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Found 4 results

  1. Dear Readers, Rising CO2 levels in the atmosphere has undeniably had a warming impact on the Earth's climate, with the planet as a whole having a mean temperature during 2020 just over 1.0C above pre-industrial averages. The warming impact has undeniably been greater in recent years in Russia, Canada, and northern Europe where- in the winter months the mean warming has been over 2.0C above pre-industrial averages for the season. Some of this warming may be related to the Earth coming out of the Little Ice Age- but some of the effect is undoubtedly due to CO2 levels since we are entering a period of quiet Sun (weaker sunspot cycles with slightly weaker Solar output) which, all else being equal ought to bring a cooling back to the conditions of the 19th Century: Plainly that is not the case. But why do middle latitudes and higher latitudes in winter warm more? The exception is interior Antarctica that has got colder in recent winters, and winter 2021 (June-August) was one of the coldest on record at the South Pole. The Antarctic Ozone Hole in the Antarctic stratosphere has also made a bit of a come-back in 2021 (during the Southern winter). Is that also in some way related to warmer, wetter winters in most middle and high latitude areas? The answer is a definitive "Yes". Most meteorologists appreciate the impact of something called the Law of Conservation of Angular Momentum on the Earth's global weather-pattern: In layman's terms, the Earth's rotation and the virtual absence of outside forces (gravitational tidal influences from the Sun and Moon, the effects of meteorites and bursts of super-charged plasma from the Sun following coronal mass ejections are largely negligible over just a few years) means that the atmosphere as a whole has to rotate with the Earth. From this, the frictional and pressure impacts of Easterlies at low latitudes and near the poles are counterbalanced by the frictional and pressure impacts of Westerlies in middle latitudes. This applies to both the Northern Hemisphere and the Southern Hemisphere and largely dictate the existence of the Westerlies in higher latitudes, but not necessarily where they occur or how strong they are. However, global weather- patterns are also (and primarily) controlled by the heat input to the Earth-Atmosphere system, how much heat there is and where it is on the Earth. It is also dependent on moisture and atmospheric temperature gradients. A warmer Earth not only means more moisture in the atmosphere but, with the edges of polar ice-caps (seasonal and year-round) retreated polewards it means that the Westerlies- intensified and largely fixed by atmospheric and near- surface temperature gradients (what meteorologists call baroclinicity) as the depressions that drive these depressions also need these zones of baroclinicity. Now, the areas of the Earth where easterlies are at the surface are called sources of Westerly Atmospheric Angular Momentum (AAM) or simply Global Atmospheric Angular Momentum (GLAAM). This arises because Easterly winds, blowing in a direction opposite to the Earth's rotation result in the Earth losing a bit of it's eastwards rotation to the atmosphere- in other words these areas with surface Easterly winds are sources of Westerly AAM (or GLAAM). Since, at least under current climatic conditions, the winds aloft do not start blowing 1,000's of miles an hour from the West and remain fairly constant in speed at the height of the winter (seldom more than 200 mph at 10,000 metres' elevation) it follows that other areas are sinks for Westerly AAM (or GLAAM). These areas are in higher latitudes where often -strong Westerly winds blowing over the sea or against hills result in a frictional force at the surface slowing the Westerlies down- and helping to speed the Earth's rotation up. The fact that the Length of Day remains fairly constant throughout the year- and from year to year (though the Length of Day is very slowly increasing by a millisecond a decade mainly due to the effects of marine tidal friction due to the Moon)- means that Westerly AAM is imparted to the rotating Earth as much as it is removed via tropical and Polar Easterlies. Now, for some interesting observations of global weather maps by a seasoned meteorologist (myself): For almost all the year the Westerlies seem to be concentrated at the highest latitude 40% of the Earth's surface (sin-1(1-0.4)=36.9 degrees, so that is Westerlies restricted to North of 36.9 degrees North and South of 36.9 degrees South). Of course, there still are some occasions with