Magnetosphere-ionosphere Interactions Research Articles

Non-extensive (Tsallis) q-statistics and auroral glow

It is well-known that the auroral region of the magnetosphere–ionosphere interaction is an open, nonlinear dissipative system far from the equilibrium state. It is in this region that auroras are regularly observed, demonstrating not only a wide variety of dynamic forms but also a wide range of temporal and spatial scales. Due to the memory effects and fractal properties of auroral plasma, as well as strong correlations between its individual parts, the dynamics of the high-latitude system are primarily determined by long-range electromagnetic forces. Therefore, it is expected that non-additive and non-extensive thermodynamic principles may characterize their macroscopic behavior. In the presented study, it is shown that pulsating auroras exhibit non-extensive properties and can be described by q-statistics. The correlation of the parameter q with traditional indicators of nonlinear dynamics, such as the flatness coefficient, standard deviation, and scaling index, has been investigated. Small-scale changes are superimposed on large-scale processes characterized by a low correlation dimension, and this leads to an increase in the correlation dimension during geomagnetic activity, which approximately coincides with increased values of q. It is concluded that the q-statistics (Tsallis distribution) can be used to analyze optical phenomena in the auroral region.

A simplified geospace model for satellite design

This study introduced a simplified, integrated computational model to estimate the drag coefficient and surface charging within the plasma wake of Low Earth Orbit (LEO) spacecraft influenced by various solar activities. The model constituted four core modules: a solver for the solar wind-magnetosphere interaction, a magnetosphere-ionosphere coupling for electric field mapping, an ionization model for the F-layer of the ionosphere, and an estimation model for excess satellite drag and plasma wake size. The initial module adopted a simplified 1D ideal Magnetohydrodynamic (MHD) model while incorporating magnetosphere-ionosphere interactions to derive electric field data near Earth’s boundary. A simplified ionospheric model for the F-layer was implemented to compute the O+ and electron densities. Subsequently, the spacecraft drag coefficient and the plasma wake size were determined for varying solar wind speed inputs corresponding to quiet, intense, and extreme space weather conditions. In the case of extreme conditions with a solar wind speed of 1000 km/s, the results indicated that the excess satellite drag coefficient and plasma wake size increased to around ten percent.

Prestorm ionospheric disturbances: Precursors or Q-disturbances?

• The foF2 deviations from quiet conditions during prestorm days are, most probably, precursors of magnetic storms. • They depend on the parameters of the following magnetic storm. • The deviations are not Q-dependences. The problem of disturbances in the parameters of the F 2 layer and upper ionosphere during the days preceding onset of a magnetic storm is known already for many decades. Many publications have been dedicated to analysis of these disturbances both in the critical frequency and height of the F2 layer and in the total electron content. The majority of researchers have drawn a conclusion that such disturbances are observed prior almost to every storm, positive events (an excess of the values in the prestorm period over the corresponding values on a geomagnetically quiet day) prevailing. Moreover, some authors claimed that the aforementioned disturbances could be considered as precursors of the coming magnetic storm. A concept of the so-called Q-disturbances, according to which the disturbances during the prestorm days are not related to the coming storm but are a result of several processes (meteorological influence on the ionosphere, changes in the magnetosphere-ionosphere interaction) which sometimes cause deviations of ionospheric parameters is an alternative to the precursor concept. Arguments are presented in favor of the precursor concept. These arguments are, first of all, based on the existence of a dependence of parameters of the prestorm disturbances on parameters of the coming storm. The dependencies on the magnetic storm intensity, local time of the storm onset SO, and time from the disturbance to SO present the strongest arguments against the Q-disturbance concept. Numerous examples of these dependencies are presented. The recent publications with new experimental data on the foF 2 and TEC behavior in the prestorm period are discussed. Arguments in favor of the prestorm concept presented in these publications are briefly considered.

