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Satoru YOKOI 1 , Y. N. TAKAYABU 1,2 , J. C. L. CHAN 3

Tropical cyclogenesis frequency simulated by CMIP3 climate models and multi-model based future projection. International Workshop on Advancement of Typhoon Track Forecast Technique (December 2, 2009). Satoru YOKOI 1 , Y. N. TAKAYABU 1,2 , J. C. L. CHAN 3

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Satoru YOKOI 1 , Y. N. TAKAYABU 1,2 , J. C. L. CHAN 3

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  1. Tropical cyclogenesis frequency simulated by CMIP3 climate models and multi-model based future projection International Workshop on Advancement of Typhoon Track Forecast Technique (December 2, 2009) Satoru YOKOI1, Y. N. TAKAYABU1,2, J. C. L. CHAN3 1: CCSR, University of Tokyo, Japan 2: JAMSTEC, Japan, 3: City U. Hong Kong, China

  2. Our project (S-5-2) Evaluations of CMIP3 Model Performances for Various Phenomena in the Atmosphere and Oceans, in the Present-Day Climate and in Future Projections • Leader: Prof. Yukari N. Takayabu (CCSR, U. Tokyo) • Organizations: U. Tokyo, MRI, JAMSTEC, Nagoya U., Hokkaido U., & Tsukuba U • Target phenomena: • Heating profile due to tropical convection • Tropical cyclone • Madden-Julian oscillation • Asian monsoon seasonal cycle • Silk road pattern • Pacific-Japan pattern • ENSO • Decadal variability Mean field Exercise using CMIP3 archive Rush into CMIP5 analysis

  3. Introduction How would global warming impact tropical cyclone (TC) characteristics? (frequency, track, intensity, etc.) • Many researchers discussed • global or ocean-basin scale frequency projection • with the use of their own sophisticated high-resolution GCM. • Most recent studies projected decrease trend of global TC number. • (e.g. Sugi et al. 2002; McDonald et al. 2005; Oouchi et al. 2006; Bengtsson et al. 2007) • How about regional trends? • TCs generated at different places tend to affect different countries. • Inter-model difference should be serious problem. Multi-model based approach will be essential.

  4. CMIP3 multi-model archive • CMIP3: 3rd phase of Coupled Model Intercomparison Project • Outputs of CGCM experiments designed for IPCC AR4. • Strong point: large number of samples • 24 CGCMs • 12 series of experiments (20th-century climate, SRES A1B, A2, and B1, etc.) • Long-term daily-mean outputs (dozens of years for each experiment) • Weak point: Relatively coarse horizontal resolution • T106 at the utmost. • TC intensity is hardly simulated, but its frequency seems to be possible. It is necessary to confirm model performance in simulating TC genesis distribution.

  5. Objective To analyze CMIP3 archives to assess global warming impact on TC genesis over the western North Pacific. Evaluation of model performance in simulating the genesis distribution. Multi-model based projection.

  6. Models • 12 models (among 24 CMIP3 models) • Horizontal resolution of the atmospheric component is T42 (~300 km) or greater. • Daily-mean outputs are archived at the CMIP3 database.

  7. Definition of TC-like disturbance (1) 850-hPa relative vorticity (z850) local maximum (=TC center) zt. (cyclonic vortex) (2) (300-hPa temperature (T300) at the center)-(environmental T300)  Tt. (warm core) (3) Conditions 1 & 2 are satisfied at least 2 time steps. (4) Genesis point is over the ocean. (5) At genesis time, maximum wind speed is greater at the 850-hPa level than at the 300-hPa level. (exclusion of extra-tropical cyclones) Thresholds (zt, Tt) are determined independently for each model.

