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  1. 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
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