SA33A-1053
Stormtime Electric Fields at High-Equatorial Latitudes as Observed by the Magnetometers, Incoherent-Scatter Radar and Satellite
During the main phase of a geomagnetic storm, the convection electric field was significantly enhanced by strong southward IMF, and was transmitted to the polar ionosphere along geomagnetic field lines. The convection electric field penetrated into low latitude ionosphere, driving DP2 currents in the global ionosphere, composed of two-cell Hall current vortices at high latitude and Pedersen currents amplified by the Cowling effect at the dayside geomagnetic equator. The penetrated electric field was mapped into the ionospheric F-region and further into the inner magnetosphere. As a result, we observed upward motion of the ionosphere at low latitude on the dayside, and rapid development of the storm ring current. During the recovery phase of the storm, on the other hand, the electric field was reversed due to the overshielding effect, resulting in the equatorial counter-electrojet. It is shown that the overshielding occurred when the auroral oval shifted rapidly poleward. Both the equatorial DP2 currents and the counter-electrojet contributed to enhance the magnitude of the geomagnetic storm at the dayside geomagnetic equator, of which magnitude was 2.7 times that of the low latitude storm. The observational facts suggest that the convection electric field penetrated to low latitude may play a crucial role in development of the ring current, while the overshielding may reduce or reverse the electric field in the inner magnetosphere, ceasing the development of the ring current. It should be noted that another kind of reversed electric field often appears during the storm main phase, which might be caused by the disturbance dynamo. In this talk, we show several examples of these three kinds of stormtime electric fields in the global ionosphere and in the inner magnetosphere, using data from the magnetometer network, Jicamarca incoherent-scatter radar and AKEBONO satellite.
SA33A-1054
Latitude and local time dependences of ionospheric currents during a geomagnetic storm
In order to clarify the distribution of electric field and current in the middle- and low-latitude ionosphere during a geomagnetic storm, we analyzed ground magnetic disturbances for the storm on September 7, 2002, with the minimum SYM-H value of -168 nT. In this analysis, we investigate magnetic field deviations of the H-component from the SYM-H as functions of the magnetic latitude (MLAT) and local time (MLT). The deviation at the low latitude (10-30 degrees in MLAT) was positive and negative in the dawn and dusk sectors, respectively, during the main phase of the storm. This local time tendency represents a remarkable dawn-dusk asymmetry in the storm-time ring current. On the other hand, the deviation at the middle latitude (35-55 degrees in MLAT) was negative and positive in the morning (9-12 h MLT) and afternoon (13-15 h MLT) sectors, respectively. This tendency coincides with that of the DP2 currents. When the interplanetary magnetic field turned northward, the storm turned into the recovery phase. We found that the deviation at the middle latitudes in the early recovery phase was in opposite sense to that of the deviation during the main phase. This implies that the overshielding occurred at the middle latitudes, due to an abrupt decrease of the convection electric field associated with the recovery phase. This may suggest that the relative magnitude of the convection and shielding electric fields determines the phase of geomagnetic storm. Finally, during the late recovery phase, the dawn-dusk asymmetry both at the middle and low latitudes became weak in all magnetic local time because of symmetrized ring current. In future analysis, we should divide storm-time magnetic field variations into the origins of ring and ionospheric currents. In this talk, we will investigate the temporal and spatial developments of the latitude and local time distributions of ionospheric currents and electric field in the entire region from the magnetic equator to middle latitude.
