<TITLE: Observational Space Physics
ACADEMIC DOMAIN: natural sciences
DISCIPLINE: physics
EVENT TYPE: lecture
FILE ID: ULEC160
NOTES: 

RECORDING DURATION: 87 min 55 sec

RECORDING DATE: 22.3.2007

NUMBER OF PARTICIPANTS: 7

NUMBER OF SPEAKERS: 1

S1: NATIVE-SPEAKER STATUS: Russian; ACADEMIC ROLE: senior staff; GENDER: female; AGE: 31-50

SU: unidentified speaker>


<S1> <REFERS TO POWERPOINT SLIDES THROUGHOUT THE LECTURE> we continue what we had before and i think that this today's lecture will a little bit messy because i still think that i have to talk about indices more and electric fields er we will have them probably after the break but we will see what what how we can be in time and well let's just start so now we are here we're <P:05> on the measurement techniques magnetic fields and space and on the ground so we are still on the magnetic fields and what i would like to tell you because about indices more about indices because i er told you er on tuesday about three i- main indices DST A-E and K-P and if you remember er i started to talk like last week i started to tell you about the magnetic field modelling which i myself have been developing so far and which other people have already been developed so , for this for the development of these models er i use not only the magnetic field data but also indices as i i told you but we er paid attention only to magnetic field data and i asked you t- to make this homework number one to go to internet and find out er which data magnetic field data is available but er that's not all as i told you and indices and especially DST index is very important in magnetospheric magnetic field modelling and for other of course magnetospheric studies er yes DST index is er like one number per hour as i showed you last time but it's calculated from the magnetic field observations of course on the ground and there are other two indices symmetric and asymmetric , why i want to talk about them because actually what i use for the modelling i use not DST values because one hour it's a long period it's too long for our modelling er purposes and for other research purposes i use this symmetric index and i would like to show you what is the difference and what why i want to use this er index so it's actually symmetric H component used in event-oriented model er so also i will i'll show you the DST index in event-oriented or overview of course and then er method of derivation of this symmetric H index DST and SYM-e- SYM- er SYM-H index comparison what's the difference and why they exist the two of them exist is DST the measure of the ring-current only this here comes the physics and still this is the question which is not answered and also contributions to this is O instead of P so it's contributions to DST index from different current systems this er was the topic of my research couple of years ago , er i told i i said in the beginning that this lecture will be a little bit messy because several topics er there will wi- will be du- er on this lecture so transformation of coordinate systems i still think that it's important to tell you about different con- co- coordinate systems er you will not use all of them of course mainly i myself i don't use them i use just one GSM usually but again it depends on your p- on the p- purposes what are you doing which type of research or what what else are you doing are you interested in coordi- coordinate systems associated with the earth or with the sun so it depends let's see this er slide was from my previous talk er fro- previous lecture how to construct event-oriented model we talked about collecting input data all available magnetic field measurements during the modelled event in the magnetosphere in the inner magnetosphere more precisely and there is a second , er point which data are we trying to collect symmetric H measurements on the ground er the idea to er how to construct the event-oriented model we have to er collect all data available during this event which can be useful for us to produce the magnetic field model of course and magnetic field is natural but also we can use the magnetic field measurements on the ground because they of course they are connected so everything is connected in the sun-earth system so we will see how i'm going to do that this is DST taken from kyoto webpage and er exactly the same er picture which i showed you ye- on on tuesday this is our march 2007 we don't have anything so no aurora in helsinki and these are numbers as i said it's just unit U-T zero one two and so on and this is the day of this march and these are numbers <P:05> er i would like to show you the results of my own own modelling and therefore i'll show the er overviews of two of four modelled storm events , er november six seven 97 we have talked er we talked about this er when i talked about magnetic modelling may second may fourth may fourth was your homework and also october 10 12 er 97 , you see this is DST index which i show for this event and this is actually not DST index because it's not one hour index it's it has much er higher resolution this is symmetric H index and this is the behaviour i don't want to talk about the details of how er does DST index behave because i would like to talk about this in details when i i will talk about storms and so on now we're just concentrated on the data getting the data and trying trying to analyse the data and actually this is the A-E index which i talked to you last time the measure of sub-storm activity somehow sub-storm activity so i use DST index and A-E index for the modelling about interplanetary things stuff we will talk about about this later , as i said not DST but symmetric H index and all actually for these type of studies with where you need to know the pi time resolution variations in the in indices you don't use DST you use symmetric H index (usually) so DST's hourly average va- values for modelling we need better time resolution we use symmetric H index er there are als- also er symmetric D component and asymmetric H and asymmetric D component in- indices we are not going to use them but they exist so i would like you to know that they exist it's lo- longitu- lo- longitudinally asymmetric er and symmetric disturbance indices that's their name , er they are so what what are they doing actually they describe the geomagnetic disturbance field in main latitudes m- main la- latitudes with high time one minute resolution and they are derived from both er H and D components of the measured geomagnetic field again since these two indices symmetric and asymmetric they are calculated in kyoto and like officially you get them the- you get them there from that page note D is not declination here i don't know why it's used like that but don't mix these two D is not declination it's D component and it's er east-west component that was east-west component that was Y component in that er picture where i showed all the elements of the geomagnetic field so H component is horizontal well like that we are we are not interested right now in D we are much more interested in H component symmetric component (xx) H is essentially the same as this DST index this is a phrase from their webpage but it's not the same i don't know how much will you need er to analyse this difference but for many purposes it's very important and for me that was really important to realise that there is a big difference between DST and SYM-H index and i will show you the difference and i will explain you why it's it was important for me differences er one minute er minute values from different sets of stations i told you that DST erm index is calculated based on the measurements from four stations on the mid-latitude so near the equator here they used different set of stations but of course all stations are near the equator and they have erm i think six yes six stations then slightly different coordinate system that means the data are transformed to the dipole coordinate system at each station so there is a difference between the dipole pole position and local geomagnetic direction er i don't think it's very important to understand all of