GEOGRAPHY GRADE 12| SUBTROPICAL ANTICYCLONES |LINE THUNDERSTORMS|COASTAL LOW|BERG WINDS |MADE SIMPLE
Summary
TLDRThe video script offers an in-depth exploration of subtropical anticyclones and their associated weather patterns, focusing on their impact on South Africa. It covers the formation and characteristics of three main anticyclones: the South Atlantic, the Kalahari, and the South Indian, detailing how they influence the country's weather, particularly the production of warm moist air from the Indian Ocean and cold dry air from the Atlantic Ocean. The script delves into the effects of ocean currents, topography, and latitudinal position on South Africa's climate. It also discusses the phenomena of the inversion layer and its role in preventing warm moist air from the Indian Ocean from penetrating the interior during winter, leading to stable and sunny weather. The impacts of line thunderstorms, coastal lows, and Berg winds are examined, including their positive and negative effects on the region, such as water restoration, nitrogen fixation, flooding, property damage, and the encouragement of veld fire spread. Strategies to combat these impacts, like wetting the soil and evacuating people and livestock, are suggested. The script emphasizes the importance of understanding these weather systems for predicting and preparing for their effects.
Takeaways
- 🌍 The video discusses subtropical anticyclones and their associated weather conditions, focusing on South Africa's weather system.
- 🌀 Three main factors affect South Africa's weather: ocean currents, topography, and the country's latitudinal position.
- 🔥 The warm Mozambique Current and the cold Benguela Current are significant ocean currents influencing the region's climate.
- 🏞️ The topography of South Africa, including the high plateau and escarpments, plays a crucial role in the country's weather patterns.
- 🌡️ South Africa is situated in the subtropical high-pressure belt, leading to the formation of three anticyclones.
- ⏱️ The strength of the Kalahari High, one of the anticyclones, changes with the seasons, affecting the country's weather.
- 🌦️ The inversion layer, formed by the interaction of warm moist air and cold air, acts as a barrier to cloud formation and rainfall.
- ⚡️ Line thunderstorms are a summer phenomenon in South Africa, bringing both positive impacts, like water restoration and nitrogen fixing, and negative impacts, such as flooding and property damage.
- 🌊 Coastal lows are low-pressure systems that develop year-round and move along the coastline, influencing weather conditions with onshore and offshore winds.
- 🍂 Berg winds, or hot and dry winds, result from the interaction between the Kalahari High and coastal lows, leading to uncomfortable conditions and an increased risk of wildfires.
- 🛡️ Strategies to combat the negative impacts of weather phenomena include wetting the soil to prevent fire spread, evacuating people and livestock, and ensuring emergency services are well-equipped and efficient.
Q & A
What are the three factors that affect South Africa's weather?
-The three factors that affect South Africa's weather are ocean currents, the topography of the country, and the latitudinal position of the country.
What are the two different ocean currents mentioned in the script and what are their effects?
-The two different ocean currents are the warm Mozambique current and the cold Benguela current. The Mozambique current on the eastern side of the country is responsible for high temperatures and the production of warm moist air after evaporation, while the Benguela current on the western side results in the production of cold dry air.
What is the significance of the Kalahari High's position during different seasons?
-The position of the Kalahari High changes with the seasons. During winter, it is strong with a high pressure system, leading to stable and sunny weather in the interior. In summer, it is weak with low pressure, allowing warm moist air from the Indian Ocean to penetrate inland, leading to rainfall and thunderstorms.
Line thunderstorms form during summer when warm moist air from the South Indian High meets cold dry air from the South Atlantic High along a moisture front. The impacts include heavy rainfall leading to water restoration in dams, nitrogen fixing which acts as a natural fertilizer, but also negative impacts such as flooding, property damage from hail, and potential injuries or fatalities from lightning.
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What is the Coastal Low and how does it affect the weather conditions along the coast?
-The Coastal Low is a low-pressure system that develops along the coast and moves from west to east. It brings different weather conditions on either side; on the western side, it brings cold dry air from the Atlantic Ocean, while on the eastern side, it brings warm moist air from the Indian Ocean, leading to rainfall.
What are Berg winds and how do they form?
-Berg winds are hot and dry winds that develop in winter as a result of the interaction between the strong Kalahari High and a coastal low. As air moves from the high pressure Kalahari High towards the coastal low, it descends the escarpment, warming up adiabatically and losing moisture, resulting in hot and dry conditions at the coastal settlements.
What is the inversion layer and how does it impact the weather during winter and summer?
-The inversion layer is a layer where the temperature increases with increasing height, which is the opposite of the normal decrease in temperature with height. During winter, the strong subsidence of cold air from the Kalahari High pushes the inversion layer down, preventing warm moist air from the Indian Ocean from penetrating inland and resulting in stable sunny weather. In summer, the inversion layer is lifted above the escarpment, allowing warm moist air to rise, cool, and form clouds, leading to rainfall.
How do the three anticyclones in South Africa affect the country's weather?
