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The Ferrel Westerlies- would weakening them Cool the North?


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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

Hello, thought I'd introduce a subject close to my heart because where the prevailing wind comes from in Britain (and in what seasons) has a pretty massive impact on our prevailing weather and climate. Like a number of us on this Forum I prefer severe cold and snow in winter (preferably something below -10C), cool fresh springs with snow lingering on the northern hills and a few frosty nights, warm dry summers with enough rain to ensure things grow (not too hot and humid) and crisp frosty mornings and bright days in the autumn. Unfortunately, the prevailing winds in northern Britain - fresh south-westerlies from autumn through spring and westerlies in high summer tend to preclude such sharp contrasts between the seasons.

The reason why we have persistent airstreams off the North Atlantic with depressions passing to the north-west to bring wet windy weather for much of the year (particularly the case for those of us, like myself, living in northern England or Scotland) is because of the mid-latitude Westerlies- so called (they tend to angle in from the south-west much more than north-west in Britain). This is part of a major system of the global winds called the Ferrel Cell (or Ferrel Westerlies, and yes sometimes these winds are feral as well!) because the wind-circulation was founded by William Ferrel in the mid nineteenth century. These Westerlies blow extensively over middle to high latitude regions for most of the year and they are part of the vast global circulation that distributes heat from low latitudes (where more heat is absorbed from the Sun than radiated to space over the course of a year) to higher latitudes where there is a net radiative heat loss during the course of a year. Hence arguably, weakening this Ferrel Cell and the surface Westerlies that are an integral part of it would reduce this heat transport so that high latitudes would cool (particularly in the winter half-year).

Leaving aside the technological feasibility of achieving such a feat, would there be other outcomes for the prevailing weather, particularly for the UK if the Ferrel Cell could be weakened or destroyed. The strong jet-stream that crosses the North Atlantic and which assists the development of depressions that drive the Westerlies would, by implication, have to be weaker and interrupted by long periods with high-pressure over and to the north of Britain which would result in north-easterly winds: This would mean less rainfall and sunny warm (but not hot) days in summer would be frequent. Clear skies combined with frequent incursions of air from high latitudes would result in frequent spells with very severe frost any time from October through the winter until April. The weakening of the North Atlantic Drift that a wholesale weakening of the Westerlies across the North Atlantic would entail combined with more frequent frigid airstreams from Russia over the Norwegian Sea would encourage pack-ice to extend south to the north coasts of Britain by February and this would persist until April. This extra ice-cover combined with clear skies would result in a strong surface net radiative heat loss that would make the region much colder than at present.

There would be warming effects at the highest latitudes caused by weakening or destroying the Ferrel Cell: The middle atmosphere over the Central Arctic would be 10 to 15C warmer in winter because of the frequent outflow of very cold air-masses from the surface and its replacement with warmer air from lower latitudes. This relatively warmer air would come via high elevations and subside through the atmosphere courtesy of persistent large surface anticyclones but the clear skies and dry atmosphere caused by such subsidence would permit intense surface radiation cooling over the Arctic pack-ice so winter surface temperatures would be little warmer there. In summer this is another matter because such displacement of cold surface  air over the Arctic due to anticyclonic subsidence would bring unbroken sunshine from clear skies which, combined with relatively warm-air advection from above would raise average temperatures.

Weak/absent westerlies in higher mid-latitudes implies few snow-bearing depressions for the Greenland ice-cap and for Canada and Russia. Little or no snowfall means that sunny summer conditions over the Greenland ice-cap could hasten its net melting although an absence of warm south-westerly winds over it might also lessen the rate of demise of the Greenland ice-cap and (in any case) clear skies at night help whatever thaws on the surface of the ice freezes at night. Over Russia and Canada little snow-cover means that when the Sun gets strong in spring the bare land is soon exposed absorbing much more heat from the Sun, however persistent north and easterly winds would bring cold air from the Arctic to delay thawing. The clear skies, light winds and persistence of dry frigid air-masses from high latitudes would still bring about extremely severe winters across Russia and Canada and without significant snow-cover the frost would penetrate deep helping to preserve the permafrost.

In order to consider how the Ferrel Cell might weaken we need to understand what causes it in the first place. As to how the Ferrel Cell and mid-latitude Westerlies are maintained we need to realise that it is a by-product of the fact that our planet rotates once a day on its axis as well as being caused (indirectly) by the imbalance of Solar heating between high and low latitudes and the (consequent) need for air to move when it acquires different densities. In the tropics and sub-tropics winds converge towards the zone of maximum heating and rising air from the north-east (a consequence of air moving south over land that rotates progressively faster the further south it gets- south of the Equator the corresponding winds are south-easterly). Thus in the tropics and subtropics the atmosphere is gaining westerly angular momentum as surface easterlies are slowed by friction with the underlying surface and this excess is transferred polewards, significantly in the vicinity of the sub-tropical jet-stream, at 12 km elevation at around 30N (and 30S). There has to be a sink for this accumulated atmospheric westerly momentum so as to satisfy Conservation of Angular Momentum laws (pp 140-142, "Atmosphere, Weather & Climate" (8th Edition), Barry & Chorley (2003)).

