SA41A-01 INVITED
The Linkage Between the Ionospheric Trough and Ring Current
We present data-model investigations of how the ring current couples to the sub-auroral ionosphere. The ring current pressure distribution during storm and substorms is highly asymetrical and sets up the region 2 current system that closes through the sub-auroral ionosphere. Of particular interest is what happens in the so-called ionospheric trough region, which is a region in the evening ionosphere with extremely low conductance (few tenths of a mho). Observations show strong westward flows in the ionospheric trough (Sub-Auroral Polarization Stream - SAPS) and sometimes highly structured and variable. The Comprehensive Ring Current Model models the ring current by using the bounce averaged Boltzmann equation and allowing the ring current to close through the ionosphere. Our model ionosphere includes dayside and auroral conductance as well as semi-empirical representation of the trough conductance. By using realistic representations of the conductances we seek to explore how the ring current pressure distribution (and therefore the region 2 current system) is linked to the presence of the trough. We use data from the IMAGE satellite, the Millstone Hill and SuperDARN radar facilities.
SA41A-02 INVITED
Global Effects of Subauroral Electric Fields on the Thermosphere
Ionospheric electric fields can have profound effects on the thermospheric composition and winds, particularly during geomagnetic activity. They influence numerous processes in the ionosphere/thermosphere (IT) system including plasma transport in the ionosphere, the ion drag force which affects neutral winds, and the Joule heating which drives much of the composition and structure of the IT system. They can extend to very low latitudes and can contribute substantially to the magnetospheric electric field structure, particularly during geomagnetic storms. Modelers have begun to understand the importance of the subauroral electric field coupling to the thermosphere, the inner magnetosphere and the plasmasphere and efforts to incorporate recent results are currently underway. We are examining the effect of the subauroral electric fields on IT coupling using an empirical model of the subauroral electric fields derived from data acquired by several low-Earth orbiting (LEO) spacecraft. The results are being incorporated into the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) to examine the global effects of the subauroral electric fields on the thermospheric structure. We will show our initial results, comparing the global thermospheric structure derived from TIME-GCM for a geomagnetic storm using a strictly high-latitude electric field model with thermospheric structure derived using an electric field model incorporating the subauroral electric field.
SA41A-03 INVITED
Ionospheric Modeling: Coupling to the Inner and Outer Magnetosphere
The Naval Research Laboratory has developed a comprehensive 3D model of the earth's ionosphere: SAMI3 (Sami3 is Also a Model of the Ionosphere). SAMI3 models the plasma and chemical evolution of seven ion species (H+, He+, N+, O+, N2+, NO2+ and O2+). The complete ion temperature equation is solved for three ion species (H+, He+ and O+) as well as the electron temperature equation. Ion inertia is included in the ion momentum equation for motion along the geomagnetic field. In addition, the E × B drift motion of the plasma is included for both zonal electric fields (vertical drifts) and meridional electric fields (zonal drifts). The neutral species are specified using the empirical NRLMSISE00 model that is based on MSIS86 and the HWM model. SAMI3 uses a nonorthogonal, nonuniform, fixed grid. The code is fully parallelized using the Message Passing Interface (MPI) method. The code has been recently upgraded to provide global coverage of the ionosphere (± 89° magnetic latitude) within the context of a single model. The code has been self-consistently electrodynamically coupled to the Rice Convection Model (RCM) and partially coupled to the LFM magnetosphere model. We report results of ionospheric dynamics associated with electrodynamic forcing by the inner and outer magnetosphere, e.g., the convection of plasma across the polar cap, the impact of storm-time penetration electric fields on the low- to mid-latitude ionosphere. Research supported by ONR.
SA41A-04
The quiet and disturbed sub-auroral electric field as observed from DMSP
Though the high and low latitude electric field has been studied and modeled extensively (e.g., Rich and Hairston, 1994, Weimer, 1995, Ruohoniemi and Greenwald, 1996, Richmond, 1995; Fejer, 1997) there has been relatively little attention to the sub-auroral region except for studies at certain longitudes (e.g., Foster and Vo, 2002). In this paper we present preliminary analyses of the quiet and disturbed sub-auroral electric field environment. The variability that is seen in mid-latitudes may partially be the result of the same factors at high latitudes. It has been shown that the configuration and strength of the high latitude electric field is dependent on the inter-planetary magnetic field orientation (e.g., Ruohoniemi and Greenwald, 1996) and geomagnetic activity. The sub-auroral electric field will also have a strong IMF and geomagnetic component, but is also expected to have significant longitudinal, seasonal, and solar cycle variation, as the mid-latitude conductivity is highly dependent on solar illumination. We use the long-term (18 years) electric field measurement dataset provided by the suite of DMSP ion drift meters (the measured ion drifts are related to the electric fields by v=(ExB)/(B*B) ). By definition, a major component of correctly identifying sub-auroral electric fields is to correctly specify the aurora boundary, as the behavior and magnitude of these fields will be drastically different away from the high-conductance auroral oval. For this analysis, we also use coincident particle flux measurements from the DMSP SSJ4 monitors. We examine the climatogical and storm-time sub-auroral electric field as a function of invariant latitude as well as gridded relative to auroral boundary. We also discuss the relationship between the sub-auroral electric field and the mid- latitude trough and region 2 field-aligned currents.
