North Atlantic Ocean Multi-Decadal Variability

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North Atlantic Ocean Multi-Decadal
Variability Phil Klotzbach Department of
Atmospheric Science Colorado State
University Climate Diagnostics and Prediction
Workshop October 23, 2007
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Outline

• Potential driver Atlantic thermohaline
  circulation
• Effects on Atlantic basin hurricanes
• Effects on United States hurricane landfalls
• Conclusions

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160oW
20oE
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SURFACE
500 METERS
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Salt Water Density
Fresh Water Density
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Courtesy of John Marshall (MIT)
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NADW
Tropics
THC - Strong
THC - Strong
20 Sr
20 Sr
Negative buoyancy
Positive buoyancy
NADW
THC - Weak
THC - Weak
10 Sr
10 Sr
Positive buoyancy
Negative buoyancy
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STRONG THC
WARM
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SSTA
SSTA -




SLPA
SLPA
gyre -
gyre


STRONG THC
WEAK THC
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THC Index (SST SLP)
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Top 20 THC Years Bottom 20 THC Years
(1878-2006) - SST
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Top 20 THC Years Bottom 20 THC Years
(1878-2006) - SLP
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FAST
FAST
SLOW
SLOW
Thermohaline Circulation
Rate of Salt Buildup from (E-P) - River 0
Salt Anomaly (S1)
(S1)
(S1)
YEARS
30
60
90
120
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Top 20 Bottom 20 THC Ratios
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THC STRONG
CAT 3-4-5 TRACKS
THC WEAK
CAT 3-4-5 TRACKS
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1950-1964 1997-2006 25 YEARS
13 Major Hurricanes
1970-1994 25 YEARS 3
Major Hurricanes
54
55
THC STRONG
THC WEAK
85
54
55
54
60
89
59
04
50
92
05
04
50
60
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FLORIDA LANDFALLING MAJOR HURRICANES
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3
11
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Conclusions

• Multi-decadal variability in Atlantic basin sea
  surface temperatures and sea level pressures
  exists and is likely driven by changes in
  strength of the Atlantic thermohaline circulation
• Atlantic basin tropical cyclone activity (and
  especially major hurricane activity) is much more
  frequent during strong THC years
• Florida peninsula and East Coast landfalls are
  dramatically altered by THC phase changes