hey everyone so i've received a lot of requests for a video on winds here it is and i hope it helps you before talking about winds let's talk a bit about surface pressure so the surface pressure of any location is plotted on a surface pressure chart these charts have lines of equal pressure known as isobars so this is a surface pressure chart and the lines you see in this these are the isobars so isobars are the lines joining places of equal pressure so for example on this one zero one six the pressure throughout the isobar will be one zero one six in fact it's joining all the places where the pressure is one zero one six so these are known as isobars and each isobar will have a number written on it which will represent the pressure of the isobar so example this is 1 0 2 4 that means that on this isobar the pressure is 1024 hectopascals right now these isobars explain a lot about wind speeds so the closeness between two isobars will give us an idea about the wind speed like if we see around this edge it stands for a high pressure area so in a high pressure area if we see the distance between two isobars it's a lot over here as well and now if you compare this distance to a low pressure area which is over here so in a low pressure area the isobars are closely packed now the closer the isobars are placed the higher will be the wind speed so in a low pressure system the wind speed will be a lot and the distance between two isobars also tell us about the pressure gradient now pressure gradient means the difference in pressure so if you see here in a low pressure area the pressure has gone from 1000 ectopascal to 1016 hectopascal in just this distance whereas if you see in a high pressure area the pressures went from 1032 to one zero two zero hectopascals which is just twelve hectopascals and here it was around 16 hectopascals so we can say the pressure gradient is higher or steeper in a low pressure area and the steeper the pressure gradient the stronger will be the winds great now let's talk about wind direction in the northern hemisphere so around a high pressure area the winds blow clockwise and around a low pressure area the winds blow anti-clockwise so for example if we look at this surface pressure chart around a high pressure the winds will be clockwise like this and around a low pressure the winds will be anti-clockwise like this also low pressure is also known as cyclone and a high pressure is known as a 90 cyclone in the southern hemisphere it will be complete opposite to this so in the southern hemisphere around a high pressure winds will be anti-clockwise and around the low pressure in the southern hemisphere winds will be clockwise now let's talk about winds so the horizontal motion of air is known as winds wind direction is always given as the direction from which the wind is blowing and the wind direction can be either in degrees true or degrees magnetic when you listen to the it is the wind direction will be expressed as magnetic and when you read a meta the winds will be in degrees true so the rule of thumb is whenever you listen to the wind direction it will be magnetic and whenever you read it from somewhere it'll be in degrees true now wind is always expressed as a combination of the wind speed and the wind direction for example you're listening to the atis and it says that the winds are 1 to 0 degrees 15 knots what this means is that the wind is coming from 1 to 0 degrees and at 15 knots so 15 knots will be the wind speed and the wind direction will be one to zero degrees so this was zero this is 90 180 and 270. now how do we measure the speed and direction of this wind so there are these instruments which we use i am sure you have seen these so this one is a cup anemometer and the one on the right is a wind vane so the anemometer is used to give us the wind speed and the wind vane gives us the wind direction now there are two very important terms you need to know about winds and these are wearing and backing so wearing means that the wind direction is changing in the clockwise direction and backing means that the direction of wind is changing in the anti-clockwise direction meaning if the wind was coming from 360 degrees and after some time the wind starts blowing from 0 3 0 degrees so here you can see that the wind direction has changed in the right which is a clockwise direction so means that the wind is varying similarly if the wind was coming from 360 earlier and now it's coming from 330 degrees then you can say that the wind is backing because it's coming from the left side now and left means anti-clockwise so these are two very important terms you need to know now let's talk about some important wind speeds which you need to know i'll just write all the wind speeds over here and you can maybe take a screenshot or write them down because you need to learn all these by heart you can get a direct question on these in the exam so these are all the important wind speeds you need to know now there are three things which you need to know now the first one is what is a gust so gust is a sudden increase in wind speed which only lasts for a few seconds increase in wind speed the second term is a squall so squall is also a sudden increase in wind speed but it lasts for a few minutes so the only difference between a gust and a skull is in the time duration squall can also bring in some cb clouds next one is a lull so this means a sudden decrease in wind speed you can get straight questions on these three as well so make sure you know the meaning of three terms now let's talk about geostrophic winds so this is a wind which experiences two forces and these two forces are the pressure gradient force and the coriolis force so i'll write over here first force is the pressure gradient force pgf and the second one is the coriolis force pressure gradient force is the force which we read over here so we talked about the pressure gradient force and it was determined by the closeness of the isobars so the closer the isobars the more the pressure gradient force and coriolis force we did in indian climatology so it remains the same i just add a few points to that now pressure gradient force is a force that acts from an area of high pressure to an area of low pressure we can determine the strength of this force by the closeness of the isobars and the stronger the