-The three anticyclones—the South Atlantic, Kalahari, and South Indian—create high pressure systems that influence the country's weather. The South Atlantic anticyclone brings cold and dry air, the Kalahari anticyclone is strong in winter and weak in summer, and the South Indian anticyclone brings warm and moist air. Their movement and strength change with the seasons, affecting weather patterns such as rainfall and temperature.
What is the role of the intertropical convergence zone (ITCZ) in the migration of weather systems?
-The ITCZ moves northwards and southwards depending on the season, following the hemisphere that experiences summer. As the ITCZ moves, it drags along weather systems such as cyclones and anticyclones. This migration affects the proximity of these systems to South Africa, influencing the country's weather during different seasons.
What strategies can be used to combat the negative impacts of Berg winds?
-To combat the negative impacts of Berg winds, strategies include wetting the soil to prevent fire spread, evacuating people and livestock to safer areas, ensuring emergency services are well-equipped and efficient for a quick response, and providing sufficient water to fight fires and hydrate victims.
How can one identify the three anticyclones on a synoptic or satellite image?
-On a synoptic weather map, anticyclones are represented by an 'H' indicating high pressure. The South Atlantic anticyclone can be identified by its position on the Namibian coast or the Atlantic Ocean. The Kalahari anticyclone is located in the interior on the plateau and is usually strong during winter. The South Indian anticyclone is situated on the Indian Ocean and will show anticlockwise movement of air. On satellite images, one would look for specific cloud formations and weather patterns associated with each anticyclone.
Outlines
🌍 Introduction to Subtropical Anticyclones
The video begins with an introduction to subtropical anticyclones, discussing their formation and associated weather conditions. It emphasizes the importance of understanding the factors affecting South Africa's weather, such as ocean currents, topography, and the country's latitudinal position. The warm Mozambique current and the cold Benguela current are highlighted for their roles in creating warm moist air from the Indian Ocean and cold dry air from the Atlantic Ocean, respectively.
🌀 Characteristics and Formation of Anticyclones
The second paragraph delves into the characteristics of anticyclones, explaining that they form due to sinking air which creates high pressure. The South Atlantic anticyclone, situated on the Namibian coast, is identified as the strongest of the three anticyclones due to its association with cold air. The effects of the anticyclones' movement, particularly during the summer, are also discussed, including their impact on the country's weather.
🔥 Kalahari Anticyclone and Its Seasonal Variations
The Kalahari anticyclone, located in the country's interior, is described as being weak during summer due to weak subsidence and strong during winter due to strong subsidence. The paragraph explains how the Kalahari anticyclone's strength changes with the seasons, influencing South Africa's weather patterns, particularly the formation of an inversion layer that affects the movement of warm moist air from the Indian Ocean.
🌬️ Impact of Kalahari High on South African Weather
This section discusses the Kalahari High's impact on South Africa's weather, particularly during winter and summer. The strong subsidence during winter leads to stable, sunny weather due to the inversion layer acting as a barrier to warm moist air. In contrast, during summer, the weak subsidence allows the inversion layer to lift, enabling warm moist air to penetrate the interior and result in rainfall and thunderstorms.
⚡ Positive and Negative Impacts of Line Thunderstorms
The video outlines the positive and negative impacts of line thunderstorms, which occur during summer. Positive aspects include water restoration in dams and nitrogen fixing through lightning, which acts as a natural fertilizer. Negative impacts include the potential for flooding and property damage due to hail and lightning. The formation of line thunderstorms is linked to the interaction between the South Atlantic High and the South Indian High, leading to the development of a moisture front and subsequent thunderstorm activity.
🌊 Coastal Low and Its Effects on Weather Conditions
Coastal lows are discussed as another type of traveling disturbance that can develop in both summer and winter. These low-pressure systems move along the coastline from west to east, causing different weather conditions on either side. On the eastern side, warm moist air from the Indian Ocean can lead to rainfall, while the western side experiences warm dry conditions due to offshore winds. The paragraph also addresses how to identify coastal lows in synoptic weather maps.
🔥 Formation and Impact of Berg Winds
Berg winds, or B winds, are hot and dry winds that develop in winter due to the interaction between the strong Kalahari High and a coastal low. As air moves from the high pressure towards the low pressure, it descends and warms up adiabatically, losing moisture and resulting in hot and dry conditions. These winds can lead to the spread of veld fires, property destruction, loss of livestock and equipment, and even loss of life. Strategies to combat these impacts include wetting the soil to prevent fire spread, evacuating people and livestock, and ensuring emergency services are well-equipped and efficient.
✅ Conclusion and Preview of Upcoming Topic
The video concludes with a summary of the concepts covered under subtropical anticyclones and associated weather patterns. It stresses the importance of understanding these weather phenomena and their impacts. The host also previews the next topic, which will be valley climates, and encourages viewers to apply the foundational principles discussed throughout the series.
