EARTH SCIENCE > Sun-earth Interactions > Ionosphere/Magnetosphere Dynamics > Plasma Waves
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Signals from manmade VLF transmitters, used for communications with submarines, can leak into space and contribute to the dynamics of energetic electrons in the inner radiation belt and slot region. We use ~5 years of plasma wave data from the Van Allen Probe A satellite to construct new models of the observed wave power from VLF transmitters both as a function of L* and MLT and geographic location. This work is reported in Meredith et al. (2019) and the data provided here enable reconstruction of all of the figures in the paper.
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We present a reanalysis of SuperDARN plasma velocity measurements, using the method of data-interpolating Empirical Orthogonal Functions (EOFs). The northern polar region's radar-measured line of sight Doppler velocities are binned in an equal-area grid (areas of approximately 110,000km2) in quasi-dipole latitude and quasi-dipole magnetic local time (MLT). Within this spatial grid, which extends to 30 degrees colatitude, the plasma velocity is given in terms of cardinal north and east vector components (in the quasi-dipole coordinate frame), with the median of every SuperDARN measurement in the spatial bin taken every 5 minutes. These sparse binned data are infilled to provide a measurement at every spatial and temporal location via EOF analysis, ultimately comprising a series of monthly reanalyses, from 1997.0 to 2009.0. This resource provides a convenient method of using SuperDARN data without its usual extreme sparseness, for studies of ionospheric electrodynamics during solar cycle 23. The reanalyses are provided in monthly sets of orthogonal modes of variability (spatial and temporal patterns), along with the timestamps of each epoch, and the spatial coordinate information of all bin locations. We also provide the temporal mean of the data in each spatial bin, which is removed prior to the EOF analysis. Funding was provided by the NERC grant NE/N01099X/1. ***** PLEASE BE ADVISED TO USE VERSION 2.0 DATA ***** This version (1.0) has an error in radar data processing that the new version corrects. This is available via the 'Related Data Set Metadata' link below
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Electromagnetic Ion Cyclotron (EMIC) wave are important for the losses of ultra-relativistic electrons from the Earth's radiation belts. In this work, statistical EMIC diffusion coefficients are calculated from Van Allen Probe A observations of EMIC waves from the entire mission. The diffusion coefficient calculations include the observed L* and activity dependent distributions in plasma density and wave spectra so that the wave-particle interactions modelled are representative of those in the radiation belts. These diffusion coefficients can be included into global radiation belt simulations such as the BAS radiation belt model. The study is published in Ross et al 2021, JGR: Space Physics. Funding was provided by National Environment Research Council Highlight Topic grant NE/P01738X/1 (Rad-Sat), National Environment Research Council grant NE/R016445/1 and NE/R016038/1.
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Radiation belts are hazardous regions found around several of the planets in our Solar System. They consist of very hot, electrically charged particles that are trapped in the magnetic field of the planet. At Saturn the most important way to heat these particles has for many years been thought to involve the particles drifting closer towards the planet. This paper builds on previous work on the emerging idea at Saturn that a different way to heat the particles is also possible where the heating is done by waves, in a similar way to what we find at the Earth. This work is reported in the paper "Acceleration of electrons by whistler-mode hiss waves at Saturn" by E.E. Woodfield et al., 2021. The data provided here enable reconstruction of all the figures in the paper. E.E.W., R.B.H., and S.A.G. were funded by STFC grant ST/S000496/1. R.B.H., S.A.G. and A.J.K. were funded by NERC grant NE/R016038/1 and R.B.H. and S.A.G. by NERC grant NE/R016445/1. J.D.M. and Y.Y.S. were supported by NASA grants NNX11AM36G and NNX16AI47G. University of Iowa (J.D.M.) was supported by NASA contract 1415150 with JPL. Y.Y.S. was supported by EC grant H2020 637302.
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This data set contains the ULF wave model output data required to produce the figures in the article: A. W. Degeling, I. J. Rae, C. E. J. Watt, Q. Q. Shi, R. Rankin and Q. G. Zong, "Control of ULF Wave Accessibility to the Inner Magnetosphere by the Convection of Plasma Density", J. Geophys. Res. (accepted Dec. 2017) doi:10.1002/2017JA024874 The dataset has a Matlab binary file format. It consists of a structure array "d" (with 325 elements). These elements correspond to the 2D parameter scan in driver frequency and elapsed time during plume development performed for this study. The elapsed time parameter has 25 elements, ranging 0 to 24 hours (i.e. 1 hour spacing), and the driver frequency parameter has 13 elements ranging from 1 to 7 mHz (with 0.5 mHz spacing). e.g. use "d = reshape(d,25,13);" to reshape the structure array into 2D with columns for the frequency scan and rows for the elapsed time scan. The Matlab function "make_PDP_figs.m" is used to read the data, perform the necessary post-processing operations and output the article figures. To produce all six figures, simply run the file without any input arguments.
