Mild Wet Autumns and Winters: Blame the Law of Conservation of Angular Momentum!

[iapennell]

27th October 2013

 

IF you, like me, despair at the persistent south-west winds bringing mild weather in the autumn and the winter months(looks like this October will be the first without air frost for nine years!) there are three culprits to blame for the tendency to persistent Westerlies and south-westerlies off the North Atlantic affecting the British Isles:

 

Firstly the sun beats down on the tropics heating the atmosphere and causing the presence of a zone of hot rising air called the Intertropical Convergence Zone.  This zone of hot and moist air sucks in air from cooler latitudes causing the Trade Winds- whilst at high altitudes the tropical air moves polewards.  This process becomes more intense in the winter when the subtropical and higher latitudes cool- the strong atmospheric temperature gradient intensifies this circulation known to meteorologists as the Hadley Circulation.  Basically, this circulation plays a major role in redistributing heat from the tropics to higher latitudes- preventing winter temperatures falling unchecked in the latitude of Britain.

 

The second factor which mitigates the climate of Britain in particular is the surrounding seas, and the fact that in the late spring and summer months the net radiation budget turns positive as the sun beats down from high elevations each day.  This net radiative heating transfers heat to the sea surfaces- heat which is slowly released again (and thus keeps the air warmer) during the autumn and winter months.  This further modifies the extremes of cold which could otherwise occur in Britain.

 

However, if it was just for these two factors alone,- the mean air temperatures in Britain would still drop to far below freezing point in the winter months- because a "thermally direct" Hadley Cell circulation would lead to high-pressure, dry subsiding air and clear skies in all higher latitudes.  This is because clear, dry atmospheric conditions permit strong net radiation heat loss from the surface and lower atmosphere in the late autumn and winter months in Britain- because this is when the days are short and the sun low in the sky at noon.  A third factor makes all the difference, though it also hinges on the other two factors above to be most effective.

 

This third factor that has an all-important impact on Britain's autumn and winter weather is related to the fact that the Earth rotates on it's axis:  It is something meteorologists and physicists term the "Law of Conservation of Angular Momentum"; and it explains why winds moving south from high latitudes curve towards the west and why air moving north from low latitudes curves towards the east- in their direction of travel.  The effect of this on winds blowing from high to low pressure areas is commonly referred to the "Coriolis Effect".  On our rotating planet a Thermally Direct cell with high-pressure in high latitudes and low-pressure at the equator would result in near-surface north-east winds north of the equator, but south-easterlies in the Southern Hemisphere- but this is never observed over entire hemisphere for the reasons I will now explain.

 

Now the Law of Angular Momentum dictates that the total angular momentum of a body unperturbed by any outside force remains constant over time.  It means that if extensive easterly winds blow over the globe they would result in the Earth's rotation rate slowing down slightly- and this could only happen if a large chunk of the atmosphere speeded up (i.e blow from west to east- much faster- in view of the atmosphere's small relative mass).  This would, of course happen, because the frictional force of extensive easterlies in slowing the rate of the Earth's rotation would cause an equal and opposite force on the atmosphere overall- this is basic Newtonian physics.  This in turn results in the upper air moving at ever-greater speeds from west to east; the strong and extensive upper Westerlies would be effective in preventing warm air from the tropics moving to high latitudes at high altitude and where the strong upper Westerlies subside this would [eventually] result in westerlies blowing at the surface.  

 

Okay, it does not happen in quite that simplistic a manner- but essentially the upshot is that you cannot have extensive easterlies near the surface throughout either hemisphere for any extended period:  This is because of the Law of Conservation of Angular Momentum- which means any extended spell of easterlies over all the Northern (or Southern) Hemisphere would result in Westerlies at high levels blowing at hundreds and then thousands of miles per hour.  Although the upper Westerlies over the subtropics and mid-latitudes do get stronger in winter they do not accelerate to this extent- and the corollary of this is that the frictional forces of Trade Wind easterlies in the tropics and subtropics (and blowing out from any Polar or Siberian Highs) must be counter-balanced by the frictional force of Westerlies elsewhere:  And Britain, with the relatively warm North Atlantic to the west is at a location of relatively least resistance to satisfy the need for a "sink" for excess Westerly atmospheric momentum.  The distribution of atmospheric pressure from the subtropical high to the sub-polar lows is also [thus] a consequence of the Law of Conservation of Angular Momentum- and this causes the winds to come in from the south-west;- bringing to Britain warm air from the Azores!

