Modelling and measurement of global-scale ionospheric behavior under solar minimum, equinoctial conditions (original) (raw)
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An empirical model of quiet-day ionospheric electric fields at middle and low latitudes
Journal of Geophysical Research: Space Physics, 1980
Seasonally averaged quiet-day F region ionospheric E x B drift observations from the Millstone Hill, St. Santin, Arecibo, and Jicamarca incoherent scatter radars are used to produce a model of the middleand low-latitude electric field for solar m'mimum conditions. A function similar to an electrostatic potential is fitted to the data to provide model values continuous in latitude, longitude, time of day, and day of the year. This model is intended to serve as a reference standard for applications requiring global knowledge of the mean electric field or requiring information at some location removed from the observing radars. INTRODUCTION Knowledge of the ionospheric electric field is useful in several branches of upper atmospheric physics. The electric field at middle and low latitudes on magnetically quiet days is believed to be produced mainly by the dynamo action of thermospheric winds [e.g., Evans, 1978; Blanc, 1979; Richmond, 1979], so that knowledge of the electric field can be used to gain further information about the winds and the dynamo mechanism. The electric field causes the ionospheric and plasmaspheric plasmas to drift perpendicular to the geomagnetic field and, consequently, is important for the dynamic variations of these plasmas [e.g., Matsushita and Tarpley, 1970;
Response of low-latitude ionosphere to medium-term changes of solar and geomagnetic activity
Journal of Geophysical Research, 2012
The paper describes results of the studies devoted to the solar activity impact on the Earth's upper atmosphere and ionosphere, conducted within the frame of COST ES0803 Action. Aim: The aim of the paper is to represent results coming from different research groups in a unified form, aligning their specific topics into the general context of the subject. Methods: The methods used in the paper are based on data-driven analysis. Specific databases are used for spectrum analysis, empirical modeling, electron density profile reconstruction, and forecasting techniques. Results: Results are grouped in three sections: Medium-and long-term ionospheric response to the changes in solar and geomagnetic activity, storm-time ionospheric response to the solar and geomagnetic forcing, and modeling and forecasting techniques. Section 1 contains five subsections with results on 27-day response of low-latitude ionosphere to solar extreme-ultraviolet (EUV) radiation, response to the recurrent geomagnetic storms, long-term trends in the upper atmosphere, latitudinal dependence of total electron content on EUV changes, and statistical analysis of ionospheric behavior during prolonged period of solar activity. Section 2 contains a study of ionospheric variations induced by recurrent CIR-driven storm, a case-study of polar cap absorption due to an intense CME, and a statistical study of geographic distribution of so-called E-layer dominated ionosphere. Section 3 comprises empirical models for describing and forecasting TEC, the F-layer critical frequency foF2, and the height of maximum plasma density. A study evaluates the usefulness of effective sunspot number in specifying the ionosphere state. An original method is presented, which retrieves the basic thermospheric parameters from ionospheric sounding data.
A fully analytic, low- and middle-latitude ionospheric model
Journal of Geophysical Research, 1989
A fully analytic ionospheric model emphasizing the low-latitude F region for various seasonal and solar cycle conditions is presented. Features such as the postsunset rise in the F layer peak height and the "equatorial anomaly" maxima in plasma density near ___ 15 ø geomagnetic latitude are designed to closely approximate those in the semiempirical low-latitude ionospheric model (Anderson et al., 1987a). Significant improvements are thus obtained over previous comparable analytic models. Numerical computations are also presented which demonstrate the importance of these large-scale plasma structures to the neutral dynamics of the low-latitude thermosphere. Equally significant effects are anticipated for electrodynamic simulations of E region/F region coupling involving flux tube integrated electrical conductivities.