The sink for the excess westerly atmospheric angular momentum is all those strong westerly winds that blow across the North Atlantic and North Pacific and (all too often) afflict Britain and much of NW Europe. The surface waters of the North Atlantic (and North Pacific) do not have a very high coefficient of friction (unless of course whipped into a stormy chaotic mass of waves by high winds!) and thus the Westerlies often have to pass over extensive land areas with higher frictional coefficients before the net westerly AAM accumulated in lower (and high) latitudes is satiated. This is particularly true from autumn through spring when subtropical and polar easterlies are stronger and there is thus a corresponding greater "need" for Westerlies in higher mid-latitudes.

All of this means that the key to getting Britain proper seasons involves finding the global circulation another (extra) sink for net westerly atmospheric angular momentum accumulated by virtue of the NE Trade Winds and Polar Easterlies. Thousands of stiff west-facing large steel "brushes" placed between 45 and 65N in the North Atlantic might do the trick as might building a 12 km high wall (with artificial trees pointing west to absorb the force of the wind) north to south over the southern USA and Mexico to intercept and slow the subtropical jet-stream. Another idea might be pumping trillions of tons of cold deep water to the surface over the subtropical North Atlantic in order to weaken the baroclinic gradient that drives the Westerlies but this would also strengthen the NE Trade Winds- the Westerlies needed to counter the NE Trade Winds might then be deflected to the Med to ruin many folks' holidays!  I am not seriously suggesting that we should try these suggestions (some folk might consider it insane!) but it's a fact that if we are ever to weaken the Westerlies (so we can have "decent" seasons in Britain and prevent the Arctic ice melting!) you have to tackle the root causes of their existence.            

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

These "Ferrel Westerly Winds" that "Have To Blow To Stop The Earth Slowing Down" get in the way of so much Properly Seasonal weather!

You can see it happening at the moment: Hurricanes kick up in the tropics and the strong easterlies on their northern flanks enter the Northern Hemisphere general circulation (north of the ITCZ)  and increase the "need" for Westerlies at higher northern latitudes. At other times a hurricane in the tropical Atlantic breaks northwards to bring a surge of warm air and (behind it) rain to affect NW Europe. Either way, the pressure drops over the still relatively warm waters of the far North Atlantic and warm, muggy buggy south-westerlies (very conducive to midges!) deliver a packet-load of drizzle and grey skies to the North in September and October.

A promising high over Russia might deliver cold frosty weather to Sweden in October but the wretched Ferrel Westerlies that have to blow to satisfy Conservation of Angular Momentum laws won't let them reach the British Isles (or at least not long enough to bring about those crisp frosty autumn mornings that bring the best colours on the trees). A general area of low-pressure stays over the North Atlantic at such times and, with high-pressure to the east and over the Azores, silly warm (for the season) moist south or SW winds then affect Britain. Those of us who like proper seasons have to suffer this indignity a lot in these globally-warmed autumns!

Solutions to this problem are three-fold:

 a) Measures to tackle global warming -which I have discussed at length elsewhere (see 

b)  Measures to reduce the "need" for Ferrel Westerlies over Britain to absorb the excess and accumulating westerly momentum in the upper atmosphere caused by extensive tropical, subtropical and polar easterlies elsewhere. This involves increasing the frictional sink for these Westerlies by erecting barriers across their path. Thousands of west-facing large steel brushes in the North Atlantic would certainly do the trick but at a more practical level the planting of large numbers of conifers along the western coasts of Ireland, Scotland and western British Columbia (in Canada) would greatly increase surface roughness and the effectiveness of these regions in acting as a sink for westerlies. This increases the likelihood of drier conditions, colder winters and warmer summers. For folk living in Scotland and the North West of England less rainfall throughout the year might be beneficial.

c) Failing (a) or (b), Emigrating to Sweden or to Canada where they have Proper Seasons!!

Edited by iapennell
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Posted
  • Location: Yorkshire Puddin'
  • Weather Preferences: cold winters, cold springs, cold summers and cold autumns
  • Location: Yorkshire Puddin'

This is another great and interesting topic!  However whilst I agree with most of this I am sceptical about paradoxical warming of the Arctic caused by the weakened Ferrel Cell.  That might occur due to readjustments caused by changing wavelengths and Stratospheric Warming but that should only be temporary.  I would have thought that a weakened and Equatorward displaced Ferrel Cell would have caused rapid cooling of the whole Arctic region at least.  The Ferrel Cell is the main heat source of both the Mid-Latitudes and the High Latitudes.  Extratropical Coastal Storms such as the Icelandic Low and Aleutian Low are also key to Arctic warm spells/heatwaves as they inject the Maritime Tropical air into the Arctic via Warm Air Advection in their Upper Level Ridges and Warm Sectors.  However these storm systems would be further south with the Ferrel Cell weakened and displaced Equatorward with the warmth unable to ever reach the Arctic.  With the Arctic Front (and Arctic Front Jetstream) and main Polar Front (and Polar Front Jetstream) further Equatorward, further cooling in the Arctic would also be caused by the inability of Continental Tropical Heatwaves to reach the Arctic from China, Central Asia, Europe and the United States.  Additionally with the Icelandic Low further Equatorward, the warm North Atlantic Drift extension of the hot Gulf Stream would be very weak if it even remains at all thus causing further cooling.

Edited by Lettucing Gutted
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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks
On 9/5/2016 at 14:41, iapennell said:

 

Solutions to this problem are three-fold:

 

I cannot believe that you are posting with a serious attitude to trying to change the overall weather patterns Ian?

