Hurricanes Smoking Guns of Climate Change or random occurrences?

Climate Change and Chaotic Dynamics: Hurricane Example Naive expectation is that steadily rising sea surface temperatures (SST) should produce increasingly strong hurricanes Naive expectation is that steadily rising sea surface temperatures (SST) should produce increasingly strong hurricanes After 2005 Katrina, Rita and Wilma there was a rash of papers on how increasing hurricane strength was now a manifestation of global climate change After 2005 Katrina, Rita and Wilma there was a rash of papers on how increasing hurricane strength was now a manifestation of global climate change Needs reality check Needs reality check

Atlantic Hurricane Formation Low pressure centers form over Sahara desert and may get amplified as they cross open ocean Low pressure centers form over Sahara desert and may get amplified as they cross open ocean Amplification depends critically on SST and available moisture in the atmosphere Amplification depends critically on SST and available moisture in the atmosphere Must also have favorable wind conditions (light winds aloft) and weak wind shear Must also have favorable wind conditions (light winds aloft) and weak wind shear It is not just SST that drives hurricanes It is not just SST that drives hurricanes

Hurricane Frequency Increasing? This is difficult to establish with a high degree of statistical confidence; Incompleteness is an important issue This is difficult to establish with a high degree of statistical confidence; Incompleteness is an important issue

Counting is always noisy RADAR in the 1950s Yellow = raw data Red = corrected

Landfall Frequency vs Decade landfalltotalproportion

Using landfall frequency as a proxy Shows that significant incompleteness (25-50%) exists in the pre-radar era Shows that significant incompleteness (25-50%) exists in the pre-radar era There is no reason to the frequency of Atlantic basin hurricanes to have any systematic in their decade averaged land fall frequency. There is no reason to the frequency of Atlantic basin hurricanes to have any systematic in their decade averaged land fall frequency. This makes it pretty clear that hurricanes are not increasing in frequency in response to slow rise of SST. This makes it pretty clear that hurricanes are not increasing in frequency in response to slow rise of SST. Decadal variations are much larger than any systematically increasing baseline Decadal variations are much larger than any systematically increasing baseline

Hurricane Energetics Total amount of energy release as latent heat (condensation of water droplets) Total amount of energy release as latent heat (condensation of water droplets) The amount of kinetic energy needed to maintain the hurricane wind field (and overall movement) The amount of kinetic energy needed to maintain the hurricane wind field (and overall movement)

Latent Heat Hurricane produces 2 cm per day averaged over a radius of 600 km Hurricane produces 2 cm per day averaged over a radius of 600 km Volume of rain = 10^16 cm^3/day = 10^16 grams per day Volume of rain = 10^16 cm^3/day = 10^16 grams per day Latent heat of vaporization is 2475 KJ/Kg (at typical hurricane temperature) Latent heat of vaporization is 2475 KJ/Kg (at typical hurricane temperature) Gives 2.5 x 10^16 Joules/per day or 3 x 10^14 Watts (300 TW !!!) Gives 2.5 x 10^16 Joules/per day or 3 x 10^14 Watts (300 TW !!!)

Kinetic Energy KE generated = amount dissipated due to friction KE generated = amount dissipated due to friction Dissipation Rate per unit area = air density * drag coefficient * velocity^3 Dissipation Rate per unit area = air density * drag coefficient * velocity^3 R o is some characteristic outer radius which is largely unknown for pre-satellite hurricanes.

Energetics Suitable averages over wind velocities (90 mph over a scale of 60 km) yields 1.5 TW of “kinetic” power Suitable averages over wind velocities (90 mph over a scale of 60 km) yields 1.5 TW of “kinetic” power The total energy output of the world in all forms is 14 TW The total energy output of the world in all forms is 14 TW 14 is bigger than 1.5 but not bigger than is bigger than 1.5 but not bigger than 300 Which energy scale is most relevant for hurricane formation and evolution? If 300 then humans are doing squat. Which energy scale is most relevant for hurricane formation and evolution? If 300 then humans are doing squat.

What does Data Tell us? A Central Pressure A Central Pressure A hurricane wind radius (quite variable) A hurricane wind radius (quite variable) A duration A duration A location (time dependent) A location (time dependent) An evolutionary timescale (spin up times) An evolutionary timescale (spin up times) Category X at landfall Category X at landfall

Decadal Location Analysis – only 1 region shows upward systematic trend in counts per decade per cell

Central Pressure Evolution

But strongest storms may be increasing Note that 2009 was weakest Atlantic Basic Hurricane Season over the last 20 years; 2005 was the strongest

Strong Decadal Location Variability on spatial scale of 3x3 degrees

Spin up Times getting faster This is a Physical Signature associated with change in convection rates but data has to support this conjecture.