Weather and Climate
1. Answer the following in one or two words.
a. The instruments that measures wind speed.
= Anemometer.
b. The instruments that measures humidity in the air.
= Hygrometer.
c. The scientific study of weather conditions.
= Meteorology.
d. The wooden shelter in which thermometers are kept.
= Stevenson's Screen.
e. The difference between the maximum and minimum temperatures in a day.
= Diurnal Temperature.
f. The unit of measurement of atmospheric pressure.
= Millibars.
g. The height of the mercury column at sea level.
= 76 cm.
h. The unit in which rain and snow are measured.
= cm or ml.
i. Lines on maps joining places having the same temperature.
= Isotherms.
j. Lines on map that join places having the same amount of rainfall.
= Isohyets.
2. Give reason to explain each of the following.
a. Equatorial areas are the warmest parts of the Earth.
= Lower altitudes closer to the Equator are generally warmer than the higher altitudes closer to the poles. Direct rays of the Sun travel shorter distance through the atmosphere and hence heat up a region more than the slanting rays, which are longer. The slanted rays of the Sun travel a longer distance through the atmosphere. The heat is spread over a large area, thus making these places less hot.
b. Deserts have very hot days and equally cold nights.
= During day time, the sand absorbs heat and the layer of air close to the ground becomes hotter during day time. At night, the air close to the surface of the ground go up taking all the heat released by the sand. The night at desert become very much cold.
c. Winter in Delhi is much more harsh than that in Chennai.
= Places close to the sea enjoy equable temperature, while those away from the sea experience extremes of temperature. This explains why winter in Delhi is much more harsh than in Chennai. As Chennai is very close to the sea and Delhi is far away from sea.
d. Low pressure is associated with stormy weather.
= Low pressure is usually associated with unsettled, and sometimes, stormy weather as it causes inflow of winds from surrounding high-pressure areas.
e. Atmospheric pressure influences movements of wind.
= Wind is guided by the distribution of atmospheric pressure. Wind always tends to blow from a region of high pressure to a region of low pressure.
f. Atmospheric pressure decreases with altitude.
= As we reach higher altitudes, pressure drops as the air becomes thinner or less dense.
g. Winds deflect from their original path in both hemispheres.
= Wind tends to deflect to the right of its path in the northern hemisphere and to the left of its path in the southern hemisphere. This deflection of the wind is controlled by the Coriolis force, which develops due to the rotation of the earth.
h. Humidity in air increases in summer.
= Higher humidity is experienced during summer as warm air expands and can hold more moisture.
i. Wind vane should not be placed over buildings and trees.
= Wind vane is a simple instrument used to determine the direction of wind. It should be placed in open areas where the wind is not blocked by buildings or trees.
j. Satellite images play a significant role in modern times.
= The artificial satellites which humans have set in orbit around the earth send images from which we can get the predictions of weather conditions.
3. Answer the following as directed:
a) Define the following:
i) Weather:- Weather is the atmospheric condition of a certain place at a particular point of time.
ii) Climate:- Climate refers to the sum total of the average weather conditions that prevail at a particular place over a long period of time.
iii) Atmospheric pressure:- Atmospheric pressure is the pressure of the column of air at one point on the Earth's surface.
iv) Humidity:- Humidity is the amount of moisture content in the air.
b) How is climate different from weather.
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c) Explain how the following affect the temperature of the place:
= i) Latitudinal position:- Lower latitudes closer to the Equator are generally warmer than the higher latitudes closer to the poles.
ii) Altitude:- The higher the altitude the lower the temperature.
iii) Distance from the sea:- Places close to the sea enjoy equable temperature, while those away from the sea experiences extremes of temperature.
iv) Ocean current:- Warm ocean currents increase the temperature of coastal areas, while cold currents lower the temperature.
v) Wind:- Winds coming from colder regions lower the temperature while those coming from the warmer region make the temperature higher.
d) Enumerate the chief elements of weather.
= The chief elements of weather are - temperature, atmospheric pressure, wind, humidity, precipitation, cloud cover, sunshine.
e) Explain the factors that determine the temperature of a place.