Mindmap
Keywords
💡Tropical Cyclones
💡Subtropical Anticyclones
💡Ocean Currents
💡Topography
💡Latitudinal Position
💡Inversion Layer
💡Traveling Disturbances
💡Line Thunderstorms
💡Coastal Low
💡Berg Winds
💡Pressure Gradient
Highlights
The video discusses subtropical anticyclones and their associated weather conditions, including traveling disturbances like line thunderstorms, coastal low-pressure cells, and South African back winds.
Three main factors affecting South Africa's weather are identified: ocean currents, topography, and the country's latitudinal position.
The warm Mozambique current and the cold Benguela current are key ocean currents influencing South Africa's climate.
The topography of South Africa, featuring a plateau and escarpments, plays a significant role in the country's weather patterns.
South Africa is situated in the subtropical high-pressure belt, leading to the formation of three anticyclones.
The South Atlantic anticyclone is the strongest of the three due to its association with cold air from the Atlantic Ocean.
The Kalahari anticyclone, located on the plateau, is weak during summer and strong during winter due to variations in subsidence.
The South Indian anticyclone brings warm and moist air from the Indian Ocean, influencing South Africa's eastern weather.
The intertropical convergence zone (ITCZ) affects the movement of anticyclones and other weather systems, following the summer hemisphere.
Line thunderstorms occur only in summer due to the interaction between the South Atlantic High and the South Indian High.
Coastal lows are low-pressure systems that develop year-round and move along the coastline from west to east.
Berg winds are hot and dry winds that form during winter as a result of the interaction between the Kalahari High and a coastal low.
The inversion layer, formed by the meeting of warm moist air and cold air, plays a critical role in South Africa's weather, particularly in the impact of the Kalahari High.
During summer, the Kalahari High's position above the escarpment allows warm moist air to penetrate the interior, leading to rainfall and thunderstorms.
The impact of line thunderstorms includes both positive aspects, such as water restoration and nitrogen fixing, and negative aspects, like flooding and property damage.
Strategies to combat the impact of Berg winds include wetting the soil, evacuating people and livestock, and ensuring emergency services are well-equipped and efficient.
The video emphasizes the importance of understanding the foundational principles of meteorology to grasp the concepts of subtropical anticyclones and their weather impacts.
Transcripts
hi again then welcome back to our grade
12 Geographic cap series I'd like to
thank you for tuning in and I hope this
video will make things as simple as
possible for you in the previous video
guys we went through tropical Cyclones
we covered the general characteristics
areas where tropical Cyclones form
factors necessary for their formation
everything okay so every single detail
or concept that you have to master you
have to know under tropical Cyclone so
if you haven't watched that video or
those videos because they actually
videos please do so they are in the
playlist of the geography caps Series so
for this video guys we are going to
cover the subtropical anticyclones and
the associated weather conditions so
we'll look at every concept that is
under subtropical anticyclones that is
also including the traveling
disturbances which are your line
thunderstorms Coastal low pressure cells
and the South African back WIS okay
their impacts their strategies we'll
also take a look at how you identify
these on a synoptic and satellite image
the most important thing is the
foundation right so we have to start
with the factors that affect South
Africa's weather and there are three of
those which is the ocean currents the
Topography of the country and also the
latitudinal position of the country so
let's start with currents there are two
different currents that we have and that
is the warm mozic current and the cold
bangua current okay so some of you may
ask what are currents so simply guys
current actually describes the movement
of an ocean or you may say that a
current is actually a fluid within a
fluid or a moving or the movement of a
fluid within another fluid or within the
same fluid okay a simple example guys
when you have a kettle H let's say your
Kettle is transparent you can see
through everything so you can see the
water movement and so on and so on so
when you switch on your Kettle and and
when the water is about to Bow you'd
find out that there are shooting
currents so currents that actually water
that is moving uh shooting upwards like
that okay those uh movements of water
within this volume of water that is what
we call currents okay we see that on a
bigger scale so you have the war mozic
current that is on the Eastern side of
the country that is in the Indian Ocean
okay this current is responsible
for the high temperatures of the Indian
Ocean it is responsible for the
production of warm moist air after
evaporation of the Indian Ocean so after
evaporation the Indian Ocean produces
warm and moist air okay remember it's an
ocean so it has to be moist and it's
warm okay so the warm mozic current is
the reason why we have warm moist air
that is produced on the the Eastern
ocean of the country and then on the
western side we have the cold benguela
current and it is of course on the
Atlantic Ocean this results in the
production of cold dry air okay let me
use blue you have cold dry air moving
Inland and this of course these uh two
ms's affect the South African weather as
we will explore and discuss that so we
have cold dry air from the Atlantic
Ocean and warm moist air from the Indian
Ocean due to these two different
currents so let's keep that in mind okay
the second factor that affects South
Africa's weather is the Topography of
the country so that means we are
referring to the shape of the land this
is to say if I were to draw a
crosssection across the country so I'm
drawing it from X here all the way to Y
there okay so I draw a cross-section I
want to figure out how does the land
change how is it shaped well the result
I'm going to get looks something like
this so i' find that as I'm moving
towards Inland the interior of the
country I'm actually going up in height
