hello learners hope that you are keeping well today's lesson is climate and weather and our focus is on mud latitude cyclones all right i'm going to simplify it i don't know why it's a challenge for for learners but the main thing is here is not just learning your workout all right and just putting it there it's about applying it and that's what makes this section actually simple okay now of course we look at the general characteristics i must just get my pen again right my highlighter rather we look at the general characteristics areas of formation conditions necessary for formation stages of formation associated weather with each of these little cold front warm front occluded front conditions uh cyclone families impact on the environment we look at the case study uh precautionary measures and management strategies identification on a synoptic map satellite images okay we look at various of these things okay and we'll go ahead and we'll simplify the thing for you all right now let's start off with the basics of our middle attitude cyclone first of all we need to know that there's alternate names temperate cyclone extratropical cyclone frontal depression wave cyclone so these are various names that can be used for calling or naming middle attitude cyclones but the common one we find is always used in exams etc is the term mid latitude cyclones now we need to know that it is a low pressure system all right and it occurs in the middle latitudes of the earth usually around 30 to 60 degrees celsius okay when we look at it here 30 to 60 degrees celsius in this region it occurs okay now it occurs north and south of the equator on both sides right of the equator you get this uh two distinct characteristics it's made up of a cold front and a warm front don't mix we find sometimes talk about uh about the eye etc this that's the tropical cyclone here we have a cold front and the warm front uh cold fronts reach and effect south africa mostly in winter sometime they're getting them coming through in late summer etc when high pressure belts are in the northerly position now i'm going to show you here remember your teachers would have told you about the itcz when it's summer in the southern hemisphere remember the itcz moves southwards all right and when it's winter in the southern hemisphere the itcz is found in the northern hemisphere and the itc itcz into tropical convergence zone is a low pressure area so what happens when it's in the southern hemisphere the itcz ends the high pressures don't move up do you understand so they stay in their suddenly position because it moves from high pressure to low pressure you understand and when they it's winter in the southern hemisphere then the itcz is obviously in the northern hemisphere and the high pressure systems will move towards this low pressure system and they'll be in a northerly position and this explains it because if these high pressure systems are in this suddenly position especially the south atlantic high it's going to reach and block the cold front from coming in okay but if it's in its northerly positions it's moving north you understand what happens now it allows the cold front to come in and effect the country okay so that is why you have cold fronts affecting the country mostly in winter all right and they bring in cold fronts effect south africa uh winter in winter bringing rainfall like in the western cape you find they receive winter rainfall because of the mediterranean climate obviously and because of the cold fronts coming in and uplifting the warming you understand creating condensation cloud cover and uh the rainfall occurs all right and there whoa criminal creeped in here all right wrong it moves from west to to east okay not east to west i apologize for that from west to east all right so it moves from here west towards east sometimes it's also known as southwest to northeast but the general direction is from west to east so i'm going to put a red line here no my apologies i'm now getting mixed up okay so it moves from west to east we'll talk a little bit more about it all right as we go through the formation and we find that what actually happens here just in a brief and i know it's not uh really making sense at the moment when i say the warm front bends southwards away from the cold front you understand in a way so therefore it does not affect south africa okay i'll go into a little bit more detail of this later on okay so we basically can sum up from here that the cold front affects our country south africa and not the warm front okay and i've got it right here it moves from west to east my apologies it's my gray hair down here that's actually made twice and put in the tropical cycle of movements so i do apologize for that okay right so but it's good actually on one hand that i showed you the difference already i'm trying to make excuses okay so it moves from west to east right now how does it form okay how does it form now if we take this area here all right the sub polar low we've learned along this area is the polar front okay the polar front it's not totally stationary although on many occasions it's considered stationary all right now that's the polar front it forms at the polar front it starts to fall okay that's what we must remember now what happens here warm moist air from the subtropical high there we have it here the warm moist air is coming in all right towards the sub polar know all right which actually has warm moist air uh pressure belt it meets with the cold dry polar high pressure hey all right at the polar front can you see there's the cold dry polar air moving in here obviously it's been deflected right due to the rotation of the earth and coriolis force so what do we have here now warm moist air from the subtropical high uh cell and cold dry air from the polar cell they meet on both sides of the polar front all right these masses blow past each other in opposite directions so if i look at this it's flowing this way all right and if i look at this it's flowing in the other direction so we have two and opposite directions on both sides of the polar front then a disturbance is created along the polar front which