this but just they have different erm they just transform all the data to dipole coordinate system and they have also a different method to subtract the base value and er S-Q er current effect these solar quiet time variations again er this thing you will probably not do yourself unless you will erm do the research which is very closely connected to the calculations of DST and other indices so but the difference at least what you need to know that differences exist so method of derivation of this symmetric H index observations from six stations they are used for this er for for this deriva- for deri- derivation of this index and they are for each month derivation procedure four steps we are interested only in the step number three but still first subtraction of geomagnetic main field and the solar quiet daily variation as i said details are not so important to calculate the disturbance fields field component okay then co- coordinate transformation to a dipole coordinate system calculations of er longitudinally symmetric component that we are interested in six stations and then asymmetric component and derivation of asymmetric indices these two actually asymmetric why i'm not talking about these asymmetric indices because i haven't done myself the research based on them but they are really important for asymmetric effects of the ring-current but right now we are here calculation of symmetric component so this symmetric component is calculated by averaging the disturbance component at each minute for six stations n- well it's the same procedure as for all er indices but since there was a statement that this symmetric H index is close to DST index so we have to have to introduce some similar procedure to calculate H index so the H component la- er for this component latitudinal correction is made on the averaged value to get the value which corresponds to equatorial DST index that means latitudinal correction means the division by this six-station average of erm cosines of dipole latitude so if you remember that was DST and then disturbance divided by the cosines of er latitude of all the stations so that's the only thing the latitudinal correction it ca- it's called , now the comparison , here is september erm four-five 2002 storm so it's quite latest late mhm quite recent event as you can see this is DST index for the whole month for september 2002 and this is taken from that kyoto page and here we have disturbances as you can see these are the features of the magne- of the magnetic storms as you as er you can re- er compare from here we don't have anything during march 2000 2007 , but here you see , these are the disturbances in DST index and we look on them when we want to study storms' effects and so on but what is most important what i took september 2002 and i took this is four actually where we have september fourth where we have this decrease in DST and these are numbers minus four minus two minus seven DST in nano-tesla it's just the beginning of this storm of course we don't have big values we have them later and here is erm quick look on these symmetric and asymmetric indices taken again from kyoto you don't see very well but this this shows the symmetric er H component indic- index so therefore i i put the numbers so exactly for this you have 16 nano-tesla 16 nano-tesla and 24 nano-tesla so even the sign is different we have minus four and 16 it doesn't matter if you are if you are looking on er the development of the storm because you are interested in these values where you have DST very depressed and so on you are not interested probably in these er in the very beginning of the storm and so on but if you are doing the modelling as for example i do this is very important because the idea of event-oriented modelling is that you have the input data and then you have the representation of the magnetic field and you try to find the best fit for the model parameters so that model produces the magnetic field the output which is very as as close as possible to the observed values so we are trying to fit this value and we are trying to fit observed values so you can see if we are trying to fit 16 nano-tesla or minus four we will get different results , this is really really important for these purposes as i said i had problems especially i think for this storm because in the storm beginning where we have these values the fitting procedure gives really bad results so the output magnetic field deviates very much from the observed magnetic field , if i use actually these values the situation is qu- quite different so difference is important DST is not the same as symmetric H index when you are looking on the small effects in modelling in er doing modelling when you are you are looking only for only on the development of the storm you can say that they are the same anyway i use SYM-H index because it's one minute time resolution , if we go back to the overview of four modelled events they are here DST indices <P:05> er , erm what can we say about this DST in- about the DST indices why it's important because DST index as i said it's a measure of currents , as A-E index for example is a measure of overall electrojet current DST index is measured on the near the equator so it's not overall electrojet it doesn't er it's not related to high latitudes it's related to low latitudes what's going on in the low latitudes we have ring-current which goes westward so here is the sun this is the cut of our magnetosphere we have the ring-current which goes westward around the earth this directi- direction is westward and this direction is eastward we have ring er tail-current which er flows across the plasma-sheet this is the plasma-sheet i- i- i- it er flows like that and then we have magnetopause currents which flow on the surface on the magnetopause these three basic current systems exist in the modelling in the very basic er magnetospheric magnetic field models and these three current systems exist in my old modelling why i say it why i ask this question DST is a measure of the ring-current only the answer is no it's important because DST can tell us about which current systems contribute to er the DST itself and how do they develop during the storm and which current system is more important in comparison with another during the storm development and when it's important so all of these questions can be answered just analysing the contributions to DST index from different current systems if you can imagine which er the cont- what does it mean contribution that means that what erm what does the current system do to the magnetic field on the earth ground so if you have magnetic field on the on the earth ring-current goes like that , so if you think that okay let's imagine that this is the surface and we put everything to the centre of the earth somewhere here so wi- what will be the direction of magnetic field produced by the current flowing in in this direction will it be upward or downward . just downward so that will be downward and that will be negative why because er i don't have this picture but still the magnetic field lines they have the direction <START DRAWING ON BLACKBOARD> if you remember if this is the earth and then this is magnetic field lines they are directed like this so if we have the ring-current flowing like this we have a depression of the magnetic field <END DRAWING ON BLACKBOARD> so the direction is different that means that the field on the earth surface will be depressed depressed means decreased so it's not the er enhancing of the earth magnetic field but decreasing then tail-current if it flows in this direction so wi- what will be effect on the earth on the erm earth surface o- on the centre of the earth decrease or increase <P:06> well this is the same as a ring-current n- it d- it doesn't go of course around the earth but still directions like that if you see this is the current and this is the point so magnetic field will be down so tail-current also produces the decrease of the earth o- of the magnetic field er or the erm earth surface or in the centre of the earth and the third one magnetopause so it's negative