Morphology and diagnostic potential of the ionospheric Alfvén resonator

The layering of the ionosphere leads to the formation of resonators and waveguides of various kinds. One of the most well-known is the ionospheric Alfvén resonator (IAR) whose radiation can be observed both on Earth’s surface and in space in the form of a fan-shaped set of discrete spectral bands (DSB), the frequency of which changes smoothly during the day. The bands are formed by Alfvén waves trapped between the lower part of the ionosphere and the altitude profile bending of Alfvén velocity in the transition region between the ionosphere and the magnetosphere. Thus, IAR is one of the important mechanisms of the ionosphere-magnetosphere interaction. The emission frequency lies in the range from tenths of hertz to about 8 Hz — the frequency of the first harmonic of the Schumann resonance. The review describes in detail the morphology of the phenomenon. It is emphasized that the IAR emission is a permanent phenomenon; the probability of observing it is primarily determined by the sensitivity of the equipment and the absence of interference of natural and artificial origin. The daily duration of the DSB observation almost completely depends on the illumination conditions of the lower ionosphere: the bands are clearly visible only when the D layer is shaded. Numerous theoretical IAR models have been systematized. All of them are based on the analysis of the excitation and propagation of Alfvén waves in inhomogeneous ionospheric plasma and differ mainly in sources of oscillation generation and methods of accounting for various factors such as interaction of wave modes, dipole geometry of the magnetic field, frequency dispersion of waves. Predicted by all models of the cavity and repeatedly confirmed experimentally, the close relationship between DSB frequency variations and critical frequency foF2 variations serves as the basis for searching ways of determining in real time the electron density of the ionosphere from IAR emission frequency measurements. It is also possible to estimate the profile of the ion composition over the ionosphere from the data on the IAR emission frequency structure. The review also focuses on other results from a wide range of IAR studies, specifically on the results that revealed the influence of the interplanetary magnetic field orien tation on oscillations of the resonator, and on the facts of the influence of seismic disturbances on IAR.

Морфология и диагностический потенциал ионосферного альвеновского резонатора

The layering of the ionosphere leads to the formation of resonators and waveguides of various kinds. One of the most well-known is the ionospheric Alfvén resonator (IAR) whose radiation can be observed both on Earth’s surface and in space in the form of a fan-shaped set of discrete spectral bands (DSB), the frequency of which changes smoothly during the day. The bands are formed by Alfvén waves trapped between the lower part of the ionosphere and the altitude profile bending of Alfvén velocity in the transition region between the ionosphere and the magnetosphere. Thus, IAR is one of the important mechanisms of the ionosphere-magnetosphere interaction. The emission frequency lies in the range from tenths of hertz to about 8 Hz — the frequency of the first harmonic of the Schumann resonance. The review describes in detail the morphology of the phenomenon. It is emphasized that the IAR emission is a permanent phenomenon; the probability of observing it is primarily determined by the sensitivity of the equipment and the absence of interference of natural and artificial origin. The daily duration of the DSB observation almost completely depends on the illumination conditions of the lower ionosphere: the bands are clearly visible only when the D layer is shaded. Numerous theoretical IAR models have been systematized. All of them are based on the analysis of the excitation and propagation of Alfvén waves in inhomogeneous ionospheric plasma and differ mainly in sources of oscillation generation and methods of accounting for various factors such as interaction of wave modes, dipole geometry of the magnetic field, frequency dispersion of waves. Predicted by all models of the cavity and repeatedly confirmed experimentally, the close relationship between DSB frequency variations and critical frequency foF2 variations serves as the basis for searching ways of determining in real time the electron density of the ionosphere from IAR emission frequency measurements. It is also possible to estimate the profile of the ion composition over the ionosphere from the data on the IAR emission frequency structure. The review also focuses on other results from a wide range of IAR studies, specifically on the results that revealed the influence of the interplanetary magnetic field orien tation on oscillations of the resonator, and on the facts of the influence of seismic disturbances on IAR.

