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 Cº) per (1000m)
height increase.
2. Radiation:is a form of energy.
Radiation
Incoming short-wave
radiation from the sun and
sky.
Reflected short wave and
long-wave from the earth.
Radiometers: are used to measure radiation.
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:
Nitrogen 80%
Oxygen 18%
Carbon dioxide
Air
Water Vapor
Other Gases
A. Absolute Humidity: the mass of water vapor per unit volume.
B. Relative Humidity: the rate particle pressure to the saturated vapor
pressure at the same temperature expressed as a
percentage at its existing temperature to
absorb further moisture.
h= (e/es)*100
Bar=105 N/m2
mbar=10-3 bar
=100pas.
=0.75 mmHg
bar=100kpas.
where:
h= relative humidity, (%);
e= actual vapor pressure;
es= saturation vapor pressure.
es (mbar) or (mm Hg)
Dew Point: the temperature at which the water vapor in a given sample
of air becomes saturated.
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
-2
es
es
1
2
P(e,t)
-20 -15 -10 -5
0
5
10 15 20 25 30 35 40
t(c)
9
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 cº, Container Temp. = 10 cº
Solution:
From table:
For t=10cº es=9.2 mmHg
For t=20 cº es= 17.53 mmHg
h= (e/es)*100
= (9.2/17.5)*100
= 52.5 %
2. By using a Psychrometer:
tw
td
Dry-bulb thermometer
Wet which
dipping in water
Wet-bulb thermometer
e= ew-γ (td-tw)
Where:
ew=saturation vapour pressure corresponding to tw;
γ = Psychrometer constant
=0.66 mbar/cº
=0.485 mmHg/cº
h= (e/es)*100