Polar Cap Ionosphere Research Articles

Polar cap plasma convection measurements and their relevance to the modeling of the high‐latitude ionosphere

Plasma convection measurements, using Digisonde ionospheric sounders, have been conducted in the central polar cap at Thule, Greenland (86° CGL) and more recently at Qaanaaq, Greenland (87° CGL), in the auroral oval at the Air Force Geophysics Laboratory Goose Bay Ionospheric Observatory (65° CGL), and at suboval latitudes at Argentia NAS (57° CGL). The plasma convection or ionospheric drift measurements conducted at Thule and Qaanaaq during campaigns from the 1983–1984 winter to the present provide evidence that antisunward convection dominates in the polar cap with velocities typically between 300 and 900 m s−1. Velocity reversals or shears were observed in association with polar cap F layer auroras during quiet magnetic conditions. Observations of the plasma drift at Goose Bay show, as expected, a drift reversal from westward to eastward around midnight CGLT, indicating the rotation of Goose Bay from the evening into the morning convection cell. Observations at Argentia, typically a suboval/trough station, provide evidence under magnetically disturbed conditions for the midnight reversal of the antisunward flow pattern. However, the data at Argentia are generally less consistent under magnetically quiet conditions. This likely indicates the proximity of Argentia to the boundary between corotating and convecting plasma. Recent theoretical calculations of electron density profiles within the high‐latitude/polar cap ionosphere demonstrate that the diurnal f0 F2 variation observed at Thule is controlled by the plasma convection pattern and the associated drift velocities. The model calculations for Bz < 0 and Bz ≈ 0 show factors of 2 to 3 differences in Nmax over Thule, supporting the stated importance of convection pattern and velocity measurements for the modeling of the high‐latitude ionosphere.

Origin of density enhancements in the winter polar cap ionosphere

Coherent and incoherent ground‐based radar measurements of the winter polar cap ionosphere at Thule and Sondrestrom, Greenland have established the existence of “patches” of enhanced ionization which drift across the polar cap in an antisunward, noon‐midnight direction. Associated with these patches is strong radio scintillation activity which severely disrupts ground‐to‐satellite communication systems and interferes with the operation of space surveillance radar at high latitudes. Several recent studies have shown that the source of enhanced ionization is the sunlit subcusp ionosphere rather than production by precipitating energetic particles. However, the question of what causes the patchiness has not been addressed. We study this problem by solving the time‐dependent plasma continuity equation including production by solar ultraviolet radiation, loss through charge exchange, and transport by diffusion and convection E×B drifts. Time and spatially varying, horizontal E×B drift patterns are imposed, and subsequent ionospheric responses are calculated to determine how enhanced plasma densities in the dark polar cap could result from extended transit of relevant flux tubes through regions of significant solar production. This would occur south of the cusp prior to convection as patches across the polar cap. It is found that a density enhancement in Nmax from 7×104 to 5×105 el/cm3 occurs at Thule when a time‐varying convection pattern is included in the simulation. The patch of ionization is generated when an initial convection pattern characterized by an 80‐kV cross‐tail potential and a 12° polar cap radius is abruptly changed to a 100‐kV cross‐tail potential and a 15° polar cap radius. The horizontal extent of the patch is related to the length of time the new convection pattern remains “turned on.”

The spatial coherence of Schumann activity in the polar cap

The spatial coherence of the first two Schumann resonant modes has been studied at two locations in the polar cap separated by 1100 km. Measurements were made at Assistance Bay and Mould Bay, which have geomagnetic latitudes of 83° and 79°, respectively, and satellite time-keeping was employed to accurately synchronise the field stations. The coherence was found to be high, typically 95% for the first Schumann mode, and was unaffected by changes in K p , a storm sudden commencement or a solar flare event. Polarization rotations were observed between the two stations, which could most likely be attributed to the coastline effect. The results are consistent with a stable propagation of Schumann activity from mid to high latitudes that is relatively unaffected by changes in the polar cap ionosphere.

