TY  - JOUR
A1  - Smirnov, Artem G.
A1  - Kronberg, Elena A.
A1  - Latallerie, F.
A1  - Daly, Patrick W.
A1  - Aseev, Nikita
A1  - Shprits, Yuri Y.
A1  - Kellerman, Adam C.
A1  - Kasahara, Satoshi
A1  - Turner, Drew L.
A1  - Taylor, M. G. G. T.
T1  - Electron Intensity Measurements by the Cluster/RAPID/IES Instrument in Earth's Radiation Belts and Ring Current
JF  - Space Weather: The International Journal of Research and Applications
N2  - Plain Language Summary Radiation belts of the Earth, which are the zones of charged energetic particles trapped by the geomagnetic field, comprise enormous and dynamic systems. While the inner radiation belt, composed mainly of high-energy protons, is relatively stable, the outer belt, filled with energetic electrons, is highly variable and depends substantially on solar activity. Hence, extended reliable observations and the improved models of the electron intensities in the outer belt depending on solar wind parameters are necessary for prediction of their dynamics. The Cluster mission has been measuring electron flux intensities in the radiation belts since its launch in 2000, thus providing a huge dataset that can be used for radiation belts analysis. Using 16 years of electron measurements by the Cluster mission corrected for background contamination, we derived a uniform linear-logarithmic dependence of electron fluxes in the outer belt on the solar wind dynamic pressure.
Y1  - 2019
U6  - https://doi.org/10.1029/2018SW001989
SN  - 1542-7390
VL  - 17
IS  - 4
SP  - 553
EP  - 566
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Smirnov, Artem
A1  - Shprits, Yuri Y.
A1  - Allison, Hayley
A1  - Aseev, Nikita
A1  - Drozdov, Alexander
A1  - Kollmann, Peter
A1  - Wang, Dedong
A1  - Saikin, Anthony
T1  - An empirical model of the equatorial electron pitch angle distributions in earth's outer radiation belt
JF  - Space Weather: the International Journal of Research and Applications
N2  - In this study, we present an empirical model of the equatorial electron pitch angle distributions (PADs) in the outer radiation belt based on the full data set collected by the Magnetic Electron Ion Spectrometer (MagEIS) instrument onboard the Van Allen Probes in 2012-2019. The PADs are fitted with a combination of the first, third and fifth sine harmonics. The resulting equation resolves all PAD types found in the outer radiation belt (pancake, flat-top, butterfly and cap PADs) and can be analytically integrated to derive omnidirectional flux. We introduce a two-step modeling procedure that for the first time ensures a continuous dependence on L, magnetic local time and activity, parametrized by the solar wind dynamic pressure. We propose two methods to reconstruct equatorial electron flux using the model. The first approach requires two uni-directional flux observations and is applicable to low-PA data. The second method can be used to reconstruct the full equatorial PADs from a single uni- or omnidirectional measurement at off-equatorial latitudes. The model can be used for converting the long-term data sets of electron fluxes to phase space density in terms of adiabatic invariants, for physics-based modeling in the form of boundary conditions, and for data assimilation purposes.
KW  - pitch angle
KW  - radiation belt
KW  - model
KW  - magnetosphere
KW  - van allen probes;
KW  - electrons
Y1  - 2022
U6  - https://doi.org/10.1029/2022SW003053
SN  - 1542-7390
VL  - 20
IS  - 9
PB  - American Geophysical Union
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Smirnov, Artem
A1  - Shprits, Yuri Y.
