ATPL Meteorology - Class 15: Fronts and Depressions.

Summary

This meteorology lesson explores weather fronts, the boundaries between air masses with different temperatures and densities. It explains how warm and cold fronts cause changes in weather, with warm fronts leading to stratiform clouds and drizzle, and cold fronts resulting in cumulonimbus clouds and storms. The script also delves into occluded fronts, global frontal activities, and the formation of frontal and non-frontal depressions, including tropical revolving storms like hurricanes and typhoons. The video provides insights into predicting weather patterns and the atmospheric processes behind various weather phenomena.

Takeaways

• 🌍 Fronts are boundaries between different air masses and can predictably change local weather conditions.
• 🔍 Weather fronts can be identified from a distance, allowing for weather predictions over short to medium time frames.
• 🌡️ The meeting of air masses with different temperatures creates fronts due to density differences that prevent them from mixing.
• ☀️ Warm fronts occur when warm air moves into an area of colder air, typically represented by a red semi-circle symbol.
• 🌀 Warm fronts slope upwards at a ratio of 1:150, spreading out over large distances and moving at about a third of the 2000-foot wind speed.
• ❄️ Cold fronts are where cold air moves under warmer air, represented by a blue icicle symbol, and have a steeper slope of 1:50.
• 🌬️ Cold fronts travel faster than warm fronts, typically at two-thirds of the 2000-foot wind speed, causing gusty wind conditions.
• 🔄 An occluded front forms when a cold front catches up to a warm front, creating a V-shape with warm air sandwiched between cold air masses.
• 🌤️ Weather associated with fronts includes stratiform conditions with warm fronts and cumulaform conditions with cold fronts.
• 📉 Warm fronts cause a gradual drop in pressure as they approach, while cold fronts lead to a rapid increase in pressure after they pass.
• 🌐 Global frontal activities include the polar front, which moves with the seasons, and the intertropical convergence zone formed by equatorial heating.

Q & A

What is a weather front?

A weather front is the border between two different air masses, often marked by a change in weather conditions. It is the point where air masses of differing temperatures and densities meet, leading to a transition from one type of weather to another.

How do weather fronts help in predicting local weather?

Weather fronts can be observed from a distance, allowing meteorologists to make predictions about the weather in a local area for the coming days or weeks. The movement and interaction of air masses at the fronts can indicate the type of weather changes expected.

What is the difference between a warm front and a cold front?

A warm front occurs when warm air moves into an area of colder air, typically characterized by a gradual slope and associated with stable, stratiform weather conditions like drizzle. A cold front, on the other hand, is when cold air moves under warmer air, creating a steeper slope and leading to more unstable, cumulaform weather such as thunderstorms and heavy rain showers.

What is the typical speed of a warm front compared to the 2000-foot wind speed?

A warm front typically moves at about one-third the speed of the 2000-foot wind, which is outside the friction layer and represents the free stream flow of air.

How does the slope of a cold front differ from that of a warm front?

The slope of a cold front is much steeper than a warm front, with a ratio of about 1 to 50, meaning for every one unit of distance forward, the front rises 50 units vertically. This is much steeper compared to the warm front's ratio of about 1 to 150.

What is an occluded front and how does it form?

An occluded front forms when a cold front catches up to a warm front. It creates a V-shape with a wedge of warm air in the middle, sandwiched between two areas of cold air. This type of front is typically associated with wet weather conditions.

What types of clouds are associated with a warm front?

With a warm front, one can expect to see cirrus clouds at the highest levels, followed by altostratus clouds in the mid-layers, nimbostratus clouds indicating rain, and eventually stratus clouds as the front approaches.

How does the pressure change as a warm front approaches?

As a warm front approaches, the pressure tends to drop because the warm air is less dense and has fewer particles to exert pressure on the Earth's surface. This results in a gradual decrease in pressure.

What is the intertropical convergence zone and how does it relate to weather fronts?

The intertropical convergence zone (ITCZ) is an area around the equator where trade winds from the Northern and Southern Hemispheres meet, often resulting in a front due to differences in temperature and moisture levels. This zone fluctuates throughout the year and is associated with the equatorial lows and Hadley cells.

What is a polar front depression and how does it differ from a frontal depression?

A polar front depression is a low-pressure system that forms when a warm air mass bulges into a cold air mass along the polar front, leading to a curved wind pattern and the formation of fronts within the system. It differs from a frontal depression in that it specifically involves the polar front and can lead to a series of weather changes as the fronts move around the depression.