  8. Evaluation of model performance- 20th-century experiment -

  9. Annual TC genesis (20th-Century experiment) Model simulations Observation 0.642 0.780 0.492 T63 with “linear” reduced Gaussian grid 0.740 0.754 0.409 Taylor (2001) diagram T63 T63 0.350 0.025 0.742 T106 0.033 0.678 0.526 T63 [(5Lat.5Lon)-1(10yrs)-1] Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

  10. Seasonal march Overall winter-to-summer contrast is well reproduced. - High performance models only - 120-150E mean k i Observation Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

  11. Monsoon trough Observation Model (example) May-Jun. Jul.-Sep. Tone: z850 Vector: vertical shear Simulated monsoon trough located to the north of the observation.  Biases in TC frequency seasonal march Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

  12. Seasonal migration of monsoon trough Monsoon trough migrates northward during April–August, and retreats southward during August–December. The trough simulated by five star models migrate northward too fast in early summer, and reaches too north during mature summer. 850-hPa relative vorticity in 120–150E Observation Yokoi, Takayabu, Chan (2009, Clim. Dyn.)

  13. Multi-model based projection

  14. 20C3M and SRES We compare the cyclogenesis frequency between 20C3M and average of three SRES experiments. 20C climate simulation (20C3M): 40-yr length. SRES A1B, A2, and B1 experiments: 80-160-yr length.

  15. Future projection (TC frequency) ALL 5 models project increase trends over central North Pacific (CNP),and decrease trends over the South China Sea (SCS) and areas to the north and east of Philippines. 20th-century experiment (5-model ensemble) Projected trends ( [SRES A1B/A2/B1] – [20C3M] ) Yellow（blue） tone: all 5 models project increase （decrease）trends. Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

  16. Comparison with ENSO signals Reasons for the increase trends can be discussed by analogy with El Nino situation. Eastward extension and intensification of monsoon trough is essential. TC genesis anomaly in El Nino years 850-hPa relative vorticity (JASON) GW impact on SST 1982-2001 ENSO signal GW impact Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

  17. Decrease trend in and around the South China Sea • Environmental conditions would become more favorable for cyclogenesis, or not show significant change. • Low-level vorticity, vertical wind shear, SST, mid-level humidity. • Observed interannual variability of cyclogenesis is not correlate significantly with ENSO signals. Projected trends in environmental fields Projected trends in cyclogenesis frequency Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

  18. Activity in tropical depression-type disturbances (TDDs) TDD activity: 3-5-day meridional wind at 850-hPa (Takayabu and Nitta 1993). An TDD active area is realistically simulated. The activity would decrease significantly over the SCS and to its southeast. Observed IAV exhibits similar pattern, implying that weakening trends of TDD activity may play a role in decrease trends in cyclogenesis. Observation Projected trends 20C3M Obs. IAV associated with cyclogenesis over the SCS Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

  19. Projected trends in genesis potential Models realistically simulate horizontal pattern of GP. GP does not represent east-west contrast in projected cyclogenesis frequency trends. GP indices proposed by other papers (e.g. Royer et al. 1998; Caron and Jones 2008) project in the same manner. 20C3M (Contour) & Obs. (shade) Emanuel and Nolan (2004) genesis potential: h850: 850-hPa absolute vorticity |u850-u200|: vertical wind shear Vpot: potential intensity (Bister & Emanuel 2002) H700: 700-hPa relative humidity Projected trends Yellow (pale blue) tones: at least 4 models project increase (decrease) trends. Yokoi, Takayabu (2009, J. Meteor. Soc. Japan)

  20. Summary Five CMIP3 models realistically simulate horizontal distribution in tropical cyclogenesis over the western North Pacific. ALL of the five models project increase trends of cyclogenesis over the central North Pacific and decrease trends over the South China Sea and regions east of Philippines. The former increase trends are primarily attributable to projected eastward extension and intensification of the monsoon trough. The latter decrease trends are associated with weakening trends in activity of tropical depression-type disturbances. References: Yokoi, Takayabu, and Chan (2009, Climate Dynamics, 33, 665–683) Yokoi, and Takayabu (2009, Journal of the Meteorological Society of Japan, 87, 525-538.

  21. Future research • Trends in occurrence frequency • Is it completely explained by trends in genesis frequency? • Improvement of genesis potential index to make it applicable to global warming problem.

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