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On December 08, 2018 the Twin Rocket Investigation of Cusp Electrodynamics 2 (TRICE 2) mission was successfully launched. The mission consisted of two sounding rockets, each carrying a payload capable of measuring electron and ion distributions, electric and magnetic fields, and plasma waves occurring in the northern magnetospheric cusp. This study highlights the ion and wave observations obtained by TRICE 2 in the cusp and observations from the magnetospheric multiscale (MMS) spacecraft at the low-latitude magnetopause two hours prior to the TRICE 2 traversal of the cusp. Within the cusp, typical ion cusp features were observed, that is, energy-latitude dispersion of injected magnetosheath plasma. However, a lower energy population was also measured near the equatorward edge of the cusp on open field lines. Pitch-angle distributions of the low-energy ions suggest that this population was magnetospheric in origin, and not from ionospheric upflows. Data from MMS show that counterstreaming ions were present in the outer magnetosphere and low-latitude boundary layer at similar energies to those observed by TRICE 2 in the cusp. Correlations between the low-energy ions within the cusp and broadband extremely low frequency waves suggest that the low-energy magnetospheric ions that filled the flux tube may have undergone wave-particle interactions. These interactions may cause pitch-angle scattering of low-energy magnetospheric ions closer to the loss cone, thereby allowing them to precipitate into the cusp and be measured by the TRICE 2 sounding rockets.

Auroral whistler‐mode radio emissions called saucers are of fundamental interest because they require an unusually stationary emission process in the dynamic auroral environment, and it is a mystery how that can happen in this or similar conditions elsewhere in geospace. The Cusp Alfvén and Plasma Electrodynamics Rocket (CAPER‐2), launched into the cusp, obtained the first rocket measurements of a large‐scale, multiple‐armed dayside saucer, similar to those observed by the DEMETER satellite, with the addition of particle measurements and ground‐based measurements. Analysis of saucer shapes, directional measurements using waveforms, and ground‐based data show that, accounting for estimated uncertainties, these originate at altitudes ∼4,000 km within the cusp, the eastern side of which is penetrated by the rocket ∼100 s after the saucers are encountered. On‐board particle instruments show dispersed electron bursts in the cusp, Alfvénically accelerated at altitudes at or above the saucer sources. publishedVersion

Wave-particle correlations, particularly of Langmuir waves and electrons, have been the subject of significant interest extending back to the 1970's. Often, these correlations have been simply observing modulation of the electrons at the plasma frequency with no phase resolution. The first phase-resolving correlators were developed at UC Berkeley in the late 1980's and reported by Ergun in the early 1990's. A design is presented which further improves on phase resolution in correlations of Langmuir waves and electrons with phase resolution of 22.5 degrees. In this technique, a phase-lock-loop (PLL) is used to lock onto the wave and subdivide the phase. Electrons are sorted on-the-fly as they arrive into the phase bins. Discussed are details of accurate timing, testing, and calibration of this system as well as results from rocket flights in which statistically significant phase correlations have been observed.

We present measurements from the Magnetospheric Multiscale (MMS) mission taken during a reconnection event on the dayside magnetopause which includes a passage through an electron diffusion region ...

Cold plasma theory and parallel wave propagation are often assumed when approximating the whistler mode magnetic field wave power from electric field observations. The current study is the first to include the wave normal angle from the Electric and Magnetic Field Instrument Suite and Integrated Science package on board the Van Allen Probes in the conversion factor, thus allowing for the accuracy of these assumptions to be quantified. Results indicate that removing the assumption of parallel propagation does not significantly affect calculated plasmaspheric hiss wave powers. Hence, the assumption of parallel propagation is valid. For chorus waves, inclusion of the wave normal angle in the conversion factor leads to significant alterations in the distribution of wave power ratios (observed/ calculated); the percentage of overestimates decreases, the percentage of underestimates increases, and the spread of values is significantly reduced. Calculated plasmaspheric hiss wave powers are, on average, a good estimate of those observed, whereas calculated chorus wave powers are persistently and systematically underestimated. Investigation of wave power ratios (observed/calculated), as a function of frequency and plasma density, reveals a structure consistent with signal attenuation via the formation of a plasma sheath around the Electric Field and Waves spherical double probes instrument. A simple, density-dependent model is developed in order to quantify this effect of variable impedance between the electric field antenna and the plasma interface. This sheath impedance model is then demonstrated to be successful in significantly improving agreement between calculated and observed power spectra and wave powers.