pressure gradient force the faster will the wind blow from high pressure to low pressure so for example this is a high pressure area and this is a low pressure area so the wind will obviously blow from high to low but the speed of this wind while blowing from high to low will be determined by the pressure gradient force the stronger the pgf the faster will the wind blow from high to low so the pressure gradient force is only there because of the pressure difference the bigger the difference the bigger the force so now let's recall what the coriolis force was so we saw in the northern hemisphere the coriolis force turns everything to the right side this was the trick as well see and everything to the right in the northern hemisphere and in the southern hemisphere it was deflecting everything to the left so this is what we'll use and now there's a formula for coriolis force and this is cf equals 2 omega rho v sine theta here omega is the angular rotational velocity of earth rho is the density v is the wind speed and theta is the latitude if you remember when we did coriolis force we also said one thing that coriolis force is zero on the equator and its maximum on the poles so here if we look at this formula it says that the latitude is directly proportional to coriolis force which means that higher the latitude the higher will be the coriolis force and if the latitude is zero then the coriolis force will be zero which is on the equator now another thing we can derive from this formula is that the wind speed is also directly proportional to coriolis force so as the wind speed increases the coriolis force acting will also increase and if the wind speed decreases the coriolis force will decrease now i'll explain the geostrophic winds so this is the northern hemisphere there are two pressure systems this one is a high pressure and this one is a low pressure so we know that the pressure gradient force will be from high to low like this and the coriolis force will be like this because it's the northern hemisphere the coriolis force will be to the right now when the pressure gradient force and the coriolis force will be equal a geostrophic wind will blow and this wind will be in a straight line and parallel to the isobars so it will be like this so this will be the geostrophic wind this wind only blows when the pressure gradient force and the coriolis force are equal and this is parallel to the straight isobars so if you think about it there will be a lot of isobars around this high pressure zone and these isobars will not be very closely packed so maybe one isobar is like this and there'll be a point when the isobar is straight so the wind that blows parallel to a straight isobar is the geostrophic wind similarly for the low pressure there'll be isobars and there'll be one isobar that is straight so the geostrophic wind will blow parallel to the straight isobar now since the coriolis force is acting on a geostrophic wind we can say that the geostrophic wind only occurs above the friction layer because below the friction layer the coriolis force will decrease because of a decrease in wind speed now i'll explain whatever i just said so what is a friction layer friction layer is a layer which is supposed to be at two three thousand feet below which the wind is disturbed due to buildings or terrain like in this diagram the friction layer is made over here and everything below the friction layer is disturbed air now this air can be disturbed due to the buildings or due to the terrain so if there are mountains or if there are houses anything the wind will be naturally disturbed and since there's a lot of friction in this layer it's known as the friction layer so now in the friction layer the wind speed will decrease and as the wind speed will decrease the coriolis force will also decrease because coriolis force is directly proportional to the wind velocity and the wind velocity decreased so the courier force will also decrease and when the coriolis force will decrease it won't be able to balance with the pressure gradient force and therefore the geostrophic wind will not exist so geostrophic wind only exists where pressure gradient is equal to the coriolis force and it is not equal to the coriolis force in the friction layer so geostrophigm only occurs above the friction layer and the geostrophic wind is also not experienced between 15 degrees north and 15 degrees south of the equator because we know coriolis force is zero around the equator so i'll just write some points about the geostrophic winds that we just discussed and please make a note of it now let's talk about the by balance law so the geostrophic winds give rise to this law and it states that in the northern hemisphere when your back is into the wind the low pressure will be on your left side and this is a very obvious thing so it is in the northern hemisphere so now let's just talk about it in this diagram itself so let's assume this is a person's back and the guy is facing that side okay so the by ballet's law says that whenever your back is into the wind the low pressure will be on your left side so that means that the geostrophic wind will be striking this person's back and now the low pressure is on his left side obviously this is his left side and this is his right side the low pressure is experienced on his left side so the wind is coming on his back and the low pressure is on his left side the person is facing this side perfect now the next wind is the gradient wind i'll explain it here so gradient wind is a wind which blows parallel to curved isobars meaning it is not in a straight line like the geostrophic wind and in a gradient wind three forces are acting on it and these three forces are the pressure gradient force the coriolis force and the centrifugal force we now know what are the pressure gradient force and the coriolis force let's see what is centrifugal force so when a body is rotating there is a force that acts away from the rotating body like this so this is rotating and there's a force that acts away from the rotating body like this that means if something is moving this way the centrifugal force will act outside okay now since the gradient wind blows parallel to a curved isobar like this there will be obviously a centrifugal force acting on it like this okay now i'll tell you more about the