Eastward propagating ∼2‐ to 15‐day equatorial convection and its relation to the tropical intraseasonal oscillation

Abstract

Anomalies of outgoing longwave radiation (OLR) in 1980–1989 were examined in a narrow latitude band about the equator to elucidate the propagation and interaction of tropical intraseasonal oscillations (TIOs) and synoptic‐scale convective activity. Hovmöller diagrams of OLR data reconstructed from two frequency bands (corresponding to periods of ∼30–60 days and ∼2–15 days, respectively) revealed a clear distinction between the phase speed of eastward moving TIOs (3–7 m s−1) and that of eastward synoptic‐scale convection (10–13 m s−1). Coherent propagation of TIOs from the Indian to the western Pacific Oceans was often observed with temporary diminution of amplitude over the maritime continent. Propagation of high‐frequency anomalies was generally confined to an individual basin. Dominance of eastward propagating synoptic‐scale convection in the equatorial zone contrasts sharply with the westward propagation of off‐equatorial convergence zones. Interaction between the TIO and high‐frequency activity resolved by daily OLR was visible as a modest enhancement of eastward synoptic‐scale events (and of high‐frequency activity in general) during the convectively active phase of the TIO.