: To improve tropical cyclone structure and intensity prediction through a research program combining high-resolution modeling and detailed observational studies to investigate physical processes by which the structure and intensity of a tropical cyclone are modified. The objective is to investigate the physical processes that occur as a tropical cyclone interacts with the environment such that intensity and structure changes occur. Specific interactions being studied are with baroclinic environments in the midlatitudes during extratropical transition. During extratropical transition, radical changes to the storm structure occur as vertical wind shear and intruding cold, dry air from the midlatitudes erode the warm core. Re-intensification to a strong midlatitude system is possible. In cases in which forecast models poorly predicted the motion and re-intensification of the storm during these transitional periods, better understanding of these processes should improve motion and intensity forecasts.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA417496&Location=U2&doc=GetTRDoc.pdf

The Extratropical Transition of Tropical Cyclones

Accurate precipitation forecasts is a perennial problem in numerical weather forecasting, necessitating the use of an appropriate cloud microphysics scheme (Thompson et al. 2004). Furthermore, recent modeling studies have indicated the sensitivity to microphysical parameters of details of storm structure (Wakimoto et al. 2004; van den Heever and Cotton 2004; Gilmore et al. 2004b) and even prototype Doppler retrievals of temperature fields (Dowell et al. 2004). In this abstract we focus on one diagnosed potential problem of the standard treatment of hydrometeor collection in microphysics scheme. Using the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), we implement a microphysics scheme where the diagnosed problem is corrected. Though we only consider the COAMPS microphysics here, the issues discussed have general applicability to other schemes. Sensitivity tests between the standard and modified scheme are performed on an idealized case involving the transformation of a tropical cyclone remnant into an extratropical system. This scenario exhibits both warm-rain and cold-rain microphysics, depending on simulation time. After describing the model setup, we discuss the modified microphysics, and then present the model comparison tests. We then conclude and mention possibilities for future work.

Relationships between mixed-phase microphysical collection and modeled precipitation in various regimes

The extratropical transition of tropical cyclones (hereafter TCs) can be a particularly complex process (e.g. DiMego and Bosart 1982; Harr and Elsberry 2000; Klein et al. 2000; Jones et al. 2003). As a general outline, however, as they progress northward they undergo what Klein et al. (2002) refer to as the transformation stage, which involves the loss of axisymmetry, an upper-level warm core, and other characteristics. However, if the TC remnant is able to interact with an upper-level system, a reintensification stage may then occur, and the system may become a potent extratropical cyclone. In order to learn more about the reintensification stage, an idealized study was performed using the An idealized modeling study (Ritchie and Elsberry 2003) was performed using the COAMPS R © regional model. A series of simulations was performed, each containing a lowlevel TC-like vortex and an upper-level trough of various strengths. It was found that, whereas the trough-induced minimum sea level pressure (SLP) was dependent on the strength of the trough, the minimum SLP of the reintensified TC remnant was almost insensitive to trough strength (and in all cases lower than that achieved in the troughonly simulations). Recently other idealized simulations have been performed to investigate the role of the trough/TC spatial configuration. In this case it was found that reintensification was highly sensitive to the details of the initial configuration (Ritchie 2005). All of the preceding simulations were performed using 27 km grid spacing on the finest, or only, grid. In this study increased resolution will be introduced into the simulations to allow a closer examination of the reintensification process, and in particular the role of resolved microphysical processes.

Brian J. Gaudet

Papers

Relationships between mixed-phase microphysical collection and modeled precipitation in various regimes

The importance of resolved microphysics to reintensification during the extratropical transition of tropical cyclones