Grade 7 Geography-Climate and Weather Chapter

Grade 7 Geography: Climate and Weather Chapter
elements of weather and climate
1. temperature
heating of earth and atmosphere
solar radiation is the only permanent and
continuous source of heat
process of giving out energy by the sun
insolation
amt of solar radiation received on earth's
surface
received as short waves
does not heat the atmosphere
varies from place to place, depends on
latitude
solar radiation per unit surface area
equator gets more direct sunlight
concentrated over a smaller area
towards poles
sun light strikes at an angle
over a larger area
spherical shape of the earth
evaporation
decreases towards poles
temperature varies between seasons
thickness of atmosphere
equator
passes through less thick atmosphere
towards poles
passes through greater thickness of
atmosphere
length of the day
longer the day the more sunlight received
distribution of land and water
land
heats up and cools down in much shorter
period
absorbs and reflects more heat
water
takes longer time to heat up and cool down
absorbs and reflects less heat
terrestrial radiation
heat is reflected back by the earth's surface
long wave radiations
heats up the atmosphere
measurement
measured with the help of a thermometer
made out of glass tube
mercury in it which expands on heating and
contracts on cooling
scale of a thermometer
celsius
boiling point-100 degrees
freezing point 0 degrees
fahrenheit
boiling point-212 degrees
freezing point-32 degrees
Six's thermometer
max and min temperature
over a particular period
types
daily range
max temp min temp for that day
Average / mean temperature
(max temp + min temp) / 2
annual range
mean temp of the hottest month mean
temp of coldest month
isotherms
lines imaginary lines drawn to connect
location having same temperature
2. atmospheric pressure
force exerted
by vertical column of air
per unit of surface area
air has weight due to great height of
atmosphere
factors effecting
altitude
pressure exerted decreases with increase in
height
decrease by 1 cm of mercury per 110
metres of ascent
highest at sea level
temperature
decreases with increase in temperature
pressure belts
created by (main factors)
unequal heating of
earth
atmosphere
rotation of the earth
typically
high temperature
low pressure
low temperature
high pressure
permanent pressure belts
Equatorial Low (doldrums)
Sub Tropical High
Sub Polar Low
Polar High
measurement
measured with the help of a barometer
simple barometer
contains mercury
difficult to carry
aneroid barometer
does not contain mercury
easy to carry
ranges
high pressure if reading > 76 cm or
1013mb
low pressure if reading <76 cm or 986 mb
measured in
cm of mercury
inches of mercury
millibars (mb)
altimeter
height of an airplane during its flight
barograph
uses aneroid barometer
provides continuous record of pressure
3. humidity
definition
amount of water vapour in the air
related to temperature of air
expressed as
absolute humidity
amount of water vapour
in grams
per cubic metre of air
e.g. 20 gm / cubic metre
relative humidity
ratio of
amount of actual water vapour present in
the air
maximum of water vapour that CAN be
held
AT A SPECIFIC GIVEN TEMPERATURE
expressed as % e.g. 25%
e.g at 25 deg C air can hold 48 gm of water
currently air has 12 gm of water
relative humidity is (12/48) * 100 = 25%
air saturation
fully saturated (cannot hold any more) =
100%
absolute dry air = 0%
measurement
relative humidity is most commonly used
for measuring humidity
saturated air has a relative humidity of
100%
dry air has a relative humidity of 0%
measured with the help of a hygrometer
wet and dry bulb thermometer
4. precipitation
process by which water falls down from the
atmosphere to the earth
no change of state of water, only location -
from atmosphere to ground
occurs when tiny droplets join to form
larger droplets to fall to the ground
types of precipitation determined by
temperature inside and outside the clouds
rain
precipitation in liquid form
most common form of precipitation
hail
precipitation in frozen lumps of ice
form inside tall cumulonimbus clouds
which are warmer at the bottom
freezing at the top
dew
precipitation in tiny water droplets which
condenses on cool surfaces
occurs on calm clear cold nights
snow
precipitation in the form ice crystals
at high latitude and mountain regions
rain is shown by isohyet
imaginary line
passes through places with same rainfall
how is rain shown on a map?
measurement
measured by a rain gauge
rain water collected through funnel for 24
hrs
water measured with a measuring glass
kept slightly above the ground (30 cm)
measured in millimeters(mm)
instrument providing continuous record of
rainfallhyetograph
snow or hail measured by melting them
into water
5. wind
air which moves from places with high
pressure to places with low pressure
characteristics
direction
speed
kinds of winds
winds coming from the east are called
easterly winds
winds coming from the west are called
westerly winds
planetary winds
winds that blow
all the time
same areas of the world
periodic /local/ regional winds
winds that blow
during particular period
day
season of the year
examples
land breeze
sea breeze
monsoon winds
measurement of wind direction and velocity
direction of wind is found with a wind vane
arrow of the wind vane points to the
direction of wind
velocity or speed is found with an
anemometer
measured in km/h
nowadays for recording continuous wind
velocity we use a anemograph
anemograph
records wind velocity continously
6. clouds
definition
large collection of very small droplets of
water or ice crystals
droplets are small and light enough to float
in the air
formed though evaporation and
condensation
classification of clouds
based on shape and height
high clouds
because of cold temp in high altitude these
clouds are made up of ice crystals
prefix-cirro
middle clouds
made out of ice crystals and water droplets
prefixalto
low clouds
made up of water droplets
prefixstrato
diff b/w weather and climate
weather
short term atmospheric conditions
existing in a
given time
given area / particular statuion
can change in a short period
influenced by
temperature
humidity
climate
aggregate over long period of time
day to day weather conditions
refers to a large area
collective effect of all its elements
meteorology
study of
weather
its elements
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