Mathematics Colloquia and Seminars

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Description

Convectively coupled equatorial waves (CCEWs) are responsible for a large portion of the rainfall variability within the ITCZ and monsoon regions. This talk will first review the statistical structure of these waves and compare that structure with that predicted by Matsuno’s classical shallow water theory on an equatorial beta plane. An Empirical Orthogonal Function (EOF) analysis is undertaken of global tropical (20S-20N) brightness temperature data filtered to retain fluctuations on various synoptic (<10 day) to submonthly (<30 day) time scales. The leading modes correspond to known CCEW disturbances. In general many of the modes also have strong extratropical signals associated with them, and extratropical forcing of the equatorial wave activity is unambiguous based on their lead-lag relationships. One common manifestation of this type of interaction involves the initiation of convectively coupled Kelvin waves within the western Pacific ITCZ, which are often triggered by Rossby wave activity propagating into the Australasian region from the South Indian Ocean storm track. The resulting waves frequently propagate eastward across the entire globe. In other cases, such as over Africa, the forcing appears to be related to wave activity in the extratropical storm track which is not necessarily propagating into low latitudes, but appears to "project" onto the Kelvin structure, in line with past theoretical and modeling studies. Observational evidence for such interactions will be presented, along with a review of some recent theoretical work aimed at explaining their dynamical causes.

Joint with Atmospheric Sciences. Note special time. Coffee and cookies will be served in MSB 1147 beginning at 4:10 pm on the day of the seminar.