Topic No. 3
Observing System Experiments for Typhoon Conson (2004)
Tropical Cyclone Ensemble Forecast
Nanjing, China
9:00 – 12:00
2011.12.15 (Thr)
Munehiko Yamaguchi
Typhoon Research Department,
Meteorological Research Institute of the Japan Meteorological Agency
Some issues to be addressed
Issues
Present
The accuracy of typhoon track forecasts has steadily improved.
Chan (2010, GPTC)
Since Chan et al. (2002) paper, research on the physics of general TC motion
has been almost non-existent, which suggests that most scientists are quite
content with the current theories of TC motion.
In reality, however, significant errors still exist and there are prediction cases
where the position error exceeds 1000 km at 3 days.
There are few studies focusing on the cause of prediction errors.
(e.g. Carr and Elsberry 2000a, 2000b）.
Approach
Lack of observations around TCs is one of the reasons
Flow of typhoon
forecasting
of TC
track prediction errors.
Obs.
Data
assimilation
NWP
Forecaster
Various causes of forecast errors
Any approach to separate them to some extent?
User
Observations by aircraft in the Atlantic basin
 According to Aberson et al. (2006), TC observations by
aircraft started in 1943 (observations at the flight level).
 Omega dropsonde was first used for the observations in 1982
(Cole et al. 1973) and GPS dropsonde took the place in
1996 (Hock and Franklin 1999).
 National Ocean and Atmosphere Administration (NOAA)
started the operational synoptic surveillance in 1997 using
both G-IV and P-3 aircrafts (Aberson and Franklin 1999).
Gulfstream IV-SP (G-IV)
NOAA/AOML/HRD website at
http://www.aoc.noaa.gov/aircraft_g4.htm
 Aberson (2010) evaluated the impact of the dropsonde
observations on the TC track predictions. The average
improvement rate is 10 to 15 %.
Observations by aircraft in the western Pacific basin
According to Aberson et al. (2006), TC observations by aircraft was
conducted in the western Pacific by the US army since early 1950’s . Guard et
al. (1992) reported that the observations started in 1945.
However, the operations stopped due to the budget issue in 1987 (Gray et al.
1991, Guard et al. 1992 )
Dropwindsonde Observations for Typhoon Surveillance near the Taiwan
Region (DOTSTAR) has been conducted by the National Taiwan University
and the Central Weather Bureau of Taiwan, along with the NOAA since 2003
(Wu et al. 2005).
Aircraft "ASTRA“
DOTSTAR website at
http://typhoon.as.ntu.edu.tw/DOTSTAR/en/intro/equip.php
Wu et al. (2007) evaluated the impact of the dropsonde observations on the
TC track predictions. The average improvement rate is 14 % to 19% at 3 day
predictions.
THORPEX Pacific Asian Regional Campaign (T-PARC) was conducted in
2008 (Nakazawa 2010).
Let’s see a case study for Typhoon Conson
(2004) to understand how assimilating
dropsonde observations improves the synoptic
features that controls the steering flow.
DOTSTAR observations for Typhoon Conson (2004)
DOTSTAR operation was
conducted for Typhoon CONSON
at 12 UTC 08 June 2004. Sixteen
dropsondes were released around
the typhoon
IR image at the time of observation
Produced by National
Institute of Informatics
Central Position
Central Pressure 960 hPa
Maximum Wind : 65 kt
Synoptic features around Conson
Geopotential height (contours) and wind (vectors)
250 hPa
500 hPa
Conson was located in a confluent area induced by
the sub-tropical high and the westerly jet
The impact of dropsonde observations on the track
Experiment (I) : No dropsonde data is assimilated
Experiment (II) : All dropsonde data is assimilated
How initial condition changed?
The assimilation of dropsondes
improved the steering flow
east of Typhoon Conson,
leading to the northeast
movement of the typhoon.
CONSON’s central position
m/s
Ensemble perturbation
Singular vectors are computed for the initial field of NODROP and the
leading singular vector is used as ensemble initial perturbation.
Vertically accumulated total
energy of 1st singular vector
Geopotential height at 500 hPa
Thin line: NODROP
Thick line: Perturbed field
The impact of initial perturbation on the track
Experiment (I) : No dropsonde data is assimilated
Perturbed run : The first singular vector is added to the initial
condition of Experiment (I)
If the dropsondes had been deployed around the westerly jet,
the track prediction would have been much more improved.
The impact of dropsonde observations on the track
Experiment (I) : No dropsonde data is assimilated
Experiment (II) : All dropsonde data is assimilated
Vertically accumulated total
energy of 1st singular vector
The impact of selected dropsonde observations on the track
Experiment (III) : DOTSTAR data within the sensitive region is assimilated
Experiment (IV) : DOTSTAR data outside the sensitive region is assimilated
Summary
1. DOTSTAR data had a positive impact on track prediction for
typhoon CONSON at 12UTC 8 Jun. 2004.
2. The assimilation of dropsondes improved the steering flow
east of Typhoon Conson, leading to the northeast movement
of the typhoon.
3. The improvement of the representation of the steering flow
was achieved by only 8 dropsondes (half the total
dropsondes) within the sensitivity area identified the singular
vector.
4. If the dropsondes had been deployed around the westerly jet,
the track prediction would have been much more improved.