| 0:00:00 | my name is wayne sure about professor of atmospheric science |
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| 0:00:03 | and i came to see issue in nineteen seventy three after graduating from ucla in |
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| 0:00:09 | the department of atmospheric science there |
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| 0:00:12 | and i work mostly in dynamic meteorology |
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| 0:00:16 | especially in tropical dynamics |
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| 0:00:19 | and i have a group here which consists of about five graduate students now |
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| 0:00:25 | and a three research associates |
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| 0:00:28 | and i'd like to show just an example of some of the work we do |
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| 0:00:31 | on a project first thing i'd like to show is an example of the inner |
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| 0:00:35 | tropical convergence on |
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| 0:00:37 | this is a satellite picture |
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| 0:00:40 | from a g a stationary satellite |
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| 0:00:42 | this is the california coast here |
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| 0:00:44 | why use out here so this the eastern pacific |
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| 0:00:48 | and this is a band of very deep convection in what's called inter tropical convergence |
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| 0:00:54 | on |
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| 0:00:55 | so that the air is going up |
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| 0:00:58 | in the atmosphere in the inner tropical convergence |
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| 0:01:01 | and it has to be drawn from the north and from the self |
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| 0:01:05 | and it gives rise to what's called the heady circulation so you can imagine a |
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| 0:01:10 | circulation where the air comes in at low levels goes up and then back in |
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| 0:01:14 | the same thing on the other side |
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| 0:01:16 | so there's two branches of the head recirculation since this is in july we call |
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| 0:01:20 | this summer hemisphere branch and this the winter atmosphere branch |
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| 0:01:25 | now what we did on our project is try to understand the relative strength of |
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| 0:01:29 | the two branches of the head of circulation |
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| 0:01:32 | now this is an example |
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| 0:01:35 | of what the heavy circulation would look like |
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| 0:01:38 | if |
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| 0:01:39 | the inter tropical "'cause" virgins overwrite on the equator this is thirty north this is |
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| 0:01:44 | the equator this is thirty self |
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| 0:01:46 | and this is vertical going from the surface |
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| 0:01:49 | to about fifteen kilometres or in pressure from about a thousand middle bars two hundred |
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| 0:01:54 | millimetres |
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| 0:01:55 | now if the |
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| 0:01:57 | inter tropical convergence somewhere right on the equator |
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| 0:02:00 | what happened is that there would circulate like this it would come in equal amounts |
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| 0:02:06 | from either hemisphere and then go up and then go out in equal amounts |
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| 0:02:11 | but on the average the inner trouble convergence zone is north the equator so we |
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| 0:02:16 | have a situation like this |
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| 0:02:18 | again this is thirty north thirty self this is equator |
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| 0:02:22 | so this an example where the inner trouble convergence zone is located at ten degrees |
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| 0:02:27 | north latitude |
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| 0:02:29 | and what happens then he's that the air is a it's again drawn in from |
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| 0:02:33 | the south and from the north |
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| 0:02:36 | but these lines indicate how strong the circulation is and if you count the number |
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| 0:02:42 | of lines here it's about three times the number of lines here which indicates that |
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| 0:02:47 | this branch of the head recirculation is running about three times the string of this |
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| 0:02:52 | print this is remember the winter |
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| 0:02:55 | hemisphere branch of the head recirculation this is the summer hemisphere branch so we've determined |
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| 0:03:01 | from this modeling it's the it's the winter hattie cell which always runs a stronger |
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| 0:03:06 | than the summer had be so |
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| 0:03:08 | and the reason for this is that |
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| 0:03:12 | what drives the circulation is the release of latent heat in the upper branch that |
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| 0:03:17 | is one water vapour is converted to liquid water |
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| 0:03:21 | he just released |
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| 0:03:22 | and that drives upward motion |
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| 0:03:25 | so |
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| 0:03:26 | the error has to come in from both directions and there's resistance to the movement |
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| 0:03:30 | of air in the nor self direction and it turns out that resistance is less |
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| 0:03:36 | at the equator then it is farther from the equator so it's easier for the |
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| 0:03:40 | error just slip along this way then this way because it this errors right close |
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| 0:03:45 | to the equator |
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| 0:03:45 | so if we go back to this diagram here what you can imagine is that |
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| 0:03:51 | you have an i t c z here at ten north |
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| 0:03:54 | and you have the summer at least so running like this |
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| 0:04:00 | and the winner had this already like this but the winter cell is running about |
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| 0:04:03 | three times a strong |
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| 0:04:05 | as the summer so in the model you can move the latitude of the head |
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| 0:04:10 | the circulation it turns out that the maximum asymmetry between the two hemispheres happens when |
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| 0:04:16 | the i t c z is located about thirteen degrees north |
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| 0:04:20 | average position maybe ten degrees north so |
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| 0:04:23 | the average position is close to the position of maximum asymmetry |
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| 0:04:28 | so if you'd like to read more about this |
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| 0:04:34 | all of this information is on a website |
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