Westerlies in lower latitudes, strong Westerlies occur on the equatorwide of hurricanes and tropical depressions when these occur but these are counterbalanced by just as strong violent easterlies on the other side of these tropical storms. South-Westerlies blow over India and adjacent parts of southern Asia during the Summer Monsoon- which will help reduce some of the need for strong Westerlies at higher latitudes of the Southern Hemisphere in the winter there, so this will not help weaken Westerlies in high Northern latitudes. Often the Tibetan Plateau gets Westerly winds in winter, but these have seldom been strong and they are restricted to those areas north of 30 degrees North. (Continued below)
  2. Dear Readers The impact of increasing global temperatures over the last forty years on Arctic sea-ice cover is clear: There has been a consistent decline in sea-ice extent compared to the long-term normal (see here for an illustration: http://nsidc.org/soac/sea-ice.html#seaice). The possibility of the Arctic Ocean becoming ice-free in summer, then remaining so into the winter is one that is of increasing concern for remote communities on the Arctic coastline and for wildlife. Less appreciated, perhaps is how an Arctic Ocean free of pack-ice year round would impact upon the prevailing (and possible extreme) weather- conditions further afield. It is certain that the loss of Arctic sea-ice would occur in the context of global temperatures just 2.5 to 3C above those of today. As the Arctic warms and the edge of the pack-ice recedes north of Spitzbergen the ice-free water absorbs heat from the Sun rather than reflecting it back to space and this helps warm the local ocean surfaces further. If Greenland remains very cold and ice-covered the baroclinic zones of sharp atmospheric temperature and pressure- gradients would extend north-eastwards and northwards from the tip of southern Greenland, this would encourage more North Atlantic depressions to push deep into the Arctic. That process would, in addition bring warm southerly winds from the North Atlantic right up into the Arctic- further exacerbating regional warming. It is clear to see that if this feedback between more ice-free waters absorbing the Sun's heat in the summer, then attracting depressions into the area in winter bringing more warmth- really took off then the entire Arctic could become free of ice one summer, then remain free of ice as autumn and winter storms moved in over the ice-free areas with warm air from lower latitudes. Once the Arctic is ice-free and the surface waters stay above the freezing-point of ocean water year-round (-1.8C) the ice-free ocean would release a large amount of warmth into the low atmosphere. This would lower surface pressures but would also have a smaller warming influence on the high atmosphere over the Arctic. The main influence of the lowest 3,000 metres of the atmosphere being some 10C warmer in Autumn and 15 to 20C warmer in Winter would be a drop in average surface-pressures over the central Arctic by 15 millibars in Autumn and 20 to 25 millibars in Winter- that fact alone combined with the stronger atmospheric temperature gradient between much warmer conditions in the low troposphere and still very-cold air in the upper-atmosphere would be strongly conducive to storm activity in Autumn and Winter. The article referred to here lends support to this thesis (https://journals.ametsoc.org/view/journals/clim/31/19/jcli-d-18-0109.1.xml). In Summer, an ice-free Arctic would be little warmer than the part-thawed pack-ice there today, unless sea-surface temperatures could get well above freezing-point: It is thus likely that the Central Arctic would not experience more summer storms in a warmer world, but hotter conditions on the continents surrounding the Arctic in a warmer would still increase the crucial baroclinic atmospheric temperature contrasts to increase cyclogenesis at the margins of the Arctic- with worrying implications for coastal erosion along the Arctic coast-lines of Canada, Alaska and Russia. This still implies, for the purposes of discussing the wider implications for mid-latitude weather-conditions, a general northwards shift in storm- tracks. We now look at what the implications of increased temperatures and storminess in the ice-free Arctic Ocean mean for regions well to the south of the Arctic Circle. There is a school of thought that believes an ice-free Arctic ushers in wetter conditions with stronger winds in temperate latitudes, with severe winter cold spells becoming a thing of the past (not least because the World would be 3C warmer and