Edited by johnholmes
to cut repeating post I refer to
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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria
12 hours ago, johnholmes said:

I cannot believe that you are posting with a serious attitude to trying to change the overall weather patterns Ian?

I was discussing possible solutions somewhat hypothetically, and in view of the dislike of a number of us on this Forum of muggy moist autumns that keep midges going through October, persistent winter wet (and a lack of snow or hard frosts) and the unpredictable summers of recent years there can be a joy in investigating methods to reduce or eradicate the prevailing south-westerly winds that cause us so much grief. 

Tackling global warming, another underlying cause of recent crappy seasons, has got to be a much bigger priority before we start tampering with climates in different parts of the World. 

Besides this, it would not be the first time that proposals have been put forward to modify climates in different parts of the World. In the 1960s and 1970s (when Global Cooling was the big worry!) the dusting of snow-fields at high latitudes with soot from fleets of suitably modified aircraft was proposed as a measure to stop the slide of the global climate towards Ice-Age conditions. The idea was that dark soot would encourage snow and ice to absorb the Sun's heat, warm up and melt, thus stopping the possible encroachment of glaciers in their tracks. Other proposals at weather modification that have actually been tried include seeding clouds with silver iodide to promote rain in dry regions, firing cannons full of the same chemical into big cumulonimus clouds to prevent large hailstones forming (by instead promoting the development of lots of smaller hailstones that would hopefully melt before reaching the large areas of croplands below). Some of these methods that have been tried have had mixed results.

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria
On 07/09/2016 at 08:18, Lettucing Gutted said:

This is another great and interesting topic!  However whilst I agree with most of this I am sceptical about paradoxical warming of the Arctic caused by the weakened Ferrel Cell.  That might occur due to readjustments caused by changing wavelengths and Stratospheric Warming but that should only be temporary.  I would have thought that a weakened and Equatorward displaced Ferrel Cell would have caused rapid cooling of the whole Arctic region at least.  The Ferrel Cell is the main heat source of both the Mid-Latitudes and the High Latitudes.  Extratropical Coastal Storms such as the Icelandic Low and Aleutian Low are also key to Arctic warm spells/heatwaves as they inject the Maritime Tropical air into the Arctic via Warm Air Advection in their Upper Level Ridges and Warm Sectors.  However these storm systems would be further south with the Ferrel Cell weakened and displaced Equatorward with the warmth unable to ever reach the Arctic.  With the Arctic Front (and Arctic Front Jetstream) and main Polar Front (and Polar Front Jetstream) further Equatorward, further cooling in the Arctic would also be caused by the inability of Continental Tropical Heatwaves to reach the Arctic from China, Central Asia, Europe and the United States.  Additionally with the Icelandic Low further Equatorward, the warm North Atlantic Drift extension of the hot Gulf Stream would be very weak if it even remains at all thus causing further cooling.

You would certainly weaken the upper Westerlies by putting a barrier in their way. This would lead to more pronounced ridges and troughs in the Circumpolar Vortex so that storm-tracks would move south-southwest to north-northeast and the strongest surface Westerlies would tend to dominate at the south-west end of the storm-tracks (and these would almost certainly be in lower latitudes where the effect of friction due to surface Westerlies in removing Westerly AAM from the atmosphere is greater). So, once weakened, there are additional dynamic feedback processes that can keep the Circumpolar Vortex weak. 

In the situation where the Circumpolar Vortex is weak storm tracks are dis-continuous with extensive north-to-south high-pressure systems east and west of the storm-tracks (these would be restricted to the North Atlantic and North Pacific in winter).  However there is no reason per-se why a weak Ferrel Cell has to be in lower latitudes and a barrier across the path of the Westerlies tends to encourage a middle -atmosphere ridge which would tend to encourage the flow of warm air towards the Arctic, at least at high altitudes. It is for this reason why weakening the Ferrel Westerlies would not necessarily cool the Arctic interior. 

You are correct in the assertion that, with high-pressure over the Arctic (very likely to happen with warm upper -level air there) that depressions won't be able to advect warm southerlies into the Arctic interior at low levels and the warm-sector conveyer belts in the atmosphere that are associated with depressions won't get into the Arctic either. That does remove a big source of warmth from high latitudes but warm air advection is likely to reach the Arctic by another means- descending through the Arctic stratosphere having been advected from low latitudes to the Arctic at high altitudes (it is this which occurs when you get those Sudden Stratospheric Warmings over the Arctic that are the prelude to very cold easterlies over Britain in winter). One of the big reasons why Antarctica is very cold all year round, aside from it's elevation and the reflectiveness of it's ice-cover is because of the intense Circumpolar Vortex of the Southern Hemisphere and persistent depressions that prevent the penetration of warmer low-latitude air into Antarctica at either low or high elevations. Indeed most of the warmth transported into Antarctica is associated with deep sub-antarctic depressions but these rarely extend deep into the continent because of the extremely cold relatively dense air over the ice-sheets. Sudden Stratosphere Warmings are almost unknown over Antarctica, which is why it is possible for Ozone holes to develop over the continent. 

