Comments on: Hurricanes and SST: isn’t it solid science? http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm Wed, 23 May 2012 12:37:58 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: pegminer http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm/comment-page-1#comment-6626 pegminer Mon, 23 Nov 2009 14:33:37 +0000 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm#comment-6626 I agree with your first statement, that hurricane strength correlates with SST. Water vapor is the fuel of hurricanes, and high SSTs supply the water vapor to the hurricane's heat engine. However, I don't think your first plot is necessarily good evidence for this. Emanuel's so-called power dissipation index (PDI) depends upon maximum wind speed cubed, and therefore the error in it depends on 3 times the error in the maximum wind speed. I don't believe that the maximum wind speed is always that well known. It is determined by Dvorak satellite image classification, which doesn't always work that well, and by dropsonde observations. However, there are often no flights into hurricanes and even if there are, they are usually separated by long intervals of time (6 or 12 hours) with no observations. Emanuel didn't put error bars on his plot, but if he did, the tight correlation would turn into a big smear around the curve. There is no doubt that high SST and low wind shear are the key ingredients for strong hurricanes. How exactly AGW translates into those parameters taken together is still subject to much debate. EDIT: To clarify a bit what PDI is, for an individual storm it is the maximum wind speed cubed integrated over the lifetime of the storm. It is a simplification of the Power Dissipation (PD), which for an individual storm is the integral over the radius of the storm and the lifetime of the storm of the surface drag coefficient times the air density times the magnitude of the radially dependent velocity cubed times the radius. Since storms are often asymmetric and it can be very difficult to determine a velocity field, Emanuel simplifies the PDI to only depend upon the maximum velocity (not the drag coefficient, density, or radial dependence). The plot you refer to is a sum over the PDI for all the individual storms. It really needs error bars, there are lots of sources of error in the PDI. I agree with your first statement, that hurricane strength correlates with SST. Water vapor is the fuel of hurricanes, and high SSTs supply the water vapor to the hurricane’s heat engine.

However, I don’t think your first plot is necessarily good evidence for this. Emanuel’s so-called power dissipation index (PDI) depends upon maximum wind speed cubed, and therefore the error in it depends on 3 times the error in the maximum wind speed. I don’t believe that the maximum wind speed is always that well known. It is determined by Dvorak satellite image classification, which doesn’t always work that well, and by dropsonde observations. However, there are often no flights into hurricanes and even if there are, they are usually separated by long intervals of time (6 or 12 hours) with no observations. Emanuel didn’t put error bars on his plot, but if he did, the tight correlation would turn into a big smear around the curve.

There is no doubt that high SST and low wind shear are the key ingredients for strong hurricanes. How exactly AGW translates into those parameters taken together is still subject to much debate.

EDIT: To clarify a bit what PDI is, for an individual storm it is the maximum wind speed cubed integrated over the lifetime of the storm. It is a simplification of the Power Dissipation (PD), which for an individual storm is the integral over the radius of the storm and the lifetime of the storm of the surface drag coefficient times the air density times the magnitude of the radially dependent velocity cubed times the radius. Since storms are often asymmetric and it can be very difficult to determine a velocity field, Emanuel simplifies the PDI to only depend upon the maximum velocity (not the drag coefficient, density, or radial dependence).

The plot you refer to is a sum over the PDI for all the individual storms. It really needs error bars, there are lots of sources of error in the PDI.

]]> By: bucket22 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm/comment-page-1#comment-6627 bucket22 Mon, 23 Nov 2009 14:33:37 +0000 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm#comment-6627 Hurricane frequency - not a lot of scientific agreement whether total number of hurricanes will increase or decrease. Wind shear is one factor that can deter hurricane formation. Hurricane intensity - there's growing consensus that hurricanes that do form will intensify on average, due to warmer ocean waters, but some contention over exactly how much. Hurricane intensity has increased over the last 30 years, although with strong year-to-year variation. Based on a cautious assessment, It's not enough to make a very strong conclusive attribution on past data, but this data does indicate the connection. Going forward, the consensus is (from your link) "It is likely that greenhouse warming will cause hurricanes in the coming century to be more intense on average and have higher rainfall rates than present-day hurricanes." On perhaps a slightly different note, there have been other recent observations linking global warming to severe storm increases: http://www.nasa.gov/centers/jpl/news/airs20081219.html Hurricane frequency - not a lot of scientific agreement whether total number of hurricanes will increase or decrease. Wind shear is one factor that can deter hurricane formation.

