1. Lecture 3 Weather forecasting

2. Units and Variables It is important to express observational data and derived meteorological variables in a standard measurement – unit system, so that they can be understood by every one.

3. The MKS System the system of units endorsed by the American Meteorological society is called the SI ( Le Système International ) or International System of Units. It is an MKS system.

4. The basic units are as follows: VariableUnitAbbreviation for unit Lengthmeterm MassKilogramkg Timeseconds

5. The derived unit of Pressure in this system take the form Force / area = mass x acceleration / area = = kg m -1 s -2 = Pa where Pa is the Pascal, and 1000 Pa = 1 kPa = 10 hPa Where kPa is the kilopascal and hPa is the hectropascal.

6. The MTS System is a system of units hardly used at all, even though it is easier to use than the MKS system. The basic units are as follows: variableUnitAbbreviation For unit Lengthmeterm Masstont Timeseconds

7. Other Useful conversion factors The unit of Velocity is usually given in Knots ( nautical miles per hour) or meter per second. 1 meter = 3.2808 feet ( ft ) 1 m s -1 = 1.94 knots ( kts ) 1 o latitude = 111.137 km Temperature o C = 5/9 * ( o F – 32 ) K = o C + 273.15 ( C degree centigrade, F degree Fahrenheit, and K Kelvin )