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Hurricanes
The prediction of both hurricane track and intensity relies heavily on
weather prediction models. However, great uncertainties
still remain in the formulation of a few key model physics components that
are critical to the development of hurricanes. One of these components is
identifying the variables (or parameterizing) of momentum and heat fluxes across the air-sea
interface. All the flux parameters currently used in the operational
models were developed using observations taken under winds weaker than
those associated with a typical hurricane. Furthermore, under hurricane
conditions, the air and sea is separated by a spray-filled transition
layer. Parameterizations of momentum and heat fluxes across such a layer
need to take into account the effect of sea spray, but they currently do
not.
Methods
Over the past decade, research has been carried out to combine
atmospheric observations, laboratory experiments and numerical modeling
studies to develop, test and improve the parameterizations of air-sea
momentum and heat fluxes under hurricane conditions.
Research Activities & Outcomes
We developed a method for parameterizing air-sea heat fluxes as an
extension of the TOGA-COARE bulk flux model, which has been refined with observations from new field
campaigns and updated theoretical understanding. The unique aspect of this
scheme is that it includes the sea-spray contribution to the air-sea heat fluxes for winds greater than 25
m/s. We are currently testing and evaluating the ESRL air-sea heat
flux parameterization scheme in the operational hurricane model (HWRF) and
the community weather research and forecast model (WRF-ARW). The goals of
the ongoing research with both the operational and research models are (1)
to determine the sensitivity of the sea-spray mediated air-sea heat flux
calculation to the uncertainties in the wave dynamics and the kinematic and
thermodynamic feedbacks of sea spray, and (2) to make the scheme more
general by including both the spray evaporation feedback and stress
reduction effects. We are also closely collaborating with researchers from
NOAA and universities to evaluate the impact of the improved air-sea flux
scheme on the marine boundary layer dynamics under hurricane conditions.