gradient wind so this is the northern hemisphere and there are two pressure systems one is a high pressure and the other one is a low pressure we saw that the geostrophic wind will blow like this completely straight geostore frequent now let's talk about the higher pressure and the low pressure separately so in the high pressure system the pressure gradient force will be in this direction from high to low and the coriolis force will be to the right because it's in the northern hemisphere so this is the coriolis force this is the pressure gradient force similarly in the low pressure area the pressure gradient force will be from high to low in this direction and the coriolis force will be towards the right like this now let's plot the centrifugal force on both of these because i told you around a high pressure area the winds blow clockwise so when the winds will be blowing clockwise centrifugal force will be acting outwards like this so this is the centrifugal force similarly in the low pressure area the winds blow anti-clockwise like this and thus the centrifugal force will be acting in this direction so earlier when the coriolis force and the pressure gradient force were equal the wind was blowing as a straight line which was the geostrophic wind but now since there's an additional centrifugal force these winds will turn and follow these curved isobars like this so this will be the new wind and this wind is known as the gradient wind it is because of the centrifugal force now if we compare the wind speeds in high pressure and the low pressure systems we can see that in the high pressure system the centrifugal force is assisting the pressure gradient force both the centrifugal force and the pressure gradient force are in the same direction meaning that the centrifugal force is assisting the pressure gradient force and in the low pressure area the centrifugal force is opposing the pressure gradient force so we can say that if we assume all isobars are equally spaced the gradient wind speed around a high pressure area will be greater than that of the low pressure area but this is just a hypothetical scenario we know that the winds are always stronger than a low pressure area right so we can also say that the gradient wind in an anti-cyclone is stronger than the geostrophic wind because in the geostrophic wind there was a pressure gradient force and the coriolis force and now since we are assisting the pressure gradient force in the anticyclone the wind speed will be more around the anticyclone and it will be a gradient wind and not the geostrophic wind alright so gradient wind is done now let's talk about winds below the friction layer so we know that the wind velocity is less in the friction layer due to the disturbances in air because of terrain and everything we saw it in this diagram that even the coriolis force decreases and obviously the coriolis force will decrease because the wind velocity will decrease and the wind velocity decreases because of all the friction in this layer so the wind that blows in the friction layer is the surface wind and we'll talk about the surface winds now so this is again in the northern hemisphere there's a low pressure area there's a high pressure area and this was the direction of a pressure gradient force and this was the coriolis force to the right and we had the geostrophic wind like this if both were equal right but in the friction layer we know that the coriolis force has been reduced so when we reduce the coriolis force let's say this is the new coriolis force which is less now since the coriolis force is lesser it won't be able to balance the pressure gradient force as a result the pressure gradient force will pull the geostrophic wind towards itself like this you just think about the pressure gradient force and the coriolis force as two strings which are pulling the geostrophic force equally from both sides now when the coriolis force is reduced obviously the force from one side of the string is reduced so the pressure gradient force side will pull the geostrophic wind towards itself like this and this is the surface wind and we can say that the surface winds will blow across the isobars because now this won't be parallel to any isobar it will be cutting through the isobars like this it will be just cutting through the isobars so we'll say that the surface winds blow across the isobars perfect now what will be the angle and the speed by which the winds will change because we saw that there was an angle by which the wind changed and since the wind velocity decreases in the friction layer we need to know that by how much value will the wind velocity decrease so the wind is backed by 30 degrees and the wind speed is decreased by 50 percent this is the scenario on land now on c since the friction layer is more stronger on the land when we talk about the sea the backing angle will be just 10 degrees so now let's see a question on this so in this question it says that the surface winds are 360 degrees at 20 knots what will be the wind at 3000 feet first we have to understand what he is asking in the question so in the question we are given surface wind and he is asking us the wind velocity above the friction layer because the surface winds come in the friction layer and we saw that in the friction layer the wind speed decreases and the wind backs so he is just asking the opposite of it so he's given us the surface wind and is asking about what will be the scenario of winds above the friction layer which we can say at 3 000 feet so now we know that the wind speed at 3 000 feet will be more than what it is at the surface because on the surface the friction layer reduces the speed and we also know that the wind is backing on the surface so at 3000 feet it should be coming from the right now we'll use the 30 degrees and 50 rule so on the surface the wind is coming from 360 at 20 knots which is in the friction layer so obviously above the friction layer this wind should be coming from this side and if we go right 30 degrees from 360 it will be 0 3 0 degrees so the wind is coming from 0 3 0 degrees and the wind speed on the surface is 20 knots we know that the wind speed is 50 on the surface to what it is above the friction layer so since it's 20 knots on the surface it will be 40 knots above the friction layer so the wind at 3 