Science from Aditya L1 by Dr. Dibyendu Chakrabarty

Indexé : 2026-05-21

[00:00:00]Okay. So, good afternoon to all of you.

[00:00:03]Today afternoon I'm going to talk about the science from Aditya L1, that's the title of my talk.

[00:00:09]And before I start, maybe I'll give you a short intro about why Aditya L1 mission is important and what kind of science potentially you can bring out from this mission.

[00:00:21]Uh just to give you a perspective of where we are at the present moment is this is the galaxy, our galaxy, which is called the Milky Way, and we are one of its arms, which is here.

[00:00:34]And the entire solar system is actually located here.

[00:00:38]And you can see if you zoom in this portion of the screen, then you see that star, which is our star, which is the sun, moving through the interstellar local interstellar cloud.

[00:00:49]And if you further zoom in, the star, the planetary system, and the tail-like feature called the heliosphere, and that is the region where we are uh the alien part, which is space that is carved out by our star.

[00:01:07]Uh this is the region where uh controlled by the activity that are going on.

[00:01:14]So, at present we don't have not much of idea that how the heliosphere really looks like on the tail side of it, whereas two spacecraft in the history of the mankind has crossed the heliosphere, it has gone out and has gone to the local interstellar medium, or which we call as LISM, which are Voyager 1 and Voyager 2.

[00:01:37]And at the end and the center of it is either the system, the planetary system here, the sun is here, the nine planet the planets are here, and you see different parts of the heliosphere, which is termination shock, uh heliosheath, pause.

[00:01:56]Now, the sun, how it will affect the different planetary environment, that is dependent on the magnetic and what the magnetic field intrinsic magnetic field or in or that is having on each planet. Not that every planet has a magnetic field of its own, but then some of these planets which are listed here, including our planet that has a magnetic field.

[00:02:24]This figure it is the rotation axis in the planetary rotation white and magnetic axis orange and you can see that they are separated and not they are not coinciding always and particularly for example in extreme cases you see planet of Uranus where it is separated by almost like 59 degree is two axis.

[00:02:49]Not only that the dipole magnetic field there in this planet is also off-centered.

[00:02:56]The even The kind of magnetic the solar effects or the sun's effect, how it affects different planets.

[00:03:06]Uh if you compare the Earth and the Uranus because the magnetic field is differently oriented, uh its effect will be entirely different. So, this is something which you have to keep in mind that the magnetic field that the each planet that greatly controls the kind of space weather on each planet. So, it's important uh before we assess the impact of sun on each planet solar activity.

[00:03:33]Space weather is space starts from 100 km onwards for the Karman line and from 100 km right up to the sun.

[00:03:42]The entire space is governed by the sun.

[00:03:47]And it consists of different plasma domains like ionosphere, magnetosphere and then the interplanetary medium.

[00:03:54]Here, they do it plasma, but the kind of plasma that you are talking about in this medium are very different from each other.

[00:04:01]And therefore, how the solar disturbances, like coronal mass ejection and the solar flare, they reach onto the planet like Earth, it also depends on how these disturbances are propagating through this medium, they which are different in nature in terms of the plasma properties and how it is the minus is the lower most light compared to this.

[00:04:24]So, therefore, it is difficult in some sense that uh to assess the impact of space weather on the planet originating from the sun, but the because the coupling is happening across multiple scales, it's difficult to uh ascertain that what will be happening at the interface of these differently uh different property plasma medium uh across the interface. And that actually the objective of uh very important objective of this field that how do we that how the disturbances one type of plasma eventually gets propagated to the other plasma domain and we the layer that we are studying.

[00:05:09]So, it is it is of uh it is of no surprise that drivers of space weather is the sun and called Aditya on screen the language uh in India.

[00:05:23]And that's why this mission that we are going to talk about today is called Aditya L1. Aditya is for the sun and L1 is the point where satellite is located and put uh in order to observe the sun in 24 the the The sun as a star is not a very special star. It's a middle-aged star. Half of its life is almost over. Half of its life is that it's remaining. And if you look at the sun, the temperature of the sun as you go up towards the surface is from the core to the surface. Core is extremely hot, and as you go up towards the surface, the temperature decreases.

