Munehiko Yamaguchi Typhoon Research Department, Meteorological Research Institute of the Japan Meteorological Agency 9:00 – 12: (Thr) Topic No. 3 Observing System Experiments for Typhoon Conson (2004) Tropical Cyclone Ensemble Forecast Nanjing, China

Some issues to be addressed  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. Present Issues  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 Obs. Data assimilation NWP User Forecaster Flow of typhoon forecasting Various causes of forecast errors Any approach to separate them to some extent? Lack of observations around TCs is one of the reasons of TC track prediction errors.

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).  Aberson (2010) evaluated the impact of the dropsonde observations on the TC track predictions. The average improvement rate is 10 to 15 %. Gulfstream IV-SP (G-IV) NOAA/AOML/HRD website at

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  However, the operations stopped due to the budget issue in 1987 (Gray et al. 1991, Guard et al )  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).  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). Aircraft "ASTRA“ DOTSTAR website at

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 operation was conducted for Typhoon CONSON at 12 UTC 08 June Sixteen dropsondes were released around the typhoon Produced by National Institute of Informatics Central Position DOTSTAR observations for Typhoon Conson (2004) IR image at the time of observation Central Pressure 960 hPa Maximum Wind : 65 kt

Synoptic features around Conson Geopotential height (contours) and wind (vectors) Conson was located in a confluent area induced by the sub-tropical high and the westerly jet 250 hPa500 hPa

The impact of dropsonde observations on the track Experiment (I) : No dropsonde data is assimilated Experiment (II) : All dropsonde data is assimilated

m/s CONSON’s central position The assimilation of dropsondes improved the steering flow east of Typhoon Conson, leading to the northeast movement of the typhoon. How initial condition changed?

Vertically accumulated total energy of 1 st singular vector Ensemble perturbation Singular vectors are computed for the initial field of NODROP and the leading singular vector is used as ensemble initial perturbation. Geopotential height at 500 hPa Thin line: NODROP Thick line: Perturbed field 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 1 st 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 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.