My PhD project in 570 words

I usually say I study the aurora. That’s a convenient lie.


Normally, when people ask what I do, I just say I study the aurora. That’s not strictly correct. Yes, the aurora is involved in my studies, but it’s not the actual topic. It’s just that when people ask me what I do, it’s way better than saying “I study plasma irregularities in the high-​latitude ionosphere and their effects on trans-​ionospheric signal links” because, well, the image explains it all. But let me try to explain, in understandable terms, what I actually study.

Ready? Let’s go!

Space physics is the study of the nearest parts of space. This includes the Sun and all the planets in the solar system, as well as the magnetic fields of the planets and their upper atmospheres. Much of the research is focused on the interaction between the solar wind (particles which are constantly streaming from the Sun), the magnetosphere (the Earth’s magnetic field) and the ionosphere (the upper part of the atmosphere, approximately 80–600 km above ground).

The best known phenomenon arising from this interaction is aurora, but it also causes a host of other effects which influence us in various ways. This is called space weather, a term that has seen a steady rise in usage since the 90’s. This is not without reason, because it is a problematic fact that severe eruptions on the Sun, should they reach the Earth, can knock out electricity grids, satellite navigation, and other satellite communication. Part of the field of space physics is therefore focused on predicting space weather, just like part of meteorology is focused on predicting “normal” weather. In fact, most areas of space physics help indirectly in this regard, since we can better predict space weather if we have a better understanding of the phenomena we are trying to predict.

The ionosphere has its name because in the upper atmosphere (around 80–600 km above ground), the radiation from the Sun is so powerful that it ionizes the atoms and molecules in the atmosphere. That means that the electrons which are content to buzz around their atoms (and would rather stay that way thank you very much) are continually knocked out, and you end up with a gas of negatively charged electrons and positively charged ions. This electrically charged gas is called a plasma. While your everyday gas (like the atmosphere) just kind of floats there, being windy and whatnot, a plasma has special properties like reacting strongly to the Earth’s highly dynamic magnetic field.

The ionosphere has a highly varying plasma density. For instance, on the sunlit side of the Earth, the plasma density is high. This is because, as I said, solar radiation is the main cause of ionization, and where there’s a lot of radiation, there’s a lot of ionization and thus a lot of plasma. Thus, on the dark side of the Earth, there is no sun and the plasma density is much lower.

However, the plasma density can vary quite a bit, not only between the sunlit and dark parts of the Earth, but over shorter distances too – from hundreds of kilometers down to a few meters. Like how ocean waves vary in length between thousands of kilometers (the tide) down to tiny ripples. These variations, or irregularities, in the plasma density is basically what my PhD project is all about.

Specifically, I study them in part using GPS receivers. This is possible because ionospheric irregularities cause disturbances on GPS signals. This can cause errors in positioning or give the receiver a hard time locating the satellites, but the upshot is that you can use specially designed scientific GPS receivers to study the irregularities that are causing the disturbances. In addition to GPS receivers I’m also using auroral cameras (basically automated cameras with fisheye lenses pointing straight up), radars which transmit signals into the ionosphere and analyze the parts of the signal that bounce back, instruments on satellites which orbit inside the ionosphere, and many other instruments.

That’s it, really. If you have even more questions now than when you started reading, I consider this a job well done.

3 minutes to readPosted inRamblings

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  1. Hey Christer
    As a nerd myself I’d love to hear some more about how the methods you described work. Would you mind explaining them or linking to further information? Do not shy away from becoming technical, I study math and can probably collect enough bits and pieces on the web to get an idea of the physics.
    Thank you for this post!

    1. Hi! I’ll send you my PhD thesis when it’s approved (my defense is in less than a month). :)