[00:06:01]And if you come to the photosphere, that is the brightest that you see from our planet, that is around 6,500 to 10,000 K. That is the visibility that we see.

[00:06:12]Uh interestingly, that how when you go above photosphere, that is in the atmosphere of the sun, which is called corona, the temperature again increases.

[00:06:21]So, it's an interesting uh in interesting fact that the temperature towards the core where nuclear fusion is taking place in the sun, hydrogen is getting converted into helium, there the temperature increases, which is for obvious reason because all the activities are taking place there.

[00:06:37]But then, when you are going away from the sun, in contrary to the to the understanding that we have in the light that if you're going closer to the source, the temperature is should be increasing and you'll feel more heat.

[00:06:52]Uh here, there is a counterexample where you are going away from the surface of the sun, and then the temperature is increasing in corona to 5 million degrees or 1 million degrees Kelvin. So, this was a puzzle that is actually surprising to at least surprised scientists for quite a long time. Some aspects of which are are still not understood very well. At least it has been realized that not a single not a single process will be able to address or explain this million degree plasma in corona.

[00:07:24]So, there are multiple processes that are invoked to understand the million degree plasma in around the sun.

[00:07:31]So, this is one problem, the coronal heating problem, which is one of the science motivation for almost like all science mission that is even happening today. And in addition to that, there are other problems that are One of such problem is that our sun is activity-wise, solar activity-wise, is not a is not a constant sun.

[00:07:52]Not a constant star. Its activity is variable, and there are various time scales that are associated with it. The most most famous of it is the 11-year time scale, where 5 and 1/2 years the sun is very active, next 5 and 1/2 years it is is actually quite So, this is 11 years, and then there are 22-year cycle, and the entire kind of periodic behavior of the sun activity.

[00:08:17]This is, as far as the temporal scales are concerned, but same is true for spatial scales uh in the in the sun and planetary medium, where around 13 spatial and temporal scales governs. Um if you if you consider it, the way the space weather couples from the or gets governed from the sun to the planet, there are almost like 13 spatial and temporal scales that are can be thought of.

[00:08:41]But, what happens that in in the midst of this kind of predictable behavior, there were periods in the past where sun was unusually very very quiet, and there was kind of ice age on that existed on the on the planet, which are called Maunder Minimum and Dalton Minimum and things like that. I see the data like that, where sun was a very very quiet at that period of time.

[00:09:04]So, these are aperiodic behavior, and for reasons that are not yet fully understood, that this actually broke the stereotypical periodic behavior of the sun and brought in aperiodic behavior, which cannot be predicted by uh by usual means.

[00:09:21]For stars, so something happens inside the sun in terms of magnetic activity, uh that goes through changes. That is very clear from this. Goes through changes that is not predictable to us.

[00:09:33]That actually uh an important problem to understand as far as the the and the space weather is concerned.

[00:09:44]So, from the Sun, the solar wind comes, it carries with it the momentum and the momentum flux that is transferred on the planet like Earth where magnetic field is there is actually called the dynamic pressure of the solar wind and is called it's actually expressed by rho v squared. Rho is the the mass density and v is the velocity.

[00:10:06]And it actually compresses the magnetosphere on the day side as you can see as the dynamic pressure increases, it actually gets compressed by the solar wind.

[00:10:15]So, the mass density and velocity is an important factor to assess the space weather on any planet like Earth where magnetic exists.

[00:10:27]But, another important factor is the magnetic field that is there in the solar wind itself and if the polarity of this magnetic field is opposite to the terrestrial magnetic field polarity, then what happens is that it uh it is almost equal and opposite on the day side magnetos field boundary.

[00:10:44]And it actually reconnects with it and then opens it up. Therefore, solar wind can enter into the magnetosphere of the Earth.

[00:10:53]And it also drags the magnetic field towards the night side and then eventually it magnetic reconnection takes place at the night side magnetosphere.

[00:11:02]And it's like a stretched string that is relaxed after the magnetic reconnection and so a lot of energy and plasma energetic plasma comes convecting towards the Earth and then it sees the closed field lines and therefore all these processes the entire magnetosphere get disturbed is called geomagnetic storm.

