Future Changes in Tropical Cyclone Activity in the North Indian Ocean Projected by the New High- Resolution MRI-AGCM - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 64

cumulus convection scheme (Randall and Pan, 1993); a new cumulus convection
scheme, called the “Yoshimura scheme” (YS) after a model developer at the
MRI; and a Kain-Fritsch (KF) convection scheme (Kain and Fritsch, 1990).
The YS scheme is based on the Tiedtke scheme. A so-called “time-slice” method
is applied for future projections. The targeted projection window for the future
climate is the last quarter of the 21st century (2075-2099).
For the SST-ensemble projections, four different projections of future SSTs
are prescribed, each of which have a different spatial SST anomaly pattern.
One of these patterns is the multi-model ensemble mean of SST computed
from future projections by the 18 CMIP3 models under the Special Report on
Emission Scenarios (SRES) A1B scenario (IPCC, 2007). The other three
patterns are created using a cluster analysis, in which normalized tropical SST
anomalies derived from the 18 CMIP3 models are grouped to avoid subjective
selection of single model. Figure 1 shows all four prescribed future changes in
the annual-mean SST. Most of the SSTs show relatively larger increase in the
Arabian Sea. In all, 15 ensemble simulations are conducted. Table 1 lists all of
the experiments.
TCs are detected in the model by evaluating six-hourly model outputs
using globally uniform criteria. These criteria are based on those described by
Murakami et al. (2012a, 2012b). In short, it considers low-level vorticity and
maximum wind speed, temperature anomaly, and duration. Some criteria are
optimized for a given model configuration to ensure that the present-day (1979-
2003) global annual mean TC number matches that observed (about 84 per
year for the period 1979-2003).

Table 1: List of ensemble simulations

CMIP3 Cluster 1 Cluster 2 Cluster 3

Model version Resolution Cumulus Mean SST SST SST SST

MRI- 20 km X

AGCM 3.1 60 km AS X

20 km X

MRI- 60 km YS X X X X

AGCM 3.2 60 km KF X X X X

60 km AS X X X X

3. Results

3.1 Projected Future Changes in TC Genesis Number

Figure 2 shows projected fractional future changes in TC genesis number for
NIO basin and sub basins. The projected NIO TC numbers are not significant
statistically except for KF scheme, although the majority of the experiments
show reductions in the Bay of Bengal and increases in the Arabian Sea.