Relationships between the polar cap ionosphere, the interplanetary magnetic field, and the solar wind

The structure and dynamics of the polar cap ionosphere are related to conditions in interplanetary space. This relationship is observed statistically between representative ionospheric and interplanetary parameters. In addition, certain ionospheric patterns may be characterized reliably by interplanetary conditions. The relationships demonstrated in this paper strongly suggest that archival canters for polar ionospheric data should also have available data that describe the conditions of interplanetary space.

Relationship between long‐term phase advances in high‐latitude VLF wave propagation and solar energetic particle fluxes

Anomalous advances of OMEGA VLF navigation system (10.2‐kHz) signals during three extended periods (totaling 60 days) of solar cosmic ray event activity during 1982 are examined and compared with energetic proton, alpha particle, and electron precipitation into the polar cap ionosphere. Time profiles of the OMEGA 10.2‐kHz Hawaii‐to‐Norway path phase advance are found to be almost congruent with the time profiles of the logarithms of the energetic proton fluxes precipitating into the polar cap as determined from instruments aboard the polar orbiting NOAA‐6 satellite and the GOES‐2 geostationary satellite. Although both energetic alpha particles and electrons contribute to the anomalous phase advance experienced by the 10.2‐kHz Hawaii‐to‐Norway OMEGA signal, a simple, empirical algorithm reasonably relates the observed phase advance to the observed differential fluxes of 6‐MeV solar cosmic ray protons.

Global characteristics of northward IMF‐associated (NBZ) field‐aligned currents

Global characteristics of large‐scale field‐aligned current (FAC) systems have been determined by analyzing the magnetic disturbances acquired with the MAGSAT satellite in the southern summer hemisphere during November 1979 through January 1980 for the three cases of the IMF Bz > By > 0, IMF By > Bz > 0, and IMF By > 0 and Bz < 0. Transverse magnetic disturbances having a half wavelength larger than 113 km at the MAGSAT altitudes in the range of ∼350 to ∼550 km were subjected to the present analysis. The global distribution was limited by the MAGSAT orbits over the south pole to latitudes above about 83° ML (magnetic latitude) on the dayside and above about 71°–72° ML on the nightside. The large‐scale FAC systems include the usual region 1 and region 2 systems and the recently found NBZ system. The NBZ system denotes the FACs which flow into and away from the polar cap ionosphere (poleward of the region 1 system) during periods of the IMF Bz > 0. The principal results of the observations include the following: (1) Global characteristics of large‐scale FAC systems consist of two distinctive parts, i.e., the dayside part and nightside part. (2) During periods of the IMF Bz > 0 the dayside part is characterized by a large NBZ system which dominates the entire polar cap and is flanked by a definite region 1 system. These NBZ and region 1 systems on the dayside become progressively asymmetric with respect to the noon‐midnight meridian as the IMF θ angle (measured from the positive z axis in the y‐z plane) rotates from near 0° (Bz > By > 0) toward near 90° (By > Bz > 0): The region 1 and NBZ systems on the prenoonside severely shrink (or almost vanish), and the NBZ and region 1 systems on the postnoonside largely expand across the polar cap and are greatly augmented; the current densities of these NBZ and region 1 systems tend to diminish from the noon toward dawn and dusk. Even when the IMF θ changes to large (>90°) angles by the Bz < 0 and By > 0, this asymmetric NBZ‐type system persists in the dayside polar cap along with an asymmetric region 1 system. (3) During periods of the IMF Bz > 0 the nightside part is characterized by a distinctive NBZ system which develops along with well‐defined region 1 and region 2 systems. For both cases of the IMF Bz > By > 0 and IMF By > Bz > 0 these NBZ and region 1 systems on the nightside exhibit the dawn‐dusk hemispheric asymmetries: The nightside NBZ system is composed of multiple current belts which run from the midnight toward both the dawn and the dusk (parallel with and poleward of the adjoining region 1 system), and their current densities tend to diminish from the midnight toward dawn and dusk; The early morningside region 1 system is confined to a smaller area, and the late eveningside region 1 system expands over a larger area. When the IMF changes to larger (>90°) angles by the Bz < 0 and By > 0, the nightside NBZ system almost vanishes from the polar cap, and well‐defined region 1 and region 2 are enhanced, dominating over the entire hemisphere on both the morningside and the eveningside. The conclusions from this study are the continuous transition in the FAC pattern (NBZ + region 1 + region 2 systems) from IMF Bz > 0 to IMF Bz < 0 and the disconnection between the dayside and the nightside parts of these FAC systems.

