HRD seminar – Dr. Benjamin Jaimes, University of Miami, RSMAS, Department of Ocean Sciences – 16 July 2015

Dr. Jaimes presented a seminar “Enhanced Wind-Driven Downwelling Flow in Warm Oceanic Eddy Features during the Intensification of Tropical Cyclone Isaac (2012): Observations and Theory”

ABSTRACT:

Tropical cyclones (TCs) typically produce intense oceanic upwelling underneath the storm’s center, and weaker and broader downwelling outside upwelled regions. However, several cases of predominantly downwelling responses over warm, anticyclonic mesoscale oceanic features were recently reported, where the ensuing upper-ocean warming prevented significant cooling of the sea surface, and TCs rapidly attained and maintained major status. Elucidating downwelling responses is critical to better understanding TC intensification over warm mesoscale oceanic features. As part of the NOAA Intensity Forecasting Experiment (IFEX), a new case of predominant downwelling responses to TC forcing was observed over Gulf of Mexico’s mesoscale eddy features during the intensification of tropical storm Isaac (2012) into a hurricane. In this seminar, these observed downwelling responses are analyzed in the context of upwelling theories that ignore or consider the contribution from background geostrophic oceanic flow. Rather than with just Ekman pumping (We), these observed upwelling-downwelling responses are consistent with the vertical velocity Ws=We-RoD(U+u’); Ws is the TC-driven pumping velocity derived from the dominant vorticity balance that considers geostrophic flow strength (measured by the eddy Rossby number Ro=Vg/f), geostrophic vorticity (Vg), Coriolis frequency (f), aspect ratio (D=h/RMW), oceanic mixed layer thickness (h), storm’s radius of maximum winds (RMW), and total surface stresses from storm motion (U) and Ekman drift (u’). These results underscore the need for initializing coupled numerical models with realistic ocean states to correctly resolve the three-dimensional upwelling-downwelling responses and improve TC intensity forecasting. (This seminar will be based on a paper with the same title that was recently published in Journal of Physical Oceanography A copy of the paper can be found at: http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-14-0176.1.)

The presentation is available on the anonymous ftp site:

ftp://ftp.aoml.noaa.gov/hrd/pub/blog/seminars/2015/Jaimes_HRD_Seminar_20150716.pptx

Jaimes presentation

Jaimes presentation

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