NZCLIMATE TRUTH NEWSLETTER NO 304X
by Dr Vincent Gray
February 19th 2013
THE ENERGY OF HURRICANES
A most interesting calculation of the energy released by hurricanes was published as a “Frequently Asked Question at
Subject: D7) How much energy does a hurricane release?
Contributed by Chris Landsea
Hurricanes can be thought of, to a first approximation, as a heat engine; obtaining its heat input from the warm, humid air over the tropical ocean, and releasing this heat through the condensation of water vapor into water droplets in deep thunderstorms of the eyewall and rainbands, then giving off a cold exhaust in the upper levels of the troposphere (~12 km/8 mi up).
One can look at the energetics of a hurricane in two ways:
- the total amount of energy released by the condensation of water droplets or ...
- the amount of kinetic energy generated to maintain the strong swirling winds of the hurricane (Emanuel 1999).
It turns out that the vast majority of the heat released in the condensation process is used to cause rising motions in the thunderstorms and only a small portion drives the storm's horizontal winds.
An average hurricane produces 1.5 cm/day (0.6 inches/day) of rain inside a circle of radius 665 km (360 n.mi) (Gray 1981). (More rain falls in the inner portion of hurricane around the eyewall, less in the outer rainbands.) Converting this to a volume of rain gives 2.1 x 1016 cm3/day. A cubic cm of rain weighs 1 gm. Using the latent heat of condensation, this amount of rain produced gives5.2 x 1019 Joules/day or 6.0 x 1014 Watts.This is equivalent to 200 times the world-wide electrical generating capacity - an incredible amount of energy produced!
- Method 1) - Total energy released through cloud/rain formation:
For a mature hurricane, the amount of kinetic energy generated is equal to that being dissipated due to friction. The dissipation rate per unit area is air density times the drag coefficient times the windspeed cubed (See Emanuel 1999 for details). One could either integrate a typical wind profile over a range of radii from the hurricane's center to the outer radius encompassing the storm, or assume an average windspeed for the inner core of the hurricane. Doing the latter and using 40 m/s (90 mph) winds on a scale of radius 60 km (40 n.mi.), one gets a wind dissipation rate (wind generation rate) of1.3 x 1017 Joules/day or
- Method 2) - Total kinetic energy (wind energy) generated:
1.5 x 1012Watts.This is equivalent to about half the world-wide electrical generating capacity - also an amazing amount of energy being produced!Either method is an enormous amount energy being generated by hurricanes. However, one can see that the amount of energy released in a hurricane (by creating clouds/rain) that actually goes to maintaining the hurricane's spiralling winds is a huge ratio of 400 to 1.
A single hurricane could provide convective cooling of 1.5x 1014 Watts per day and latent heat transfer of 6x1014 Watts per day. If a hurricane lasts a week and there are 11 hurricanes a year. If the area of the earth is 5x 1014m2 each day supplies 0.3Wm-2of convection and 2,1Wm-2 of latent heat negative forcing.
and it is spread over 365 days to get an annual average, If,a hurricane lasts a week and there are 11 hurricanes a year 77 days of hurricane forcing has to be spread over 365 days to get an annual average. So multiply by 77/365 and we get 0.032Wm-2 from convection and 0.25Wm-2 from latent heat.
And this was only hurricanes. There are 180 thunderstorms each year plus normal convection and evaporation. The IPCC gives an annual figure of 17Wm-2 for convection loss and 80Wm-2 for latent heat loss, but these have been recently increased to 20Wm-2 and 85Wm-2
This should be compared with the 1.5Wm-2 claimed to have been supplied by the greenhouse effect between 1750 and 2005, 0.006 Wm-2 increase per year.
The IPCC projects between 5 and 9 Wm-2 increase in radiative forcing from increases in greenhouse gases between 1990 and 2010, an annual averge of between 0.045 and 0.082Wm-2 over this period.
The enormous amounts of energy involved in convection and latent heat exchanges are removed in one place and deposited elsewhere, partly in the oceans, partly reducing cooling at night and partly, as Landsea says, radiated to space. Their behaviour, dependent on the chaotic properties of fluid flow, is unpredictable. They conceal any possible much smaller effects of greenhouse gases which could never be identified. The models are not only wrong. They are irrelevant.
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