[00:11:22]And because the energy is stored in the magnetosphere as I shown here and so if there are changes in the solar wind parameters like changes in the magnetic field polarity or dynamic pressure then you what you see is also something called magnetic field sub-storm where magnetic field can suddenly changes its configuration from a tail-like configuration it can go to bipolar configuration and then releases energy. And those particles energized particles can follow magnetic field line come to the polar region and creates aurora on the night side.

[00:11:57]So, these are called sub-storms, magnetospheric sub-storms.

[00:12:01]And that can create uh a lot of reconfigurates magnetic field reconfigurations on the night side of the uh or inter-magnetospheric and energizes particles and these are important for space assets as well in order to I mean, they can damage the assets that are there in geoorbit as well.

[00:12:25]One of the way that space weather can affect it can affect the operation of International Space Station and the in this particular example it shows that on the x-axis the months and the y-axis the height. The orbit is written here and you can see that in regular intervals the International Space Station had to be maneuvered and taken up to high altitude because the orbital decay happens because at the height of 400 or 430 km the atmospheric drag is still significant so that it it actually causes the orbital decay of the space station and eventually you have to keep the station at a specific altitude for its safe operation in order to maximize the lifetime of operation therefore you have to give it up and this activity this goes on for the maintain of the orbit of the space station.

[00:13:16]But during storms this can cause significant problem in terms of orbital decay and that is why it's very significant important to know that our sun behaves and how the terrestrial magnetic field or thermosphere uh and terrestrial upper atmosphere response to those episodic disturbances that happens on the sun and solar wind.

[00:13:38]>> [music] >> This is an example which is very famous and the SpaceX lost the Starlink satellites.

[00:13:46]This happened in February 2022.

[00:13:50]SpaceX didn't imagine or as per their model they didn't imagine the kind of drag that is expected during this particular storm but then eventually thermospheric drag but came out to be the response to this storm was way larger than what is expected and therefore therefore the drag was unmanageable and the spacecraft was lost.

[00:14:12]It also affects disturbances from the sun. It also affects ionosphere.

[00:14:20]medium and it causes turbulence in the medium that affects the radio propagation.

[00:14:25]Therefore for communication, HF communication and navigational purposes when the airplane moves over like polar region or over any airspace the radio propagation from the satellite that can get severely disturbed. There can be loss of lock also as far as these transmissions are concerned and posing great dangers to the communication to the navigation navigational application. So this is an important aspect that needs to be taken care of as far as space weather management is concerned and because happens due to the local turbulence in the atmosphere and also the solar processing these turbulence in the magnetosphere.

[00:15:05]So there are three primary goals of space weather research. One is that do we understand the space environment that we live in? There are three goals. One of the goals is that whether we understand the space environment.

[00:15:18]Second is can we predict the solar disturbances? Third is can access focus the impact.

[00:15:25]And therefore, when it pulls this problem, there are if we simplify this that how to handle this problem, and there are solution that is you can simplify it, right? We need to understand the effects that are coming through magnetic field and radiation and particles.

[00:15:43]Radiation come can come through different wavelengths. Particle can come in different energies and magnetic field turbulences can happen because of the solar wind magnetic field interacting with the planetary magnetic Now, what kind of disturbances now once we know that these disturbances are happening through magnetic field radiation and particles, it's also important to know that what are the disturbances that we are talking.

[00:16:15]Now, we can summarize it to be due to five major disturbances. One is solar flare, second is coronal mass ejection, third is stream and corotating interaction region, fourth is solar energetic particle effect and fifth is cosmic rays.

[00:16:32]This is a typical example of coronal mass ejection as you can see that if you cover the disc of the sun, which is extremely bright bright on some occasions, you see that a huge chunk of mass coming out from the from the sun, and these are basically energetic plasma tied up with the magnetic field and the scale size of this particular structures are extremely large and you can compare by putting that that picture here, and you can see the kind of size or spatial scale you're talking about.

[00:17:01]So, when it is launched from the sun, it actually carries magnetic field and charged particle element you pick, and it comes towards this planet, and it can completely engulf the planet and can cause severe disturbances to the magnetosphere and elsewhere system and the plasma daring causing great damage.

[00:17:19]Can cause great damage to the space assets that are there at the Leo and Geo orbits.

[00:17:26]When there are disturbances like solar stream interaction region or stream interaction region, this is come this comes because of the consequence or the result of interaction between the fast and slow solar wind.

