Annual Number of Peer Reviewed Articles with Hurricane or Tropical Cyclone in their Titles, according to Meteorological and Geoastrophysical

Transcription

1 Hurricanes and Climate Kerry Emanuel Program in Atmospheres, Oceans, and Climate MIT

2 Program Potential Intensity Role of potential ti li intensity it in storm intensity it Role of potential intensity in storm frequency Records of tropical cyclone activity Outflow temperature

3 Annual Number of Peer Reviewed Articles with Hurricane or Tropical Cyclone in their Titles, according to Meteorological and Geoastrophysical Abstracts

4 Theory: Interest Stimulation PRP Atl 2 PRP N t 6 years Scientist Attention Span PRP Annual peer reviewed publications N Atl Number of Atlantic TCs per year

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6 Source: Wikipedia Tracks of all tropical cyclones,

7 Energy Production

8 Total rate of heat input to hurricane: r0 * 3 0 k 0 D Q 2 C V k k C V rdr Surface enthalpy flux Dissipative heating In steady state, energy production is used to balance frictional dissipation: r 0 3 D 2 C V rdr D 0

9 Plug into Carnot equation: T T C rdr C k k rdr r0 r 3 0 s o * 0 D V 0 k V 0 T o If integrals dominated by values of integrands near radius of maximum winds, 2 C k T s T o V * max k 0 k C D T o Note: This equation can be derived exactly from the governing equations

10 Theoretical Upper Bound on Hurricane Maximum Wind Speed: Surface temperature C T T V 2 k s o k * k pot C T 0 D o Ratio of exchange Outflow Air sea enthalpy coefficients i of temperature disequilibriumilib i enthalpy and momentum

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12 Annual Maximum Potential Intensity (m/s) 60 o N 30 o N 0 o 30 o S 60 o S 0 o 60 o E 120 o E 180 o W 120 o W 60 o W

13 Condition of convective neutrality: s b = s* of free troposphere Also, s* of free troposphere is approximately spatially uniform (WTG approximation) 2 C T T V k s o * pot Ts s 0 s C D T o * approximately constant What matters, apparently, is the SST (s 0 *) relative to the tropospheric temperature (s*)

14 Combine expression for potential intensity, V max, with energy balance of ocean mixed layer: V 2 max SST Outflow T Net surface radiative i flux s o rad Ocean mixed layer depth Mixed layer heat flux T T F d T C V o D s Focean Drag coefficient Mean surface wind speed Valid on time scales > thermal equilibration time of ocean mixed layer (~ 2 years)

15 Dependence on Sea Surface Temperature (SST):

16 Relationship between potential intensity (PI) and intensity of real tropical cyclones

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19 Empirical Evidence for the Importance of Potential Intensity to TC Genesis: A Genesis Potential Index (GPI) Base choice of predictors on physics, intuition, past experience 850 hpa absolute vorticity (h) hpa shear (S) Potential ti lintensity it (PI) Non dimensional subsaturation of the middle troposphere: s* s600 s * s* 0

20 New Genesis Potential Index: GPI PI ms (20 ms S ) 850 hpa absolute vorticity (h) hpa shear (S) Potential intensity (PI) Non dimensional subsaturation of the middle troposphere: s* s600 s 0 * s*

21 Performance

22 Basin Frequencies

23 TC Activity Metric: Hurricane Power (Power Dissipation Index) 3 max PDI V dt 0 A measure of the total frictional dissipation of kinetic energy in the hurricane boundary layer over the lifetime of the storm

24 High Correlation between North Atlantic TC Power Dissipation and MDR SST Continues

25 Tropical cyclone power dissipation has nearly tripled since the 1980s, though there has been an increase of only o C in sea surface temperature t

26 Observed Tropical Atlantic Potential Intensity Emanuel, K., J. Climate, 2007 Data Sources: NCAR/NCEP re analysis with pre 1979 bias correction, UKMO/HADSST1

27 Potential Intensity, North Indian Western North Pacific Southern Hemisphere North Atlantic Eastern North Pacific From NCAR/NCEP reanalysis data

28 Dependence on Sea Surface Temperature (SST):

29 Potential intensity has been increasing by about 12 ms 1 K 1, compared to accepted value of 4 ms 1 K 1. What is the source of this discrepancy? Stay Tuned for Next et Talk!

30 Trends in outflow temperature From NCAR/NCEP reanalysis data