SA33A-1055
Parametrization of ion Upwelling for Auroral Precipitation
Plasma outflow into the magnetosphere is of considerable importance for mass loading of the magnetosphere. It is generally believed that ion outflow occurs in two steps, the first of which is upwelling of ions which increases the concentration of heavier ions at higher altitudes as the source population for secondary upward acceleration. In this simulation study, heating and ionization due to auroral electron precipitation is considered the main cause of for ion upwelling. The model solves neutral and ion momentum equations which include basic plasma transport coefficients, ionization and recombination terms as well as plasma-neutral collisions. The model also includes generalized Ohm's law considering self-consistent terms for resistivity, electron pressure gradients and Hall physics. The energy equations consider temperature contact terms between electrons, ions, and neutrals and the heat conduction term. Our model results demonstrate that ion upwelling is caused by pressure gradient forces due to ionization and electron heating from auroral precipitation. Softer auroral precipitation leads to larger upward fluxes and velocities because pressure gradients develop at higher altitudes in less collision dominated regions. Input parameters of the characteristic energy and the energy flux are used to parameterize properties of the ion upwelling such as particle fluxes, velocities, force densities, and acceleration.
SA33A-1056
Pulsating Ion and Neutral Polar Winds
New simulations at Utah State University using the 3-D neutral and ion polar wind code with realistic convection and precipitation inputs for a large geomagnetic storm have been conducted. The model solves for five species; H+, O+, Hs, Os, and e- in a background neutral atmosphere. The simulation shows a pulsing of the total particle outflow on the order of hours, with large outflows occurring over spatially separated areas, principally in the auroral oval. The neutral steam outflows (the neutral polar wind) are produced in charge exchange reactions between the ion polar wind and the background thermal and geocoronal neutrals. The neutral hydrogen stream total hemispheric number flux is highly correlated to the electron precipitation energy input, the H+ and O+ ions show large upward and downward fluxes related to the amount of heating added to the auroral oval by the precipitating electrons, and the neutral oxygen stream particles show a downward total number flux at all times due to a lack of kinetic affects in the model. Ionosphere/magnetosphere coupling through mass, momentum, and energy transport has been calculated as a flow from an entire polar cap region in terms of the number of particles per second. This number is typically on the order of 1025 particles/sec for H+, and 1025-1026 particle/sec for O+, which is consistent with the model results. Also, the outflow flux at high-latitudes has been shown, using satellite data, to vary temporally by as much as four orders of magnitude, and the model results also demonstrate the temporal variability of the vertical flows.
SA33A-1057
High-Latitude Ionospheric Upwelling as a Function of Cross-Cap Potential and Solar Wind Pressure
We have examined characteristics of the vertical ion flux of thermal O+ in the topside high-latitude ionosphere from under a variety of solar activity conditions from 1998 to 2002 using measurements of the vertical ion drift and ion number density made by the DMSP F13 spacecraft. During geomagnetically quiet times typical upward fluxes of approximately 108--109 cm-2s-1 are observed in the auroral zones with somewhat smaller downward fluxes in the polar caps. Immediately following the onset of a geomagnetic storm upward fluxes reach and sometimes exceed 1010 cm-2s-1 and are observed with vertical velocities of 500--1500 m s-1. At the same time downward fluxes at the higher latitudes reach unusually high values of 109 cm-2s-1. Separately integrating the upwards and downwards fluxes over the high-latitude region (auroral zone and polar cap) for each spacecraft pass allows for the observation of total upflow/downflow during various geomagnetic activity levels. Analysis of these integrated fluxes indicates a positive correlation of the upward and downward flux magnitudes to the polar cross-cap potential. In addition, the magnitude of the upwelling flux increases by approximately a factor of 2 during the change from conditions of low solar wind dynamic pressure to high dynamic pressure. Solar cycle effects will also be discussed.
SA33A-1058
Comparisons of Thermal Plasma Upflow observed on DMSP with escaping ion fluxes observed at Polar during geomagnetic quiet intervals
Most magnetospheric models lack species dependent dynamics. O+ is known to be present in the magnetosphere and to have a significant impact on some magnetospheric processes. One of the significant hurdles to including heavy ions such as O+ into magnetospheric models is a method to calculate or estimate the fraction of upwelling heavy ions with less than escape energy that acquire escape energy above the ionosphere. This paper presents a statistical comparison of thermal plasma upwelling flux with the flux of escaping ions. The thermal plasma is measured at 800 km by the Defense Meteorological Satellite Program (DMSP) Special Sensors-Ions Electrons and Scintillation (SSIES) instrument suite. The escaping flux of ions is measured by the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) on the Polar spacecraft at ~7,000 km over the southern polar cap. This is a climatological study and as such focuses on geomagnetically quiet intervals determined by Dst less than -50nT during the solar minimum period (1996 - 1998) of solar cycle 23.
