Re: The weather and the many different factors that drive it...

From: Alastair McDonald (alastair_at_abmcdonald.leavethisout.freeserve.co.uk)
Date: 03/12/05 

Date: Sat, 12 Mar 2005 11:26:46 -0000

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" <peter.bantick@tiscali.co-dot-uk.no-spam.invalid> wrote in
message news:42320f3b$1_1@127.0.0.1...
> 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/Study/NAO_200307/Images/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/Study/NAO_200307/Images/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/DrDewpoint/Library/1372/fig01s.jpg
>
> negative:
> http://www.intellicast.com/DrDewpoint/Library/1372/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 *** 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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