New Computer Fund

Monday, March 18, 2013

The Isolation of the Southern Pole

One of the fascination I have with with the various theories of the ice ages is the Drake Passage and the thermal isolation of the southern pole.  When the Drake passage opened some millions of years ago it created the Antarctic Circumpolar current improving the heat sink efficiency of the southern oceans. The Arctic has the Bering Strait as its main circumpolar path, but due to the depth and orientation with the Coriolis Effect, it is not capable of keeping the regions oceans open or mainly free of ice.

Toggwieller et al. estimated that the Drake Passage cooled the Southern Hemisphere while warming the Northern Hemisphere with a net cooling of possibly 4 C degrees.  Depending on the actual average surface temperature used, that would be in the range of 16 to 20 Wm-2 of additional heat loss due to the thermal isolation of the southern pole.

The area for the region from 55S to the south pole is 46.4 million kilometers square or roughly 9% of the total surface area of the globe.  If the Drake Passage effectively removed that area from the thermodynamic workings of the globe, the global impact could be in the range of 16/.09 to 20/.09 or have an impact on a source average energy of 177 Wm-2 to 222 Wm-2 with a rough average of 199 Wm-2, which is the current range of the estimated Effective Radiant Layer (ERL) energy range.  This would shift the thermal equator northward by roughly 16 to 20 Wm-2.

-90 to -55 -90 to equ -55 to equ 20S to 20N Equ to 55 equ to 90 55 to 90
0.54 16.89 19.95 27.25 23.08 19.90 2.21

Since I have the nomads SST data, I determined averages by the zones about.  You can see the imbalance between the hemisphere, but if you notice the -55 to equ versus the equ to 90, the average temperatures are virtually identical.  The global meridional energy balance is shifted north just a Toggweiler et al. 2000 noted.

-90 to -55 -90 to equ -55 to equ 20S to 20N Equ to 55 equ to 90 55 to 90
318.15 401.29 418.50 461.72 436.67 418.24 326.07

Using the Stefan-Boltzmann equation, I used the absolute temperatures to estimate the effective energy of the same regions.  The difference between the non isolated southern pole and the new -55 to equ  is roughly 17.2 Wm-2 or 3.15C is you use the upper temperature table.

There have been a few more papers on the impact of the Drake Passage since Toggweiler et al.

The establishment of the modern meridional and zonal SST distributions leads to roughly 3.2 degrees C and 0.6 degrees C decreases in global mean temperature, respectively. Changes in the two gradients also have large regional consequences, including aridification of Africa (both gradients) and strengthening of the Indian monsoon (zonal gradient). Ultimately, this study suggests that the growth of Northern Hemisphere ice sheets is a result of the global cooling of Earth's climate since 4 Myr rather than its initial cause.  Brierley, C.M. et al. 2010

The "modern meridional and zonal SST distributions would be the result of the Drake Passage opening.

I think that 3.2 and 3.15 are pretty close considering the alleged inaccuracy of satellite temperature data.  

Shifting the thermal equator would require shifting the atmospheric radiant balance.  For the Earth to have a stable climate, you can't have major imbalances that are not compensated for in one way or another.

South pole to equ North pole to Equ South pole to equ. S North pole to equ N
143.56 135.64 100.36 92.44
So in this table I compared the meridional flux relationships.  From the Equator, there is a larger southward energy flux than northward.  From the lower latitudes (equ S and Equ N) to the poles there is also and imbalance.  But the difference in both cases is exactly 43.20 Wm-2 or roughly the atmospheric window energy value.  

I didn't do this to prove Toggweiller et al. or Brierley et al. know what they are talking about, but to see roughly how much accuracy I could expect from the Nomads OI v2 data set.  I must say I am again impressed with the satellite data.  This was just a quick comparison so there may be more information available, but currently I am more curious about the zonal SST distribution and that 0.6 C that could be part of the longer term natural climate oscillations also estimated by Toggweiler et al. 1994.

No comments:

Post a Comment