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Appendix 2: SI Units,
Constants and Conversions
Constants
a - average radius of the Earth: 6.37 x 106m
cp - specific heat at constant pressure: 1004 J kg-1
K-1 (for dry air);
1952 J kg-1 K-1 (for water vapor)
cv - specific heat at constant volume: 717 J kg-1
K-1 (for dry air); 1463 J kg-1 K-1 (for
water vapor)
g - effective gravity (gravitational acceleration plus centrifugal
effect): 9.81ms-2 at sea level at equator
g*o - average gravitational acceleration at sea level:
9.85 ms-2
G - gravitation constant: 6.673 x 10-11 Nm2kg-2
M - mass of the Earth: 5.9742 x 1024 kg
Md - average molecular mass for dry air: 28.966g mol-1
Mv - average molecular mass for water vapor: 18.016
g mol-1
R* - universal gas constant: 8.314 J mol-1 K-1
Rd - gas constant for dry air: R*/Md
= 287 J kg-1 K-1
Rv - gas constant for water vapor: 461 J kg-1
K-1
Ω - angular velocity of the Earth’s rotation: 7.292 x 10-5
s-1
 - kinematic viscosity:
1.5 x 10-5 m2s-1 (Earth atmosphere),
1.0 x 10-6 m2s-1 (Earth ocean)
π - pi: 3.14159
Units
Primary SI Units (Système International d’Unités)
Length: Meter (m)
Mass: Kilogram (kg)
Temperature: Kelvin (K)
Time: Second (s)
Derived Units
Force: Newton (N): = kg m s-2
Pressure: Pascal (Pa): = N m-2 = kg m-1 s-2
Energy: Joule (J): = kg m2 s-2
Other Commonly Used Units in Atmospheric Science
Pressure: Millibar (mb): 1 mb = 100 Pa = 1 hPa
Pressure: hectoPascal (hPa): 1 hPa = 100 Pa = 1 mb
Temperature interval: degree Celsius (°C): 1°C = 1°K
Temperature: Celsius degrees (°C): °C = K - 273.15
Temperature: Celsius degrees (°C): °C = (°F-32°F) / (1.8
°F °C-1)
Temperature: Fahrenheit degrees (°F): °F = [°C x (1.8 °F
°C-1)] + 32 °F
Wind Speed: Knots (kts): 1 kt = 0.51 ms-1
Wind Speed: Miles per hour (mph): 1 mph = 0.48 ms-1
Wind speed: Kilometers per hour: (kph): 0.28 ms-1
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