and when I get to the interior I am on
top of this High Ling flat mountain
which we call the plateau okay so this
is the plate and on the sides of the
plate okay so you see these big bumps on
the side of on either side of the
plateau those big bumps is what we call
escapements so there we go so we have
those escapements on either side of the
plateau as you can see and as you move
away from the interior towards the coast
of course the altitude drops okay so
this is critical guys because as you
will see this influences South Africa's
weather and winter and and in summer
okay as we will explore and then the
third factor that affects South Africa's
weather is the latitudinal position of
the country where is the country
situated or located in terms of of of
its latitude so the country is actually
situated over the
30° latitude 30° South so that is the
subtropical high pressure belt uh so if
you remember your geography well guys
from um grade 10 and 11 you should be
able to understand that okay and this
results in the formation of three
anticyclones that we are going to
discuss in this video so because of the
latitudinal position of sa which means
that it is situated along the which is
situated along the subtropical high
pressure belt this results in the
formation of three anticyclones the
three anticyclones and before we
actually get into that let's first
discuss because let's remind ourselves
of an anticyclone guys what did we say
are the characteristics of an anti
Cyclone okay so an anticyclone forms as
a result of sinking air so you have air
that is
sinking and it is putting pressure of
course against the ground and hence you
form an area of high pressure so
anticyclones and High Press cell those
are the same things okay and so as of
course we discussed in the very first
video of this geography series we found
that um there's
anticyclonic movement of air okay um
inside this anticyclone so as it is uh
sinking down is actually rotating
anticlockwise okay and as it sinks down
guys we said that it actually gets
warmer and warmer okay so we start to
see
warm air As you move towards the surface
which is what we call adiabatic warming
and we said that there's no condensation
that occurs in high pressure cells and
hence we see a calm weather we see a
sunny weather no cloud formation so
there's zero cloud cover and of course
as I said guys we see um anticlockwise
movement of air okay and we also see the
surface uh Divergence okay so if you
haven't watched that video guys please
do it's the very first video of this
series okay so let's get into it then so
these are the three anticyclones that we
are referring to okay so we'll start
with this one that is on the western
side of the country this anticyclone is
situated on the namibian coast and U you
can also say it is situated on the
Atlantic Ocean and this anticyclone is
the South Atlantic anticyclone okay it's
very important guys that you remember
the name of the anticyclone okay so that
you can be able to identify it they do
ask you to name it okay so it's very
critical that you understand the
position of each one of them the
location of them and of course they
names okay so that means within this we
see anticlockwise movement of air okay
so we have air uh moving away from these
high pressure cells okay so it can also
move inwards okay so air that is moving
from the ocean towards the land we call
it onshore winds and remember air from
the South Atlantic anticyclone is cold
and it's dry okay has little moisture
cold air tends to retain very little
moisture guys okay we also see that
South Atlantic anticyclone can sometimes
move okay um all of them actually can
move um we'll talk talk about that but
when it actually does move southwards
okay which usually happens during the
summer you'd find that it can actually
block the mid latitude cyclone from from
affecting the country right so it can
actually block this mid latitude cyclone
from entering Inland and so when it
blocks the mid latitude cyclone we say
that it reaches okay so we call it ring
okay that's it moving further southwards
and hence blocking the mid latitude
cyclone from entering into Inland okay
okay so we also have another type of
anticyclone that is situated on the
interior of the country okay and by the
way the South Atlantic anticyclone is
the strongest of the three okay because
it has cold air okay because it's
associated with cold air cold air that
is used by the Atlantic Ocean presses so
cold air presses or puts a higher
pressure on the ground than relatively
warmer air okay and so because this is
the South Atlantic anticyclone is
associated with cold air and hence it is
the strongest of the three now in the
interior we have another anticyclone
which we call the
Kari anticyclone okay so this is in the
interior it's actually on the
plate situated on the plate so the plate
that we referring to there so you
actually have the Kalahari that is
present over the plateau during a
particular season that we will discuss
so the Kalahari anticyclone okay so you
can say anticyclone or high pressure so
it really has multiple terms okay so
this is on the interior of the country
and it's weak during the summer very
weak because there's weak subsidence and
during the the winter is actually strong
because there's strong subsidence and
for those of you who don't know
subsidence guys we're actually referring
to a sinking down okay so if it is
strong subsidence that means you have
cold air that actually pushes against
the ground cold air creates a strong
subsidence a strong uh sinks strongly
and presses against the ground puts a
lot of pressure against the ground okay
so this happens during the winter when
you have cold air during the summer
there's weak subst okay we'll discuss
this don't worry about that now and then
on the Eastern side you actually have
the South Indian anticyclone as you can
see guys situated on the Indian Ocean
and of course it brings because it is in
the Indian Ocean C this there will be
anticlockwise movement from this high
pressure okay which means that you are
going to have onshore winds but they
will be warm and moist so warm and moist
air will come from the north okay from
the Northeast and cold and dry air gets
in from the southwest okay so okay I
need you to note that right so these are
the three anticyclones and their
locations and some of their
