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EARTH SCIENCE > Sun-earth Interactions > Ionosphere/Magnetosphere Dynamics

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  • Whistler mode chorus is an important magnetospheric wave emission playing a major role in radiation belt dynamics, where it contributes to both the acceleration and loss of relativistic electrons. In this study we compute bounce and drift averaged chorus diffusion coefficients for 3.0 < L* < 6.0, using the TS04 external magnetic field model, taking into account co-located near-equatorial measurements of the wave intensity and fpe/fce, by combining the Van Allen probes measurements with data from a multi-satellite VLF wave database. The variation of chorus wave normal angle with spatial location and fpe/fce is also taken into account. We find that chorus propagating at small wave normal angles has the dominant contribution to the diffusion rates in most MLT sectors. However, in the region 4 <= MLT < 11 high wave normal angles dominate at intermediate pitch angles. In the region 3 < L* < 4, the bounce and drift averaged pitch angle and energy diffusion rates during active conditions are primarily larger than those in our earlier models by up to a factor of 10 depending on energy and pitch angle. Further out, the results are similar. We find that the bounce and drift averaged energy and pitch angle diffusion rates can be significantly larger than the new model in regions of low fpe/fce,eq, where the differences can be up to a factor of 10 depending on energy and pitch angle. Funding was provided by the Natural Environment Research Council (NERC) Highlight Topic grant NE/P01738X/1 (Rad-Sat) and the NERC grants NE/V00249X/1 (Sat-Risk), NE/R016038/1 and NE/X000389/1.

  • We conduct a global survey of magnetosonic waves and compute the associated bounce and drift averaged diffusion coefficients, taking into account co-located measurements of fpe/fce, to assess the role of magnetosonic waves in radiation belt dynamics, where fpe is the plasma frequency and fce is the electron gyrofrequency.. The average magnetosonic wave intensities increase with increasing geomagnetic activity and decreasing relative frequency with the majority of the wave power in the range fcp < f < 0.3fLHR during active conditions, where fcp is the proton gyrofrequency and fLHR is the lower hybrid resonance frequency. In the region 4.0 <= L* <= 5.0, the bounce and drift averaged energy diffusion rates due to magnetosonic waves never exceed those due to whistler mode chorus, suggesting that whistler mode chorus is the dominant mode for electron energisation to relativistic energies in this region. Further in, in the region 2.0 <= L* <= 3.5, the bounce and drift averaged pitch angle diffusion rates due to magnetosonic waves can exceed those due to plasmaspheric hiss and very low frequency (VLF) transmitters over energy-dependent ranges of intermediate pitch angles. We compute electron lifetimes by solving the 1D pitch angle diffusion equation including the effects of plasmaspheric hiss, VLF transmitters and magnetosonic waves. We find that magnetosonic waves can have a significant effect on electron loss timescales in the slot region reducing the loss timescales during active times from 5.6 to 1.5 days for 500 keV electrons at L* = 2.5 and from 140.4 days to 35.7 days for 1 MeV electrons at L* = 2.0. The research leading to these results has received funding from the Natural Environment Research Council (NERC) Highlight Topic grant NE/P01738X/1 (Rad-Sat) and the NERC grants NE/V00249X/1 (Sat-Risk) and NE/R016038/1.

  • The data files in this directory were used to create Figures 2-7 in the paper: Horne et al. (in press - 2018/7/18). Figure 1 of the paper was constructed using publically available data from other sources.

  • 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.

  • Whistler mode chorus is an important magnetospheric emission, playing fundamental roles in the dynamics of the Earth''s outer radiation belt and the production of the Earth''s diffuse and pulsating aurora. In this study we extend our existing database of whistler mode chorus by including ~3 years of data from RBSP-A and RBSP-B and an additional ~6 years of data from THEMIS A, D, and E, greatly improving the statistics and coverage in the near-equatorial region (|MLAT|<18^o). We produce new global maps of whistler mode chorus as a function of spatial location and frequency. This work is reported in Meredith et al. [2020] and the data provided here enable reconstruction of all of the figures in the paper. The research leading to these results has received funding from the Natural Environment Research Council (NERC) Highlight Topic grant NE/P01738X/1 (Rad-Sat) and the NERC grant NE/R016038/1. Wen Li and Xiao-Chen Shen received funding from NASA grants NNX17AG07G and 80NSSC19K0845, NSF grant AGS-1847818, and the Alfred P. Sloan Research Fellowship FG-2018-10936. Jacob Bortnik received funding from NASA grants NNX14AI18G, and RBSP-ECT and EMFISIS funding provided by JHU/APL contracts 967399 and 921647 under NASA''s prime contract NAS5-01072.