middle-latitudes are not far from the unfrozen Arctic Ocean region that will be 20C or more warmer in winter). Certainly this means that any northerly winds coming from the Arctic interior will not bring severe cold to Britain during the winter months, but this does not rule out cold air coming from the east even if sea-surface temperatures around Britain are 4C warmer at the start of the winter. And there is no guarantee that that will be so because if the North Atlantic Drift weakens in response to weaker Westerlies sea surface temperatures around the UK may not be much warmer than today. The main influence of an ice-free Arctic Ocean, at least in Autumn and Winter will, from the above, be to steer the deep depressions (that normally push north-east from Iceland to north of Norway in Autumn and Winter nowadays) much more northwards along the East Greenland Coast and into the Arctic interior. Furthermore a much warmer Arctic in Winter would even ensure that the upper-atmosphere warmed a little (as cyclonic cloudy convection transfers heat into the upper-air)- increasing the 500 mb heights by 200 metres or more. That process alone would help decrease the strength of the Circumpolar Vortex by 10% or more, not least over the North Atlantic west of the UK. On the other side of the ledger, if the North Atlantic is 4C warmer in early winter that almost doubles the latent heat available to fuel deep depressions and could help tighten and strengthen the Circumpolar Vortex twice as much as the reduced Circumpolar Vortex might weaken it. That is particularly possible if Greenland is still ice-covered and Greenland/ north-east Canada still get very cold in winter, the sharp baroclinic temperature gradients in the atmosphere between Greenland/ NE Canada and a warmer North Atlantic would be a very potent source of cyclogenesis- but the question then becomes where do the depressions go, i.e. eastwards or northwards up the East Greenland Coast into the ice-free Arctic Ocean. If the depressions that normally headed just north of Norway in the past travel up the East Greenland Coast towards the North Pole in a warmer world that has very profound implications for the climate of western Europe (including the UK). Continued below.
  3. Hello. Apologies for my absence for several months- I have been busy with my new business! Those of you who have a basic grasp of meteorology will know that the large- scale circulation in both the Northern and Southern hemisphere's consists of three cells: 1) The Hadley Cell- where air rises at the Equator over the hottest lands and ocean surfaces moves at high- levels towards the subtropics and descends in the subtropical high- pressure belts. Low- level north- east and south- east Trade Winds complete the circulation by bringing this air beack towards the Equator. 2) The Ferrel Cell- where air descends on the polewards flanks of the subtropical-highs and blows towards higher latitudes at lower levels. These winds, deflected by the coriolis effect cause surface south- westerlies in the Northern Hemisphere and surface north-westerlies in the Southern Hemisphere. This air then rises in the sub- polar low- pressure belts, rises and returns to the polewards flanks of the subtropical highs at high altitudes. 3) The Arctic/ Antarctic Cells- where air descends over frozen seas and lands near the North and South Pole's respectively, blows outward near the surface, rises on the polewards flank of the sub-polar lows and returns to the interior polar areas at high elevation. The Hadley and Arctic/ Antarctic Cells are thermally direct, being driven by the principle of warm air rising and cool air sinking. The Ferrel Cell tries to operate in reverse and the only reason for it's existence is the fact that the Earth rotates and because constraints placed on the Global Circulation by the Law of Conservation of Angular Momentum require that the extent and strength of surface Westerlies counterbalance that of easterlies in both high and low latitudes. The Ferrel Cell is not, perhaps a uniform feature of weather maps, as the weather- patterns in areas dominated by the Ferrel Cell are affected by individual deep depressions that track eastwards (usually between 50 and 75N in the Northern Hemisphere) and the ridges of high pressure that (usually) extend north from the subtropical- highs in between the passage of depressions further north: In the Northern Hemisphere persistent high- pressure over Siberia may block out the Ferrel Cell over much of northern Asia, but even here depressions skirting around the north edge of the high still demonstrate the Ferrel Cell is able