On SEC disturbances in the polar cap ionosphere and their relation to the solar wind parameters

Based on the analysis of the occurrence ofSEC disturbances in the polar cap ionosphere under varying solar wind parameters, the relation between the generation ofSEC-type ionospheric disturbances and interplanetary and magnetospheric conditions is discussed. It is emphasized that the Farley-Buneman instability in the E-layer of the ionosphere, reflected in ionograms as anSEC disturbance, depends on the complex effect of the solar wind parameters, the orientation of the interplanetary magnetic field playing an important role.

Long‐term (solar cycle) and seasonal variations of upflowing ionospheric ion events at DE 1 altitudes

A statistical analysis is presented of the long‐term variations of upflowing ionospheric ion (UFI) occurrence morphology in the high‐altitude (8000–23,300 km) auroral and polar cap ionosphere, using data from the Dynamics Explorer 1 Energetic Ion Composition Spectrometer from 1981 to 1984. The study is based on over 100,000 data samples, each consisting of pitch angle distributions of H+ and O+ intensities at 0.01–1, 1–4, and 4–17 keV/e. The data samples were grouped into 91‐day intervals (seasons). Within each interval they were sorted into altitude, invariant latitude, magnetic local time, and magnetic activity (Kp index) bins, and the occurrence frequency and intensity characteristics of H+ and O+ UFI in the respective bins were determined. The September 1981 to May 1984 period coincides with the declining phase of solar cycle 21, when the solar radio flux at 10.7 cm, , decreased from a high of 222 (× 10−22 W m−2 Hz−1) in September 1981 to a low of 93 in November 1983. The observed occurrence frequency, intensity, and angular characteristics of O+ UFI exhibited marked variations which correlate with variations in the solar radio flux (and which envelop those of magnetic activity and seasonal origins). In contrast, the H+ UFI morphology did not display any observable long‐term variations. At both quiet (Kp ≤ 2+) and active times (3‐ ≤ Kp ≤ 5+) the solar maximum O+ data displayed (1) a factor of 2–3 increase in the occurrence frequency of intense UFI; (2) a similar increase in the occurrence frequency of transversely accelerated ions above 8000 km; and (3) an increase in conic abundance (fraction of ion conics in UFI). Together, items (1) and (3) imply about a twofold increase of energetic O+ outflow to the magnetosphere at solar maximum; items (2) and (3) indicate an upward shift in the perpendicular ion acceleration region. The correlation of O+ UFI abundance and occurrence with variations of the solar radio flux, in the absence of magnetic and other geophysical variations, suggests solar activity variations related to the solar flux to be the causative factor in the long‐term variations in observed UFI morphology. Seasonal variations in UFI occurrence were present in O+ and absent in H+. The O+ frequencies in the summer periods were found to be significantly higher than the values in winter periods of comparable solar activity. The observed solar activity and seasonal variations are interpreted in terms of increased ionospheric and atmospheric scale heights at solar maximum and summer solstice, which effectively shift the O+‐H charge exchange altitude upward and facilitate O+ injection to higher altitudes. The observed variations are compared with solar cycle variations in the ring current density, and their magnetospheric implications are discussed.