causes unstable air so what happens along the polar front there's a disturbance a bend you understand or i can make a bend like that okay so what happens is the cold air moving yeah all right as shown down here and there's the warm air moving this way can you see it it moves southwards this disturbance this bend all right will then cause the cold air to come in here and force some of the warm air up here and if it does that you understand unstable is moving up all right this creates a low pressure around that point because once a is uplifted you will find a low pressure being created that is your start now obviously when this starts happening it results in a circulation of air obviously you can see the cold air on this side moving warmer that side and you can see a clockwise direction okay because the warmer is pushed further south and the cold air is moving more northwards okay and that starts the circulation i'm going to draw something here okay there's it moving that way and that way now the circulation has started in that area and then you start getting your magletto cyclone starting to form okay we just got a rough idea that that is why we have to bring in our grade 11 work to look at it and this obviously is in the westerly balance okay you've done that in grade 11. okay let's go further now let's look at the stages okay now i know there's a debate we call it the initial stage and we always debate this nothing has really happened this is how the flow happens at the polar front but we're not going to look at it that way we're going to call it the first stage all right now you already saw that the warm air from the uh subtropical high coming in the cold polar air we're not showing the deflection here but that's how it comes in they're flowing in opposite directions all right so we say there is a boundary the polar front separating the warm air to the north okay that's in the north from the colder to the south that's your polar air coming in the air masses do not mix they on both sides of the polar front all right and air moves parallel to each other can you see this one in this direction as shown by the arrow and this one in this direction the cold dry eh all right from the polar so they move more less parallel to each other in opposite directions okay can you see it again opposite directions the polar front is often stationary it stays in one bit not always all right the polar front can move it's not always at 60 degrees so it can move but on many occasions it can be considered stationary but overall is not always stationary we must remember that right now what's going to happen all right this is when the cyclone really starts to form the middle attitude cyclone and we say a wave forms on the polar front all right there's the wave here can you see it all right it can be surface obstructions also but one of the big things that actually caused this wave all right uh in the upper level sorry uh a wave forms in the polar front as an upper level disturbance embedded in the jet streams so upper air disturbance happens here all right can be surface also by the upper level and now this jet stream will cause a disturbance what is a jet stream all right uh jet streams are currents of high above the earth they are found there they move eastwards at attitudes of 8 to 15 kilometers so there it's moving eastwards all right these jet streams and as they move all right they create a disturbance here all right it moves over the front over the polar front can you see it moving there all right and the front develops a curve all right it moves eastwards red develops a curve okay where the wave is developing the bend and the wave is developing of course the warm air is now uplifted because of the curve the cold air is moving in northward southwards and warm air gets uplifted all right pressure decreases here all right pressure you decrease in pressure right and you can see it clearly here because the air is rising so the pressure is decreasing in the southern hemisphere cold air moves northwards can you see the cold air now it's moving this way because the disturbance has been played the wave is there it's moving northwards and the warm air moves southwards as i showed you earlier i'm repeating myself but it's good that we do that because it's pushed like that all right of course the opposite is true for the northern hemisphere in the sense that it's facing that way all right so we have a situation where the cold front if it's sitting like that and we have a disturbance then the cold front will move southwards okay southwards right precipitation starts to occur and heaviest along the frontal boundary along this area so we already start having precipitation in this area all right so that's the development then we reach the mature stage now first of all you see the wave there and you see two distinct fronts here now they are completely uh away from each other all right can you still see the northward movement here and the eastward movement of that due to the disturbance when the jet streams came in all right so it's clear it's distinct we have two clear distinct fronts cold front warfare and that's how you know it's in the mature stage they do meet at the apex at the low pressure so cold air moves quickly northwards there's it moving rapidly now all right forcing the warm front southwards and the warm front moves gently all right because it's also not you must remember this pressure gradient is steeper at the cold front because it's cold dense you understand so it moves its steeper gradient you understand there's more movement and of course it's warmer at the warm front so the gradient is more gentle a slower movement all right southwards okay obviously it's the opposite in the northern hemisphere okay the easy a clearly defined cold front and warm front and warm sectors so there you can see clear there's no mixing like this warm cold whatever it's clear just a cold front i call them the thorns you can see and a clear warm front this is the mature stage i call them the semicircles and in between the warm sector clearly show all right clearly show okay rainfall occurs with the heaviest rainfall along the cold front