SA33A-1059
The Effect of Downward Electron Heat Flow and Electron Cooling Processes in the High- Latitude Ionosphere
The electron energy balance in the terrestrial ionosphere is affected by numerous local heating and cooling processes, as well as transport processes. The thermal electrons gain energy from photoelectrons, auroral electrons, hot thermal ions, and a downward flow of heat from high altitudes. The thermal electrons lose energy in elastic collisions with ions and neutrals (N2, O2, O, He, H), rotational excitation of N2 and O2, vibrational excitation of N2 and O2, excitation of the fine structure level of atomic oxygen, and electronic excitation of atomic oxygen. The transport processes include thermal conduction and thermoelectric heat flow. Recently, new cooling rates have been calculated that are substantially different from those in current use, which are more than thirty years old. We will present model simulations showing the impact these new cooling rates have on the electron temperatures and ion densities in the mid- and high-latitude ionosphere. Additionally, recent work based on DMSP satellite data has made it possible to estimate the proper values of the downward electron heat flow in the polar cap. This important parameter has typically been ignored in the past, due to a lack of measurements. We present the results of model simulations driven by the new estimates of the heat flow.
SA33A-1060
Thermospheric Wind Gradients and Horizontal Divergence Measured During the HEX-1 Rocket Mission
On March 25, 2003, three trimethyl-aluminum trails were deployed by rockets near a stable pre-midnight auroral arc lying 400 km north of Poker Flat, Alaska. Drift of these trails over time yielded wind measurements in the height range 120 km to 180 km. The trail geometry allowed direct height-resolved measurements of all three wind components, as well as their meridional and vertical gradients. Although zonal gradients of the three wind components were only directly measured at one height, the zonal gradient of zonal wind could be inferred indirectly, using the equation for mass conservation. Our analysis yielded horizontal divergence estimates up to 0.002 s-1, which is surprisingly large given that very quiet geomagnetic conditions prevailed. As a possible mechanism, we examine the hypothesis that the observed wind perturbations are primarily the signature of a monochromatic field of plane gravity waves, propagating approximately geomagnetically westward along the auroral oval, and parallel to the background wind. We show that a plane monochromatic perturbation obeying the gravity wave dispersion and polarization relations can be fitted to match, in most cases, the amplitudes and phases of the observed wind components and of the inferred horizontal divergence. Although the wind perturbation amplitudes are large (22 m s-1 vertically and 75 m s-1 horizontally) the inferred wave parameters are well within the ranges observed previously. Further, because the calculated dissipation time constant for the fitted perturbation is long compared to the wave period, the inferred wave field is one that could reasonably exist at these heights.
SA33A-1061
Thermospheric Winds in an Intense Auroral Substorm: The HEX-2 Sounding Rocket Missions
Thermospheric composition at high latitudes is altered through heating in auroral substorms and geomagnetic storms. The HEX-1 investigation in March 2003 targeted a stable, quiet arc to directly observe the upward, vertical winds believed to be driven by this heating. However, no upward winds were observed. A logical conclusion at the time was that too little energy was delivered to drive the anticipated vertical motions in the thermosphere. To test this, a more complex HEX-2 investigation was executed with rocket flights into the lower thermosphere under conditions of intensely active auroral. Specifically, four sounding rockets were launched within 16 minutes into intense aurora on February 14, 2007, some 42 minutes after substorm onset. The flights were designed to release six nearly vertical TMA puffed trails over a range of altitudes, as well as a single nearly horizontal trajectory created, as in HEX-1, by an in-flight reorientation of the third stage before ignition and subsequent dispersal of TMA at nearly constant altitude over a wide range of latitudes. Neutral wind vectors were obtained by ground-based triangulation of individual TMA puffs. Densities and temperatures were obtained on all up and down legs of the vertical trajectories with cold cathode ionization gauges. The SuperDARN and AMISR radars provided concurrent observations of the ionosphere. As expected, the two missions observed quite dissimilar wind fields. But unexpectedly, HEX-2 encountered a weaker and more spatially uniform wind field than HEX-1, despite HEX-2 having flown during much more disturbed geomagnetic conditions. Equally unexpectedly, HEX-2 also failed to observe any significant upward wind. These and other observations will be presented and discussed, along with some developing interpretations.