this and the magnetopause currents they flow in the po- in the opposite direction in comparison to the ring-current so they will produce increase so all these current systems contribute to the DST and to the magnetic field on the earth this actually is external component of the geomagnetic field which was er said by gauss when he said that it's the internal which comes from the earth and this is the internal which comes from other current systems which flow far from the earth so magnetic field again internal magnetic field it's due to the currents which flow inside the earth and we are not interested in that external magnetic field which is everywhere is due to currents flowing in the magnetosphere these currents are produced due to interaction somehow between the sun and the earth , that's that's that's the point therefore if we know the contributions from different current systems to DST if we know how much and ho- and what and when and where exactly do the spec- specific current system produce on the earth er surface and we can measure this value actually we are measuring this value then we know the evolution for example of different current systems we measure just magnetic field just 200 nano-tesla 400 nano-tesla that's all there is absolutely no way to get any information of the contributors themselves from the measurements on the ground the biggest problem this is the biggest problem actually we don't know we just measure the ma- value that's all and as i said , is DST is a measure of ring-current no but many many years it was like that it has been like that DST is the only measure of the ring-current there is no influence of different current systems on the earth o- on the erm surface of the earth of of the earth and this not true and i would like to show you my own results and the i just copied some slides from from old presentations where i showed er some er some words about different methods of modelling of the magnetospheric magnetic field is this tsyganenko as i mentioned global er models and this is our model event-oriented magnetospheric magnetic field model models what they can do the- they can provide they provide an accurate representation of magnetos- magnetospheric configuration for a specific event and then what is most important is this we can study the evolution of different current systems during different storms and their relative contribution to DST which is completely im- absolutely impossible to study without any modelling the number on the earth surface doesn't tell us anything when we know we have the model we can estimate , well it depends of @course@ how how good is your model usually if it's bad but still we can get some information at least , then coming back to this quiet time DST quiet time ring-current and so on the base-line which we have to substract i told you on on tuesday that it's somehow complicated and so on but it's important and that's true it is important because we had this problem when we tried to estimate the contributions from different current systems to DST index we had to substract this ri- er this er quiet time ring-current for official DST calculations they suggest that during quiet days DST is equal to zero it's not true for us because we don't use measurements where it is sugge- somehow assumed we use model results we model DST not measure and compare of course the measurements but we have to substract the er quiet time ring-current when we have quiet times ring-current is not equal to zero and we have this some some sort of a procedure i don't i don't know if you need this or not but still i will tell you how we can cal- we calculate the DST index or actually symmetric H index from the model result so er yes there are we com- we compute the magnetic field given by our model on the stations so how six six different stations and actually why because the we want to to somehow to act as a magnetosphere ourselves we want to produce the magnetic field which is measured but we want to produce this somehow measured magnetic field by ourselves plus er by our model so what we do er first of all we decrease DST index by 25 per cent to remove the effect of induced earth currents no comments on that i think because well it's not so important but we we do that because it's important for our purposes and for each modelled storm event we get the quietest day of the months as i told you it's er there are tables in mhm kyoto again at kyoto page where you can find the quietest day of the months model the whole quiet day with our model just model the configuration of the magnetosphere during this quiet day we will not get any interesting effects of course but we need this then obtain model magnetic field at DST stations if it's quiet we get magnetic field on the stations and this is our er quiet time ring-current this is the quiet time DST well say ring-current because it w- it has been believed that it's all DST is produced by the ring-current but it's not true so i i say this works like ring-current but it's er it's better to say quiet time DST so we obtain quiet time DST and we consider this value as as a quiet level for a given storm event that's as simple as that o- then we obtained contributions from ring tail and magnetopause currents due to this quiet level and these are them er actually SYM-H not DST but still we put DST er ring-current is red negative tail-current is blue negative and green is magnetopause currents positive so quite correct values which we get for contributions and then we substract this , er quiet time contributions from different current systems to DST from the modelled results so we somehow get this er base-level of er our model measurements and we want to er to assume that what what we get in the be- in the end is close er is clo- very close to the observed ones to the observed DST index so this is the procedure , now modelling results what i would like to show you because it it er somehow when i'm saying like telling you all of this it sounds really rather simple er all of these contributions just er just er substraction and so on but in general and it sounds like well just contributions and so on but in in reality it provides a lot of information physical information what's going on in the magnetosphere during storms for example which we're we we are interested in storms er now so four storms we modelled them and these are the contributions to DST index so black is measurements red is always ring-current blue is tail-current and green is magnetopause currents actually what we are interested in we are interested in the tail-current and the ring-current of course magnetopause currents can be somehow c- er the influence of the magnetopause currents can be co- erm corrected and there are there are ways to correct to to remove all of these magnetopause contributions because they are positive as we as we show as we saw w- we are mostly interested in those two currents and still open questions still a lot of discu- a lot of er the discussion's going on why because it's really difficult to separate these two currents current systems you see ring-current is here but there is no border like this is the end there there is no ring-current anymore here this tail-current starts no because there is nothing like that in nature of course er plasma-sheet goes er far far far in the tail <MAKES SOME NOISE> sorry and then it comes ba- comes close to the earth and even it goes around the earth so everything is plasma-sheet so everything is somehow mixed everything is together there is no s- exact separation between the ring-current and near-earth tail-current so therefore contributions are important since even you cannot say a- at se- at er special distances what is the ring-current and what is the tail-current the only possible way to separate them just to set in the model that's all so and let's see the the results they are here . DST is not the measure of the ring-current why this is the ring-current and this is the tail-current so contribution from the tail-current is much higher than the contribution from the ring-current and this is only inner magnetosphere it's nothing