Future Changes in the Western North Pacific Tropical Cyclone Activity Projected by a Multidecadal Simulation with a 16-km Global Atmospheric GCM

Abstract

How tropical cyclone (TC) activity in the northwestern Pacific might change in a future climate is assessed using multidecadal Atmospheric Model Intercomparison Project (AMIP)-style and time-slice simulations with the ECMWF Integrated Forecast System (IFS) at 16-km and 125-km global resolution. Both models reproduce many aspects of the present-day TC climatology and variability well, although the 16-km IFS is far more skillful in simulating the full intensity distribution and genesis locations, including their changes in response to El Niño-Southern Oscillation. Both IFS models project a small change in TC frequency at the end of the twenty-first century related to distinct shifts in genesis locations. In the 16-km IFS, this shift is southward and is likely driven by the southeastward penetration of the monsoon trough/subtropical high circulation system and the southward shift in activity of the synoptic-scale tropical disturbances in response to the strengthening of deep convective activity over the central equatorial Pacific in a future climate. The 16-km IFS also projects about a 50% increase in the power dissipation index, mainly due to significant increases in the frequency of the more intense storms, which is comparable to the natural variability in the model. Based on composite analysis of large samples of supertyphoons, both the development rate and the peak intensities of these storms increase in a future climate, which is consistent with their tendency to develop more to the south, within an environment that is thermodynamically more favorable for faster development and higher intensities. Coherent changes in the vertical structure of supertyphoon composites show system-scale amplification of the primary and secondary circulations with signs of contraction, a deeper warm core, and an upward shift in the outflow layer and the frequency of the most intense updrafts. Considering the large differences in the projections of TC intensity change between the 16-km and 125-km IFS, this study further emphasizes the need for high-resolution modeling in assessing potential changes in TC activity.

Past and Projected Changes in Western North Pacific Tropical Cyclone Exposure

“…simultaneously as a northeastward migration (Murakami et al 2012;Colbert et al 2015;Roberts et al 2015), and one model projects a southeastward shift (Manganello et al 2014). While tempering our results with knowledge of this lack of firm consensus in model projections of WNP TC track variability, here we expand on previous work by analyzing the tracks of TCs formed in a suite of CMIP5 models and downscaled from CMIP5 environmental data (Emanuel 2013(Emanuel , 2015, focusing on changes in f LMI and associated patterns of change of TC exposure, and comparing these patterns to observed patterns.…”

“…A number of previous studies have explored relationships between WNP TC track characteristics and anthropogenic climate change and have identified systematic shifts in TC genesis location and steering flow that combine to cause TC track shifts (Wu and Wang 2004;Li et al 2010;Wang et al 2011;Murakami et al 2011Murakami et al , 2012Yokoi et al 2013;Bell et al 2013;Mori et al 2013;Manganello et al 2014;Wu et al 2014;Colbert et al 2015;Mei et al 2014Mei et al , 2015Roberts et al 2015;Wang and Wu 2015). There is, however, some divergence among the model projections in some of these studies.…”

A 20-Year Climatology of a NICAM AMIP-Type Simulation

“…In such cases, statistical downscaling approach (Zhao et al 2010) may be useful to investigate the historical and future TC intensity. Recent studies have shown that AGCMs with a finer horizontal resolution, such as 10-20 km, reproduce more realistic TC intensity histograms (Murakami and Sugi 2010;Manganello et al 2012;Manganello et al 2014). However, the simulated TC intensity also strongly depends on the cumulus convection scheme (Murakami et al 2012).…”

Evaluating the Emanuel-Nolan genesis potential index: Contrast between North Atlantic and western North Pacific

“…As in most previous studies, only TC systems reaching at least the tropical storm intensity (i.e., the maximum sustained wind speed v max ≥ 35 knots) during the period from 1979 -2010 are counted here. While a number of metrics have been designed to stratify various aspects of the basin-scale seasonal TC activity, including the "accumulated cyclone energy index" (Bell et al 2000;Waple et al 2002), "power dissipation index" (Emanuel 2005), and their revised versions (Yu et al 2009;Yu and Chiu 2012), we prefer to use the "number of tropical cyclones" (NTC) to characterize the magnitude of basin-scale seasonal TC activity as in most previous studies (Chan and Liu 2004;Holland and Webster 2007;Murakami and Wang 2010;Murakami et al 2012;Manganello et al 2014).…”

“…In the first approach, the occurrence frequency of TC-like vortices is explicitly simulated using high-resolution coupled climate models, typically with a horizontal resolution less than 20 km (Murakami and Wang 2010;Murakami et al 2012;Manganello et al 2014;Vecchi et al 2014). Since this approach utilizes coupled climate models with full dynamics and physics, it is often referred to as the "dynamical method" in the TC-climate interaction study.…”