SA33A-1062
Comparisons of Observational and Model Estimates of Auroral Electron Precipitation
Upper atmosphere numerical models require accurate specification of magnetospheric forcing of the high latitude ionosphere-thermosphere system. This includes both the imposed electric field and the energetic particle precipitation energy flux and distribution. The former has a greater effect on ionosphere/thermosphere changes during geomagnetic storms, but the latter is also crucial because it controls the conductance pattern through which magnetospheric currents flow, alters the chemical composition of the polar regions, and contributes to heating. However, there is little agreement on various estimates of the basic magnitude of auroral energy fluxes. In this paper, we examine several empirical representations of the electron hemispheric power and morphological distribution, compare them to each other, and to magnetospheric MHD model specifications. These are also compared to measurements obtained during selected auroral events. We then apply differing auroral forcing to the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) to evaluate the effect on some key observables: global neutral density and auroral nitric oxide. The model estimates are compared to measurements of these quantities to lend some guidance to the process of obtaining appropriate levels of auroral precipitation for coupled model simulations.
SA33A-1063
Polar-Region Distributions of Poynting Flux: Global Models Compared With Observations
Low-altitude distributions of electric potential, field-aligned current and Poynting flux derived from the Lyon- Fedder-Mobarry global simulation model of the magnetosphere are compared with distributions derived from SuperDARN, the Iridium satellite constellation, and the Weimer 2005 empirical model for a one-hour interval (1400-1500 UT) on 23 November 1999 during which the interplanetary magnetic field was steady and southward. Synthetic measurements along a pseudo-satellite track are also obtained from each distribution and compared with measurements from the DMSP F13 satellite. Previous studies of the event are supplemented here with updated simulation results for the electric potential and field-aligned currents, new simulation diagnostics for the Poynting flux incident on the ionosphere, and comparisons of observational and simulation results with the Weimer empirical model. The location and extent of the simulated Poynting fluxes that occur in the afternoon sector, between the Region-1 and 2 currents, are consistent with the observed and empirically modeled locations, but the magnitudes exhibit significant differences (locally up to ~100% both higher and lower). Elsewhere, the distribution of simulated fluxes more closely resembles the empirically modeled values than the observed ones and in general is greater in magnitude by about 100%. Additionally, the fraction of simulated Poynting flux that flow into the polar cap region (above 75 deg) is about one third of the total flowing into the ionosphere above 60 deg; a similar value is found for both the observed and the empirically modeled fluxes. The effect of including the parallel potential drop in the self-consistent mapping of electric potential between the ionosphere and inner boundary of the simulation domain is also examined. Globally the effect is small (< 5%); however, in regions where the field-aligned potential drop is appreciable, local changes of 100% or more are found in the magnitude of the simulated Poynting flux.
SA33A-1064
Electromagnetic Energy Deposition and Transport during the November 2004 Storm
During the magnetic storm of 9 - 11 November 2004, the polar-orbiting DMSP, CHAMP and GRACE satellites sampled ionospheric and thermospheric responses at local times extending from dusk into the post-midnight sector. We compare Poynting fluxes measured by sensors on four DMSP satellites on 10 November with those predicted by the Weimer model. Both show intermittent, peak energy deposition rates of 80 mW/m**2. during the day. Neutral densities inferred from the accelerometers on CHAMP and GRACE showed remarkably fast increases during times when Poynting fluxes were high. This suggests that rapid coupling between ions and neutrals leads to fast changes in thermospheric densities during storms, behavior not captured by current models. Further, local neutral density maxima are seen to progress from high to low latitudes on orbit-to-orbit time scales, suggesting that stormtime winds transport much of the deposited energy from the auroral oval towards the equator.