characteristics okay it's very important
that you understand this okay so um we
talked about the location uh we talked
about reaching okay and so when it comes
to migration guys we mean that all of
these um anticyclones are not stationary
they do move okay so due to the ITC that
migration northward migration so during
winter right so let me just
throw okay this so the itz which is the
intertropical convergence so I'm not
sure if I did uh talk about that uh
discussed that in the tropical cyclone
and mid Cyclone videos but if did not I
apologize for that and so the
intertropical convergence so moves um
northwards and southwards depending on
the season of that particular hemisphere
the itcz follows summer so it follows
the hemisphere that has sum okay or in
which there is sum so if there is sum in
the Northern Hemisphere and there is
winter in the southern hemisphere that
means the intertropical Convergence Zone
will move towards the north okay so if
it moves towards the north it drags
along with it all of the um of the
weather systems so your Cyclones okay
your M latitud Cyclones your tropical
Cyclones your
anticyclones um all of them move towards
the North and of course when it is
summer in the southern hemisphere the
intertropical conversion Zone moves
further south okay so if it moves
further South that means all of those
weather systems also move further south
okay so they follow the intertropical
converence so so of course as you might
imagine these become closer during
winter because during winter that would
mean it is summer in the northern
hemisphere and hence the itcz will move
to the north dragging along with it
these anticyclones and hence if they
were here okay at the beginning um then
they will move further north to this
current position that they are in now
okay so this makes them closer to the
land and hence they are able to affect
South Africa during the winter okay so
very prominent during the winter okay
this is not to say they do not affect
the country during summer okay but we do
see a lot of interaction during winter
Okay so we've covered that and so we
also covered this Kalahari strength
which changes of course as I said weak
in summer strong in Winter okay so those
are the three anticyclones guys okay so
let's move on then to the Kalahari High
pressures impact on South Africa's
weather and before we actually get into
that here I think it's critical that we
first discuss this phenomenon which we
call the inversion layer what happens is
that okay I think I did explain this in
one of the past videos okay but I don't
mind doing that again so the Indian
Ocean of course so this is a
cross-section from this area to there
okay so it's a cross-section it views
the side view um of this area okay or
the the cross-section of this area so we
know that there is a plateau in the
interior and there is an escapement
there and so we know that there is also
warm moist air that is coming in Inland
from the Indian Ocean so what happens is
that when you have this warm moist air
this warm moist air tends to rise up
okay so it rises along the escarment so
you'll have warm moist air Rising along
the escarment like that okay there we go
and so as it rises we know that air
cools down guys right so as this warm
air rises it actually cools down so it
becomes cooler and cooler
right
okay and we also have because of the
Kalahari High we also have cold air okay
we also have sinking air okay sinking
air as we said and as sinking air sinks
or descends what happens to it
guys okay so as air sinks we said that
it actually warms up okay so you have
warm you have cold air becoming warmer
and warmer duee to a diabatic warming
and so now this air warms up okay warms
up as it is sinking down it warms up
becomes warmer and warmer as you can see
right and so now looking at this section
okay if we can just observe this
particular section here okay so in this
section you actually find out
that as you are let's say this was you
rising up the mountain so maybe you were
mountain climbing so as you are rising
up you're actually going to find out
okay that the
temperature actually Rises as the height
Rises up okay normally we know that as
you are rising up a mountain the
temperature drops okay it gets colder
and colder okay that's the normal um
condition right so when then you have
this phenomenon where you have Rising
temperature with Rising height this
layer right here this is the layer that
we call the inversion layer so the
inversion layer is
formed okay it's inverted okay um it's
not normal okay so that's what we call
the inversion layer it's the opposite of
the decreasing temperature with
increasing height but rather now it's um
increasing temperature with increasing
height okay so that's how we form the
inversion layer guys right so let's then
move on okay and discuss the Kalahari's
impact on South African weather okay and
again guys this inversion layer is
critical when you're explaining the
Kalahari High's impact on South African
we so we're saying that during winter
the Kalahari high is strong okay or has
a strong subsidence okay so as you would
see so as you would expect you have cold
air which will sink down okay creating
an area of high pressure so even in
synoptic weather maps you are going to
find there is a strong high pressure so
there will be an H okay so in a synoptic
weather
map okay in the interior of the C you'll
find there is a a high pressure there so
this would be an indication to you that
this is actually winter because that
means that this Kalahari high pressure
right here is strong okay and You' find
that during summer there's actually a
low pressure there okay because there's
Rising air right Rising air puts low
pressure on the ground and hence
creating a low pressure system on the
surface so this is what we call the
thermal Low by the way right and of
course this is the Kalahari being strong
um during winter okay
right so during winter we know that
there is a strong
subsidence of cold air so there's cold
air that is pushing against the ground
it creates an area of high pressure okay
pushing against the
ground right and so as it pushes against
the ground it actually
also results in the inversion layer
being pushed downwards okay so the
inversion layer is being pushed
downwards by this cold by this cold air
mass okay due to this strong subsidence
so it pushes down this inversion layer
