- Types of clouds:
- High clouds:
- Cirrus: indicate fair weather and good sunset. Look fibrous or wispy.
- Cirrocumulus: Appear like white globular mass.
- Cirrostratus: resemble thin white sheet or veil.
- Medium clouds:
- Altocumulus: indicate fair weather.
- Altostratus; dense, grayish clouds
- Low clouds:
- Stratocumulus: rough, bumpy cloud
- Stratus: Brings dull weather with light drizzle.
- Nimbostratus: Rain clouds. It also brings snow or sleet.
- Clouds with great vertical height:
- Cumulus: Typically seen in tropical, humid regions.
- Cumulonimbus: Thunder cloud brings rain with thunder and lightning.
Phenomenon caused by High Humidity
Haze: It is caused by smoke or dust in industrial areas or when there is unequal refraction of light in air of different densities in lower atmosphere. This is seen in regions of low humidity [Relative humidity < 75%].
Mist: It occurs in areas of high humidity where relative humidity is 75% +. Condensation of water vapor in air causes small water droplets to float about in lower atmosphere forming clouds.
Fog: These are formed when water vapors condense on smoke or dust particles. A dense ground cloud is formed reducing visibility. Although fogs are seen in tropics and temperate areas, they are denser in high and middle latitudes than tropics. Fogs are more common over seas than land and prevalent in coastal areas.
Haze and Mist occur more commonly in dry interiors.
Clouds and their types
cumulus are fair weather clouds.
vertical development are cumulonimbus which is stormy clouds
and an indicator of cyclonic heavy rainfall.
Fig 1: Types of clouds
Rainfall and its types
The term "rainfall" is used to describe
precipitation in the form of water drops of sizes larger than 0.5
mm. Other forms are snow, drizzle, glaze, sleet and hail.
cyclonic - Seen in temperate regions and is
reason for rainfall during winters there. Warm air
rises over cool air and is cooled due to it. this leads to
condensation and rain.
- Hot air formed due to sun's heating effect on
oceans rises upwards and condenses. This rain is seen in equatorial
- This is seen where moist air is forced to climb a mountain barrier. The windward sides of mountains see this rainfall. It is also called “Relief rain”. The leeward side of mountain however doesn’t receive much rainfall and are called “Rain shadow regions”. E.g:
Fig 2: Types of rainfall
Pressure systems of the world:
is divided into four pressure belts. Belts aren’t continuous but
pockets of low or high pressure. Low pressure is created by
heat and rising movement of air. High pressure is created by
low temperature and descending air.
high pressure belt
low pressure belt
pressure belt OR inter tropical convergence zone:
direct insolation leads to low pressure as the air is
heated. The heated air rises upwards and condenses to bring
evening rain.: The region along the equator and within 5 degree North and South is the equatorial low pressure belt is called Doldrums.
rain is common throughout the year in equatorial areas.
with slow winds.
high pressure belt:
above the equator moves towards the poles but due to Coriolis
force it is deflected and its path increases. The air loses
energy and cools down; it descends and creates a high pressure
low pressure belt:
air from the poles moves to the equator but the warm air of the
sub tropic high pressure zone collides with it. The warm air
rises here and creates a low pressure zone. About 30 degree North and South is the area of descending air currents or wind divergence or anticyclones. These are the horse latitudes. 60 degree North and South are the temperate low pressure belts and zones of cyclonic activity. Then at 90 degree north and south are the polar high pressure belts.
from the low pressure sub polar belt descends here creating high
pressure. Also the low temperature cools air.
Fig 3: Pressure belts
blow in the same direction throughout the year. But due to
Coriolis force their direction is deflected. Winds tend to blow from high pressure belts to low pressure but due to Earth’s rotation are deflected to right in north hemisphere and left in south hemisphere - “Ferrel’s law”. Coriolis force to is absent at the equator but increases towards the poles. Due to large expanse of oceans in the Southern hemisphere compared to North, planetary winds blow harder.
from sub tropical high to the equatorial low. They are deflected
from east to west due to Coriolis force.
winds blow from east to west. But they lose moisture as they
pass over the continents. The western margins of the continents
don’t receive rain. Hence deserts are formed called trade wind
reason for deserts is they are on contact with cold currents
that reach the western margins of the desert. These cold
currents create a desiccating effect on the trade winds.
from sub tropic high pressure zone to sub polar low pressure
zone. Their direction is from west to east due to Coriolis
force. Due to absence of land mass in southern hemisphere they
have high velocities.
Polar Regions to sub Polar Regions. Direction is east to west.
monsoon winds in Indian subcontinent. The easterlies blow from
north to south in winter and south to north in summer over some
is earth tilted axis which causes apparent movement of the sun
in the north during June - July. This causes shifting of the low
pressure belt or ITCZ to the north.
rainfall to India.
morning the sea gets heated slower than land. The land remains
under low pressure and sea is high pressure. Thus we get sea
breeze. In the night the land cools faster than sea due to lower
specific heat. This creates low pressure over sea and the high
pressure over land. Hence we get land breeze.
use this system to move from land to sea and back.
has a different situation than at land. Here there is high
pressure over the equator and low over the poles. They blow from
west to east “Westerlies”. In these winds there are strong,
narrow band of winds called Jet Streams [speed – 300
Fig 4: Jet streams
Fig 5: Cyclone map
Movement from east to west. They are created due to thermal
conditions. Their path is difficult to predict. They have winds
of high speed but quickly dissipate on land. They mostly affect
of Bengal, western pacific i.e. Philippines etc and Gulf of
Mexico when formed over these areas they make
landfall hence the coastal parts of these areas are largely
regions where they are formed but can’t make landfall are
Arabian sea, east coast of Africa, west coast of Mexico and
south west USA.
in the sea surface temperature causes air to warm and rise. This
air also has moisture. The low pressure zone at sea level is
where air converges.
As air moves upwards the
Coriolis force causes spiral movement. After reaching the top it
of above causes a cyclone where a high pressure eye is
surrounded by low pressure region. But as this cyclone is
fueled by moisture when it makes landfall it dissipates
quickly. This is due to being cut off from moisture.
Movement from west to east. They are formed due to movement of
air [rising]. They have winds at 40-50 mph. They don’t dissipate
quickly and cause destruction.
located on the western coast of USA and Europe. They are
influenced by the Westerlies.
Score more than 80% marks and move ahead else stay back and read again!