Weather and Climate

Weather is defined as the state of air temperature, atmospheric pressure, humidity, precipitation and winds in the atmosphere at a given place and time. The conditions of different elements of weather keep changing from time to time and from place to place. Thus, the change in weather is a continuous phenomenon. Climate is defined as the average overall condition of the air temperature, atmospheric pressure, humidity, precipitation and winds over a large region and for a long period of time. The climate of a place remains more or less the same year after year.

Solar radiation — The sun radiates heat and light energy. This is called solar radiation.

Insolation — The amount of solar radiation received by the earth's surface is called insolation.

Terrestrial radiation — The earth's surface absorbs maximum insolation during the day. At night, the heat which was absorbed during the day, is radiated back. This is called terrestrial radiation.

The atmosphere exerts its weight as pressure on the earth's surface. This is called atmospheric pressure.

The variations in the atmospheric pressure on the earth's surface is due to:

1. Temperature of the air
2. Density of the air
3. Height of a place above the mean sea level
4. Amount of moisture present in the air.

Three differences between planetary and periodic winds are:

The different forms of condensation are:

1. Dew — In winters, the moist air comes in contact with cold surfaces and the water vapour condenses on them. The water droplets thus formed are called dew.
2. Frost — If the temperature falls below freezing point, tiny ice crystals are formed in place of water droplets. This is called frost.
3. Clouds — When water droplets condense around dust or smoke particles in the air, the mass thus formed is called cloud.

The different forms of precipitation are:

1. Rain — When precipitation occurs in the form of water drops, it is called rain.
2. Drizzle — It is a light continuous rainfall in which the rain drops are of very small size.
3. Hail — It is a kind of solid precipitation consisting of balls or irregular lumps of ice, each of which is called a hailstone.
4. Snow — When air temperature is below freezing point, the water vapour present in clouds condenses to form tiny ice crystals called snow.
5. Sleet — When snow and rain fall together, it is called sleet.

When precipitation occurs in the form of water drops, it is called rain and it is the most important form of precipitation. Rainfall can be classified into three types. They are:

1. Orographic rainfall
2. Convectional rainfall
3. Cyclonic rainfall

Convectional rainfall — When air comes in contact with the hot surface of the earth, it gets heated, becomes light and rises in form of air current. After the warm air current reaches the upper layers of the atmosphere, it expands and loses heat. This leads to condensation and the formation of cumulus clouds. These clouds give sudden and heavy rainfall accompanied by thunder and lightning. Convectional rainfall occurs every day in the equatorial region.

The frigid zone lies between the Antarctic Circle (66.5° S) and the South Pole (90° S) in the southern hemisphere.

The atmospheric pressure is measured in Millibar(mb).

The sea breeze is a periodic wind.

The cirrus clouds have hair-like appearance.

The ice pellets that fall with rain are called hailstones.

At night, due to radiation, land is cooler than the adjoining sea. This leads to the development of a high pressure area over the land and the cooler wind from the land blows towards the sea. This wind is called the land breeze.

When a mountain comes in the path of moisture-laden winds, moist air ascends along the slope of windward side which leads to cooling followed by condensation and precipitation. On the leeward side of the mountain, the air descends and becomes warmer. Thus, the leeward side gets less rainfall and is known as the rainshadow area.

The three elements of weather are:

1. Air temperature
2. Atmospheric pressure
3. Humidity

True

The incoming solar radiation is called insolation .

An area of low pressure is created by warm air.

The pressure belts on the earth are:

1. Equatorial low pressure belt
2. Subtropical high pressure belts
3. Sub-polar low pressure belts
4. Polar high pressure belts

The horizontal movement of air is called wind .

The trade winds are planetary winds.

False

Corrected Statement — The land breeze blows during the night.

The amount of water vapour present in air is called humidity.

Cumulonimbus is a rain-bearing cloud.

terrestrial radiation

three

Africa

drizzle

Convectional

False

Corrected Statement — The torrid zone receives maximum insolation.

False

Corrected Statement — The atmospheric pressure is the highest at the mean sea level.

True

True

False

Corrected Statement — The frontal rainfall is common in the belt of the westerlies.