below the
escapement okay so this is what happens
during winter those are your first um
points okay you start by uh the strong
subsidence during winter and then cold
air pushing down this inversion layer um
below the escarment
now this means that the warm moist air
that originates from the Indian Ocean
cannot enter through cannot penetrate
through cannot enter and hence affect
the
interior weather okay and hence um
result in um cloud formation and so that
will not happen because now you actually
have this inversion layer which acts as
um which acts as a barrier that prevents
this warm waste air from getting through
to the interior of the country okay so
due to this okay so if of course if the
warm air would be able to get through it
would cause it would rise up it it would
rise up cool down condense form clouds
and result in rainfall but because this
does not happen actually is prevented to
go from going through and hence this
results in a sunny so we we so during
winter we get stable sunny weather okay
remember this cold a is sinking down
it's not rising up and hence because it
is sinking down there is no condensation
that occurs there is no cloud formation
that occurs and hence we see no cloud
cover we see a
sunny weather okay so that's what we see
during winter okay in the interior of
the country right now let's talk about
during summer so in summer what happens
now so in summer you actually have weak
you actually have weak subsidence okay
remember it's summer and so there's more
air rising up than descending down okay
so because it is warm the land heats up
the air air rises up okay and so now
you'd find find out that the Kalahari
high is actually above way above the
escapement okay it has a weak subsidence
and you'll find it in higher altitudes H
because there's war there's more Rising
air than sinking air and hence now this
inversion layer is therefore lifted up
okay so it's therefore lifted up and it
is lifted up above the escapement so as
you can see this inversion layer is
above the escapement and hence the warm
moist air from the Indian Ocean is able
to get through to the interior of the
country okay gets through to the
interior of the country it rises up it
cools down it condenses forms clouds
right and hence this results in
rainfall okay and mind you this air is
actually coming from from the south um
Indian High moving towards the land why
is it going to move towards the land
well because there is an area of low
pressure in the interior there is the
low there is the thermal low in the
interior of course air will want to move
from the high pressure to the low
pressure so this results in an unstable
weather this results in heavy rainfall
this results in thunderstorms so as you
can see during summer that's why we have
a lot of uh
flooding okay on the Eastern side of the
country okay because there's a lot of
rain okay because of this influence of
the Kalahari right so it's very
important that you are able to put it in
words guys okay be able to put it in
words um and also be able to um draw it
okay but when you are drawing it make
sure that you annotate okay make sure
you're right down so warm air cannot
pass through inversion layer is lowered
so on and so on okay right so let's move
on then uh so we move on to the
traveling disturbances so traveling
disturbances there's actually three of
them there's the line thunderstorms
there's Coastal low and lastly there is
the B winds okay we are going to explain
their formation and their impact so
let's start with the line thunderstorms
Okay so the line thunderstorms first of
all develop only in summer so I've
underlined this because I know that we
can we can switch things up okay it's
very critical that you remember that
line thunderstorms only okay in summer
and um you should and it should make
sense okay and so we saying that so
let's start with the affirmation so
during summer a theral low is present in
the interior so during summer as we know
guys okay the the sun heats up the land
and that heat is transferred via
conduction um to the air and then air
rises up puts a a little pressure on the
ground and hence we create an area of
low pressure okay on the ground so this
is what you will find on any synoptic
weather map during the summer so there
is a thermal low during the summer okay
in the interior of the country and
because you have the South Atlantic High
and you have the South Indian high on
the Eastern side and we know that there
is anticlockwise movement of air okay
Within These so we say that so we're
saying that this creates a pressure
gradient okay so pressure gradient guys
really um so this speaks to the movement
or the attraction that air has uh
towards the low pressure okay from the
high pressure um we also talk about the
pressure gradiant force uh which is of
course the force that um is responsible
for the movement of air from in the area
of high pressure towards an area of low
pressure so this creates a pressure
gradient and leads to warm moist South
Indian high pressure
air
okay from the
Northeast and uh or converging with cold
dry South Atlantic High Press air from
the southwest okay I hope that doesn't
doesn't make things difficult for you so
we have the South Atlantic high pressure
right we're saying that it is invited or
it moves towards this
thalo and you have the South Indian high
pressure air okay which is warm and
moist okay it also moves towards this
low pressure this thermal low and they
they actually meet
up
at this line or this front that we call
the moisture front Okay so and it
stretches um from of course the North
West to the South East okay and so these
two ms's me up along this moisture front
Okay and the reason why we call it a
moisture front because that's because on
either side of it
you actually have different ms's of
moisture so we say that saying that
because we know that on the E side of
the moisture front you have
warm moist air okay that is coming in
from the
south um Indian high pressure cell and
then on the western side of this
moisture front you actually have
cold dry air that is coming in from the
South Atlantic High and and hence the
dry
air and moist air they are divided by
this front or this boundary that we call
the moisture front because these are two
ms's of different moisture contents this
one is moist this one is dry okay so
that's why we call it moisture front