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Whistler-mode chorus waves play a key role in driving radiation belt dynamics by enabling both acceleration of electrons to relativistic energies as well as their loss into the atmosphere via pitch-angle scattering. The ratio between the electron plasma frequency (fpe) and the electron gyrofrequency (fce) significantly influences the efficiency of these processes, with electron acceleration being most effective during periods of low fpe/fce. In this study, a combined total of approximately 24.5 years of THEMIS wave data are analyzed to show how chorus wave intensity and spatial location vary with relative frequency, geomagnetic activity and fpe/fce. Results demonstrate that the strongest chorus emissions are observed during active conditions. At these times, equatorial chorus at low relative frequencies (flhr<f<0.1fce) is strongest when fpe/fce is high (fpe/fce>10) primarily in the region 5<L*<8, from 22:00-12:00 MLT. In sharp contrast at high relative frequencies (0.5fce<f<0.7fce), the equatorial chorus is strongest when fpe/fce is low (fpefce<6) mainly in the region 4<L*<6 from 21:00-09:00 MLT. At intermediate relative frequencies (0.3fce<f<0.4fce), equatorial chorus is strongest in the region 3.5<L*<8 from 21:00-12:00 MLT. In the off-equatorial region the strongest waves are seen in the frequency range (0.1fce<f<0.3fce) between 5<L*<8 and 06:00-15:00 MLT and again are mostly independent of fpe/fce. We show that the location of the strongest waves can be largely explained in terms of the source electrons being in the required energy range for resonance and the absence of Landau damping and highlight the regions where electron acceleration to relativistic energies is likely to be mostly significant.
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Signals from VLF transmitters can leak from the Earth-ionosphere wave guide into the inner magnetosphere, where they propagate in the whistler mode and contribute to electron dynamics in the inner radiation belt and slot region. Observations show that the waves from each VLF transmitter are highly localised, peaking on the nightside in the vicinity of the transmitter. In this study we use ~5 years of Van Allen probe observations to construct global statistical models of the bounce-averaged pitch angle diffusion coefficients for each individual VLF transmitter, as a function of L*, Magnetic Local Time (MLT) and geographic longitude. We construct a 1D pitch-angle diffusion model with implicit longitude and MLT dependence to show that VLF transmitter waves weakly scatter electrons into the drift loss cone. We find that global averages of the wave power, determined by averaging the wave power over MLT and longitude, capture the long-term dynamics of the loss process, despite the highly localised nature of the waves in space. We use our new model to assess the role of VLF transmitters waves, hiss waves, and Coulomb collisions on electron loss in the inner radiation belt and slot region. At moderate relativistic energies, E~ keV, waves from VLF transmitters reduce electron lifetimes by an order of magnitude or more, down to the order of 200 days near the outer edge of the inner radiation belt. However, VLF transmitter waves are ineffective at removing multi-MeV electrons from either the inner radiation belt or slot region. Funding was provided by the NERC grant NE/P01738X/1.
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Radiation belts are hazardous regions found around several of the planets in our Solar System. They consist of very hot, electrically charged particles that are trapped in the magnetic field of the planet. At Saturn the most important way to heat these particles has for many years been thought to involve the particles drifting closer towards the planet. This paper adds to the emerging idea at Saturn that a different way to heat the particles is also possible where the heating is done by waves, in a similar way to what we find at the Earth. This work is reported in the paper "Rapid electron acceleration in low density regions of Saturn's radiation belt by whistler mode chorus waves" by E.E. Woodfield et al., 2019. The data provided here enable reconstruction of all the figures in the paper. The research leading to these results has received funding from: Natural Environment Research Council (NERC), UK, grants NE/R016038/1 and NE/R016445/1 Science and Technology Facilities Council (STFC), UK, grants ST/I001727/1 and ST/M00130X/1. NASA grants NNX11AM36G and NNX16AI47G. The research at the University of Iowa was supported by NASA through Contract 1415150 with the Jet Propulsion Laboratory. European Council (EC) grant H2020 637302.
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A forecast model of the northern high-latitude ionospheric plasma motion as observed by the SuperDARN radars. The model comprises a set of regression coefficients. The user needs to specify the day-of-year and the monthly mean of the solar radio flux at 10.7 cm/2800 MHz, often called the f10.7 index. They also need to provide the value of the interplanetary magnetic field (IMF) component By and the Sun-Earth component of the solar wind velocity Vx, both in geocentric solar magnetospheric (GSM) coordinates. The regression coefficients are provided as two files, one can be used to model the north-south (NS) component of the plasma motion and the other to model the east-west (EW) component of the motion. Funding was provided by NERC standard grant numbers: NE/V002732/1, NE/N01099X/1, NE/V00283X/1, NE/V002686/1 and NE/T000937/1.
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The data set contains electron flux measurements from the Van Allen Probes A and B satellites, from the REPT, MagEIS and HOPE instruments for the period 2014-10-18 to 2014-10-28, a set of BAS-RBM simulations covering the same time period, and plasma density dependent chorus diffusion coefficients used to drive the BAS-RBM. The output of a coupled-density model is also included. When coupled with the density model, the density dependent chorus diffusion coefficients improve the BAS-RBM reproduction of ultra-relativistic electron acceleration. Funding: This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-19-1-7039. Richard Horne and Sarah Glauert were also supported by the Natural Environment Research Council (NERC) grant NE/V00249X/1 (Sat-Risk) and National and Public Good activity grant NE/R016445/1. Giulio Del Zanna acknowledges support from STFC (UK) via the consolidated grant to the astrophysics group at DAMTP, University of Cambridge (ST/T000481/1). Jay Albert acknowledges support from NASA Grant No. 80NSSC20K1270.
NERC Data Catalogue Service