HRD seminar – Annette Foerster, University of Hawai’i, Manoa – 8 September 2015

Annette presented a seminar “Radar-Derived Buoyancy and its Role in Hurricane Intensity Change.

ABSTRACT:

Ordinary tropical convection is generally forced by positive buoyancy, but rotational forces and a strengthening warm core play a progressively important role in organizing convection as a TC intensifies. Axisymmetric conceptual and numeric models of the eyewall are characterized by moist neutral ascent forced by boundary layer convergence. In contrast, three-dimensional models suggest that a significant fraction of eyewall convective elements may contain positive buoyancy, and that asymmetric forcing by vertical shearing flow and mesoscale vorticity anomalies may play an important role. Further clarification is needed to determine the role of buoyancy in TC intensity change throughout its life-cycle.

Buoyancy cannot be observed directly, nor is it defined uniquely. Buoyancy can be deduced from simultaneous measurements of kinematic and thermodynamic fields, but high-resolution measurements of these fields in a tropical cyclone only exist along an aircraft track or a dropsonde profile. An indirect retrieval approach will be presented, which allows to estimate buoyancy values for the entire eyewall region using aircraft radar observations. The methodology and a preliminary analysis of the structure and buoyancy of eyewall convection in Hurricane Rita (2005) will be presented.

The presentation is available on the anonymous ftp site:

ftp://ftp.aoml.noaa.gov/hrd/pub/blog/seminars/2015/Foerster_HRD_Seminar_20150908.mp4

Foerster presentation

Foerster presentation