What are some global frontal activities mentioned in the script?

The script mentions the polar front, which moves north and south throughout the year, separating tropical maritime and polar maritime air masses. It also discusses the intertropical convergence zone formed by equatorial lows and Hadley cells, as well as thermal lows that can lead to monsoons or tropical revolving storms like hurricanes, typhoons, and cyclones.

Outlines

00:00

🌤️ Weather Fronts and Their Impact

The script introduces the concept of weather fronts as boundaries between different weather systems, which can be predicted to understand upcoming weather changes. It explains how air masses with varying temperatures meet, creating fronts that are characterized by their shapes and slopes. Warm fronts, represented by a red semi-circle, occur when warm air moves into a colder area, causing the air to rise slowly and leading to stratiform weather conditions such as cirrus, altostratus, nimbostratus, and stratus clouds. Cold fronts, symbolized by blue icicles, represent the denser cold air pushing under warmer air, resulting in steeper slopes and cumulaform weather with cumulus and cumulonimbus clouds. The speed of these fronts is related to the wind speed at 2000 feet, with warm fronts moving slower and cold fronts moving faster. An occluded front forms when a cold front catches up to a warm front, creating a V-shape with warm air in the middle and is typically associated with wet weather.

05:01

🌡️ Changes in Pressure and Wind Direction

This section delves into the effects of weather fronts on air pressure and wind direction. As a warm front approaches, the pressure drops due to the increase in warm, less dense air, which has fewer particles to exert pressure on the Earth's surface. Conversely, a cold front causes an increase in pressure as it advances, filling air columns with colder, denser air that exerts more pressure. The change in wind direction, or veering, is also discussed, with the wind direction changing sharply across the cold front and more gradually across the warm front. The script also touches on the global distribution of air masses and the formation of fronts in different regions, such as the polar maritime and tropical maritime regions over the North Atlantic Ocean.

10:03

🌍 Global Frontal Systems and Depressions

The script discusses global frontal systems, including the polar front, which fluctuates with temperature and seasons, and the intertropical convergence zone, where trade winds meet and form fronts. It explains how these fronts can lead to the formation of polar front depressions, which are low-pressure areas with distinct boundaries between warm and cold air masses. The weather associated with these frontal depressions includes a sequence of cloud types and weather conditions similar to those experienced when a warm front is followed by a cold front. The section also covers non-frontal depressions, such as thermal depressions, which form in areas of intense heating, like the Indian subcontinent during the summer monsoon season, and the formation of tropical revolving storms, including hurricanes, typhoons, and cyclones, which are extreme forms of thermal depressions.

15:04

🌪️ Formation and Characteristics of Tropical Revolving Storms

This part of the script focuses on the formation and characteristics of tropical revolving storms, such as hurricanes, typhoons, and cyclones. It describes how these storms form over warm, moist ocean areas, with low pressure and rising air leading to cloud formation and the release of latent heat, which further fuels instability. As these systems move away from the equator, the Coriolis force causes them to begin spinning, creating the characteristic eye of the storm and violent weather conditions at the edges. The script notes that these storms are most common at the end of summer when ocean temperatures are highest and can cause significant disruption in regions they impact, such as the Caribbean, Japan, and other areas prone to these weather phenomena.

20:04

🌬️ Frontal Dynamics and Global Weather Patterns

The final paragraph summarizes the dynamics of weather fronts and their global implications on weather patterns. It reiterates the movement speeds and symbols associated with warm and cold fronts, and the weather conditions they bring, such as drizzle for warm fronts and thunderstorms for cold fronts. The script also explains how occluded fronts form and the weather sequence they produce. It discusses the global frontal activities, including the polar front's seasonal movement and the intertropical convergence zone's role in creating trade winds and fronts. Additionally, it mentions the impact of thermal effects, such as local heating over land or sea, which can lead to the formation of non-frontal and frontal depressions, contributing to the variety of weather experienced in different regions of the world.

Keywords

💡Weather Fronts

Weather fronts are boundaries between two air masses with different temperatures and densities. They are central to the video's theme as they are responsible for changes in weather conditions. The script explains that fronts can be identified and tracked, allowing for weather predictions. For instance, the video describes how warm and cold fronts bring different weather phenomena, with warm fronts causing stratus clouds and drizzle, while cold fronts can lead to thunderstorms and heavy rain showers.