 

So we have the sun beating down on the tropics causing a zone of hot, moist and rising air, in winter higher latitudes cool more and thus intensify the temperature and pressure gradient driving the NE Trade Winds (these winds blow from the NE due the effects of the Earth's rotation).  In summer the sun heats the mid-latitude seas and oceans so that this heat can be released to temper the strong cooling of the winter months over nearby lands.  And finally the effects of the Earth's rotation mean prevailing west or SW winds in the autumn and winter months over Britain- these bring the heat from the subtropics and the heat stored in the North Atlantic over the preceding summer across Britain to prevent snow and hard frosts for most of the time.  And the depressions- also a product of the summer-sun warmed North Atlantic and the effects of the Earth's rotation are also responsible for the annoying bouts of Wet 'n Windy (as well as mild weather) that dominate the Winter-Half-Year in this country.

 

So there you go!:  If we could find a way of slowing down the Earth (or even causing a large volcano over the deep tropics to block out the Sun and weaken the Hadley Cell)- we could reduce this "Need" for Westerlies in higher latitudes;- and in so doing we could solve the problem of Mild, Wet Autumns/Winters in Britain!!

 

Ian Pennell    

 

 

 

 

Edited October 27, 2013 by iapennell

[iapennell]

No offence..but do you need to shout

 

Apologies, and I have toned it down a bit.  However, I know some folk struggle to read small writing!

[Relativistic]

That was really interesting so thank you

I love physics and I love meteorology so that was a really great read!

[Mark Neal.]

A thoroughly interesting read, thanks for posting! 

[Sideways escort]

Thanks good read that

[Summer of 95]

If Earth rotated the other way (like Venus), would it mean east coasts of mid-latitude landmasses getting the maritime mild muck, and west coasts getting the continental climates?

 

Sounds good, what could do it without causing a mass extinction? Maybe a close pass by a stray planet sized object that was close enough to cause all sorts of gravity/tidal perturbations without an impact (but would we be able to keep the Moon in that scenario?) Or an almighty blast from the solar wind turning it backwards, with aurorae all over the planet heralding the first western sunrise?

 

More realistically, what if anything will happen to the climate when the magnetic poles reverse?

[iapennell]

If Earth rotated the other way (like Venus), would it mean east coasts of mid-latitude landmasses getting the maritime mild muck, and west coasts getting the continental climates?

 

Sounds good, what could do it without causing a mass extinction? Maybe a close pass by a stray planet sized object that was close enough to cause all sorts of gravity/tidal perturbations without an impact (but would we be able to keep the Moon in that scenario?) Or an almighty blast from the solar wind turning it backwards, with aurorae all over the planet heralding the first western sunrise?

 

More realistically, what if anything will happen to the climate when the magnetic poles reverse?

 

IF we could just find some way of slowing down the Earth's Rotation to about a third of what it is now- i.e days 72 hours long, 121 days per year the Coriolis forces would be much-reduced and diurnal heating cooling would compound the weakening of the easterly component of Trade Winds by causing stronger (and more extensive) sea/land breezes in the Tropics.  The "Need" for westerlies in higher latitudes would be greatly weakened and there would be much more scope for Thermally Direct cells (with surface winds blowing more directly from the north) over higher latitudes.

 

This would mean a much higher frequency of cold Arctic winds over Britain (and less mild south-westerlies), long nights (due to the slow rate of Earth's rotation) would mean frosts could develop even in mid summer; hard frosts will become much more frequent and severe in winter with the increased likelihood of cold Arctic air and clear nights with light winds (lasting for 50 hours without solar interruption)!

 

We need to find a few (thousand) asteroids and fly them into the Earth at very high speed near the Equator (travelling east to west) to achieve the desired effect.

 

A much more realistic idea (perhaps) is to build up the Rocky Mountains into a barrier nine kilometres high- so that it intercepts the jetstream- and in so doing provides a satifactory sink to absorb the "Need" for mid-latitude Westerlies at low levels from a Conservation of Angular Momentum consideration:  Result- lots more blocking and north/east winds over Britain in autumn/winter- there would be no more of this "No air frost 'til November" rubbish and mild snowless winters!! 

[syed2878]

thank u that was an interesting post makes an interesting reading.

[iapennell]

If Earth rotated the other way (like Venus), would it mean east coasts of mid-latitude landmasses getting the maritime mild muck, and west coasts getting the continental climates?

 

Sounds good, what could do it without causing a mass extinction? Maybe a close pass by a stray planet sized object that was close enough to cause all sorts of gravity/tidal perturbations without an impact (but would we be able to keep the Moon in that scenario?) Or an almighty blast from the solar wind turning it backwards, with aurorae all over the planet heralding the first western sunrise?

 

More realistically, what if anything will happen to the climate when the magnetic poles reverse?

