Magnetosphere-ionosphere System Research Articles

Response of the Earth's Magnetosphere and Ionosphere to Solar Wind Driver and Ionosphere Load: Results of Global MHD Simulations

Three-dimensional global magnetohydrodynamic simulations of the solar wind–magnetosphere–ionosphere system are carried out to explore the dependence of the magnetospheric reconnection voltage, the ionospheric transpolar potential, and the field aligned currents (FACs) on the solar wind driver and ionosphere load for the cases with pure southward interplanetary magnetic field (IMF). It is shown that the reconnection voltage and the transpolar potential increase monotonically with decreasing Pedersen conductance (σP), increasing southward IMF strength (Bs) and solar wind speed (vsw). Moreover, both regions 1 and 2 FACs increase when Bs and vsw increase, whereas the two currents behave differently in response to σP. As σP increases, the region 1 FAC increases monotonically, but region 2 FAC shows a non-monotonic response to the increase of σP: it first increases in the range of (0,5) Siemens and then decreases for σP > 5 Siemens.

Poker flat radar observations of the magnetosphere–ionosphere coupling electrodynamics of the earthward penetrating plasma sheet following convection enhancements

The plasma sheet moves earthward (equatorward in the ionosphere) after enhancements in convection, and the electrodynamics of this response is strongly influenced by Region 2 magnetosphere–ionosphere coupling. We have used Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) observations associated with two relatively abrupt southward turnings of the IMF to provide an initial evaluation of aspects of this response. The observations show that strong westward sub-auroral polarization streams (SAPS) flow regions moved equatorward as the plasma sheet electron precipitation (the diffuse aurora) penetrated equatorward following the IMF southward turnings. Consistent with our identification of these flows as SAPS, concurrent DMSP particle precipitation measurements show the equatorial boundary of ion precipitation equatorward of the electron precipitation boundary and that westward flows lie within the low-conductivity region between the two boundaries where the plasma sheet ion pressure gradient is expected to drive downward R2 currents. Evidence for these downward currents is seen in the DMSP magnetometer observations. Preliminary examination indicates that the SAPS response seen in the examples presented here may be common. However, detailed analysis will be required for many more events to reliably determine if this is the case. If so, it would imply that SAPS are frequently an important aspect of the inner magnetospheric electric field distribution, and that they are critical for understanding the response of the magnetosphere–ionosphere system to enhancements in convection, including understanding the earthward penetration of the plasma sheet. This earthward penetration is critical to geomagnetic disturbance phenomena such as the substorm growth phase and the formation of the stormtime ring current. Additionally, for one example, a prompt electric field response to the IMF southward turnings is seen within the inner plasma sheet.

The effects of an interplanetary shock on the high-latitude ionospheric convection during an IMF <I>B<sub>y</sub></I>-dominated period

Abstract. On 6 January 1998 an interplanetary shock hit the magnetosphere around 14:15 UT and caused a reconfiguration of the northern high-latitude ionospheric convection. We use SuperDARN, spacecraft and ground magnetometer data to study such reconfiguration. We find that the shock front was tilted towards the morning flank of the magnetosphere, while the Interplanetary Magnetic Field (IMF) was By-dominated, with By<0, IMF Bz>0 and |By|>>Bz. As expected, the magnetospheric compression started at the first impact point of the shock on the magnetopause causing an increase of the Chapman-Ferraro current from dawn to dusk and yielding an increase of the geomagnetic field at the geostationary orbit and on the ground. Moreover, the high-latitude magnetometer data show vortical structures clearly related to the interaction of the shock with the magnetosphere-ionosphere system. In this context, the SuperDARN convection maps show that at very high latitudes above the northern Cusp and in the morning sector, intense sunward convection fluxes appear, well correlated in time with the SI arrival, having a signature typical for Bz>0 dominated lobe reconnection. We suggest that in this case the dynamic pressure increase associated to the shock plays a role in favouring the setting up of a new lobe merging line albeit |By|>>Bz≥0.

