R. L. Lin

A statistical study of EMIC waves observed by Cluster : 1. Wave properties

Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the L-MLT frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001-2010) of data from Cluster, totaling 17,987 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The current paper focuses on the wave occurrence distribution as well as the distribution of wave properties.

Mercury's three‐dimensional asymmetric magnetopause

Mercurys magnetopause is unique in the solar system due to its relatively small size and its close proximity to the Sun. Based on 3 years of MErcury Surface, Space ENvironment, GEochemistry, and Ranging orbital Magnetometer and the Fast Imaging Plasma Spectrometer data, the mean magnetopause location was determined for a total of 5694 passes. We fit these magnetopause locations to a three-dimensional nonaxially symmetric magnetopause which includes an indentation for the cusp region that has been successfully applied to the Earth. Our model predicts that Mercurys magnetopause is highly indented surrounding the cusp with central depth ~0.64 RM and large dayside extension. The dayside polar magnetopause dimension is, thus, smaller than the equatorial magnetopause dimension. Cross sections of the dayside magnetopause in planes perpendicular to the Mercury-Sun line are prolate and elongated along the dawn-dusk direction. In contrast, the magnetopause downstream of the terminator plane is larger in the north-south than the east-west directions by a ratio of 2.6 RM to 2.2 RM at a distance of 1.5 RM downstream of Mercury. Due to the northward offset of the internal dipole, the model predicts that solar wind has direct access to the surface of Mercury at middle magnetic latitudes in the southern hemisphere. During extremely high solar wind pressure conditions, the northern hemisphere middle magnetic latitudes may also be subject to direct solar wind impact.

Testing linear theory of EMIC waves in the inner magnetosphere: Cluster observations

In this paper, we test whether time periods with hot proton temperature anisotropy are associated with electromagnetic ion cyclotron (EMIC) waves and whether the plasma conditions during the observed waves satisfy the linear theory threshold condition. We identify 865 events observed by the Composition Distribution Function instrument onboard Cluster spacecraft 4 during 1 January 2001 to 1 January 2011 that exhibit a positive temperature anisotropy (A(hp)=T-h/T-vertical bar h-1) in the 10-40keV protons. The events occur over an L range from 4 to 10 in all magnetic local times and at magnetic latitudes (MLATs) within 50 degrees. Of these hot proton temperature anisotropy (HPTA) events, only 68 events have electromagnetic ion cyclotron (EMIC) waves. In these 68 HPTA events, for those at 3.8 1.0 nT(2)/Hz mainly appear in the region with f(EMIC)/f(H,eq) H bands satisfy A(hp)/(A(hp)+1)>f(EMIC)/f(H,lo), A(hp)/(A(hp)+1)>0.45xf(EMIC)/f(H,lo), and A(hp)/(A(hp)+1) 0.25. By testing a threshold equation for the EMIC instability based on linear theory, we find that for EMIC waves with |MLAT|10 degrees in the He, H, and>H bands, the percentages that satisfy the predicted conditions for wave growth by the threshold equation are 15.2%, 24.6%, and 25.6%. For the EMIC waves with |MLAT|>10 degrees the percentages that satisfy the wave growth predicted conditions are only 2.8%, 2.6%, and 0.0%. Finally, possible reasons for the low forecast accuracies of EMIC waves are suggested. Key Points We do the statistical analysis of EMIC waves from a 10year Cluster observation We test the A_hp versus EMIC wave frequency formula of Kennel and Petschek (1966) We test the linear theory derived by Blum et al. (2009)

A statistical study of EMIC waves observed by Cluster : 2. Associated plasma conditions

This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10years (2001-2010) of Cluster observations. In the first paper, ...

A new solar wind driven global dynamic plasmapause model: 1. Database and Statistics

A large database, possibly the largest plasmapause location database, with 49119 plasmapause crossing events from the in-situ observations and 3957 plasmapause profiles (corresponding to 48899 plasmapause locations in 1 h MLT intervals) from optical remote sensing from 1977 to 2015 by 18 satellites is compiled. The responses of the global plasmapause to solar wind and geomagnetic changes and the diurnal, seasonal, solar cycle variations of the plasmapause are investigated based on this database. It is found that the plasmapause shrinks towards the Earth globally and a clear bulge appears in the afternoon to pre-midnight MLT sector as the solar wind or geomagnetic conditions change from quiet to disturbed. The bulge is clearer during storm times or southward IMF. The diurnal variations of the plasmapause are most probably be result of the difference between the magnetic dipole tilt and the Earths spin axis. The seasonal variations of the plasmapause are characterized by equinox valleys and solstice peaks. It is also found that the plasmapause approaches the Earth during high solar activity and expands outward during low solar activity. This database will help us study and understand the evolution properties of the plasmapause shape and the interaction processes of the plasmasphere, the ring current and the radiation belts in the magnetosphere.

A new solar wind-driven global dynamic plasmapause model: 2. Model and validation

A new solar wind driven global dynamic plasmapause (NSW-GDP) model has been constructed based on the largest currently-available database containing 49119 plasmapause crossing locations and 3957 plasmapause profiles (corresponding to 48899 plasmapause locations), from 18 satellites during 1977 – 2015 covering four solar cycles. This model is compiled by the Levenberg-Marquardt method for nonlinear multiparameter fitting and parameterized by VSW, BZ, SYM-H, and AE. Continuous and smooth MLT-dependence controlled mainly by the solar wind driven convection electric field ESW is also embedded in this model. Compared with previous empirical models based on our database, this new model improves the forecasting accuracy and capability for the global plasmapause. The diurnal, seasonal and solar cycle variations of the plasmapause can be captured by the new model. The NSW-GDP model can potentially be used to forecast the global plasmapause shape with upstream solar wind and IMF parameters and corresponding predicted values of SYM-H and AE, and can also be used as input parameters for other inner magnetospheric coupling models, such as dynamic radiation belt and ring current models and even MHD models.

Frequency sweep rates of rising tone electromagnetic ion cyclotron waves: Comparison between nonlinear theory and Cluster observation

Resonant pitch angle scattering by electromagnetic ion cyclotron (EMIC) waves has been suggested to account for the rapid loss of ring current ions and radiation belt electrons. For the rising tone EMIC wave (classified as triggered EMIC emission), its frequency sweep rate strongly affects the efficiency of pitch-angle scattering. Based on the Cluster observations, we analyze three typical cases of rising tone EMIC waves. Two cases locate at the nightside (22.3 and 22.6 magnetic local time (MLT)) equatorial region and one case locates at the duskside (18MLT) higher magnetic latitude (λ = –9.3°) region. For the three cases, the time-dependent wave amplitude, cold electron density, and cold ion density ratio are derived from satellite data; while the ambient magnetic field, thermal proton perpendicular temperature, and the wave spectral can be directly provided by observation. These parameters are input into the nonlinear wave growth model to simulate the time-frequency evolutions of the rising tones. The simulated results show good agreements with the observations of the rising tones, providing further support for the previous finding that the rising tone EMIC wave is excited through the nonlinear wave growth process.

A statistical study of EMIC waves observed by Cluster: 1. Wave properties

Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on particle dynamics, detailed information about the ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the L-MLT frame within a limited MLAT range. In this study, we present a statistical analysis of EMIC wave properties using ten years (2001–2010) of data from Cluster, totaling 17,987 minutes of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The current paper focuses on the wave occurrence distribution as well as the distribution of wave properties.