Ionospheric structures in the polar cap: Their origin and relation to 250‐MHz scintillation

An investigation of the polar cap ionosphere near the peak of the last solar cycle identified polar cap F layer arcs and ionization patches as unique features of the polar cap ionosphere, and as sources of severe scintillations observed on 250‐MHz satellite beacon signals. The continuing investigations in January and December 1983 and January 1984 have shown that arcs and patches persist as the dominant features of the winter polar cap ionosphere during periods of low sunspot numbers. Improved ionospheric soundings made at Thule, Greenland (86°CGL), showed a clear diurnal variation for the occurrence of the patch‐type ionization. Discussion of various possible mechanisms producing the observed ionization patches leads to the conclusion that the solar produced ionosphere equatorward of the dayside cusp is the source region of the ionization patches. Polar plasma convection transports this ionization across the cusp and the central polar cap. The local time dependence of the occurrence of the patches at Thule is shown to be a manifestation of the well‐known universal time control of the polar cap F region. A strong positive solar cycle dependence of the scintillations was measured during three extended campaigns and confirms earlier measurements. The diurnal variation of scintillations is almost flat at solar maximum and has a local time variation very similar to that of the patch type ionization at solar minimum. Both arcs and patches contribute to substantial scintillations around solar maximum, while only the patches are responsible for the considerably weaker scintillations during solar minimum.

On the origin of polar ion streams

It is reaffirmed in this reply that the "classical" polar wind is based on the thermal escape of the light ions H+ and He+. It is asserted that the polar ion flow observations presented in the Gurgiolo and Burch [1985] comment paper, made by the High Altitude Plasma Instrument (HAPI) instrument on Dynamics Explorer‐1 (DE), are O+ and that the probable origin of these ions, which is consistent with the observations, is a highly localized region in the dayside polar cleft ‐ a distinctly different source region than that of the polar wind. Velocity and mass selection, as a result of E × B convection acting on ions from a localized source region in the polar cusp or the dayside polar cap boundary, determines the measured HAPI ion distribution. The Retarding Ion Mass Spectrometer (RIMS) instrument on DE, during the same time period, was measuring the light ion polar wind with flow energies of less than 2.5 eV which originated in the polar cap ionosphere very near the north magnetic pole.

Plasma conditions in the polar ionosphere observed in SPW experiments of PPS system on board the Ohzora (EXOS-C) satellite.

The data of the stimulated plasma wave experiments (SPW) obtained from the planetary plasma sounder (PPS) aboard the Ohzora (EXOS-C) satellite have been analyzed for the initial three months. From the ionograms of SPW experiments 1) vertical profiles of the topside ionosphere, 2) irregularity of the plasma distribution and 3) identification of the modes of the naturally emitted plasma waves have been obtained. The studies on these subjects lead to the following results.(i) In the polar region ionosphere, the auroral particle precipitations generate the intense plasma waves even in the satellite level.(ii) Associated with the generations of the intense plasma waves caused by the particle precipitation, there are irregularities of the plasma distribution in the topside ionosphere which become the origin of the scattering effects on the transmitted RF pulses.(iii) Enhancement of the electron density takes place caused by the enhanced precipitation of the auroral particles in the auroral region. At the same time remarkable heat input which is indicated by increasing of the electron temperature is also confirmed.(iv) Near the auroral zone in the lower latitude side than the auroral regions, there is also the region where the heat input is taking place in milder manner than the case of the auroral regions.(v) Large energy input into the auroral zone triggers a relatively large scale disturbance propagating in the polar cap ionosphere in the form of the traveling ionospheric disturbance (TID).

Theoretical aspects of ionosphere-magnetosphere-solar wind coupling

We initially review magnetospheric plasma distributions emphasising the explanative power of the open model of the magnetosphere. Next we turn attention to the role of MHD wave phenomena both as transients and as standing structures in the coupled flow system. Finally the physics of the magnetopause flux transfer events is discussed. The logic of the existing interpretation suggests a miniature twin vortex convection system should be created in part of the polar cap ionosphere magnetically connecting to the magnetopause flux tube.

