SA51A-0235
Ionosphere Electrodynamics and its Influence on the Main Ionospheric Trough and Equatorial Ionization Anomaly
In the given work the numerical simulation results of global distributions of the zonal current in the Earth's ionosphere and the critical frequency of the F2-layer of the ionosphere are presented. The calculations are executed with use of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in West Department of IZMIRAN and added by the new block of calculation of the electric field of the dynamo and magnetospheric origin. The calculations are executed for quiet geomagnetic conditions during various seasons and levels of Solar activity without taking into account the electric field, and also with taking into account only dynamo-field or superposition of a dynamo-field and magnetospheric convection field with and without taking into account the shielding by field aligned currents of the second zone. It is shown, that the Main Ionospheric Trough is formed without taking into account the electric field as a result of joint action of processes of ionization, recombination and diffusion. The account of the dynamo-field alters this trough, and magnetospheric convection completes formation of the trough. Equatorial Ionization Anomaly is not formed in the absence of the electric field. The main part in formation of Equatorial Ionization Anomaly plays a dynamo-field. Zonal component of dynamo-field together with diffusion of thermal plasma along geomagnetic field lines under action of the pressure gradients in the Earth's gravity field cause a fountain effect at geomagnetic equator. Equatorial Electrojet is formed by the dynamo-field. Magnetospheric convection at presence of shielding weakly influences on behavior of Equatorial Electrojet. Without the shielding of magnetospheric convection electric field by Alfven layer electric field the magnetospheric convection influence on Equatorial Electrojet becomes stronger. It occurs during magnetospheric disturbances when the shielding is broken due to fast changes of the field aligned currents of the first zone. The Auroral Electrojet is formed mainly by magnetospheric convection electric field and depends on conditions of shielding and conductivity of a high-latitude ionosphere which depends on photoionization and ionization by fluxes of precipitating particles. There are presented the seasonal, Solar-cyclic and UT-variations of Equatorial and Auroral Electrojets, Main Ionospheric Trough and Equatorial Ionization Anomaly.
SA51A-0236
Cross-Wavelet Spectrum Analysis of the Ring Currents Using Magnetic Records from Multiple Low-Latitude Stations
Ground magnetic disturbances in equatorial regions are directly connected to the spatial and temporal variations of the ring currents, which have both the symmetric and asymmetric components, as well as many local-time dependent M-I currents. In this study, we applied the wavelet analysis technique, which is especially appropriate for the data with impulsive and time-dependent spectrum features, to the magnetic records from multiple low- latitude stations in order to study the dynamic behaviors of the symmetric and asymmetric parts of the ring currents for both quiet and storm conditions. First, we decomposed the magnetic records into various details in wavelet spectrum domain and systematically studied the temporal and frequency properties of the magnetic disturbances for various geomagnetic and seasonal conditions. Then we performed cross-wavelet spectrum analysis on the data from multiple stations in both UT and LT time frames in order to separate and elucidate the effects of the symmetric and asymmetric parts of the ring currents. Our results show that slow time-varying components of the ring currents are largely globally symmetric and during quiet times, the magnetic effect of this symmetric part is comparable to that of the asymmetric (or local-time dependent) part. During storm times, the magnetic disturbances associated with both the symmetric and asymmetric parts of the ring currents increase significantly, but the increase of the symmetric current is much larger than that of the asymmetric current and it becomes dominant during storm times. Our results also indicate that there are substantial residues of the magnetic effects of local-time dependent currents left in the Dst index and this further proves that the Dst is not an ideal index for the description of the symmetric ring current.
