Today’s class being a continuation of the last class, started with a
brief introduction on – “Local winds”
a) Local winds are winds that blow over a particular
region.
b) There are a lot of local
winds – around 70 to 80.
c) Non-periodical local
winds can be classified as hot winds and cold winds.
HOT WINDS:
1)CHINOOK AND FOEHN
a) Chinook and Foehn - warm winds descend from the mountains Rockies and
Alps (leeward side) respectively, which increases the temperature of that
region.
b) Arrival of these winds melts the snow under these mountain’s
foothills and makes them suitable for grazing. Hence Chinook – also known as
“Snow eater”.
c)These plains in USA are called bread basket of the world/Granary of
the world due to these winds.
d) Chinook being a westerly wind (West to East), Foehn blows from South
to North - “Southernly wind”
2)HARMATTAN – “THE
DOCTOR”
a) Hot, dry winds - arrives from the Sahara Desert, blows towards
equatorial region of Africa.
b) Reduces humidity of that region and prevents the spread of diseases.
c)Dust storms, heat waves may occur in such equatorial places of Africa.
3)SIROCCO
a) Arrives from Atlas Mountains towards Southern coast of Europe.
b) Sirocco winds carry red soil from Atlas Mountains.
c) After reaching southern coast of Europe (Alps), these winds give rainfall
mixed with red soil known as “Blood rain”.
Ø Other warm winds are:
Loo winds – Produce heat waves in India(Delhi)
Khamsin – Egypt region
Santa Ana – Californian region
COLD WINDS:
1)BORA
a) It’s an extremely cold and dry North Easterly wind.
b) Flows along the shore of Adriatic Sea.
c) While passing through the Adriatic Sea, Bora picks up some moisture.
2)MISTRAL
a) Cold local wind – blows in Spain and France.
b) Direction: Northwest to Southeast.
c) These winds adversely affect air navigation, road traffic.
d) Arrival of Mistral winds cause sudden drop in air temperature – below
freezing point.
3)BLIZZARD
a) Violent stormy cold winds.
b) Produce dry snow (less moisture) mostly prevalent in Siberia, Canada,
USA, North and South Polar regions.
Example: Snow in New York, Ontario - caused by Blizzard
HUMIDITY AND
CONDENSATION:
Presence of water vapor in air is called humidity.
When water vapor changes to rainfall – condensation
Relative humidity:
a)
Measures water vapor relative to the temperature of
the air.
b)
It’s a relation between absolute humidity and
humidity capacity.
c)
Expressed in percentage
Absolute humidity: Measure of actual amount of water vapor present
in 100kg of air. Higher the amount of water vapor per kilogram, higher the
absolute humidity.
Humidity capacity: Capacity to hold the water vapor in the air parcel.
FORMULA:
Relative humidity = (Absolute humidity/Humidity capacity) x 100
Ø
Relative humidity decreases with increase in
temperature.
Ø Relative
humidity of the saturated air is 100%.
(When absolute
humidity = humidity capacity)
Ø DEW POINT: The
temperature at which air particles get saturated.
CLOUDS:
a)
Clouds are formed when water vapor (invisible gas)
gets converted into liquid water droplets.
b)
Many water droplets along with dust particles surround
the particular hygroscopic/condensation nuclei and forms cloud.
c)
When the cloud contains excess water droplets, it
falls down as rainfall due to gravity(precipitation).
TYPES OF CLOUDS – FOUR (Based on latitude)
1)
High altitude clouds – above 6km
Cirrus, Cirrocumulus, Cirrostratus
è CIRRUS: Feathery,
fibrous and appears as wisp cotton in blue sky.
Indicates
fair weather, gives brilliant sunsets.
è
CIRROCUMULUS: Appears as white globular masses,
forming a mackerel sky
è
CIRROSTRATUS: Resembles a thin white sheet. Sun and
moon shines through these clouds and forms “halo”.
2)
Middle altitude clouds – 2 to 6km
Altocumulus, Altostratus
è
ALTOCUMULUS: Wooly, bumpy clouds arranged in layers
(appear like waves in blue sky)
è
ALTOSTRATUS: Covers the entire sky due to presence of
ice crystals and water droplets (Fog appearance). The sun is slightly visible.
3)
Low altitude clouds – 0 to 2km
Stratus, Stratocumulus, Nimbostratus
è
STRATUS: Layered clouds that appear to be fog and
produce dull weather. It is a hindrance to air transport as it reduces
visibility, blot out sunlight completely.
è
STRATOCUMULUS: They have a dark honeycomb-like
appearance.
è
NIMBOSTRATUS(Ni-St): It brings moderate rain, snow,
sleet and called as “Rainy clouds”.
4)
Vertical clouds – expand vertically
Cumulus, Cumulonimbus
è
CUMULUS: Cauliflower shaped clouds associated with
convectional process in tropical region.
è
CUMULONIMBUS: Extends around 10-12km vertically. They
are seen in cold front and tropical cyclone region, heavy rainfall accompanied
with lightning and thunder.
Precipitation is the falling of water from the sky in different forms.
FORMS OF PRECIPITATION:
The main form of precipitation includes drizzle, rain, sleet, snow,
graupel and hail.
Fog and mist are not precipitation but suspensions.
Rain: Drops larger than 0.5mm are considered as rain.
Drizzle: They float while following air currents and fall to the ground. These
are fine drops less than 0.5mm.
Snow: It is a precipitation that falls in the form of ice crystals.
Snowfall happens when individual snowflakes fall from clouds.
Graupel: When snow falls in the form of a ball instead of snowflakes.
Sleet (Ice pellets): Precipitation of transparent and translucent pellets
of ice.
Hail: It forms when cold water droplets freeze as soon as they touch dust or
dirt. Hailstones are the size of a small rock (maximum – 15cm and weighs more
than a pound).
Virga: Type of precipitation that begins to fall from clouds, but evaporates
before it reaches Earth’s surface.
WORLD CLIMATIC TYPES: (11 types)
1)Hot wet equatorial climate - Equatorial rain
forest in Asia
2)Monsoonal type – Southwest monsoon forests in Asia
3)Sudan type – Savannah/Tropical Grasslands in Africa & Asia
4)Hot Desert type – Sahara Desert, Thar desert
5)Mediterranean type – winter rainfall & dry summer
6)China type – Warm wet forests Eastern margin
7)Steppe type – Prairies in North America
8)Wester margin pressure type – Deciduous forests, all
4 seasons seen.
9)Central continent Siberian type (Taiga climate) – Evergreen, coniferous
forests. Absent in Southern Hemisphere.
10)Eastern Margin Laurentian type – Mixed forests. Cold
ocean currents like Labrador currents may flow.
11)Arctic or Polar type: Tundra vegetation, mosses and lichens. Seen in both
Southern and Northern Hemisphere.
CREDITS: LEO PRANEETHA