Distribution of upflowing ionospheric ions in the high‐altitude polar cap and auroral ionosphere

A statistical study is presented of the occurrence frequency distribution of upflowing ionospheric ions (UFI) in the high‐altitude (8000–23,000 km) auroral and polar cap ionosphere, using measurements from the energetic ion composition spectrometer aboard Dynamics Explorer 1. In this survey, distinction is made between UFI of different masses (H+ and O+), energies (0.01–1, 1–4, and 4–17 keV/e), and pitch angle characteristics (within 20° from , between 20° and 80° from , and transverse to ). The increased statistical accuracy of the data and the added dimensions in this study relative to earlier work at lower altitudes provide a more detailed picture of UFI events. Occurrence frequencies are determined for both H+ and O+ UFI at the different energies as a function of altitude, invariant latitude, magnetic local time, and magnetic activity (Kp index). It is shown that the occurrence frequency and intensity distribution of O+ UFI have a marked magnetic dependence, whereas the H+ UFI occurrence displays little variation with magnetic activity. The occurrence frequency of O+ conics decreases with altitude, in relation to that of H+ conics. Also, ≈90° H+ conics occur 2–3 times more frequently than O+. The invariant latitude‐local time distribution of the occurrence frequency for both H+ and O+ is auroral‐oval‐like in that the frequency peaks at a more equatorward latitude and has a broader latitudinal extent in the nightside than in the dayside. However, this association with the auroral oval is energy‐dependent, the oval for low‐energy UFI being distinctly more poleward than that for energetic UFI. The low‐energy O+ UFI occurrence is relatively uniform in local time; the H+ UFI occurrence frequency distribution shows a broad distribution peaking in the noon sector. Both the H+ and O+ conics distributions display a dawn‐dusk asymmetry in favor of the dusk sector. In the polar cap (poleward of the statistical auroral oval), the H+ and O+ ion outflows (≈2×1024 s−1 and 3×1024 s−1, respectively, at quiet times, and ≈3×1024 s−1 and 1×1025 s−1 at disturbed times) represent a significant ionospheric source to the magnetotail. The results of this study are shown to be consistent with previous, less detailed surveys of UFI at lower altitudes and provide a basis with which to examine possible acceleration mechanisms.

An analysis of the spatial distribution of dayside cleft optical emissions

An analysis of measurements of the 4278‐Å, 5200‐Å, 5577‐Å, and 6300‐Å emissions obtained from a rocket launch through the postnoon dayside cleft into the polar cap ionosphere is reported. The 4278‐Å and 5577‐Å emissions show a clearly defined decrease in intensity at the poleward edge of the dayside particle precipitation, while the 5200‐Å emission extends well into the polar cap with only a slight decrease in intensity. The 6300‐Å emission displays a behavior intermediate between these extremes. The optical data are analysed by using a dynamical model of dayside cleft auroral processes incorporating transport by ion and neutral winds. It is concluded that neutral winds are responsible for modifying the spatial distribution of the 5200‐Å and 6300‐Å emission, while the ion drift component is negligible. In addition, it is found that (1) 80% of the 4278‐Å emission intensity is due to resonance fluorescence in the sunlit cleft ionosphere, (2) the reaction O2(c¹Σu−) + O → O2 + O(¹S) is consistent with the 5577‐Å data if the yield of O(¹S) from the dissociative recombination of O2+ is about 2%, and (3) the rate of the reaction N2+ + O → NO+ + N is apparently higher in the ionosphere than indicated by the laboratory measurements.

Effects of interplanetary magnetic field and magnetospheric substorm variations on the dayside aurora

