1. Reason for the failure of the simulation of heavy rainfall during X-BAIU-01 - Importance of a vertical profile of water vapor for numerical simulations - KATO, Teruyuki 1, Yoshiaki Sato 2, 1 Meteorological Research Institute / Japan Meteorological Agency 2 Meteorological Satellite center / Japan Meteorological Agency and X-BAIU-01 observation group

2. Background / Motivation In 2001, a special field observation (X-BAIU-01) was conducted in western Japan during the rainy season, and a 5km-horizontal resolution nonhydrostatic model was operated twice a day to support this observation. In 2001, a special field observation (X-BAIU-01) was conducted in western Japan during the rainy season, and a 5km-horizontal resolution nonhydrostatic model was operated twice a day to support this observation. 5km-NHM usually predicted rainfalls successfully, but it failed to predict the heavy rainfall observed in the morning of 23 June. 5km-NHM usually predicted rainfalls successfully, but it failed to predict the heavy rainfall observed in the morning of 23 June. In this study, by inspecting the reason of this failure it is examined what is significant for the formation of heavy rainfall over the Baiu frontal zone. In this study, by inspecting the reason of this failure it is examined what is significant for the formation of heavy rainfall over the Baiu frontal zone.

3. Content ・ Characteristics around the Baiu frontal zone (Mean field analysis produced from GANAL) (Mean field analysis produced from GANAL) ・ Heavy rainfall observed on 23 June 2001 ・ Numerical simulations ・ Comparison with observations ・ Sensitive experiments using the modified initial field and using the modified initial field and 4DVar method 4DVar method ・ Trace back of an air inducing a heavy rainfall ・ Conclusion

4. Averaged fields during intense convective activity phase over the Baiu frontal zone Westerly wind Moist tongue Pacific high S-SWS-lies Baiu frontal zone S-SWS-lies

5. Westerly wind Moist tongue Pacific high 130E 45N 15N Vertical cross sections during intense convective activity phase over the Baiu frontal zone 15N 45N Moist tongue Subsidence of Pacific high Baiu frontal zone 15N45N Moist tongue Baiu frontal zone 15N45N

6. Characteristic features of the Baiu frontal zone in Japan SouthNorth Tropopause Relative humidity ~ 100% S-SWS-lies Depth ~ 1.5km Baiu frontal zone Subsidence of Pacific high Moist tongue （ from China or East China Sea ） Continental cold and dry air mass Westerly wind Baiu front, water vapor front, is usually analyzed here Heavy rainfalls often occur at the southern edge of moist tongue. Region with strong convective activities

7. Precipitation intensity observed by JMA radar 10 JST 23 June After 08 JST MCS almost stagnated. At 04 JST a MCS suddenly formed over sea southwest of Kyushu Is., and then rapidly developed. Time cross section in a S-N direction

8. Surface weather map 09 JST 23 June 2001 Baiu front crossed over Kyushu Is. Typhoon ７００ｈ Pa weather map Moist tongue Subsidence of Pacific high

9. Infrared imagery （ GMS-5)

10. Cloud systems suddenly formed in the area without clouds where the subsidence of Pacific high could dominate.

11. Numerical models ７５０ｋｍ RSM: JMA regional spectral model Precipitation scheme Precipitation scheme: Large scale condensation + Moist adjustment + Arakawa-Schubert Resolution: 20km Grids Resolution: 20km ， Grids: 325 x 257 x 40 5km-NHM ： Nonhydrostatic model (MRI/NPD-NHM, Saito et al, 2001) Precipitation scheme Precipitation scheme: Cold rain, predicting the mixing ratios of water vapor, cloud water, cloud ice, snow, and graupel. Resolution: 5km Grids Resolution: 5km ， Grids: 150 x 150 x 38

12. Reproduction of the heavy rainfall by numerical models

13. Heavy rainfall failed to be reproduced.

14. "Observation of Baiu front over East China Sea and Kyushu in 2001" （ X-BAIU-01 ） "Observation of Baiu front over East China Sea and Kyushu in 2001" （ X-BAIU-01 ） Observation period: 7 June – 8 July 2001 Aerosonde

15. Prediction between 1km-1.5km well corresponds with observation. Low-level water vapor fields after the MCS formed Comparison between prediction of 5km-NHM and observation by AEROSONDE 12JST 23 June 5km-NHM failed to reproduce the southerly inflow of humid air below 1 km. Atmosphere below 1km in 5km-NHM initial/boundary initial/boundaryconditions is considerably drier than it is in reality.

16. Before MCSs formed Comparison between TPW predicted by 5km-NHM and those derived by TRMM TMI data 03JST 23 June GSM IR-image Large (Wet) TPW Small (Dry) Subsidence of Pacific high could exist in this area (no cloud). 5km-NHM TRMM TPW : Small Low-level water vapor ： Small

17. Modification Sensitive experiments with the modified initial field of 5km-NHM 4DVar with TMI -retrieved TPW Modification of low-level water vapor 15N45N Baiu frontal zone Low-level atmosphere is humidified to the south of Baiu frontal zone. Forecast hour(t) 00 03 06 09 12 15 18 21 24 ● ○ ○ ○ ○ ○ ○ ○ ○ ↓ ↓ ↓ ↓ ↓ ↓ ↓ 00 03 06 09 12 15 18 ○○○○○○○○○○○○○○○○○○○ Analysis ● ： Regional Analysis Output ○ ： Output Supply of data ↓ ： Supply of data This is improved by the following two methods. 100% 1.5km Modification MOD: 4DV:

18. Forecast results Valid time ： 10JST 23 June CNTL MOD ４ DV Observation

19. Improvement of low-level water vapor field Initial time : 03JST 03JST 23 June 23 June CNTL CNTL MOD MOD South North

20. South No convection forms, insofar as no strong upward motion exists Convection can form over the region with weak updrafts, i.e., in the south side of the Baiu frontal zone. Initial time : 03JST 03JST 23 June 23 June CNTL CNTL MOD MOD Lifting condensation level (Left) Level of free convection(Right)

21. Modification of low-level water vapor field MOD MOD Initial time : 03JST 03JST 23 June 23 June 4DVAR 4DVAR SouthNorth SouthNorth Water vapor is not concentrated below 1.5km. No strong convective instability. Heavy rainfall can not occur. CNTL

22. TRACE BACK of the area with underestimated TPW (RSM forecasts)

23. Air with low TPW passed between two upper-air sounding sites, Ishigaki and Naha. Ishigaki Naha x x

24. １０ Ｎ ２０ Ｎ ３０ Ｎ ４０ Ｎ １４ ０Ｅ １３ ０Ｅ １２ ０Ｅ １１ ０Ｅ × Upper-air sounding points sounding points Open space Occurrence of heavy rainfall Special observation for the low-level and assimilation of satellite data are necessary. Airs pass the open space Inflow of low-level humid air Upper–airobservation by sonde

25. Conclusion To reproduce heavy precipitation systems well, accuracy of vertical water vapor analysis is very significant. Future issues for four-dimensional assimilation When TPW in the first guess is smaller than the observation, 4DVAR is not necessary to humidify the lower atmosphere. To use TPW data effectively, dense observations of upper-air sounding are necessary in the spatial and temporary.

26. Analysis of water vapor field The estimation of a water vapor field among upper-air sounding points is difficult due to its being a passive tracer, while dynamical fields such as temperature and wind can be reasonably interpolated by 4DV. 100% 1.5km 100% 1.5km Modificationwithout weight function Modificationwith This modification can be used only for such a case as the present event. Modification of water vapor profile by assimilating TPW with 4DV in areas without rain.