(1) The ratio of the water vapour content of the mixture to the total air content on a mass basis.
(2) It is expressed in grams of vapour per kilograms of air.

i) Isolines are those which join the places of equal values.
ii) Isolines are given different names based on the weather element they represent.

i) The weight of air above a given area on the earth's surface is called atmospheric pressure or air pressure.
ii) The air pressure is measured by Barometer.
iii) The standard air pressure at sea level is 1013.25 mb.

(i) Insolation is the solar radiation that reaches the earth's surface.
(ii) It is measured by the amount of solar energy received per square centimetre per minute.
(iii) Insolation affects temperature.
(iv) The more the insolation the higher the temperature.

1. Weather is the day today conditions of the atmosphere at any place as regards sunshine, temperature, cloud cover, Wind fog condition, air pressure, humidity, precipitation and such other elements.
2. It refers to short periods like a day, a week, a month or a little longer.
3. Weather changes from time to time in a day and one period to the other in a year.
4. The weather is cool in winter and hot in summer.

(1) It lies between the Arctic circle and the North Pole and between the Antarctic circle and the south Pole.
(2) Since it receives the extremely low temperature throughout the year. These regions are covered with show.
(3) So it is called frigid zones.

Reasons:
1. At very high altitudes, atomspheric pressure and available oxygen get so low.
2. Mountain climbers take time to get used to the attitude as the quick move from high pressure to low pressure can cause decompression sickness.

Reasons:
As you increase in elevation, there is less air above you thus the pressure decreases.
As the pressure decreases, air molecules spread out further and the temperature decreases.

Reasons:
The amount of solar radiation, the chemistry of the atmosphere, clouds and the biosphere all affects earth's weather and climate as global climate changes, weather patterns are changing as well."

The horizontal movement of air is called wind.
The winds move from high pressure to low pressure.
Winds get their name from the direction from which they blow i.e, wind blows from south west is called southwest monsoon.
The wind systems are broadly categorized into three as follows.
i) Planetary winds
ii) Seasonal winds
iii) Local winds
Planetary winds:
These Winds are the ones which blow almost in the same direction throughout the year. So, they are called as Permanent or planetary winds.
Eg: Trade winds, Westerlies and polar easterlies.
Seasonal winds:
Seasonal winds are those which change their direction according to season in a year.
They are called as monsoon winds.
These winds blow from sea to land during summer and land to sea during winter.
Local winds:
These winds are the winds blow over a small area only during a particular time of a day or a short period of a year.
Eg: Land breeze and sea breeze.