Re: EL NINO OR LA NINA causes which type of weather?
- From: Weatherlawyer <Weatherlawyer@xxxxxxxxxxx>
- Date: 28 Apr 2007 13:10:56 -0700
On Apr 28, 8:26 pm, Weatherlawyer <Weatherlaw...@xxxxxxxxxxx> wrote:
On Apr 26, 9:02 pm, Bob Brown <.> wrote:
Is it El Nino or La nina that tends to cause more, at least above
average, tornadoes in the USA?
I'm asking because it seems the US tornado events seem to be way ahead
of average and it's only April?
It also seems the tornadoes are on average stronger on a strength/# of
tornadoes ratio.
So do we look at El Nino or La Nina for a glimpse into tornado numbers
and/or strength?
There is or was a negative aspect to the oscillation of one ocean
basin at the moment somewhere.
I don't know where but I do know what to look for and it isn't a
fraction of a degree difference in the average surface sea
temperatures.
What it is is the pressure differences between Low pressure areas and
High ones. In the North Atlantic the areas concerned are the Icelandic
Low and the Azores or Bermuda High.
When there is very little activity in Iceland, Low pressure areas seem
to move directly up into the Arctic rather than hitting Scotland or
Norway.
My predictions go haywire and the whole world seems to suffer or enjoy
unusual weather. I managed to score a small hit with my methods only
because I was expecting something not an Hurricane and not an
earthquake (a 7 M or so.)
Here was my stab at it:http://groups.google.com/group/alt.talk.weather/browse_frm/thread/369...
Which didn't answer your question.
The answer to the question:
Is it El Nino or La nina that tends to cause more, at least above
average, tornadoes in the USA?
The el Nino theory was first mooted about 100 or more years ago when
statisticians noted that there was a period or cycle in activity in
the Indian Ocean when the average air pressures seemed to reverse.
anomalously high:From the Encyclopeadia Britannica Note words and phrases such as
The Southern Oscillation.
At the turn of the century, the British climatologist Gilbert Walker
set out to determine the connections between the Asian monsoon and
other climatic fluctuations around the globe in an effort to predict
unusual monsoon years that bring drought and famine to the Asian
sector. Unaware of any connection to El Niño, he discovered a coherent
interannual fluctuation of atmospheric pressure over the tropical Indo-
Pacific region, which he termed the Southern Oscillation (SO).
During years of reduced rainfall over northern Australia and
Indonesia, the pressure in that region (e.g., at what are now Darwin
and Jakarta) was anomalously high and wind patterns were altered.
Simultaneously, in the eastern South Pacific pressures were unusually
low, negatively correlated with those at Darwin and Jakarta. A
Southern Oscillation Index (SOI), based on pressure differences
between the two regions (east minus west), showed low, negative values
at such times, which were termed the "low phase" of the SO.
*******
That's as far as the correct stuff goes. Satellite data is set up for
radiation not air pressure so the theorists started to make quantum
leaps to get the pieces fitted into a model:
During more normal "high-phase" years, the pressures were low over
Indonesia and high in the eastern Pacific, with high, positive values
of the SOI. In papers published during the 1920s and '30s, Walker gave
statistical evidence for widespread climatic anomalies around the
globe being associated with the SO pressure "seesaw."
In the 1950s, years after Walker's investigations, it was noted that
the low-phase years of the SOI corresponded with periods of high ocean
temperatures along the Peruvian coast, but no physical connection
between the SO and El Niño was recognized until Jacob Bjerknes, in the
early 1960s, tried to understand the large geographic scale of the
anomalies observed during the 1957-58 El Niño event. Bjerknes, a
meteorologist, formulated the first conceptual model of the large-
scale ocean-atmosphere interactions that occur during El Niño
episodes. His model has been refined through intensive research since
the early 1970s.
During a year or two prior to an El Niño event (high-phase years of
the SO), the westward trade winds typically blow more intensely along
the equator in the equatorial Pacific, causing warm upper-ocean water
to accumulate in a thickened surface layer in the western Pacific
where sea level rises. Meanwhile, the stronger, upwelling-favourable
winds in the eastern Pacific induce colder surface water and lowered
sea levels off South America. Toward the end of the year preceding an
El Niño, the area of intense tropical storm activity over Indonesia
migrates eastward toward the equatorial Pacific west of the
international date line (which corresponds in general to the 180th
meridian of longitude), bringing episodes of eastward wind reversals
to that region of the ocean. These wind bursts excite extremely long
ocean waves, known as Kelvin waves (imperceptible to an observer),
that propagate eastward toward the coast of South America, where they
cause the upper ocean layer of relatively warm water to thicken and
sea level to rise.
The tropical storms of the western Pacific also occur in other years,
though less frequently, and produce similar Kelvin waves, but an El
Niño event does not result and the waves continue poleward along the
coast toward Chile and California, detectable only in tide-gauge
measurements. Something else occurs prior to an El Niño that is not
fully understood: as the Kelvin waves travel eastward along the
equator, an anomalous eastward current carries warm western Pacific
water farther east, and the warm surface layer deepens in the central
equatorial Pacific (east of the international dateline). Additional
surface warming takes place as the upwelling-favourable winds bring
warmer subsurface water to the surface. (The subsurface water is
warmer now, rather than cooler, because the overlying layer of warmer
water is now significantly deeper than before.) The anomalous warming
creates conditions favourable for the further migration of the
tropical storm centre toward the east, giving renewed vigour to
eastward winds, more Kelvin waves, and additional warming. Each
increment of anomalies in one medium (e.g., the ocean) induces further
anomalies in the other (the atmosphere) and vice versa, giving rise to
an unstable growth of anomalies through a process of positive
feedbacks. During this time, the SO is found in its low phase.
After several months of these unstable ocean-atmosphere interactions,
the entire equatorial zone becomes considerably warmer (2-5 C) than
normal, and a sizable volume of warm upper ocean water is transported
from the western to the eastern Pacific. As a result, sea levels fall
by 10-20 centimetres in the west and rise by larger amounts off the
coast of South America, where sea surface temperature anomalies may
vary from 2 to 8 C above normal. Anomalous conditions typically
persist for 10-14 months before returning to normal. The warming off
South America occurs even though the upwelling-favourable winds there
continue unabated: the upwelled water is warmer now, rather than
cooler as before, and its associated nutrients are less plentiful,
thereby failing to sustain the marine ecosystem at its prior
productive levels.
*******
<Kook mode on>
The above would do better with paragraph spacing but I have a better
take on it than everyone else on the planet at the moment.
Since all this anomalous stuff is the result of wave harmonics, it
stands to reason that the outcome will be seen on various parts of the
planet as different phenomena. All one has to do is nail the harmonic
and that, it turns out, is quite easy.
.
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