Transcript *Dynamically simulated tropical storms in a changing climate and

Dynamically simulated tropical
storms in a changing climate and
their impact on the assessment of
future climate risk
Ray Bell
Supervisors – Prof. Pier Luigi Vidale, Dr. Jane
Strachan and Dr. Kevin Hodges
Tropical Hour – 11th Jul
Tropical cyclones and climate change
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About me
Previous studies
Models
Tracking algorithm
Results
Future work
About me
• MOcean – NOCS
Wind and Wave variability in the North
Atlantic
• Met office placement 2010
Ocean wave ensemble forecasting
Air-Sea interactions in TCs?
Motivation
• Impacts on the climate system, removing heat and
moisture from the ocean affecting large scale
circulation
• Socio-economic impacts
• Associated risk with climate change
Katrina 2005.
Current damage $91.5bn
(ICAT, 2011)
PhD questions
• Will there be a change in TC activity (location, intensity,
frequency, lifetime) with climate change?
• How well are the governing mechanisms represented in climate
models and how does resolution affect their representation?
• How do TCs change in a warmer world with increasing
resolution?
• What is the role of teleconnections - Possible ENSO changes
on NAtl TC activity?
• [What is the role of coupling with the ocean?]
Previous studies
• Uncertainties in future dynamical and thermodynamical changes due
to anthropogenic warming in the tropics.
Change in precursors (e.g. AEWs...)
• Current trends and attribution
Natural variability (Pielke et al, 2005) vs. Climate change (Webster et al, 2005)
Limitations in the quality and availability of data (Kossin et al, 2007)
• Theory (Emanuel, 1987) and high resolution modelling studies (Knutson et al.
2004; Oouchie et al. 2006) predict TCs will become more intense.
• Little theory explaining the change in TC frequency - likely to become
less frequent in a warmer world.
Previous studies
• Global increase in TC intensities of 2-11% (surface wind speed). (3-21%
decrease in central pressure) by 2100 (A1B scenario) (Knutson et al, 2010)
• Decrease in globally averaged frequency of TCs by 6-34%
- Weakening of the tropical circulation (Increase in dry static stability) (Sugi,
2002)
- Increase in q* causes larger Xm (moist S in middle of troposphere and that
of the BL), therefore takes longer to moisten mid-trop where intensification
can occur (Emanuel, 2008)
• More robust decrease in the SH – smaller increase in SST and increase wind
shear (Vecchi, 2007; Zhao et al, 2009)
• Increase of 20% in precipitation rate within 100km of the storms centre
(Knutson et al, 2010)
• Higher resolution models needed to pick up a warming
related intensification (<60km) (Bengtsson et al, 2007)
Previous studies (Knutson et al, 2010)
Large Regional Uncertainties
Models
NH
May - Nov
HadGAM -135km
HiGEM - 90km
NUGAM - 60km
TRACK Hodges (1995); Bengstsson et al. (2007)
• T42 ξ850 (0o-60oN)– Reduce noise. Comparison of different spatial
resolution data
• Minimum lifetime of 2 days and no constraint on the minimum
displacement distance. Capture more of TC lifecycle
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Cyclogenesis (0-20oN over land, 0-30oN over ocean)
Coherent vertical structure and warm core
Max T63 vor at each level from 850hPa to 250hPa
Intensity threshold T63 ξ850 > 6x10-5 s-1, ξ850 – ξ200 > 6x10-5 s-1 , for at
least 1 day (4 x 6hr)
• Associate full res data with tracks
• Wind speed must attain 20m/s at 850hPa (change in slightly more
intense TCs)
• Statistical packages
Jane’s previous work
HiGEM CTRL TC activity
•Lack of re-curving in NWPAC - SSTs in the NWPAC?
HiGEM CTRL TC frequency
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Obs from
http://www.wunderground.com/blog/JeffMasters/archive.html?year=2011&month=04
Using IBTrACS (not same criteria as tracking)
* att is attain 850hPa wind speed >20m/s dataset
• Reduced ATL activity – Cold bias?
- ATL known to the most sensitive basin to SST (Emanuel, 2008)
• Max intensity ~cat 3 (50m/s +)
My results - Change in track densities
Change in frequency
* att is attain 850hPa wind speed >20m/s dataset
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ATL shows largest decrease
EPAC shows an increase at 2xCO2
NIND shows an increase
- attain 850hPa wind speed 20m/s gives a + change in TC
freq. Suggesting largest decrease of TCs from weaker
storms
Change in intensity ξ850
Change in intensity (850hPa wspeed)
Regional change of 850hPa wspeed
Change in duration
30 years
Change in structure
100 most intense TCs at most intense
2xCO2
Earth relative winds
4xCO2
10o radius
Future work
• Attribution of change in TC activity
- SST – Local vs. Remote changes in each basin
- Wind shear
- Change in other parameters? (dry static stability, low level
vor, RH, genesis parameters)
• Changes in SH
• ENSO influence on NATL activity (IBTrACS, re-an, ctrl,
future)
• Model HiGEM SSTs on HadGAM (TCs in other model
resolutions)
Questions/Comments/Suggestions ?