SA33A-1065
Effects of high-latitude ionospheric electric field variability on global thermospheric Joule heating and mechanical energy transfer rate
Effects of high-latitude ionospheric electric field variability on the estimation of Joule heating and mechanical energy transfer rate are investigated by incorporating realistic spatial and temporal characteristics of electric field variability derived from observations into the forcing of a thermosphere and ionosphere electrodynamics general circulation model. First, the characteristics of sub-grid scale variability are examined from a spectral analysis of Dynamic Explorer-2 (DE-2) plasma drift measurements. The analysis reveals that the sub-grid scale electric field varies with magnetic altitude, magnetic local time, interplanetary magnetic field, and season in a manner distinct from that of the resolved-scale electric field and of the climatological electric field. Second, the spatial-temporal structure of resolved-scale electric fields are characterized from various electromagnetic observations taken during the storm period of January 10-11, 1997, using a space-time separable covariance model derived from the DE-2 observations. Finally, the modeling results show that the estimated amount of Joule heating in the thermosphere is significantly altered by taking into account the electric field variability and its space-time structure.
SA33A-1066
Thermospheric Temperature Variability from Incoherent Scatter Radar Long-duration Experiments at Millstone Hill
Incoherent scatter radar experiments at Millstone Hill conducted for 30 consecutive days have been conducted in October 2002, September 2005 and March 2006, enabling this study of the day-to-day thermospheric variability. Based on the radar's plasma temperature and electron density observations, daytime thermospheric parameters, in particular, exospheric and thermobase temperatures, are derived using an established technique. Solar and magnetic influences on the thermospheric variability are investigated. Our results indicate, even for very weak magnetic activity, a very clear correlation between the upper atmospheric temperaure and Dst index. There is also a very clear correlation between the temperature and solar 10.7 cm flux. It is shown that the major part of the day-to-day varibaility in thermospheric temperature at Millstone Hill is due to solar flux variability with additional contribution due to magnetic activity. We also discuss quantively effects of these major sources of variability.
SA33A-1067
Low and middle latitude westward thermospheric wind jets during geomagnetic storms
Previous studies have shown that at low and middle latitudes zonal thermospheric winds can be significantly enhanced between ~150 km and 200km, forming westward jets during and after major geomagnetic storms. In this presentation we study these jets using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. We found that: 1) there are significant enhancements of westward neutral wind at low and middle latitudes during and after the storm around 180 km in the model simulations; 2) a diagnostic analysis of the model outputs indicates that momentum advection from the high latitudes to the low and middle latitudes are the cause of these neutral wind jets; and 3) the specific altitude range in which the jets occur is related to the height distribution of the ion drag coefficients at high latitudes.