like because this er tail-current erm 200 earth radii doesn't produce anything on this earth surface of course it's the inner magnetosphere it's (xx) only in the tail that was somehow moderate storm because there is a classification of course of a sto- of of a- all storms because DST it was not big like minus 80 nano-tesla we will talk about this also later i just want to show you two er f- four different storms actually they are different the profile DST profile is completely different and here we can see it was about say 120 more or less but that was intense storm that was minus 200 even 250 nano-tesla this is intense storm and that was also more or less moderate say and what did our model give us but completely impossible to get from any other observations that during moderate storms we obtain that the contribution from the tail-current can be even higher than the contribution from the ring-current but during the intense storm the contribution from the ring-current is always higher than the contribution from the tail-current that means that even even this modelling result shows how each storm differ s- differs from another and it tells us information about the evolution of current systems you see we can w- i i will not er tell you all of these comparisons but i i did it in like in in papers and so on it's very important when exactly which current system started to decrease or increase or and so on so you ha- you can get a lot of information just from these curves when you you know where to look at so this is er the result of of the modelling er now this is i think the summary which i have already said the DST the information DST provides information for er about the er size of the storm and so on . and here i want i wanted to just to show you different er er results from different models why because as i said the only way to get the information about the contributions from different current systems is to use magnetic field model there are several of them and you will get different really different results if you use different models so it's another problem actually , er there were two events which we modelled with erm like a als- also two different storms as you can see it's minus er less than one mi- mi- 100 nano-tesla like moderate storm and then it's intense storm less than 200 nano-tesla so just for comparison and we used three different models actually that was our model that was tsyganenko model the latest that time latest version er special storm-time magnetospheric magnetic field model and that was another model which i'm not going to talk about it but still it's it's from er from er my own institute previous institute from the moscow state university so as you can see well they contribute differently if you use different models you will get different contributions here for example in the middle er in the er maximum of the storm this tsyganenko model gives the same contribution from the ring-current and tail-current our model says that because it's a moderate storm we get the main contribution from the tail-current not from the ring-current and actually close results gives er this er it's called paraboloid model but it doesn't matter so close results give the this paraboloid me- er model that was moderate storm and that was er the er intense storm and also as you can see there are a lot of different results tsyganenko gives contribution from the tail-current which is mhm which is obvious obviously not correct our model gives the contribution during the during the maximum of the storm contribution from the our ring-current and actually these paraboloid models also gives a contribution from the ring-current er bi- biggest contribution comes from the ring-current during the maximum of the storm actually during all the storm so the results the re- er the conclusions the physical conclusions which we can get from this from the analysis they depend very much on the modelling of course the only thing which we can be sure that er our model produces good er or accurate distribution of the magnetic field for this specific event so therefore the only way to be sure that this is this model works and we can trust the results we obtained is that our model provides not bad say distribution of magnetic field or better distribution of magnetic field for this specific event than other models that's all about this so that was <SIGH> about , er SYM-H modelling and so on and i think that now you have some at least some understanding how magnetic field data is used for the modelling purposes and which type of the magnetic field data and so on and this is like briefly before the break i would like to tell you about the coordinate systems er the only way to understand it it's not just listen to what i say because i say just the the official description that's all the better the best way is to imagine of course yourselves and try to plot to to to draw the <SIC> axises </SIC> to draw the earth to draw the li- er the sun and then to draw <SIC> axises </SIC> and see where you are so er there are several but as i said mainly used er mainly er mainly GSM coordinate system is used and of course also these er geographic well geographic is used of course and geomagnetic is used when you are er on the earth surface so there is this for example the geocentric equatorial inertial system i have never used that system but it exists where there's X-axis pointing from the earth towards the position of the sun mhm i don't know even what does it mean exactly but still if if this erm mhm er this actually , erm coordinate systems they are all related to earth so they are not related to somehow the er the centre of these coordinate systems is in the centre of the earth Z-axis is parallel to the rotation axis of the earth and Y completes the right-handed orthogonal set okay it doesn't matter so geographic coordinates everybody knows what does it mean geomagnetic coordinates the only difference is that Z-ax- Z-axis is parallel t- to geomagnetic dipole axis so it's not geographic not the rotation axis of the earth like a geographic north it's the magnetic dipole axis that's the only 11 degrees as i said shifted from the true north the geographic north er okay so Y-axis is perpendicular to the geographic poles and X-axis completes the right-handed orthogonal set yes okay so GEO erm geographic coordinates of the dipole axis derived from IGRF model this is just the trans- transformation from geographic coordinates to the geomagnetic cro- er coordinates of course and this er magnetic pole is moving as i told you i think last time with some speed of 2.6 kilometres per year in sun direction the transition usually you don't need to calculate yourself there are programs where everything has been done and everything is included and everything is correct so you have to just to be careful to set the initial coordinates and to get the correct output coordinates in in another system and there is a package of course ab- er c- er containing all of these transformations and so on then there is a geocentric solar ecliptic system GSE and there are some i think data which is provided in this coordinate system so if you see i think that was that was erm when you look on i i gave you the page where you can see the orbits yeah that th- this is for homework one where you can see the orbits of satellites and er their coordinates are in G-S- er GSE coordinate system but don't be afraid or don't pay pay too much attention to that it's just coordinates and actually what you are looking for when you are looking for the data it's GSM as i said so X-axis pointing from the earth towards the sun these are somehow the set of models where always X-axis points towards the sun from the earth towards the sun Y-axis er is chosen to be the ecliptic plane pointing towards dusk and then Z is parallel to the ecliptic pole this is related to sun of course then there is geocentric solar equatorial system which is again i don't think you will going to use it but still X-axis pointing towards the sun from the earth are the same Y-axis is parallel to the sun's equatorial plane which is inclined in- er