References
Bengtsson, L., Hodges, K. I., and Esch, M. (2007). Tropical cyclones in a T159 resolution global climate model:
comparison with observations and re-analysis. Tellus A, 59, 396–416.
Bengtsson, L., Hodges, K. I., Esch, M., Keenlyside, N., Kornblueh, L., Luo, J-J., Yamagata, T. (2007) How may Tropical
cyclones change in a warmer climate. Tellus A, 59, 539-561.
Emanuel, K. A. (1987) The dependence of hurricane intensity on climate. Nature, 326, 483-485 .
Hodges, K.I. (1995) Feature tracking on a unit sphere Mon. Weath. Rev. 123, pp 3458-3465.
Knutson, T. R., McBridge, J. L., Chan, J., Emanuel, K., Holland, G., Landsea, C., Held, I., Kossin, J. P., Srivastava, A. K.,
and Sugi, M. (2010). Tropical cyclones and climate change. Nat. Geosci., 3, 157–163.
Knutson, T.R., and Tuleya, R.E. (2004) Impact of CO2-induced warming on simulated hurricaned intensity and
precipitation: sensitivity to the choice of climate model and convective parameterization. J. Climate. 17. 34773495.
Kossin, J.P., Knapp, K. R., Vimont, D.J. Murnane, R. J., Harper, B.A. (2007) A globally consistent reanalysis of hurricane
variability and trends. Bull. Amer. Met. Soc. 88, 1767-1781
McDonald, R., Bleaken, D., Creswell, D., Pop e, V., and Senior, C. (2005). Tropical storms: representation and
diagnosis in climate models and the impacts of climate change. J. Climate, 18, 1275–1262.
Oouchie, K., Yoshimura, J., Yoshimura, H., Mizuta, R., Kusunoki, S. And Noda, A. (2006) Tropical cyclone climatology
in a global-warming climate as simulated in a 20-km mesh global atmospheric model: frequency and wind
intensity analysis. J. Met. Soc. Jap. 84, 259-276
Pielke, R. A. J., Landsea, C., Mayfield, M., Laver, J., and Pasch, R. (2005). Hurricanes and global warming. Bul l. Amer.
Meteorol. Soc., 86, 1571–1575.
Webster, P., Holland, G., Curry, J., and Chang, H.-R. (2005). Changes in tropical cyclone number, duration, and
intensity in a warming environment. Science, 309, 1844–1846.
Questions/Comments/Suggestions ?
References
Sugi, M. Noda, A., Sato, N. (2002) Influence of global warming on tropical cyclone
climatology: an experiment with the JMA global model. J. Met. Soc. Jap. 80,
249-272.
Vecchi, G. A. And Soben, B. J. (2007) Increased tropical Atlantic wind shear in
model projections of global warming. Geophys. Res. Let. 34, L08702
Zhao, M., Held, I. M., Lin, S-J. And Vecchi, G. A. (2009) Simulations of Global
Hurricane Climatology, Interannual Variability, and Respone to Global Warming
using a 50-km Resolution GCM. J. Climate. 22. 6653-6678
Previous studies
• Stong upward trends of short lived (<2 days) and no change in > 2 days
(Landsea et al. 2009) – possible changes in obs. Procedure.
- Downscalling studies suggest no change in duration Emanuel (2008)
• Some potential for the poleward movement of TC to ETC transition but
lack of studies
• Possible Increase in genesis in central ocean basins, especially Central
Pacific (Li, 2010)
• Yoshimura and Sugi (2005) did experiments changing SST and CO2. Found
SST had little affect and CO2 had large affects.
• Many studies find dynamic factors (low level vorticity and vertical wind
shear) play a more important role than thermodynamic factors (SST and
moist instability).
Change in genesis densities
Change in lysis densities
Future work
• Track transient data (Last 30 years – First 30 years)
Comparisons to CTRL and 2xCO2, 4xCO2
• CMIP5 models if res is high enough
• HiGEM SSTs on HiGAM – Lead to More intense/More
frequent TCs?
• Ocean coupling on different time scales?
- CTRL and CO2 inc runs?