💡Warm Front

A warm front is characterized by warm air moving into an area of colder air, creating a semi-circular shape on a weather map. The video explains that warm fronts slope upwards at a ratio of 1:150, spreading out over a large area and moving at about one-third the speed of the wind at 2000 feet. The script uses the warm front to illustrate the gradual change in weather, with high cirrus clouds developing into lower stratus clouds as the front approaches.

💡Cold Front

A cold front represents the movement of a cold air mass under warmer air, forcing the warm air to rise rapidly. The video mentions that cold fronts have a steeper slope of 1:50 and move at two-thirds the speed of the 2000-foot wind. The script describes how cold fronts are associated with cumulonimbus clouds and unstable weather conditions, such as thunderstorms, which are a significant part of the video's discussion on weather changes.

💡Occluded Front

An occluded front occurs when a cold front catches up to a warm front, forming a V-shape with warm air sandwiched between two cold air masses. The video script explains that occluded fronts are typically associated with wet weather conditions and can lead to a combination of weather phenomena seen with warm and cold fronts. This concept is used in the script to illustrate the complexity of weather systems and the merging of different weather conditions.

💡Air Mass

An air mass is a large body of air with relatively uniform temperature and humidity characteristics. The video script discusses how air masses move over the Earth and interact with other air masses, leading to the formation of weather fronts. The concept is foundational to understanding the video's theme of weather changes, as it explains the interactions that lead to different weather conditions.

💡Pressure Changes

The video script explains how pressure changes occur as different weather fronts approach. With warm fronts, pressure drops as more warm, less dense air replaces the colder air. Conversely, pressure increases rapidly after a cold front passes due to the influx of colder, denser air. These pressure changes are crucial for understanding the dynamics of weather systems and are used in the video to explain the shifts in weather conditions.

💡Isobars

Isobars are lines on a weather map that connect points of equal air pressure. The video script describes how isobars change direction sharply at the front of a cold front, indicating a change in wind direction. This concept is important for understanding weather patterns and the video uses it to illustrate the meteorological phenomena associated with weather fronts.

💡Polar Front

The polar front is a boundary between the cold polar air masses and the warmer tropical air masses. The video script discusses how this front moves with the seasons and is associated with the formation of frontal depressions. This concept is key to understanding large-scale weather patterns and their impact on regional climates, as explained in the video.

💡Intertropical Convergence Zone (ITCZ)

The ITCZ is a region around the equator where trade winds from the Northern and Southern Hemispheres converge. The video script explains that this zone is associated with the formation of fronts due to differences in temperature and moisture levels. This concept is used in the video to describe the global weather patterns and the formation of weather systems near the equator.

💡Frontal Depression

A frontal depression is a low-pressure system that forms at the boundary between two air masses, typically a warm air mass bulging into a cold air mass. The video script describes how these systems can lead to a sequence of weather changes, starting with conditions associated with a warm front and followed by those of a cold front. This concept is integral to the video's discussion on weather systems and their impact on regional weather.

💡Thermal Depression

A thermal depression, as mentioned in the video script, forms due to surface heating, causing air to rise and creating an area of low pressure. This concept is used to explain local weather phenomena, such as the monsoon season in India, where heating over land leads to the formation of low-pressure areas and subsequent storms. The script also connects thermal depressions to the formation of tropical revolving storms, which are extreme versions of these weather systems.

Highlights

Fronts are the border between weather systems and can be identified by changes in weather conditions.

Weather fronts can be predicted from a distance, aiding in forecasting local weather over days or weeks.

Air masses meeting due to temperature differences create fronts with distinct shapes and sizes.

Warm fronts occur when warm air moves into an area of colder air, represented by a red semi-circle symbol.

Cold fronts are characterized by cold air moving under warmer air, symbolized by blue icicle shapes.

The slope of a warm front is much gentler than that of a cold front, affecting weather spread and travel speed.

Occluded fronts form when a cold front catches up to a warm front, creating a V-shape of warm air between cold air masses.

Weather at fronts is influenced by air mass density differences, leading to stratiform or cumulaform conditions.

Pressure changes occur as fronts approach, with warm fronts causing a drop and cold fronts an increase.

Isobars show distinct patterns around fronts, indicating changes in wind direction and pressure.