inclined to the ecliptic and then Z-axis is chosen to be the same sense as ecliptic pol- po- pole to northward then geocentric solar magnetospheric system actually it's solar magnetospheric system er X-axis from the earth to the sun , Y-axis is defined to be perpendicular to the earth magnetic dipole it sounds somehow probably but the most important thing that this X-Z plane contains the dipole axis so the dipole axis means just the direction of the dipole so this 11 11 degrees shifted from the north er true north so and then positive direction of Z-axis is chosen to be at the same sense as the northern magnetic pole i will show you later what does it mean er two main points is that X-axis and from the earth to the sun and then in the plane X-Z plane this dipole axis is actually lies in this plane so it cannot go away why it's important because it's earth you know earth rotates and it's not always that er dipole axis is er along this er Z-axis it's not because earth is r- er rotating so y- but the plane is the same where there is this erm X-axis Z-axis and then dipole axis it's they are all in the same plane these two is important points the difference between GSM system and this GSE is simply a rotation about X-axis that's all the coordinate system rotates again there are matrices you can calculate it not necessary to calculate yourself everything exists not to make any er mistakes solar magnetic coordinates S-M Z-axis is parallel to north magnetic pole Y-axis perpendicular to sun-earth line towards d- dusk and X er axis does not point directly at sun because Z-axis is parallel to north magnetic pole i will show you i will show you er i think the yes this is it this is the the picture of all coordinate systems this GEO is red you can see and then this shows this transformation where you can and then magnetosphere er geomagnetic this is geomagnetic it's here in black you see these are the 11 degrees shift and GSM GSM is er , green there . here is i don't know why but still it's nice i think to see the difference between all of these <SIC> axises </SIC> especially Z- <SIC> axises </SIC> but here you see this is this er GSM the rotation of the earth erm if we suppose that this is the the er er or any X-axis so sun is going here it's always like that rotation of the earth X- w- er axis is always to the sun and you see it's only this plane contains the dipole axis dipole axis is this black one so it's the plane this this and this they are always in the same plane and the earth rotates so here you can you can imagine what is it the coordinate system and Y of course Y-axis is just perpendicular this what i wanted to s- what i was trying to show and what i tried to to plot why i plotted it like this very simple because usually when you try to imagine something or to you try to draw some picture you go like that this is the sun and X- er axis of GSM coordinate system points towards the sun that means the positive numbers is here are here , sun and earth here is this magnetopause and so on so magnetopause is positive er erm po- is erm lies on positive X somehow numbers and then tail when i say minus that means that X values are negative they are here this is Y this is Z and this is the dipole axis so they are in the same plane and dipo- i- i- and it's er rotates as i showed you on this on this picture so the only thing what i would like you to know and to remember and i will ask on the exam of course what is this GSM GSM coordinate system and what is the difference between geographic and geomagnetic coordinate systems these are most important things to remember and to imagine of course all of this so i think that's all for this part of our lecture and we will be to on er electric fields after 15 minutes (xx) break so (xx) </S1>
<15 MIN BREAK, TRACK CHANGE>
<S1> <START MISSING> more pleasant things to me at least <SU> @@ </SU> we will go to particles yeah i made i have made already a lot of study and i like them very much and i will show you all these very beautiful structures and i hope you will learn how to look on them and understand what does it mean but so i like er spectrograms @much better than@ magnetic fields and then magnetograms so particles are number one but so electric fields this is really , difficult thing first when i tried to plan this er lecture i thought i will tell you about instruments i will show you measurements i will show you just real electric what is measured how it's calculated but then i decided that no it's really mixed and it's really difficult and the only person the only er people who know how to do that who who did this themselves they can explain it really because electric field is big problem for us for the magnetospheric physicists it's still very big problem why the main reason is that the errors are higher than the numbers @so you get errors@ where you have to remove to to clean the data and they are higher than the numbers itself than the magne- the electric field itself or potential actually itself and well everything can introduce these errors everything so and er people who are er working with electric field data , they do a very great job a very very big work i think but still it's really difficult and we don't have good measurements or we have measurements but still we cannot be sure that the values we obtain are real still but let's start er main instruments for measurements of electric field as i said it's very difficult to perform accurate electric field measurements electric field is generally weak , er yes important corrections have to be applied as i said errors are higher than b- larger than the numbers itself characteristics of electric field instruments there are two main instruments double probe and electric beam experiment double probe double probe's working principle is potential difference what is measured is potential difference and then electric field is calculated er so er er electric field perpendicular to spin axis er to the of the space craft is measured electric beam experiment working principle is drift of electrons what is measured is electric field and also magnetic field can we measure it in this instrument actually the (xx) and also there are possibilities to measure electric fields parallel to magnetic fields it's they are very important extremely important for overall physics and the principle is mirroring of electrons there are variations of course all of these instruments and there is there are books where everything is written but i decided to to speak more <SIGH> in a sim- in a more simple way probably i'm right i hope so so double probes for measurements of electric fields first observations in dense plasma , er principle electric field probe measures the difference of electric potentials at two locations in space , consists of two electrodes one two usually of spherical shape because usually it's spherical spherical double probes this is the words these words are used in papers and so on they are fixed on booms at a significantly long distance 40 metres from the spacecraft they are here , then instrument provides electric field component perpendicular to spacecraft spin axis as i said determined from the potential difference between two electrodes so and their separation length this formula of course you know it's how the potential is related to electric field actually it looks easy that's all actually this is the principle of the electric field probe but now we have this figure where you have all of these errors shown like this and all of these numbers and they are all these errors which are very difficult to determine which provide a lot of mess for the measurements and which just just spoil all measurements @actually@ so this er U-P-one and U-P-two are the plasma potential er potentials at the location of electrodes electrodes here then er this lambda-D D is the diameter of the region of plasma potential decrease around P-one so because of the effects which i will er say later on the next slide there is a decrease of this potential what we measure is not or i- er is not what is real what is the pote- or this should be here . potential alterations or well