A Theoretical Study of the High-Latitude Winter F Region at Solar Minimum for Low Magnetic Activity

We combined a simple plasma convection model with an ionospheric-atmospheric composition model in order to study the high-latitude winter F region at solar minimum for low magnetic activity. Our numerical study produced time dependent, three-dimensional ion density distributions for the ions NO+, O2 +, N2 +, O+, N+, and He+. We covered the high-latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. The main result we obtained was that high-latitude ionospheric features, such as the ‘main trough,’ the ‘ionization hole,’ the ‘tongue of ionization,’ the ‘aurorally produced ionization peaks,’ and the ‘universal time effects,’ are a natural consequence of the competition between the various chemical and transport processes known to be operating in the high-latitude ionosphere. In addition, we found that (1) the F region peak electron density at a given location and local time can vary by more than an order of magnitude, owing to the UT effect that results from the displacement between the geomagnetic and geographic poles; (2) a wide range of ion compositions can occur in the polar F region at different locations and times; (3) the minimum value for the electron density in the main trough is sensitive to nocturnal maintenance processes; (4) the depth and longitudinal extent of the main trough exhibit a significant UT dependence; (5) the way the auroral oval is positioned relative to the plasma convection pattern has an appreciable effect on the magnetic local time extent of the main trough; (6) the spatial extent, depth, and location of the polar ionization hole are UT dependent; (7) the level of ion production in the morning sector of the auroral oval has an appreciable effect on the location and spatial extent of the polar ionization hole; and (8) in the polar hole the F region peak electron density is below 300 km, and at 300 km, diffusion is a very important process for both O+ and NO+. Contrary to the suggestion based on an analysis of AE-C satellite data obtained in the polar hole that the concentration of NO+ ions is chemically controlled, we find diffusion to be the dominant process at 300 km

How uncertainty in the neutral wind limits the accuracy of ionospheric modeling and forecasting

One of the most important input fields for an ionospheric model is the horizontal neutral wind. The primary mechanism by which the neutral wind affects ionospheric densities is the inducement of an upward or downward ion drift along the magnetic field lines; this affects the rate at which ions are lost through recombination. The magnitude of this effect depends upon the dip angle of the magnetic field; for this reason, the impact of the neutral wind is somewhat less in polar regions than at mid-latitudes. It is unfortunate that observations of the neutral wind are relatively scarce, as compared for example with observations of the Earth’s electric field or auroral precipitation, and that the existing climatological models of the neutral wind are thus sharply limited in theirresolution. The observational data base of thermospheric winds is not sufficient to adequately constrain a three-dimensional model across a variety of conditions such as solar cycle, season, geomagnetic activity, and so on. Using the physics-based Time Dependent Ionospheric Model (TDIM) of Utah State University, we look for a quantitative answer to this question: How severe is the limitation imposed on ionospheric models by an uncertain specification of the neutral wind? We find that ionospheric modeling depends upon a detailed specification of the neutral wind to the extent that, if a climatologically averaged wind model is being used as a driver, this will lead to unavoidable uncertainties of 20-30% in the modeled F-region densities or Total Electron Content (TEC)

Ionospheric ion temperature forecasting in multiples of 27 days

he ionospheric variability found at auroral locations is usually assumed to be unpredictable. The magnetosphere, which drives this ionospheric variability via storms and substorms, is at best only qualitatively describable. In this study we demonstrate that over a 3 year period, ionospheric variability observed from Poker Flat, Alaska, has, in fact, a high degree of long-term predictability. The observations used in this study are (a) the solar wind high speed stream velocity measured by the NASA Advanced Composition Explorer satellite, used to define the corotating interaction region (CIR), and (b) the ion temperature at 300 km altitude measured by the National Science Foundation Poker Flat Incoherent Scatter Radar over Poker Flat, Alaska. After determining a seasonal and diurnal climatology for the ion temperature, we show that the residual ion temperature heating events occur synchronously with CIR-geospace interactions. Furthermore, we demonstrate examples of ion temperature forecasting at 27, 54, and 81 days. A rudimentary operational forecasting scenario is described for forecasting recurrence 27 days ahead for the CIR-generated geomagnetic storms. These forecasts apply specifically to satellite tracking operations (thermospheric drag) and emergency HF-radio communications (ionospheric modifications) in the polar regions. The forecast is based on present-day solar and solar wind observations that can be used to uniquely identify the coronal hole and its CIR. From this CIR epoch, a 27 day forecast is then made

