Tuesday, August 30, 2011

Ryan Maue, hurricanes & ACE (accumulated cyclone energy)

I received a comment that I believe deserves it's own post:
T said...
I think that in denying the Denier, you might have missed this: hurricane ACE (accumulated cyclone energy) levels are historically low levels - worldwide, according to Dr. Ryan Maud.


In the process of looking up T's link and I came across another one of Patrick Michaels awful essays "Where Have All the Blowhards Gone?" focusing on the ACE as though it contains all we need to know about hurricanes.

It's another example of that art of taking a sliver of real fact and morphing it into some creature that has nothing to do with learning, instead being all about reinforcing that "free market" dogma, that refuses to allow any recognition of the situation we are creating for ourselves to shine through. . . but, i digress.

Mr. T suggested I consider the ACE, so consider it I shall.

For starters the paper has a misleading title, it should have read:
“Ryan_Maue_FSU_Global_ACE_ levels_historical_lows”
because ACE is a one eyed indicator of actual cyclone intensity and doesn't serve as an accurate measure of a cyclone's total energy expenditure, nor its potential destructive power.

ACE - Accumulated Cyclone Energy is:
“The ACE index is a wind energy index, defined as the sum of the squares of the maximum sustained surface wind speed (knots) measured every six hours for all named storms while they are at least tropical storm strength.”

ACE does not take into account moisture/water content,
nor does it factor in cyclone size.  

Like trying to balance a stool on one leg.

ACE happens to be the easier data to collect and has it purposes, but when trying to understand global warming’s impact on cyclones, it is decidedly horse’n buggy stuff that has no right being waved around without seriously considering the full spectrum of the available science, something "skeptics" refuse to do.  

I know, I know, I'm not a scientist, don't take my word for it, check out this link. . .

18th Conference on Applied Climatology
The misuse and misinterpretation of the ACE and PDI indices for hurricane energetics
Angela M. Fritz, Georgia Institute of Technology, Atlanta, GA; and J. I. Belanger, J. A. Curry, and G. J. Holland

The Accumulated Cyclone Energy (ACE) index and the Power Dissipation (PDI) Index are widely used as metrics to quantify seasonal hurricane activity both in the Atlantic basin and worldwide.

It can be shown that both of these indices are based on inaccurate assumptions that lead to a misuse and misinterpretation of the resulting index.

Towards advancing the indices of hurricane energetics that are associated with potential damage, we develop a new methodology for calculating an integrated kinetic energy (IKE) climatology. A simple, observation and dynamical – based radial wind speed model is used with the Extended Best Track dataset to calculate IKE for North Atlantic Hurricanes from 1988 to 2008. {...}
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Since this started with concern over increasing extreme weather events it's worth adding a few more informative links:

From the good folks over at SkepticalScience.com

"What is the link between hurricanes and global warming?":

"There are two aspects to hurricane activity that are often confused so it helps to consider them separately. Specifically, does global warming cause more frequent hurricanes and does it cause more intense hurricanes? . . ."
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And a couple from Joe Romm at ThinkProgress.org

Stunning NOAA map of Tennessee’s 1000-year deluge

By Joe Romm on May 26, 2010
15 sites had rainfall exceeding maximum associated with Hurricane Katrina landfall

". . . Climate Progress has been documenting the woefully underreported Tennessee deluge of 2010 aka Nashville’s ‘Katrina’. It was an off-the-charts extreme weather event that human-caused global warming set the table for and almost certainly made more intense, as a leading climate scientist explained to me (interview to be posted next week).

But I didn’t understand just how unprecedented this superstorm was until I saw the above map from the Office of Hydrological Development at NOAA/NWS. . ."
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How Does Global Warming Make Hurricanes Like Irene More Destructive?

By Joe Romm on Aug 27, 2011

Climate science suggests that global warming will make hurricanes like Irene more destructive in three ways (all things being equal):

Sea level rise makes storm surges more destructive.

“Owing to higher SSTs [sea surface temperatures] from human activities, the increased water vapor in the atmosphere leads to 5 to 10% more rainfall and increases the risk of flooding,” as NCAR Senior Scientist Kevin Trenberth put it in an email to me today.

“However, because water vapor and higher ocean temperatures help fuel the storm, it is likely to be more intense and bigger as well,” as Trenberth writes

On the third point, warming also extends the range of warm SSTs, which can help sustain the strength of a hurricane as it steers on a northerly track. As meteorologist and former hurricane hunter Dr. Jeff Masters has explained:

… this year sea surface temperatures 1 – 3°F warmer than average extend along the East Coast from North Carolina to New York.

Waters of at least 26°C extend all the way to Southern New Jersey, which will make it easier for Irene to maintain its strength much farther to the north than a hurricane usually can.

During the month of July, ocean temperature off the mid-Atlantic coast (35°N – 40°N, 75°W – 70°W) averaged 2.6°F (1.45°C) above average, the second highest July ocean temperatures since record keeping began over a century ago (the record was 3.8°F above average, set in 2010.)

These warm ocean temperatures will also make Irene a much wetter hurricane than is typical, since much more water vapor can evaporate into the air from record-warm ocean surfaces.

'Extensive flooding' expected as Lee batters Louisiana
Posted: Sep 4, 2011 9:41 AM by CNN Wire Staff

(Tropical Storm) Lee is expected to produce 10 to 15 inches of rain from the central Gulf Coast northward into the Tennessee Valley, with some areas getting as much as 20 inches by Monday night, the National Hurricane Center said. "These rains are expected to cause extensive flooding and flash flooding," the center said in an advisory.

Some coastal residents said they were prepared. 'We are a sturdy people. All Gulf Coasters are willing and able to weather any storm," said Andrew Kaile of Metairie, Louisiana, just west of New Orleans, in an iReport Saturday.

As of 11 a.m. ET Sunday, Lee was "drifting northeastward over south-central Louisiana," the hurricane center said. Its maximum sustained winds were 45 mph, and it was moving at only 3 mph.


Please note that
this storm rates fairly low on the ACE scale,
because that scale don’t factor in water.
I'd love to ask the wordsmith Mr. Michaels what is the ACE actually good for so far as understanding the developing situation? Can you explain it?

Back to the story,
This storm is an example for the fact that global warming HAS increased atmospheric moisture around 7% above pre-70s levels.

Consider what happens to hurricanes when they encounter higher SSTs (sea surface temperature) within this atmosphere of higher amounts moisture/water and energy?


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