Saturday, May 25, 2013

A New Hurricane Metric

The huge amount of damage done by Hurricane Sandy -- about $75 billion, with 275 deaths along its path -- has been causing scientists to rethink how they classify storms. Now there's a paper out introducing "TIKE" -- Track Integrated Kinetic Energy.

From Wikipedia:
"On October 25, Sandy hit Cuba as a Category 3 hurricane, then weakened to a Category 1 hurricane. Early on October 26, Sandy moved through the Bahamas. On October 27, Sandy briefly weakened to a tropical storm and then restrengthened to a Category 1 hurricane. Early on October 29, Sandy curved north-northwest and then moved ashore near Brigantine, New Jersey, just to the northeast of Atlantic City, as a post-tropical cyclone with hurricane-force winds."
Technically it didn't count as a "major hurricane," a term which the National Hurricane Center reserves for hurricanes that reach maximum sustained 1-minute surface winds of at least 50 m/s (111 mph) -- equivalent of category 3, 4 and 5 on the Saffir-Simpson scale.

Yet its size -- the largest Atlantic hurricane on record (as measured by diameter) certainly contributed to it doing major damage. The size of a storm determines its surge, and for big storms damage from coastal flooding is often larger than wind damage.

The existing hurricane metrics -- Accumulated Cyclone Energy (ACE) and Power Dissipation Index (PDI) don't take size into account, only wind speed:

\text{ACE} = 10^{-4} \sum v_\max^2

with the PDI being the same summation with with velocity cubed.

By contrast, TIKE, as defined by Misra et al,  is calculated by:

Of course, in practice the integral is going to be a summation, which Misra et al do every 6 hours (as for ACE and PDI), with wind speed and radii data from the Colorado State University Extended Best Track dataset.

Wunderground writes:
According to Misra, Hurricane Sandy had a higher TIKE value than any other tropical storm or hurricane in the North Atlantic Ocean Basin since 1990. Hurricane Lily, which occurred in 1996, was the runner-up, followed by 2010’s Igor, 1995’s Luis, 1997’s Erica, and Hurricane Olga, which occurred in 2001.
They obtain results since 1990:

1 comment:

Anonymous said...

why no mention of the following

sandy came ashore on a 6ft high tide and
a 1 ft full moon and a 1ft warmer ocean(than 200 years ago) which makes the storm surge about 8 ft lower than the Great September Gale of 1815