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?

thanks

In article , Bob Brown .
says...
Is it El Nino or La nina that tends to cause more, at least above
average, tornadoes in the USA?

Neither. There's a suggestion that La Nina is associated with more
tornadoes in the Ohio Valley, but the effect is small (Marzban and
Schaefer, 2001: The Correlation between U.S. Tornadoes and Pacific Sea
Surface Temperatures. Monthly Weather Review

Abstract:

The correlation between tornadic activity in several regions of the
United States and the monthly mean sea surface temperature over four
zones in the tropical Pacific Ocean is examined. Tornadic activity is
gauged with two mostly independent measures: the number of tornadoes per
month, and the number of tornadic days per month. Within the assumptions
set forth for the analysis, it is found that there appears to exist a
statistically significant but very weak correlation between sea surface
temperature in the Pacific Ocean and tornadic activity in the United
States, with the strength and significance of the correlation depending
on the coordinates at which the sea surface temperatures are assessed
and the geographic region of the United States. The strongest evidence
found is for the correlation between the number of days with strong and
violent (F2 and greater) tornadoes in an area that runs from Illinois to
the Atlantic Coast, and Kentucky to Canada and a cool sea surface
temperature in the central tropical Pacific. However, there is only
about a 53% chance of this relationship occurring in a specific month.


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?


No.

Harold
--
Harold Brooks

On Thu, 26 Apr 2007 16:02:41 -0400,
Bob Brown , in
wrote:
+ Is it El Nino or La nina that tends to cause more, at least above
+ average, tornadoes in the USA?

http://www.cpc.noaa.gov/products/ana...html#TORNADOES

Of course, they don't discuss strength, more location.

Here's a very relevant quote:

None of the statistical comparisons that we presented allow us
to differentiate tornado activity as a function of the ENSO
phase. There are some indications of a weak signal with F2 and
greater tornadoes over Florida and with the ACF over tornado
alley. Perhaps if one subdivided either the time window, or the
areas considered some statistically significant correlations
might be obtained. However, with only 10 El Ninos and 8 La
Ninas over the 47 years of this study, the data is rather
sparse. Tornadoes are even rarer. If the regions of study
become too small, the validity of the study would be dubious no
matter how great the statistical significance.

http://www.spc.noaa.gov/publications...er/el_nino.htm

+ I'm asking because it seems the US tornado events seem to be way ahead
+ of average and it's only April?

Here are the numbers:

TORNADO TOTALS AND RELATED DEATHS...THROUGH 7 AM CDT 04/25/2007
NWS STORM PREDICTION CENTER NORMAN OK
1120 AM CDT WED APR 25 2007

...NUMBER OF TORNADOES... NUMBER OF KILLER
TORNADO DEATHS TORNADOES
..2007.. ..2006.. 2005 2004 3YR 3YR 3YR
PREL SEG PREL SEG FIN FIN AV 07 06 05 04 AV 07 06 05 04 AV
JAN 29 - 45 48 33 3 28 2 1 4 0 2 1 1 2 0 1
FEB 89 - 15 12 10 9 10 22 0 0 0 0 3 0 0 0 0
MAR 225 - 226 143 62 50 85 26 11 1 0 4 10 7 1 0 3
APR 143 - 324 244 132 125 167 8 37 0 8 15 3 9 0 1 3
MAY - - 168 139 123 509 257 - 3 0 7 3 - 1 0 5 2
JUN - - 137 139 316 268 241 - 0 0 2 1 - 0 0 2 1
JUL - - 68 71 138 124 111 - 0 0 0 0 - 0 0 0 0
AUG - - 99 79 123 179 127 - 1 4 3 3 - 1 3 1 2
SEP - - 91 83 133 297 171 - 1 1 8 3 - 1 1 5 2
OCT - - 66 74 18 79 53 - 0 0 3 1 - 0 0 1 0
NOV - - 53 - 150 150 102 - 9 28 4 14 - 1 5 4 3
DEC - - 40 - 26 26 14 - 2 0 1 0 - 2 0 1 1
---- ---- ---- ---- ---- ---- ---- -- -- -- -- -- -- -- -- -- --
SUM 486 - 1333 1032 1264 1819 1366 58 66 38 36 46 17 24 12 20 18

February and March where well ahead of average, but April is about on
target. Presuming, of course, that the counts are 100% correct, which
they likely aren't.

Here's a semi-pretty picture (which helps a lot):

http://www.spc.noaa.gov/wcm/TornadoTrend2.jpg

2004 was quite the year.

As they say on financial commericals "past history is no indicator of
future performance". On the other hand, it only takes one to really
louse up your whole year.

--
Consulting Minister for Consultants, DNRC
I can please only one person per day. Today is not your day. Tomorrow
isn't looking good, either.
I am BOFH. Resistance is futile. Your network will be assimilated.

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.t...5b21269aacc5/#

On Apr 28, 8:26 pm, Weatherlawyer 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.t...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.

From the Encyclopeadia Britannica Note words and phrases such as
anomalously high:

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.

"Bob Brown" . a écrit dans le message de news:
...
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?

you can see an oustanding paper by C.WOODHOUSE for an approach of this
problem.

--

Lucien COSTE