CAN WE OBSERVE THE PARAMETERS AND PROCESSES INVOLVED IN TC INTENSITY CHANGE ADEQUATELY?
Christopher S. Velden
University of Wisconsin - Cooperative Institute for Meteorological Satellite Studies
TC intensity change remains as one of the atmospheric science's greatest mysteries. Although some headway has been made in recent years through research conducted by the NOAA Hurricane Research Division's program, the problem remains unresolved due to the complexity and the scale interactions involved. Improved understanding and skillful forecasts will depend on our ability to observe the critical parameters and processes governing the modulation. These observations are a necessary first step towards providing an adequate initial state for model predictions.
The questions and issues this paper hopes to raise are centered around whether
our current knowledge base is adequate enough to identify these critical
parameters and processes. Even if we can identify them, does our present
observational capability allow us to focus on these parameters with the precision
necessary to resolve the processes acting to modulate TC intensity?
A recent report by the US Weather Research Program Prospectus Development
Team #5 (PDT5) identified three suspected influences on TC intensity: 1)
internal storm dynamics, 2) interactions with upper-tropospheric environmental
circulations, and 3) interactions with underlying ocean circulations. The relative
importance of these three influences with respect to each other is not known.
However, it is imperative that we further partition these rather broadly stated
influences into more specific foci in order to direct our observational
It is inconceivable that we can begin to address the complex questions and issues
outlined above without a concentrated effort that squeezes the maximum out of
our current observational resources. Focusing our measurements on the TC
intensity problem will have to involve a challenging blend of experience,
intuition and creativity. It is imperative that we exploit the capabilities and
strengths of each of the candidate observing systems in an optimal way to target
measurements that will address all scales of the problem.
In the author's view, a dedicated field program will be necessary to collect the
needed observations. This should be attended by a careful (yet vigorous)
post-analysis to explore the scale interactions and define the relative role of the
complex array of physical processes governing the TC intensity. The
optimization of 4D assimilation of the collected data into high-resolution fields
should not be overlooked. Accurate kinematic fields and diagnostics will depend
highly on this step.
The data collection program should build on existing initiatives with
enhancements through intensive observational periods involving special
resource deployments and sampling strategies. In this regard, it is arguable that
the western Atlantic basin should serve as the playing field. The rationale
behind this is supported by: 1) An existing field program directed by NOAA's
AOML-HRD with many components either directly or indirectly related to our
quest, 2) Routine AF reconnaissance aircraft support, 3) Availability of
Gulfstream-IV high-level jet observations and GPS sondes, 4) Availability of
mobile/transportable observing systems, 5) WSR-88D coastal radar network, 6)
Unsurpassed geostationary satellite sensing capabilities (GOES) with
programmable sampling, and 7) A strong oceanic program in place (and
enhancements possible) headed by NOAA and RSMAS.
It is assumed that the basic knowledge gained by such an investigation in the
Atlantic basin will apply in a universal way to other TC basins, at least in terms
of the fundamental physical processes which are acting and their relative roles in
TC intensity modulation. The bottom line is to utilize the number of existing
tools in new and innovative ways in concert with emerging technologies to
focus an integrated approach towards targeting the processes involved in
To answer the question put forth in the title of this paper, it is the belief of this
author that an improved understanding of the processes modulating TC intensity
change can be achieved through an integrated and focused observational
program. It is imperative that the measurements are keenly directed to observing
the three primary areas (influences) outlined above, with attention to all of the
relevant scales. This observational study, coupled with idealized model-based
simulations, should lead us to a better understanding of the problem, improved
model parameterizations, and ultimately increased skill in predicting TC
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