1 / 18

Chap. 5.5 Tropical cyclones (TC) (terme générique signifiant dépression tropicale)

Chap. 5.5 Tropical cyclones (TC) (terme générique signifiant dépression tropicale). Source : d’après Chris Landsea et le site internet de la NOAA http://www.nhc.noaa.gov. Tropical cyclone with maximum sustained winds of less than 17 m/s (34kt, 39 mph) are called ‘tropical depression’

uriah-wright
Download Presentation

Chap. 5.5 Tropical cyclones (TC) (terme générique signifiant dépression tropicale)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chap. 5.5Tropical cyclones (TC) (terme générique signifiant dépression tropicale) Source : d’après Chris Landseaet le site internet de la NOAA http://www.nhc.noaa.gov • Tropical cyclone with maximum sustained winds of less • than 17 m/s (34kt, 39 mph) are called ‘tropical depression’ • Tropical cyclone reaching 17m/s are called ‘ tropical storm’ • and are baptized.

  2. Chap. 5.5Tropical cyclone Dina, 22/01/2002 image infrarouge colorée. Source : Météo-France Dina, 22/01/2002 • If winds reach 33 m/s (64 kt, 74 mph), tropical cyclones • are called : • ‘hurricane’ (N. Atlantic, NE Pacific east of dateline, • South Pacific east of 160E) • ‘typhons’ (NW Pacific west of dateline) • ‘severe tropical cyclone’ (SW Pacific west of 160E, • SE Indian Ocean east of 90E) • ‘severe cyclonic storm’ (N. Indian Ocean) • ‘tropical cyclone’ (SW Indian Ocean)

  3. Chap. 5.5Tropical cyclone : OMM classification Sustained wind speed are used for classification of tropical cylones; Threshold are the same all over the world, but the mean of the wind is realized over a period of 1 mn over USA and their survey zones (Atlantic N. and Pacific N.) and 10 mn elsewhere échelle Beaufort et vitesse du vent (kt) 7B 8/9B 10/11B 12B 64 34 115 91 48 Baptism threshold (only lettre of Alphabet • This scale is used around the world except for hurricanes • of N. Atlantic North. and NE Pacific where they use • SAFFIR scale. • Each year, 85 Tropical storm occurred whose 9 over • northern Atlantic

  4. Which difference between extra-tropical cyclone and tropical cyclone ? Chap. 5.5Tropical cyclone Source : Merrill, 93 • Extra-tropical cyclone : storm system that primarly gets • its energy from horizontal gradient temperature. They are • called mid-latitudes or baroclinic storms and low pressure • systems are associated with cold fronts, warm fronts, and • occluded fronts • Tropical cyclones, in contrast, typically have little to no • gradient horizontal temperature across the storm at the • surface and winds are derived from release of energy due • to cloud/rain formation from the warm moist air 5.6.2 :struct. hurricane

  5. Chap. 5.5Tropical cyclone 6 conditions necessary for the development of tropical storms (Gray, 79) 3 thermodynamical conditions : 1. SST>26.5° (80°F) over 50 m. at least (summer, early fall) 2. Atmosphere is conditionnaly unstable (at least, at the early stage of the TC); so no occurrence with trade inversion 3. Hu>70 % between 700 and 500 hPa 3 dynamical conditions : 4. Coriolis force; outside of 3-5° latitude (usually between 5 and 25°) 5. A strong disturbance = weak low with cyclonic circulation 6. Very little vertical shear (surface easterlies and upper tropospheric easterlies) usually S<12 m/s between surface and upper troposphere

  6. Chap. 5.5Tropical cyclone These 6 conditions necessary for initiation of tropical storm explain the spatial distribution Source : d’après Gray, 1979 • No initiation • over land • inside the equatorial zone (5°N/5°S) • over S. Atl. and Pacific SE (no ITCZ and SST too cold) • why no initiation over Central Pacific ? Answer, next slide