We present a statistical survey of the latitudinal structure of the fast magnetosonic wave mode detected by the Van Allen Probes spanning the time interval of 21 September 2012 to 1 August 2014. We show that statistically, the latitudinal occurrence of the wave frequency (f) normalized by the local proton cyclotron frequency (f(sub cP)) has a distinct funnel-shaped appearance in latitude about the magnetic equator similar to that found in case studies. By comparing the observed E/B ratios with the model E/B ratio, using the observed plasma density and background magnetic field magnitude as input to the model E/B ratio, we show that this mode is consistent with the extra-ordinary (whistler) mode at wave normal angles (theta(sub k)) near 90 deg. Performing polarization analysis on synthetic waveforms composed from a superposition of extra-ordinary mode plane waves with theta(sub k) randomly chosen between 87 and 90 deg, we show that the uncertainty in the derived wave normal is substantially broadened, with a tail extending down to theta(sub k) of 60 deg, suggesting that another approach is necessary to estimate the true distribution of theta(sub k). We find that the histograms of the synthetically derived ellipticities and theta(sub k) are consistent with the observations of ellipticities and theta(sub k) derived using polarization analysis.We make estimates of the median equatorial theta(sub k) by comparing observed and model ray tracing frequency-dependent probability occurrence with latitude and give preliminary frequency dependent estimates of the equatorial theta(sub k) distribution around noon and 4 R(sub E), with the median of approximately 4 to 7 deg from 90 deg at f/f(sub cP) = 2 and dropping to approximately 0.5 deg from 90 deg at f/f(sub cP) = 30. The occurrence of waves in this mode peaks around noon near the equator at all radial distances, and we find that the overall intensity of these waves increases with AE*, similar to findings of other studies.

Using the Van Allen Probes, we investigate the enhancement in the large-scale duskward convection electric field during the geomagnetic storm (Dst similar to-120nT) on 1 June 2013 and its role in ring current ion transport and energization and plasmasphere erosion. During this storm, enhancements of similar to 1-2mV/m in the duskward electric field in the corotating frame are observed down to L shells as low as similar to 2.3. A simple model consisting of a dipole magnetic field and constant, azimuthally westward, electric field is used to calculate the earthward and westward drift of 90 degrees pitch angle ions. This model is applied to determine how far earthward ions can drift while remaining on Earth's nightside, given the strength and duration of the convection electric field. The calculation based on this simple model indicates that the enhanced duskward electric field is of sufficient intensity and duration to transport ions from a range of initial locations and initial energies characteristic of (though not observed by the Van Allen Probes) the earthward edge of the plasma sheet during active times (L similar to 6-10 and similar to 1-20keV) to the observed location of the 58-267keV ion population, chosen as representative of the ring current (L similar to 3.5-5.8). According to the model calculation, this transportation should be concurrent with an energization to the range observed, similar to 58-267keV. Clear coincidence between the electric field enhancement and both plasmasphere erosion and ring current ion (58-267keV) pressure enhancements are presented. We show for the first time nearly simultaneous enhancements in the duskward convection electric field, plasmasphere erosion, and increased pressure of 58-267keV ring current ions. These 58-267keV ions have energies that are consistent with what they are expected to pick up by gradient B drifting across the electric field. These observations strongly suggest that we are observing the electric field that energizes the ions and produces the erosion of the plasmasphere.

The FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission provides comprehensive measurements of the full vector magnetic and electric fields in the reconnection regions investigated by MMS, including the dayside magnetopause and the night-side magnetotail acceleration regions out to 25 Re. Six sensors on each of the four MMS spacecraft provide overlapping measurements of these fields with sensitive cross-calibrations both before and after launch. The FIELDS magnetic sensors consist of redundant flux-gate magnetometers (AFG and DFG) over the frequency range from DC to 64 Hz, a search coil magnetometer (SCM) providing AC measurements over the full whistler mode spectrum expected to be seen on MMS, and an Electron Drift Instrument (EDI) that calibrates offsets for the magnetometers. The FIELDS three-axis electric field measurements are provided by two sets of biased double-probe sensors (SDP and ADP) operating in a highly symmetric spacecraft environment to reduce significantly electrostatic errors. These sensors are complemented with the EDI electric measurements that are free from all local spacecraft perturbations. Cross-calibrated vector electric field measurements are thus produced from DC to 100 kHz, well beyond the upper hybrid resonance whose frequency provides an accurate determination of the local electron density. Due to its very large geometric factor, EDI also provides very high time resolution (similar to 1 ms) ambient electron flux measurements at a few selected energies near 1 keV. This paper provides an overview of the FIELDS suite, its science objectives and measurement requirements, and its performance as verified in calibration and cross-calibration procedures that result in anticipated errors less than 0.1 nT in B and 0.5 mV/m in E. Summaries of data products that result from FIELDS are also described, as well as algorithms for cross-calibration. Details of the design and performance characteristics of AFG/DFG, SCM, ADP, SDP, and EDI are provided in five companion papers.

Whistler mode chorus waves in the outer Van Allen belt can have consequences for acceleration of relativistic electrons through wave-particle interactions. New multicomponent waveform measurements have been collected by the Van Allen Probes Electric and Magnetic Field Instrument Suite and Integrated Science's Waves instrument. We detect fine structure of chorus elements with peak instantaneous amplitudes of a few hundred picotesla but exceptionally reaching up to 3 nT, i.e., more than 1% of the background magnetic field. The wave vector direction turns by a few tens of degrees within a single chorus element but also within its subpackets. Our analysis of a significant number of subpackets embedded in rising frequency elements shows that amplitudes of their peaks tend to decrease with frequency. The wave vector is quasi-parallel to the background magnetic field for large-amplitude subpackets, while it turns away from this direction when the amplitudes are weaker.

[1] The ACES-High rocket, part of the Auroral Current and Electrodynamics Structure (ACES) mission launched from Poker Flat Research Range on 29 January 2009, obtained the first in situ measurements indicative of both of the observational characteristics associated with the ionospheric feedback instability as it flew through an auroral arc and its associated return current region. ACES-High observed Alfvenic wave structures localized in areas of roughly 10 km near the boundaries of the return current region associated with the discrete auroral arc and increased electron density with a temperature characteristic of a cold ionosphere. This density enhancement is believed to be caused by the excavation of plasma from lower altitudes via the ponderomotive force produced by the ionospheric Alfven resonator, as shown by Streltsov and Lotko (2008). While this density is lower than expected from simulations and other observations by as much as an order of magnitude, the ratio of the enhancement to the background density is in agreement with predictions. The observations made by ACES-High agree with the model results by Streltsov and Lotko (2008) but show the localized wave structures only near the boundaries of the return current region and not throughout it. This can be explained by strong small-scale magnetic field-aligned currents that are generated by the interaction between the large-scale downward current and the ionosphere at these boundaries. Finally, a new model, based on that by Streltsov and Marklund (2006), was run with only one downward current region and produced results very similar to the observations seen by ACES-High.

The Electric and Magnetic Field Instrument and Integrated Science (EMFISIS) investigation on the NASA Radiation Belt Storm Probes (now named the Van Allen Probes) mission provides key wave and very low frequency magnetic field measurements to understand radiation belt acceleration, loss, and transport. The key science objectives and the contribution that EMFISIS makes to providing measurements as well as theory and modeling are described. The key components of the instruments suite, both electronics and sensors, including key functional parameters, calibration, and performance, demonstrate that EMFISIS provides the needed measurements for the science of the RBSP mission. The EMFISIS operational modes and data products, along with online availability and data tools provide the radiation belt science community with one the most complete sets of data ever collected.

High-resolution, in situ measurements of dc and wave electric fields, magnetic fields, and plasma number density have been gathered by instruments on a diagnostic payload at which a high-velocity, overdense aluminum ion beam was directed from a separate payload spaced 468 m away. The experiment, called the Active Plasma Physics Experiment, was carried out in the Earth's high-latitude ionosphere at 360-km altitude using a sounding rocket. The experimental data clearly show a large diamagnetic cavity with a 93 % depletion of the Earth's magnetic field within a narrowly confined ( 1.5 V/m perpendicular to the magnetic field were observed that represented both the E × B bulk plasma velocity and a magnetosonic wave, which preceded the arrival of the beam that was also evident in the AB magnetometer data. The electric field data also show the presence of electric fields parallel to the magnetic field, including a bipolar electric field signature presumably set up to ensure current continuity. Other plasma waves associated with the release include Alfven perturbations, intense broadband turbulence extending to frequencies beyond 1 MHz, whistler-mode electromagnetic emissions at the ambient O + lower hybrid frequency, and ion acoustic turbulence. The measurements provide a self-consistent picture of the electrodynamics surrounding a high-velocity, overdense ion beam released in the high-latitude ionosphere.

