TCs and Climate Change

Greg Holland

• 1975 to present, number of hurricanes has decreased

• proportion of Cat 4-5 has increased by 40%.• related to 0.8 deg increase in global temp • When hurricanes form they’re finding it easier

to reach higher intensities

Jim Elsner

• Sensitivity of hurricane strength to ocean heat. • Sensitivity 8.2± 1.19m s-1/°C for hurricanes over

oceans hotter than 25 °C. • Significantly lower (1.5 ± 0.60 m s-1/°C ) in high-

res dynamical model. • Results indicate the likelihood of more powerful

hurricanes during 21st Century as oceans continue to warm, but call into question usefulness of current models.

TCGI in HIRAM, great present climate, improvement on GPI, but has problems in the future climate

Suzanna Camargo

Ming Zhao

• Hurricane frequency response to SST anomalies late 21st Century

• Large inter-model spread• N. Atlantic, the E. Pacific and the S. Indian basins, most

of the inter-model variance in storm frequency response is explained by a simple relative SST index:

• basin's storm development region SST minus the tropical mean SST

• Eastward and poleward migration of genesis frequency in both the N. Pacific and the N. Atlantic oceans

Hiroyuki Murakami

• New 20 km MRI model simulating climatology and numbers of Cat 4&5 storms really well. (first time for a GCM)

• Northward shift in NWP TCs and increase Cat5• Not as large intensity increases as previous

version• In S. Pacific there is a large windshear resulting

in decrease in TC intensity.

Tim Merlis

• Aquaplanet, idealised study. • Found an increase in frequency of TCs in

future (!)• Linked to a poleward shift in the ITCZ. - More

favourable for TC genesis• If the location of the ITCZ remains the same

finds a decrease in frequency.

James Done

• Internal variability (unpredictability) of TCs• Produces large spread in seasonal NA TC counts• IN RCM (WRF) internal variability in long-lived

TC-vortices rather than formation of initial vortex

• Contrib factors:– Vortex intensity and vertical extent– Large-scale environment

Jason Dunion – Uni Miami/NOAA

• Diurnal pulsing (cold signal)• Forms in storms inner core at sunset• Evolves and moves out of centre• Several km’s away by following afternoon• Marked structural changes to storm as pulse

evolves and moves out

GOES IR (storm relative) GOES BT Diff (storm relative)

Hurricane Emily: 14-15 July 2005