Photometric observations of dayside auroras are compared with simultaneous measurements of geomagnetic disturbances from meridian chains of stations on the dayside and on the nightside to document the dynamics of dayside auroras in relation to local and global disturbances. These observations are related to measurements of the interplanetary magnetic field (IMF) from the satellites ISEE-1 and 3. It is shown that the dayside auroral zone shifts equatorward and poleward with the growth and decay of the circum-oval/polar cap geomagnetic disturbance and with negative and positive changes in the north-south component of the interplanetary magnetic field ( B z ). The geomagnetic disturbance associated with the auroral shift is identified as the DP2 mode. In the post-noon sector the horizontal disturbance vector of the geomagnetic field changes from southward to northward with decreasing latitude, thereby changing sign near the center of the oval precipitation region. Discrete auroral forms are observed close to or equatorward of the Δ H = 0 line which separates positive and negative H-component deflections. This reversal moves in latitude with the aurora and it probably reflects a transition of the electric field direction at the polar cap boundary. Thus, the discrete auroral forms observed on the dayside are in the region of sunward-convecting field lines. A model is proposed to explain the equatorward and poleward movement of the dayside oval in terms of a dayside current system which is intensified by a southward movement of the IMF vector. According to this model, the Pedersen component of the ionospheric current is connected with the magnetopause boundary layer via field-aligned current (FAC) sheets. Enhanced current intensity, corresponding to southward auroral shift, is consistent with increased energy extraction from the solar wind. In this way the observed association of DP2 current system variations and auroral oval expansion/contraction is explained as an effect of a global, ‘direct’ response of the electromagnetic state of the magnetosphere due to the influence of the solar wind magnetic field. Estimates of electric field, current, and the rate of Joule heat dissipation in the polar cap ionosphere are obtained from the model.

Structure and dynamics of the winter polar cap F region

All‐sky imaging photometer measurements and ionospheric soundings taken at Thule, Greenland (86° corrected geomagnetic latitude), in December 1979 and January 1982 reveal the large‐scale organization of the winter polar cap ionosphere. Three groups of forms have been identified: (1) The most predominant features are sun‐aligned, generally unstructured, subvisual, F region arcs, extending for more than 1000 km (limit of all‐sky field of view) across the polar cap. In general, these arcs drift from dawn to dusk at speeds between 100 and 250 m s−1; however, stagnation of arc drift and drift reversals have been observed. The arcs are produced by soft particle precipitation. (2) During a magnetically disturbed period the arcs disappeared, and large patches of enhanced F region ionization drifted at speeds of 250 to 700 m s−1 across the field of view in the antisunward direction. Although arcs are produced by soft particle precipitation, preliminary results from the Dynamics Explorer satellite do not indicate any localized soft electron precipitation into the patches. (3) On a few occasions both forms were observed simultaneously. Between F region sun‐aligned arcs, which were drifting from dawn to dusk, small patches of ionization were observed moving at much higher speed in the antisunward direction. Both the arcs and the patches appear as strong localized irregularities in the ionospheric soundings. The Doppler information provided by the aircraft's Digisonde 128PS was used to relate backscatter traces to individual arcs or patches and to track individual features over more than 1500 km. For a large number of observations the time variation of measured Doppler velocities suggests specular reflection from electron density enhancements associated with the optical forms, rather than scatter from field‐aligned irregularities imbedded in the arcs or patches. A simple velocity filter applied to the ionogram data permitted the generation of range‐time characteristics for selected ionization drift velocities. A tendency for high velocities to occur during magnetically active periods was found. The ionospheric soundings showed that the F region arcs are bands of enhanced ionization, imbedded in a background ionosphere with a base height (h′F) of approximately 250 km and a critical frequency of approximately 4 MHz (∼2 × 105 el cm−3). The virtual heights in the ionograms did not change during transit of the arcs through the zenith. During the active periods, when the antisunward moving patches were observed, the background ionization dropped to less than 3 MHz (105 el cm−3) while the base height (h′F) moved up to heights above 400 km. The strongly ionized patches (f0 F2 > 8 MHz), however, were observed to reach a minimum virtual range of ∼250 km during the zenith transit, leading during their passage through the zenith to rapid h′F fluctuations of the order of 200 km within minutes.