Hurricane intensity - there’s growing consensus that hurricanes that do form will intensify on average, due to warmer ocean waters, but some contention over exactly how much. Hurricane intensity has increased over the last 30 years, although with strong year-to-year variation. Based on a cautious assessment, It’s not enough to make a very strong conclusive attribution on past data, but this data does indicate the connection. Going forward, the consensus is (from your link) "It is likely that greenhouse warming will cause hurricanes in the coming century to be more intense on average and have higher rainfall rates than present-day hurricanes."

On perhaps a slightly different note, there have been other recent observations linking global warming to severe storm increases:

http://www.nasa.gov/centers/jpl/news/airs20081219.html

]]> By: Dana1981, Master of Science http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm/comment-page-1#comment-6628 Dana1981, Master of Science Mon, 23 Nov 2009 14:33:37 +0000 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm#comment-6628 Well, if you're only concerned about potential damage to US property via hurricanes, it might make sense to focus on US hurricane landfall. Otherwise no, just like it makes no sense when certain people focus on US or local temperatures, it makes no sense not to focus on global hurricane strength and frequency. And according to a recent study, hurricanes are indeed becoming stronger. Well, if you’re only concerned about potential damage to US property via hurricanes, it might make sense to focus on US hurricane landfall. Otherwise no, just like it makes no sense when certain people focus on US or local temperatures, it makes no sense not to focus on global hurricane strength and frequency.

And according to a recent study, hurricanes are indeed becoming stronger.

]]> By: johnnyrockets16 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm/comment-page-1#comment-6629 johnnyrockets16 Mon, 23 Nov 2009 14:33:37 +0000 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm#comment-6629 Focusing on the "number of hurricanes which strike the US" is the same as saying it's been cold in the US, but ignoring the temps of the rest of the world's regions. There is a lot more happening out there. Focusing on the "number of hurricanes which strike the US" is the same as saying it’s been cold in the US, but ignoring the temps of the rest of the world’s regions. There is a lot more happening out there.

]]> By: bravozulu http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm/comment-page-1#comment-6630 bravozulu Mon, 23 Nov 2009 14:33:37 +0000 http://hurricanequestions.com/hurricanes-and-sst-isnt-it-solid-science.htm#comment-6630 I just posted that hurricanes are stronger, just like thunderstorms when the air above is colder. The air is warmed as the water condenses and cold air aloft enhances more rapid rising. Since the air isn't actually warmer in the mid troposphere relative to the ground and that invalidates greenhouse warming, you could get more hurricanes. It just hasn't happened based on the data. Warmer water makes hurricanes more powerful. Warmer air aloft reduces it. It is a simple a distortion to pretend that global warming increases hurricane number or strength despite your strong desire for it to be true. Unfortunately for you, you live in the real world and the climate doesn't care what you want. http://www.nhc.noaa.gov/pastdec.shtml I just posted that hurricanes are stronger, just like thunderstorms when the air above is colder. The air is warmed as the water condenses and cold air aloft enhances more rapid rising. Since the air isn’t actually warmer in the mid troposphere relative to the ground and that invalidates greenhouse warming, you could get more hurricanes. It just hasn’t happened based on the data. Warmer water makes hurricanes more powerful. Warmer air aloft reduces it. It is a simple a distortion to pretend that global warming increases hurricane number or strength despite your strong desire for it to be true. Unfortunately for you, you live in the real world and the climate doesn’t care what you want.
http://www.nhc.noaa.gov/pastdec.shtml

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