Ionospheric disturbances under low solar activity conditions
Advances in Space Research, 2014
The paper is focused on ionospheric response to occasional magnetic disturbances above selected ionospheric stations located at middle latitudes of the Northern and Southern Hemisphere under extremely low solar activity conditions of 2007-2009. We analyzed changes in the F2 layer critical frequency foF2 and the F2 layer peak height hmF2 against 27-days running mean obtained for different longitudinal sectors of both hemispheres for the initial, main and recovery phases of selected magnetic disturbances. Our analysis showed that the effects on the middle latitude ionosphere of weak-to-moderate CIR-related magnetic storms, which mostly occur around solar minimum period, could be comparable with the effects of strong magnetic storms. In general, both positive and negative deviations of foF2 and hmF2 have been observed independent on season and location. However positive effects on foF2 prevailed and were more significant. Observations of stormy ionosphere also showed large departures from the climatology within storm recovery phase, which are comparable with those usually observed during the storm main phase. The IRI STORM model gave no reliable corrections of foF2 for analyzed events.
Journal of Atmospheric and Terrestrial Physics, 1988
The University College London Thermospheric Model and the Sheffield University Ionospheric Convection Model have been integrated and improved to produce a self-consistent coupled global thermospheric/high latitude ionospheric model. The neutral thertnospheric equations for wind velocity, composition, density and energy are solved, including their full interactions with the evolution of high latitude ion drift and plasma density, as these respond to convection, precipitation, solar photoionisation and changes of the thermosphere, particularly composition and wind velocity. Four 24 h Universal Time (UT) simulations have been performed. These correspond to positive and negative values of the IMF BY component at high solar activity, for a level of moderate geomagnetic activity, for each of the June and December solstices. In this paper we will describe the seasonal and IMF reponses of the coupled ionosphere/thermosphere system, as depicted by these simulations. In the winter polar region the diurnal migration of the polar convection pattern into and out of sunlight, together with ion transport, plays a major role in the plasma density structure at F-region altitudes. In the summer polar region an increase in the proportion of molecular to atomic species, created by the global seasonal therrnospheric circulation and augmented by the geomagnetic forcing, controls the plasma densities at all Universal Times. The increased destruction of F-region ions in the summer polar region reduces the mean level of ionization to similar mean levels seen in winter, despite the increased level of solar insolation. In the upper thermosphere in winter for BY negative, a tongue of plasma is transported anti-sunward over the dusk side of the polar cap. To effect this transport, co-rotation and plasma convection work in the same sense. For IMF BY positive, plasma convection and co-rotation tend to oppose so that, despite similar cross-polar cap electric fields, a smaller polar cap plasma tongue is produced, distributed more centrally across the polar cap. In the summer polar cap, the enhanced plasma destruction due to enhancement of neutral molecular species and thus a changed ionospheric composition, causes F-region plasma minima at the same locations where the polar cap plasma maxima are produced in winter.
High-latitude ionospheric currents during very quiet times: their characteristics and predictability
Annales Geophysicae, 2004
CHAMP passes the geographic poles at a distance of 2.7 • in latitude, thus providing a large number of magnetic readings of the dynamic auroral regions. The data of these numerous overflights were used for a detailed statistical study on the level of activity. A large number of tracks with very low rms of the residuals between the scalar field measurements and a high degree field model were singled out over both the northern and southern polar regions, independently. Low rms values indicate best model fits and are therefore regarded as a measure of low activity, although we are aware that this indicator also has its limitations. The occurrence of quiet periods is strongly controlled by the solar zenith angle at the geomagnetic poles, indicating the importance of the ionospheric conductivity. During the dark polar season, about 30% of the passes can be qualified as quiet. The commonly used magnetic activity indices turn out not to be a reliable measure for the activity state in the polar region. Least suitable is the D st index, followed by the K p . Slightly better results are obtained with the P C and the IMAGE-AE indices. The latter is rather effective within a time sector of ±4 hours of magnetic local time around the IMAGE array.