to punch through cold-air anticyclones near the surface. The main feature of the Ferrel Cell, overall, is it's propensity to bring warmer air polewards at the surface over wide areas of mid- latitudes: It's reach is extensive and dominant over large areas of mid- latitudes. The Ferrel Cell brings damp mild weather: The northwards movement of warmer air below and an equatorwards movement of colder air aloft means an unstable atmosphere prone to producing cloud and rain- certainly over the UK where south-westerlies blow off the North Atlantic. The cloud cover and persistent advection of mild air does mean- at this time of year- an absence of freezing temperatures; cloud, dampness and no frost has so totally dominated this month of December even in the north of England! If there were some major geo- engineering initiative that could weaken the Ferrel Cell enough at this time of year, those who like frosty snowy winter weather ought to favour it. The Ferrel Cell, as I have mentioned, owes it's existence to a "need" for the frictional force of easterly winds in high and low latitudes to be counter-balanced by Westerlies elsewhere. Sadly, the Westerly atmospheric angular momentum (AAM) that the global winds pick up from the frictional interaction of the NE and SE Trade winds in the tropics and sub-tropics never magically drifts off into space (which would allow the Earth to slow down a bit- so we could fit more into 25 hour days) it always returns to the surface. The excess Westerly AAM is transferred polewards in the vicinity of the subtropical jet- stream- about 12 km up over 30N and 30S. So Donald Trump needs to be persuaded to build a huge north- south 12-km-high wall in the Mojave Desert to intercept the subtropical jet-stream (his US-Mexico border wall is not going to be high enough and it would be orientated the wrong way), slowing it down so that this very high wall becomes the sink for Westerly AAM in the Northern Hemisphere. Without the "need" for so much of a sink for Westerly AAM elsewhere, there would be less mild south- westerlies encroaching Europe, less depressions in the North Atlantic and North Pacific and this would eliminate coastal erosion along the US and Canadian coasts as well as those of the UK and northern Europe. Maybe Donald Trump could be persuaded to spend £1 trillion dollars to save on coastal erosion costs for the next century- maybe Britain could offer to give the USA Bermuda and all its coastal waters free of charge as an additional incentive! Think how many well -paid jobs that would provide for the USA We would have much more high -pressure in Britain to bring cold frosty autumn mornings and dry winters with hard frosts. Summers would be warm and sunny! It remains for me to wish all on here a happy and peaceful Christmas and all the best for 2019 Ian Pennell
  4. As promised I have piece together macroscale developments of sea-surface temperature and regional wind/pressure anomalies to provide a preliminary forecast for the coming winter.During October the global winds, pressure and temperature-patterns across the Northern Hemisphere gravitate towards their winter states, which they will tend to retain until late March. First thing though we need to list what we know so far: 1) Sea surface temperatures are, in general well above normal across the North Atlantic with anomalies close to 4C for early October in the European Arctic section with anomalies of +6C off the eastern coast of the USA and in the Baltic. The section is part of the mid-North Atlantic about 45 to 55N and 20 to 40W where sea surface temperatures are up to 2C colder than usual. Such warmer than usual waters around the UK would directly warm any winds blowing over them more and would tend to support milder weather and more evaporation from the warmer seas would support increased rainfall. The cool patch in the North Atlantic is sufficiently far west for it to cause the southern part of the strong upper Westerlies to re-curve south over it and just to the east whilst the upper air would be encouraged to "re-curve" northwards having crossed the warmer waters around Britain: This would place an upper trough near to the UK and enhance wet, windy weather. 