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.
0 Comments
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 going back through files on my computer today looking for old "nuggets" (short science blurbs) and happened upon this. The physics teacher at my old high school asked me a while ago to write a generic letter to a "girl interested in math and physics". I re-read the letter, and it really hit home today. Lately I've been worried about funding, about my ability to stay in the field, whether I really deserve to be a Ph.D. in physics or not. I read what I stated I had accomplished and realized it was incomplete and not a bad list. That list doesn't match how I felt this morning. I may have written this letter for a random girl in high school questioning if she should continue in the sciences, but today I needed this.
Now time to go see if my cheerleaders want to grab a cup of coffee and talk. To the girl who loves math and science, You might wonder why I am writing this, and to be honest I’m not sure why I am either. Someone who cares about you, who thinks you are smart, talented, and have a ton of potential asked me to write a supportive letter to you, a women in STEM, thinking that I may be someone who could be looked up to as a role model. Some days I agree that what I’ve done is pretty cool, and many more days I feel like I’m completely faking it and in way over my head. Turns out that many physicists and many more women in STEM feel this way all the time; that the fraud police are just around the corner. They may have asked me to write this note because of what I have done and the degrees I have. Currently, I am working at Dartmouth College and NASA Goddard. I was just interviewed for Discover magazine, have a bunch of publications, and am working on a number of grants and NASA-funded missions. I have received honors and awards and served on advisory committees in the field. I have a Ph.D. in physics, masters in Astro Physics and Planetary Sciences, a bachelor degree in Math and Physics, but still, everyday I fear that someone may come and take them away from me (I’ve been told that can’t happen...) They may have thought that I would be a good person to write about the struggles of college and graduate school. I had a Prof. in undergrad who told me that women should not work and should instead stay at home and raise the kids. He tried to fail me in a class until I approached another Prof. about it. He ended up “only” giving me a C while the guys, who had made the same and worse mistakes on the homework and in the tests got A’s. I had a Prof. while I was doing my masters who told me how others had offered sex in return for grades subtly implying, or so it felt, that I should offer sex for an improved grade (and no I still don’t feel comfortable really talking about that experience or sharing the guy's name in fear of the repercussions that I would face. It’s not fair and is not right, but as one person told me, I need to make sure that I make it in order to be in a position where I can affect change. Writing that makes it feel more like an excuse for not coming forward at the time or even now, but there you have it.) That Prof. wrote a question for our quals that was on a topic not covered by any of our classes with the express intent, as he proclaimed told others, of trying to fail us. I had a Prof. in my Ph.D. tell me that I should never use my first name because people would know that I was a girl then and would judge me more harshly and that would hurt my chances of making it in the field. A lab tech in my Ph.D. who was gathering all our titles told me that they would only include "real" masters assuming that my masters degree wasn't in the sciences. I had students that I was teaching refuse to believe anything that I was saying, report me to the Prof. about how what I was telling them was completely wrong, only to find out that what I said was indeed correct. I had students try to physically intimidate me into giving them better grades. I had a friend tell me that the only reason I was offered a post-doc position was because “who wouldn’t rather have a cute girl in the lab instead of another guy?” I’ve been talked over, had my ideas laughed at until another white male either states the same thing getting the credit, or validates my statement. I have not been physically harassed although I have had friends who have been. But... I have to remember, and sometimes have others remind me, that those are all things that happened to me, they do not speak to my ability to be a scientist, even a good scientist, and hopefully on the best of days, a f*cking awesome scientist. The same is true for you. If today you found that you didn’t do as well on a test as you hoped for; if your lab mates all seemed to understand the lab and not let you participate as you wanted to make sure to not wire that circuit incorrectly thus ruining a perfectly good breadboard; if you raised your hand all day during class and weren’t called on, or worse, were called on when you didn’t know the answer thus feeling embarrassed in front of the class, don’t worry, that ultimately has little to do with determining if you will become a fantastic scientist. In fact, most of the people who I’ve met who were incredibly book smart and did amazing in the qualifying exams and classes all the way through graduate school often had trouble with the primary part of science which is coming up with something interesting question to ask and research. Now, this is not an excuse to not study. On the contrary, if you really love science, and I think you do, then every time you don’t grasp something, every time you do poorly on an exam, I have a feeling that you will go back and study it even more ultimately gaining a better, and much deeper understanding of the material. It might not show up in your grade, but it will show up in your research! Some advice that I wish I was told:
Good luck and I know that you will succeed in whatever you decided to do, The girl who was you in high school *There are some women jerks too, but they’re jerks so ignore them and remember the rest of us are all here to be supportive of you! |
Archives
June 2020
Categories
All
|