Study of the ionospheric variability within the Euro-Asian sector during the Sundial/Atlas 1 mission
Journal of Geophysical Research, 1996
In order to quantify, and to identify possible origins of, subauroral ionospheric variability during periods of moderate geomagnetic activity, ionospheric observations taken during the SUNDIAUATLAS -1 campaign (March 24 to April 2) from 10 stations were analyzed in conjunction with observations from EISCAT, geomagnetic observations from magnetometer networks in Scandinavia and the United Kingdom, and auroral particle energy input observations from the NOAA -12 satellite. The network of ionospheric stations spanned longitudes from 13~ to 90~ but were relatively confined in geomagnetic latitudes so that longitudinal and local time dependencies in ionospheric variability are more clearly exposed. The ionospheric observations were analyzed in terms of both llfJ'2, the difference between the hourlyfJ'2 at a given station and tlle mOJlthly medianfJ'2 for that hour, and a new daily variability index AfJ'2. The analysis using both parameters demonstrated an apparent longitudinal variation in ionospheric variability with a reversal at about 55° E from a negative to a positive phase in the departure of ionospheric conditions from their median values. An analysis of these ionospheric data in conjunction with the NOAAlrIROS estimates of pOwer deposition by auroral particles demonstrated a significant local time dependence in midlatitude ionospheric responses to auroral activity. This dependence may arise from the premidnight to postmidnight asymmetry in high-latitude convection electric fields. 26,759
Ionospheric Models Including the Auroral Environment
Modelling of the ionospheric-plasmaspheric electrondensity height profile N(h), as well as other parameters like the ion composition or electron and ion temperatures, over the whole altitude range for all geographical positions, time spans, and geophysical conditions is an essential part of ionospheric physics and a critical element in the development of practical schemes for ionospheric space weather applications. This paper attempts to review recent progress in electron-density profile modelling. The various types of models available are described, and their applicability to space weather forecasting is assessed.
On the latitudinal variations of the ionospheric electric field during magnetospheric disturbances
Journal of Geophysical Research, 1983
A joint alert campaign was organized during the month of October 1980 by the incoherent scatter radars in the American sector: namely, Jicamarca, Arecibo, Millstone Hill, and Chatanika. The campaign, which met with success, was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions. The Arecibo data in this campaign support present and previous observations at Jicamarca that suggest that when the convection E field suddenly decreases, the Alfv6n layer shielding field becomes unbalanced and penetrates the plasmasphere. While this type of observation is reasonably convincing, others are more difficult to categorize. We suggest that, beside the high-latitude electric fields, time-varying auroral conductivity models will have to be considered in order to understand the morphology of the low-latitude E field disturbances. We present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 ø geometric latitude (Arecibo) to the field at 0 ø (Jicamarca). Other highlights of the paper are a discussion of DP2, which may help clarify the controversy surrounding it, and a discussion of the sensitivity of low-and mid-latitude radars to disturbances of magnetospheric origin. We show that this sensitivity maximizes at the magnetic equator. 1. INTRODUCTION This paper is the third in a series of publications related to disturbances of the plasmaspheric electric field during periods of magnetic activity [Fejer et al., 1979b; Gonzales et al., 1979]. While the first two papers were concerned mostly with the electric field at the equatorial ionosphere, this study, for the first time, covers mid-latitudes by including data from the Arecibo and Millstone radars in addition to data from auroral (Chatanika) and equatorial (Jicamarca) radars. The data presented here resulted from a joint alert campaign for measuring F region E x B drifts in which several incoherent scatter radars participated. The campaign took place during October 1980. It is significant to note that three of the radar sites are located at nearly the same meridian and extend from the equator to the auroral zone: namely, Jicamarca, Arecibo, and Millstone Hill. The Chatanika radar also participated in the project and yielded very valuable auroral zone data. Difficulties in the logistics of the experiment prevented us from getting all radars to operate during all desired periods. However, our rate of success was still rather remarkable: out of three possible runs, two coincided with the two most active days of October 1980. The third run occurred during one of the quietest periods of the same month and thus provided an excellent baseline for comparative studies. A summary of the campaign is presented in Figure 1. Two basic approaches have been taken in the study of the magnetospheric electric field coupling with the low-latitude ionosphere. In statistical studies [Blanc, 1983a; Gan•Iuly et al., 1983; Wand and Evans, 1981] the average electric field is obtained for various levels of magnetic activity as measured by the Kp index. These averages are then compared with the electric field during low Kp in order to determine the direction and magnitude of the disturbance attributed to magnetospheric effects. Although useful, this approach suffers from •Arecibo Observatory, National Astronomy and Ionosphere Center.