SA51A-0237
New Theoretical Tools for Studying Ionospheric Electrodynamics
Two different theoretical approaches are commonly used to study ionospheric plasma motion. Dynamo theory and the conductivity equation is used to study currents caused by plasma motion. Ambipolar diffusion models are used to study changes in plasma density caused by vertical plasma motion. The conductivity equation, which states that the current density vector equals the product of the conductivity tensor and the electric field vector, is derived from the conservation of momentum equations after the effects of gravity and pressure gradients are neglected. These terms are crucial for ambipolar diffusion. The two different theoretical approaches are inconsistent. On Earth, the dynamo region (75 km to 130 km, altitude controlled by magnetic field strength and collision frequencies) occurs below regions (F region) where ambipolar diffusion affects plasma number densities, so the theoretical inconsistencies are rarely noticed. However, the inconsistencies are present in most thermosphere-ionosphere-electrodynamics models and will affect the results of such models, particularly in the F region. We present an extension of the conductivity equation that can self-consistently describe ionospheric currents and plasma diffusion.
SA51A-0238
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 Another 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 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 to the Lyon/Fedder/Mobarry (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, and sub-auroral polarization streams. \smallskip Research supported by ONR and NASA.
SA51A-0239
Energetic Neutral Atom observations from Low Earth Orbit
In recent years, space based measurements of Energetic Neutral Atoms (ENA) have yielded new insights into the behavior of the Earth's inner magnetosphere. Instruments aboard the IMAGE spacecraft have taken the bulk of these useful ENA measurements from a polar vantage point near its apogee at 7 Earth radii. In this work, we will show that the techniques that have been applied to the high altitude observations of IMAGE can be adapted to observations made in Low Earth Orbit (LEO). In addition to mission cost (i.e., launch cost, less stressing radiation environment), there are several advantages to making ENA observations from LEO - including finer local time resolution and the ability to reduce seasons of poor viewing and periods of observation interruptions (e.g., radiation belt passes) that are common for platforms in highly elliptical orbits. We present energetic ion distribution retrievals derived from simulations of Energetic Neutral Atom (ENA) observations from LEO. These simulations show that a large portion of the inner magnetosphere can be observed from a single spacecraft and that quantitative results can be obtained from LEO. We also demonstrate that useful results can be obtained even in cases where the magnetic field topology is not known exactly.
SA51A-0240
Electric potential in low latitude ionosphere: Influence of neutral wind.
Upgraded Prairie View Dynamo Code is utilized to study the dependence of electric potential in low latitude ionosphere on the intensity of neutral wind. As a matter of fact, the wind and Hall and Pedersen conductances are the main internal parameters that determine the electric potential in the ionosphere, in response to the changes in polar cap caused by interplanetary magnetic field and solar wind plasma variations, and by associated substorms in the magnetosphere. In this work, we consider the solution of the Poisson equation for electric potential, with boundary condition imposed on the division line between the open and closed field lines of IGRF- 10+T89 model field. The boundary conditions and results are dependent also on universal time, since mutual orientation of the ionospheric and the magnetospheric field is changing diurnally. The electric potential on the boundary is set from Weimer's empirical model. We present results of calculations of electric potential, for strong and moderate storms, as well as for quiet times. For better accuracy it is more important to set correctly neutral wind in quiet times, while in disturbed and stormy ones the result becomes sensitive only to boundary conditions and the ionospheric conductances distributions used in the calculation.
SA51A-0241
Effects of the field-aligned currents and potential drops in the magnetosphere on the coupling of the ionosphere with the magnetosphere
Models for the field-aligned currents and electric potential drops in the magnetosphere are presented on the basis of observational data, and are introduced in the upgraded Prairie View Dynamo Code, by adding extra field- aligned current term and potential drop term into the Poisson equation. The effects of the field-aligned currents and potential drops on the coupling of the ionosphere with the magnetosphere are examined under different solar wind and geomagnetic conditions for different dates and diurnal times.