A1  - Allison, Hayley
A1  - Aseev, Nikita
A1  - Drozdov, Alexander
A1  - Kollmann, Peter
A1  - Wang, Dedong
A1  - Saikin, Anthony
T1  - Storm-Time evolution of the Equatorial Electron Pitch Angle Distributions in Earth's Outer Radiation Belt
JF  - Frontiers in astronomy and space sciences
N2  - In this study we analyze the storm-time evolution of equatorial electron pitch angle distributions (PADs) in the outer radiation belt region using observations from the Magnetic Electron Ion Spectrometer (MagEIS) instrument aboard the Van Allen Probes in 2012-2019. The PADs are approximated using a sum of the first, third and fifth sine harmonics. Different combinations of the respective coefficients refer to the main PAD shapes within the outer radiation belt, namely the pancake, flat-top, butterfly and cap PADs. We conduct a superposed epoch analysis of 129 geomagnetic storms and analyze the PAD evolution for day and night MLT sectors. PAD shapes exhibit a strong energy-dependent response. At energies of tens of keV, the PADs exhibit little variation throughout geomagnetic storms. Cap PADs are mainly observed at energies < 300 keV, and their extent in L shrinks with increasing energy. The cap distributions transform into the pancake PADs around the main phase of the storm on the nightside, and then come back to their original shapes during the recovery phase. At higher energies on the dayside, the PADs are mainly pancake during pre-storm conditions and become more anisotropic during the main phase. The quiet-time butterfly PADs can be observed on the nightside at L> 5.6. During the main phase, butterfly PADs have stronger 90 degrees-minima and can be observed at lower L-shells (down to L = 5), then transitioning into flat-top PADs at L similar to 4.5 - 5 and pancake PADs at L < 4.5. The resulting PAD coefficients for different energies, locations and storm epochs can be used to test the wave models and physics-based radiation belt codes in terms of pitch angle distributions.
KW  - pitch angle
KW  - pitch angle distributions
KW  - electrons
KW  - radiation belts
KW  - magnetosphere
KW  - van alien probes
Y1  - 2022
U6  - https://doi.org/10.3389/fspas.2022.836811
SN  - 2296-987X
VL  - 9
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Usanova, Maria E.
A1  - Shprits, Yuri Y.
T1  - Inner magnetosphere coupling
BT  - Recent advances
JF  - Journal of geophysical research : Space physics
N2  - The dynamics of the inner magnetosphere is strongly governed by the interactions between different plasma populations that are coupled through large-scale electric and magnetic fields, currents, and wave-particle interactions. Inner magnetospheric plasma undergoes self-consistent interactions with global electric and magnetic fields. Waves excited in the inner magnetosphere from unstable particle distributions can provide energy exchange between different particle populations in the inner magnetosphere and affect the ring current and radiation belt dynamics. The ionosphere serves as an energy sink and feeds the magnetosphere back through the cold plasma outflow. The precipitating inner magnetospheric particles influence the ionosphere and upper atmospheric chemistry and affect climate. Satellite measurements and theoretical studies have advanced our understanding of the dynamics of various plasma populations in the inner magnetosphere. However, our knowledge of the coupling processes among the plasmasphere, ring current, radiation belts, global magnetic and electric fields, and plasma waves generated within these systems is still incomplete. This special issue incorporates extended papers presented at the Inner Magnetosphere Coupling III conference held 23–27 March 2015 in Los Angeles, California, USA, and includes modeling and observational contributions addressing interactions within different plasma populations in the inner magnetosphere (plasmasphere, ring current, and radiation belts), coupling between fields and plasma populations, as well as effects of the inner magnetosphere on the ionosphere and atmosphere.
KW  - inner magnetosphere
KW  - ring current
KW  - radiation belts
KW  - magnetosphere
KW  - ionosphere interactions
KW  - plasmasphere
KW  - solar wind
Y1  - 2016
U6  - https://doi.org/10.1002/2016JA023614
SN  - 2169-9380
SN  - 2169-9402
VL  - 122
IS  - 1
SP  - 102
EP  - 104
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Walker, Simon N.
A1  - Boynton, Richard J.
A1  - Shprits, Yuri Y.
A1  - Balikhin, Michael A.
