Hurricanes Smoking Guns of Climate Change or random

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 n 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 n Needs reality check n

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

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

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

Landfall Frequency vs Decade landfall total proportion 1900 27 40 0. 675 1910 29 37 0. 78378378 1920 25 42 0. 5952381 1930 36 47 0. 76595745 1940 34 50 0. 68 1950 34 69 0. 49275362 1960 26 61 0. 42622951 1970 23 49 0. 46938776 1980 21 52 0. 40384615 1990 24 64 0. 375 2000 40 74 0. 54054054 585 1900 -1949 151 216 0. 69907407 1950 -2009 168 369 0. 45528455

Using landfall frequency as a proxy • 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. 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

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

Latent Heat Hurricane produces 2 cm per day averaged over a radius of 600 km n Volume of rain = 10^16 cm^3/day = 10^16 grams per day n Latent heat of vaporization is 2475 KJ/Kg (at typical hurricane temperature) n Gives 2. 5 x 10^16 Joules/per day or 3 x 10^14 Watts (300 TW !!!) n

Kinetic Energy KE generated = amount dissipated due to friction n Dissipation Rate per unit area = air density * drag coefficient * velocity^3 n Ro 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 n The total energy output of the world in all forms is 14 TW n 14 is bigger than 1. 5 but not bigger than 300 n Which energy scale is most relevant for hurricane formation and evolution? If 300 then humans are doing squat. n

What does Data Tell us? • A Central Pressure • A hurricane wind radius (quite variable) • A duration • A location (time dependent) • An evolutionary timescale (spin up times) • 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 3 x 3 degrees

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