In-situ and optical observations of sub-ion magnetic holes

The magnetotail dipolarization during substorms is a mesoscale dynamical phenomenon, well documented by in-situ spacecraft observations, numerical simulations, and ground-based optical measurements. The magnetic energy release during substorms results in significant plasma heating and the formation of strong temperature and density gradients behind the dipolarization front. Such gradients are the source of many plasma instabilities that are responsible for further transport of energy to smaller spatial scales. In this study, we investigate an example of in-situ and optical observations of the nonlinear stage of one class of such instabilities, associated with the formation of sub-ion scale magnetic holes in the equatorial dipolarized magnetotail. THEMIS in-situ measurements demonstrate that these holes propagate dawnward and are associated with strong gradients of electron thermal pressure (~100−200 km in scale-size). Optical observations of THEMIS all sky imagers show comparably small-scale structures (accounting for magnetic mapping), just poleward of the active region associated with the dipolarization front and plasma flows. Comparison of in-situ and optical observations confirms their association and agreement in propagation direction. Our results demonstrate that sub-ion (electron dominated) magnetic field structures can be a source of small-scale aurora, and thus can host magnetosphere-ionosphere interactions at small scales.

AMPERE polar cap boundaries

Abstract. The high-latitude atmosphere is a dynamic region with processes that respond to forcing from the Sun, magnetosphere, neutral atmosphere, and ionosphere. Historically, the dominance of magnetosphere–ionosphere interactions has motivated upper atmospheric studies to use magnetic coordinates when examining magnetosphere–ionosphere–thermosphere coupling processes. However, there are significant differences between the dominant interactions within the polar cap, auroral oval, and equatorward of the auroral oval. Organising data relative to these boundaries has been shown to improve climatological and statistical studies, but the process of doing so is complicated by the shifting nature of the auroral oval and the difficulty in measuring its poleward and equatorward boundaries. This study presents a new set of open–closed magnetic field line boundaries (OCBs) obtained from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) magnetic perturbation data. AMPERE observations of field-aligned currents (FACs) are used to determine the location of the boundary between the Region 1 (R1) and Region 2 (R2) FAC systems. This current boundary is thought to typically lie a few degrees equatorward of the OCB, making it a good candidate for obtaining OCB locations. The AMPERE R1–R2 boundaries are compared to the Defense Meteorological Satellite Program Special Sensor J (DMSP SSJ) electron energy flux boundaries to test this hypothesis and determine the best estimate of the systematic offset between the R1–R2 boundary and the OCB as a function of magnetic local time. These calibrated boundaries, as well as OCBs obtained from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) observations, are validated using simultaneous observations of the convection reversal boundary measured by DMSP. The validation shows that the OCBs from IMAGE and AMPERE may be used together in statistical studies, providing the basis of a long-term data set that can be used to separate observations originating inside and outside of the polar cap.

Estimation of the contributions of conductance and electric field to the intensity of field-aligned currents in the night polar ionosphere during substorm expansion phase

Based on the output data of the magnetogram inversion technique, we analyze the dynamics of the Pedersen ionospheric currents and field-aligned currents (FACs) in the night mesoscale cells of the three main large-scale Iijima and Potemra Regions (R1, R2 and R0) during the expansion phase of the summer and winter substorms. FACs play a key role in the ionosphere-magnetosphere interaction. The continuity equation for the electric current density contains two types of possible feedback within the electric circuit parts that connect Pedersen currents and FACs in each cell. Pedersen ionospheric conductivity is dominant to Type 1, and the electric field dominates in Type 2 feedback. This paper studies both types of physical feedback in mesoscale cells of downward and upward FACs on the night side of the polar ionosphere from the data of two selected substorms of the summer and winter seasons in the northern hemisphere.

Bio effectiveness of the geo-space agents at the Spitsbergen archipelago

A high degree of variability of psycho-physiological indicators of the state of the body in the subjects was revealed in the study conducted on healthy volunteers in the Spitsbergen archipelago. A dynamics of the indicators of the state of the organism in all persons (100%) correspond to fluctuations of the certain geophysical agents associated with solar activity and the magnetosphere-ionosphere interactions in the polar cusp. It was found that psycho-emotional state, as well as heart rate variability, are modulated by ground physical agents associated with events in the near the Earth’ space. At the same time, many questions remain concerning the nature of the physical agents affecting on the organism, which can only be answered by conducting cooperative studies in the field of the polar cusp.

Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US–CRCM

Abstract. During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases (“dropouts”) in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere–ionosphere (M–I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US–CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open–closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M–I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M–I coupling aspects that have not previously been investigated. Keywords. Magnetospheric physics (magnetosphere–ionosphere interactions; magnetospheric configuration and dynamics); space plasma physics (numerical simulation studies)

On the role of neutral flow in field-aligned currents

Abstract. In this brief note we explore the role of the neutral atmosphere in magnetosphere–ionosphere coupling. We analyze momentum balance in the ion rest frame to form hypotheses regarding the role of neutral momentum in the lower ionosphere during geomagnetic storms. Neutral momentum that appears in the ion rest frame is likely the result of momentum imparted to ionospheric ions by solar wind flow and the resultant magnetospheric dynamics. The resulting ion-neutral collisions lead to the existence of an electric field. Horizontal electron flow balances the momentum supplied by this electric field. We suggest a possible role played by the neutral atmosphere in generating field-aligned currents due to local auroral heating. Our physical interpretation suggests that thermospheric neutral dynamics plays a complementary role to the high-latitude field-aligned currents and electric fields resulting from magnetospheric dynamics. Keywords. Ionosphere (ionosphere–magnetosphere interactions; polar ionosphere) – magnetospheric physics (magnetosphere–ionosphere interactions)

Dynamic aurora sequence recognition using Volume Local Directional Pattern with local and global features

Aurora event consists of the spatial structure and temporal evolution of aurora luminosity, which attributes to the effects of the solar wind-magnetosphere interaction and the physics of the magnetosphere-ionosphere interaction. Dynamic aurora event provides a meaningful projection of effects from plasma processes of outer space and also reveals some certain physical phenomenon and principle. Aurora sequence recognition is one of the key procedure in the analysis of dynamic aurora event. Lots of effective features for static aurora image classification are proposed. If these features for static image classification are utilized to recognize the dynamic aurora sequence, it will result in higher computational complexity. The dynamic features of aurora sequence are seldom proposed due to its complexity. To this end, this paper proposes an efficient aurora sequence descriptor which combines local and global spatial information with temporal location information, which is called as Volume Local Directional Patterns. The ring-section spatial pyramid partition structure is used in the VLDP code image which is coded by Volume Local Directional Patterns to obtain the local spatial feature. After combining the global feature of VLDP code image, the final RSPLDP feature is obtained. Finally, the STSC (self-tuning spectral clustering) method is used to classify the aurora sequence. The experimental results on the dataset which is captured from All-sky Imager (ASI) at the Chinese Yellow River Station demonstrate the effectiveness of the proposed classification scheme.

Victor Trakhtengerts: His contribution to space plasma physics

A brief overview is given of the works by Victor Trakhtengerts (1939–2007) to show his contribution to the development of space plasma physics. The focus is on the following areas of his research: cyclotron interaction of waves and particles in the Earth’s magnetosphere and related matters; resonance processes in magnetosphere-ionosphere interaction; nonlinear phenomena accompanying the impact of powerful HF radiation on ionospheric plasma; and collective effects in atmospheric electricity.

