Planetary Temperature: Hurricane and Ice Question from Comments

Arun asks:

Facts
1. Polar ice melt this summer was unusual.
2. Atlantic hurricane season was very quiet.

Question - hurricanes are a byproduct of necessary energy transfer from the tropics to the higher latitudes; but some mechanism is already working better than expected, melting so much polar ice. Is that why the hurricane season has been so quiet? I'd expect the Pacific season also to have been quiet. If the Antarctica has not been seeing unusual melts, the southern ocean cyclones should have been the same or worse.


The Northern Hemisphere ice melt has been spectacular, but the South is pretty much trucking along as usual - peak ice was actually (barely) a record. See the charts at http://arctic.atmos.uiuc.edu/cryosphere/ (Cryosphere Today).


This year's Atlantic hurricane season has been odd, but not actually especially quiet by long term standards.


Now to the point: If we look at net Northward heat transport (ocean plus atmosphere) as a function of latitude, it is nearly a sine wave, with the zero at the equator. At peak (45 degrees latitude), the transport is about 6 x 10^15 Watts (annual average). By comparison, a hurricane in action extracts energy at about 1/10 that rate from a tropical ocean (6 x 10^14 Watts), and most of that energy is given up in the tropical or mid latitudes. As a result, hurricane heat transport is a small fraction of the total, especially of the total reaching the far North.


Remember also that Summer is the season of minimum transport of atmospheric and oceanic heat into the Arctic - only about 80% of the winter values. Arctic melting is poorly understood - at least by me - but involves import of warm air and ocean water, export of ice (80 cal/gm), and, especially, heat absorbed from the Sun and radiated to space. Wind plays a key role in the first three, but the heat absorbed is mainly a function of albedo (high for clean ice, very low for open water), and heat radiated from the top of the atmosphere depends significantly on CO2 concentration - more important in the polar regions because the atmosphere is so dry that H2O is less important as a greenhouse gas than it is in the tropics or mid latitudes.


If Eli reads this, maybe he can critique my analysis.


UPDATE/RESPONSE TO WILLIAM CONNOLLEY:


I neglected to discuss the actual mechanisms of heat transport in the midlatitudes. William points out that midlatitude storms pack a punch energetically, but I tend to think of them as symptom rather than cause. If you look at our planet's large scale cloud patterns, or better still, some water vapor loops, you can see that the atmosphere continually writhes and spins in an ever changing pattern of waves, loops, and vortices. It is these waves and vortices that transport heat, moisture and momentum north in exchange for colder, dryer air. They give rise to the mid latitude cyclones that produce most of our weather. They, in turn, are driven by the baroclinicity of our atmosphere - the tilting of atmospheric pressure surfaces due to differential heating at equator and pole.


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