Ocean Rossby waves as a triggering mechanism for primary Madden-Julian events

Webber, BGM, Matthews, AJ, Heywood, KJ and Stevens, DP (2012) Ocean Rossby waves as a triggering mechanism for primary Madden-Julian events. Quarterly Journal of the Royal Meteorological Society, 138 (663). pp. 514-527. ISSN 1477-870X

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Abstract

The Madden–Julian Oscillation (MJO) is sporadic, with episodes of cyclical activity interspersed with inactive periods. However, it remains unclear what may trigger a Madden–Julian (MJ) event which is not immediately preceded by any MJO activity: a ‘primary’ MJ event. A combination of case-studies and composite analysis is used to examine the extent to which the triggering of primary MJ events might occur in response to ocean dynamics. The case-studies show that such events can be triggered by the arrival of a downwelling oceanic equatorial Rossby wave, which is shown to be associated with a deepening of the mixed layer and positive sea-surface temperature (SST) anomalies of the order of 0.5–1 °C. These SST anomalies are not attributable to forcing by surface fluxes which are weak for the case-studies analysed. Furthermore, composite analysis suggests that such forcing is consistently important for triggering primary events. The relationship is much weaker for successive events, due to the many other triggering mechanisms which operate during periods of cyclical MJO activity. This oceanic feedback mechanism is a viable explanation for the sporadic and broadband nature of the MJO. Additionally, it provides hope for forecasting MJ events during periods of inactivity, when MJO forecasts generally exhibit low skill.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
Faculty of Science > School of Mathematics
Related URLs:
Depositing User: Rhiannon Harvey
Date Deposited: 13 Mar 2012 15:31
Last Modified: 31 Oct 2019 13:20
URI: https://ueaeprints.uea.ac.uk/id/eprint/38191
DOI: 10.1002/qj.936

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