Jan J. Sojka

Global Assimilation of Ionospheric Measurements (GAIM)

Abstract : Our primary goal is to construct a real-time data assimilation model for the ionosphere-plasmasphere system that will provide reliable specifications and forecasts. A secondary goal is to validate the model for a wide range of geophysical conditions, including different solar cycle, seasonal, storm, and substorm conditions.

Parameterized Ionospheric Model: A Global Ionospheric Parameterization Based on First Principles Models

We describe a parameterized ionospheric model (PIM), a global model of theoretical ionospheric climatology based on diurnally reproducible runs of four physics based numerical models of the ionosphere. The four numerical models, taken together, cover the E and F layers for all latitudes, longitudes, and local times. PIM consists of a semianalytic representation of diurnally reproducible runs of these models for low, moderate, and high levels of both solar and geomagnetic activity and for June and December solstice and March equinox conditions. PIM produces output in several user selectable formats including global or regional latitude/longitude grids (in either geographic or geomagnetic coordinates), a set of user specified points (which could lie along a satellite orbital path), or an altitude/azimuth/elevation grid for a user-specified location. The user selectable output variables include profile parameters (ƒ0F2, hmF2, total electron content, etc.), electron density profiles, and ion composition (O+, NO+, and O2+).

Modeling Polar Cap F-Region Patches Using Time Varying Convection

Here the authors present the results of computerized simulations of the polar cap regions which were able to model the formation of polar cap patches. They used the Utah State University Time-Dependent Ionospheric Model (TDIM) and the Phillips Laboratory (PL) F-region models in this work. By allowing a time varying magnetospheric electric field in the models, they were able to generate the patches. This time varying field generates a convection in the ionosphere. This convection is similar to convective changes observed in the ionosphere at times of southward pointing interplanetary magnetic field, due to changes in the B[sub y] component of the IMF.

Ionosphere-Thermosphere Space Weather Issues

Abstract Weather disturbances in the ionosphere-thermosphere system can have a detrimental effect on both ground-based and space-based systems. Because of this impact and because our field has matured, it is now appropriate to develop specification and forecast models, with the aim of eventually predicting the occurrence, duration, and intensity of weather effects. As part of the new National Space Weather Program, the CEDAR community will focus on science issues concerning space weather, and this tutorial/review is an expanded version of a tutorial presentation given at the recent CEDAR annual meeting. The tutorial/review provides a brief discussion of weather disturbances and features, the causes of weather, and the status of weather modeling. The features and disturbances discussed include plasma patches, boundary and auroral blobs, sun-aligned polar cap arcs, the effects of traveling convection vortices and SAID events, the lifetime of density structures, sporadic E and intermediate layers, spread F and equatorial plasma bubbles, geomagnetic storms and substorms, traveling ionospheric disturbances (TIDs), and the effects of tides and gravity waves propagating from the lower atmosphere. The tutorial/review is only intended to provide an overview of some of the important scientific issues concerning ionospheric-thermospheric weather, with the emphasis on the ionosphere. Tutorials on thermospheric and magnetospheric weather issues are given in companion papers.

Storm-Time Density Enhancements in the Middle Latitude Dayside Ionosphere

[1] Enhancements of the total electron content (TEC) in the middle-latitude dayside ionosphere have often been observed during geomagnetic storms. The enhancements can be as large as a factor of 2 or more, and many sightings of such structures have occurred over the United States. Here we investigate the effectiveness of an expanded convection electric field as a mechanism for producing such ionospheric enhancements. As a test case, we examine the storm period of 5-7 November 2001, for which observations from the DMSP F 13 are used to drive the Time Dependent Ionospheric Model (TDIM). Our findings indicate that at favorable universal times, the presence of the expanded electric field is sufficient to create dayside TEC enhancements of a factor of 2 or more. The modeled enhancements consist of locally produced plasma; we do not find it necessary to transport high-density plasma northward from low latitudes.