Mid-latitudes are the flip-side of the coin: In these locations a weaker Ferrel Cell would certainly be a cooling influence. The change to more frequent north and easterly winds bringing more frequent snow-cover (though snowfalls would be less the cold air would help maintain snow-cover) and extensive winter sea-ice would be profound cooling effects. Less cloud-cover in summer ought to mean higher temperatures then but this would be countered by the more frequent advection of air from higher latitudes and from autumn through spring the dry clear atmosphere brought about by more north-easterly winds and high-pressure to the north would result in much more radiative heat-loss to space than increased solar radiation absorption (and with much more snow and ice cover winter and spring most solar radiation would be bounced back to space!). So destroying the Ferrel Cell would have a profound cooling influence on all locations equatorwards of about 70N (and 70S).

The strong Ferrel Cell in the Southern Hemisphere means that southern South America, South Australia and New Zealand rarely get serious cold-waves. It is headline news if snow falls and temperatures drop below -5C at low levels in any of these regions! Of course the vast Southern Ocean has something to do with it but so too does the ever-present steep pressure drop from about 40S down to the Antarctic Coast. 

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

Some of you might wonder why locations in mid-latitudes of the Southern Hemisphere have annual average temperatures somewhat cooler than those over lowland Britain and other low-lying parts of NW Europe if a stronger Ferrel Cell is to warm mid-latitudes.

Firstly NW Europe is not typical of the climates of mid-latitudes of the Northern Hemisphere. Average temperatures across much of the North Atlantic and North Pacific at similar latitudes to Britain are (on average) 4 to 5C colder during the course of a year. Most of Canada and Russia between 50 and 55N has a mean annual temperature close to freezing point at low elevations and Newfoundland and Kamchatka (off the East Russian Coast) have annual means below 0C. Thus if you calculated average annual temperatures at all locations along 50S and then did the same along 50N you would probably find mean annual temperatures a little lower along 50N. The reason for the lower average temperature across Northern mid-latitudes is therefore due to a weaker Ferrel Cell in the Northern Hemisphere that allows frigid Arctic air to sweep south across extensive regions from autumn through spring on a regular basis. 

The extensive oceans of Southern mid-latitudes mean that the strong Westerlies tend to blow across isobars to a relatively low extent and the strong winds blow surface currents predominantly from west to east. Thus the warm -air advection that would occur over land happens less over the expanses of oceans in the Southern Hemisphere. There is also a persistent cloud-cover associated with deep depressions passing to the south and this certainly helps depress spring and summer temperatures but this would be a warming influence in winter. 

In lower latitudes a weakened Ferrel Cell would be a cooling influence and normally arid locations dominated by the subtropical high would (not infrequently in winter or spring) periodically be affected by cut-off lows bringing colder air south behind them. This would happen because a very weak Ferrel Cell would be associated with a weak Circumpolar Vortex with very pronounced ridges into high latitudes and troughs into sub-tropical latitudes. More often there would be great wedges of surface high-pressure extending from high latitudes right down to the tropics and this would permit the unimpeded flow of Arctic air to tropical latitudes rather more frequently than happens nowadays. This would be a significant cooling effect on lower latitudes and there would be a small increase in winter and spring rainfall in some locations. 

There is evidence that the weaker Ferrel Cell in the Northern Hemisphere makes the sub-tropics of the Northern Hemisphere quite varied in the weather that occurs at different times and in different locations. SE Asia sometimes gets cold dry northerlies that bring freezing nights in winter, Israel sometimes has snow to low elevations in winter and Egypt sometimes has violent and hot dust -storms from the south-west in spring as a depression skirts the Egyptian Coast. By contrast the sub-tropics of the Southern Hemisphere are dependably dry and sunny throughout the year, SE Brazil is probably the only significant exception to this. A strong general circulation with strong Ferrel Westerlies permits few deviations from wet stormy higher mid-latitudes with equable temperatures and dry warm sunny sub-tropics. Quite boring really!! 

Edited by iapennell
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Posted
  • Location: Camborne
  • Location: Camborne
7 hours ago, iapennell said:

The extensive oceans of Southern mid-latitudes mean that the strong Westerlies tend to blow across isobars to a relatively low extent and the strong winds blow surface currents predominantly from west to east. Thus the warm -air advection that would occur over land happens less over the expanses of oceans in the Southern Hemisphere. There is also a persistent cloud-cover associated with deep depressions passing to the south and this certainly helps depress spring and summer temperatures but this would be a warming influence in winter. 

In lower latitudes a weakened Ferrel Cell would be a cooling influence and normally arid locations dominated by the subtropical high would (not infrequently in winter or spring) periodically be affected by cut-off lows bringing colder air south behind them. This would happen because a very weak Ferrel Cell would be associated with a weak Circumpolar Vortex with very pronounced ridges into high latitudes and troughs into sub-tropical latitudes. More often there would be great wedges of surface high-pressure extending from high latitudes right down to the tropics and this would permit the unimpeded flow of Arctic air to tropical latitudes rather more frequently than happens nowadays. This would be a significant cooling effect on lower latitudes and there would be a small increase in winter and spring rainfall in some locations. 

