On the role of a Rossby wave train during the extratropical transition of hurricane Helene (2006). (14th June 2012)

• Record Type: Journal Article
• Authors: Pantillon, F.; Chaboureau, J.‐P.; Lac, C.; Mascart, P.
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 139:Number 671(2013:Jan.)
• Page Start: 370
• Page End: 386
• Publication Date: 2012-06-14
• Subjects: Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.1974
• Languages: English
• ISSNs: 0035-9009

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Three successive interactions of hurricane <bold><italic>Helene</italic></bold> (2006) with a Rossby wave train during the extratropical transition of <bold><italic>Helene</italic></bold> over the North Atlantic were investigated. Numerical experiments were performed with different horizontal resolutions and configurations, over a domain that stretches from the eastern Pacific to the Western Mediterranean to encompass <bold><italic>Helene</italic></bold> and the whole Rossby wave train. In particular, a cloud‐resolving run offered an explicit representation of strong diabatic effects involved in the three successive interactions.</p> <p>While the circulation and moisture anomaly of <bold><italic>Helene</italic></bold> were essential to its own reintensification, it is shown that the Rossby wave train played an important role in the track and intensity of <bold><italic>Helene</italic></bold> and in explosive cyclogenesis downstream. First, the Rossby wave train steered <bold><italic>Helene</italic></bold> in such a way that a small difference in phasing resulted in large errors in the track of <bold><italic>Helene</italic></bold>. Only a run at kilometre scale was able to correctly forecast the 5‐day track of <bold><italic>Helene</italic></bold>. Second, through the formation of three filaments, the Rossby wave train created a quasi‐diurnal cycle in the intensity of <bold><italic>Helene</italic></bold>. <bold><italic>Helene</italic></bold> responded with strong diabatic activity that prevented the superposition of an upstream trough and enhanced a downstream ridge. Finally, model errors in the outflow of <bold><italic>Helene</italic></bold> propagated downstream with the group speed of the Rossby wave train, leading to the loss of predictability of a tropical‐like cyclone over the Mediterranean. This study suggests that, in addition to the horizontal resolution, uncertainty from the model microphysics and from initial conditions need to be characterized to improve mid‐range forecast downstream from an extratropical transition. Copyright © 2012 Royal Meteorological Society</p> </abstract>