Temporal variability of the 40–50‐day oscillation in tropical convection

Abstract

The temporal variability of the structure and two-dimensional phase propagation of the 40-50-day oscillation in tropical convection are diagnosed using complex empirical orthogonal function (CEOF) analysis of the 1974-1988 outgoing longwave radiation (OLR) data.Results from autoregressive spectrum analysis of the OLR time series indicate that apart from the well-known 40-50-day peak, there are other significant spectral peaks near 2C30 and 17 days. In much of the tropics, excluding the equatorial Indian and western Pacific Oceans, these higher frequency peaks appear to be distinct from the 4&50 day spectral peak.The dominant spatial mode of the 40-50-day oscillation consists of the well-known equatorial dipole and associated eastward propagation. Interactions between this mode and the extratropical 40-50-day oscillation are manifested through the propagation of convection anomalies to and from the tropics via the North Pacific, north-east Atlantic and north-east African subtropics. The sense of this propagation varies from season to season and year to year.Analysis of the oscillation during individual summers and winters and each of the

Observed Changes in the Lifetime and Amplitude of the Madden–Julian Oscillation Associated with Interannual ENSO Sea Surface Temperature Anomalies

“…Both relationships disappear for the latest 30 yr. These relationships had not been depicted in previous studies (Fink and Speth 1997;Vincent et al 1998;Anyamba and Weare 1995;Slingo et al 1999), because the opposite sign of the correlations between winter and summer cancel when averaged over the annual cycle. In addition, many works focused on the two or three latest decades during which satellite data were available; but these years also correspond to the period during which the teleconnection patterns show barely significant results.…”

“…However, no simultaneous significant correlations between the amplitude of MJO activity and ENSO have been found to date (Anyamba and Weare 1995;Slingo et al 1996;Slingo et al 1999). Here, we explore the interdecadal variability of MJO activity, and reexamine the link between MJO activity and the state of ENSO, with a longer dataset that has been used before.…”

“…However, the spatial envelope of MJO activity extends farther east than usual during El Niño conditions, beyond the date line into the central Pacific, associated with the warmer sea surface temperatures (SSTs) there (Anyamba and Weare 1995;Fink and Speth 1997;Vincent et al 1998;Kessler 2001). Lagged relationships were also recently discovered between MJO activity in spring and the state of El Niño in subsequent autumn/winter seasons (Hendon et al 2007).…”

Modulation of the Madden-Julian Oscillation by ENSO: Inferences from Observations and GCM Simulations

“…In the December-February season during El Niñ o events, enhanced (suppressed) activity of the intraseasonal 850 mb zonal wind was found east (west) of the dateline. Using OLR data, Anyamba and Weare (1995) reported that during two out of the three warm ENSO events considered, there was more eastward penetration of intraseasonal activity or the MJO envelope over the central Pacific, and the propagation speed is slower. Later studies using OLR data with a longer base period (Fink and Speth 1997;Vincent et al 1998;Hendon et al 1999;Kessler 2001) came to similar conclusions.…”

Synoptic evolution of composite wet spells over northern Tanzania

“…Rui & Wang (1990) documented the development and dynamic structure of tropical intraseasonal convection anomalies using pentad outgoing longwave radiation (OLR) and ECMWF-derived 200 and 850 hPa wind divergence. Murakami (1988), Anyamba (1992) and Matarira & Jury (1992) have discussed intra-seasonal variability in the African sector; however, the evolution of synoptic-scale forcing and its relationship to local convection have not been described.External precursors and regional controls of wet spells over tropical east Africa are documented here for the November onset event. Rainfall during this period contributes up to 40% of the annual total in northern Tanzania (Nyenzi 1988).…”