Global frontal activities include the polar front and the intertropical convergence zone, influenced by seasonal temperature fluctuations.

Polar front depressions form when a warm air mass bulges into cold air, creating a low-pressure area with distinct fronts.

Thermal depressions occur due to surface heating causing air to rise and form low-pressure areas with unstable conditions.

Tropical revolving storms or hurricanes are extreme forms of thermal depressions, causing significant atmospheric instability.

Frontal depressions bring a sequence of weather changes, from warm front conditions to cold front instability.

Non-frontal depressions like thermal lows can also influence weather, especially in regions with intense surface heating.

The interplay of fronts, air masses, and pressure systems drives the complexity and predictability of weather patterns.

Transcripts

fronts are the border between one

weather system and another and they come

in various shapes and sizes but what

happens when these fronts approach and

pass over our location

let's find out

[Music]

hi i'm grant and welcome to class 15 in

the meteorology series

today we're going to be taking a look at

weather fronts weather fronts bring with

them a change in the weather conditions

it could be for the better could be for

the worse but in any case it is a change

and we can often see these fronts

approaching from quite far away so it

can help us to make predictions about

what's going to happen to the weather in

our local area for example over the next

couple of days or even couple of weeks

when air masses move over the earth they

sometimes meet other air masses which

are hotter or colder and because of the

temperature difference that means that

there's a density difference

and the air masses tend not to mix and

instead there is a quick transition from

one air mass to the other which we call

a front this is the border between two

different air masses

and fronts come in a few different

shapes and sizes

the first one is a warm front

a warm front is when warm air moves into

the area of colder air unsurprisingly

the line on the earth will look like

this and have sort of semi circles

think of as half sun shapes is what i do

to remind me that it's a hot front and

it's usually red in color

and that'll show the line at the earth's

surface

and the front itself doesn't stay

vertical it instead slopes up towards

um the colder air because the hot air is

rising above the cold air the ratio of

what it does this is about one to one

hundred fifty so we go up one meter and

a long 150 meters so it's quite shallow

and it spreads out quite far it could be

in the region of about 600 700 nautical

miles in total length that this warm

front um

covers

and the warm front travels at a certain

speed and it's usually a third

of the speed of the 2000 foot wind and

why the 2000 feet wind well

at 2000 feet we're sort of outside the

friction layer so it's the free stream

flow of air and the warm front moves a

third of that speed

the opposite to a warm front is a cold

front

and this is where cold air mass moves in

and forces its way

under warmer air

due to it being higher density and it's

given this symbol which is sort of like

icicles i think of it as and it'll be

blue in color

the slope of a cold

front

is much steepers normally has a ratio of

150 so we go forward one and up 50 which

is a lot steeper than the warm front and

this means that it's not as spread out

typically

uh only nears a distance of around 100

nautical miles in total length

and a cold front can often be held at

the surface by surface friction and it

can lead to an overhang forming which is

known as a cold nose

and this cold nose repeatedly forms and

collapses and forms and collapses which

leads to sort of gusty wind conditions

as it's doing that

the speed of travel of a cold front is

faster than a warm front it's typically

two-thirds of the two thousand foot wind

or two-thirds of the wind outside of the

friction layer

occasionally

a

cold front

will catch up to a warm front this is

because the cold front is obviously

moving at two-thirds the wind speed and

warm front is only one third the wind

speed so occasionally they catch up and

we get something known as an occluded

front

an occluded front basically forms a v

shape of warm air

in the middle where the two fronts

become connected and ahead of it you get

cold air behind it you get cold air just

with this little sandwich of warm air in

the middle

an occluded front front is normally just

associated with wet weather conditions

so weather is formed at the fronts

because

some air mass is being forced to rise

above another air mass because of those

different densities

with a warm front we see

stratiform weather

so the ascending air is forced up quite

slowly because of this gradual

slope

and we'll see

fairly stable stratiform conditions and

it will lead

the actual line of the front on any

charts because the line

shows it on the surface and obviously

we're sloping towards that so you'd

start off with maybe cirrus clouds very

high up

getting towards alto stratus clouds

again stable in that mid layer

nimbostratus

around sort of this region and

eventually stratus behind it

and you'll basically see the cloud base

the lowest level of cloud lowering

as the

front approaches your position if we

were standing here and this is passing

over us

our cloud base starts all the way up

here and starts to lower as this front

approaches in contrast

a cold front forces its way

underneath warm air at quite a quick

rate at 1 in 50.