Effect of High Latitude Ionospheric Convection on Sun-Aligned Polar Caps

A coupled magnetospheric-ionospheric (M-I) MHD model has been used to simulate the formation of Sun-aligned polar cap arcs for a variety of interplanetary magnetic field (IMF) dependent polar cap convection fields. The formation process involves launching an Alfvén shear wave from the magnetosphere to the ionosphere where the ionospheric conductance can react self-consistently to changes in the upward currents. We assume that the initial Alfvén shear wave is the result of solar wind-magnetosphere interactions. The simulations show how the E region density is affected by the changes in the electron precipitation that are associated with the upward currents. These changes in conductance lead to both a modified Alfvén wave reflection at the ionosphere and the generation of secondary Alfvén waves in the ionosphere. The ensuing bouncing of the Alfvén waves between the ionosphere and magnetosphere is followed until an asymptotic solution is obtained. At the magnetosphere the Alfvén waves reflect at a fixed boundary. The coupled M-I Sun-aligned polar cap arc model of Zhu et al. (1993a) is used to carry out the simulations. This study focuses on the dependence of the polar cap arc formation on the background (global) convection pattern. Since the polar cap arcs occur for northward and strong By IMF conditions, a variety of background convection patterns can exist when the arcs are present. The study shows that polar cap arcs can be formed for all these convection patterns; however, the arc features are dramatically different for the different patterns. For weak sunward convection a relatively confined single pair of current sheets is associated with the imposed Alfvén shear wave structure. However, when the electric field exceeds a threshold, the arc structure intensifies, and the conductance increases as does the local Joule heating rate. These increases are faster than a linear dependence on the background electric field strength. Furthermore, above the threshold, the single current sheet pair splits into multiple current sheet pairs. For the fixed initial ionospheric and magnetospheric conditions used in this study, the separation distance between the current pairs was found to be almost independent of the background electric field strength. For either three-cell or distorted two-cell background convection patterns the arc formation favored the positive By case in the northern hemisphere

Dayside midlatitude ionospheric response to storm time electric fields: A case study for 7 September 2002

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95503/1/jgra21582.pd

Dynamical Effects of Ionospheric Conductivity on the Formation of Polar Cap Arcs

By using a magnetosphere-ionosphere (M-I) coupling model of polar cap arcs [Zhu et al., 1993], a systematic model study of the effects of ionospheric background conductivity on the formation of polar cap arcs has been conducted. The variations of the ionospheric background conductivity in the model study cover typical ionospheric conditions, including solar minimum, solar maximum, winter, and summer. The simulation results clearly indicate that the ionospheric background conductivity can dynamically affect the mesoscale features of polar cap arcs through a nonlinear M-I coupling process associated with the arcs

Hemispherical Shifted Symmetry in Polar Cap Patch Occurrence: A Survey of GPS TEC Maps From 2015–2018

Much theoretical and observational work has been devoted to studying the occurrence of F region polar cap patches in the Northern Hemisphere; considerably less work has been applied to the Southern Hemisphere. In recent years, the Madrigal database of mappings of total electron content (TEC) has improved in Southern Hemisphere coverage, to the point that we can now carry out a study of patch frequency and occurrence. We find that Southern Hemisphere patch occurrence is very similar to that of the Northern Hemisphere with a half‐year offset, plus an offset in universal time of approximately 12 hr. This is further supported by running an ionospheric model for both hemispheres and applying the same patch‐to‐background technique. Further, we present a simple physical mechanism involving a sunlit dayside plasma source concurrent with a dark polar cap, which yields a patch‐to‐background pattern very much like that seen in the TEC mappings for both hemispheres

Sugarbeet Production Under Reduced Tillage Prospects And Problems

A study was initiated in the fall of 1977 to obtain base line data on the applicability of reduced tillage sugarbeet production in the Red River Valley. Three reduced tillage systems were compared to a conventional system which consisted of fall plow plus secondary tillage. Results indicated warmer early spring soil temperatures, better seedling emergence, lower ground-level wind speed and no significant yield loss under reduced tillage as compared to the conventional system

Observations of the Diurnal Dependence of the High-Latitude \u3ci\u3eF\u3c/i\u3e Region Ion Density by DMSP Satellites

Data from the DMSP F2 and F4 satellites for the period December 5-10, 1979, have been used to study the diurnal dependence of the high-latitude ion density at 800-km altitude. A 24-hour periodicity in the minimum orbital density (MOD) during a crossing of the high-latitude region is observed in both the winter and summer hemispheres. The phase of the variation in MOD is such that it has a minimum during the 24-hour period between 0700 and 0900 UT. Both the long term variation of the high-latitude ion density on a time scale of days, and the orbit by orbit variations at the same geomagnetic location in the northern (winter) hemisphere for the magnetically quiet time period chosen show good qualitative agreement with the diurnal dependence predicted by a theoretical model of the ionospheric density at high latitudes under conditions of low convection speeds (Sojka et al., 1981a)