Hi Peter,

I got your name from your e-mail address. I am posting your message on
to sci.geo.meteorology and uk.sci.weather. It will be interesting to see
what the experts think of your essay.

Cheers, Alastair.

"climateshift" wrote in
message ...
hi everyone,just thought I'd make a topic on the weather and also the
many different factors and how everything forms(this will be a very
long post but hopefully very informative..so firstly we should start
off wih some basics.

For those who don't know what those "Highs" and "Lows" stand for on
the charts here is a brief description of them,which you will
hopefully understand,Air pressure is a measure of how much air is
pushing down on the surface of the Earth at a given point. Generally,
high- and low-pressure systems form when air mass and temperature
differences between the surface of the Earth and the upper atmosphere
create vertical currents. In a low-pressure system, these vertical
winds travel upwards and suck air away from the surface of the Earth
like a giant vacuum cleaner, decreasing the air pressure above the
ground or sea. This decrease in surface air pressure in turn causes
atmospheric currents moving parallel to the surface of the Earth near
the base of the low to spin counter clockwise (clockwise in the
Southern Hemisphere). Conversely, in a high-pressure system, air is
being pushed down on the ground like a vacuum put in reverse. The
downward vertical winds cause an increase in air pressure on the
ground and force atmospheric currents to spin clockwise (counter
clockwise in the Southern Hemisphere). Both lows and highs function
like giant slow-moving hurricanes and anti-cyclones, respectively.
The higher in pressure a high-pressure system gets or the lower in
pressure a low-pressure system gets, the more robust and larger this
spinning circulation pattern becomes.

http://earthobservatory.nasa.gov/Stu.../low_still.jpg

A low pressure system will pull in air from the surrounding area.
Winds around a low spiral counter-clockwise (in the Northern
Hemisphere, clockwise in the Southern Hemisphere) and upwards towards
the centre of the system.

http://earthobservatory.nasa.gov/Stu...high_still.jpg

while the opposite happens with high pressure.

so the first two real drivers off the weather is the NAO and PNA.A
semi-permanent low-pressure system exists over Greenland and
Iceland(Icelandic low), and a permanent high-pressure system exists
over a group of islands roughly 900 miles (1400 kilometers) west of
Portugal, known as the Azores(Azores high). For most of the year, the
high and the low are mild, and their influence on the Atlantic basin
climate is minimal. When winter hits, however, all of this begins to
change. Both pressure systems grow much more intense and begin to
fluctuate from week to week between two different states. In one
state, which scientists call a positive NAO, the high-pressure system
grows especially high, while the low-pressure system grows especially
low, creating a large pressure difference between the Azores and
Iceland. In the other state, known as a negative NAO, the
high-pressure system weakens and the low becomes shallow, creating a
milder pressure difference between the two regions of the Atlantic.
As the low and high intensify and relax, the winds revolving around
their centers increase and decrease in both strength and in extent.
During a strong positive NAO, the two pressure systems can just about
cause all the currents in the northern half of the northern Atlantic
to spin counterclockwise and all those currents in the southern half
to spin clockwise.

The PNA or Pacific North American Pattern is characterized by
atmospheric flow in which the west coast of North America is out of
phase with the Eastern Pacific and Southeast United States. It tends
to be most pronounced in the winter months.There can be 3 defined
states of the PNA- rather like the NAO- We have Positive, Negative
and Neutral.
When we are in a neutral phase or a 'High index' Phase of the jet
stream the typical west to east flow of Low pressure systems remains
largly Un-interupted.so here is two out off the three phases:

positive:
http://www.intellicast.com/DrDewpoin...372/fig01s.jpg

negative:
http://www.intellicast.com/DrDewpoin...372/fig02s.jpg

now here is where we move onto the jet stream.There are several
different branches off the jet stream,the main two are the
sub-tropical jet and the most important,Polar front jet.The Polar
Front Jet as its name implies, this jet stream is associated the
boundary of polar air to the north and sub tropical warm air to the
south . It meanders markedly in response to atmospheric changes and
has its own distinctive tropopause level. The other jetstreams of the
northern hemisphere are the sub tropical jet to our south ,the
stratospheric night jet far to our north and the tropical easterly
jet far to our south.

To understand a bit more about the PFJ we must look a bit closer at
the levels in the atmosphere involved. The troposphere which is where
our weather lives is the lowest layer , above this is the Stratosphere
where very little air movement occurs.Just below the boundary in the
Troposphere is the tropopause and this is generally where the
jetstream lives.This would imply that we are only interested in the
Troposphere where in reality the Stratosphere has a part to play.