000 feet will be 0 3 0 degrees at 40 knots i hope you understood this question in this we just reversed whatever we learned about the surface wind we learned that whatever the wind was coming above the friction layer the surface wind comes from the left of it and now if you're given the surface wind and we have to find the wind above the friction layer so obviously the wind above the friction layer come from right of what the surface wind was coming from okay so surface wind is done now let's talk about some other winds okay so the next one is the sea breeze this one is the sea breeze and this is the land breeze we'll talk about both so now what happens in the coastal areas is that during the day the land heats up more quickly than water so let's assume this is the land and this is the water okay so because of the sun the land heats up faster than water this is a property of land so there is a low pressure experienced on the land this low pressure is because the air starts to rise because land is heating up and the sea is not heating up that fast so there is a low pressure experienced on the land and a high pressure is set above it because all the air molecules that are rising from the land are coming up so which will lead to a high pressure above and a low pressure below on the ground now on the sea since it's heating lesser than the land a comparatively higher pressure is experienced near the surface so here will be a high pressure now this is not a very high pressure this pressure is just higher than this because land was eating faster so there will be a comparatively higher pressure on the sea and at an altitude above the sea there will be a comparatively lower pressure to what it was here right so this is a pressure system set in the coastal areas during day the land heats up which creates a low pressure on the surface and high pressure above and on the sea there's a comparatively higher pressure on the surface and low pressure above so now the wind will start blowing from high to low pressure like this on the surface and there will be a cycle formed because this blows from high to low and then over the surface the air molecules were rising so this will go up and again there's a pressure difference above here so the wind will go back to low pressure from high and it becomes heavy and starts sinking so this is a cycle and this wind blows from the sea to the land and is known as the sea breeze now a similar thing happens at night it is known as the land breeze now this is after the sunset when the land cools down and the land cools down faster than the sea so a reversal of sea breeze takes place so it is high pressure over here because all the cold air sinks and since it's a high pressure over here there'll be a low pressure above there's a comparatively lower pressure on the surface at the sea compared to this high pressure and there's a higher pressure over here as compared to what it was here so again another type of cycle sets in in which the winds blow from high to low pressure like this and here the air was sinking because of the temperature and a cycle is set like this now out of these two sea breeze is stronger because the sun is there and because of the sun there is a bigger pressure difference between these two and the bigger the pressure difference the more the pressure gradient forced will be and stronger will be the wind blowing from sea to the land so sea breeze is stronger now the next two winds are experienced in the mountains and valleys so this one is the catapatic wind and this is the anabatic wind katamatic wind is the one which flows down a valley at night so what happens is that at night the air around the valley becomes cold so all this air around the valley becomes cold and cold air sinks same happens on this side as well now these winds which blow down the hill at night are known as catabatic winds so i'll write at night down the hill now what happens during the day is that all the wind that's in the valley starts rising because of the sun we know hot air rises up so the wind that goes up the hill is known as the anabatic winds all right during the day and up the hill so these two were the winds that blow in a valley now which one do you think will be stronger the catabatic wind is stronger the reason is that in the antibiotic wind the wind is blowing opposite to the force of gravity so this is gravity by the earth and this wind is going up which is opposing the force of gravity and if you see over here the katabatic wind is also coming down and the force of gravity is also pulling it down so this is stronger and it is stronger because it is not opposing the force of gravity okay now the last wind is known as the phone wind so this is a warm dry air that's blowing on the leeward side of the mountain so this wind over here is the form wind this part i'll explain how it's formed so when it rains in the mountains there's a lot of moisture around and the air is moist now when this moist air is forced to climb up a mountain maybe due to some wind for example there is a wind from this side which is forcing the moist air to climb up the hill so this moist air will quickly become saturated and will cool down and clouds are formed because when it reaches the condensation level we see the formation of clouds so the winds were blowing and this moist air started to climb and clouds are formed now these clouds will give rainfall making the wind lose its moisture so now the wind does not have moisture over here it will not be a moist air but a dry air and if the dry air is stable it will come down on the leeward side of the mountain like this we know that the stable air comes down and when the air will be coming down its temperature will increase because when you go up the temperature decreases and when you come down it increases so now this is dry and warm air on the lever side of the mountain and this dry and warm air is known as the foreign wind and this wind is very turbulent because of the friction it encounters when coming down and this friction gives a lot of turbulence okay so with this we come to an end of this video i've covered all the important stuff from this chapter from the exam point of view but i would suggest you go through the book real quick before sitting for the exam let me know if you have any questions and thanks for watching