Research output: Contribution to journalArticle

    Abstract

    The study compares the simulated poleward migration characteristics of boreal summer intraseasonal oscillations (BSISO) in a suite of coupled ocean-atmospheric model sensitivity integrations. The sensitivity experiments are designed in such a manner to allow full coupling in specific ocean basins but forced by temporally varying monthly climatological sea surface temperature (SST) adopted from the fully coupled model control runs (ES10). While the local air-sea interaction is suppressed in the tropical Indian Ocean and allowed in the other oceans in the ESdI run, it is suppressed in the tropical Pacific and allowed in the other oceans in the ESdP run. Our diagnostics show that the basic mean state in precipitation and easterly vertical shear as well as the BSISO properties remain unchanged due to either inclusion or exclusion of local air-sea interaction. In the presence of realistic easterly vertical shear, the continuous emanation of Rossby waves from the equatorial convection is trapped over the monsoon region that enables the poleward propagation of BSISO anomalies in all the model sensitivity experiments. To explore the internal processes that maintain the tropospheric moisture anomalies ahead of BSISO precipitation anomalies, moisture and moist static energy budgets are performed. In all model experiments, advection of anomalous moisture by climatological winds anchors the moisture anomalies that in turn promote the northward migration of BSISO precipitation. While the results indicate the need for realistic simulation of all aspects of the basic state, our model results need to be taken with caution because in the ECHAM family of coupled models the internal variance at intraseasonal timescales is indeed very high, and therefore local air-sea interactions may not play a pivotal role.

    Original languageEnglish (US)
    Pages (from-to)851-867
    Number of pages17
    JournalClimate Dynamics
    Volume37
    Issue number5
    DOIs
    StatePublished - Sep 1 2011

    Fingerprint

    oscillation
    air-sea interaction
    moisture
    summer
    anomaly
    ocean
    experiment
    Rossby wave
    ocean basin
    energy budget
    anchor
    advection
    monsoon
    sea surface temperature
    convection
    timescale
    simulation

    ASJC Scopus subject areas

    • Atmospheric Science

    Cite this

    Poleward propagation of boreal summer intraseasonal oscillations in a coupled model : Role of internal processes. / Ravindran, Ajaya; Annamalai, H.; Luo, Jing Jia; Hafner, Jan; Yamagata, Toshio.

    In: Climate Dynamics, Vol. 37, No. 5, 01.09.2011, p. 851-867.

    Research output: Contribution to journalArticle

    Ravindran, Ajaya ; Annamalai, H. ; Luo, Jing Jia ; Hafner, Jan ; Yamagata, Toshio. / Poleward propagation of boreal summer intraseasonal oscillations in a coupled model : Role of internal processes. In: Climate Dynamics. 2011 ; Vol. 37, No. 5. pp. 851-867.
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