Extreme Stratospheric Events (ESEs) defined as days when the AO index
exceeds a given threshold either positively or negatively are
followed by anomalous weather regimes (unusual weather) at the
surface that persist for up to two months (Baldwin and Dunkerton
2001). The fact that extreme AO values arise in the upper
stratosphere first gives the misleading impresion that EDEs originate
in the upper Stratosphere.Since the AO is a very good proxy for the
strength of the polar night jet in the strotosphere it should be
clear that ESEs correspond to instances of either anomalously week or
strong stratospheric polar vortices. Anomalous low upward wave
activity fluxes at 100hPa preceed ESE's and anomalous surface values
of the AO up to 60 days later (Polvani and waugh). These upward wave
fluxes are associated with planetary-scale waves propagating from the
troposphere to the stratosphere.

These Planetary Waves are produced largely because the atmosphere in
motion encounters barriers to its progress, and is forced to ascend
(by the changing surface level), then allowed to descend (under
gravitational influence), and the resultant "squashing" and
"stretching" respectively of the air columns involved lead to
alterations to the rates of "spin" of the air flow (vorticity). When
considering the northern hemisphere, air that is forced to ascend
tends to turn to the left, and as it descends again, it tends to turn
to the right, inducing a ridge/trough pattern to the broadscale
westerlies. Major mountain chains provide obvious sources of such
deflection, and the Rockies and the Andes, which lie astride the
westerly flow in each hemisphere, provide good examples. These
long-waves are key elements in the atmospheric circulation, and can
be traced well into the stratosphere. At any one time, there are
between 3 and 7 such waves, the number in any particular latitude
band dependent upon a fine balance between the speed of the airflow
through the trough/ridge system and the wavelength.In general, a
strengthening zonal flow drives the major long-waves apart; a
weakening zonal flow allows a 'closing-up' of the wave pattern.
In other words the PFJ is more likely to arch up when the air flow
weakens and the strength of the jet determines our weather.

It is well established that the temperature in the winter polar region
of the stratosphere is determined by the balance of two factors:
radiative cooling and adiabatic, dynamical heating (Andrews, Holton,
and Leovy, 1987). The latter is caused by downwelling in the
stratospheric polar region, induced by global-scale wave-driven
meridional circulation and thus depends on planetary-wave activity
generated in the troposphere. It is such dynamical heating that is
responsible for forcing winter polar temperatures above the radiative
equilibrium temperature during polar night. Fusco and Salby (1999) and
Salby et al. (2000) found that on interannual timescales stratospheric
ozone and temperature in the Arctic polar region in winter is
regulated by the upward Eliassen-Palm (E-P) flux across the
tropopause, and that the two have a strong correlation.

What else can affect these planetary waves, well we know that tropical
SST is leading the SIO (stratospheric interannual oscillation) by up
to around 9 months, which suggests a strong impact of El
Niño/Southern Oscillation (ENSO) on the SIO. Planetary waves tend to
be bent poleward in the midstratosphere when there is a warm event.
The situation tends to be reverse during a cold event. This does
imply that with the recent strongly negative SO index we may expect
some unusual weather next autumn.

Although stratospheric circualtion anomalies are believed to be caused
mainly by upward propagating planetary scale waves the QBO also plays
a part. The Quasi-biennial oscillation (QBO) in the equatorial
stratosphere modulates the wave guide for upward propagating
planetary waves so that major statospheric warmings are less likely
when the equatorial statospheric winds are westerley.Weak vortex
regimes are twice as likely when the QBO is easterly and strong
vortex regimes are more likely when the QBO is westerly.The QBO has
just entered a neutral phase and will change to a easterly phase over
the coming months.

We also need to look at the MJO (Madden-Julian Oscillation) which is a
naturally occurring component of our coupled ocean-atmosphere system.
It significantly affects the atmospheric circulation throughout the
global Tropics and subtropics, and also strongly affects the
wintertime jet stream and atmospheric circulation features over the
North Pacific and western North America. As a result, it has an
important impact on storminess and temperatures over the U.S. During
the summer the MJO has a modulating effect on hurricane activity in
both the Pacific and Atlantic basins. Thus, it is very important to
monitor and predict MJO activity, since this activity has profound
implications for weather and short-term climate variability through
the year.Years of eastward QBO phases at 50 hPa typically have 50%
more named storms 60% more hurricanes, and 200% more intense
hurricanes than years of westward QBO phase.This does lead to a link
between hurricane activity during the summer to a mild winter. This
does also suggest that we may have a fair number of hurricanse this
year and a wetter summer and correspondingly mild winter.

The Sun's varying ultraviolet emissions affect the production of ozone
in the Earth's atmosphere, changing our ozone layer, and affecting the
large-scale circulation of air. Secondly, the solar wind's gusts
affect the electrical properties of the Earth's upper atmosphere
which somehow affects the lower layers of the atmosphere. Thirdly,
during the solar minimum, the solar wind is weaker which enables
galactic cosmic rays (GCRs) to enter the Earth's atmosphere more
easily. GCRs are particles that are heavier and more energetic than
those carried by the solar wind and are accelerated much farther away
in space. Scientists believe that the movement of GCRs, which is
influenced by the solar wind, generates conditions that promote the
formation of low-altitude clouds.Some scientists have suggested that
there has been a marked changein the GCRs and the solar wind this
century.Studying the interaction between solar variability and the
Earth environment is a science known as 'space weather'.