[00:17:39]And fast solar wind can come through coronal holes, the slow solar wind can come from helmet streamers like from here and they can interact with the at the interplanetary medium and if part happens to go through this region and then what happens is that this can cause severe disturbances magnetic field environment of the earth and that can cause disturbances in the magnetosphere, the ionosphere and Geo and Leo satellites, that things like that.

[00:18:10]So, particularly CMEs are more frequent during solar maximum and CIRs and SIRs, whichever way you call them, this is more frequent during the solar minimum.

[00:18:23]Now, those are because of the the particles and magnetic fields. Now, in terms of radiation, the damage comes through the solar flares which are the explosive explosions that happen on on the sun and these are millions of nuclear bombs that gets detonated that kind of equivalent energy that comes from these particular explosions. These are solar flares and you can classify it based on post x-ray flux observations, 1 to 8 angstrom, and x-class as a are the most energetic solar flare events and you can see an order difference as you go up from as you go down from x-class to m-class c-class and b-class in terms of decreasing intensity of the x-ray flux that come from this flaring region.

[00:19:09]And the kind of effect that it can cause is that the this x-ray fluxes can cause an additional additional ion emission very short period of time in the lower part of ionosphere and causing short wave radio to plan. This can cause major communication problem to the And therefore it has an additional implication.

[00:19:33]And it's very important to understand that what kind of effect it can bring in uh from the sun during solar flares. So, these are some of the the process related problem that can happen in terms of space weather management.

[00:19:49]In data particles, ions, and electrons that can come from the sun that is always coming from the sun through solar wind. And there are three kind of particles that I can talk in when we talk about ions. Those are slow and fast solar wind particles, super thermal particles, and solar energetic particles.

[00:20:06]They are of increasing energy here and one gets converted So, if you accelerate this thing becomes super thermal. If you accelerate super thermal it becomes SEP. And the other way around is also true. If you decelerate solar energetic particle, it becomes super thermal particles and then super thermal particles when it slows down eventually it goes back to the slow fast solar wind energies.

[00:20:31]And so, these particles are coming particularly the energetic particles are the fluxes are very large during disturbance time like when solar flare happens and coronal mass ejection happens.

[00:20:44]And that is the time you see the fluxes of these particles can happen over multiple orders of magnitude in terms of these fluxes and it can actually incur all the space assets that we have.

[00:20:59]Space walker at space walker at that point of time it can affect uh and cause radiation exposure uh to the astronauts. So, these are some of the problems because of solar energetic particle events.

[00:21:11]There are two kind of particle events out there. One is gradually events which are associated with coronal mass ejection. The shock associated with these events has a larger longitudinal extent. Whereas impulsive SEP events associated flares and it has a small has a smaller longitudinal extent for the impulsive SEP and it comes from the flaring region on the sun to the space satellites.

[00:21:37]And it doesn't sustain as long as the gradual SEP.

[00:21:43]Then there are of course cosmic rays and cosmic rays are high energetic particles from outer space. These are coming from mostly comes from the extra galactic in origin. It's coming from supernova explosion or by neutron stars or black holes. These are extreme energy particles. Fortunately, the flux of cosmic rays are less and it has a dependence with the solar activity. When the solar activity is the heliospheric magnetic field is less, that is the time the cosmic ray fluxes from extra galactic regions that we enter into heliosphere in larger quantities. But when sun is active, as a consequence the magnetic field within the heliosphere is active. That is the time the cosmic ray fluxes are expected to be less inside.

[00:22:27]Cosmic rays, what happens is they enter the atmosphere and because of secondary ionization and nuclear reactions and some part of it eventually reach to the surface. Some of these neutrons will reach to the surface and neutrons being chargeless particles, neutral particles, you can measure it from the ground and therefore in over the globe there are various places you see neutron monitors that are placed in order to understand the neutral fluxes that are neutral fluxes that are reaching on the ground.

[00:22:58]Not only because solar wind plasma is quasi-neutral, so in in terms of solar wind electrons uh so when ions exist, there are electrons as well, and these electrons, they follow the magnetic field lines and carry the electron heat flux from the sun to the heliosphere. And this is also uh is a very important component of the solar wind plasma, and so there are various measurements that we that are planned in order to uh measure solar wind electrons flow.