A1  - Drozdov, Alexander
T1  - Forecast of the energetic electron environment of the radiation belts
JF  - Space Weather: The International Journal of Research and Applications
N2  - Different modeling methodologies possess different strengths and weakness. For instance, data based models may provide superior accuracy but have a limited spatial coverage while physics based models may provide lower accuracy but provide greater spatial coverage. This study investigates the coupling of a data based model of the electron fluxes at geostationary orbit (GEO) with a numerical model of the radiation belt region to improve the resulting forecasts/pastcasts of electron fluxes over the whole radiation belt region. In particular, two coupling methods are investigated. The first assumes an average value for L* for GEO, namely LGEO* L-GEO* = 6.2. The second uses a value of L* that varies with geomagnetic activity, quantified using the Kp index. As the terrestrial magnetic field responds to variations in geomagnetic activity, the value of L* will vary for a specific location. In this coupling method, the value of L* is calculated using the Kp driven Tsyganenko 89c magnetic field model for field line tracing. It is shown that this addition can result in changes in the initialization of the parameters at the Versatile Electron Radiation Belt model outer boundary. Model outputs are compared to Van Allen Probes MagEIS measurements of the electron fluxes in the inner magnetosphere for the March 2015 geomagnetic storm. It is found that the fixed LGEO* L-GEO* coupling method produces a more realistic forecast.
KW  - radiation belt forecasts
KW  - data based NARMAX modeling
KW  - verb simulations;
KW  - geostationary orbit
KW  - electron flux forecasts
Y1  - 2022
U6  - https://doi.org/10.1029/2022SW003124
SN  - 1542-7390
VL  - 20
IS  - 12
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Dedong
A1  - Shprits, Yuri Y.
T1  - On How High-Latitude Chorus Waves Tip the Balance Between Acceleration and Loss of Relativistic Electrons
JF  - Geophysical research letters
N2  - Modeling and observations have shown that energy diffusion by chorus waves is an important source of acceleration of electrons to relativistic energies. By performing long-term simulations using the three-dimensional Versatile Electron Radiation Belt code, in this study, we test how the latitudinal dependence of chorus waves can affect the dynamics of the radiation belt electrons. Results show that the variability of chorus waves at high latitudes is critical for modeling of megaelectron volt (MeV) electrons. We show that, depending on the latitudinal distribution of chorus waves under different geomagnetic conditions, they cannot only produce a net acceleration but also a net loss of MeV electrons. Decrease in high-latitude chorus waves can tip the balance between acceleration and loss toward acceleration, or alternatively, the increase in high-latitude waves can result in a net loss of MeV electrons. Variations in high-latitude chorus may account for some of the variability of MeV electrons.
KW  - radiation belts
KW  - chorus waves
KW  - high latitude
KW  - acceleration
KW  - loss
KW  - modeling
Y1  - 2019
U6  - https://doi.org/10.1029/2019GL082681
SN  - 0094-8276
SN  - 1944-8007
VL  - 46
IS  - 14
SP  - 7945
EP  - 7954
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wang, Dedong
A1  - Shprits, Yuri Y.
A1  - Zhelayskaya, Irina S.
A1  - Agapitov, Oleksiy
A1  - Drozdov, Alexander
A1  - Aseev, Nikita
T1  - Analytical chorus wave model derived from van Allen Probe Observations
JF  - Journal of geophysical research : Space physics
N2  - Chorus waves play an important role in the dynamic evolution of energetic electrons in the Earth's radiation belts and ring current. Using more than 5 years of Van Allen Probe data, we developed a new analytical model for upper‐band chorus (UBC; 0.5fce < f < fce) and lower‐band chorus (LBC; 0.05fce < f < 0.5fce) waves, where fce is the equatorial electron gyrofrequency. By applying polynomial fits to chorus wave root mean square amplitudes, we developed regression models for LBC and UBC as a function of geomagnetic activity (Kp), L, magnetic latitude (λ), and magnetic local time (MLT). Dependence on Kp is separated from the dependence on λ, L, and MLT as Kp‐scaling law to simplify the calculation of diffusion coefficients and inclusion into particle tracing codes. Frequency models for UBC and LBC are also developed, which depends on MLT and magnetic latitude. This empirical model is valid in all MLTs, magnetic latitude up to 20°, Kp ≤ 6, L‐shell range from 3.5 to 6 for LBC and from 4 to 6 for UBC. The dependence of root mean square amplitudes on L are different for different bands, which implies different energy sources for different wave bands. This analytical chorus wave model is convenient for inclusion in quasi‐linear diffusion calculations of electron scattering rates and particle simulations in the inner magnetosphere, especially for the newly developed four‐dimensional codes, which require significantly improved wave parameterizations.
