Statistical-dynamical Downscaling

Asuka Suzuki-ParkerNCAR Earth System Laboratory

National Center for Atmospheric Research

NCAR is Sponsored by NSF and this work is partially supported by the Willis Research Network and the Research Program to Secure Energy for America

Approach

1. Randomly place a weak

storm

2. Determine trajectory based on

large-scale info and

probabilistic perturbation

3. Calculate intensity based on

large-scale info along the

trajectory

4. Majority of storms don’t

reach TC intensity, but

some do

Large-scale info from bias corrected CCSM

Current: 1950-1999 (20C3M)Future: 2000-2099 (A2)

Genesis Distribution

Pretty good agreement with current observationexcept for tropical Atlantic

North AtlanticTC frequency projection

No trend in annual

frequency

Intensity projection

No change in intensity

either

Genesis location projection

Why no trends?

More favorable

Less favorable

Stat-dyn downscale genesis location Projected large-scale trends

Compared to observation, stat-dyn downscale technique is producing more storms in high latitutdes, and less in tropics

As North Atlantic as a whole, trend gets canceled out

TC duration projection

Increasing average TC

duration

PDI increases

TC size projection

Reduction in TC size

is projected

Summary

• Stat-dyn downscaling is successful in reproducing general global TC formation

• Little TC formation in tropical Atlantic– Fails to capture large-scale trend– No trend in frequency or intensity as

whole North Atlantic

• Storm size and duration trends in agreement with NRCM

Comparisons among three techniques

NRCM Stat-dyn GP

Frequency Increase Steady Depends on area

Intensity Increase Steady

Genesis location Southward shift Steady Southward shift

Size Decrease Decrease

Duration Increase Increase