Transcript Lecture 2

Lecture 3
Weather forecasting
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.
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.
The basic units are as follows:
Variable
Unit
Abbreviation
for unit
Length
meter
m
Mass
Kilogram
kg
Time
second
s
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.
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:
variable
Unit
Abbreviation For unit
Length
meter
m
Mass
ton
t
Time
second
s
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
1o latitude =
( kts )
111.137 km
Temperature
oC
= 5/9 * ( oF – 32 )
K
= oC + 273.15
( C degree centigrade, F degree Fahrenheit , and K Kelvin )