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Genesis Potential Index and ENSO

Genesis Potential Index and ENSO. Suzana J. Camargo. Collaborators:. Kerry A. Emanuel Program in Atmospheres, Ocean and Climate Massachusetts Institute of Technology, Cambridge, MA Adam H. Sobel Department of Applied Physics and Applied Mathematics

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Genesis Potential Index and ENSO

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  1. Genesis Potential Index and ENSO Suzana J. Camargo

  2. Collaborators: • Kerry A. Emanuel Program in Atmospheres, Ocean and Climate Massachusetts Institute of Technology, Cambridge, MA • Adam H. Sobel Department of Applied Physics and Applied Mathematics Department of Earth and Environmental Sciences Columbia University, New York, NY

  3. Motivation • Genesis potential index: dependent on large scale fields developed using statistical fitting to observed genesis of tropical cyclones globally. • Examine how the Genesis potential index describes ENSO – Tropical Cyclone (TC) variability globally. • Comparison with various tropical cyclone indices in different basins. • Possible use in forecasting seasonal TC variability using large scale fields from AGCMs. • Analysis of which variables are responsible for the ENSO response in the Genesis Potential index.

  4. Genesis Potential Index • Refinement of Gray’s tropical cyclone genesis index using Reanalysis data (Emanuel & Nolan 2004). GP= |105η|3/2 (H/50)3 (Vpot/70)3 (1+0.1 Vshear)-2 η= absolute vorticity at 850hPa (s-1) H= relative humidity at 700hPa (%) Vpot = potential intensity (m/s) Vshear = magnitude of the vertical wind shear between 200 and 850hPa (m/s). K.A. Emanuel and D. Nolan, BAMS 85, 667-668 (2004).

  5. Potential Intensity Variables that enter the definition of the potential intensity (taking into account dissipative heating): • SST – sea surface temperature • SLP – sea level pressure • CAPE – convective available potential energy • Atmospherictemperature (various pressure levels) • Mixing ratio(various pressure levels) K.A. Emanuel, JAS 52, 3969-3976 (1995). M. Bister and K.A. Emanuel, Meteor. Atm. Phys. 52, 233-240 (1998)

  6. Genesis Potential Climatology Febr. Sept.

  7. Maximum Genesis Potential Index Climatology

  8. Climatology - Basins Genesis Potential Number of Tropical Cyclones

  9. Genesis Potential Anomalies & ENSOASO (August - October) El Niño La Niña

  10. Genesis Potential Index and ObservationsDifference:El NiñoandLa Niña- ASO Genesis Potential Index Observed Genesis Density

  11. Genesis Potential Index and ObservationsDifference:El NiñoandLa Niña– ASO II Genesis Potential Index Observed Track Density

  12. Genesis Potential Anomalies & ENSOJFM (January-March) El Niño La Niña

  13. Genesis Potential Index and ObservationsDifference:El NiñoandLa Niña- JFM Genesis Potential Index Observed Genesis Density

  14. Genesis Potential Index and ObservationsDifference:El NiñoandLa Niña- JFM Genesis Potential Index Observed Track Density

  15. Interannual Variability - Atlantic

  16. Correlations: Genesis Potential & Number of Tropical Cyclones Eastern North Pacific Atlantic

  17. Correlations: Genesis Potential & Number of Tropical Cyclones

  18. Genesis Potential Index Difference:El NiñoandLa Niña- ASO

  19. Various Correlations:Genesis Potential - South Pacific Number of TC days

  20. Correlations Tropical Cyclone variability indices variables with positive correlation with Genesis Potential Index in various basins: • Number of tropical cyclones • Number of named tropical cyclones • Number of hurricanes • Number of major hurricanes • Number of Tropical Cyclone days (track density) • ACE (Accumulated Cyclone Energy)

  21. Interannual Variability • Consistent highest correlations (for all variables): • South Pacific • Atlantic • Eastern Pacific • Western Pacific • pre-typhoon season (FMA-MJJ) • Eastern Part – year around • Western Part – JFM-AMJ, OND-NDJ, Year • Other basins: specific TC variables for definite seasons, mainly pre or post the peak of the tropical cyclone season. Example: Australian basin: OND - peak JFM. ENSO connection

  22. Variables responsible for ENSO variability Recalculated genesis potential index using climatology for 3 of the 4 variables and varying only the 4th variable. Example: • Vorticity, humidity, potential intensity: climatological values • Vertical wind shear: observed values. Other combinations also tested (2 variables climatology, 2 observed values & 1 variable climatology, 3 observed values).

  23. Genesis Potential – ENSO Difference ASO

  24. Genesis Potential ENSO Variability ASOOne variable observations & 3 variables climatology VORTICITY HUMIDITY Potential Intensity Vertical Wind Shear

  25. Conclusions • Genesis Potential index pattern reproduces well known ENSO effects on TC activity. • Genesis potential index and number of tropical cyclones per basin is correlated in basins with large ENSO influence (South Pacific, Atlantic). • Genesis potential index is correlated with various tropical cyclone activity indices (number of hurricanes, ACE, number of major hurricanes, track density values – number of TC days).

  26. Conclusions II • Most important variables responsible for genesis potential shifts can be identified in different regions: • Atlantic: wind shear (mainly) and SST (PI). • Western North Pacific: combination of humidity, vorticity and wind shear • Eastern North Pacific: wind shear and SST (PI). • Possible application – forecasting TC activity using Genesis Potential index in AGCMs.

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