So what did we look at? We looked at how space weather can impact long pipes or wires in the ground and on the surface of the Earth, or well, a proxy for that. The pipes and wires may be power grids, oil or water pipe lines, or telephone or telegraph wires. It was often thought that this type of space weather effect was only important for higher latitudes around the poles. However, in this paper we showed that it can also be important around the magnetic equator. This region during the day has what is called the electrojet which can enhance the space weather impact on the power grids which sit underneath it. A model of the equatorial electrojet can be seen below.
The paper we are going to talk about today, "Interplanetary shocks and the resulting geomagnetically induced currents at the equator" is perhaps one of my favorites... not that I have favorites, I love all my papers equally... but if I had any favorites, this would be one of them. So what made this paper special? Part of it was being able to work with good friends on it. It is always a pleasure to be able to work with friends, especially when you know the work you are doing will be useful to others. And that's another reason why this paper is special. Often the work I do is more than a few steps removed from being able to be applied to our everyday lives. This project is much closer to helping others. So what did we look at? We looked at how space weather can impact long pipes or wires in the ground and on the surface of the Earth, or well, a proxy for that. The pipes and wires may be power grids, oil or water pipe lines, or telephone or telegraph wires. It was often thought that this type of space weather effect was only important for higher latitudes around the poles. However, in this paper we showed that it can also be important around the magnetic equator. This region during the day has what is called the electrojet which can enhance the space weather impact on the power grids which sit underneath it. A model of the equatorial electrojet can be seen below. Often the change in the local magnetic field strength is used to determine how big of an impact space weather will have. We looked at what the impact was under the equatorial electrojet compared to just outside it. We found that this impact was just as large as in the polar regions. We often like to use global indices or proxies, but this helped lead us to the idea that more local data. For instance, knowing the average temperature on Earth is nice and a useful proxy for some studies, but it isn't going to help you if you are trying to decide how many layers of clothes to put on in the morning.
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Every mission needs a great all encompassing paper... if not a few. This was ours. "The Balloon Array for RBSP Relativistic Electron Losses (BARREL)" (the other one was the Woodger et al 2015 paper). This first paper was written prior to the first mission. It was a way to ensure that the community knew this mission and it's data was forthcoming, as well as provided detailed information on the instruments. The BARREL mission was a mission of opportunity for the Van Allen Probes... Okay, so what does that mean. NASA has large missions. I mean if you are going to send something into space, it's not every day that one gets to do that, so you often try to get the most out of each opportunity. Financially and practically, you can't fit all the instruments or have all the observations that you may like to have though on any given mission. However, for a fraction of the price of the original mission, you can have a mission of opportunity that will add to the value of the primary mission. That is where BARREL came in. The Van Allen Probes mission was the first mission in about 20 years which was launched with the specific intent to study the Earth's radiation belts. They were designed to be two spacecraft which would fly through the radiation belts every 9 hours. This would allow them to study how the particles that are trapped in the radiation belts change during space weather events. The Van Allen Probes would attempt to see what fraction of these particles would fall and be lost in the Earth's atmosphere, but that is hard to do from their orbit. The BARREL mission was designed to study what particles from the radiation belts were lost to the atmosphere. Both missions have their own goals which will advance science on their own. But, they are synergistic and better together! The proof is always in the pudding. Given the number of papers from the Van Allen team, and the BARREL team, I'd say that we had a successful mission of opportunity. We were able to test different theories of wave-particle interactions, see how shocks can cause particle loss, and study more about other loss processes. So why do you care... Well the radiation belts are filled with particles which can cause harm to satellites, and when lost to the atmosphere, disruptions to communication systems and increase radiation at aviation altitudes. Being able to study one aspect - say just the loss to the atmosphere or just the stuff that stays trapped in the radiation belts - is nice, but it doesn't give you the whole picture. Even with these two missions we don't have the whole picture. We have more than what we've ever had, but there is still a lot of unanswered questions. But that's the way of science, slow and steady progress to understanding how nature works. And of course - Here's my video about the BARREL mission that NASA helped publish! I was very proud of that. During my Ph.D. I lived and breathed electromagnetic ion cyclotron waves... as my brother would say, I am a nerd. These waves are often abbreviated as EMIC and there is a debate as to if you pronounce it Ee-Mic or you spell it out E-M-I-C when you talk about them. Either way, they were the topic of my dissertation. I loved them and still do. They are just so cute and unassuming but can have a large impact. So what are these things? Well, it's in the name, they are an electromagnetic ion cyclotron wave... I know doesn't help. They are a wave that we see in both the electric and magnetic fields. They resonate with ions. When Ions are around in the magnetic field, they start moving in a circle around it. When the conditions are right, the particles moving around the field line can start growing these EMIC waves. As the waves grow, they can start scattering the particles as shown in the youtube video below from NASA. This of course then changes the conditions around the wave and ultimately the wave is turned off. It's a bit self defeating. So why do we care about these emo waves? It's because of what particles they interact with. The ions themselves are important. They carry a lot of energy and are often found in the region call the ring current. In fact, they carry so much energy that they can change the observed strength of the magnetic field at Earth. These EMIC waves are thought to resonate with those ions and ultimately push many of them into the Earth's atmosphere. Another group of particles that they resonate with are the very very very very energetic electrons in the radiation belts. Like with the ions, the EMIC waves can ultimately push these particles into the Earth's atmosphere where they become lost - ionizing the upper atmosphere. Below