and so it causes the warm air

located here to rise quite rapidly

and makes that unstable conditions which

is cumulaform weather producing as a

result so you get cumulus nimbus clouds

those storm clouds you get cumulus

clouds and eventually you get

altocumulus up in this sort of region up

here

and with an occluded front we see

a wedge of warm air produced

in between the two colder air masses and

as a result we get a bit of a stratiform

area leading in and a cumuliform

area after the front and again you get

nimble stratus and cumulative just

associated with wet weather in general

if we think of a few columns of air

where a front passes we can

easily figure out what happens to the

pressure as these fronts approach so

first we'll have a little look at a warm

front

so each column of air

will have a different proportion of warm

air and cold air due to the slope of

this front you can see this has a lot of

cold air whereas this has a lot of warm

air

warm air is less dense which means there

are fewer particles per unit area

so this column on the right has a small

proportion of air with not many

particles in it

and the particles are being pulled down

by gravity and imparting a pressure onto

the surface of the earth that surface

pressure that we're going to measure

as we move to the left or you can think

of it as this warm front passing over

this same column and this just being

three

time shots

of that same column

and

basically more and more of the column

is made up of this warmer less dense air

and that means that there's fewer

particles in the air and that means that

there's fewer particles being pulled by

down by gravity and imparting that

pressure onto the surface

so overall you can see that as a warm

front approaches

the pressure drops as a result you get

one zero one zero

one double eight one two six and so on

and so on as the pressure

drops as the front approaches

a cold front is a bit different because

the cold air is forcing its way under

the warm air

and if we have a look at the columns of

air then as the front approaches

nothing's actually happening it's only

once the front hits that we start to get

parts of these columns made up of

that colder more dense air because it's

more dense there's more particles more

particles get cooled down by gravity

therefore more pressure

as a result and you will see

that

it will increase the pressure rapidly

just after the front's passed and it'll

be rapid because you've got that steep

um steeper angle

so quickly you get more and more

of these columns made up of colder

basically higher pressure air so both

fronts will do something interesting to

isobars let's just take a look at the

cold front for example so we know that

the pressure increases rapidly after the

front has passed so we've got 1006

here and here and then it goes to 1008 1

0 1 0 and so on so if we

were to draw these individual pressures

joined up

in isobars

then we'll see something quite

interesting

so once the lines are all joined up on

all these spot pressures joined up we

can see that there's a very definite

change as we pass over the cold front in

terms of the direction

of these isobars there's a very

sharp angle at the front and that

basically means the wind direction

changes as well

so at the surface you would get one

that's not exactly aligned with the

isobars because

in the northern hemisphere the wind

backs as it goes down

but then if you still take a

fairly standard backing of maybe like 40

degrees and apply over here as well

you can see that the wind has changed in

angle

by the same proportion as the isobar has

changed

so as a cold front passes the wind veers

round

and the same thing happens when a warm

front passes as well

so across the world there are different

air masses that dominate certain regions

such as the tropical maritime

region and the polar maritime region

over the north atlantic ocean

and where these air masses meet a front

is formed and depending on the time of

year this polar front this boundary will

be higher in latitude or lower in

latitude

as the warming areas warm and cold areas

sorry fluctuate with the temperature and

the seasons

they will also vary with pressure

patterns and other factors such as

competing ear masses

and this front changes and it's very

rarely a straight line like this and it

can cause bumps and

indentations into each other's air

spaces

and something

that forms sometimes is called a polar

front depression which we're going to

have a look at just after i've explained

something else

another common frontal zone exists

around the equator in something known as

the intertropical convergence zone

so what happens is at the equator

it's very hot so that surface heating

causes

air to rise out which ascends up

it spreads out starts to cool down and

then descends back to earth in the

hadley cells i've mentioned them before

in previous classes this creates high

pressure areas around the tropics

air likes to flow from high to low

pressure so it flows back in towards the

low pressure area caused by this surface

heating at the equator as it starts to

flow it gets pulled round to the right

in the northern hemisphere and to the

left in the southern hemisphere this

creates some predictable winds known as

the trade winds which are north east in

direction in the northern hemisphere and

south east in direction in the southern

hemisphere

where these winds meet a front is

produced because the air masses will

have slightly different temperature and

moisture levels

and it will vary throughout the year in

