New paper predicts decreased global tropical cyclones over the 21st century

A new paper published in Geophysical Research Letters models ocean temperatures, greenhouse gases, and aerosols from 1872 to 2099 and predicts "a clear decreasing trend of global tropical cyclone frequency throughout the 228 years of simulation." 

GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L19805, 5 PP., 2012
doi:10.1029/2012GL053360

Decreasing trend of tropical cyclone frequency in 228-year high-resolution AGCM simulations

Key Points

• Model simulations indicate a clear decreasing trend of TC [tropical cyclone] frequency
• The same model projects a decrease of TC [tropical cyclone] frequency in the future
• The decresing trend of TC is closely related to that of upward mass flux

Masato Sugi

Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan

Meteorological Research Institute, Tsukuba, Japan

Jun Yoshimura

Meteorological Research Institute, Tsukuba, Japan

We conducted 228-year long, three-member ensemble simulations using a high resolution (60 km grid size) global atmosphere model, MRI-AGCM3.2, with prescribed sea surface temperature and greenhouse gases and aerosols from 1872 to 2099. We found a clear decreasing trend of global tropical cyclone (TC) frequency throughout the 228 years of the simulation. We also found a significant multidecadal variation (MDV) in the long term variation of Northern Hemisphere and Southern Hemisphere TC count in addition to the decreasing trend. The decreasing trend and MDV in the long term variation of TC count correspond well to a similar decreasing trend and MDV of upward mass flux averaged over the TC genesis region and active TC season. It has been shown that the upward mass flux decreases primarily because the rate of increase of dry static stability, which is close to that of surface specific humidity, is much larger than the rate of increase of precipitation, which is nearly the same as that of atmospheric radiative cooling. Thus, it is suggested that the decreasing trend of TC count is mainly caused by the decreasing trend of upward mass flux associated with the increasing dry static stability.