![]() Where these simplified models are valid, they allow considerable insight into the physical processes at work. We are investigating this mechanism in various plasma configurations, comparing the results of observations and computationally intensive particle simulations against simple analytical results and quasilinear models (the lower figure shows the result of one such calculation). These waves interact stochastically with electrons, increasing the average electron energy and changing the particle distribution function. in the magnetic field) or unstable particle distributions. ![]() Waves in the plasma are driven by spatial variations (e.g. One type of process which can produce electron acceleration is resonant wave-particle interaction: An example is the magnetic reconnection which occurs in solar flares (shown in the top figure) or in the earth's magnetosphere: a large proportion of the energy is released in the form of semirelativistic electron beams and heated plasma. Many space phenomena cause very strong electron heating, but the mechanisms are often either unknown, or not well understood. Here, we show the predicted radio emission increased by 5dB (left panel) to better match the levels detected by the Geotail satellite (right panel). data comparison for terrestrial foreshock radio emission: the levels of second harmonic radio emission predicted by our model generally underpredict the observed levels by a factor of a few. A dynamic spectrum obtained from a crossing of Earth's bow shock by the Wind spacecraft showing first and second harmonic radio emission in the foreshock region.įigure 3. Schematic illustration depicting the terrestrial foreshock region, immediately upstream of Earth's bow shock and downstream of the connecting interplanetary field line.įigure 2. We have made specific theoretical predictions for the radio emissions from other planetary foreshocks which will be testable with forthcoming space missions.įigure 1. We have also generalised our foreshock radio emissions model for applications to other planets and also to planetary satellites such as our own Moon. Our results have been directly compared with data from the Geotail satellite currently orbiting Earth (see Fig. ![]() We have developed a quantitative model for the terrestrial foreshock radio emissions that takes into account electron acceleration at the bow shock, stochastic growth of Langmuir waves from unstable electron beam distributions, and nonlinear interactions between the Langmuir waves with other waves to produce the electromagnetic waves. Earth's foreshock is naturally the most accessible in the solar system and spacecraft observations over many decades have confirmed that it contains a rich variety of energetic, unstable electron distributions and plasma waves, including Langmuir waves and electromagnetic (radio) waves (see Fig. 1).Ĭonsequently, the region immediately upstream of a bow shock, known as a foreshock, is a propitious site for energetic particle and plasma wave phenomena. The continuous interaction of the solar wind with solar system bodies produces a standoff shock known as a bow shock at which incoming particles from the solar wind are promptly accelerated (see Fig. The reason is that these regions all contain plasmas, the so-called "Fourth State of Matter", in which atoms are either partially or fully ionised into electrons and ions, thereby being strong influenced by electromagnetic waves and vice-versa. Plasma physics is the basic underlying sub-discipline of physics. It is also crucial for modern astrophysics, since space plasmas are the only extraterrestrial plasmas available for detailed in situ study and comparison of theory with data. Space physics is essential for understanding humanity's local environment and solar system. The range of space physics studied here is from Earth's ionosphere to the Sun's surface to the outer boundaries of the heliosphere and solar system, where the Sun's "solar wind" interacts with the local interstellar medium.Īs such it includes the solar corona and solar wind (sometimes called the interplanetary medium), the ionospheres and magnetospheres of Earth and the other planets, and the "Space Weather" that results from interactions between the Sun and Earth. Space science covers everything from Earth's surface to the Sun and then out into the galaxy.
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