Altitude and vertical thermal structure of the atmosphere
Exponential decay of Pressure with Height Approximate relationship: P=P 0 exp(-z/8100) Where P 0 =1013 mb and 8100 m = e- folding distance or “scale height”
Common Unit Conversions and Conventions in Meteorology 5 • Temperature: C ( F 32 ) 9 9 F C 32 5 K C 273 . 15 • Pressure: Surface pressure is usually measured in mb or in. Hg and adjusted mathematically to the pressure that would be read if the station were at sea level. 1013 mb = 101300 Pa = 1013 hPa = 1 atm = 760 mm Hg = 29.92 in Hg • Winds: Compass rose with wind blowing FROM 0 degrees denoting a North Wind, 90 an East Wind, 180 a south wind and 270 a West wind 1 kt = 1.15 mph ; 1 mph = 1.61 km/hr • Lengths Large lengths usually in km or mi; small dimensions almost always in meter fractions m = 3.28 ft; 1 mi=5280 ft; 1 mi=1.61 km; 1 mm= 1x10 -3 m; µm= 1x10 -6 m • Areas 1 sq. mi = 2.6 km 2 =2.6x10 6 m 2 ; 1 acre=4087 m 2 • Volumes 1m 3 = 1x10 9 mm 3 ; 1 ml=1cm 3 =1x10 -6 m 3 • Energy The energy required to heat 1 ml of water 1 degree C is a calorie – a food Calorie (large C) is 1000 calories (small c) 1 cal = 4.184 J • Power Power expresses the rate of energy W=1 J/s
The Station Model for surface observations WIND Wind is plotted in increments of 5 knots (kts), with the outer end of the symbol pointing toward the PRESENT WEATHER: direction from which the wind is blowing. The wind speed is determined by adding up the total of flags, lines, and half-lines, each of which have the following individual values: Indicates presently occuring precipitation. Other unusual phenomena may also be indicated in Flag: 50 kts text report. Visibility is often indicated to the left Line: 10 kts of this symbol. Half-Line: 5 kts If there is only a circle depicted over the station with no wind symbol present, the wind is calm. Below are some sample wind symbols:
PRESSURES and TRENDS Sea-level pressure is plotted in tenths of millibars (mb), with the leading 10 or 9 omitted. For reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample conversions between plotted and complete sea-level pressure values: PRESENT SKY COVER: 410: 1041.0 mb Usually, but not always in quarters of cloud 103: 1010.3 mb cover. Traditionally observed in eighths. 987: 998.7 mb 872: 987.2 mb The pressure trend has two components, a number and symbol, to indicate how the sea-level pressure has changed during the past three hours. Trends are often omitted The number provides the 3-hour change in tenths of millibars, while the symbol provides a graphic illustration of how this change occurred. Below are the meanings of the pressure trend symbols:
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