Initial results from the Active Plasma EXperiment North Star experiment are presented. The North Star active experiment included two separate plasma jet injections, both perpendicular to the Earth's magnetic field. The objective of the experiment is to investigate the interaction of high-speed (7–40 km/s) plasma jets with the ionospheric plasma and the coupling to the magnetosphere and lower ionosphere. The plasma jets were produced using an Explosive Type Generator device. This device is a shaped-charge device that vaporizes porous aluminum inside the generator and forces the vaporized products out of a nozzle, resulting in the production of a high-speed, partially ionized aluminum plasma jet. Instrumentation on three different payloads was used to obtain multi-point observations of the plasma jet properties, optical radiation from the jets, and ionospheric perturbations. Imagery, high-speed photometry, and spectrographic imagery using ground- and space-based sensors were used to monitor the dynamics and spectral content of the plasma jet. This paper describes the experiment and summarizes the initial results from the North Star experiment.

Precipitating auroral electrons can produce discrete auroral arcs that contain signatures of the magnetospheric auroral source region. Differential number flux observations over two discrete aurorae were obtained by the Auroral Currents and Electrodynamics Structure sounding rocket mission, which successfully launched in 2009. These observations were made at E region altitudes of approximately 130 km. A model of precipitating auroral electrons as described by Evans (1974) was fit to the electron differential number flux obtained by the payloads, and parameters from the model were used to infer properties of the auroral source region. It is shown that the field-aligned precipitating electrons were better fit by a kappa distribution function versus a Maxwellian distribution function for the equatorward side of the first, quasi-stable, auroral arc crossing. The latter half of the first auroral arc crossing and second auroral crossing show that the precipitating electrons were better fit by a Maxwellian distribution function, which provides additional observational confirmation of previous studies. The low-energy electron population determined by the Evans (1974) model was within a factor of 2 of the observed differential number flux. The source region parameters determined from fitting the model to the data were compared with relevant studies from sounding rockets and satellites. Our observations are consistent with the results of Kletzing et al. (2003) that the plasma sheet electrons mapping to auroral zone invariant latitudes are characterized by kappa distribution functions.

Electric field wave measurements gathered on a sounding rocket flown in the presence of polar mesospheric summer echoes reveal a distinct layer of irregularities between 83 - 86 km with broadband amplitudes of > 10 mV/m rms. The waves are characterized by bursty, spiky waveforms with lower frequencies (∼ 10 Hz) dominant in the upper portion of the layer near 85 km and broader band emissions, extending to higher frequencies (∼ 1000 Hz) dominant in the lower portion of the layer near 83.5 km. The lower altitudes correspond to a region of weak optical emissions associated with a noctilucent cloud. The waves appear in and around regions where charged/neutral aerosols (1 - 10 nm) and large electron density depletions were observed. The irregularities likely result from a variety of processes including space charge inhomogeneities, mixed neutral and plasma motions, and complex effects associated with charged aerosols of varying sizes.

Small-scale solitary electric potential structures are commonly observed on auroral field lines with the Polar Electric Field Instrument (EFI). This study focuses on observations of solitary structures in the southern hemisphere auroral zone at altitudes between 5500 and 7500 km. Some of the potential structures are similar to those observed previously by the S3-3 and Viking satellites and are inferred to be negative potential pulses traveling upward along the auroral magnetic field lines, associated with upgoing ion beams and upward currents. The velocities of these “ion” solitary potential structures are estimated, using spaced EFI measurements, to be distributed within the range of ∼75 – 300 km s−1. In addition to these structures, a different type of solitary potential structure with.opposite polarity has been observed with faster propagation velocities. These faster structures (termed “electron” solitary potential structures) are distinguishable from the slower, ion solitary structures in that their distinctive bipolar electric field signature, common to both types of solitary structure, is reversed. The ultimate distinction for the electron solitary potential structures is that they are observed on auroral field lines in conjunction with magnetically field-aligned upflowing electron beams. The electron solitary potential structures propagate up the field line in the same direction as the electron beam. An example is shown of the polarity reversal from ion to electron solitary potential structures coincident with a simultaneous shift from upgoing ion beams to upgoing electron beams.

