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Taiwan’s Effort on Meiyu Heavy Rainfall Problems

Taiwan’s Effort on Meiyu Heavy Rainfall Problems. George Tai-Jen Chen （陳泰然）. Chair Professor/Distinguished Professor, Department of Atmospheric Sciences National Taiwan University. June 28, 2012, 09:00 –09:45 University of Hawaii at Manoa.

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Taiwan’s Effort on Meiyu Heavy Rainfall Problems

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  1. Taiwan’s Effort on Meiyu Heavy Rainfall Problems George Tai-Jen Chen （陳泰然） Chair Professor/Distinguished Professor, Department of Atmospheric Sciences National Taiwan University June 28, 2012,09:00–09:45 University of Hawaii at Manoa

  2. Ι. Heavy Rainfall Problems in a Changing Society of Taiwan II. National Effort on Disaster Prevention Research III. Taiwan’s Research Effort on Meiyu Heavy Rainfall IV. Recent Research Effort on MeiyuFrontal Systems V. Climate Change and Taiwan’s Meiyu

  3. Ι. Heavy Rainfall Problems in a Changing Society

  4. Heavy Rain/Flash Flood Event of May 28, 1981 0700 LST May 28 0800 LST May 28

  5. Hourly and 3-h rainfall amounts at some stations in northern • Taiwan for extremely heavy rain of May 28, 1981 • Effect and size of meteorological disaster in a changing society: • agricultural era  industrialized era • Heavy rainfalls and severe floods of May 28,1981 caused a loss of • 300 M US $

  6. Meiyu in East Asia Meiyu in southern China and Taiwan (mid-May – mid-June)

  7. Japan Baiu (late-May – late-June)

  8. Meiyu in Yangtze River Valley (mid-June – mid-July)

  9. Korea Changma (mid-July – mid-August)

  10. II. National Effort on Disaster Prevention Research Taiwan Typhoon and Flood Research Institute Disaster Prevention Research NationalS&T Program 1982 2003 1980 1990 2000 2010 1997 2007 National Center for Disaster Reduction Research(NCDR) NSC Disaster Prevention Research Program APEC Center for Typhoon and Society

  11. III. Taiwan’s Research Effort on Meiyu Heavy Rainfall C  F What is the current capability of heavy rain forecast ? Why? The illustration of  Threat Score. F is the forecast,is the observation, C is the correct forecast. Prefigurance: ThreatScore: Postagreement: Bias:

  12. Heavy rain forecast capability of CWB  • Synoptic-scale process v.s. Mesoscale process • Lack of basic understanding of the mesoscale process • responsible for the low TS and PF of heavy rain in Meiyu • season.

  13. Response of meteorological community to Meiyu heavy rainfall  TAMEX Field Phase 1978 1992 2008 1987 1970 2000 1980 1990 2010 TIMREX Field Phase Post-TAMEXForecastExperiment National ConferenceonDisastrousWeathersinTaiwan

  14. National ConferenceonDisastrousWeathersinTaiwan Typhoon, drought, cold surge, and Meiyu were identified to be the 4 major disastrous weathers in Taiwan. Research focus on these phenomena was suggested and then became NSC policy.

  15. 2. TAMEX (1983-1993) • Goal:Toimprove,throughbetterunderstanding,theforecasting • ofheavy precipitationeventsthatleadstoflashfloods • ScientificObjectives: 1) To study the mesoscale circulation • associated with the Meiyu front; • 2) To study the evolution of the • mesoscale convective systems (MCSs) • in the vicinity of the Meiyu front; • 3) To study the effects of orography on • the Meiyu front and on mesoscale • convective systems.

  16. Participants in TAMEX Field Phase（May 1-June 30, 1987）

  17. Human Resources Mobilized in Field Phase USA：70 scholars and experts from 10 universities and 3 research institutions. Taiwan：80 scholars and experts and 1000 professional technicians from 4 universities /colleges and 11 government agencies.

  18. 1981 1982 1983 1986 • Important Events Prior to the Field Phase of TAMEX May 28, 1981 Heavy rainfalls and severe floods caused a loss of 300 M US $ TAMEXproject was proposed to NSC Planning Stage of TAMEX (1983–1986) Taiwan：40 experts and scholars from 5 academic institutions and 3 meteorological operational agencies (CWB, CAF, and CAA) USA：50 professors, scientists and experts from 15 universities and 4 research institutions Disaster Prevention Research Program was pushed by the NSC

  19. 1988 1989 1990 1991 1992 • Important Events of the Follow-up Basic Research of • TAMEX from 1988 December A special issue of TAMEX research was published in TAO 24–26September symposium@NCAR 9–11February symposium@NCAR 1993 3-6 December International Symposium on Mesoscale Meteorology and TAMEX@Taipei 22–30 June symposium@Taipei 26–30April A Retrospective Symposium on Mesoscale Research and TAMEX Project@Taipei November A special issue of TAMEX research was published in Mon. Wea. Rev.