  • Ionospheric boundary locations derived from IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite FUV (Far Ultra Violet) imager data covering the period from May 2000 until October 2002. These include poleward and equatorward auroral boundary data derived directly from the three imagers, WIC (Wideband Imaging Camera), SI12 (Spectrographic Imager 121.8 nm), and SI13 (Spectrographic Imager 135.6 nm). These also include the OCB (open-closed magnetic field line boundary) and EPB (equatorward precipitation boundary) derived indirectly from the auroral boundaries. The data set also includes model fitted circles for all the boundary data sets for all measurement times. Chisham et al. (2022) also describe that the v2 data set also includes estimates of the OCB at each time, derived from a combination of the poleward auroral boundary measurements in combination with modelled statistical offsets between the auroral boundary and the OCB as measured by the DMSP spacecraft. The v2 data set also includes estimates of the EPB at each time, derived from a combination of the equatorward auroral boundary measurements in combination with modelled statistical offsets between the auroral boundary and the EPB as measured by the DMSP spacecraft. The v2 data set also includes model circle fit boundaries for all times for all eight raw data sets. These model circle fits were estimated using the methods outlined in Chisham (2017) and Chisham et al. (2022), which involves fitting circles to the spatial variation of the boundaries at any one time. The raw auroral boundaries were derived as outlined in Longden et al. (2010) (the original v1 data set) with the application of the additional selection criteria outlined in Chisham et al. (2022). For the creation of the original v1 data set, for each image, the position of each pixel in AACGM (Altitude Adjusted Corrected Geomagnetic) coordinates was established. Each image was then divided into 24 segments covering 1 hour of magnetic local time (MLT). For each MLT segment, an intensity profile was constructed by finding the average intensity across bins of 1 degree magnetic latitude in the range of 50 to 90 degrees (AACGM). Two functions were fit to each intensity profile: a function with one Gaussian component and a quadratic background, and a function with two Gaussian components and a quadratic background. The function with a single Gaussian component should provide a reasonable model when the auroral emission forms in a continuous oval. When the oval shows bifurcation, the function with two Gaussian components may provide a better model of the auroral emission. Of the two functions fit to each intensity profile, the one with the lower reduced chi-square goodness-of-fit statistic was deemed to be the better model for that profile. The auroral boundaries were then determined to be the position of the peak of the poleward Gaussian curve, plus its FWHM (full-width half-maximum) value of the Gaussian, to the peak of the equatorward Gaussian, minus its FWHM. In the case of the single Gaussian fit, the same curve is used for both boundaries. A number of criteria were applied to discard poorly located auroral boundaries arising from either poor fitting or incomplete data. Following Chisham et al. (2022), additional criteria were used to refine the data for the v2 auroral boundary data sets. These included dealing with anomalous data at the edges of the image fields of view, and dealing with anomalous mapping issues. Funding was provided by: STFC grant PP/E002110/1 - Does magnetic reconnection have a characteristic scale in space and time? NERC directed grant NE/V002732/1 - Space Weather Instrumentation, Measurement, Modelling and Risk - Thermosphere (SWIMMR-T). NERC BAS National Capability - Polar Science for Planet Earth.

  • 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.

