Monday, 11 January 2016
Convectively coupled Kelvin waves (CCKWs) are atmospheric weather systems that propagate eastward along the equatorial wave guide with phase speeds between 8 and 15 m s-1. They are an important constituent of the convective envelope of the Madden-Julian Oscillation (MJO), for which ocean-atmosphere interactions play an important role. Hence, ocean-atmosphere interactions within CCKWs may be important for MJO development and prediction, and for tropical climate in general. Although the atmospheric structure of CCKWs has been well studied, their impact on the underlying ocean is uncertain. In this presentation, the ocean-atmosphere interactions in CCKWs are investigated by a case study from November 2011 during the CINDY/DYNAMO field experiment, using in situ oceanographic measurements from an ocean glider. The analysis is then extended to a 15-year period using precipitation data from the Tropical Rainfall Measuring Mission (TRMM) and surface fluxes from the TropFlux analysis. A methodology is developed to calculate trajectories of CCKWs. CCKW events are strongly controlled by the MJO, with twice as many CCKWs observed during the convectively active phase of the MJO compared to the suppressed phase. Coherent ocean-atmosphere interaction is observed during the passage of a CCKW, which lasts approximately 4 days at any given longitude. Surface wind speed and latent heat flux are enhanced, leading to a transient suppression of the diurnal cycle of sea surface temperature (SST), and a sustained decrease in bulk SST of 0.1°C. Given that a typical composite mean MJO SST anomaly is of the order of 0.3°C, and more than one CCKW can occur during the active phase of a single MJO event, the oceanographic impact of CCKWs is of major importance to the MJO cycle.
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