Comparison of S3‐3 polar cap potential drops with the interplanetary magnetic field and models of magnetopause reconnection

Measurements of the cross polar cap electric potential, by the double probe electric field experiment aboard S3‐3, from 55 orbits in the dawn‐dusk plane are compared with the reconnection electric fields predicted by a variety of models, both theoretical and experimental. The purpose of these comparisons is to understand the extent to which nonreconnection contributions to the polar cap potential must be included, to determine the time response of the polar cap potential to time varying reconnection rates, and to determine the efficiency and saturation levels of the reconnection process. It is found that (1) After several hours of northward interplanetary magnetic field, the cross polar cap potential declines to progressively lower values than those after 1 hour of northward interplanetary magnetic field. This suggests that it requires several hours for the ionospheric polar cap potential to respond to the ‘turning off’ or ‘turning down’ of the reconnection process. (2) The decay of the polar cap potential is used to demonstrate that contributions to the polar cap potential not associated with the reconnection process can be limited to less than 20 kV. It is shown that contributions to the polar cap potential that scale with the dynamic pressure of the solar wind are limited to less than 1 kV. (3) The cross polar cap electric potential is best predicted by a weighted sum of contributions from interplanetary magnetic field parameters over the 4 hours previous to the measurement. The weighting functions have the form of an exponential decay of 2–3 hours with the strongest weight on interplanetary parameters over the 1 hour previous to the measurement. (4) For values of the dawn dusk component of the interplanetary electric field less than about 0.5 mV/m, the measured polar cap potential is consistent with reconnection of all the interplanetary magnetic flux incident on a 30 RE wide frontside magnetopause. For larger values of the dawn dusk component of the interplanetary electric field, the proportion of field lines reconnecting is less, indicating saturation of the reconnection process. The above results are obtained when the extended response time of the magnetosphere to changes in interplanetary parameters is considered. They are independent of the detailed reconnection model assumed, and they are quite different from the viscous contribution, saturation levels of reconnection, and reconnection efficiencies inferred from comparisons of polar cap potentials to single hour averages of interplanetary parameters.

A rocket observation of the 6300 Å/5200 Å intensity ratio in the dayside aurora: Implications for the production of O(¹D) via the reaction N(²D) + O2 → NO + O(¹D)

An analysis of rocket AMF‐VB‐41 measurements of the spatial variation of the I6300/I5200 intensity ratio in the dayside cleft and polar cap ionosphere is reported. The measured variation of the I6300/I5200 ratio is not consistent with significant production of 6300 Å emission via the reaction N(²D) + O2 → NO + O(¹D). An upper limit to the O(¹D) yield of 0.1 is obtained for this mechanism.

The polar ionosphere as a source of energetic magnetospheric plasma

The energetic ion composition spectrometer on Dynamics Explorer‐1 regularly observes ions with energies from a few eV to a few hundred eV flowing upward out of the polar cap ionosphere. Since O+ is usually the dominant species observed, these fluxes are not consistent with the expectations for the polar wind. These fluxes are most likely the source of the tail lobe ion streams and probably represent a significant source of plasma for the maintenance of the plasma sheet.

On the orientation of the polar cap electric field

Using realistic models of the ionospheric conductivity and the field‐aligned currents, we have determined how the distribution of the electric field in the polar cap ionosphere is controlled by the day‐night contrast in conductivity and by the relative strengths of the region 1 and region 2 field‐aligned currents. The sunward directed conductivity gradient acts to set up a space charge in the polar cap which crowds the equipotentials toward the dawn sector for current sources of both region 1 and region 2 polarity; this effectively shifts the polar cap convection pattern toward dawn. Our results show further that for a given conductivity distribution the orientation of the electric field in the central polar cap depends sensitively on the relative strengths of the Birkeland current pairs: for very weak region 2 currents (quiet times) the polar electric field is directed ≈ 60° east of noon, for equal region 1 and 2 currents (disturbed times) the direction is ≈ 10° east of noon, and for stronger region 2 than 1 currents (which may happen on occasion) the electric field points into the prenoon sector. These findings imply that the orientation of the polar cap electric field should serve as a measure or index of the ratio of region 1 to region 2 net current intensity and should possess correlations with geomagnetic activity similar to those of this ratio. This analysis does not include effects of possible source currents in the region of the polar cusp.