SA33A-1068
Thermal Expansion Effects on F-region Height Changes During Geomagnetic Storms
The increased high-latitude energy input during geomagnetic storms, mainly resulting from Joule heating, causes the atmosphere to heat and expand at thermospheric heights. As a consequence, a global wind surge is generated and propagates from both polar regions to low latitudes and into the opposite hemisphere. Those winds are driven by the pressure inequalities due to temperature differences between high and equatorial regions. Divergence in horizontal winds drive vertical upward winds across pressure surfaces, the so-called "divergence velocity". Conversely, convergent horizontal winds are associated with a downward "divergence wind". The circulation is closed by a return flow in the lower thermosphere. At the same time, the expansion and contraction of a fixed pressure level atmospheric parcel cause vertical winds, the so-called "barometric velocity". Barometric winds are related to the thermal expansion of the atmosphere, while vertical divergence winds are associated to the conservation of mass relative to the levels of fixed pressure. In this study, the relative contribution of the horizontal thermospheric winds, the divergence winds and the barometric winds in the thermosphere-ionosphere response to geomagnetic storms is examined and analysed using the global, three- dimensional, time-dependent, non-linear coupled model of the thermosphere, ionosphere, plasmasphere, and electrodynamics (CTIPe). In order to simulate a thermospheric storm-time heating which does not create the global wind surge at high latitudes that propagates towards the equator, the neutral temperature in the thermosphere is uniformly enhanced. By doing this, it is expected no changes in the horizontal thermospheric winds, so the uplift of hmF2 by the horizontal wind mechanism is due to the vertical movement of the pressure level caused by the heating of the thermosphere. The neutral molecules on this pressure level move upwards, colliding with ions and electrons and driving them up along the geomagnetic field lines, as long as they are inclined. Ionosonde data from various mid-latitude stations are used to compare and support results provided by the physical model.
SA33A-1069
CHAMP Density Dependence on Geomagnetic Indices
The STAR accelerometer on the CHAMP satellite has made it possible to accumulate near-continuous records of thermosphere density at approximately 400 km altitude since May 2001. The response of the thermosphere under extremely quiet geomagnetic conditions, as well as for virtually every significant geomagnetic storm and all levels of activity in between, has been recorded during this period. The solar activity has decreased since the beginning of the mission, when the solar cycle was at its peak, to minimum conditions or nearly so at the end of 2006. CHAMP is in a near-polar and quasi-circular orbit, and complete local time sampling is obtained about every 4 months. Therefore, this density dataset offers unique opportunities to study the variability of the thermosphere due to geomagnetic disturbances in relation to solar activity, season, solar local time, and latitude. In the present study, the complete CHAMP density database is analyzed in terms of orbit-to-orbit variability (global response of the thermosphere) as a function of geomagnetic indices, such as ap and sectorial am (index given for 9 latitude-longitude sectors). Density residuals, obtained by de-trending the data using moving averaging windows, are computed to that purpose. The variability is characterized by the large-scale (600 – 5600 km) and medium-scale (160 - 600 km) disturbances, which are isolated by forming the residuals. Secondly, latitude- dependent (i.e., local response) variability is evaluated by binning the densities in pertinent latitude bands (e.g., equatorial, sub-auroral, auroral).
SA33A-1070
Simultaneous Observation of Traveling Ionospheric Disturbances and Traveling Atmospheric Disturbances Using a GPS Receiver Network and the GRACE Satellites
The variations of the thermospheric mass density and the ionospheric electron density inside Large Scale Traveling Ionospheric Disturbances (LSTIDs) were studied with the GRACE accelerometer data and the GPS total electron content (GPS TEC) data. LSTIDs were detected by a GPS receiver network in Japan, GEONET, which is operated by Geographical Survey Institute. The characteristics of the LSTIDs, such as time, location, amplitude, wavelength, and propagation velocity, were derived from the TEC data of GEONET. The thermospheric total mass density at 500km altitude was derived from the high-accuracy accelerometers on board the GRACE satellites. The GRACE satellites flew over the LSTIDs during two events in August 2003 and November 2003. In both two events, wave-like structures of the thermospheric mass density were detected. They propagated from the high latitude to the low latitude in about 300m/s and 500m/s, and the spatial scales of the structures were about 2000km and 2500km, respectively. The velocities and the spatial scales of these Traveling Atmospheric Disturbances (TADs) were similar to those of LSTIDs detected by GEONET TEC in both events. In both two events, the ratio of the perturbation component of the neutral mass density to the background was about 11% and 18%, while that of the TEC was about 6% and 8%. These thermospheric total mass density variations of TADs are interpreted to cause the electron density variations of LSTIDs. We will discuss the relationship between LSTIDs measured by GPS receivers, and TADs detected by the GRACE accelerometers in this presentation.