Global ionosphere‐polar wind system during changing magnetic activity

A time-dependent, three-dimensional, multi-ion model of the global ionosphere-polar wind system was used to study the systems response to an idealized geomagnetic storm for different seasonal and solar cycle conditions. The model covered the altitude range from 90 to 9000 km for latitudes greater than 50° magnetic in the northern hemisphere. The geomagnetic storm contained a 1-hour growth phase, a 1-hour main phase, and a 4-hour decay phase. Four storm simulations were conducted, corresponding to winter and summer solstices at both solar maximum and minimum. The simulations indicated the following: (1) O + upflows typically occur in the cusp and auroral zone at all local times, and downflows occur in the polar cap. However, during increasing magnetic activity, O + upflows can occur in the polar cap, (2) The O + upflows are typically the strongest where both T e and T i are elevated, which generally occurs in the cusp at the location of the dayside convection throat, (3) The upward H + and O + velocities increase with T e , which results in both seasonal and day-night asymmetries in the ion velocities, (4) During increasing magnetic activity, O + is the dominant ion at all altitudes throughout the polar region, (5) For solar minimum winter, there is an H + blowout throughout the polar region shortly after the storm commences (negative storm effect), and then the H+ density slowly recovers. The O + behavior is opposite to this. There is an increase in the O + density above 1000 km during the storms peak (positive storm effect), and then it decreases as the storm subsides, and (6) For solar maximum summer, the O + and H + temporal morphologies are in phase; but the ion density variations at high altitudes are opposite to those at low altitudes. During the storms peak, the H + and O + densities increase at high altitudes (positive storm effect) and decrease at low altitudes (negative storm effect).

Polar cap arcs: a review

Abstract This article reviews both the observational and theoretical studies of polar cap arcs. These arcs are the auroral arcs that occur in the polar cap or in the poleward regions of the auroral oval. The following related topics are briefly discussed in the article: (1) dayside aurora; (2) oval/substorm aurora; and (3) large-scale convection, current, and precipitation configurations at high latitudes during northward interplanetary magnetic fields

Ionospheric Weather Forecasting on the Horizon

In an effort to mitigate the adverse effects of the ionosphere on military and civilian operations, specification and forecast models are being developed that employ state-of-the-art data assimilation techniques. Utah State University has recently developed two data assimilation models for the ionosphere as part of the USU Global Assimilation of Ionospheric Measurements (USU GAIM) program. One of these models is currently being implemented at the Air Force Weather Agency for operational use. The USU-GAIM models are also being used for scientific studies, and this should lead to a dramatic advance in our understanding of ionospheric physics similar to what occurred in meteorology and oceanography after the introduction of data assimilation models in those fields.

CEDAR Electrodynamics Thermosphere Ionosphere (ETI) Challenge for systematic assessment of ionosphere/thermosphere models: NmF2, hmF2, and vertical drift using ground‐based observations

[1] Objective quantification of model performance based on metrics helps us evaluate the current state of space physics modeling capability, address differences among various modeling approaches, and track model improvements over time. The Coupling, Energetics, and Dynamics of Atmospheric Regions (CEDAR) Electrodynamics Thermosphere Ionosphere (ETI) Challenge was initiated in 2009 to assess accuracy of various ionosphere/thermosphere models in reproducing ionosphere and thermosphere parameters. A total of nine events and five physical parameters were selected to compare between model outputs and observations. The nine events included two strong and one moderate geomagnetic storm events from GEM Challenge events and three moderate storms and three quiet periods from the first half of the International Polar Year (IPY) campaign, which lasted for 2 years, from March 2007 to March 2009. The five physical parameters selected were NmF2 and hmF2 from ISRs and LEO satellites such as CHAMP and COSMIC, vertical drifts at Jicamarca, and electron and neutral densities along the track of the CHAMP satellite. For this study, four different metrics and up to 10 models were used. In this paper, we focus on preliminary results of the study using ground-based measurements, which include NmF2 and hmF2 from Incoherent Scatter Radars (ISRs), and vertical drifts at Jicamarca. The results show that the model performance strongly depends on the type of metrics used, and thus no model is ranked top for all used metrics. The analysis further indicates that performance of the model also varies with latitude and geomagnetic activity level.

Recent Approaches to Modeling Ionospheric Weather

Abstract The ionosphere is a complex and dynamic medium that exhibits weather features at all latitudes and longitudes. The weather features are driven by internal processes as well as by interplanetary and magnetospheric phenomena. Because ionospheric weather can have a detrimental effect on both ground-based and space-based systems, a large international effort has been devoted to developing both specification and forecast models, with the aim of predicting the occurrence, duration, and intensity of weather features. Currently, the most promising ionospheric weather models are the physics-based data-driven models that use Kalman filter data assimilation techniques. The data assimilation is used both to obtain the inputs needed by the physics-based models and to adjust the model outputs, i.e., the calculated electron density distribution. The data sources used in the physics-based assimilation models include ground-based GPS/TEC data, bottomside electron density profiles obtained from digisondes, in situ DMSP satellite measurements, satellite-to-satellite occultation data, TECs obtained from satellites with radio beacons, and UV data obtained via remote sensing. The status of the modeling will be reviewed.