* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Weather Wisdom - with Martin Babakhan AIR PRESSURE Knowledge of atmospheric pressure is of great assistance for weather observers. Because air acts like a fluid; high pressure in a locality will result in a air moving outwards towards comparatively low pressure areas. The actual atmospheric pressure at a station is called ‘Station level pressure”. This pressure at a given place and time is dependent upon: The altitude of a station. The effect of gravity, and the amount of air above the station. The movement of pressure systems: The passage of a well-developed pressure system often is accompanied by a change of 5 hPa or more in atmospheric pressure. Change in intensity of pressure system can occur: This is because of the deepening or filling of a low pressure system. A daily variation: This variation, which may be thought of as an atmospheric tide, is fairly strong in equatorial latitudes but vanishes about latitude 60º. The pressure is greatest due to this effect at 10 a.m and 10 p.m local standard time and lowest at 4 a.m and 4 p.m. This variation amounts to about one (hPa) in middle latitudes and more than 5 hPa in tropical regions. This is significant in tropical region because falling pressure may be due only to the daily variations and may not indicate the approaching of a storm. BAROMETER 1. A barometer will not give a true reading of static pressure if it is subject to the influences of gusty winds. It may be necessary to relocate the barometer to a more sheltered location. 2. Barometers must not be installed in "sealed" Room , where the air pressure inside the building is liable to be different to that outside Mercury barometers: These should be placed in a room in which the temperature is constant or changes only slowly, and in which temperature gradients do not occur. They should be shielded from direct sunshine at all times and should not be placed near any heating or cooling device. It is preferable to hang a mercury barometer on a solid inside wall which is free from vibration. Accurate work, the best position is in an insulated, unheated windowless room, such as a basement, with a small fan to prevent any stratification of temperature. 2 Aneroid barometers: Most aneroid barometers used for meteorological purposes are temperature compensated for fluctuations in temperature in the ranges likely to be experienced in sheltered conditions in Australia. However, they should be protected from differential heating from direct sunlight, heaters or any form of air conditioning. You also find great information from the Bureau of Meteorology Web site “How to measure air pressure using a Barometer” http://www.bom.gov.au/info/weatherkit/section2/barom.shtml HOW TO CALLIBRATE YOUR BAROMETER Open the Australian Bureau or Meteorology homepage http://www.bom.gov.au/ Clickable Map 1. 2. 3. 4. 5. 6. Click on NSW on the weather map Click on All Latest NSW weather observations Click on Clickable Map Click on Armidale Airport or Tamworth Airport Refer to the second last column headed “Press MSL hPa” which will give sea level pressure which is updated every 3 hours. Wait until just after an update before calibrating your barometer.