KW  - chorus waves
KW  - radiation belt electrons
KW  - ring current electrons
KW  - analytical model
KW  - wave-particle interactions
KW  - diffusion coefficients
Y1  - 2019
U6  - https://doi.org/10.1029/2018JA026183
SN  - 2169-9380
SN  - 2169-9402
VL  - 124
IS  - 2
SP  - 1063
EP  - 1084
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Woodfield, Emma E.
A1  - Glauert, Saraha A.
A1  - Menietti, J. Douglas
A1  - Averkamp, Terrance F.
A1  - Horne, Richard B.
A1  - Shprits, Yuri Y.
T1  - Rapid Electron Acceleration in Low‐Density Regions of Saturn's Radiation Belt by Whistler Mode Chorus Waves
JF  - Geophysical research letters
N2  - Electron acceleration at Saturn due to whistler mode chorus waves has previously been assumed to be ineffective; new data closer to the planet show it can be very rapid (factor of 104 flux increase at 1 MeV in 10 days compared to factor of 2). A full survey of chorus waves at Saturn is combined with an improved plasma density model to show that where the plasma frequency falls below the gyrofrequency additional strong resonances are observed favoring electron acceleration. This results in strong chorus acceleration between approximately 2.5 R-S and 5.5 R-S outside which adiabatic transport may dominate. Strong pitch angle dependence results in butterfly pitch angle distributions that flatten over a few days at 100s keV, tens of days at MeV energies which may explain observations of butterfly distributions of MeV electrons near L = 3. Including cross terms in the simulations increases the tendency toward butterfly distributions. Plain Language Summary Radiation belts are hazardous regions found around several of the planets in our Solar System. They consist of very hot, electrically charged particles 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 toward 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. We use recent information from the Cassini spacecraft on the number and location of particles and also of the waves strength and location combined with computer simulations to show that a particular wave called chorus is excellent at heating the particles where the surrounding number of cold particles is low.
Y1  - 2019
U6  - https://doi.org/10.1029/2019GL083071
SN  - 0094-8276
SN  - 1944-8007
VL  - 46
IS  - 13
SP  - 7191
EP  - 7198
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Woodfield, Emma E.
A1  - Horne, Richard B.
A1  - Glauert, S. A.
A1  - Menietti, J. D.
A1  - Shprits, Yuri Y.
A1  - Kurth, William S.
T1  - Formation of electron radiation belts at Saturn by Z-mode wave acceleration
JF  - Nature Communications
N2  - At Saturn electrons are trapped in the planet’s magnetic field and accelerated to relativistic energies to form the radiation belts, but how this dramatic increase in electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an electron energy spectrum that closely approaches observed values without any transport effects included.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-07549-4
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - GEN
A1  - Woodfield, Emma E.
A1  - Horne, Richard B.
A1  - Glauert, Sarah A.
A1  - Menietti, John D.
A1  - Shprits, Yuri Y.
A1  - Kurth, William S.
T1  - Formation of electron radiation belts at Saturn by Z-mode wave acceleration
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - At Saturn electrons are trapped in the planet's magnetic field and accelerated to relativistic energies to form the radiation belts, but how this dramatic increase in electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates electrons to MeV energies inside 4 R-S (1 R-S = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an electron energy spectrum that closely approaches observed values without any transport effects included.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1032 
KW  - astrophysical plasmas
KW  - giant planets
KW  - magnetospheric physics
KW  - diffusion
KW  - pitch angle
KW  - plasma
KW  - radio
KW  - region
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-468342
SN  - 1866-8372
IS  - 1032
ER  -