Characteristics of Western North Pacific Tropical Cyclones in the Regional Spectral Model

1
Characteristics of Western North Pacific Tropical
Cyclones in the Regional Spectral Model

• Suzana J. Camargo,
• Huilan Li and Liqiang Sun

2
Motivation

• IRI currently produces experimental tropical
  cyclone activity forecasts based on tropical
  cyclone-like structures in an AGCM (ECHAM4.5).
• Issues low-resolution of the AGCM large weak
  tropical cyclones, mean number of TCs in the
  AGCM is low.
• Explore the possibility of using RSM forced by
  AGCM to improve these forecasts.
• Choice Western North Pacific basin with 30
  of the TCs in the globe, IRI has projects in the
  Philippines, which is largely affected by typhoon
  activity.

3
Description of the Experiment

• RSM (60km) forced by the ECHAM4.5 AGCM (T42).
• Period June November (typhoon season).
• 10 ensemble members
• Years 1994 (high typhoon activity) and 1998 (low
  typhoon activity).

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Number of Named Tropical Cyclones
1998
1994
5
Detecting and Tracking Tropical Cyclone-like
structures

• Using the output of the AGCM and RSM integrations
  (and NCEP Reanalysis), tropical cyclone-like
  structures are detected and tracked.
• Variables used in the detection and tracking
  algorithms
• Vorticity, sea level pressure, wind speed,
  temperature
• Algorithm description
• S.J. Camargo S.E. Zebiak, Wea. Forecasting,
  2002.

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Typical AGCM Tropical Cyclone
Winds
Vorticity
Humidity
Precipitation
7
Typical RSM Tropical Cyclone
Winds
Vorticity
Humidity
Precipitation
8
Number of Tropical Cyclones 2
9
First Positions of TCs
FIRST POSITIONS
Observations
RSM
ECHAM
ECMWF Rean.
10
TRACKS
OBS
RSM
ECHAM
ECMWF Rean.
11
Track Distribution Difference
1994 - 1998
OBS
RSM
ECHAM
12
Intensity - ACE
13
Sea Level Pressure Difference1998-1994
X 100
RSM
LOW activity HIGH activity
ECHAM
ECMWF Reanalysis
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Zonal Winds 1000hPa
RSM 1994
RSM 1998
ECMWF Reanalysis 1994
ECMWF Reanalysis 1998
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Conclusions

• Using RSM forced by AGCM improves characteristics
  of the tropical cyclones related to the
  horizontal resolution (structure, size,
  intensity).
• Characteristics of the tropical cyclone activity
  for the whole season seems to be degraded by the
  downscaling compared with the AGCM.
• In order to have a better idea of the skill of
  RSM it would be necessary to perform the
  simulations for more years.