errors first electrodes alter the plasma potential so that potential decrease decreases it's this this decrease you see , here for example because electron current in the surrounding plasma towards the electrodes is larger than the ion current so electrodes are in plasma and they are electrodes so two currents exist electron current and ion current and in the dense plasma so it's it's important dense plasma this electron current towards the electrodes is larger than the ion current and therefore the decrease of the potential appears or well this is the error actually it's this , second s- er so electrodes themselves the the the source of the errors second alteration of the measured potential due to the energy gained er if if an electron penetrates into the electrodes it's here , just like i'm saying so the e- the electron can penetrate inside the electrodes and this also provides the change to the measured potential difference as you can see these alterations vary with time and location i don't ask i will not ask you of course to reproduce this like scheme or something like that the only thing which i would like you to understand and to remember that there are two main processes and they introduce changes in the real measured potential difference from which we calculate electric field and also i show you this er U U U U U and so on er the these all of these errors or all of these variations in the er measured potential diff- er difference so it's here you see there are so many components where we have to estimate and to remove to correct to get the real potential difference to calculate magne- er electric field the onl- or the main thing is correction terms are not small compared to the main terms biggest problem , methods to ste- separate the main terms from the correction terms because we know that there are correction terms but how to how to extract them and how can we be sure what we we extracted all terms and we er we er what we have now it's the real potential difference no way actually still no way to be sure so one er method is er er rotating spacecraft actually i try to show you what i found in some book that the rotation how does the rota- how does rotation work how so signal flom from plasma potential difference varies with the phase angle of rotation because if spacecraft rotates the signal varies of course the correction terms remain constant this is one way to remove the correction terms because they er rem- er remain constant and we can try to estimate and to throw it away and get the real the clean potential difference er yes so this is what do we have what we have and then additional induced term due to spacecraft rotation can can be determined and included in the corrections this term also we know because we know what is the rotation and so on so this is des- dense plasma what actually we have we have this tenuous plasma in this plasma ion current from ambient plasma to electrode is er to electrodes is negligible in tenuous tenuous plasma the electron current still exists this is the difference between the previous case so largest impact comes from secondary electrons produced by photo-emissions because we are exposed to the sun and interaction with energetic partic- particles impinging on electrodes so it doesn't matter actually from where it comes but it comes it's secondary electrons which produce the errors the the potential difference the decrease the alteration of the measured potential difference source of errors due to secondary electron emissions so electrode potential becomes positive relative to plasma potential small changes of current density lead to large changes of measured potential so even if we have , small emission of secdory secondary electrons it produce small changes of current density around these electrons and we have large changes of measured potential so big s- er source of errors how we can reduce it again i am talking er all of this you don't need to to know in details of course but it i i would like you to understand and to imagine to to have a understanding that there are some methods to reduce it application of a bias current to electrodes probe potential to small variations and bias current applied to the satellite to avoid asymmetric effects of photoelectrons so that's the methods we don't we will not go into details and er so that was that was the double probe two ele- main principle two electrodes as i let's let's once again say erm no main principle two electrodes at some separation difference far from the spacecraft we try to avoid the influence of the spacecraft we measure potential difference we know the distance at which these two electrodes are situated we can calculate the electric field a lot of errors , because electrodes are electrodes and they are in the er immersed in the plasma and all of this er electron erm ion currents , are generated around these electrodes and still all of these electro- electrons can penetrate and so on next second one second experiment electron beam experiment , here what we use here first it's the early version of electron beam experiment this experiment can provide measurements of the electric field perpendicular to the induction B magnetic field of the ambient magnetic field so perpendicular component er which principle is used motion of electron in homo- homogenous magnetic field it's this one it's circular this is the the orbit of the electron er er gyro gyro period is here you probably you know because you have to know it from this hannu koskisen k- koskinen er course it's er it's like that then there is no electric field added it's just magnetic field we know everything when we have the additional electric field , and what we have we have that the orbit is not circular any more there is a displacement because in these crossed E cross B fields we have the drift and the drift is perpendicular to E to E and to B what i would w- can tell you right now is that E cross B drift is one of the most important things which happen in the , plasma-sheet <START DRAWING ON BLACKBOARD> if we have this and this is our earth and this is plasma-sheet , and this is the direction of the of the field and we have the direction of elec- magnetic field and drift er V-E E cross B <END DRAWING ON BLACKBOARD> it will be towards the earth this drift E cross B drift is very important and actually , it's here this is E cross B drift called E cross B drift so it's not circular orbit anymore there is a displacement and this displacement is due to the electric field applied so we can estimate the electric field applied by looking on this displacement this is the principle that's all but we have to have these electrons of course artificially beamed therefore it called it's called electron beam experiment so we have to artificially put some electrons and then measure their displacement and then calculate the electric field this is the principle so drift-speed is electron drifts perpendicular to electric and magnetic fields as i showed you orbit is not circular there is a displacement it's just the example of numbers real numbers when you have electric field 10 power minus three volt per metre and then you have 100 nano-tesla magnetic field you will get a displacement about 3.6 metres . yes it's what i said in the electron beam experiment displacement delta is measured and electric field is then calculated principle . er i show you two , i well at least let's try i show you two er experiments on GEOS satellite and this is different from GOES it's it was when well i don't remember long time ago and i think GEOS is european mission GOES is US mission er yes so electron source for the beam located on the boom at distance D from the satellite this is the satellite and this is this electron beam we have to put the satellite beams this or satellite e- electrons yes detector to monitor the returning beam located in the main body of satellite returning beam mean means we start this beam it goes like that these electrons and then it comes to some other point not circular orbit this displacement delta we are interested in we c- that's called returning beam as i as i i i wrote you