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Interaction of the tropical cyclone Ivan with the ocean

Interaction of the tropical cyclone Ivan with the ocean. by Guillaume Samson, D. Barbary, H. Giordani, F. Roux LACy - CNRM/GAME. 12/02/2008 18:00Z. 17/02/2008 06:00Z. Tropical Depression (28 kts – 33 kts). Tropical Storm (34 kts – 63 kts). Tropical Cyclone (> 64 kts). Synopsis. PERIOD 1.

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Interaction of the tropical cyclone Ivan with the ocean

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  1. Interaction of the tropical cyclone Ivan with the ocean by Guillaume Samson, D. Barbary, H. Giordani, F. Roux LACy - CNRM/GAME

  2. 12/02/2008 18:00Z 17/02/2008 06:00Z Tropical Depression (28 kts – 33 kts) Tropical Storm (34 kts – 63 kts) Tropical Cyclone (> 64 kts) Synopsis PERIOD 1 PERIOD 2 51 m/s MSLP pressure (hPa) wind (m/s) 10M WIND 942 hPa

  3. PERIOD 1 PERIOD 2 Motivations MSLP COLD POOL SST < 23°C WARM POOL INITIAL SST SST > 29°C Pressure (hPa) Temperature (°C) • Influence of the « cold pool » ? (PERIOD 1) • Role of the ocean in the rapid intensification of Ivan ? (PERIOD 2) • SST – MSLP relationship ? • Influence of the coupling with the ocean ?

  4. Full-physics atmospheric model Méso-NH : • non-hydrostatic + deep convection explicitely resolved + shallow convection parameterized (KF) • 350 x 600 (4km) x 35 grid points, Δt = 5 s • Tori -> CPU: 6 proc 350000s MEM: 30Gb (12h) Experimental Set-up ECUME surface flux parameterization • 1D ocean model with 1.5 TKE closure scheme: • horizontal resolution of 4 km • 20 vertical levels (5m-resolution in the OML) • coupled every 600 s with Méso-NH Bathymetry ETOPO 20’ Lebeaupin et al. 2008

  5. Initial Conditions: Atmospheric component • ALADIN-Reunion • French operational meso-scale (~10 km) LAM • Hydrostatic, 60 vertical levels • 3D-VAR data assimilation with 3D wind bogus pseudo-observations • Analysis used as initial atmospheric field and forcing every 6 hours • Initial analysis errors: position ~ 10 km, MSLP ~ 1 hPa, Max Wind ~ 2 m/s

  6. MERCATOR PSY3V1 MERCATOR Initial Conditions: Oceanic component REMSS Initial SST (°C) along Ivan track SATELLITE OBSERVATIONS • MERCATOR PSY3V1 • French operational global ocean model at ¼° • Based on the research model OPA 8.2 • 46 vertical levels (10 levels in the first 100m) • Assimilation of sea level anomalies • Maximum initial SST error: 1°C

  7. Validation: Simulated ocean cooling (°C) Ocean-1D model Satellite observation

  8. Validation: Méso-NH VS Best-TrackInfluence of the coupling with the ocean TRACK BEST-TRACK FORCED COUPLED Madagascar Mauritius La Réunion POSITION ERROR (km)

  9. Validation: Méso-NH VS Best-TrackInfluence of the coupling with the ocean PERIOD 1 PERIOD 2 MSLP (hPa) 9 hPa (-20 %) BEST-TRACK FORCED COUPLED BEST-TRACK FORCED COUPLED 10 m/s 10M WIND SPEED (m/s) (-35 %)

  10. Wind-pressure relationship BT 1 BT 2 FORCE COUPLE Vent max à 10m (m/s) Pression (hPa)

  11. QSCAT (25km) TRMM (25km) MESO-NH (4km) MESO-NH(4km)

  12. Period 1: Influence of the cold pool Convective rain band No CAPE « reload » Over the cold pool CAPE « reload » Over warm waters COLD POOL No deep convection development CAPE (J/kg) Radar reflectivity 500 hPa (dbz) Dry air from downdraft in the convective rain band over high QS Cold air from downdraft in the convective rain band over high SST COLD POOL COLD POOL Cold air from the cold pool over high SST Dry air from the cold pool over high QS Sensible heat flux (W/m2) Latent heat flux (W/m2) CAPE « used » by deep convection

  13. Period 1: Influence of the cold pool Azimuthal and radial mean: FORCED COUPLED LATENT HEAT FLUX Surface heat flux (W/m2) SENSIBLE HEAT FLUX SURFACE HEAT FLUXES GOVERNED AND MODULATED BY THE DIURNAL CYCLE OF THE CONVECTIVE ACTIVITY

  14. Period 2: Rapid intensification FORCED COUPLED 300 W/m2 LATENT HEAT FLUX Surface heat flux (W/m2) SENSIBLE HEAT FLUX - 40% LATENT HEAT FLUX DURING THE RAPID INTENSIFICATION PERIOD AND COMPARED TO THE FORCED SIMULATION - 60% SENSIBLE HEAT FLUX COUPLING WITH THE OCEAN - 20% MSLP - 35% MAXIMUM WIND

  15. Summary PERIOD 1 PERIOD 2 MSLP Pressure (hPa) Temperature (°C) INITIAL SST Period 1: • important increase of the SST but not of the intensity • influence of the « cold pool » inhibition of the deep convection in the left hand-side of Ivan Period 2: • no more influence of the « cold pool » formation of a complete convective eye-wall • start of the rapid intensification • strong influence of the coupling with the ocean (35% reduction of the RI in terms of 10m wind)

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