[00:23:30]In order to uh understand uh the behavior of the sun, its impact on the heliosphere, and how it is going to impact the terrestrial magnetosphere dynamics system Aditya-L1 mission uh is planned, and Aditya-L1 mission is the first dedicated solar observatory from India for solar and heliospheric studies.

[00:23:52]Uh its official mission life is 5 years, but we expect it to survive much longer than that because the instruments are operating fine. And there are seven experiments on board Aditya-L1 mission.

[00:24:03]Uh it was launched in 2023, 2nd September, and the halo orbit insertion at the L1 point that took place on 6th January 2024.

[00:24:16]Now, when it comes to the L1 point, I just wanted to mention here that in a sun-earth uh system there can be uh if you put a satellite, it's actually a three-body system. In that three-body system, there can be five points uh you can find. It is It is not possible to solve it analytically, but if one makes some some approximation, then some approximate solution can emerge in the form of five gravitationally stable points, which are Lagrange points, they are called. And the first Lagrange point is between the sun and earth at a distance of 1% of the sun-earth distance.

[00:24:52]Uh so 1% of one astronomical unit, and the satellite is placed here in an orbit which is from the earth if you look at it either it is clockwise or anticlockwise if it is a halo orbit. And then if it is is either class one or class two depending on whether you are looking it clockwise or anticlockwise direction.

[00:25:16]Uh but there is another kind of orbit and some of the L1 satellites are put in Lissajous orbit as well. And in case of Lissajous orbit orbit is not a periodic orbit.

[00:25:26]They are not periodic orbit whereas halo orbits are periodic orbit and in case of Aditya L1 this periodicity of uh the is around six months. So if the satellite starts from one part of the orbit and comes back to the same part uh after six months after six months or so.

[00:25:46]And the advantages of putting a satellite for solar observation is that at L1 point there are three advantages we can think of.

[00:25:54]One is that we can observe the sun 24/7 without any eclipse from L1. And the second is one we can sample pure solar wind because the satellite is completely outside the earth's magnetosphere. The third aspect is if you take a typical solar wind velocity of 400 km/s it's almost like 45 minutes to one hour away the the satellite from the earth.

[00:26:19]And therefore if you can telemetrically manage telemetry from the satellite to the ground station then you have telemetry can happen pretty fast in 16 seconds or 32 seconds or so. So you get a priority information of the disturbances that are reaching at L1.

[00:26:35]And so before the solar wind hits the earth it is possible to send those information down to the ground station and therefore make a space weather forecasting possible.

[00:26:48]possible.

[00:26:50]So in Aditya L1 primarily it a science mission. It's a science mission and therefore the kind of science objective and the uniqueness are listed here. Then some of these uniqueness are are very important because uh through these instrument uh what is Aditya L1 is trying to do is that uh first of all it's trying to look the CME eruption or CME dynamics very close to the solar disk.

[00:27:16]And it has a coronagraph which is looking at very close to the sun. Which at present is not uh no other satellite is doing.

[00:27:24]Second is it is looking at near ultraviolet band which is uh and looking at it in a spatially resolved manner.

[00:27:32]Then it is looking at the entire flare spectrum, the soft and X-ray without any break or sensitivity change. And fourth is it's looking at electrons, protons, alpha particles, and magnetic field uh with direction to solve manner. So, these are some of the uniqueness of the mission that is associated with Aditya L1.

[00:27:52]These are the seven instruments.

[00:27:57]So, VELC, SUIT, Helios, SoLEX, PAPA, ASPEX, and MAG.

[00:28:03]PAPA at present is not functioning as expected, but then all the six experiments are operating uh very nicely.

[00:28:11]In this the remote sensing experiments are VELC, SUIT, Helios, and SoLEX and in situ measurements are PAPA, ASPEX, and MAG.

[00:28:21]VELC as I was pointing out is called the Visible Emission Line Coronagraph. And what it does is any coronagraph is actually blocks the the solar disk by a by something called occultor. And then it looks very close to the solar surface.

[00:28:37]Uh and then what it does is that on that circle the how it can help us uh to determine that how the CME dynamics works at the very initial phases when it is a launch of the corona.

