Global pressure belts - class-IX

Areas with low pressure do not have much of the wind, a characteristic of the Equatorial low-pressure belts and the circumpolar high-pressure belts. Hence, they have a dry weather. 

Trade winds are result of combination of both convection of air currents and rotation of earth.

Due to warmer air at equator the process of convection takes place where heat is transferred to the lower heat areas from higher heat areas.

Thus warmer winds are moved towards the each pole respectively from equator and due to rotation of earth these winds fall back to the equator.

These winds blow nearly constantly and always in the same direction. The trade winds have been used for many centuries to decrease the transit time of ships traveling around the world.

Atmospheric pressure is the weight of atmosphere pushing down on itself.

Earth exerts gravitational force that tends to pull the gas molecules present in the atmosphere towards its center. This creates atmospheric pressure.

Atmospheric pressure is sometimes expressed in terms of the number of inches in a column of Mercury

Atmospheric pressure is measured with a barometer.

• Winds originate due to the pressure gradient i.e. winds travel from higher pressure region to the lower pressure region. The more the pressure gradient, the greater will be the wind speed and vice-versa. Hence option C is correct.
• Rotation of the earth may affect wind direction eg Ferrel's law, but they do not govern the wind speed.

Sub-Tropical high pressure belt,

Equatorial trough of low pressure is the zone of convergence of trade winds blowing equatorward from the sub-tropical belts of high pressure in the northern and southern hemisphere. Within this belt the winds are light and variable with frequent calms. That is why this belt is also known as doldrums.

True,

Ferrel's law states that due to the Coriolis effect caused by the Earth's rotation, winds are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

The trade winds blow equatorward from the sub-tropical belts of high pressure in the northern and southern hemispheres. Within this belt, the winds are light and variable with frequent calms. That is why this belt is called the doldrums. The word doldrum means the zone of no wind.

Subtropical high-pressure belt,

 The sub tropical high pressure belts exists at 30 degree north latitude and 30 degree south latitude.The polar high pressure belt experiences severe cold throughout the year. As a result,the air remains chilled under the extreme cold that prevails over the poles.

The sub-polar low-pressure belt (around 60-65 degrees latitude) is created where warm westerlies meet cold polar easterlies, causing the warmer air to rise and creating a low-pressure zone.