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Or, is it worth skiving off tomorrow?

Or, is it worth skiving off tomorrow?. METEOROLOGY FOR SLACKERS. Meteorology for Slackers. Introduction. Meteorology is a hideously complex subject, from which we attempt to distil enough information to equip us for the tribulations of gliding flight

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Or, is it worth skiving off tomorrow?

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  1. Or, is it worth skiving off tomorrow? METEOROLOGY FOR SLACKERS

  2. Meteorology for Slackers Introduction • Meteorology is a hideously complex subject, from which we attempt to distil enough information to equip us for the tribulations of gliding flight • Thankfully we can disregard many of the more complex atmospheric phenomena and concentrate on what occurs in the lower levels of the atmosphere. • With no other demands upon your time then simply putting your head out of the window is the best method!

  3. Meteorology for Slackers Introduction The main factors influencing weather from a pilot’s perspective are: • Insolation • The air mass and its recent history • temperature • humidity • Air Pressure • stability

  4. Meteorology for Slackers Coriolis Coriolis effect determines the airflow about a depression or anticyclone: • HIGH pressure forms an ANTICYCLONE, about which the wind rotates CLOCKWISE. • LOW pressure forms a DEPRESSION (which may be described as CYCLONIC) and about which the wind rotates ANTICLOCKWISE.

  5. Meteorology for Slackers Coriolis This can be expressed as Buys Ballot’s Law: In the Northern Hemisphere a person standing with his back to the wind will have high pressure to his right and low pressure to his left. ie Low on your Left

  6. Meteorology for Slackers Gradient Wind • Balance of pressure gradient force, PG and geostrophic, GF coriolis forces. • Blows parallel to isobars. • Measured at 1000 m. • Usually clockwise of wind at lower altitude. • At 50°, 4mb between Deal & Scillies = 10 Kt.

  7. Meteorology for Slackers Pressure Systems High Pressure • Air mass subsiding. • Little/No convection cloud. • Inversions marked • Thermals may be suppressed • Turbulence at inversions. • Wind on hill may be accelerated below inversion. • Wind on hill be not generate lift if inversion below launch. • Insolation unimpeded • Occasionally,thermals can be surprisingly strong, but often short lived • May become hot & humid • Risk of CuNb if inversion(s) break

  8. Meteorology for Slackers Pressure Systems Low Pressure • Air mass rising. • Significant convection cloud. (Cu, Cb, Ac, S, Sc) • Wind on hill will generate lift • Inversions weak/absent • Thermals strong to cloudbase and beyond • visibility good • Insolation impeded • Cloud cover may impede insolation after cumulus build up • risk of spreadout - Cu merge to form S/Sc.

  9. Meteorology for Slackers Pressure Systems Forecasts

  10. Meteorology for Slackers Pressure Systems

  11. Meteorology for Slackers Pressure Systems

  12. Meteorology for Slackers Pressure Systems

  13. Meteorology for Slackers Pressure Systems Bracknell

  14. Meteorology for Slackers Pressure Systems

  15. Meteorology for Slackers Pressure Systems Bracknellhttp://meteonet.nl/aktueel/brackall.htmhttp://www.itadvice.co.uk/weatherjack/charts-all.htmlhttp://www.airworks.co.uk/links.htm

  16. Meteorology for Slackers Pressure Systems

  17. Meteorology for Slackers Pressure Systems ExpertWeatherOnline Isotachs: http://expert.weatheronline.co.uk/is10_frame.htm

  18. Meteorology for Slackers Pressure Systems

  19. Meteorology for Slackers Pressure Systems

  20. Meteorology for Slackers Pressure Systems

  21. Meteorology for Slackers Pressure Systems

  22. Meteorology for Slackers Pressure Systems

  23. Meteorology for Slackers Satellite Imagery http://www.metoffice.gov.uk/satpics/latest_uk_vis.jpg

  24. Meteorology for Slackers Satellite Imagery http://www.metoffice.gov.uk/satpics/latest_uk_ir.html

  25. Meteorology for Slackers Satellite Imagery http://130.92.54.203/rsbern/noaa/dw/realtime/current/n1bcurr.jpg

  26. Meteorology for Slackers Satellite Imagery http://www.sat.dundee.ac.uk/abin/browseleaf Requires registration

  27. Meteorology for Slackers Topography Don’t forget topographic effects: eg in an easterly airflow the wind is accelerated through the channel and also around the Wilmington/Beachy Head massif, such that forecast wind strengths are often as much as a factor of two too low!

  28. Meteorology for Slackers Tephigrams Is the day likely to be any good? Don’t forget about soundings!

  29. Meteorology for Slackers Tephigrams • Soundings help you to: • Work out approximately what time the day will kick off & when it will die. • Know at which altitudes to expect maximum climb rates. • Be aware of any risk of over-development or spread-out.

  30. Meteorology for Slackers Tephigrams Lapse Rate • For every 1000 feet gain of altitude, dry air cools 3°C - The Dry Adiabatic Lapse Rate • Saturated air cools by only 1.5°C/1000’ - The Saturated Adiabatic Lapse Rate. This is only an approximation - the rate changes slightly with height.

