in this video we'll try and understand
water easterlies westerlies subtropical
highs and sub polar lows actually this
topic is part of class 11 chapter 10
atmospheric circulation and weather
systems now there's going to be a full
video on that chapter but in this video
I wanted to particularly discuss about
atmospheric circulation and its patterns
and I believe it needs a separate video
so here we go now there are these two
months in a year that you need to
specifically remember January and July
because during the month of January the
northern hemisphere has the ongoing
winter season and I think you can easily
figure that out because in the month of
December and January it's winter and
chilly now what that means is the
northern hemisphere of Earth is tilted
away from the Sun and that makes these
southern hemisphere exposed more towards
the sunrays likewise in the month of
July the northern hemisphere witnesses
summer season now this time the southern
hemisphere of the earth is tilted away
from the Sun and that makes the northern
hemisphere exposed more towards the sun
rays now whether it is January or July
one thing you must keep in mind is that
near the equator the sea-level pressure
is always low and the areas known as
equatorial low and the reason behind
that is however the earth moves or
rotates the equator receives insulation
all throughout the earth and that makes
the equatorial region warm throughout
the year and warm temperature makes the
surrounding a normal as we know warm a
rise and that leads to a low pressure
zone alright to remember this point okay
let's move from equatorial region to 30
degrees north and 30 degrees south now
these two regions are called subtropical
region it's a tiny little place between
tropical and temperate zone let me first
tell you what this region is about and
then I'll explain so this region has a
lot of high pressure areas and that's
how it is known as the subtropical highs
ok now let me explain why this region is
called subtropical high the reason
behind that is Hadley cell to understand
Hadley cell you will have to look at
this illustration the Sun is the
ultimate source of energy that drives
the Earth's weather
now this fact should be absolutely clear
to you most of the energy of the Sun
reaches the equatorial region and the
least energy reaches the poles I'm
talking about northern South Pole now if
there is a lot of insulation at the
equatorial region then obviously it will
make that place warm
similarly northern South Pole is school
because minimum solar energy reach there
if I have to say this concept in some
other way then just remember this as we
go away from the equator towards the
poles temperature drops I hope so far
everything is clear and you are able to
follow up now let's try to understand
the atmospheric circulation pattern
because this is what redistributes heat
on earth and makes life possible
alright so moments back I told you that
however the earth moves or rotates the
equator receives insulation all
throughout the year and that makes the
equatorial region warmth water and we
know that warm air expands and rise now
having said that the warm air at the
equatorial region rises and moves
towards the poles that's why you will
find clouds and rain in the tropical
region and you will also find that
tropical region is moist now the air
rising near the equator goes up to a
height of 10 to 15 kilometers above the
surface and starts moving towards the
poles while going on its way to the
poles it comes down or sinks at the
subtropical region now this pattern of
atmospheric circulation is called Hadley
cell it is named after George Hadley he
was a famous meteorologist who proposed
this mechanism anyways as the air moves
towards the subtropics it comes down
over the oceans and that creates a high
pressure zone because you see in the
northern hemisphere these high pressure
systems are located over the North
Pacific and North Atlantic Ocean the
famous Bermuda Triangle is also located
at the North Atlantic Ocean and that's a
high pressure zone so if anyone asks you
the secret of Bermuda Triangle this is
the possible logical reason so the air
that moves from the equator towards
subtropical region that air is warm and
then you also have to understand that
there is cold air that is flowing toward
still low latitudes from poles because
as I said
the atmospheric circulation
redistributes the heat that means cold
and warm air keeps moving here and there
when cold air from the poles arrive
towards the low latitude and then we
know that warm air from equatorial
region moves towards the pole what do
you think will happen cold and warm air
will collide and they will collide at
mid latitude that is the subtropical
region always remember this point when
warm air meets cool air that is when
turbulence occurs it's a highly unstable
situation for pilots and aviation
industry the air will converge meaning
it will sink now I want you to think for
a while when the warm air moves up at
the equatorial region it reaches the end
of troposphere now at the end of
troposphere you will find thin layer of
cool air because always remember air is
warm at the bottom of the troposphere
that is near the ground level and as the
altitude increases it gets colder
so this warm air has to deal with the
cool layer of the troposphere and the
cool air from the poles you see it's a
two-on-one situation it makes it all the
more easier for the warm air to sink
over the subtropical region and become
subtropical high because converging
means sinking and that's what creates a
high pressure belt anyways just keep in
mind warm air and cool air collides and
sinks at this subtropical region giving
rise to subtropical high another
important point to remember is when air
sinks and comes down closer to the
surface it again gets divided into two
parts one part of the wind heads back to
the equator and the other goes towards
the pole just keep this in mind I'll get
back on this in a while now let's go