the same way as this polar front does

through the seasons

so i talked earlier about how the front

between the tropical and polar maritime

air masses kind of fluctuate and bulge

and sometimes a frontal depression will

form a polar front depression we call it

this is when a warm air mass or the

tropical maritime air mass bulges up

into the cold air and the wind starts to

curve around the air the bulge as a

result and a low pressure area is formed

at the tip of the warm air and forms a

shape that looks like this

the air masses will have distinct

boundaries with the warm air moving

northeast

and the colder air mass moving southeast

and a front forming at the cold and the

warm areas respectively this low

pressure area is a depression and it has

fronts in it hence the name frontal

depression and the fronts will then be

moved with the prevailing wind around

the depression and the depression itself

will move in the direction of the wind

in the warm sector so you get these

fronts starting to move round the low

pressure zone like this but the overall

bulge will move horizontally like this

and this is why in europe we experience

a lot of these frontal depressions these

waves of weather coming in and you might

associate

places like ireland

uk with constantly having

rain

and storms and stuff like that this is

one of the reasons why because these

fronts

move in and hit

ireland in the uk all the time the

weather associated with a frontal

depression is the same as if we had a

warm front then followed by a cold front

so at the warm front we will see slowly

rising air over a long distance which

means we get

cirrus clouds up top

and then altostratus and nimbostratus

and stratus clouds the cloud base will

be lowering as the front approaches our

position

and as the front passes over our

position we'll see a temperature

increase as we go into the warm sector

we will see an increase in the humidity

of the air and therefore a higher dew

point as a

result and we'll also see the pressure

falling off as we saw earlier

and

again with that pressure and that

frontal drop off we'll see the isobars

changing so we'll get a change in the

wind direction in the warm sector we'll

see low stratus clouds as the warrior is

maritime air it's full of moisture but

the low

the high temperature air is slightly

more stable so we don't associate with

very cumuloformed clouds and as the cold

front approaches and passes we will

start to see the rapid ascent of this

warmer air leading to unstable

conditions thunderstorms heavy rain

showers etc and as the front passes

we'll see the pressure increasing the

temperature will fall as we go back into

the colder air which means the dew point

falls and the humidity falls as well

eventually we will get occluded fronts

forming where the cold front catches up

to the warm front

this happens first where they're closest

together so it'll be at that tip of the

um the sort of triangular pattern

and

then they'll start to spread down and

eventually you end up with a fully

occluded front it's almost like if you

zip up

the polar front depression that's how

the occluded fronts form so just as

there are depressions with fronts in

them frontal depressions there's also

some without fronts in them which are

non-frontal depressions surprisingly

there is one

sort of non-frontal depression that

there is worth adding a bit of extra

information about

and which is called a thermal depression

so these form in certain areas year

round like the equity equatorial lows

and hadley cells that we looked at

previously but they can also form in

specific areas depending on the season

so thermal lows form because the surface

temperatures heat up and cause the air

to rise creating an area of convergence

at the surface

and rising unstable air in the center of

the low pressure area something that

also happens

is

as a cloud is formed by the rising air

and the

um

condensing air into clouds

some latent heat is released from the

air mass itself and that means that the

rising air is now warmer than the

surrounding air because of this latent

heat release which can cause even more

unstable conditions

a common place that this happens is

somewhere like india

throughout the summer gets very hot and

as a result there's a large low pressure

area

which is formed over the land and it can

move over the ocean

lead to a lot of air rising over the

ocean moisture filled air huge clouds

and storms

form as a result towards the end of the

summer which is the monsoon season

tropical revolving storms or

hurricanes cyclones or typhoons

are another version of these thermal

depressions but in its most extreme form

so a very deep depression will form in a

warm equatorial region

over the ocean

these areas of low pressure start to

move away from the equator and if they

move over dry land then there's not

enough evaporation to form any storms so

it's no issue but if they move over the

ocean then there's more moisture in the

air it's a more humid environment and it

rises and it condenses to form clouds

this releases a large amount of latent

heat and causes even more instability in

the atmosphere

once this area of low pressure and cloud

moves sufficiently far away from the

equator about 500 kilometers then it

starts to feel the effect of the

coriolis force and a spin starts to form

this spinning motion starts to spread

the clouds away from the center and an

eye

form the eye of the storm

and at the edge of the eye we have the

most

violent weather conditions experienced