SA51A-0242
Satellite based determination of Ionospheric Conductances due to solar illumination and particle precpitation
The Pedersen conductance is an important parameter that determines the intensity of currents coupling the ionosphere and the magnetosphere and the rate of electromagnetic energy exchange between the two. Short of running a full ionosphere/thermosphere model, studies of ionosphere/magnetosphere coupling are forced to rely on various sets of emperical or parameterized theoretical results to determine local or global conductance. Under steady state conditions Ampere's and Ohm's laws can be combined to obtain the relationship between magnetic perturbations and electric fields measured at satellite altitudes in regions of field-aligned currents. In intervals where E and δ B are highly correlated the height integrated Pedersen conductivity can be written as ΣP = (1/μo) Δ δ BZ/ Δ EY, and be determined directly from in situ measurements. We use this approach with magnetometer and driftmeter data from two DMSP satellites (F16 and F17) to determine Pedersen conductances under quiet to mildly distrubed conditions, in regions close to the terminator where solar illumination and particle (ion and electron) precipitation play competing roles in determing ionospheric conductivities. Results from this study are compared with commonly used expressions for conductances ( Robinson and Vondrak, 1984; Robinson et al., 1987) and results of numerical simulations.
SA51A-0243
A mechanism for the formation of plasma patches in the high-latitude ionosphere1
One of the important features of the high-latitude ionospheric plasma is the occurrence of plasma patches. Statistical studies of their size distribution indicates that plasma patches are typically 300-400 Kms in extent and have density enhancements of at least a factor of two compared to the background density. We present results on 2D and 3D simulations addressing the issue of structuring of a large tongue-of-ionization which enters the polar region through the cusp. The dissipative Kelvin-Helmholtz instability in the localized anti-sunward flow of the two-cell convection pattern for southward IMF provides a natural mechanism for the creation of structures comparable to the width of the flow channel. This can provide one possible explanation of the occurrence of patches in the high-latitude ionosphere. 1 Work supported by NSF
SA51A-0244
IFM-Modeled Response of the High-Latitude Ionosphere to Auroral Dynamics Based on Auroral Observations Acquired with the Visible Imaging System(VIS) on the Polar Spacecraft
Global physics-based models for the high-latitude ionosphere have been developed to such an extent that the large and small ionospheric features during magnetic storms and substorms can be studied. These models, however, require inputs for the magnetospheric forcing, i.e. Magnetospheric convection and particle precipitation. More specifically, for these models to yield reliable results during magnetic storms and substorms, reliable global maps for the high-latitude magnetospheric convection and auroral electron particle precipitation patterns as a function of time are needed. Over the last decades several statistical models for the high-latitude convection and particle precipitation have been developed and used to drive ionospheric models. However, due to the statistical nature of these models, they represent the average characteristics of the true convection and precipitation patten and they are very limited to simulate the effect of magnetic storms and substorms. Recently, with the realization of the Visible Imaging System (VIS) on the Polar Spacecraft, auroral images that yield information of auroral dynamics on a global scale with a spatial resolution of less than 100 km and temporal resolution of ~ 1 minute have become available. These images can be used to calculate reliable global maps for the particle precipitation parameters, electron energy flux and average energies, as a function of time. In this poster we present the preliminary results of our attempt to drive the Ionosphere Forecast Model (IFM) using global maps for the electron precipitation parameters calculated from the corresponding VIS images. In order to elucidate the effect of auroral dynamics on the high-latitude ionosphere, a one-day data set of VIS images during which the aurora was highly active is selected for this study. Then, these images are used to calculate global maps for the electron precipitation parameters using the Lumerzheim model. Next, the maps obtained in the previous step are used as inputs to the IFM and the corresponding plasma parameters are calculated. As a reference against which to compare the ionospheric simulations obtained in the previous step, the same simulations are repeated again but this time using statistical patterns for the particle precipitation parameters obtained from the Hardy statistical model. From the comparison of the two simulations, the impact of the auroral dynamics on the high-latitude ionosphere is elucidated.
SA51A-0245
Development of An Electrodynamically Coupled Model between RCM and CTIPe
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 geomagnetically active conditions. Modeling of the storm-time ionospheric electrodynamics 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 control the shielding process of the high latitude convection electric field, and the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, used to calculate the time-dependent conductivities and neutral winds that are the key to produce the disturbance dynamo as well as the quiet-time ionospheric wind 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. In this paper, the electrodynamic interactions will be discussed using the fully self-consistently coupled model.