  7. Chap. 5.5Tropical cyclone Mean vertical shear between 850 and 200 hPa in august Source : d’après Gray, 1968 ‣ The strong vertical shear (20-40 kt)over Central Pacific prevents initiation of Tropical Storm contents chap.5

  8. Chap. 5.5Tropical cyclone Annual frequency of Tropical storm Sources : Gray 68, Allard 84, Basher 95, Holland 84a, Holland 84b, Holland 84c, McBride 81a, McBride 82

  9. Chap. 5.5Tropical storms over North Atlantic Source : D’après Atkinson, 1971. 9 per year

  10. Chap. 5.5Tropical storms over Eastern North Pacific 17 per year Source : D’après Atkinson, 1971.

  11. Chap. 5.5Tropical storms over Western North Pacific Source : D’après Atkinson, 1971. 27 per year

  12. Chap. 5.5Tropical storms over Southwest Pacific Source : D’après Atkinson, 1971. 5 per year

  13. Chap. 5.5Tropical storms over North Indian Ocean Source : D’après Atkinson, 1971. 4.5 per year Why not TC in july -august while SST is the highest ?

  14. Chap. 5.5Tropical storms over North Indian Ocean Mean vertical shear between 850 and 200 hPa in august Source : d’après Gray, 1968 ‣ strong vertical shear > 40 ktoverNorth Indian Ocean in august (SW monsoon flow in surface, Tropical Easterly Jet at 200 hPa) prevents initiations of tropical storms

  15. Chap. 5.5Tropical storms over Southwest Indian Ocean Source : D’après Atkinson, 1971. 13 per year

  16. Chap. 5.5Tropical storms over Southeast Indian Ocean Source : D’après Atkinson, 1971. 10 per year

  17. - Allard, R. A., 1984 : ‘A climatology of the characteristics of tropical cyclones in the Northeast Pacific during the period of 1966-1990’. Master of Science Thesis, Texas Tech. Univ., Lubbock, TX, 106 p. • Atkinson, G. D., 1971 : Forecaster’s guide to tropical meteorology. USAF Air Weather Service, Technical Report N°240, 364 p. • Basher, R. E. and Zheng X. Z., 1995 :Tropical cyclones in the Southwest Pacific : Spacial patterns and relationships to Southern Oscillation and sea surface temperature’. J. Climate, Vol.8, p. • 1249-1260 • Gray, W. M., 1968 : ‘Global view of the origin of tropical disturbances and storms’. Mon. Wea. Rev., Vol. 96, p .669-700 • Gray, W. M., 1979. Hurricanes : Their formation, structure and likely role in the tropical circulation. In ‘meteorology Over the Tropical Oceans’ (D. B. Shaw, ed.), p. 151-218. Royal Meteorological Society, London. • Holland, G.J., 1984a : ‘On the climatology and structure of tropical cyclones in the Australian/Southwest Pacific Region. I. Data and tropical storms. Austra. Meteor. Mag., 32, p.1-16 • Holland, G.J., 1984b : ‘On the climatology and structure of tropical cyclones in the Australian/Southwest Pacific Region. II. Data and tropical storms. Austra. Meteor. Mag., 32, p.17-32 • Holland, G.J., 1984c : ‘On the climatology and structure of tropical cyclones in the Australian/Southwest Pacific Region. III. Data and tropical storms. Austra. Meteor. Mag., 32, p.33-46 References (1)

  18. McBride, J.L., 1981a :’observational analysis of tropical cyclone formation. Part I. Basis definition of data sets. J. Atmos. Sci., Vol.38, p. 1132-1151 • McBride, J. L. and T. D. Keenan, 1982 : ‘Climatology of tropical cyclone genesis in the Australian region’. J. Climate., Vol.2, p.13-33 • Merrill, R. T., 1993 : ‘Tropical Cyclone Structure’ –Chapter 2, Global Guide to Tropical Cyclone Forecasting, WMO/Tropical Cyclone- N°560, Report N° TCP-31, World Meteorological Organization; Geneva, Switzerland References (2)

More Related