There is evidence that the weaker Ferrel Cell in the Northern Hemisphere makes the sub-tropics of the Northern Hemisphere quite varied in the weather that occurs at different times and in different locations. SE Asia sometimes gets cold dry northerlies that bring freezing nights in winter, Israel sometimes has snow to low elevations in winter and Egypt sometimes has violent and hot dust -storms from the south-west in spring as a depression skirts the Egyptian Coast. By contrast the sub-tropics of the Southern Hemisphere are dependably dry and sunny throughout the year, SE Brazil is probably the only significant exception to this. A strong general circulation with strong Ferrel Westerlies permits few deviations from wet stormy higher mid-latitudes with equable temperatures and dry warm sunny sub-tropics. Quite boring really!! 

Blow across isobars?

Anyway all of this can be neatly summed up thus.

The westerlies of the southern hemisphere are stronger and more constant in direction than those of the northern hemisphere because the broad expanses of ocean rule out the the development of stationary pressure systems.However the apparent zonality of the western circumpolar vortex does conceal considerable synoptic variability of wind velocity.

In short any idea of altering the global wind zones is totally impractical and bordering on madness. To even consider tinkering with such a complex interdependent system seems to me a waste of time that could be more usefully used elsewhere.

A quick glance at the global wind zones

G.jpg

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

@knocker, Just to answer a couple of points you raised, winds near the surface do tend to blow across isobars to varying degrees depending on a) the latitude of the location concerned and b) the surface roughness of the underlying surface. In the Northern Hemisphere winds blow in the direction one is facing when low-pressure is on your left (Buy's Ballots Law),but below the free atmosphere (usually about 500 metres above the surface, though dependant on surface conditions to a considerable extent) winds directions angle in towards the low-pressure.  With strong winds over the sea in middle and high latitudes the effect is not great with wind direction deviating about 10 to 15 degrees from geostrophic and angling in by this 10 to 15 degrees towards the low  pressure. Over land in mid-latitudes the greater surface roughness means that such a strong wind would blow nearer 25 degrees towards the low-pressure on average (which is why, in the land-dominated mid-latitudes of the Northern Hemisphere the Ferrel Westerlies are really more often south-westerlies near the surface with considerable polewards transfer of warmer air from lower latitudes). However this effect of surface friction causing winds to blow across isobars and towards low -pressure depends on the surface roughness of the underlying surface. A strong wind blowing over an Ice-sheet would encounter little friction from the underlying surface and so the deviation of the wind-direction would probably be less than over the ocean (with the angle of cross-isobar flow likely to be around 10 degrees).

Over middle and high latitude locations with greater surface roughness such as forests and with lighter winds the effect of surface friction is so much greater and the deviation of wind-direction towards low pressure is about 45 degrees. In other words, winds blow as much towards the low-pressure centre as along isobars (lines of equal surface pressure on the weather map) with low-pressure to the left in the Northern Hemisphere (low-pressure to the right in the Southern Hemisphere). 

In low latitudes where the effect of the Earth's rotation on wind direction (the Coriolis Effect) is less winds tend to blow across isobars towards areas of low-pressure much more readily. At the Equator the Coriolis Effect is zero and winds blow directly towards low-pressure at the surface. Even at elevation in the atmosphere wind-direction are from high to low pressure at the Equator, I.e. across isobars at 90 degrees. 

As regards your second point, it is indeed the absence of extensive land areas in Southern Hemisphere mid-latitudes that permit the Southern Westerlies to blow with full force. There is perhaps a second factor in the intense baroclinic atmospheric temperature gradient between the frigid Ice-sheet of Antarctica and the warm oceans of lower mid-latitudes combined with an abundant supply of moisture to help fuel the sub-antarctic depressions, that ensures the Southern Westerlies are strong in all seasons. 

Finally, as I have already pointed out on this particular thread, I am not seriously proposing that we should try and destroy the Ferrel Westerlies in the Northern Hemisphere. As you point out the global Wind-Belts are vast and they are driven primarily by the fact that warming air expands, cooling air shrinks and becomes denser and the global winds are a function of the atmosphere trying to even things up between the heat of the tropics and cold at higher latitudes. The second major control on the Global Wind-Belts is the fact that the Earth rotates and our rotating Earth and atmosphere is controlled by the constraints placed upon it by the physical Law of Conservation of Angular Momentum. 

All that said, the mid-latitude Ferrel Cell is what is known as a Thermally Indirect Cell and it's sole Raison d'etre is because the tropical and subtropical easterlies and high latitude Polar Easterlies continually add westerly Atmospheric Angular Momentum to the global atmospheric system through frictional interaction with the underlying surface. There needs to be a sink for this accumulated westerly AAM elsewhere otherwise the upper atmosphere would end up being composed of Westerlies blowing at many 1000s of miles per hour. This does not happen so clearly this Westerly momentum is returned to the surface and the mid-latitude Westerlies of the Ferrel Cell perform that vital task.

However, the Westerlies of mid-latitudes are not the only agents acting as a sink for Westerly AAM. Mountain ranges in mid-latitudes (and higher mountains in lower latitudes) reach the elevations where the Circumpolar Vortex blows and, in the case of the the lower fringes of the subtropical Jetstream on occasion. These are very strong upper Westerly winds, particularly in winter and anything intercepting them removes Westerly AAM from the atmosphere. This is one reason why the Ferrel Westerlies of the Northern Hemisphere sometimes become dis-continuous in the winter months. 

