Towards a homogeneous 50 year climatology of typhoons in SE Asia.

Hans von Storch and Frauke Feser

Twelfth Pacific Congress on Marine Science and Technology, PACON 2006: Marine Science and Technology in Asia, Yangon, Myanmar, June 11-15, 2006

Downscaling approach• Regional phenomena = mainly

a result of interplay large-scale state and of regional dynamics.

• Added value provided by regional atmospheric modeling when large scales are constrained (= spectral nudging; cf von Storch et al., 2000)

• Successfully implemented for NE Atlantic climate.

• Results in a homogeneous realistic description of past storminess (and, possibly of scenarios of futures) and marine wind impacts.

Downscaling SE Asian marine weather

• We now implement the dynamical downscaling approach for SE Asian marine weather.

• The key question is if we will master the description of typhoons.

• Presently: Case studies – formation of typhoons induced by large scale dynamics and NOT by initial values.

• Similar study underway at GFDL (Tom Knutson) dealing with N Atlantic hurricanes

• No “white” publications yet.

A case study:

Simulating tropical storm Winnie

(August 1997)with a regional a climate model

-Sensitivity to spectral nudging

-Sensitivity to horizontal resolution

with regional atmospheric modelCLM; initiated at or close to1. August 1997.

Conventional RCM-simulations

with spectral nudging

NCEP

16.8.1997

Dates refer to time of initialization of simulation

Effect of spectral nudging and different initial states

CLM run with 0.5º grid

Effect of horizontal grid configuration: 0.5º; double nesting 0.5º→0.165º

Effect of horizontal grid configuration: double nesting 0.5º→0.165º and direct 0.165º

Core pressure development

Max wind speed development

Conclusions

• (Some) typhoons can be described by regional atmospheric models run in the climate model.

• Lateral boundary value control is insufficient to reconstruct number and track of typhoons

• Higher resolution, obtained through double nesting, gives better results.

• Results represented are preliminary.• We need better data for validation.