OpenGGCM Simulations for the THEMIS Mission

The THEMIS mission provides unprecedented multi-point observations of the magnetosphere in conjunction with an equally unprecedented dense network of ground measurements. However, coverage of the magnetosphere is still sparse. In order to tie together the THEMIS observations and to understand the data better, we will use the Open Geospace General Circulation Model (OpenGGCM), a global model of the magnetosphere-ionosphere system. OpenGGCM solves the magnetohydrodynamic (MHD) equations in the outer magnetosphere and couples via field aligned current (FAC), electric potential, and electron precipitation to a ionosphere potential solver and the Coupled Thermosphere Ionosphere Model (CTIM). The OpenGGCM thus provides a global comprehensive view of the magnetosphere-ionosphere system. An OpenGGCM simulation of one of the first substorms observed by THEMIS on 23 March 2007 shows that the OpenGGCM reproduces the observed substorm signatures very well, thus laying the groundwork for future use of the OpenGGCM to aid in understanding THEMIS data and ultimately contributing to a comprehensive model of the substorm process.

AGW as a seismo-ionospheric coupling responsible agent

The seismo-ionospheric coupling is one of the hot topics of modern scientific research. The importance to shed more light to this process is connected with the study of ionospheric earthquakes precursors in the ionosphere, monitoring of which could be a further step to the scientifically substantiated solution of the problem of earthquakes warning. The energy transmission channel “from below” in the lithosphere–atmosphere–ionosphere–magnetosphere system is analyzed and atmospheric gravity waves are identified as the most probable energy carriers for the troposphere–ionosphere coupling.

Novel sensor design methodology for measurements of the complex solar wind–magnetospheric–ionospheric system

This paper describes the results of an applied novel design methodology for engineering optimised macroscale fluxgate sensors for low-power consumption. The study is used in conjunction with the development of a new fully digital system measuring the Earth’s magnetic field and extracting the necessary parameters for measuring the complex solar wind–magnetospheric–ionospheric system. The results are of interest to the aerospace and defence industries, since macroscale fluxgate sensors exist in airborne and spaceborne systems for many decades. Lowering power consumption is followed by simplification of the accompanying electronic circuits.

Modeling seasonal and diurnal effects on ionospheric conductances, region-2 currents, and plasma convection in the inner magnetosphere

[1] The present study focuses on a modeling of the seasonal and diurnal effects on the dynamics of the coupled magnetosphere-ionosphere system under different solar illumination conditions, to try to reproduce some of the observations concerning the region 2 (R2) field-aligned currents (FAC). This is performed by introducing in the Ionosphere Magnetosphere Model (IMM) the Earth's rotation axis tilt, the dipole axis tilt and an eccentric dipole. The simulated patterns of the R2 FAC agree rather well with the observations. In particular the dayside FAC density is two times greater in the summer hemisphere than in the winter one. The results show that seasonal tilt of the dipole axis affects the distributions of the Pedersen conductances and FAC by 28.5–52.8% and do not have much influence on the distribution of the magnetospheric plasma, which is modified by only 0.9–3.9%. The diurnal variations induced by the tilt of the dipole axis are of the same order of magnitude, 5.5–29% for the Pedersen conductances and FAC and 0.4–7.1% for the magnetospheric plasma. They modulate the interhemispheric asymmetry of the FAC by 26–59%. The eccentric dipole induces an increase (decrease) of the daily variations of the conductances and the FAC by a factor 1.2–2.3 in the Southern (Northern) Hemisphere, irrespective of the season, which contributes to increase the asymmetry between the two hemispheres. This results in an increase of the daily variations of the ion maximum pressure and of the electron maximum energy flux at the December solstice and at the March and September equinoxes, but a decrease at the June solstice. The maximal variation of the magnetospheric plasma distribution amounts to 6.7% at December solstice. These results underline the importance of considering the three different effects at the same time.

Effect of Interplanetary Shocks on theALandDstIndices

[1] The question of how much interplanetary shock (IP) events contribute to the geoeffectiveness of solar wind drivers is assessed through numerical experiments using the WINDMI model, a physics-based model of the solar wind-driven magnetosphere-ionosphere system. Analytic fits to solar wind input parameters (B⊥IMF, usw, nsw) allowed shocks and associated shock-sheath plasma to be removed while leaving other features of the solar wind driver undisturbed. Percent changes in WINDMI-derived AL and Dst indices between runs with and without the observed shock and sheath signatures were taken as a measure of its relative contribution to the geoeffectiveness. The major magnetic storms during 15–24 April 2002 and 3–6 October 2000 were selected for this experiment. In both cases, the IP shock and sheath features contributed significantly to the geoeffectiveness of the solar wind driver. The magnetic field compressional jump is important to producing the changes in the AL during these two storm intervals.