so violent in fact that of course it

causes massive disruption to

places like the caribbean or you know

japan gets hit by these quite hard and

it's only certain places that these form

because we need very specific conditions

we need a warm ocean

with a low pressure area that is very

large

so

they tend to happen

normally at the end of summer as well

because the oceans had a large amount of

time

to heat up and form this low pressure

area

so over the atlantic when they hit

places like the united states and the

caribbean we call them hurricanes what

happened towards the end of summer in

july october time

in the pacific in general in japan

and

places like the philippines

they would call them typhoons usually

and again it would be the northern

hemisphere end of summer so july to

october

and in the indian ocean over the south

of the indian ocean

they tend to call them cyclones

and they'll happen in the

at the end of the summer

for the southern hemisphere which would

be sort of january to march time but if

they hit the indian ocean in the

northern hemisphere it would happen

again at the end of summer which would

be july to october but still called

cyclones in summary then you've got a

warm front which moves at one third of

the 2000 foot wind speed it's got a

slope of about 1 to 150 it's given this

little red

half sun symbol

it slopes up very slowly and gradually

leading to stratiform conditions which

lead ahead of where this cold front

sorry the warm front actually is on the

surface you get cirrus altostratus

nimbostratus and stratus clouds typical

stable sort of conditions

and drizzle that sort of thing

a cold front is the opposite it moves at

two-thirds of the 2000 foot wind speed

it's got a slope of one to 150

and it

forces its way under warmer air causing

that warm air to rise rapidly it can

lead to very cumulaform clouds

as a result

and cumulonimbus big storm clouds and

it's given the symbol of this sort of

pointy blue line

and

most of the weather will be in and

around the cold front itself

and because it's not got this very low

gradual slope leading ahead of it it

actually slopes behind it

because of the cold front moving faster

than the warm front eventually the cold

front will catch the warm front ahead of

it

and you get an occluded front as a

result which basically means you get

warm front weather

followed by cold front weather

and the warm sectors kind of squeezed up

into this v shape it's given the symbol

which is just a combination of the two

for cold front and warm front so as the

front approach interesting things happen

to the pressure think of the columns of

air

and the warmer air being less dense

colder air being more dense

uh air that is less dense fewer

particles to push down on the earth and

create pressure

so if we look at the warm front first

which is these figures up the top we'll

see that as the warm front approaches

more and more of these columns are made

up of hot air

and or warm air and the pressure drops

as a result quite gradually

a cold front would be the opposite

we see that the pressure

increases

rapidly after the cold front has passed

because there's more

cold air in each of these columns more

dense more particles more amount of

particles pushing down on the earth's

surface and it's faster change than the

slope

because of the

it's a faster change than the warm front

because of the slope difference between

the two so you get various global

frontal activities you get the polar

front which moves north and south

throughout the year it's the board line

between the tropical maritime and the

polar maritime

you get the equatorial or sorry the

inter-tropical conversion zone which is

formed by the equatorial lows and the

hadley cells

the warm air the equator rises creates

low pressure zone that air starts to

spread out falls back down to earth

creating high pressure the

tropical zones

air flows from high to low gets pooled

around with the coriolis force we get

the trade winds as a result which are

north easterly in the northern

hemisphere southeasterly in the southern

hemisphere where those winds meet

into tropical convergence zone a front

is formed there we also get more local

versions of this sort of thermal effect

and where we get

a lot of heating

over land causes a lot of air rising or

even over the sea

and the most extreme version would be a

tropical revolving storm we got a large

area of low pressure lots of rising air

because it's so full of moisture

those clouds start to condense out

as they condense it creates heat that

heat leads to these parcels of air being

even more unstable more rising and as it

moves away from the equator it starts to

spin causing a lot of damage as it does

so hurricanes typhoons cyclones whatever

you want to call them tropical revolving

storms so as you get non-frontal

depressions we get frontal depressions

frontal depressions basically form from

a bulge in the polar front or indeed it

could be the intertropical conversion

zone

and essentially you see

weather from a warm front then a warm

sector where there's low stratus clouds

and then you see weather from a cold

front so as one of these passes you'll

see the pressure start to drop it'll

start to stabilize for a bit and then it

will increase rapidly behind

you get all the weather that's

associated with it you get the wind

direction changing

um

and this sort of thing happens a lot to

northern europe these

polar front depressions

blow over the atlantic and we've got

lots of frontal activity in northern

europe as a result