2) The North Pacific north of 20N is substantially warmer than normal with sea surface temperature anomalies generally 3 to 4C warmer than normal for early October. However the Equatorial central and eastern Pacific is colder than usual with anomalies up to 2C below normal. The development of La Nina with cool equatorial waters would promote weaker north-easterly Trade Winds over the Pacific between the Equator and a weaker subtropical high-pressure belt centred over warmer than usual waters of the North Pacific around 30 to 35N: Weaker NE Trade Winds impart less westerly atmospheric angular momentum (AAM) to the Northern Hemisphere's atmospheric circulation through frictional interaction with the sea-surface- particularly as less wind means a calmer sea-surface with very low coefficient of friction. There is correspondingly need for less of a sink for accumulated westerly momentum in higher latitudes which implies weaker westerlies reaching Britain with a correspondingly higher chance of cold-air outbreaks from Russia or the Arctic. 3) Arctic sea-ice extent has recovered remarkably during September and it's extent is close to the seasonal norm east of Greenland but the sea-ice extent remains some 500 km north of its normal October extent north of Alaska and the extreme east of Siberia. Open waters in the Arctic Ocean surrounding the sea-ice remains substantially (i.e. widely up to 4C warmer than normal for October however): This is likely to encourage the Circumpolar Vortex to be contracted as well as displaced towards the UK by up to 200 km, however the warmth of Arctic seas would encourage the strong baroclinic gradients to be shifted towards the Arctic. This lends support to deeper depressions encircling the Arctic close to 70N, particularly in the North Atlantic sector and the warmth of the oceans just to the south of them means rather more moisture latent-heat potential to fuel these storms. The northwards displacement of the Westerlies is likely to encourage them to be strong in any case because they have to blow harder closer to the axis of the Earth's rotation to offset the tropical, subtropical and polar easterlies as required by Conservation of Angular Momentum laws. 4) Also supportive of a mild wet and windy winter is the fact that the Quasi Biennial Oscillation (QBO) at 30mb high above the Equator remains in Westerly phase. During August these stratospheric Equatorial Winds averaged just over 10 metres per second (23 mph) from the west. These stratospheric winds feed down into the general circulation and reach the mid-latitude jet-streams and Westerlies over three or four months. This suggests (strongly) that the coming winter will be mild wet and stormy. 5) The Sun is now entering the quiet phase towards the end of Schwabe cycle 24: Indications are that the Sun is indeed going quieter than it has been for a few years. An active Sun produces Solar Flares which interact with the atmospheric circulation to increase the strength of the Circumpolar Vortex. Instead few (if any) magnetic storms from the Sun will be interacting with the Earth's atmosphere and instead (if anything) that just leaves tidal friction due to the Sun and Moon which affects the atmosphere as well as the oceans. The tidal effects on the atmosphere are very weak but these act to reduce the Earth's rotation by very mall amounts (these are significant over time, which is why Leap Seconds are added at the end of each year). The net effect of all this (weak phase of Solar Cycle, atmospheric tidal friction) would be to weaken the Westerlies a little. 6) At least until mid November, the fact that sea-surface temperatures in the tropical Atlantic and Pacific just north of the Equator is likely to enhance tropical storm activity. More hurricanes and typhoons with strong easterlies on their northern flanks that enter the Northern Hemisphere circulation add Westerly AAM to the global atmospheric circulation. This increases the need for stronger Westerlies in higher latitudes to counter-balance them: This strongly hints to late autumn/early winter being wet, mild and stormy. However, from late January onwards the Intertropical Convergence Zone (ITCZ) will be south of the Equator and the fact that sea-surface temperatures in tropical waters just south of the Equator are also warmer than normal now suggests more tropical storms will occur there; Southern Hemisphere tropical depressions (sliding westwards along the ITCZ) have strong westerlies on their northern flank and it is these that will affect the Angular Momentum Budget of the Northern Hemisphere circulation by removing Westerly AAM through frictional impact with the underlying surface: This points to weaker Westerlies coming across the North Atlantic in January/February which would, other things being equal, increase the chances of much colder, drier spells reaching Britain from the east. We can now put all this together to get some sort of prediction for Winter 2016/17: (Continued below)
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