The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously from Poker Flat Research Range, AK on January 29, 2009 into a dynamic multiple-arc aurora. The ACES rocket mission was designed to observe electrodynamic and plasma parameters above and within the current closure region of the auroral ionosphere. Two well instrumented payloads were flown along very similar magnetic field footprints, at different altitudes, with small temporal separation between both payloads. The higher altitude payload (apogee 360 km), obtained in-situ measurements of electrodynamic and plasma parameters above the current closure region to determine the input signature. The low altitude payload (apogee 130 km), made similar observations within the current closure region. Results are presented comparing observations of the electric fields, magnetic components, and the differential electron energy flux at magnetic footpoints common to both payloads. In situ data is compared to the ground based all-sky imager data, which presents the evolution of the auroral event as the payloads traversed through magnetically similar regions. Current measurements derived from the magnetometers on the high altitude payload observed upward and downward field-aligned currents. The effect of collisions with the neutral atmosphere is investigated to determine if it is a significant mechanism to explain discrepancies in the low energy electron flux. The high altitude payload also observed time-dispersed arrivals in the electron flux and perturbations in the electric and magnetic field components, which are indicative of Alfven waves.

International audience; [1] The Geoelectrodynamics and Electro-Optical Detection of Electron and Suprathermal Ion Currents (GEODESIC) sounding rocket encountered more than 100 filamentary density cavities associated with enhanced plasma waves at ELF (

Measurements of the dispersion relation for shear Alfv\'en waves as a function of perpendicular wave number are reported for the inertial regime for which ${V}_{A}g{V}_{Te}$. The parallel phase velocity and damping are determined as ${k}_{\ensuremath{\perp}}$ varies and the measurements are compared to theoretical predictions. The comparison shows that the best agreement between theory and experiment is achieved for a fully complex plasma dispersion relation which includes the effects of electron collisions.

[1] Observations from a new wave-particle correlator show clear evidence of phase bunching of the electrons by a monochromatic Langmuir wave electric field which varied slowly in amplitude. The electrons are found to be bunched at 90° with respect to the wave field indicating that they are the reactive component of the perturbed distribution function. This is in agreement with theory that predicts this phase relation for the transit of electrons through a very long wave field.

[1] Rocket observations of electron time dispersion which occurs at energies below the primary inverted-V electron precipitation exhibit a variety of characteristics in the dispersion timescale and flux intensity distribution. We present simulation results that illustrate how different dispersion signatures can be produced by resonant acceleration and deceleration of auroral electrons by inertial Alfven waves. We investigate the individual effects of relevant parameters such as the altitude of the inverted-V potential, Alfven wave amplitude, wave velocity, and source electron population. The energies to which Alfven waves can accelerate electrons are primarily determined by the peak Alfven speed below the DC potential drop and to a lesser extent by the amplitude of the wave parallel electric field. The observed electron signatures can be used to obtain information about the peak Alfven speed, the wave parallel electric field, the DC electric field, and plasma environment through which the waves propagate.

[1] The HIgh Bandwidth Auroral Rocket (HIBAR), launched into active pre-midnight aurora, encountered two bursts of 2–10 mV/m upper hybrid waves just below fuh = 2fce at approximately 377 and 390 km altitude. These waves occur in association with a density “shoulder” and enhancement, respectively. The waves show several bands of frequency structure with 4–8 kHz spacings and, within these, bands of frequency sub structure with 1–2 kHz spacings. At the time of the waves, the measured electron distribution indicates wave instability for frequencies 1–1.2% percent below the electron cyclotron harmonic. These results agree qualitatively with theoretical work predicting banded structure associated with upper hybrid waves trapped in density enhancements.