СПУТНИКОВЫЕ ИССЛЕДОВАНИЯ ИОНОСФЕРНЫХ ПРОЯВЛЕНИЙ РАСПРОСТРАНЕНИЯ АКУСТИКО-ГРАВИТАЦИОННЫХ ВОЛН

The response of the ionospheric plasma on the propagation of acoustic-gravity waves (AGW) studied at altitudes of 250 − 350 km using the satellite Dynamics Explorer 2 measurements. Wave perturbations are analyzed according to simultaneously measured data of temperature, concentration and velocity of neutral particles and ions at high and middle latitudes. The following features of ionospheric manifestations of acoustic-gravity waves have been established: 1) relative variations of temperature of neutral particles and ions are roughly the same for these latitudes, except for the regions of auroral ovals; 2) variations in total plasma concentration are antiphase to those in concentration of neutral particles, their relative amplitude being severatimes larger than the amplitude of neutral particles; 3) concentration of molecular ions is in phase with neutral particles;4) vertical velocity of the ions at high latitudes is consistent with that of neutral particles, thus showing their mutual movement along the magnetic field lines. In the high-latitude ionosphere, toseparate the ionospheric manifestations of acoustic-gravity waves from other types of disturbances, the simultaneous analysis of different parameters should be used. Key words: acoustic-gravity waves, moving ionospheric disturbances, auroral zone, ionosphere, atmosphere Manuscript submitted 13.05.2014 Radio phys. radio astron. 2014, 19(3): 206-216 REFERENCES 1. BURMAKA, V.P., TARAN, V. I., andCHERNOGOR, L. F., 2005. Results of the study of wave disturbances in the ionosphere by incoherent scattering. Uspehi sovremennoi radioelectroniki . no. 3, pp. 4–35 (in Russian). 2. LIZUNOV, G. V. and FEDORENKO, A. K., 2006. Atmospheric Gravity Waves Generation by Solar Terminator According to "Atmosphere Explorer-E" Satellite Data. Radio Phys. Radio Astron. , vol. 11, no. 1, pp. 49–62 (in Russian). 3. FEDORENKO, A. K., 2009. Determination Characteristics of Atmospheric Gravity Waves in the Polar Regions Using Mass-Spectrometer Satellite Measurements. Radio Phys. Radio Astron ., vol. 14, no. 3, pp. 254–265 (in Russian). 4. CARIGNAN, G. R., BLOCK, B. P., MAURER, J. C, HEDIN, A. E., REBER, C. A., and SPENCER, N. W., 1981.The neutral mass Spectrometron Dynamics Explorer. Space Sci. Instrum . vol. 5, pp. 429–441. 5. SPENCER, N. W., WHARTON, L. E., NIEMANN, H. B., HEDIN, A. E., CARIGNAN, G. R., and MAURER, J. C., 1981.The Dynamics Explorer wind and temperature spectrometer. Space Sci. Instrum. , vol. 5, pp. 417–428. 6. DUDIS, J. J. and REBER, C. A., 1976. Composition effects in thermospheric gravity waves. Geophys. Res. Lett ., vol. 3, No. 12, pp. 727–730. DOI: https://doi.org/10.1029/GL003i012p00727 7. RATCLIFFE, J. A., 1975. An Introduction to the Ionosphere and Magnetosphere . Moscow: Mir Publ. (in Russian). 8. BRYUNELLI, B. E. and NAMGALADZE, A. A., 1988. Physics of the Ionosphere . Moscow: Nauka Publ. (in Russian). 9. LYATSKY,W. B. and MALTSEV, Y. P., 1983. Magnetosphere-Ionosphere Interaction . Moscow: Nauka Publ. (in Russian).

Evolution of Dst index, cosmic rays and global temperature during solar cycles 20–23

We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.

Determining field-aligned currents with the Swarm constellation mission

Field-aligned currents (FAC) are the prime mechanism for coupling energy from the solar wind into the upper atmosphere at high latitudes. Knowing their intensity and distribution is of pivotal importance for the selection of quiet time data at high latitudes to be used in main field analysis. At the same time FACs can be regarded as a key element for studies of magnetosphere-ionosphere interactions. The Swarm satellite constellation, in particular the lower pair, provides the opportunity to determine radial currents uniquely. The computation of FACs from the vector magnetic field data is a straightforward and fast process, applying Ampere’s integral law to a set of four magnetic field values. In this method the horizontal magnetic field components at a quad of measurement points sampled by the two satellites moving side-by-side are interpreted. The presented algorithm was implemented as described here in the Swarm Level-2 processing facility to provide the automatically estimated radial and field-aligned currents. It was tested with synthetic data in the Swarm Level-1b format. The resulting currents agree excellently with the input currents of the synthetic model. The data products are computed along the entire orbits. In addition, the L2 processor calculates also FACs with a 1 Hz time resolution individually from the three single Swarm satellites.