  20. 3. Post-TAMEX Forecast Experiment: Important Events of the Follow-up Applied and Operational Researches of TAMEX from 1988 1989 1990 1991 1992 November 22Planning group of Forecast Experiment was established. December 15Project Office of Forecast Experiment was established. December 308working groups of Forecast Experiment were established (60 professors/experts). February 26 – March 3Taiwan/USA Planning Meeting (I)@Taipei. May 14working groups and training team were re-integrated. December 17a 6-person advising team was established; working groups were expanded to 10 (80 professors/experts). May 1–June 30Post-TAMEXForecast Experiment was conducted using the Weather Integration and Now casting System(WINS) established by CWB April 22–23 & May 1–3Taiwan/USA Planning Meeting (II)@Taipei. May 19–June 20Pilot experiment @Taipei. June 25advising team meeting @NCAR December 7–10Taiwan/USA Planning Meeting (III)@Heng-chun

  21. Goal:Application of results obtained through basic and • applied researches in TAMEX program, to improve the • forecasting capability of the short-range and nowcasting • of heavy rain. • Objectives: • To establish the new forecasting concept in the mesoscale forecast system. • Using the newly established WINS of the CWB and the new forecasting techniques obtained through TAMEX, to improve the short-range forecast and nowcasting capabilities of heavy rain and quantitative precipitation. • Constructing the base line of nowcasting and short-range forecast, to provide the reference for the future forecast improvement. • To test the forecast capability of different forecasting methods for heavy rain and quantitative precipitation in the 0-24 h forecast period.

  22. 4. Taiwan WRP (2000-2010): TIMREX (SoWMEX;TAMEXII) May-June 2008 • Goal: To improve the capability and accuracy of the QPE and QPF (within 24-36 hours) in county city and/or watershed scales during the prevailing southwesterly monsoonal flow to meet the urgent need of disaster reduction in the Taiwan area

  23. Scientific Objectives: 1) Dynamic and thermodynamic characteristics of southwesterly monsoonal flow upstream of Taiwan and its relation with the Meiyu front and the formation, organization and maintenance of the MCSs and their downstream development (SW monsoon, Meiyu front, environmental characteristics) 2) Kinematic, thermodynamic, and microphysical precipitation characteristics of MCSs and the precipitation mechanisms for heavy rain (storm and cloud dynamics and microphysics) 3) Taiwan coastal and topographic effects on the impinging SW flows and on the intensifying and/or suppressing the development of MCSs (Topographic effect) 4) Radar data assimilation and short term QPF experiment (NWP development)

  24. Participants in TIMREX

  25. Strong(large ▽T; large ζ, q, ) Baroclinicity Weak(small ▽T; large ζ, q,) Meiyu front Dynamically(propagation) Movement Kinematically(advection) ▽T↑ ζ↑ q↑ CISK Deformation Cyclogenesis Frontogenesis Deformation CISK IV. Recent Research Effort on MeiyuFrontal Systems Low Level Jet (LLJ) • Formation mechanism • Relationship with extremely heavy rainfall

  26. (a) Case 1: 12-13 June 1990(Chen et al. 2003, Mon. Wea. Rev., 2680-2696) Mei-Yu frontogenesis 850 hPa weather map and PV at 12Z 12 June Wind shear and PV (10-2 PVU) accompanying the front.

  27. (b) 850 hPa weather map and PV at 00Z 13 June PV along the front significantly increase (frontogenesis) with a LLJ formation to the south of the front during the 12 h.

  28. PV inversion techniques(Davis and Emanuel 1991, Mon. Wea. Rev.) • PV: conserved property and invertibility. • Nonlinear balance equation (Charney 1962, Proc. Symp. Numerical Weather Prediction, Tokyo) • Given a known distribution of PV and specified boundary conditions, the system can be solved to give height and wind fields under nonlinear balanced relationship.

  29. Piecewise inversion The PV anomalies can be divided into any number of parts and the height and the wind field associated with each part can be obtained. • Prognostic system q/t, /t, /t, , and  under nonlinear balanced condition can be obtained.

  30. Scheme for q’ partitioning and contributions to frontal intensity from all processes at 850 hPa PV anomaly (109.125-117E; 29.25-30.375N ) associated with latent heat release (ms) were responsible for the frontogenesis.

  31. B A w GMS IR imagery and vertical motion as computed by PV prognostic system along AB at 00Z 13 June Upward motion (cm s-1) computed by prognostic system was closely matching the position of deep convection on cloud imagery.