remember the cold front has got a steep pressure gradient i'll do that in a little more detail we'll look at the cross section also steep pressure gradient you understand so it's gonna if it's a steep pressure gradient watch my hands there's the warmer here it comes in and lifts this rapid up movement all right of the warm air in front because of this steep pressure gradient and pushes it up that is why you'll find cumulative numbers clouds etc forming here but we'll talk about that later all right so heaviest rainfall along the cold front due to the upliftment and i would like to say rapid upliftment of the warm air so it's heavier you will get rain at the warm front but it'll be less you get consistent rainfall soaking rainfalls etc then we have the next stage which is the occluded stage now what happens here remember the cold front is moving faster than the warm front you know why now it's deeper pressure gradient than whatever so what happens is the cold front moving faster than the warm front catches up with the warm front can you see it here catches up with the warm front you understand can you see them here clearly indicated all right and then the cold front overtakes the warm front forming an occluded front you understand generally the term occlusion the upliftment of warming you understand so in all types of occlusions you must remember warm air is uplifted you understand or the warmer eh is uplifted sometimes you get a mistake we think warm we talk 20 degrees or whatever let's put it the warmer air is uplifted and then of course last one and i don't have a diagram for it because now the cyclone doesn't exist anymore so we have the dissipating stage yeah the warm air all the warm air is uplifted from the ground so the warming is gone what stays at the ground now it's the cold day of course pressure will increase you understand and there's no low pressure now okay because all the warm air has been pushed up and then what happens is the cyclone dissipates well finished and of course rainfall will seize because there's no more warm air rising okay and therefore the cyclone is gone okay now let's look at the cross-section of this okay i showed you a view of how it look cold front all right warm front all right this is the occlusion but i'm showing you here cold front warm front okay it works like that and depending where you're talking about why i put these two diagrams if you get a cross section you ask you draw a cross section and you look at this and you see occlusion you understand also must draw an occluded front watch where the examiner is asking you to draw the cross section and if you look here he's asking you or she's asking you from a to b is there any occlusion at a to b no so watch be careful about that if it was down here was a different story there's an occlusion but it's a to b there's no occlusion occurring there the warm front the cold front and the warm front are separated now learners please you guys lose marks you do everything correctly when an examiner asks you to draw or your teacher asks you in the test or whatever to draw a cross-section you do everything but what do you do wrong you draw the symbols yeah you understand no once you draw the symbols then it becomes the symbol it's not a cross section notice it's just a line and it's labeled as the cold front warm front obviously you want to do red and blue if you want to you can do so in terms of the cross section you just have a pen in front of you it doesn't matter about the colors okay so please note that okay that it's just lines representing them not those thorns as i call them or semi-circles it's incorrect you get no marks for that okay we've got that clear see let's start off with this cold front all right we can see down there there's this cold front okay so cold front pressure gradient at the cold front is steep you can see it it's steep because of the cold air you understand it's steep right resulting in rapid uplift of warm air right when steep gradient comes in like a bulldozer all right and forces this warm air up so there's rapid uplift and you just wrap it up loof love movement there's it goes to a higher extent and as it cools it's gonna form a cloud of vertical extent cumulonimbus clouds can you see that is why you get your big clouds in those areas right obviously right the temperature decreases because it's a cold front coming in the pressure decreases because if the air is uplifted at this point there's less air here am i right resulting in a low pressure that's how you read it right i know many resources you have just says pressure decreases but why because the air is getting uplifted therefore less area pressure decreases with the cold sector all right uh but increases with the coal sector as it says warmed up then the cold sector comes in there's more air near the surface less rising it obviously the pressure will decrease or increase rather because now it's subsiding so the pressure increases humidity decreases because of this air coming in here the cold front you're insane and cold sector right cloud cover increases because all the moisture is being forced up you understand this condensation and the stimulant numbers cloud is forming so cloud cover increases and you get this cumulative numbers clouds because a is rapidly uplifted so we get this cloud of vertical extent chances of precipitation increases it can be heavy rain for snow that may happen right over these areas all right so precipitation increase you can get heavy rainfall we'll do a case study later you'll see that all right it can be heavy rainfall snow happening etc all right even due to veering and backing wind direction changes all right veering and backing now what is that okay veering is when warm eh all right due to advection all right actually has a change and it turns anticlockwise all right in the southern hemisphere as it rises it turns anti-clockwise in the atmosphere that is veering all right anti-clockwise and in the southern hemisphere and backing when cold air advection takes place there is a clockwise circulation in the southern hemisphere so veering changes anti-clockwise as the warm air advection occurs when