Times of maximum sunspot activity are associated with a very slight
increase in the energy output from the sun. Ultraviolet radiation
increases dramatically during high sunspot activity, which can have a
large effect on the Earth's atmosphere. The number of sunspots in this
cycle reached a peak in May, 2000 where the number of sunspots were
measured at near 170. A secondary sunspot maximum occurred near the
beginning of 2002 where the sunspot number was about 150. The next
sunspot minimum is forecast to occur in late 2006.The short cycle and
projected minimum in 2006 only point to a slight cooling trend this
year.

A comparison with the Northern Hemisphere land temperature during the
last 130 years does show a remarkably good correlation with the
smoothed curve of the varying solar cycle length indicating that this
parameter was possibly a better indicator of a solar activity
variations (Friis-Christensen and Lassen, 1991) (This is not sunspot
activity but the length of the sunspot cycle). Only during winter the
correlations are not statistical significant but this could be
improved by grouping the data according to the phase of the
Quasi-Biannual Oscillation (QBO).

Just to introduce some controversy, bulging of the Earth's crust may
relate to a combination of things, such as a magnetic field jerk in
1998, ocean mass transport caused by El Niño between 1997 and
1998.The unexplained bulging of the Earth at the equator that began
in 1998 , is related to pressures and the movement of magma
convection currents that circulate between the core of the Earth and
the tectonic surface plates that float above. This bulging at the
earths crust has been blamed for the extremes in weather over the
past few years although the link has not been proven yet.

Cohen et al. (2001) demonstrated that the winter AO may originate as
an autumn sea level pressure anomaly over Siberia. (Saito et al
demonstrated that the winter AO may be associated with autumn
stationary wave activity flux anomalies over Eurasia.Interannual land
surface snow perturbations can be substantial enough to exert a
modulating influence on the AO mode of variability (Gongland et al)
Anomalously high Siberian snow increase local uward stationary wave
flux activity, weakens the stratospheric polar vortex and causes
upper tropospheric stationary waves to refract poleward. This is
propagated back downwards over a few weeks.Less snow and wetter soil
conditions weaken the siberian high and affects SST's over the
Atlantic.So snow cover and surface conditions over Russia may give a
clue to future weather conditions as well.

Observations of North Atlantic sea surface temperature for 1856-1999
reveal a 65-80year cycle with a 0.4 °C range, referred to as the
Atlantic Multidecadal Oscillation (AMO) byKerr [2000]. Although the
signal appears to be global in scope, with apositively correlated
co-oscillation in parts of the North Pacific, it is most intense in
the North Atlantic and covers the entire basin there.Though the exact
relationships between low-frequency SST modes, higher frequency
(~7–25 yr) atmospheric modes (e.g., North Atlantic Oscillation/Arctic
Oscillation), and terrestrial climates must still be resolved.


Perhaps we should be looking at the fact that a positive link exists
between the NADC penetration into the Norwegian Sea and the North
Atlantic Ocean (NAO) index.High NAO indices imply that only a narrow
flow extends northward of the Faeroe-Iceland Strait, resulting in a
sea-surface temperature (SST) cooling at the scale of the Greenland
and Norwegian basins, owing to the spread of polar waters eastward.
During these conditions, flow is simultaneously intensified in the
narrow band along the Norwegian shelf, northwards towards Svarlbad.As
can be seen from the SST anomalies the flow north of iceland is
warming the sea and the lesser flow by norway is colling the seas.
This points to a Negative NAO persisting until these conditions
change.Overall, a 13-15 year see-saw pattern oscillation between the
Gulf Stream and the NADC was observed, and also found to affect the
tropical Atlantic (Moron et. al., 1998). At times of increased trade
wind strength, tropical and subtropical waters are forced across the
equator, enhancing the pool of warm water to be transferred to the
high latitudes of the North Atlantic via the Gulf Stream and North
Atlantic Drift, thereby increasing the pull of the thermohaline
convective conveyor. The increased supply of warm water to the polar
regions of the northern hemisphere increases the ice-ocean moisture
gradient and can accelerate ice sheet growth (Little et. al.,
1997).So thats all I know,I'm sure there are other things that could
be covered as the relationship between the sun and our
weather,however I really want to go into that!

Thanks for reading,many years off knowleadge has gone into this,and
many hours as well!!! :wink:


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Thanks for that, an interesting read. A few variables then. Little wonder
that those who look at a couple of GFS charts keep getting it wrong! I bet
this guy struggles with credibility with his publications though. snip and
also found to affect the tropical Atlantic (Moron et. al., 1998). ;-)

Dave