Erl Happ comment on how the weather works

erlhapp says:

October 12, 2010 at 6:56 am

I want to cite two recent Journal articles so that readers can tune into the issues. Otherwise what I say below may be dismissed as irrelevant nonsense:

Atmospheric science: Early peak in Antarctic oscillation index
Julie M. Jones & Martin Widmann

The principal extratropical atmospheric circulation mode in the Southern Hemisphere, the Antarctic oscillation (or Southern Hemisphere annular mode), represents fluctuations in the strength of the circumpolar vortex and has shown a trend towards a positive index in austral summer in recent decades, which has been linked to stratospheric ozone depletion and to increased atmospheric greenhouse-gas concentrations. Here we reconstruct the austral summer (December–January) Antarctic oscillation index from sea-level pressure measurements over the twentieth century and find that large positive values, and positive trends of a similar magnitude to those of past decades, also occurred around 1960, and that strong negative trends occurred afterwards. This positive Antarctic oscillation index and large positive trend during a period before ozone-depleting chemicals were released into the atmosphere and before marked anthropogenic warming, together with the later negative trend, indicate that natural forcing factors or internal mechanisms in the climate system must also strongly influence the state of the Antarctic oscillation.

Relationships between the Antarctic Oscillation, the Madden-Julian Oscillation, and ENSO, and Consequences for Rainfall Analysis
Journal of Climate, Jan 15, 2010 by Pohl, B, Fauchereau, N, Reason, C J C, Rouault, M

The Antarctic Oscillation (AAO) is the leading mode of atmospheric variability in the Southern Hemisphere mid- and high latitudes (south of 20°S). In this paper, the authors examine its statistical relationships with the major tropical climate signals at the intraseasonal and interannual time scales and their consequences on its potential influence on rainfall variability at regional scales. At the intraseasonal time scale, although the AAO shows its most energetic fluctuations in the 30-60-day range, it is not unambiguously related to the global-scale Madden-Julian oscillation (MJO) activity, with in particular no coherent phase relationship with the MJO index. Moreover, in the high southern latitudes, the MJO-associated anomaly fields do not appear to project coherently on the well-known AAO patterns and are never of an annular nature. At the interannual time scale, a strong teleconnection with ENSO is found during the peak of the austral summer season, corroborating previous studies. El Nino (La Nina) tends to correspond to a negative (positive) AAO phase. The results are statistically significant only when the seasonal mean fields averaged for the November through February season are considered.

Put these three points together:
1. The current La Nina is due to an enhancement of the pressure differential between 30-50° of latitude and 10N-10S. It is the strongest for many decades. Since 2007, La Nina has prevailed for most of the time. Before that, El Nino was dominant. La Nina involves stronger than usual trade winds and a cooler tropical ocean. That’s due to enhanced evaporation and upwelling of cold water.
2. The Antarctic Oscillation Index is currently positive indicating a loss of atmospheric pressure at the pole. It can be observed that a loss of atmospheric pressure at the pole is associated with rising atmospheric pressure in the mid latitudes.
3. It can be observed that when the Dst index (that measures the strength of the ring current above the equator) goes negative (which it does with increased geomagnetic activity) the Antarctic Oscillation index and the Arctic Oscillation index both rise indicating a loss of atmospheric pressure at the poles and increasing atmospheric pressure in mid latitudes.

And that is all you really need to know to understand the warming and cooling cycles in the tropics that we call ENSO.

Why is this statistically significant only for the November to February period? Because that is when Antarctic pressure is at its seasonal minimum and the trades are at peak seasonal strength. So, any increase in Antarctic pressure (plenty of scope for that given the seasonal minimum) robs the high pressure cells of the mid latitudes and weakens the trades. At this time of the year (November to February) the trades have to be strong to take the heat out of the tropical ocean as it rises to its seasonal maximum temperature in March-April.

In the Arctic air pressure is relatively invariable across the year. But it changes with ring current activity generally moving with the Antarctic.

In a regime of gradually declining geomagnetic activity (gradually weakening solar cycles) the ring current is gradually de-energised allowing the poles to recover atmospheric pressure (The AAO falls). The El Nino warming cycle is dominant for the duration of the decline. This is so whether we are talking 11 year cycles, 100 year cycles or 200 year cycles. Of course, there are short term swings all the time but they are like ratchets or one step after another in climbing or descending the stairs.

No need for mysterious ocean cycles. No need for cosmic rays. No need for changing levels of irradiance. The climate cycle in the tropics is driven by the solar wind energising the ring current. The ring current influences the distribution of the atmosphere. The distribution of the atmosphere determines the strength of the trade winds.

A caution: In this case tests of statistical significance will be misleading. Here are some influences that appear to impinge on the relationship.

1. Once energised the ring current takes time to lose energy. So, not every pulse of geomagnetic activity will yield the same atmospheric response.
2. Pressure at the southern pole varies strongly between summer and winter and with it the scope for change. Like all females Mother Earth has a period of peak susceptibility. Catch her at your time of choosing and she may be unresponsive.
3. Some influence unknown to me causes a tug of war between the poles. Sometimes polar pressure moves in the same direction and sometimes in opposite directions.
4. The earth has two very different hemispheres and the warming cycle heats the northern more than the southern. When the southern trades advance fast the northern trades can suffer. The Arctic Oscillation is a strong player so far as the northern hemisphere is concerned. When pressure rises at mid latitudes the warm winter westerlies affect higher latitudes, winter temperatures increase and the Arctic ice should melt. This has long been known. the index has been calculated from 1950.
5. The atmosphere needs to be ionised in order to react to the solar wind but it appears that the strongest pressure (and ENSO) response is when the atmosphere is most compact. Perhaps the ring current is more influential when the ionised and the non ionised portions are more intimate.

The global temperature response also depends upon cloud cover which determines irradiation at the surface. In the cloudier mid and high latitudes there appears to be warming as the tropics cool and this could well be related to the flux in ozone that depends upon the strength of the polar vortex. An increase in geomagnetic activity robs the vortex of air (rising AAO and AO) diminishing the flow of nitrogen oxides from the mesosphere resulting in extra ozone, and this could mean reduced cloud cover in the ice cloud zone of the upper troposphere/lower stratosphere. So, it could ultimately be the mid and high latitudes that determine whether the globe warms or cools rather than the tropics. In this scenario falling geomagnetic activity brings atmosphere back to the pole, enhances the vortex, reduces ozone levels, cools the stratosphere and the upper troposphere and increases cloud cover. So, the earth cools as the solar cycle falls away……..and this is more like we observe. One notes that the southern hemisphere, where most of the ocean is, has been cooling for as while.

Either way, it’s the solar wind that matters. And that has long been known or guessed. And the Earth is not a closed system.

Best compliments to Tallbloke and to Kim who is missed and thanks to Anthony for the opportunity.

Thanks to William for his contributions.

Erlhapp ^

Filed under: In other online forums,Natural Processes — by Richard Holle @ 6:56 am on October 12, 2010


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