An Analysis of the Impacts of Western North Pacific Tropical Cyclones on Their Local and Large Scale Environment PDF Download

Author: Benjamin Alan Schenkel
Publisher:
ISBN:
Category : Atmospheric physics
Languages : en
Pages :

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Book Description
ABSTRACT: The following study examines the spatiotemporal response of the local scale and large scale environment to tropical cyclone (TC) passage. The research presented here is broken up into three chapters that can be separated into two parts. Given that the analysis of the environmental response to TC passage heavily relies upon the use of atmospheric reanalysis datasets, the first half of this dissertation (Chapter 2) will examine the fidelity of TC intensity, position, and intensity life cycle within five reanalyses to determine what reanalyses can be used for when studying TCs. The results of this analysis show an underestimation of reanalysis TC intensity beyond what can be attributed to the coarse grid resolution of reanalyses. Moreover, the mean life cycle of normalized TC intensity within reanalyses exhibits an underestimation of pre-peak intensification rates as well as a delay in the timing of peak TC intensity relative to the Best Track. Significant discrepancies between reanalysis and Best-Track TC position are noted to exist particularly in regions that are observation deficient. Of the five reanalyses examined, the NCEP Climate Forecast System Reanalysis (CFSR) and JMA 25-yr Japanese Reanalysis (JRA-25) have the most robust representation of TCs particularly within the North Atlantic (NATL) and Western North Pacific (WPAC). The second half of this study examines the local scale (Chapter 3) and large scale (Chapter 4) impacts of WPAC TCs upon their environment using storm-relative composites. On local scales, TCs are found to cool sea surface temperatures (SSTs) for at least a month following TC passage. The feedbacks from the SST cold wake combined with an initial net flux divergence of energy from the column yields a significant cooling and drying of the atmosphere that is strongest in the lower troposphere. Restoration of the environment is eventually achieved through a return of SSTs to climatology and a net flux convergence of potential energy aloft. The large scale response of the environment is primarily associated with an anomalous drying of the lower and middle tropospheric atmospheric environment to the west and southwest of the TC. The drying appears to be caused by upper level convergence resulting from the interaction of the TC outflow with its environment. On the western side of the TC, both the upper level flow from the anticyclone of the Asian monsoon and the increasing inertial stability with latitude due to the meridional gradient of planetary vorticity limit the ventilation to the west of the TC yielding upper level convergence and subsidence. The area of anomalous drying to the southwest is associated with the convergent upper level flow from the right exit region of the anticyclonically curved equatorward outflow jet of the TC. Lastly, the meridional transport of total energy by TCs results in a substantial cross hemispheric export of dry static energy nearly 4000 km southwards as result of the upper level outflow jet of the TC. The meridional dry static energy transports by TCs appear to comprise a substantial portion of the total atmospheric dry static energy transports at the equator during late summer and early fall. In their totality, these results suggest that TCs may significantly impact their environment both on long temporal scales and large spatial scales with potentially significant aggregate climate impacts in the WPAC given the high frequency of TC occurrence.