A Wide Field Auroral Imager (WFAI) for low Earth orbit missions

Abstract. A comprehensive understanding of the solar wind interaction with Earth's coupled magnetosphere-ionosphere system requires an ability to observe the charged particle environment and auroral activity from the same platform, generating particle and photon image data which are matched in time and location. While unambiguous identification of the particles giving rise to the aurora requires a Low Earth Orbit satellite, obtaining adequate spatial coverage of aurorae with the relatively limited field of view of current space bourne auroral imaging systems requires much higher orbits. A goal for future satellite missions, therefore, is the development of compact, wide field-of-view optics permitting high spatial and temporal resolution ultraviolet imaging of the aurora from small spacecraft in low polar orbit. Microchannel plate optics offer a method of achieving the required performance. We describe a new, compact instrument design which can observe a wide field-of-view with the required spatial resolution. We report the focusing of 121.6 nm radiation using a spherically-slumped, square-pore microchannel plate with a focal length of 32 mm and an F number of 0.7. Measurements are compared with detailed ray-trace simulations of imaging performance. The angular resolution is 2.7±0.2° for the prototype, corresponding to a footprint ~33 km in diameter for an aurora altitude of 110 km and a spacecraft altitude of 800 km. In preliminary analysis, a more recent optic has demonstrated a full width at half maximum of 5.0±0.3 arcminutes, corresponding to a footprint of ~1 km from the same spacecraft altitude. We further report the imaging properties of a convex microchannel plate detector with planar resistive anode readout; this detector, whose active surface has a radius of curvature of only 100 mm, is shown to meet the spatial resolution and sensitivity requirements of the new wide field auroral imager (WFAI).

Alfvén wings at Earth's magnetosphere under strong interplanetary magnetic fields

Abstract. A number of recent studies have shown that the upstream Mach number may play a significant role in the energy transfer between the solar wind and the magnetosphere. Magnetohydrodynamic (MHD) simulation results of the magnetosphere-ionosphere system are presented that show the transition from nominal solar wind and interplanetary magnetic field driving to extremely strong driving. One of the predominant features of the magnetosphere that becomes apparent during low Mach number conditions is the formation of Alfvén wings above and below the magnetosphere. Alfvén wing are cavities of low flow, and have been observed at Io and Ganymede, both of which reside in regions of sub-Alfvénic flow. It is shown that Alfvén wings exist even during nominal Mach number time periods – the wings fold over to form what has been classically viewed as the magnetotail. The regions of low flow within the Alfvén wing limit the electric field applied across the ionosphere, hence causing the ionospheric cross polar cap potential to be dependent upon the Mach number, and in turn, causing the saturation of the potential.

Present status and future challenges of modeling the Sun–Earth end-to-end system

Several research groups are presently modeling key portions of the solar–terrestrial environment. Large-scale models of the solar corona, of the interplanetary medium, and of the coupled magnetosphere–ionosphere system are providing important insights into the dynamics and temporal evolution of these regions during normal, as well as disturbed, conditions. Some collaborative groups are now working on even more grand syntheses of models and are striving for a true end-to-end modeling capability. The challenges of such integrated modeling are immense: vastly different spatial and temporal scales must be addressed and codes must be synchronized to a high degree. Because much of the underlying physics at micro- and meso-scales remains unknown (or only poorly known), many key interface regions must be treated using empirical or semi-empirical methods. Validating the results from such global-scale models is, in itself, a major undertaking. And last, but by no means least, the question of how available (sparse) data are assimilated into end-to-end models remains a major challenge to the community. This paper provides an overview of the present status and future challenges in end-to-end modeling of the Sun–Earth system.

The magnetosphere–ionosphere system from the perspective of plasma circulation: A tutorial

This tutorial review examines the role of O + in the dynamics of magnetosphere–ionosphere coupling. The life cycle of an O + plasma element is considered as it circulates from the mid- to high-latitude ionosphere. Energization and diversion of the convecting plasma element into outflows involves Alfvénic turbulence at the low-altitude base of the cusp and plasmasheet boundary layer and in downward-current “pressure cookers.” Observational evidence indicating that O + dominates the plasmasheet and ring current during extreme storm intervals is reviewed. The impacts of an O +-enriched plasma on solar wind–magnetosphere–ionosphere coupling are considered at both the micro and global scales. A synthesis of results from observation, theory and simulations suggests that the presence of O + in the magnetosphere is both a disruptive and a moderating agent in maintaining the balance between dayside and nightside magnetic merging.

Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals

Abstract. We investigate variations in the location and intensity of the auroral electrojets during magnetic storms and substorms using a numerical method for estimating the equivalent ionospheric currents based on data from meridian chains of magnetic observatories. Special attention was paid to the complex structure of the electrojets and their interrelationship with diffuse and discrete particle precipitation and field-aligned currents in the dusk sector. During magnetospheric substorms the eastward electrojet (EE) location in the evening sector changes with local time from cusp latitudes (Φ~77°) during early afternoon to latitudes of diffuse auroral precipitation (Φ~65°) equatorward of the auroral oval before midnight. During the main phase of an intense magnetic storm the eastward currents in the noon-early evening sector adjoin to the cusp at Φ~65° and in the pre-midnight sector are located at subauroral latitude Φ~57°. The westward electrojet (WE) is located along the auroral oval from evening through night to the morning sector and adjoins to the polar electrojet (PE) located at cusp latitudes in the dayside sector. The integrated values of the eastward (westward) equivalent ionospheric current during the intense substorm are ~0.5 MA (~1.5 MA), whereas they are 0.7 MA (3.0 MA) during the storm main phase maximum. The latitudes of auroral particle precipitation in the dusk sector are identical with those of both electrojets. The EE in the evening sector is accompanied by particle precipitation mainly from the Alfvén layer but also from the near-Earth part of the central plasma sheet. In the lower-latitude part of the EE the field-aligned currents (FACs) flow into the ionosphere (Region 2 FAC), and at its higher-latitude part the FACs flow out of the ionosphere (Region 1 FAC). During intense disturbances, in addition to the Region 2 FAC and the Region 1 FAC, a Region 3 FAC with the downward current was identified. This FAC is accompanied by diffuse electron precipitation from the plasma sheet boundary layer. Actually, the triple system of FAC is observed in the evening sector and, as a consequence, the WE and the EE overlap. The WE in the evening sector comprises only the high-latitude periphery of the plasma precipitation region and corresponds to the Hall current between the Region 1 FAC and Region 3 FAC. During the September 1998 magnetic storm, two velocity bursts (~2–4 km/s) in the magnetospheric convection were observed at the latitudes of particle precipitation from the central plasma sheet and at subauroral latitudes near the ionospheric trough. These kind of bursts are known as subauroral polarization streams (SAPS). In the evening sector the Alfvén layer equatorial boundary for precipitating ions is located more equatorward than that for electrons. This may favour northward electric field generation between these boundaries and may cause high speed westward ions drift visualized as SAPS. Meanwhile, high speed ion drifts cover a wider range of latitudes than the distance between the equatorward boundaries of ions and electrons precipitation. To summarize the results obtained a new scheme of 3-D currents in the magnetosphere-ionosphere system and a clarified view of interrelated 3-D currents and magnetospheric plasma domains are proposed.

A numerical model of the ionospheric signatures of time-varying magnetic reconnection: III. Quasi-instantaneous convection responses in the Cowley-Lockwood paradigm

Abstract. Using a numerical implementation of the cowlock92 model of flow excitation in the magnetosphere-ionosphere (MI) system, we show that both an expanding (on a ~12-min timescale) and a quasi-instantaneous response in ionospheric convection to the onset of magnetopause reconnection can be accommodated by the Cowley-Lockwood conceptual framework. This model has a key feature of time dependence, necessarily considering the history of the coupled MI system. We show that a residual flow, driven by prior magnetopause reconnection, can produce a quasi-instantaneous global ionospheric convection response; perturbations from an equilibrium state may also be present from tail reconnection, which will superpose constructively to give a similar effect. On the other hand, when the MI system is relatively free of pre-existing flow, we can most clearly see the expanding nature of the response. As the open-closed field line boundary will frequently be in motion from such prior reconnection (both at the dayside magnetopause and in the cross-tail current sheet), it is expected that there will usually be some level of combined response to dayside reconnection.