[00:28:50]And that has importance because that helps us to understand that what are the processes that helps or that actually arises before the CME events of the sun.

[00:29:02]So this is an interesting problem to handle and VLS is an instrument which is helping us to address or understand.

[00:29:11]The second instrument is solar ultraviolet imaging telescope or suit.

[00:29:15]It has 11 different channels and the the eight of them are narrow band which are marked by NB and two of them are broad band spectral channels which are marked by BB.

[00:29:28]And you can see the narrow near ultraviolet is the central wavelengths are and the band pass of these filters are marked here.

[00:29:39]The idea is to understand the coupling.

[00:29:41]So these emissions are coming from different heights of the photosphere, chromosphere and the transition region.

[00:29:47]And the idea is to understand that by looking at these emissions through these multiple wavelengths.

[00:29:53]There is we want to understand the coupling and dynamics of the solar atmosphere and what are the processes which the energy is channelized and transferred from one region to the other region.

[00:30:06]So this is typically the specially resolved in UV full disk images at different wavelengths. NB is narrow band and BB is broad band and you can see the features that are specially resolved in these working bands and these are emissions are coming from different heights of photosphere, chromosphere transition region.

[00:30:26]Helping us to understand that how this clearing region or coronal transients are are actually evolving through different heights of the of the solar atmosphere.

[00:30:39]It also has an atmospheric science application because if you can observe in full disk, then it can give us the total solar irradiance, which is between 200 to 400 nanometers as well, and which is an application for for ozone and climatic studies.

[00:30:59]The other two instrument which is also remote sensing in nature is looking at the soft and the hard x-ray measurements. One is called SoLEXS, which is in full form Solar Low Energy X-ray Spectrometer.

[00:31:13]And other one is High Energy L1 orbiting spectrometer. SoLEXS look at actually targeting to understand the thermal energy of solar flares, whereas HELIOS is targeting the how the non-thermal energy are released during solar flares. So, the So, by doing that, what SoLEXS and HELIOS can do is that they can get the entire light curve of the entire spectrum of low energy to high energy part. And therefore, uh the energy release, the triggering mechanism, it can help us by combining the thermal and non-thermal emission.

[00:31:50]Uh it can help us to understand the flare evolution as well.

[00:31:57]The instrument which we have made or designed and fabricated is the Aditya Solar Wind Particle Experiment. The whole idea was of this instrument was to observe solar wind in multiple directions.

[00:32:11]And we wanted to separate the alphas and protons, which are the main composition of the solar wind. And we wanted to observe in both low and high energies.

[00:32:21]The low energy spectrometer is called SWIS, the Solar Wind Ion Spectrometer.

[00:32:26]If you expand it, the energy that you're trying to cover is 100 electron volts to 20 kV. Interesting point is that it is covering 360° in in across the ecliptic plane. and both the protons and alpha particles are separated in the ecliptic and integrate areas ecliptic plane and and the across the ecliptic plane.

[00:32:49]Okay. And uh STEPS is SupraThermal and Energetic Particle Spectrometer, and it is uh following a totally different measurement approach. These are solid state detector, and this one is a top and analyzer electrostatic analyzer.

[00:33:05]And STEPS is looking at six directions, and these are radial partner, and these are intermediate partner. So, four of these sensors of each are working perfectly well, and two of them are having some light saturation at this point of time.

[00:33:21]And so, therefore, this SWEA and STEPS are being used are actually spread all across the spacecraft, and to have a clear directional coverage including the backside of the spacecraft. So, we are looking at solar wind and energetic particles in multiple directions. And that's the whole science motivation of having this measurements.

[00:33:47]So, to give you a just a flavor, the SWEA top and analyzer THA is part of SWEA instrument. It actually the top hat where in the particle enters from the top. Here, it applies the top hat here bias voltage, and you kind of scan it, and then different energies are filtered here, then through a magnetic field, which actually bends the particle in a certain manner depending on the mass by charge ratio, and then you detect it through microchannel plate or resistive anode detector.

[00:34:22]And it has a field of view of 360° by plus minus 1.5° in both the gaps, both in and across the ecliptic plane.

[00:34:31]In terms of STEPS unit, these are the six units it is covering different FOVs in different directions, the sun radial, intermediate, park spiral, earth pointing, and south pointing.