 

Returning to the theme of modifying the Global Winds,  yes it would be crazy to even consider given the sheer enormity of our planet! However, as I have already said, the Ferrel Cell is indirect and if we ever have to consider ameliorating some of it's effects then alleviating some of it's Raison d'etre (by planting forests in the west of Canada and in Scotland to absorb the force of the Westerlies and reduce the need for them elsewhere to reduce Westerly AAM) is not perhaps so far -fetched. On a smaller scale in the past such woods absorbing the force of the wind were called wind-breaks. 

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  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

I don't know how much folk are aware of this but the Ferrel Westerlies (and the pressure patterns that cause them) often cause southerly-quarter winds in mid-latitudes to the east (or even to the north-east) of where they are most dominant. Southerly winds like this also bring mild, often wet and generally yucky weather in autumn and winter. Let me explain:

Strong Westerlies occur where you have got high-pressure to the south and low-pressure to the north (in the Northern Hemisphere). Further east and further north you have southerly winds with the low-pressure being most intense to the west/NW and this set-up is not uncommon in the autumn and winter months over Western Europe when you have higher pressure over eastern Europe, a deep Icelandic low and a fairly constant subtropical high. Warm air commonly gets advected north from the Azores up through Britain and right up into the Arctic north of Norway. Worst of all, these warm winds can come round the Icelandic Low and angle in from the south-east creating "Need" for more Ferrel Westerlies to satisfy the Law of Conservation of Angular Momentum (what a waste of a south-easterly, I say!).

At other times, a high-pressure system that has to support Ferrel Westerlies to it's north brings warm southerly winds to places further west and south. Highs rather often occur over continental Europe in autumn and winter and bring warm southerlies to Britain (though sometimes if one is lucky in winter the air is cold in the high over Europe and colder southerlies can then reach Britain if this air has been over the continent).

Weakening the Ferrel Westerlies, if it could ever be done at all, would also reduce the occurrence of warm southerly winds over Britain (at least if it encouraged the Siberian High to move right in). Gentle southerly winds can bring some of Britain's most boring weather in late autumn and winter- often quite dry, not clear enough to allow strong night-time cooling (thick fog lasting days would at least be worthy of comment!) and generally mild.  

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

Unusually warm northerly and easterly winds that reach Britain and other mid-latitude locations from autumn through spring also occur on occasion: These can also (invariably) be blamed on the mid-latitude Ferrel Cell because the passage of depressions and the south-westerly winds south of them or isolated ridges of high-pressure extending north from the Azores High in the NE Atlantic with warm south-westerlies west and north of them. If such a ridge of high-pressure extends north to the latitude of Scotland just west of the UK with the Ferrel Westerlies coming round its north-west flank there can be northerly or north-westerly winds over the UK but these will not be cold having originated over lower mid-latitudes of the North Atlantic. And if this is a winter situation there is also likely to be a good deal of strato-cumulus associated with such an Atlantic High that would have the effect of preventing radiation cooling.

Easterly winds can occasionally occur when high-pressure over Europe extends a ridge north-westwards to Scotland and when pressure is even higher to the southeast over the eastern Mediterranean with the Ferrel Westerlies passing to the north over Scandinavia and being strong over the North Atlantic. If this happens in the autumn the easterlies bring warmer air from lower latitudes (i.e from over SE Europe) and there is warm sunny weather over most of the country. At other times, a deep depression can stall over southern Ireland and east or SE winds affect the UK, these (again) will often be mild and wet because the airmass will have come round the depression from the Ferrel Westerlies to its south! 

The conclusion is that the mid-latitude Ferrel Cell has a warming and wetting influence on mid-latitudes that is even greater than the vast regions where it directly engages with the surface! Weakening it significantly would be the only way to put paid to the persistent mildness and wetness of recent autumns and winter!!

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

The Ferrel Westerlies were blowing last night in the North Pennines. They were coming in from the south-west and, as so often happens here, the warmth they brought was not dry! It has now clouded over! 

The constant "Need"  for Westerly winds to counter-balance tropical and Polar easterly winds, so as to satisfy Conservation of Angular Momentum laws on our rotating planet is at the root of so much of the crappy weather that we get in this country. Without this Need for Westerlies there need not be depressions with all the cloud, drizzle and wet they bring! You could all dine Al'fresco all summer long, even if you are on the Outer Hebridees! All October nights would be clear, crisp and frosty ; the sort of weather that would bring the very best colours on the trees.

Only problem is that after a few years without rain there would be no trees, no lovely summer meadows and no crops. Completely eliminating the Ferrel Cell altogether would mean Britain turns into a desert in a few years, and as some have already pointed out it would be madness to even consider it!! 

However,  the regular problems we have had with winter (and summer) flooding, storm-damage, coastal erosion, mild and damp in winter and summer that allow bugs to bring pestilence (remember Foot and Mouth?) and damage our crops as well as a lack of proper seasons over recent years can all be blamed on The West Winds That Need To Blow To Stop The Earth Slowing Down!! And Global Warming over recent years has made this problem worse by causing the Westerlies to retreat northwards overall (following the retreating margins of Arctic ice) so that these wretched rainy cloudy mild winds have to blow even harder, more persistently and more extensively to stop the Earth slowing down (because they blow closer to the axis of the Earth's rotation). 

The discussion of technologically feasible solutions to at least weakening these Ferrel Westerlies (and at least locally!) surely needs to be had, therefore.  By far the best solution would be solutions to tackle Global Warming, and governments around the World are procrastinating rather than making serious efforts to really reduce CO2 emissions. 

