Future Changes in Tropical Cyclone Activity Projected by the New High-Resolution MRI-AGCM

New versions of the high-resolution 20- and 60-km-mesh Meteorological Research Institute (MRI) atmospheric general circulation models (MRI-AGCM; v3.2) have been developed and used to investigate potential future changes in tropical cyclone (TC) activity. Compared with the previous version (v3.1), v3.2 yields a more realistic simulation of the present-day (1979–2003) global distribution of TCs. Moreover, the 20-km-mesh v3.2 is able to simulate extremely intense TCs (Categories 4 and 5), which is the first time a global climate model has been able to simulate such extremely intense TCs through a multi-decadal simulation.

Future (2075–2099) projections under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario are conducted using v3.1 and v3.2, showing consistent decreases in the number of TCs globally and in both hemispheres as climate warms. Although projected future changes in basin-scale TC numbers show some differences between the two versions, the projected frequency of TC occurrence shows a consistent decrease in the western part of the Western North Pacific (WNP) and in the South Pacific Ocean (SPO), while it shows a marked increase in the Central Pacific. Both versions project a future increase in the frequency of intense TCs globally; however, the degree of increase is smaller in v3.2 than in v3.1. This difference arises partly because v3.2 projects a pronounced decrease in mean TC intensity in the SPO. The 20-km-mesh v3.2 projects a northward shift in the most intense TCs (Category 5) in the WNP, indicating an increasing potential for future catastrophic damage due to TCs in this region.

Basin-scale future changes in TC frequency and mean TC intensity are inconsistent between the two versions, in terms of both degree and sign. These regional discrepancies highlight continuing uncertainties regarding how and to what degree TC activity is likely to change at the basin scale.

Reference: Murakami, H. and coauthors, 2011: Future changes in tropical cyclone activity projected by the new high-resolution MRI-AGCM. J. Climate, In press