Probability tails of wavelet coefficients of magnetometer records

[1] The ground-based magnetometer network has long been a powerful tool for monitoring and observing the variations of the currents flowing in the magnetosphere-ionosphere (M-I) system. The time series of magnetograms are nonstationary and their frequency behavior changes over time. They are therefore not amenable to traditional time domain or spectral (Fourier) analysis. In recent years, various new mathematical techniques have been developed to analyze magnetometer data and the wavelet technique has stood out as being particularly relevant. In order to correctly make statistical inferences based on wavelet analysis, the wavelet coefficient distributions of magnetograms must be examined. In this work, we apply the discrete wavelet transform to the 1-min magnetometer records and then use several statistical techniques to analyze the probability distributions of the wavelet coefficients. It is found that the distributions of these coefficients for both storm and quiet times are highly nonnormal and can be classified as being heavy tailed. This finding suggests that when applying statistical techniques to the wavelet coefficients of the magnetograms, one must make sure that these techniques are robust to large departures from Gaussianity manifested by the presence of heavy probability tails. It is also found that the tail indexes for storm times are on average smaller than those of quiet times, which reflects the stronger impulsive and nonstationary features in magnetometer data during storm times, and the shifts are most significant for the wavelet coefficients corresponding to physical scales of 4–8 min.

Oscillation of Quasi-Steady Earth's Magnetosphere

A three-dimensional magnetohydrodynamics (MHD) code is designedspecially for global simulations of the solarwind–magnetosphere–ionosphere system. The code possesses a highresolution in capturing MHD shocks and discontinuities and a lownumerical dissipation in examining possible instabilities inherent inthe system. The ionosphere is approximated by a spherical shell withuniform height-integrated conductance. The solar wind is steady, and theinterplanetary magnetic field is either due northward or due southward.The code is then run to find solutions of the whole system. It is foundthat the system has never reached a steady state, but keeps oscillatingwith a period of about one hour in terms of density variation at thegeosynchronous orbit. However, if a certain artificial resistivity isadded either in the whole numerical box or in the reconnection sitesonly, the reconnections change from intermittent to steady regime andthe oscillation disappears accordingly. We conclude that the Earth'smagnetosphere tends to be in a ceaseless oscillation status because ofthe low dissipation property inherent in the magnetospheric plasma, andthe oscillation may be driven by intermittent magnetic reconnectionsthat occur somewhere in the magnetopause and/or the magnetotail.

Space- and ground-based investigations of solar wind–magnetosphere–ionosphere coupling

This paper provides a brief review of the understanding of the coupled solar wind–magnetosphere–ionosphere system that can be attained from observations of the size of the ionospheric polar caps from space and the ground. These measurements allow the occurrence and rate of dayside and nightside reconnection to be deduced. The former can be correlated with upstream interplanetary magnetic field observations to give an estimate of the effective length of the dayside reconnection X-line. The latter allows a preliminary statistical study of flux closure during substorms and other, smaller nightside reconnection events.

Cases for which the Earth's magnetosphere does not act as a “low-pass filter”

In the first place, this work will demonstrate that there are at least several cases for which the magnetosphere–ionosphere system “does not behave as a low-pass filter”, or better it transmits high frequencies. In one selected case study, a monochromatic solar wind pressure wave in the Pc5 band directly excites the same frequency of ground pulsations. The other two case studies are composed of repetitive solar wind pressure pulses, like quasi-periodic solar wind pressure waves, which are associated to ionospheric currents in a one-to-one correspondence. Our most interesting case shows that the magnetosphere sometimes has the ability to respond in such small timescales as 2.7 min. The same case provides strong evidence that the successive solar wind pressure pulses excite a global mode wave in the magnetosphere. We further discuss these events under the perspective established by the three recent papers of Sarafopoulos (2004a. Distinct solar wind pressure pulses producing convection twin-vortex systems in the ionosphere. Annales Geophysicae 22, 2201–2211; 2004b. Repetitive X-line Hall current structures over the dawnside ionosphere induced by successive exo-magnetosphere pressure pulses. Annales Geophysicae 22, 4153–4163; 2005. Pseudo-field line resonances in ground Pc5 pulsation events. Annales Geophysicae 23, 593–608) that the solar wind pressure pulses produce pseudo-field-line resonances on the ground station data; and this result certainly do not support the cavity mode model. Previously, many researchers have suggested that the magnetosphere acts as low-pass filter with a threshold separating the driven from the loading–unloading processes that are based on the inherent system dynamics. Essentially, their works are based on the AE (or AL) index. Our suggestion here is that the methodology whereby the AE index was introduced may eliminate the power density in high frequencies. The AE index may fail to carry the high-frequency part of input information. Neighboring ground stations with a phase-shift in their recorded waveforms may produce a no fluctuating AE index. The research efforts using AE may result in an error estimate of the cutoff frequency for the magnetosphere considered as a low-pass filter. Additionally, these works are not able to capture high-frequency couplings between the solar wind and the magnetosphere because they use low-resolution measurements. The presented high-frequency couplings emphasize the complementary character of this work. We shall not search special mechanisms or conditions permitting or preventing the direct entry of Pc5 frequency activity on Earth and any statistical approach is beyond the scope of this paper.