Planting billions of trees is a sound solution (better if we can develop light coloured hybrids that reflect the Sun) to both Global Warming (they remove CO2 from the air) and to act as a brake on the Ferrel Westerlies (provided trees were planted in locations such as British Colombia, Canada, western Ireland or western Scotland where the trees are in locations that regularly get westerly gales). Such a proposal would also find favour with the Environmentalists! 

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria

NEATL1.jpg

At times like this, when the Ferrel Westerlies seem prone to just blow in and bring cloud to prevent cold crisp autumn nights (like now when this wind is ruining a possible frost to start October 2016 with) and with a longer seasonal outlook considering the effects of more winter storms bringing rain rather than frost/snow, one can see that the Ferrel Westerlies are very effective at a) preventing real severe late autumn and winter cold and b) bringing persistent wet and potential flooding. None of this is ideal weather for a good many of us who use this Forum!

Above is a map of Britain and the NE Atlantic: As much as the coastal areas of Ireland and western Scotland, the Hebrides, Rockall and the Faroe Islands need to be covered in tall wind-resistant trees as soon as is practically possible: This provides an effective extra sink for westerly Atmospheric Angular Momentum (AAM) through greatly-increased surface-roughness over extensive areas which in turn means westerlies don't have to blow as strong elsewhere (particularly downwind). The next step is to try and build north-south orientated artificial islands on the shallow continental shelves just west of Scotland and Ireland (and around Rockall) and on these plant more trees to intercept and slow the Westerlies before reaching Britain.

Planting trees along the west of Ireland and western coasts of Scotland is certainly practical and should be undertaken soon; conifers are usually best because they tend to retain their leaves (and thus their resistance to the wind) throughout the winter. Building new north-south islands along the continental shelves, by dredging the sea-beds around where the new islands are to be would certainly tax mankind's Civil Engineering capabilities however, but if Hong Kong had a new island built in order to accommodate a new airport then there is a chance it is doable if resources are put into it. If that seems a stretch too far, then the offshore shallow continental shelves could have a million large steel brushes facing west arrayed in north-south lines to absorb the force of the Westerlies, remove AAM from the atmosphere and thus weaken the westerlies downwind. Again there is precedent, thousands of wind-mills built in the seas off Britain's coasts!!

A solution to the problem of persistent stiff south-westerlies bringing muggy moist autumns, mild rainy winters (and often disagreeable showery summers) is worth working towards, of that I am sure. Global warming is making the winter storms more intense and rainy, increasing flooding and coastal erosion and the lack of dry cold means bugs thrive throughout the winter to bring increased pestilence to wildlife, to crops and to humans.

 

 

NE ATLANTIC MAP.docx

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Posted
  • Location: Horsham, West sussex, 52m asl
  • Location: Horsham, West sussex, 52m asl

you could try a large satellite far enough into space to eclipse part of the earth. or use some of our surplus nuclear weapons to melt the greenland ice-cap. or detonate a few under yellowstone and/or deep inside krakatoa, tambora or similar...

or get superman to fly around the earth to get it spinning the other way... actually that would be quite an interesting question- what if the earth spun in the opposite direction?...

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria
54 minutes ago, bobbydog said:

. actually that would be quite an interesting question- what if the earth spun in the opposite direction?...

@bobbydog, IF it were theoretically possible to get the Earth spinning at the same rate in the opposite direction (i.e. from east to west) the prevailing winds in Britain would be easterlies (and north-easterlies in winter owing to very cold dense air spilling out of Scandinavia in an anti-clockwise direction). The Norwegian Sea would be much colder as prevailing polar northerlies bring very cold Arctic air and would push pack-ice southwards from the Arctic for most of the year thanks to high-pressure further north and east over Scandinavia and the central Arctic. In summer, prevailing winds would become more south-easterly because of low-pressure systems moving west from the Baltic towards northern Scotland and there would be wary warm, thundery weather for a time.

Summer excepted, the period from September through May would be much colder. Southern England would have a cold continental-type climate whilst for the North and Scotland it would be drier and Arctic like with permafrost and (in the Scottish mountains) permanent ice-fields. Our climate would mirror that of NE Canada today where north-westerlies prevail much of the year to bring long, extremely severe winters but short warm summers. And whilst we would have a much colder climate if the Earth spun in the opposite direction SE Canada and the NE USA would be much milder and wetter in winter (but with somewhat cooler but less humid summers) as the prevailing winds became east/south-easterly (i.e. off the North Atlantic). Northern Japan and the far SE of Siberia would also have milder, wetter winters for similar reasons although they would still get very cold spells courtesy of icy NW winds from high-pressure over northern Siberia, the same would happen for eastern North America. Because of the shape of the continents one suspects that bitterly cold high-pressure would still form over far NE Canada and Greenland, as well as NE Siberia in winter and that means that SE Canada, the NE USA and Japan would still get cold spells at times (and rather more frequently than Britain and NW Europe get frigid NE winds in winter today). It means that, if the Earth rotated in the opposite direction, northern mid-latitudes would be colder than today overall (and probably drier) and the Arctic would be much colder because warm currents would no longer flow from the North Atlantic to the Arctic Ocean via the Norwegian Sea because the prevailing winds would oppose it.

