This project will undertake the following: (i) establish the large-scale eastern North Pacific tropical cyclone (TC) climatology and variability, including investigating the near-coastal versus open ocean variability of TC activity and the large-scale circulation patterns associated with the modes of variability; (ii) extend of the current database of near-coastal TC remnants both in time as well as to include 3-dimensional atmospheric information; and (iii) perform the statistical analysis of characteristic circulation patterns associated with particular rain swath patterns across the southwestern U.S. region. The research will increase fundamental understanding of the climate variability of eastern North Pacific tropical cyclones and how a changing climate will alter their impacts on the sensitive southwestern U.S. and Mexico regions. Better understanding of the large-scale circulation patterns that increase TC landfall activity may lead to improved seasonal forecasts of these phenomena as well as resource and management planning into the future.

Project Report

We have studied the impacts of eastern North Pacific landfalling tropical cyclone (TC) on the SW U. S. and Mexico over the period 1989-2009, which yielded 167 cases. Statistical analysis shows that there are specific large-scale atmospheric patterns that produce particular tracks and particular spatial rainfall swaths as these TCs make landfall in this region (Figs. 1, 2) (Wood and Ritchie 2013a). We have studied the structural evolution of eastern North Pacific TCs over the 42-yr period 1971-2012 and established that there are 4 basic lifecycles these TCs can evolve through (Fig. 3): 1) remain tropical; 2) transition from warm-core to cold-core before dissipating; 3) remain warm core as they dissipate; and 4) complete extratropical transition – this category produces the majority of the landfalling cases mentioned in 1 (Wood and Ritchie 2014a). We have studied the extratropical transition (ET) group in more detail as this group has the potential to produce significant impacts (particularly rainfall) in the S.W. U.S. Over the same 42-yr period we found that 9% (55/631) TCs completed ET, which is a smaller number than in other tropical basins globally. Several large-scale factors contribute to the much smaller population of TCs that undergo ET in the eastern North Pacific including a rapidly decreasing sea-surface temperature to the north of the main TC development region and a strong ridge that extends from the North American continent west over the eastern North Pacific. Furthermore, there is a strong correlation with the El Niño – La Niña phenomenon in the Pacific Ocean with higher frequency of ET in El Niño (warm) years and no activity in La Niña (cold) years (Wood and Ritchie 2014b). Finally, we have been investigating the relationship between convective available potential energy (CAPE) and the maximum potential intensity (MPI) of TCs in the tropical regions. References: Wood, K. M., and E. A. Ritchie, 2013: An Updated Climatology of Tropical Cyclone Impacts on the Southwestern United States. Mon. Wea. Rev., 141, 4322–4336. Wood, K. M., and E. A. Ritchie, 2014a: A 32-year reanalysis intercomparison of tropical cyclone structure in the eastern North Pacific and North Atlantic. An abstract submitted to the 31st Conference on Hurricanes and Tropical Meteorology, March 31 – April 4 2014, San Diego, CA. Wood, K. M., and E. A. Ritchie, 2014b: A 40-y climatology of extratropical transition in the eastern North Pacific. J. Climate. (In Review).

National Science Foundation (NSF)
Division of Atmospheric and Geospace Sciences (AGS)
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Anjuli S. Bamzai
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University of Arizona
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