is a you tube video showing how particles move through the radiation belts. This is all fine and good, but this is a post about a paper... This paper became the fourth chapter of my dissertation. It was focused on observations of these waves from one mission, CRRES. One of the debates going on at the time was if EMIC waves were seen during the main part of geomagnetic storms, or only when the magnetosphere was recovering from a geomagnetic storm. Many people were using what is called a superposed epoch. A superposed epoch picks a point in an event and then you line all events up by this time. For EMIC wave studies, most people picked either the start of a geomagnetic storm, or when it is at its most intense period, and then looked a day to 6 before the epoch and a day to 6 after the epoch. Once everything is lined up like this, you can take the average and/or look at other statistics. Assuming that all events are similar and have similar lengths, you are likely then to start to see trends. However, if the events vary in length a lot, trends may get smoothed out. In our paper, EMIC wave activity during geomagnetic storm and nonstrom periods: CRRES results, we used a multi-epoch study. We know that different mechanisms are happening in different parts of the storm. For instance, when the solar storm hits the magnetosphere, it pushes it closer to the Earth and this can affect the ions in the magnetosphere making them more likely to produce EMIC waves. This only happens at the beginning of the geomagnetic storm. We also know that the main phase of the storm is when you have ions coming from far in the magnetosphere into the inner magnetosphere where the satellite sits and that this too can then produce the waves. So we picked two epochs, the start of the storm and the point where it was most intense. We then also picked the end of the storm to give us the third epoch. This last epoch was important because some storms last less than a day and others can last more than a few. We didn't want to have a non-storm condition mixed in with our storm periods.
Now after all of this what did we find? We found that waves were more common during storms than not and that they happen more at noon and dusk than at midnight and dawn. Why does one care? We care because it helps us understand how much area is affected by these waves, and thus how much they will affect the radiation belts. This is important to know because it helps us better understand what types of space weather may impact satellites, communication, and radiation at aviation altitudes. There are of course a few steps in between this study and these applications, but it is all part of the processes. One of my favorite parts of this paper though was the method. We picked this multi-epoch approach and that was quite novel at the time. But, it had one major failing. This was not the method used by others, so how could we compare our results to theirs. They had used different data sets than us, so were our results different because of the method used or because of the different data. In order to try to answer that question, we did a second small study where we used a similar method to the previous papers. Lo and behold we got the same results of them. What we had found was that our interpretation of what was going on was impacted by the method. Our new multi-epoch analysis allowed us to better understand what parts of the storm had the conditions where you might find an EMIC wave. This is sort of like saying we see that schools close when there is snow vs the schools close when there has just been a snow storm and there hasn't yet been time to clear the roads. It might not seem like a big difference but is important if you are predicting when schools will close in Minnesota. (But the first approach might be okay if trying to predict when schools will close in Georgia). As my career has progressed, I have moved on to looking at a much wider set of space weather activities. But I have been fortunate enough to continue to work with EMIC waves from time to time. They really are a neat type of wave seen in our magnetosphere... My brother is right, I really am a nerd. This paper, A parametric analysis of magnetospheric energy budgets of non-stormtime substorms, was centered around some of my Master thesis work. It was a fun little project. I had been reading all of these papers that had empirical relationships (estimates based on data) of how energy moved through the magnetosphere. Some looked at energy input from the solar wind into the magnetosphere, some at how energy was lost to the atmosphere. However, they were often studied individually. That bothered me. Conservation of energy is kinda important in physics. This whole energy in equals energy out is not something to mess around with. So I figured why not see if energy is conserved in this system with our empirical estimates. We had multiple ways of estimating the energy into the magnetosphere, and we think we had identified and found estimates for all the major loss terms. I took the bold step and put them together. Sources + losses should = 0.
What we didn't show in the paper was that if you do this for say a year, on average everything comes out to zero. That gave us confidence that we were on the right track. What we found and showed in the paper was a bit different. We were looking specifically at substorms, a type of space weather - kind of like a space tornado. One thought is that as we fill the magnetosphere up with energy, it eventually needs to be released and that's what drives a substorm. It was thought (and I think still is) that there is a growth phase where energy input into the magnetosphere is increased. The growth phases last for typically upwards of an hour. However, if there has been not much going on, it could be longer. When we look at these time scales, we found that there was a continuous loss of energy from the system. This tells us there are potentially a couple of different things happening:
In the paper, we focused more on looking at how the different terms affected the estimate. For example, while the Dst may be a proxy for loss from the ring current - it is really just measuring the change in the magnetic field (not an energy term). We considered that perhaps it's not the best proxy or needs to be better adjusted to reflect the energy loss. This was really a fun project and paper to be involved in. It's a simple approach and provides quite a bit of insight into the system. I was very fortunate to be able to be involved with research as an undergrad. At the time, it was quite rare and I owe a lot to both my undergraduate advisor Mark Engetson, and to the entire lab there at Augsburg University. They set me up to be able to hit the ground running when I got to my Masters and PhD, and have continued to be a source of support.
This paper, my first paper, has perhaps had a lasting impact on my research. Latitudinal and Seasonal Variations of Quasiperiodic and Periodic VLF Emissions in the Outer Magnetosphere. Within this project I was able to determine that there were many different types of events and making sure to quantify them in a systematic manner impacts how you interpret the results. This is a lesson that has stuck with me ever since. |
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