  31. Meteorology for Slackers Tephigrams Stability • Air is stable if after being displaced vertically it returns to its original altitude. • Air is absolutely unstable if the environmental lapse rate is greater then the DALR.

  32. Meteorology for Slackers Tephigrams How high is cloudbase likely to be? A simple rule of thumb is: (temperatures in °C) 400*(forecast temperature - dew point temperature) = Cu base in feet i.e. cloudbase = 400(T-DP) This does not hold true once the day starts to cool, but is adequate for the main part of the day.

  33. Meteorology for Slackers Tephigrams A more accurate method of determining cloud base involves using atmospheric soundings, known as Tephigrams. The dry adiabat is the temperature line that dry air would follow The saturated adiabat is the temperature line that saturated air would follow. The SALR is a curve because the 1.5°/1000’ ‘rule’ is actually only an approximation

  34. Meteorology for Slackers Tephigrams Given a dew point of 19 °C* & a forecast temperature of 25°C, follow these two lines up their respective adiabats until they meet. This is cloudbase. *(ie the air contains sufficient water that once cooled to 19 °C it will start to condense out.)

  35. Meteorology for Slackers inversion Tephigrams The Met office take regular soundings of the atmosphere and produce an environmental line on the graph. This is the actual temperature at any given altitude

  36. Meteorology for Slackers Tephigrams Any thermal will continue to rise until its temperature is equal to that of the surrounding air. Thus our cloud will build until the saturated adiabat meets the environmental line. Without an inversion, the thermal would rise to the tropopause, becoming a Cb. inversion

  37. Meteorology for Slackers inversion inversion inversion Tephigrams A thermal rises because it is warmer & thus less dense than the surrounding air. The greater the difference, the faster the rate of ascent. Any thermal will continue to rise until its temperature is equal to that of the surrounding air. Given this environmental line

  38. Meteorology for Slackers Tephigrams A thermal trigger temperature of 21°C is needed before they will release but they will stop at the top of the 500’ inversion. At a trigger temperature of 24 °C the thermal will rise quickly at first, slowing towards 2000’ then continuing slowly to the 3000’ inversion. At a trigger temperature of 26 °C the thermal will rise quickly at first, slowing towards 3000’ then continuing slowly to the 4500’ inversion.

  39. Meteorology for Slackers Tephigrams Taking the last case , a trigger temperature of 26 °C, plotting the difference between the red & blue lines will yield the anticipated thermal buoyancy vs. altitude. Remember air has mass so changes are not instantaneous Inversion has stopped climb Mildly buoyant, climb poor Still fairly buoyant, climb good Still very buoyant, acceleration moderating Very buoyant, accelerating fast, hang on to breakfast

  40. Meteorology for Slackers Tephigrams Where can I get one? • Noaa - http://www.arl.noaa.gov/ready/cmet.html? • Met Office - Herstmonceux or Camborne

  41. Meteorology for Slackers Tephigrams

  42. Meteorology for Slackers Tephigrams

  43. Meteorology for Slackers Tephigrams

  44. Meteorology for Slackers Tephigrams

  45. Meteorology for Slackers Tephigrams Tephigrams in Summary • A graph of air mass properties with height. • In the real world plotted on a variety of different axes

  46. Meteorology for Slackers Airmass Is the day likely to be any good? What about the airmass?

  47. Meteorology for Slackers Airmass Air masses affecting the British Isles can be broadly categorised in terms of their source and their path. This leads to four possible types. • Tropical maritime - warm and moist • Tropical continental - warm and dry • Polar maritime - cold and (fairly) moist • Polar continental - cold and dry • To these must be added another air mass - returning polar maritime - which consists of polar air that has moved southwards over the sea and then turns northwards and approaches the British Isles from the south.

  48. Meteorology for Slackers Airmass • Tropical continental air usually comes with south-easterly or southerly airstreams. • It originates in North Africa and often travels over the Mediterranean Sea, Spain and France before reaching the British Isles. In summer, even easterly winds from central Europe or the Ukraine could be included in this category, as the continent becomes so hot at this time of year. • The air picks up some moisture over the Mediterranean/ Bay of Biscay, but overall the air tends to be quite dry and the skies are typically cloudless. Tropical Continental Air

  49. Meteorology for Slackers Airmass Tropical Continental Air • Strictly speaking, an air mass cooled from below on its northward journey should be stable. • Sometimes, however, moisture may have found its way to medium levels in the atmosphere. • Then, if there is a layer of unstable air and a trigger to set off convection, altocumulus castellanus clouds can develop, looking like turrets. • These are often the forerunner to tremendous thunderstorms, which can occur by day or night.

  50. Meteorology for Slackers Airmass • The majority of tropical continental airstreams give a marvellous heat wave (in summer) • The lack of moisture usually causes the visibility to be good. However, in the air there may be desert dust, fine soil or pollution particles, which can lead to moderate visibility (often described as 'heat haze'). • Also, the cloudless sky sometimes looks milky because of pollutants. Tropical Continental Air

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