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Current Category » Agricultural Meteorology

Temperature Variation

Air temperature at any location is changes during a day, week, month, year or for any period.  On this basis it is classified as-

A Periodic variation.
1. Annual temperature variation or Annual temperature cycle.
2. Diurnal temperature variation or Daily temperature cycle.

B. Horizontal variation

C. Vertical Variation.

A) Periodic Temperature Variation:
The temperature continuously changes during a day, week, month, year or any period and this change is called periodic temperature variation.Periodic temperature variations are -
1. Annual temperature variation or Annual temperature cycle:
The annual temperature Variation gives rise to seasons i.e. summer and winter.  The annual temperature range varies greatly from place to place.  It reflects the daily increase in insulation from mid-winter to mid-summer and decrease in the same from mid-summer to mid-winter summer and decrease in the same from mid-summer to mid-winter usually there is a temperature lag of 30 to 40 days after the period of maximum and minimum insulation

In the Northern hemisphere winter minimum occurs in January and summer maximum in July and vice versa in the southern hemisphere.  The smaller range occurs near equator and largest in high latitudes.  The difference between the highest and lowest temperature for a given period is known as temperature range.  In the northern hemisphere it is summer from 21st of March to 22nd of September and winter from 23rd September to 20th March and vice-versa in southern hemisphere.

2. Diurnal Temperature Variation or Daily Temperature Cycle.
The Diurnal Temperature Variation give rise to daily maximum and Minimum temperatures.

From the sun-rise, sun energy continuously supplied and the Temperature continuously rises, recording maximum at about 2.00 to 4.00.P. m. though the maximum amount of solar radiation is received at the solar None (i.e. 12.00 hrs). This delay in occurrence of maximum temperature is Caused by gradual heating of the air by convective heat transfer from the Ground which is known as thermal lag or thermal inertia.
Similarly minimum air temperature occurs shortly offer sunrise due to lag in transfer of heat form the surface to the air / space.

B Horizontal Temperature Variation:
The rate of change of change of temperature with a horizontal distance is known as Temperature Gradient.

Maximum solar energy is received in equatorial region and therefore and Therefore highest temperatures are observed in equatorial region. As the latitude Increases the solar energy received on the earth correspondingly decreases and so also temperature decreases with increase in latitude being lowest on the pole.
The Sum crosses the equator twice in a year therefore two maxima And two minima are observed in annual cycle. Outside this zone only one Maxima and one minima is observed.
Isotherm is defined as the line on the weather map joining the places of equal temperature.
C.Vertical Tempe ration Variation:
Vertical temperature variation does not show uniform behavior and The atmosphere can be divided into four spheres.
1. Troposphere - Temperature decreases from 150 C at earth surface up to - 60 0C at 11 km height.
2. Stratosphere - Temperature increases from -600C to 00C at 50km Height.
3. Mesosphere   - Temperature fall and reaches about -900C at 80 km Height.
4. Thermosphere- Temp increases. Due to absorption of solar radiation by
Atomic oxygen, up to 9500C at 350 km height and 17000C at undefined upper Limit.        


Current Category » Agricultural Meteorology