Okay so you have this air coming from
the
Northeast okay this war moist air from
the south Indian high pressure and you
have the cold dry air from the South
Atlantic high pressure coming in from
the
southwest okay and they meet up along
that moisture front Okay so you have
warm air and cold air meeting up okay at
the center at the interior of the
country along the moisture front and so
what happens now when you have cold air
and uh warm air meeting up okay so we
know this from the mid latitude cyclone
we know that cold air will lift the warm
air okay and so this means that during
this
interaction cold air so warm air will
rise up and cold air will wge underneath
so this what so this cross-section will
look like this cold air will actually
rise
up and warm air will actually rise up
and cold air will wge underneath so of
course as cold as warm air rises up it
will cool down and it will
condense okay
and form
clouds in this case it will form huge
tall cumulon numus clouds okay so it
rises up cools down and condenses
forming tall cumulonimbus clouds okay so
we start to see clouds that will form
along this moisture front Okay and it
will rain on the Eastern side of the
moisture front so the result is your
thunderstorm s heavy rainfall hail that
is on the that will rain on the Eastern
side of this front Okay because there's
cold air here there's sinking air on
this side there's Rising air on that
side okay so this promotes um this
promotes this prep precipitation to ur
on the Eastern side of this
okay okay so I hope that made it easier
for you okay so it's very important that
you actually write each and every little
detail because this can have a lot of
marks okay and and so please be detail
uh please be specific and do not skip
points guys okay do not
rush and be precise okay so when it
comes to the impact that these line
thunderstorms have so we'll start with
the positives and then the negatives so
the positive impact that these have of
course this brings a lot of rain on the
Eastern side of the country and hence
when we talking about was water
restoration uh water storage that means
that we are going to restore water in
dams we are going to fill up our dams
which of course are responsible for
storing our water okay and the second
one is that lightning okay remember
lightning is one of the precipitation
that will occur after condensation after
cloud formation so lightning this is
what we call nitrogen fixing so you have
lightning so light due to its heat it
converts the nitrogen molecules that are
in the air converts them into nitrates
okay in the soil so You' have a
molecule okay so it actually because it
has a lot of heat it actually can break
up that molecule and this now you will
have atoms free atoms of nitrogen
nitrogen atoms uh they bond with oxygen
atoms and so and then during um
precipitation they fall into the soil
and so now the soil will have a lot of
nitrogen content and hence it's good um
it's fertiliz natural fertilizer guys
for the soil okay so that is good for
farmers and um natural plants wild
plants and so let's move on the negative
impact is that you have heavy rainfall
okay which will cause flooding okay
we've seen numerous incidents where you
have flooding especially last year and
this year flooding of course you cannot
forget that guys uh we also see hail
okay uh which are those um little ice
masses that actually destroy cars
destroy a lot of property so hail and
lightning actually can cause damage to
property and it can also injure or kill
people okay so those are the two
negative impacts of ler storms and two
positive impacts right okay so those are
line thunderstorms guys I hope I've made
it simple enough enough for you right so
we move on then to the coastal low so
Coastal low is another traveling
disturbance and it actually develops in
summer and winter so as the word suggest
it is a coastal low so it's a low
pressure so it's a cyclone and so we see
clockwise movement in the Southern
Hemisphere okay clockwise rotation of
air and it moves along the coastline
guys from west to east okay the usually
like asking the question of let's say
they would have this particular Coastal
low and let's say this is um Cape Town
and they would ask you if this Coastal
law has actually passed Cape Town or is
actually still approaching Cape Town
okay because you know the direction um
of the coastal load you would of course
say that it is still approaching Cape
Town because it is moving from where
West moving along the coast affecting
all these areas moving towards the east
right okay so be aware of those
questions okay expect them another thing
that we know that we see here is that
because of this clockwise rotation that
means that air so air from the Atlantic
Ocean will enter inlands okay that means
that that we call that means that will
be onshore winds okay and and we know
that that is cold dry air okay remember
this is the Atlantic Ocean which is
affected by the cold bangua current so
you have cold dry air moving in of
course they have small moisture or
limited moisture they move in inlands
okay so they bring cold dry conditions
in land okay and again because of the
continuous rotation of air inside this
Coastal low you also have air that is
moving outside the land okay moving
towards the ocean and that is called
offshore winds okay so offshore winds
because they are coming in from Inland
remember the land does not have a lot of
water surfaces and hence it is dry so
it's warm and it is dry with no moisture
so those conditions will be experienced
by people that are living on this side
of the coastal low okay and on this side
of the coastal low they will experience
these particular conditions okay so the
weather is different the weather
conditions are different from on either
side of the costal low okay and then on
the Eastern side uh we know that we have
the the Indian Ocean and hence the
Indian Ocean produces warm moist air
okay so warm moist air because of this
rotation again we will have warm waste
air coming Inland okay and because you
have warm was air warm waste
air and so it will rise up it will cool
down and it will form clouds and that
will result in rainfall on this side so
people on this side might experience
rainfall and people on this on this side
of the coastal low they will experience
warm dry conditions with limited
