~~• Sebastian Ortega Arango
• Date, time and location of the presentation: Tuesday, October 4th, beginning at 2pm in ES&T L1114
• Committee members:
o Dr. Peter J. Webster - School of Earth and atmospheric Sciences - GeorgiaTech
o Dr. Judith A. Curry - School of Earth and atmospheric Sciences - GeorgiaTech
o Dr. Annalisa Bracco - School of Earth and atmospheric Sciences - GeorgiaTech
o Dr. Yi Deng - School of Earth and atmospheric Sciences - GeorgiaTech
o Dr. Predrag Cvitanović - School of Physics - GeorgiaTech

•  Title of the talk: "The planetary-scale circulation of the upper tropical troposphere and its influence on tropical weather"

• Abstract (from the PhD candidacy form):
We study the upper tropospheric circulation of the tropical atmosphere as seen through its potential vorticity (PV) field. The PV field provides a picture of the upper troposphere where the tropics and the midlatitudes continually interact. There, Rossby waves constantly travel eastward on the subtropical jets, break on the westerly ducts over the Pacific and Atlantic Ocean, and are then advected southwards towards the equator, and westward on the equatorial westerly winds, as eddies that are remnants of the breaking Rossby waves.
Through analytical arguments, we show that these breaking Rossby waves generate equatorward fluxes of PV that are mostly compensated by the poleward fluxes of PV generated by deep tropical convection. Additionally, we argue that these fluxes must always occur and be expected, making of zonal asymmetric structures of the tropical circulation, such as the westerly ducts, an integral response of the tropical atmosphere to deep convection.
With observational analyses, we further suggest that these PV fluxes may also affect tropical weather. We focus on the quasi-biweekly oscillations of the South Asian Monsoon, and note that these oscillations often co-evolve in both the upper and lower troposphere.