 

Another way of solving this Mild Wet Autumn/Winter Problem without invoking the huge expense of trying to build up the Rockies (let alone trying to slow the Earth's rotation down!) would be to fire very powerful cannons directly at the sun where and when it is overhead at midday:  A few million very, very powerful rockets and the recoil action from all these rockets would push the Earth away from the Sun bit by bit.  Once the Earth's orbit is a million miles further out the solar constant would drop by about 2%- reducing the heat arriving at the Equator and reaching high latitudes in summer.  Thus the oceans would cool and the Arctic ice would expand further south in winter putting Britain into the path of bitter Polar Easterlies more often; even the strong Westerlies would become cold enough to bring snow and frost to much of Britain in February.  There would certainly be a lot less of the mild, rainy muck- and it might be more technologically feasible than the suggestions above! 

[AderynCoch]

Yeah, what could be easier than firing a few million super-powerful rockets into the Sun in an attempt to shift the Earth's orbit?

[cheese]

If Earth rotated the other way (like Venus), would it mean east coasts of mid-latitude landmasses getting the maritime mild muck, and west coasts getting the continental climates?

 

Sounds good, what could do it without causing a mass extinction? Maybe a close pass by a stray planet sized object that was close enough to cause all sorts of gravity/tidal perturbations without an impact (but would we be able to keep the Moon in that scenario?) Or an almighty blast from the solar wind turning it backwards, with aurorae all over the planet heralding the first western sunrise?

 

More realistically, what if anything will happen to the climate when the magnetic poles reverse?

If the Earth rotated clockwise rather than counter-clockwise, weather systems would move from east to west rather than west to east, and I think Britain would become the Kamchatka Peninsula of Europe.

 

Hull might end up being Petropavlovsk-Kamchatsky.

 

Speculation of course. I like iapennell's explanation! I read a good article recently about the Rockie Mountains and how they are partly or largely responsible for the mildness of UK winters, and the mildness of the Pacific NW.

 

http://www.americanscientist.org/issues/issue.aspx?id=999&y=0&no=&content=true&page=5&css=print

Edited October 29, 2013 by cheese

[Polar Maritime]

I certainly wouldn't grumble.

[bobbydog]

Yeah, what could be easier than firing a few million super-powerful rockets into the Sun in an attempt to shift the Earth's orbit?

 

nuking the rocky mountains apparently.....

 

If the Earth rotated clockwise rather than counter-clockwise, weather systems would move from east to west rather than west to east, and I think Britain would become the Kamchatka Peninsula of Europe.

 

Hull might end up being Petropavlovsk-Kamchatsky.

 

Speculation of course. I like iapennell's explanation! I read a good article recently about the Rockie Mountains and how they are partly or largely responsible for the mildness of UK winters, and the mildness of the Pacific NW.

 

http://www.americanscientist.org/issues/issue.aspx?id=999&y=0&no=&content=true&page=5&css=print

[Winter wonder]

 All good stuff but there may another way and it may already have started.  A Grand Solar Minimum may be coming our way. Current Solar cycle 24 is the weakest in decades and about to decline.  Many Solar scientists think we may be on the verge of a Dalton or Maunder minimum that would herald decades of very cold northern European winters as last seen in Europes Little Ice Age 1645- 1715 which was still being felt in the 1800's.  Roll on frost fairs on the frozen Thames!.

[Evening thunder]

Alternatively turn the Thermohaline Circulation off

 

Hello Younger Dryas.. 

[iapennell]

Alternatively turn the Thermohaline Circulation off

 

Hello Younger Dryas.. 

 

 

Not sure of the technical feasibility of this- perhaps getting the Canadians and Russians to divert a few big rivers into the north Atlantic/Arctic- or nuking the Greenland Icecap so it releases masses of meltwater-  freshwater does not sink so easily. 

[iapennell]

I am not sure of the technical feasibility of this- perhaps getting the Canadians and Russians to divert a few big rivers into the north Atlantic/Arctic- or nuking the Greenland Icecap so it releases masses of meltwater-  freshwater does not sink so easily.

 

EDIT:

 

Maybe we should persuade the Americans to blast into the massive Supervolcano Magma Chamber underneath Yellowstone National Park:  That would trigger the (apparently long overdue) Supervolcano that would inject so much dust and sulphur into the stratosphere that the sun's heat would be cut off- to bring about freezing summers as well as bitter winters in higher latitudes:  It would trigger the next Ice Age because by the time the volcanic dust settled so much snow and ice would be established over the northern continents that the heat reflected back to space would mean that the Northern Hemisphere stays frigid- despite rising CO2 levels!!    

Edited November 7, 2013 by iapennell