Use of single-component wind speed in Rankine-Hugoniot analysis of interplanetary shocks

We have extended and deployed a routine designed to run independently on the Web providing real-time analysis of interplanetary shock observations from L_1. The program accesses real-time magnetic field, solar wind speed, and proton density data from the Advanced Composition Explorer (ACE) spacecraft, searches for interplanetary shocks, analyzes shocks according to the Rankine-Hugoniot (R-H) jump conditions, and provides shock solutions on the Web for space weather applications. Because the ACE real-time data stream contains the wind speed but not the three-component wind velocity, we describe modifications to the R-H analysis that use the scalar wind speed and show successful results for analyses of strong interplanetary shocks at 1 AU. We compare the three-component and one-component solutions and find the greatest disagreement between the two rests in estimations of the shock speed rather than the shock propagation direction. Uncertainties in magnetic quantities such as magnetic compression and shock normal angle relative to the upstream magnetic field show large uncertainties in both analyses when performed using an automated routine whereas analyses of the shock normal alone do not. The automated data point selection scheme, together with the natural variability of the magnetic field, is inferred to be a problem in a few instances for this and other reasons. For a broad range of interplanetary shocks that arrive 30 to 60 min after passing L_1, this method will provide 15 to 45 min of advanced warning prior to the shock's collision with the Earth's magnetopause. The shock, in turn, provides advance warning of the approaching driver gas

Temperature of the Plasmasphere from Van Allen Probes HOPE

We introduce two novel techniques for estimating temperatures of very low energy space plasmas using, primarily, in situ data from an electrostatic analyzer mounted on a charged and moving spacecraft. The techniques are used to estimate proton temperatures during intervals where the bulk of the ion plasma is well below the energy bandpass of the analyzer. Both techniques assume that the plasma may be described by a one-dimensional E→×B→ drifting Maxwellian and that the potential field and motion of the spacecraft may be accounted for in the simplest possible manner, i.e., by a linear shift of coordinates. The first technique involves the application of a constrained theoretical fit to a measured distribution function. The second technique involves the comparison of total and partial-energy number densities. Both techniques are applied to Van Allen Probes Helium, Oxygen, Proton, and Electron (HOPE) observations of the proton component of the plasmasphere during two orbits on 15 January 2013. We find that the temperatures calculated from these two order-of-magnitude-type techniques are in good agreement with typical ranges of the plasmaspheric temperature calculated using retarding potential analyzer-based measurements—generally between 0.2 and 2 eV (2000–20,000 K). We also find that the temperature is correlated with L shell and hot plasma density and is negatively correlated with the cold plasma density. We posit that the latter of these three relationships may be indicative of collisional or wave-driven heating of the plasmasphere in the ring current overlap region. We note that these techniques may be easily applied to similar data sets or used for a variety of purposes

Kinetic model of the inner magnetosphere with arbitrary magnetic field

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95311/1/jgra21699.pd

Solar wind electron suprathermal strength and temperature gradients: Ulysses observations

International audienc

Postmidnight depletion of the high‐energy tail of the quiet plasmasphere

The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures the high‐energy tail of the thermal plasmasphere allowing study of topside ionosphere and inner magnetosphere coupling. We statistically analyze a 22 month period of HOPE data, looking at quiet times with a Kp index of less than 3. We investigate the high‐energy range of the plasmasphere, which consists of ions at energies between 1 and 10 eV and contains approximately 5% of total plasmaspheric density. Both the fluxes and partial plasma densities over this energy range show H+ is depleted the most in the postmidnight sector (1–4 magnetic local time), followed by O+ and then He+. The relative depletion of each species across the postmidnight sector is not ordered by mass, which reveals ionospheric influence. We compare our results with keV energy electron data from HOPE and the Van Allen Probes Electric Fields and Waves instrument spacecraft potential to rule out spacecraft charging. Our conclusion is that the postmidnight ion disappearance is due to diurnal ionospheric temperature variation and charge exchange processes.Key PointsOne to ten eV ion depletion in quiet time postmidnight sectorDepletion varies by ion species not ordered by massStrong diurnal variation in high‐energy tail of plasmaspherePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111226/1/jgra51633.pd

Observations of interplanetary shocks from well-separated spacecraft

International audienc

Observations of interplanetary shocks from well-separated spacecraft

International audienc

Local time variations of highâ energy plasmaspheric ion pitch angle distributions

Recent observations from the Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument revealed a persistent depletion in the 1â 10 eV ion population in the postmidnight sector during quiet times in the 2 < L < 3 region. This study explores the source of this ion depletion by developing an algorithm to classify 26 months of pitch angle distributions measured by the HOPE instrument. We correct the HOPE low energy fluxes for spacecraft potential using measurements from the Electric Field and Waves (EFW) instrument. A high percentage of low count pitch angle distributions is found in the postmidnight sector coupled with a low percentage of ion distributions peaked perpendicular to the field line. A peak in loss cone distributions in the dusk sector is also observed. These results characterize the nature of the dearth of the near 90° pitch angle 1â 10 eV ion population in the nearâ Earth postmidnight sector. This study also shows, for the first time, lowâ energy HOPE differential number fluxes corrected for spacecraft potential and 1â 10 eV H+ fluxes at different levels of geomagnetic activity.Key PointsDeveloped new pitch angle sorting algorithm for Van Allen ProbesFound 90 degree pitch angle population depletion in nearâ Earth postmidnight sectorCorrected low energy HOPE ion fluxes for spacecraft potentialPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134226/1/jgra52723_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134226/2/jgra52723.pd

Observations of interplanetary shocks from well-separated spacecraft

International audienc