In the tropics and subtropics you would get NW Trade Winds and strong heating over North Africa in summer would mean a heat low pulling humid air north and east from the west coast so the Sahara would get substantial rainfall and thunderstorms in summer (in the manner that southern China gets in summer nowadays). Meanwhile, summer heat over southern Asia would cause north or north-east winds further east so that southern China, Myanmar and Vietnam become the Great SE Asian Desert. Much of the eastern USA down to Florida would also turn to desert whilst California and Oregon get more summer thunderstorms (and bitterly cold winter northerlies with -20C cold-waves like eastern China today).

In the Southern Hemisphere tropics and subtropics Brazil would largely become desert due to prevailing south-westerly Trade Winds but coastal Peru and Ecuador would become hot and wet due to westerly Trade Winds bringing very warm moist air from the equatorial Pacific. The Atacama Desert would get enough summer rain to become a tropical grassland. There would be, instead of El Nino and La Niná a permanent strong El Nino because the Humboldt Current flowing north off the west coast of South America would reverse and warm tropical waters would flow south instead. Antarctica would be much the same as before but with the Polar Easterlies blowing off the continent becoming Polar Westerlies.        

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Posted
  • Location: Alston, Cumbria
  • Weather Preferences: Proper Seasons,lots of frost and snow October to April, hot summers!
  • Location: Alston, Cumbria
On 01/10/2016 at 23:31, bobbydog said:

thats at a rough guess then ian...:wink:

It certainly is, predictions made using one's own grasp of meteorology (which I have to degree level).  On the very basis of meteorological fundamentals such as the propensity for very cold dense air to flow outwards into warmer regions around it, for clear skies at higher latitudes from autumn through spring to promote strong net radiation cooling of the surface and lower atmosphere there is little doubt in my mind that weakening the Ferrel Westerlies would result in a cooler and drier climate in Britain. 

Numerous are occasions when there is high-pressure over NE Europe whilst deep depressions move eastwards in the sub-arctic North Atlantic during the winter half -year. Most of the time the resultant Ferrel Westerlies over the North Atlantic (and the Need for these Westerlies to counter-balance easterlies elsewhere to satisfy Conservation of Angular Momentum laws) are just too strong and they gain the upper hand over Britain whilst Sweden remains under the influence of frigid easterlies from Russia. One can anticipate that just weakening the Ferrel Westerlies by 20%, achievable if man uses his wits and technological resources to the maximum in my view, then the bitter easterlies from Russia due to high-pressure over Finland would prevail in the face of Westerlies off the North Atlantic much more frequently during the autumn and winter months. British winters would quickly become much colder, snowier and drier. 

Indeed, if our planet rotated at a speed just 10% less than it does today such a weakening of the Ferrel Westerlies could be achieved. The Ferrel Westerlies only owe their very existence to the fact that the Earth rotates and that as a result, easterlies in both high and low latitudes provide a source for Westerly AAM. The slower Earth rotates the Coriolis Effect in low latitudes becomes a tiny bit weaker so that the Trade Winds angle in a couple of degrees more from the North (or in the Southern Hemisphere, the south). So what,  you might think, that would not make much difference because would not the Trades also blow a bit stronger and anyway would not the Ferrel Westerlies have more of a south to north inclination?  Reducing the Earth's rotation by 10% would actually have a big effect because there would be longer days and nights everywhere but the effect would be greatest in the tropics where there would be stronger land and sea breezes near the coasts that would dilute the impact of NE and SE Trade Winds in putting Westerly AAM into the atmosphere. Secondly, the Trade Winds don't blow uniformly from exactly the same directions in all longitudes and all tropical and subtropical latitudes. The subtropical high is not uniform and influences of tropical waves disrupt the north to south surface pressure drop on a regional scale. In some sectors the pressure drop may be NW to SE causing NNE winds( in the Northern Hemisphere). In other sectors the pressure drop may be NE to SW thereby causing east to south-east winds. Now then, a slight slowing down of the Earth's rotation would make all these winds back a few degrees but it is the impact on Trade Winds where the pressure gradient today would cause NE or NNE winds but with a slightly slower rotation rate would cause them to become more NNE and due northerly that matters. This is because a surface northerly wind does not cause any Westerly AAM to be added to the global atmospheric circulation through frictional interaction with the underlying surface and this change to the Trade Winds will affect those that already have substantial northerly components (in the Northern Hemisphere). This is the case for a sizeable proportion of the North East Trade Winds. Consequently a small reduction in the Earth's rotation has an impact proportionally larger on the higher-latitude sink for Westerly AAM. 

That, of course, is not all. The Westerlies at low levels result from what remains of Westerly AAM after high mountain ranges absorbing the impact of the much-stronger upper Westerlies , downdraughts from tropical thunderstorms and smaller tidal impacts from the Sun and moon have taken their cut of Westerly AAM. All of which means that a 10% reduction in the Earth's rotation rate could weaken the surface Westerlies overall by more than 20%. Given the importance of strength in the winter Westerlies in preventing frigid dense air over Siberia from reaching western Europe the climatic impact on this country could be huge. 

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Posted
  • Location: Powys Mid Wales borders.
  • Location: Powys Mid Wales borders.

Well speaking of westerlies as we head into October it looks like a persistant easterly is coming in,eventually bringing some cooler upper air in,but surface air temps will get colder.

Edited by Snowyowl9
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