METEOROLOGICAL DATA

METEOROLOGICAL DATA

1. Temperature: air temperature recorded by thermometers housed
by open lovered box, about 1.25 m above ground.
Protection is necessary from precipitation and the
direct ray of the sun.

*Max. and Min. temperature thermometers are usually used.
*Temperature measured in degree Celsius.
Mean Temp. of the day=(Max. Temp.+Min. Temp.)/2
Mean Temp. of the Month =(? of mean Temp. of all days)/No. of days
Mean Temp. of the Year =(? of mean Temp. of all Months)/12
*Temperature decreases with height at a rate of (5.6 C?) per (1000m)
height increase.



2. Radiation:is a form of energy.

Radiation
Radiometers: are used to measure radiation.
Radiation: is measured in Langley per min. = cal.cm.min.

3. Wind:
Wind speed measured by anemometer.
Wind direction measured by vane.
Because of the frictional effects of the ground, wind speed increases with height:
(u/u0)=(z/z0)n

Where:
U0= wind speed at height zo,
U=wind speed at higher level z,
n=exponent
=0.15

4. Humidity:






A. Absolute Humidity: the mass of water vapour per unit volume.

B. Relative Humidity: the rate particle pressure to the saturated vapoure pressure at the same temperature expressed as a
percentage at its existing temperature to
absorb further moisture.

h= (e/es)*100
where:
h= relative humidity, (%);
e= actual vapour pressure;
es= saturation vapour pressure.


Dew Point: the temperature at which the water vapour in a given sample
of air becomes saturated.









Relative Humidity Measurement:

1. By Using Metal Container: the container is cooled until the surface of the container becomes clouded with condensed moisture. Temperature of the air and container are measured.

Example:
Air Temp. =20 c?, Container Temp. = 10 c?
Solution:
From table:
For t=10c? es=9.2 mmHg
For t=20 c? es= 17.53 mmHg
h= (e/es)*100
= (9.2/17.5)*100
= 52.5 %

2. By using a Psychrometer:














e= ew-? (td-tw)

Where:
ew=saturation vapour pressure corresponding to tw;
? = Psychrometer constant
=0.66 mbar/c?
=0.485 mmHg/c?

h= (e/es)*100