The emergence of shallow easterly jets within QBO westerlies
Journal of the Atmospheric Sciences
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Hitchcocka, P., Haynes, P., Randel, W., & Birner, T. (2018). The emergence of shallow easterly jets within QBO westerlies. Journal of the Atmospheric Sciences, 75 (1), 21-40. https://doi.org/10.1175/JAS-D-17-0108.1
© 2018 American Meteorological Society. A configuration of an idealized general circulation model has been obtained in which a deep, stratospheric, equatorial, westerly jet is established that is spontaneously and quasi-periodically disrupted by shallow easterly jets. Similar to the disruption of the quasi-biennial oscillation (QBO) observed in early 2016, meridional fluxes of wave activity are found to play a central role. The possible relevance of two feedback mechanisms to these disruptions is considered. The first involves the secondary circulation produced in the shear zones on the upper and lower flanks of the easterly jet. This is found to play a role in maintaining the aspect ratio of the emerging easterly jet. The second involves the organization of the eddy fluxes by the mean flow: the presence of a weak easterly anomaly within a tall, tropical, westerly jet is demonstrated to produce enhanced and highly focused wave activity fluxes that reinforce and strengthen the easterly anomalies. The eddies appear to be organized by the formation of strong potential vorticity gradients on the subtropical flanks of the easterly anomaly. Similar wave activity and potential vorticity structures are found in the ERA-Interim for the observed QBO disruption, indicating this second feedback was active then.
European Research Council ACCI Grant Project 267760. IDEX Chaires d’Attractivité programme of l’Université Fédérale de Toulouse, Midi-Pyrénées. This work was partially supported by NASA GNSS Remote Sensing Science Team Grant NNX16AK37G. The National Center for Atmospheric Research is sponsored by the National Science Foundation.
European Research Council (267760)
External DOI: https://doi.org/10.1175/JAS-D-17-0108.1
This record's URL: https://www.repository.cam.ac.uk/handle/1810/276495