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 requirements.

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 intensity change.

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 intensity change.

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