the liquid moves in the atmosphere horizontally you understand you get a anti-clockwise and with the cold infection you have a clockwise circulation now these changes actually change the direction of the movement of the a all right of course the opposite is in the northern hemisphere all right not never see as the opposite veering is uh clockwise backing is anti-clockwise in the northern hemisphere and because of these movements the winds get stronger all right stronger because directions are changing at times and the winds get stronger that is basically your cold front situations in the warm sector there's decrease in wind speeds all right because it's warm there's not much upliftment happening here until the cold front comes in you understand so it's just warm conditions and if it's warm there's not much upliftment wind speeds are low all right karma conditions because wind speeds are low therefore it'll be karma conditions right it's not moving possibility of sun drizzle if there's a little condensation but sometimes we have no rainfall here and the higher humidity here because the air is moist there's not much condensation so the humidity is higher can you see what i'm doing to this i'm making sense of it let's look at the warm front now and you see the warm front the pressure gradient at the warm front is gentle and if you notice this steep pressure gradient here can you see it like the bulldozer as i always say it's a steep pressure gradient it's forcing rapid upliftment but yeah it is gentle it's can see the gentle gradient here so what happens here a riser along this front okay it rises all right so as it rises obviously it's going to cool and cause some rainfall so temperature increases because it is the warm front pressure will decrease because air is rising therefore there's less air here not such a rapid movement but still air is moving up so pressure will decrease humidity increases because as the air moves all right and then cloud cover occurs because as it moves up you understand it cools and condenses but you're not going to get this huge cloud here you're going to get more of a horizontal i would say at an angle it can't be totally horizontal but you'll get a more one stretching out and that is your number stratus clouds right precipitation here is soft soaking rainfalls differences from the cold front to the steep pressure gradient rapid approvement here the air rises along the warm front so you've got different type of rainfall everything you have reasons for and it makes things simpler to understand okay i've got a little diagram here that shows you the different types of clouds can you see it cumulative numbers here this shows you a better vertical extent it shows you the anvil shape etc okay so that is your cross section and the weather stations all right now the occluded stage and you know an occlusion takes place when warmer air is uplifted i'd like to change that to warmer eh all right whoa man i want to add that r e r to here warmer okay so i don't get a misconception it's 20 some odd degrees whatever it can be much lower but it is warmer than the other a all right warmer air is uplifted that's an occlusion all right now let's look at we got two types of occlusions a cold front and a warm front occlusion i learned as you've i don't know why you find the difficulty in this but let's look at some simple things in identification all right you know that's the cold front that's the warm front right that's the cold front that's the warm front here okay the warm frontier now one way of identifying it is if it's a cold front occlusion it seems like the cold front is touching the surface can you see it if it's a warm front occlusion the warm front is touching the surface that's one thing that you can identify and if they are if anytime a question like that comes out then you know hey cold front warm front occlusion all right so warm front cold front touching cold front occlusion warm front touching warm front occlusion right now let's look a little bit more at this cold front occlusion results when the statically more stable a behind you understand the cold front okay so this now if you look at it there all right the cold front now undercuts the warm front okay so we say is more stable it's colder all right when we say the statically more stable a this means it's very cold can you see it and it's cold here right so this air relatively is warmer than that okay so what actually happens here is because this a is heavy it's stable a steep pressure gradient okay what it's gonna do it's gonna go and undercut the warm front and as it goes through it undercuts and pushes the air up okay in the occlusion stage that's a cold front occlusion okay cold air from cold front coming through all right because it's more stable it's colder it's forcing the warm air up it's going underneath under cutting and pushing it up that is why it's touching the surface with the warm front occlusion now watch this when the cold air behind the occluded front is warmer can you see it's cool here and it's cold here can you see it so behind there it's cooler and cold so relatively this air is warmer than this air so what happens now then the air ahead of it can you see cold cool so what happens now in the warm occlusion acts in a similar way to a warm front the cold air behind the front is less dense can you see it because it's cooler and that's cold then even the colder air above it it's colder yeah so it passes over the colder air so because this is colder it's more stable and this is cooler behind the occluded front so what happens with this egg it goes over the colder air and that is why the warm front touches the surface okay so again both cases the so-called warmer air is pushed up you understand yeah this is the warm air the cold front is more stable the air behind it is more stable it undercuts and forces the warm air up yeah the air behind the system is cool and the air head is cold so the cool air rises above okay it overrides the cold air it goes over okay i can understand it's quite a complex thing guys but you remember those simple things i spent a little time on it now remember that to identify alone