Mechanism of the Indian Ocean Tropical Cyclone Frequency Changes due to Global Warming - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 40

mechanism of the global and regional TC frequency changes due to global
warming (Table 1). We consider two effects: CO 2 effect and SST effect. In the
CO 2 effect, the overlap of CO 2 and water vapour long wave absorption bands
is playing an important role (Sugi and Yoshimura, 2004). The atmospheric
cooling will decrease due to the overlap effect when CO 2 is increased, leading
to a reduction of precipitation, upward mass flux and global TC frequency. On
the other hand, in the SST effect a static stability change is playing an important
role. When SST is increased, atmospheric temperature and moisture will
increase, leading to an increase in precipitation. However, since the increase in
dry static stability is larger than the increase in precipitation, the upward mass
flux in the tropics will decrease, leading to a decrease in global TC frequency.
3. Model and Experiment
In order to further explore the mechanism of global and regional TC frequency
changes due to global warming, five 25-year experiments have been conducted
using the 60 km-resolution MRI-AGCM3.2 (Mizuta et al., 2012) as shown in
Fig. 1. For the present climate run (P run), observed sea surface temperature
(SST) and atmospheric concentration of greenhouse gases (GHG) including
CO 2 and aerosols are prescribed. For the future climate run (F run), the CMIP3
ensemble mean SST anomaly is added to the present observed SST and GHG
and aerosols at the end of 21st century of A1B scenario is prescribed. For the
future SST run (SSTF run), future SST and present GHG are prescribed, while
for the future CO 2 run (CO 2 F run), future GHG and present SST are prescribed.
In addition, for the uniform SSTA run (USSTA run), future GHG is used as in
CO 2 F run but uniform 1.83K (global mean of CMIP mean SSTA) is added to
the present observed SST.
The difference between CO 2 F run and P run (CO 2 F-P) or F run and SSTF
run (F-SSTF) indicates the CO 2 effect, while the difference between SSTF run
and P run (SSTF-P) or F run and CO 2 F run (F-CO 2 F) indicates the SST effect.
Fig. 1: Experiments.