  • This dataset contains the data produced by four Gorgon Global magnetohydrodynamic (MHD) simulations of Fast-Forward Interplanetary Shocks of increasing strengths interacting with the Earth''s magnetosphere, as described in the study of Desai et al. (2021). Further description of the Gorgon MHD model can be found at Mejnertsen et al., (2016,2018) and Eggington et al., (2020). The data was produced on the Imperial College High Performance Computing Service (doi: 10.14469/hpc/2232). The MHD equations were solved in the magnetosphere on a regular 3-D cartesian grid of resolution 0.5 Earth radii (RE), covering a domain of dimensions (-20,100) RE in X, (-40,40) RE in Y and (-40,40) RE in Z with an inner boundary at 3 RE. In this coordinate system the Sun lies in the negative X-direction, the Z axis is aligned to the dipole in the 0 degree tilt case (where positive tilt points the north magnetic pole towards the Sun), and Y completes the right-handed set. Output data is timestamped in seconds and is defined at the centre of the grid cells. The simulation data corresponding to each shock are stored in separate directories ''ShockX'' where X=I-IV. The data are stored in hdf5 format. The magnetospheric variables are stored in the files: ''Gorgon_[YYYYMMDD]_MS_params_[XXXXX]s.hdf5'' where XXXXX is the simulation time in seconds. The magnetospheric data includes the magnetic field, (''Bvec_c''), velocity, (''vvec''), plasma density, (''rho1''), and ion temperature, (''Ti''), after 2h of simulation, over the course of 10 minutes. The data for the magnetic field, (''Bvec_c''), and velocity, (''vvec''), are of shape (240,160,160,3) where the first 3 dimensions are the grid indices in (X,Y,Z) indexed from negative to positive, and the final dimension is the cartesian vector component in (i,j,k). The data for the density, (''rho1''), and ion temperature, (''Ti''), is of shape (240,160,160) where the first 3 dimensions are the grid indices in (X,Y,Z) indexed from negative to positive. Funding was provided by NERC Highlight grant to NE/P017347/1 (Rad-Sat)

  • This dataset contains two NetCDF files: Chorus_daa.nc (labelled from here as a) which contains the chorus pitch angle diffusion coefficients presented in Figure 1 of Reidy et al (2020) and Combined_daa.nc (labelled from here as b) containing the combined pitch angle diffusion coefficients which can be used to do the analysis presented in the remainder of the Reidy et al (2020) paper. These data sets include: a. A matrix containing the pitch angle diffusion coefficients for chorus waves at the angle of the loss cone for energies of 30, 100 and 300 keV between L*= 2-7.5, a full range of MLT sectors and for low (1 < Kp < 2), moderate (2 < Kp < 3) and high (4 < Kp < 7) geomagnetic activity levels. These were calculated from an average wave model presented in Meredith et al (2020) to capture the effect of wave-particle interactions in the BAS Radiation Belt Model (BAS-RBM). Also the arrays containing the energy, L*, MLT and Kp dependence are also included. b, A matrix containing the combined pitch angle diffusion coefficients for chorus, hiss and EMIC waves and coulomb collisions between alpha = 0.5deg -9.45deg, Energy = 28.18-2511.89 keV , L* = 4.25-7.25, MLT = 0-24 and 6 different activity levels. The arrays containing the pitch angle, energy, L*, MLT and Kp dependence are also included. Funding was provided by NERC Highlight Topic Grant NE/P01738X/1 and NERC National Capability grants NE/R016038/1 and NE/R016445/1

  • Auroral oval boundary locations derived from IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite FUV (Far Ultra Violet imager) data covering the period from May 2000 until October 2002. Three sets of boundary data were derived separately from the WIC (Wideband Imaging Camera) and SI12/SI13 (Spectrographic Imager 121.8/135.6 nm) detectors. For each image, the position of each pixel in AACGM (Altitude Adjusted Corrected Geomagnetic) coordinates was established. Each image was then divided into 24 segments covering 1 hour of magnetic local time (MLT). For each MLT segment, an intensity profile was constructed by finding the average intensity across bins of 1 degree magnetic latitude in the range of 50 to 90 degrees (AACGM). Two functions were fit to each intensity profile: a function with one Gaussian component and a quadratic background, and a function with two Gaussian components and a quadratic background. The function with a single Gaussian component should provide a reasonable model when the auroral emission forms in a continuous oval. When the oval shows bifurcation, the function with two Gaussian components may provide a better model of the auroral emission. Of the two functions fit to each intensity profile, we determine the one with the lower reduced chi-square goodness-of-fit statistic to be the better model for that profile. For the version 1.1 boundary location data, the fitting process was performed over 200 iterations to achieve each fit. The auroral boundaries were then determined to be the position of the peak of the poleward Gaussian curve, plus its FWHM (full-width half-maximum) value of the Gaussian, to the peak of the equatorward Gaussian, minus its FWHM. In the case of the single Gaussian fit, the same curve is used for both boundaries. A number of criteria were applied to discard poorly located auroral boundaries arising from either poor fitting or incomplete data. A further correction can be applied to the data, to estimate the location of the Earth''s magnetic field''s OCB (open-close boundary). These corrections have been tabulated in a separate file; if this correction is required the adjustments should be made to the poleward boundary value.