  32. - + - + q/t /t PV tendency and height tendency as computed by PV prognostic system along AB at 00Z 13 June Positive PV tendency and negative height tendency (frontogenesis) at low level were related to the MCSs.

  33. Mei-Yu fronotogenesis by CISK • q/t is directly proportional to both the vertical gradient of heating/cooling rate and the absolute vorticity. • In a quasi-barotropic system, the vertical component of η is rather close to q. • q/t is proportional to q→ nonlinear interaction.

  34. w q/t If ms is reduced by ½ at 00Z 13 June - + Similar vertical motion pattern with much less PV generation at the low level.

  35. Conclusion • PV perturbations related to latent heat release from MCSs were responsible for the frontogenesis. • CISK mechanism proposed by Cho and Chen (1995) was observed to be responsible for the Mei-Yu frontogenesis.

  36. Case 2 : 7-8 June 1998(Chen et al. 2006, Mon. Wea. Rev., 874-896) Northward retreating Mei-Yu front Formation of LLJ • Although this phenomenon is not rare, the mechanism has never been investigated.

  37. GMS IR images Frontal cloud band with an organized MCS over the frontal disturbance moved northeastward.

  38. Synoptic maps at 850 hPa between12Z 7 and 06Z 8 June Trough deepened in association with the organized MCS, and the southwesterly winds intensified (LLJ formation) to the south of the MCS.

  39. Composite vorticity and divergence at 925 and 850 hPa normal to and across the MYF (at 0) during 12Z 7 - 06Z 8 June Vorticity in phase with convergence. Comparable values of vorticity at both levels. Nearly no vertical tilt.

  40. Retreat of the front Time variations of vorticity budget across the front at 850 hPa Effect of horizontal vorticity advection (10-5 s-1(6h)-1) mainly caused the northward retreat of the front. (The vital role of the LLJ to the southwest of the front.)

  41. Scheme for q’ partitioning and contributions to frontal intensity at 850 hPa from all processes PV anomaly associated with latent heat release (LLh) were mainly responsible for the frontogenesis.

  42. LLJ formed and intensified largely through the Coriolis acceleration of ageostrophic winds( z). ( // z shaded) T The formation of LLJ: ageostrophic wind analysis 12Z 7 June 18Z 7 June 06Z 8 June 00Z 8 June

  43. 12Z 7 June 00Z 8 June 06Z 8 June The formation of LLJ: PV perspective PV anomaly due to latent heating (LLh) and the associated (inverted) balanced winds at 850 hPa • Front intensified through latent heat release. • LLh caused the increase of southwesterly wind components to the southeast of the MCS.

  44. Wind vectors averaged over a hexagonal domain centered along the axis of the LLJ from different PV anomaly components at 00Z 8 June When southwesterlies associated with LLh are superimposed upon the background SW monsoonal flows → LLJ formation.

  45. Conclusion • Strong southwesterly flow (LLJ) led to rapid retreat of the front while the movement was dominated by horizontal advection. • Enhanced gradient of height tendency induced ageostrophic winds, and the LLJ formed through Coriolis acceleration of these winds.

  46. (a) (b) (c) Case 3: 8-14 June 2000 (Chen et al. 2007, Mon. Wea. Rev., 2588-2609) Mei-Yu frontogenesis and frontal movement Thick dashed lines indicate the position of 925-hPa Mei-Yu front based on temperature gradient and winds. The thermal gradient of Mei-Yu front increased from 8 June to reach a maximum at 1200 UTC 10 June then remained quite strong until after 12 June 2000.

  47. (a) 2000 Jun 8 00Z (b) 2000 Jun 10 12Z (c) 2000 Jun 13 00Z Using 2-D frontogenetical function of Ninomiya (1984). F: frontogenetical function (d|H|/dt) Contributing terms: FG1: diabatic processes; FG2: horizontal convergence; FG3: deformation; GT: magnitude of horizontal potential temperature gradient (|H |) Formation stage S N intensification stage S N The Mei-Yu frontogenesis and the maintenance of the front were attributed to both deformation and convergence. decaying stage S N

  48. (a) 2000 Jun 8 00Z (b) 2000 Jun 10 12Z (c) 2000 Jun 13 00Z Movement of the Mei-Yu front : GT, the distribution of frontal strength : F, frontogenetical function : LT, local tendency of S N : ADV, horizontal advection of LT = F + ADV （frontal motion: phase difference between LT and frontal zone） S N The total frontogenetical function (F) that peaked ahead of the frontal zone contributing toward the southward propagation of the Meiyu front, in addition to the transport by advection of the postfrontal cold air. S N

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