= The following are the factors that determine the temperature of a place -
i) Difference in the latitudinal position:- Lower latitudes closer to the Equator are generally warmer than the higher latitudes closer to the Poles.
ii) Altitude:- The higher the altitude the lower the temperature.
iii) Distance from the sea:- Places close to the sea enjoy equable temperature, while those away from the sea experience extremes of temperature.
iv) Ocean currents:- Warm ocean currents increase the temperature of coastal areas, while cold currents lower the temperature.
v) Wind:- Winds coming from colder regions lower the temperature while those coming from the warmer regions make the temperature higher.
vi) Vegetation cover:- Forest areas provide shade and bring down the temperature.
f) Name the factors that influence atmospheric pressure. Explain in brief.
= The factors that influence the atmospheric pressure are - altitude, temperature, humidity, rotation of the earth.
*As we reach higher altitudes, pressure drops as the air becomes thinner or less dense.
*Pressure is closely related to the temperature of a place. If temperature becomes higher, the air expands and raises up.
*Wet air exerts less pressure than dry air.
*The rotation of the Earth deflects winds and either causes them to pile up to form high pressure zones or scatters them to form low-pressure zones.
g) State the conditions when the humidity is higher in the air.
= i) Warm air holds more moisture than cold air. So humidity is higher in the lower altitudes where the air is warmer than in the higher latitudes.
ii) Humidity is also higher in coastal areas than in the interior with continental location.
iii) Moreover, higher humidity is experienced during summer as warm air expands and can hold more moisture.
h) How does rainfall occur?
= Rainfall occurs due to the condensation of water vapour into tiny particles of water. These droplets eventually coalesce to form larger particles, which join to form clouds. When clouds becomes too heavy, they con not remain suspended in the air and thus come down as rain.
i) How clouds are formed? Name the four main types of clouds and explain their characteristics in brief.
= When the dew point of air has been reached, further cooling leads to the condensation of water vapour around small particles of dust, which form the condensation nuclei. These minute particles of water vapour eventually form clouds.
The four main types of clouds are - Cirrus, Cumulus, Stratus and Nimbus.
Cirrus clouds:- These are high level clouds. They are thin and wispy. They look like the tail of a horse. So they are called 'mare's tails'. They are seen during fair weather.
Cumulus clouds:- These are low-level and fluffy clouds. They look like the head of a cauliflower. They are seen during fair weather.
Stratus clouds:- These are low-level, horizontal layering clouds with grey and white colour. They are thick enough. They cause drizzle and snowfall.
Nimbus clouds:- These are the dark rain clouds. These are the 'thunderhead' that brings storm, hail and tornadoes, and also precipitation.
j) What is weather forecast? What is its significance?
= Weather forecast is the prediction of weather conditions issued by the meteorological department of a country on the basis of the data collected by the use of various instruments and more importantly from images sent by the artificial satellites.
The significance of weather forecast are -
i) It helps to guide air traffic.
ii) It helps the farmers to prepare for any changes in weather conditions.
iii) Military operations, geographical expeditions, important sports events, all take into consideration weather forecasts and recordings.
iv) It also helps to avert damages caused by natural climatic disasters such as hurricanes and cyclones. Climate scientists play an important role in alerting people of extreme weather conditions.
k) What is meteorology? Who are meteorologists?
= The scientific study of weather conditions is called meteorology.
Scientists who collect these data by using various instruments to record and prepare weather reports are known as meteorologists.
l) Name the two scales in which temperature is measured. State the boiling point and the freezing point of water in each of the scales.
= Temperature is measured in two types of scales - Fahrenheit and Celsius.
The freezing point and the boiling point of water in the Fahrenheit scale is 32℉ and 212°F, respectively, while in the Celsius scale it is 0°C and 100°C respectively.
m) Explain how the maximum and minimum temperature of a day are measured?
= The maximum temperature of a day is recorded in a Six's maximum and minimum thermometer between 1 pm and 3 pm.
The minimum thermometer records the minimum temperature reached during the day between 4 am and 6 am.
n) Why Stevenson's screen used?
= The maximum and minimum temperatures that we see in daily news papers or TV are shade temperatures. These are recorded by placing the the thermometers in a standard meteorological shelter for instruments known as Stevenson's screen
o) Why is rain gauge placed below the ground?
= The rain gauge is placed below the ground so that only 30 cm of it remains above the ground. This prevents splashing and evaporation of water collected in the jar.
p) How many parts does a wind vane have? State their uses.
= A wind vane consists of two parts -
A pointer mounted on a pole that moves freely and points to the direction from which the wind is blowing.
A fixed marker, showing the cardinal directions namely north, south, east and west, which helps to determine the direction of the wind.