beyond subtropical high in between 50 to
70 degree in the northern hemisphere and
50 to 70 degree in the southern
hemisphere this region also lies at the
border of temperate and frigid zone and
it is a low pressure belt okay and
that's how it is known as this subpolar
low nothing for a while all this time we
read that low pressure is supposed to
develop due to warm air because if you
look at the equator that region is warm
and warm a rise and that's how low
pressure belt is created me at the
equator
but over here it is supposed to be cold
I mean from temperate zone it starts
getting colder so how is it that this
region is called as subpolar low it
sounds a little confusing right the
straightforward logic of temperature and
its relation to pressure doesn't seem to
apply well over here right so what do
you think would be the reason now let's
go step by step and try to understand
the logic so the first thing that we are
clear about is that the low pressure in
this region is not caused by deep
temperature
and the second thing that you need to
understand is that the low pressure belt
is mainly found above the oceans because
the landmass as we know is cold or as
some places it's covered with snow and
ice now if you remember moments back we
were talking about subtropical highs we
learned that it's a high pressure zone
and we also saw how to becomes a high
pressure zone you know the warm air from
the equatorial region it rises and moves
through a sea subtropical region and
there it collides with the cold air
coming from the poles that makes the air
sink over the Atlantic and Pacific Ocean
and that's how high pressure belt is
created that's the whole story now if
you remember I told you the air that
sinks at the subtropical region that
forms the subtropical high it gets
divided into two parts one part goes
towards the equatorial region and the
other part goes to her sleep poles now
the same thing that happened in
subtropical region happens here as well
the part of the wind that goes towards
the poles collides with the vent coming
from the poles but the vent collides
nearer to this surface and let me tell
you this these are cool dry winds when
they collide and converge near the
surface they don't have any place to
sink so they rise and when air rise it
is associated with clouds and
precipitation you see it's creating a
similar condition that exists in the
skies of equatorial region that's how it
creates a low-pressure zone which is
called as cipolla low and if you
remember the wind that went from
equatorial region to subtropical region
the pattern of atmospheric circulation
was called as Hadley cell over here the
name of the atmospheric circulation
pattern is called as Farrell cell
again the air that rises at the subpolar
low it gets divided into two parts one
goes towards the poles like the extreme
part of the poles and the other goes
towards subtropic and that's how a chain
or a loop is created where the air keeps
moving from equator to poles and vice
versa
always remember equator has low-pressure
zone subtropical region has high
pressure zone
then comes the Cipolla region with low
pressure zone and finally the poles that
has high pressure zone and all these
pressure positions keeps changing with
the movement of Earth on its axis
because that's what affects the sun's
heating of the surface for example
during January when northern hemisphere
is tilted away from the Sun that's when
northern hemisphere has winter season
the Hadley cell moves towards the lower
latitude of the northern hemisphere
likewise in the month of June or July it
is somewhere in the northern hemisphere
the Hadley cell shifts to higher
latitudes of northern hemisphere so with
this I hope you understood the
atmospheric circulation and its patterns
now let's quickly understand what are
these westerlies and
easterlies now before I begin explaining
that you need to understand that
Coriolis force affects the velocity and
direction of the wind to a great extent
so all that we have read till now the
creation of low pressure and high
pressure zones it's all due to the
movement of air from one place to
another
basically atmospheric circulation is the
large-scale movement of air which
redistributes heat energy on the surface
of earth so what is Coriolis force we
know that Earth spins in its own axis
that's how we witness day and night
every day the Sun rises in the east and
sets in the west that means the earth is
spinning on its axis from west to east
since earth is a sphere and wider at the
equator so the rotational velocity of
Earth at the equator
is more than what it is at higher
latitudes for example at 30 degree north
and south the rotational velocity is
less than what it is at 0 degree equator
due to the rotational velocity of the
earth winds get deflected now an easy
example to understand the concern
you must have taken a ride on this
revolving circular platform in a
playground or in some amusement park now
two people sitting on the opposite end
of this ride threw a ball at each other
you'll notice that the ball will change
its direction with this demonstration
you can easily understand that how wind
on earth gets deflected due to the
rotational velocity of Earth and this
phenomena is known as Coriolis effect
now coming to westerlies if a moving
object is going towards north or south
from the equator it will deflect towards
East due to Coriolis force
so westerlies are prevailing winds that
blow from west to east in between thirty
to sixty degrees north and south
similarly if a moving object is going
from north or south towards the equator
it will deflect towards west and again
due to Coriolis force
so easterly's are prevailing winds that
blow from east to west in polar and
tropical region I hope this video was
helpful and served its purpose I'll make
all the pictures in illustration
available on the website I'll put the
link in the description just have a look
at it let me know your thoughts in the
comment section thanks for watching and
I'll see you in the next one