moisture because this is offshore winds
that are coming actually from the land
which is dry okay so that's what you
need to note guys when it comes to
Coastal lows
okay right and it's very critical that
you are able to identify them in
synoptic weather maps Okay so they will
look like something like that okay low
pressure something like that so that you
would know if it is along the coast then
that is a coastal low okay be able to
identify them and when it comes for and
for line thunderstorms you'd find out
there's a lot there's cloud formation
that is that actually stretches
diagonally like that okay then you would
know that those are your life
thunderstorms in your satellite images
let's get into the last concept we have
which is called the bag winds okay so B
winds are simply hot and dry winds okay
which develop in winter so they usually
affect settlements before mid latitude
Cyclones arrive uh let's discuss how
they form so beg winds are are a result
of an interaction between the strong
Kalahari High and a coastal low during
winter we know that there is a strong
Kal har high right so we know that in
our synoptic weather maps we will have H
there that represents our kalahar high
and because we said that a coastal low
actually develops in both winter and
summer we have a coastal low okay that
is on the coast and so because now you
have a high pressure and a low pressure
this will create a pressure gradient
such that now you will have air moving
in from the high pressure towards the
coast okay to that low low pressure okay
so that pressure gradient you say that
it is created because of the strongar
high and the coastal low in win okay and
then so air will flow from the Kalahari
High towards the coastal low but the
Kalahari high as we said that we said
that it is situated on the plate right
so it is actually on Higher Grounds or
um higher altitudes so you have this
Kalahari High here and and towards the
coast okay right over here you have that
Coastal low so now air will move from
the kalahar
high in the plateau and will actually
move down in altitude in height moving
towards the coast okay so it's critical
that you describe all of that so as it
is moving towards the coastal low it's
actually descending down the escarment
okay and as it descends down the
escarment guys so when air is descending
what happens it warms up okay so this
will actually warm up as it descend so
it will warm up adiabatically and of
course this removes moisture as we know
so when you warm up air more you get rid
of the moisture that it has and hence
that and hence we say that it is dry so
when it arrives in these settlements
right over here they will experience hot
air because of the ad diabatic warming
and they will experience dry air because
um you got rid of moisture as you were
warming that air up okay so by the time
it reaches these coastal areas it will
be hot and dry okay so that's how you
form back winds it's an interaction
between Kalahari High and the coastal
low okay so that's what we're saying
here so as this a subsides down the
escapement it warms up adiabatically
removing its moisture okay and so this
hence uh causes hot and dry conditions
okay these are actually uncomfortable
okay dry air is very
uncomfortable um and so of course these
will have an impact on people and the
environment and animals okay and plants
so the impact is that it will initiate
and encourage the spread of felt fires
okay so we seen a lot of fa fires um
during winter because of these uh back
winds okay so this spreads okay F fires
because in order to have a f fire you
have to have dry conditions and then up
the temperature okay because the and so
it's easy to for a fire to spread when
the environment is actually dry okay so
it can have fire spreading through out
uh and covering a lot of hectars because
it is because the soil is dry the
environment is dry okay so we see saying
that we see a spread of f fires we also
see that farmers have their properties
destroyed remember this is fire and so
fire destroys Burns fire destroys
shelters okay and so we will see
properties destroyed and Equipment as
well so there's loss of livestock
there's loss of equipment okay a lot of
farmers have lost a lot of livestock
they have lost a lot of equipment due to
fire due to these faires okay we also
see loss of lives people get injured
people um um lose their lives because of
these back winds okay and because these
occurs these
occurs in any type of environment
whether it's the the forest whether it's
open space um whether it's grassland so
on and so on so um animal habitats get
destroyed and people and animals suffer
from dehydration
okay right and so how can we combat this
impact how can we minimize it okay okay
so we have strategies here so what can
we do okay so we can first of all wet
the so oil okay in order to prevent
spread of fires okay remember we said
that fires spread if the environment is
dry okay so if you can actually wet the
soil um um then you would be actually
preventing the spread of fires okay
because wet soil
prevents um fires from spreading and
covering larger distances okay evacuate
people and livestock uh to safer areas
okay uh so this is to prevent the loss
of lives um the injuries on Livestock on
people and imer Emergency Services
should be well equipped and efficient
that means quick okay there should be a
quick response guys because these fires
can spread pretty quickly okay um we
also see that we have to provide
sufficient water okay uh to fight the
spreading uh fires and to hydrate
victims Okay so again that speaks to
your emergency services that speaks to
your firefighters they should have
sufficient water that will be able to
fight these um fires and also provide
people with drinking water okay so that
they can be able to hydrate okay so
these uh are the concepts that are under
the subtropical anticyclones and
Associated weather patterns guys so um
with this I've equipped you with the
necessary knowledge it's very important
that you are able to describe every
little detail it should make sense to
you okay and also always refer back to
the foundation principles that we
referred to in the first in the very
first video of this series okay I hope
this was as simple as possible okay so
I'll see you in the next video we'll be
doing Valley climates okay cheers is
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