he- here electron beam emitted perpendicular to the boom it's to measure the electric field then er there is an angle this angle but that really (xx) but still er there is an angle between the electric field and perpendicular to the boom varies from zero to 360 for each satellite rotation so satellites rotate and this angle changes the returning beam displaced along the boom by the d- distance delta and here're here are these formulas where you can get this erm delta and there are , uh-huh this is the this is the er the e- the final formula where you can actually er calculate the electric field and there are two positions where returning beam is observed at the spacecraft when delta is equal to D , and in this case the direction of electric field is derived from the phase angle corresponding to this gyro erm er radius of the electron that's all that's all the the the the the principle how to calculate these are all details er related to this GOES er GEOS satellite and for in this er version we er we were able to calculate the perpendicular component of the electric field this is the main the main thing here and again it's it's er the returning beam of of the electrons which which were placed here and the distance that's all then beam experiment on cluster , cluster had it has considerably improved version of the beam experiment comparison com- in comparison with GEOS satellite what is what are the improvements that electron beam is steerable in azimuth and elevation so it's not just as in GEOS perpendicular to the spacecraft axis high-time resolution measurements are possible and then instrument can be used for large number of magnetic field directions so it's not just electric field po- perpendicular to magnetic field and that's all so we can get er elec- a magnetic field well electric field er with er different different components of the electric field so er actually there are two anti-parallel beams and they are ha- have times and the electric field c- can be determined from the difference between flight times , this is the principle and also er magnetic field as i as i said to you in the beginning magnetic field can be obtained from this because we know this gyro period if we know this we can calculate the magnetic field . er that was <SIGH> beam experiment and the third third erm row in that table in the beginning was the observation of electric field component parallel to magnetic field this i found myself is also p- probably the most difficult stuff and actually when you go closer to the earth especially on these auroral latitudes where er electric fields parallel to the magnetic field are important you have a whole set of different er physical processes and you have to be very careful here in the tail you don't have any parallel electric field and you can be sure that you can use that you can say that magnetic field lines are equipotentials and what you have on the earth electric field you can just map to the magnito tail and say that they are the same er i'm saying you this all of this because i'm going to talk about physics later about the res- real research later but near the earth you cannot do that they are not equipotentials you cannot just map the ma- electric field near the earth somewhere no th- because there are parallel electric fields they are important and on cluster it's possible to measure that so electric field component parallel to magnetic field is very important yes and then i- indirect meas- method to measure electric beam is ejected from a spacelab er spacelab <WHISPERING> or that's what i think </WHISPERING> i don't remember again when electron spirals spiral around magnetic field lines against the direction of electric field force and they are fi- finally mirrored by this force and return again we have the displacement what we are measuring returning electrons can be observed directly on satellite or un- indirectly by secondary effects and electric field is calculated from the observation of returning electrons so they return and they have the displacement and we cal- we know the displacement and calculate again electric field that's all but what we have in reality the actual measurements beam generates plasma instabili- instabilities and when we come to instabilities , well we have to take into account waves and so on it's another difficult question any simple deduction of electric field not possible it sou- it sounds really simple that you have electron beam you know what it does it go er on circular orbit you know it drifts you can er estimate the drift velocity and then you can get electric field but in reality it's not like that there are a lot of stuff like that for example instabilities you have to take into account near the earth parallel ma- electric field examples i decided to show you examples because i want you to understand how messy is it this is it and how er much work we still have to do to get the real er electric field data the clean electric field data this is the polar satellite my favourite one i like it very much and there is this electric field instrument here i plotted just the orbit for 98 to for you to see what is the polar satellite orbit this is Z- and er X-plane and this is this er meridional meridional plane erm ni- noon to midnight er meridion- meridional plane so it's this orbit night earth radii to earth radii it it looks above the polar cap above the the pole like that , the instruments as i said this is example of polar satellite instruments we are interested in this electric field instrument which can provide three components of the ambient vector electric field and the thermal electron density , er these are the objectives of this electric field instrument and they are just saying you that why it's important to measure the electric field i think you know why but still le- let's see what what is it so electric field instrument measures along the polar orbit vector electric field and thermal electron density the electric field may be related to motion of magnetic fields that are carried past the spacecraft with the ambient plasma convection electric fields it's here , structures of waves associated with the aurora these are parallel electric fields and they are lower closer to the earth they can be used to study the origin and nature of auroral zone processes such as electro- ele- energetic electron precipitation into the atmosphere well generation of auroral electromagnetic noise emission here comes instabilities and waves and so on their role in deposition of there are who electric field's role deposition of electric fiel- ele- erm solar wind energy into the magnetosphere ionosphere upper atmosphere through their ability to accelerate particles either directly in the ch- in the case of charged particles or through collisions between accelerated charged particles and ambient neutral particles actually this is long but this is what i'm interested in or what i am doing the role of electric fields in the acceleration of particles or in the acceleration and transport of particles from the plasma-sheet towards the earth and the formation of the ring-current ring-current is very important element in the magnetic storms magnetic storms are important for space weather space weather is a magic word what you have to use when you are talking about our research to to to understand the (xx) and to get money so this is the connection about from lectures which i'm giving here the research which i'm doing and the way how i can survive to get money so and then manner in which the different scale structures oh this is also my favourite one different sca- different scale structures large-scale hundreds to to thousands of kilometres and small-scale less than kilometre structures and waves are related fields are really different different and i will talk about this when i will talk about erm research which i'm trying to do and this erm is related to again to the particle transport from the plasma-sheet to the to to the inner magnetosphere there are different scales of electric field convection which is here which i showed it's a large-scale it's exist it exists everywhere but