again the cold front is touching the surface cold front occlusion the warm front is touching the surface warm front occlusion here the air behind is colder so it uplifts the air or undercuts the air in front of it of the warm front which has a higher temperature yeah it's behind the air is cooler and the air head is uh is cool and the air head is cold lower temperature and therefore the cooler air overrides it goes over and rises okay i've spent a lot of time and your data on that okay right let's look at some synoptic interpretations etc now can you see here the dense cloud cover learners that is your cold front you can see the cumulonimbus clouds dense cloud cover all right that's your cold front hitting southern africa here can you see it all right there's another one coming in down here you can see that white patch all right there it is down here and this one has come through can you see it here how the synoptic map is made by looking at the satellite and you can clearly see the high pressures are in the northerly positions can you see that so it's allowing the cold fronts to come in so this is more typical of a summer condition what do you notice about the weather symbols down here where the cold front does it it's completely black in color all right because it shows you cloud cover cumulative numbers clouds can you see it cumulo numbers clouds as it's moving yeah you may see some clear patches i do apologize it's not very clear that the map itself but you see some clearer patches partially cloudy etc okay because the cold front has not gone there yet okay see one where the symbols will show changing in wind speeds greater wind speeds all right overcast conditions all right so this is your summer northerly position right uh it shows you another one here a satellite photograph can you see the band of clouds yeah cold front the band of clouds yeah cold front is now moved over cold front you understand brilliant if you look at these satellite images from here the synoptic map is made all right i found this one very enjoyable all right because this is the buga as i say this one is the south atlantic is very strong and this is the one that reaches okay look at this one this kalahari high is doing some raging yeah okay so it's quite unusual that you see that and it's blocking to a certain extent you notice they're starting to move norway they're starting to move northwest to a certain extent so if i had to look at the season of this this higher order it's towards the latter part of your winter season so they still uh uh it's starting to uh sorry your the winter season is moving towards your summer season all right it's moving towards your spring and then your summer i'm forgetting my seasons also okay so it's starting to move up but there's still some blocking and i found this to be interesting how the kalahari high is doing some blocking mostly this one does the blocking of the when it reaches of the cold fronts okay and you look at the word yeah learners family of france when there's a few uh uh mutual attitude cyclones coming in we call it a family of mid-latitude cyclones so i'm going to change this word france and put a cross and call it family of mid-latitude cyclones when there's few like there's three mid-latitude cyclones it is a family of middle cyclones that's occurring a few like three occurring in the area look at this a beautiful occlusion is starting can you see this is in the mature stage of this area all right although this is older than this why is it older than this because it moves from west to east you understand therefore this one will be older than this one that we have here okay that's also working out which one is older and which one is new west to east okay some interesting stuff there uh we can see a nice one here all right it's a beautiful one here and what is this clearly you notice yo high pressure systems are in the southerly position all right so it's more summer conditions eh and it's can you see the region this one does the most it ridges okay and blocks the cold fronts from affecting the country it's gonna push it further south okay so typical sort of uh summer conditions even this one we don't mustn't forget about this one it's also doing some reaching the south indian high and blocking it from coming in all right so these are some things and if you look at these summer winter conditions then you get a brilliant idea on a synoptic map how it looks okay and then lastly i want to look at this okay i'm not trying to make my face bigger i'm not that important look at the cold front brings rain and winds and floods to the western cape you can see it here the amount of water gale force northwesterly winds of 65 to 80 kilometers so it can bring strong winds that packing and fearing changing the direction of the winds all right i expected between table bay and caper galas and the cape metropolitan islands central karoo see the area that it covers moderating in the evening cooling off heavy rains leading to localized flooding is possible over the cape uh metropole the western parts of the cape winelands large areas look at this high seas with wave heights of six to seven meters i expected between cape columbine and cape agallis so it can be very destructive it can destroy uh whether it's the farming [Music] road networks people's homes especially living in informal settlements and damaging the natural environment so we can do a lot of things and damage but we must also remember that sometimes it brings good rains so it can have a positive effect you understand it brings in good rains which allow for crops to grow natural vegetation water supply so it can be positive depending on the intensity of the rainfall and winds etc it's very positive even your snow you understand can be positive people love to see snow tourism etc which is brilliant for the economy of the area all right the farming of the area so it can have a positive or negative effect learners i hope you enjoyed the lesson i'm not putting any questions here you've got loads of past papers i've done some revision lessons also on youtube which you can refer to so i hope you enjoyed it all the best goodbye you