Comparison of Antarctic riometer radio wave absorption and THEMIS mission energetic electron fluxes

Simultaneous observations of in situ plasma properties in the tail of the Earth’s magnetosphere and of ground based instruments, lying on the same geomagnetic field lines, have recently proved to yield significant new results. In most cases magnetosphere ionosphere interactions during the night-time northern hemisphere conditions are studied. Here, observations of energetic electrons in the tail of the Earth’s magnetosphere made by the THEMIS mission satellites are compared with auroral radio wave absorption determined by riometers in the Antarctic for sunlit conditions. Days for which satellites and riometers are connected by the same geomagnetic field line are selected using a geomagnetic field model. The six days analysed show clear associations between fluxes and absorptions in some cases. However, these do not necessarily correspond to conjugacy intervals. Hours of positive associations are 1.65 times those for negative associations, all hours and days considered (1.42–3.6 on five days and 0.58 on the other day). These computations are assumed appropriate since the footprints of the satellites used approximately follow corrected geomagnetic parallels for all six days studied. The use of a finer parameterization of geomagnetic models to determine conjugacy may be needed.

Model of magnetosphere-ionosphere interactions in the field of auroral electrojets

The magnetosphere and ionosphere are coupled into a power circuit by field-aligned currents. If there were only Hall current in the ionosphere, the problem of magnetosphere-ionosphere interaction would not have arisen. Field-aligned currents could be seen as emerging as a result of the break in the magnetospheric current across the tail, since the Hall current is divergence-free and does not perform any work. In fact, the current in the ionosphere is complex. It always has a Pedersen component, and the ionosphere is a real energy consumer. Together with energy, an extrinsic electrical current should flow into the ionosphere. The current coming from the generator in front of the bow shock is a part of the extrinsic current. The aim of this paper is to generalize the previously obtained partial solution to the problem of magnetosphere-ionosphere interactions in the region of auroral electrojets, also taking into account the generation of the extrinsic current in front of the bow shock.

Electrodynamics of the vertical coupling processes in the atmosphere-ionosphere system of the low latitude region

Abstract Dynamical, electro-dynamical and electrical coupling processes originating from upward propagation of atmospheric waves, and magnetosphere-ionosphere interaction are responsible for the large degree of variabilities observed in the low latitude ionosphere. One of the most outstanding aspects of its phenomenology is related to the sunset electrodynamical processes responsible for the evening enhancements in zonal and vertical electric fields and the associated spread of F/plasma bubble irregularity development. Recent observational results have provided evidence of significant contribution to their quiet time variability arising from thermospheric wind patterns, upward propagating planetary waves and possibly sporadic E layers. This paper provides an overview and some new results on planetary wave coupling with the equatorial F region, the E layer conductivity as key connecting mechanism, a possibly interactive role by sporadic E layers, and the resulting day-to-day variability in the evening prereversal electric field enhancements with consequences on spread F development.

Volumetric imaging of the auroral ionosphere: Initial results from PFISR

The Poker Flat Incoherent Scatter Radar (PFISR) is the first dedicated ISR built with an electronically steerable array. This paper demonstrates the capabilities of PFISR for producing three-dimensional volumetric images of E -region ionization patterns produced by the aurora. The phase table was configured to cycle through 121 beam positions arranged in an 11 × 11 grid. A 13-baud Barker coded pulse was used, which provided ∼ 1.5 - km range resolution out to a maximum range of 250 km. Backscattered power was converted to electron density by correcting for path loss and applying the Buneman approximation assuming equal electron and ion temperatures. The results were then interpolated onto a three-dimensional cartesian grid. Volumetric images are presented at 5-min, 1-min, and 14.6-s integration times (corresponding to 960, 192, and 48 pulses-per-position, respectively) to illustrate the tradeoff between spatio-temporal resolution and data quality. At 14.6 s cadence, variability in plasma density within the volume appears to be fully resolved in space and time, a result that is supported by both observational evidence and theoretical predictions of ionospheric response times. Some potential applications of this mode for studying magnetosphere–ionosphere interactions in the auroral zone are discussed.