there are small-scale fields the connection between large-scale electric fields small-scale electric fields still is a very big question is i can i showed you that everything which is related to fields is unknown mainly n- of course there there were measurements i don't know 73 60 i don't remember that was 73 i think explorer it was was not D-C one D-C dynamic dynamic explorer yes dynamic explorer one and dynamic explorer two but still everything is un- almost everything is unknown so wide field of research erm well i don't know if you need this but still it's a picture which is official where is it electric field ins- instrument on the polar spacecraft is designed to measure the vector yes okay that's the third time already er posit- er provide measurements er from two to nine earth radii because it's orbit er no it i i haven't got but still because it's orbit er amplitude for vector electric fields er is quite big as you can see from 0.02 to 1000 millivolt per metre so in general it's able to measure different structures different scales large-scale and small-scale also called electron densities but we are not talking about this includes three sets of double spherical probes two pairs extend to separations well they have separation on wire-booms in the spacecraft spin plane and third pair is placed along the spacecraft spin axis on rigid boom that keeps them 14 me- metres apart these are be- why three because we want to measure components of the electric field not just one component which is parallel this is the data which you can get and actually , there are several parameters key key parameters where you can get when you go to internet you go to this webpage for er this electric field instrument on polar , well i don't know there are a lot of variations a lot of noise and you are not sure as i said you are not sure that the values are correct and you are not s- you cannot separate actually looking on these figures you are you cannot separate this chaos and so on you have to be very very careful analysing this sort of data it's not as for magnetic field for magnetic field we can create a model if we know magnetic field variations we know er which at least we imagine that we know which er current systems can produce these variations of the magnetic field we can fit or i don't know what to do with the observed and then we can get the model but here no we cannot do that we don't have model we don't have correct representation of the electric field we have several models and i will talk later about the modelling model- modelling of course we have yes but it's not so easy even we have measurements of electric field but they are not straightforward as for magnetic field and even i tried to find a- mhm as best picture as possible but i couldn't do that actually i tried to find very good picture with electric field measurements of course with electric field to explain to you and to myself also but i couldn't find it maybe i will find some later or something like that but still still it's a mess for me the same as for you probably there are several er er as i said key parameters and er here is this E-X-Y and E-Z components in millivolt millivolt per metres and they are they as i said they are they show this very very complicated er complicated behaviour , then cluster also er i don't think we i just again i just took it from the internet from the official page of this instrument and i found it extremely <SIC> unuseful </SIC> for my for example purposes and it's really er funny why probably it's really difficult but since i'm not myself i'm not doing anything with electric fields right now actually i would like to but i'm not doing anything and i was really surprised to to find out that why w- th- that actually there are no real output from this instrument that for example we know that in this distance magnetic field is 100 nano-tesla and actually there is nothing no information like that concerning the electric fields like at this distance we have 10 millivolt per metre or 10 is too much but still it's like 0.5 millivolt mil- millivolt per metre so like that erm yeah yes yes that instrument as you can see that instrument was a set three sets of double spherical probe first type of instrument and cluster instrument is er electron drift instrument that means this is the second type electron beam experiment so i show you two e- two examples (xx) is able to make accurate and highly sensitive measurements of electric fields and and so on er while cluster has been designed primali- primarily to study small-scale structures in three dimensions in the earth plasma environment okay uh-huh so that's just official objectives and i think i don't want to read all of this possible to obtain and then the difference can be used to form yes okay that's just official information and here is their example i don't know for me even for me that's completely i don't know @@ so here is the example and they have all of this from these E-D-I measurements and they have all of these raw counts and and variations so you see you have to to learn a lot you have to have a lot of experience to work with electric field data and actually i think there are tons of data which is not analysed which are not ana- analysed so it's er for future this is the only reasonable result recent result from cluster electric field measurement from my point of view again i'm interested in the distribution of electric fields in the magnetosphere in order to study the particle transport so it's not auroral fields it's no auroral effects and so on this is what is this this is the convection electric fields field at four to 10 earth radii the most interesting region which shows average electric field magnitudes and convection directions from approximately 15 months of cluster data E-D-I data and then it's er just measurements were mapped to the equatorial plane and binned using one hour local time intervals and one earth radii distance intervals from four to 10 radii so here er direction is direction it's arrow and the length of this arrow is the value , just how nice is it let's see at least put e- er heavy this these measurements here like this we can construct a model but still we will be not sure that this model work for all conditions of course since it's it was extremely difficult to extract and to produce this model and this is equatorial plane actually but magnetic field is a magnetic field it's not in the equatorial plane and when we are talking about magnetic field we know the magnetic field along magnetic field line here we have completely no idea what's going on above the equatorial plane this is the question number i don't know three or something w- well let's say two because first question is the distribution of electric field itself and the second question what's going on above the equatorial plane what is the dif- the changes along magnetic field line absolutely no idea many people say that they are equipotentials and we can say that the electric field is the same i don't know so maybe it's the same maybe not you cannot do that measurements along magnetic field line you cannot put 100 satellites and measure it unfortunately but i think i found this is i think that even the no it's lost here but still it's rather ni- n- nice results and i think i have to read this paper once more to understand myself er this is all for today and i will not ask you to do any homework because actually i didn't i didn't invent any homework @for you@ concerning these electric fields really since i have i haven't used them myself and i found them extremely difficult so , i would like you to give me homework of course and to have after these lectures in your after two weeks of lectures in your mind about some information about electric field magnetic field and indices next week i think we will go to particles and then i will talk more about instruments of course and i will show you a lot of data and i w- in that case i will ask you to go to internet and find the data and maybe not plot but look it on the on the quick-looks mainly so that's all questions and homework always welcome so thanks </S1>