SA41A-05
Ionospheric Response During Four Intense Geomagnetic Storms: Similarities and Differences
Large magnitude and hemispheric-scale increases in ionospheric plasma content are observed for daytime local times during intense geomagnetic storms. Ionospheric increases during the main phase of geomagnetic storms were identified many years ago and categorized as the "positive phase" ionospheric response. This talk will explore what we can learn using satellite data and distributed ground-based measurements, to understand the geoeffective processes at work in creating the positive phase for intense storms. The importance of electric fields penetrating to low latitudes on the dayside has received a great deal of attention recently, and is leading to revised theoretical and modeling constructs to account for the observations in a quantitative manner. We will present ground and space-based Global Positioning System (GPS) electron content data for four storms and analyze the data in light of the upstream conditions with a common epoch analysis. Modeling studies of the storm-time ionospheric behavior will be shown, using the ASPEN-TIMEGCM fully-coupled thermosphere- ionosphere (T-I) model with low-latitude electrodynamics. The ASPEN-TIMEGCM model contains storm-time effects such as winds and the resulting dynamo electric fields, but penetration E-fields including shielding are not currently included. The model runs are driven by carefully reconstructed high latitude time-dependent drivers based in part on the AMIE high latitude electrodynamics model. The time history of a modeled storm will be compared with observations. We will highlight outstanding science questions that are revealed in this study.
SA41A-06
A Self-consistently Coupled Model of the Inner Magnetosphere and Thermosphere- Ionosphere-Plasmasphere system
We have developed a self-consistent first-principles model of the inner magnetosphere and thermosphere- ionosphere-plasmasphere, in order to understand the response of the electrodynamic interactions within the coupled system and the role of the electrodynamics in restructuring the ionosphere, plasmasphere and thermosphere, in particular, during the geomagnetic disturbances. Modeling of the storm-time ionospheric electric fields requires a description of the two disturbance mechanisms: prompt penetration and disturbance dynamo. We have coupled the Rice Convection Model (RCM), used to calculate the region 2 field aligned currents from the inner magnetosphere which controls the shielding process, and the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, driven, in part, by RCM-computed electric fields, used to calculate the time-dependent conductivities and neutral winds which are the key to produce the disturbance dynamo. Self-consistency in the electrodynamic coupling between RCM and CTIPe is accomplished by using a common global electrodynamic solver. As compared to the historical picture of prompt penetration, our previous model results from the non self- consistent coupling suggest the possibility that penetration effects can have a longer lifetime when the IMF Bz is large and negative as a consequence of the ineffective shielding resulting from the magnetospheric reconfiguration. Furthermore, our simulations indicate that the arrival of the disturbance dynamo effect in the low latitude ionosphere can possibly be faster than previously believed, as the disturbance dynamo is modified by the changes in the conductivity and neutral wind initiated by the penetration effect. Comparison of the results from the combined models with observations under a variety of conditions demonstrates that our models are capable of reproducing many of the measurements in the ionosphere. On the other hand, the feedback of the storm-time conductivity and neutral wind on the inner magnetospheric electric field has a larger impact on the night side, indicating that the disturbance dynamo can modify the penetration electric field. In this presentation, the above issues of the electrodynamic interactions will be addressed by the fully self consistently coupled model.
SA41A-07
Modeling of Equatorial Anomaly Development and Collapse at Dusk Observed by TIMED/GUVI Over Indian Longitudes
The GUVI instrument on NASA's TIMED satellite acquires images of 135.6-nm emission in the Earth's ionosphere/thermosphere system. The brightness of the GUVI images is approximately proportional to the square of the electron density and, as such, the images can be used to monitor the equatorial F region ionization anomaly. The intensity and separation of these bands are controlled by the equatorial E-B drift and the meridional neutral wind. Further, the collapse of the anomaly has been linked to the suppression of irregularities causing scintillations. The SAMI3, another model of the ionosphere, has been utilized to model the evening collapse of the anomaly in the Indian longitude sector where measurements of TEC, scintillations and estimates of the daytime vertical drifts are available. Preliminary results from SAMI3 show that the collapse of the anomaly at dusk can be simulated by a reduction of the vertical drift, and its reversal in mid-afternoon in agreement with the drift estimates from magnetometer observations. Introduction of neutral winds into SAMI3 reproduces the dusk behavior of TEC at low latitude stations in India. While preliminary results from SAMI3 provide some insights into the day-to-day variation of scintillations, much further work is necessary, particularly on the relative effects of the pre-reversal enhancement of the vertical drifts, time of reversal, neutral winds and the conductivity in the E-region on the generation and suppression of instabilities. We hope these modeling efforts will eventually lead to the isolation of a unique set of drivers that control large and small scale plasma structuring.