High-latitude electromagnetic and particle energy flux during an event with sustained strongly northward IMF

Abstract. We present a case study of a prolonged interval of strongly northward orientation of the interplanetary magnetic field on 16 July 2000, 16:00-19:00 UT to characterize the energy exchange between the magnetosphere and ionosphere for conditions associated with minimum solar wind-magnetosphere coupling. With reconnection occurring tailward of the cusp under northward IMF conditions, the reconnection dynamo should be separated from the viscous dynamo, presumably driven by the Kelvin-Helmholtz (KH) instability. Thus, these conditions are also ideal for evaluating the contribution of a viscous interaction to the coupling process. We derive the two-dimensional distribution of the Poynting vector radial component in the northern sunlit polar ionosphere from magnetic field observations by the constellation of Iridium satellites together with drift meter and magnetometer observations from the Defense Meteorological Satellite Program (DMSP) F13 and F15 satellites. The electromagnetic energy flux is then compared with the particle energy flux obtained from auroral images taken by the far-ultraviolet (FUV) instrument on the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft. The electromagnetic energy input to the ionosphere of 51 GW calculated from the Iridium/DMSP observations is eight times larger than the 6 GW due to particle precipitation all poleward of 78° MLAT. This result indicates that the energy transport is significant, particularly as it is concentrated in a small region near the magnetic pole, even under conditions traditionally considered to be quiet and is dominated by the electromagnetic flux. We estimate the contributions of the high and mid-latitude dynamos to both the Birkeland currents and electric potentials finding that high-latitude reconnection accounts for 0.8 MA and 45kV while we attribute <0.2MA and ~5kV to an interaction at lower latitudes having the sense of a viscous interaction. Given that these conditions are ideal for the occurrence of the KH instability at the magnetopause and hence the viscous interaction, this result suggests that the viscous interaction is a small contributor to coupling solar wind energy to the magnetosphere-ionosphere system.

Heater-induced phenomena in a coupled ionosphere–magnetosphere system

Experimental results from HF pumping experiments in the nightside auroral E and F region are reported. The experiments were carried out by the use of the EISCAT HF heating facility located near Tromsø, Norway, allowing HF pumping the ionosphere in a near magnetic field-aligned direction. We present experimental results from multi-instrument observations related to heater-induced phenomena in a coupled ionosphere–magnetosphere system. The following results have been observed on different occasions: a reverberation effect in scattered signals observed simultaneously on two diagnostic paths which is an indication of Alfvén wave generation. This phenomenon was seen under specific disturbed background geophysical conditions, namely, a high electron density in the F region up to 8 MHz produced by soft electron precipitation from the magnetosphere along with low electron density in lower ionosphere; increased ionospheric electric fields; ion outflows from the ionosphere. On another occasion a magnetospheric response to heater turning on and off was found from magnetic pulsation observations over a frequency range up to 5 Hz (the upper frequency limit of the sensitive magnetometer at Kilpisjarvi, located near Tromsø). The response manifests itself about 1 min after the heater is turned on and off. Other results have shown the modification of a natural auroral arc and local spiral-like formation. It is thought that a local heater-driven current system is formed. An interesting feature is the generation of the heater-induced ion outflows from the ionosphere. They are observed in night hours under both quiet and disturbed magnetic conditions.