The seasonally-varying interaction between the Madden-Julian Oscillation (MJO) and .the northern extratropics, specifically the North Atlantic and Europe region, on intraseasonal timescales is studied. When the MJO is observed using composite and Monte-Carlo significance testing, a direct response to the tropical dynamics is found over the North Atlantic and Europe. When the MJO convection is active over the Indian Ocean, significant anticyclonic anomalies at the 95% confidence level are frequently found over the UK and eastern North Atlantic region. Approximately 10 to 20 days later, when the MJO convection is active over Indonesia, the extratropical anomalies occur in similar locations with opposite sign. Using a systematic two-month sliding season approach to investigate the interaction, the anomalies are present for the majority of the year, favouring the boreal spring. The relationship between the MJO and the North Atlantic Oscillation (NAO) for each of the 12 seasons throughout the year is quantified for the first time using regression analysis. Although correlations between the MJO and NAO are weak, further regressions between the MJO and a North Atlantic 1000 hPa geopotential height index just east of the UK gives very strong boreal springtime correlations of up to r=0.50 and anti-correlations of r=-0.53. An Intermediate Global Circulation Model (IGCM) is used to model the MJO to investigate the mechanisms behind the strong tropical-extratropical interactions. Various stages of representing the MJO in the model are presented using fixed and time dependent heating profiles and many of the observed extratropical features are reproduced as a response to the forcing. Direct comparisons between the observations and the model results are made and the level at which it is able to reproduce the North Atlantic and European anomalies is discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:490613 |
| Date | January 2007 |
| Creators | Charlesworth, Oliver |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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