[1] We explore a mechanism by which density depletions associated with lower-hybrid cavities and similar structures are a direct consequence of ion trajectories resulting from transverse energization localized on scales comparable to the ion gyroradius. Specifically, a heating region localized to a flux tube having a diameter of the order of a few ambient thermal ion gyroradii will be depleted of ions because of heated-gyroradius-scale excursions of the ions away from the heating region. Cooler ions outside will have smaller average gyroradii and will be unable to compensate for the depletion inside the heating region. The outflux of energized ions from the heated region results in a density enhancement at its periphery. Motivated by space observations, we characterize density perturbations resulting from an idealized, cylindrically symmetric Gaussian temperature enhancement, using Monte Carlo simulations and an orbit-averaged density calculation. Our model generates density depletions of the order of 10% for a two-fold increase in Ti over the background value and 50% for a fifty-fold increase. In addition to density depletions the model predicts density-enhanced shoulders around cavity perimeters and shows how heated ion tails superimposed on cool ionospheric plasmas can be explained by hot, Maxwellian ions originating on nonlocal flux tubes. We present examples of shoulders observed by sounding rockets and by the Freja satellite. Finally, we use sounding rocket measurements to demonstrate that the distribution of cavity widths (or chord lengths) is relatively narrow (16 ± 10 m), with an average width that remains nearly unchanged even as plasma density varies over five orders of magnitude. This result is consistent with gyroradius being the key scaling parameter, although it does not rule out other scaling predictions that do not depend on plasma density.

[1] We present simultaneous observations of ion distribution functions and plasma waves in the high-latitude topside ionosphere (500–1000 km) near local midnight during substorm activation. Using a new instrument, the Suprathermal Ion Imager (SII), we are able to explore two-dimensional ion distribution functions with unprecedented resolution in time (93 s−1) and energy, focusing on the lowest-energy core (

Measurements of shear Alfven waves are used to test the predictions of a variety of different electron collision operators, including several Krook collision operators as well as a Lorentz collision operator. New expressions for the collisional warm-plasma dielectric tensor resulting from the use of the fully magnetized collisional Boltzmann equation are presented here. Theoretical predictions for the parallel phase velocity and damping as a function of perpendicular wave number k⊥ are derived from the dielectric tensor. Laboratory measurements of the parallel phase velocity and damping of shear Alfven waves were made to test these theoretical predictions in both the kinetic (vte⪢vA) and inertial (vte⪡vA) parameter regimes and at several wave frequencies (ω

Measurements of the dispersion relation for shear Alfv\'en waves as a function of the perpendicular wave number are reported for the regime in which ${V}_{A}\ensuremath{\simeq}{V}_{Te}$. By measuring the parallel phase velocity of the waves, the measurements can be compared directly to theoretical predictions of the dispersion relation for a parameter regime in which particle kinetic effects become important. The comparison shows that the best agreement between theory and experiment is achieved when a fully complex, warm plasma dispersion relation is used.

The first sounding rocket flight into the dayside cusp with dark ground and northward interplanetary magnetic field (IMF) conditions was launched from the new SvalRak range at Ny-Alesund in the Svalbard archipelago in early December 1997. Extensive ground observations of auroral emissions and radar backscatter provided contexts for in situ rocket measurements. Real-time interplanetary measurements from the Wind satellite aided launch selection with foreknowledge of impending conditions. NASA rocket flight 36.153 was launched near local magnetic noon while the IMF was dominated by positive B X and had lesser northward B Z and negative B Y components. The rocket's westward trajectory carried it toward auroral forms associated with morningside boundary layers. The rich set of vector dc electric and magnetic fields, energetic particles, thermal plasma, plasma waves, and optical emissions gathered by the rocket reveal a complex electrodynamic picture of the cusp/boundary-layer region. Four factors were important in separating temporal and spatial effects: (1) Near the winter solstice the Earth's north magnetic pole tilts away from the Sun, (2) at the UT of the flight the dipole axis was rotated toward dawn, (3) the variability of solar wind driving was low, and (4) B X was the dominant IMF component. We conclude that no signatures of dayside merging in the Northern Hemisphere were detected in either the rocket or ground sensors. Electric field variations in the interplanetary medium directly correlate with those observed by the sounding rocket, with significantly shorter lag times than estimated for simple propagation between Wind and the ionosphere. The correlation requires that the observed Northern Hemisphere convection structures were stirred in part by merging of the IMF with closed field lines in the Southern Hemisphere, thereby adding open flux to the northern polar cap. Subsequent motions of adiaroic polar cap boundaries were detected in the rocket electric field measurements. The observations indicate that IMF B X significantly affected the location and timing of merging interactions.