[00:34:44]And these are the FOVs that are mentioned here. And having shown you this instrument, we can I can show you how this data is nicely getting compared and internationally and nationally people are using extensively the ASPECT data.

[00:35:00]Um very well and I I am happy to tell you this one of the most downloaded data in the ISSDC website. The data is freely available. Uh now, why it is because the ASPECT data when it is compared with all the existing missions, it's actually the data quality is extremely good. Here is an example where we are comparing with the NASA wind satellite measurements and you can see uh you can see that uh this is the comparison. This is the CAB arrival time and you can see the features nicely well in this. In fact, being is a aging satellite and so therefore some of the features are very nicely captured and in fact, it is captured in the major way ASPECT sensor.

[00:35:47]The way it is done is that the velocity distribution functions are constructed uh based on those measurement at different energies uh by having those particle measured by uh by top and etc. And then you construct a distribution function, you treat it and calculate different moments. And different moments give rise to different bulk characteristics of the solar wind. That's a basic whole idea and we have developed it in the in in our team and we are generating the solar wind bulk parameter like density, temperature, and velocity. And this is along with the flux data also is getting posted at the Indian Space Science Data Center, which is called ISSDC. So, what you have to do is to register and get the data freely downloaded from the site, so you can do that once you have an account.

[00:36:40]So, it is you can see a comparison of the ASPECTS data and the WIND data.

[00:36:46]Uh and here is a comparison of the number density.

[00:36:49]You can see that these two satellites are two different places uh at L1 and the comparison is pretty good. This is for speed and this is for uh thermal speed. This is for bulk speed and this is for thermal speed and you can see that uh the data quality is very consistent with individual satellites.

[00:37:10]This is for energetic particle and if you see that the data is compared with the ASPECTS data for all four directions.

[00:37:19]1 2 3 and 4 are compared with AS EULIS and AS EPAM. And the consistency is pretty good, which is brought out by these very good correlations that you see in terms of at different energy bands. The AS EULIS data and and the STIS IMAPS and STIS EPS is compared here. STIS EPS are compared here. So, if you compare inter comparison and intercalibrate between different instruments that are presently available, you see that very good consistency, which gives a lot of credence to the kind of quality of data that that Aditya L1 is producing.

[00:37:55]This is plasma and later package for Aditya, which is called PAPA. And this is this specialty of this instrument was that it was supposed to measure the electrons and heavier ions, but unfortunately, the the this instrument is not working really well at the present moment of time.

[00:38:13]And so, the initial data are available, but not uh the present data. So, these are some of the comparison. And initially, when the data was coming very well, the data quality was extremely good. So, some part of it malfunctioned and therefore it's not able to produce the data at the present moment.

[00:38:30]Magnetometer is also there. It's a fluxgate magnetometer, so it gives interplanetary magnetic field components in three directions, Px, Py, and Pz. And here is a comparison of magnetic field data with the Discover satellite magnetic field. You can see the consistency of different magnetic fields uh components between these two satellites.

[00:38:53]So, I'm almost done with this. I just wanted to uh tell you that with Aditya L1 uh uh at the present moment, the status is that NASA has launched uh IMAP and uh NOAA has launched SOHO L1.

[00:39:12]And these two satellites, along with Aditya L1, ACE, WIND, and Discover, there are almost six satellites at present or SOHO. There are six satellites at present at L1.

[00:39:24]Giving an unprecedented opportunity to study solar wind from and because the Aditya L1 data are uh good and quality is extremely good, so uh several studies using this constellation is possible now. This opening up a new field based on the L1 constellation of data.

[00:39:46]But, the um Parker Solar Probe has launched very close to the Sun and Solar Orbiter has also gone closer and across the ecliptic it has made measurement of the solar poles.

[00:40:00]And therefore, it's an exciting period of solar and heliospheric physics.

[00:40:04]There, one approach is we are going closer to the Sun, other approach is we are having sophisticated measurement from the L1 point.

[00:40:11]And we have just taken the first step uh towards understanding it through Aditya L1 and our idea is to build on this initiative through Aditya L1 and to understand sun, space, heliosphere, and space weather really much better and comprehensively.

[00:40:30]Thank you very much.