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. 1974; Kohl, 1976], and by influencing the magnitude of ion iations of the electric field, which are not incorporated into drag through redistribution of ionization [e.g., Anderson and Richmond's [1976] model. The present model thus supersedes Roble, 1974]. Knowledge of the global ionospheric electric that earlier one, field is also useful in providing an upper boundary condition on calculations of middle atmosphere electric fields such as those performed by Roble and Hays [1979]. Substantial collections of ionospheric electric field data exist for the incoherent scatter radar observatories at Millstone Hill, St. Santin, Arecibo, and Jicamarca. In spite of the large day-to-day variability of the electric fields, earlier analyses were able to determine clear average daily variations [e.g., Woodman, 1970, 1972; Evans, 1972; Carpenter and Kirchhojf,, 1974; Kirchhoff and Carpenter, 1976; Richmond, 1976; Blanc et al., 1977]. More recent analyses have quantified the seasonal DATA BASE Data are used from the four incoherent scatter radar stations listed in Table 1. These radars measure the ion velocity, whose component v perpendicular to the geomagnetic field B is related to the electric field E by v = E • B/B • (•) At each station, F region ionization drifts were typically measured on a few days each month within the interval indicated. Depending on the mode of operation, projections of v onto one or more station-dependent axes can be determined at a given time. The measured components of v are averaged in height to improve accuracy, a process justified by the expectation that E and v vary only slightly with altitude within the F region, owing to the near-equipotentiality of magnetic field lines and to the large-scale nature of the global electric field. The mean altitude of the measurements is roughly 300 kin. All stations except St. Santin determine vector velocities by combining line-of-sight velocities measured at different directions from the transmitter/receiver, corresponding to different volumes of the ionosphere. The assumption is then made that the ionospheric drift vectors are the same for all volumes of measurement from a particular station. For further information about the measurement techniques, see Paper number 80A0414.

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 Alfvén 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° geometric latitude (Arecibo) to the field at 0° (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.

Since 1978, radar observations of F region electric fields within the region 55° < Λ < 75° have been made from Millstone Hill (42.6°N, 71.5°W). Averge convection patterns have been calculated from the ion drift data gathered in 109 of these experiments conducted between January 1978 and August 1981. Most of the experiments lasted between 24 and 48 hours, and over 3,700,000 values of the line‐of‐sight velocity were determined and included in the averages. The observed velocities were sorted into “bins” of ½‐hour intervals of magnetic local time and 2° intervals of apex latitude. Each of these cells had been viewed by the radar over a wide range of aspect angles in the course of the 109 experiments, allowing the average vector velocity to be determined. The data were separated further into three levels of Kp, according to whether the interplanetary magnetic field (IMF) was “toward” or “away” from the sun, and by season. The average patterns are discussed and compared with earlier models based on satellite and incoherent scatter data. There is an expansion and intensification of the pattern with Kp for all seasons and IMF orientations. The polar cap entry and exit points of the plasma, the center of the cells, and the polar cap boundary all depend on the IMF. The Harang discontinuity, which can be seen clearly on individual days, is largely lost in the averages.

F region ion temperature measurements were made by the Chatanika and Millstone Hill incoherent scatter radars as part of the Magnetosphere‐Ionosphere‐Thermosphere Radar Studies program of coordinated high‐latitude observations. At both radars, periods of enhanced ion temperature associated with Joule heating events were detected. A regular feature of the observations was the existence of larger and longer lasting temperature enhancements in the morning sector as contrasted with the evening sector during periods of comparable electric field magnitudes. Because the ion temperature increases in proportion to the square of the vector difference between the ion and neutral velocities, the morning/evening temperature enhancement asymmetry implies a morning/evening neutral wind asymmetry. The neutral wind in the evening must be more closely aligned to the ion flow vector. This might arise as a consequence of the higher plasma density in the evening sector, enabling the ions to set the neutral air in motion. Comparison of the simultaneous plasma density and ion velocity measurements with the ion temperature data supports the foregoing explanation for the observed greater morning sector temperature enhancements.

From January 1971 to March 1973, five satellites of the Navy Navigation Series (Transit) in polar orbits at 1000 km altitude were tracked from Millstone Hill to secure differential‐Doppler measurements of N‐S gradients in the ionosphere. In all, over 2000 passes were observed, encompassing all local times and seasons. All of the differential‐Doppler records have been scanned to secure statistical information on the incidence, wavelength, amplitude, and location of the traveling ionospheric disturbances detected. Most of the TID's had wavelengths in the range of 150–350 km and were seen to the south of the station, suggesting that they were traveling from north to south. The incidence peaked at 60% of all passes at 0800 local time and dropped to less than 5% for a few hours before sunrise. The seasonal variation is less clear‐cut, but the incidence seems to be increased in winter and the equinoxes and reduced in summer. This may be simply a consequence of the dependence of the detectability on total content. While the character of the fluctuations and a north‐to‐south motion would be consistent with a source in the auroral ionosphere, there seems to be no increase in incidence during magnetically disturbed times. Moreover, in summer the waves are seen equally to the north and the south of the station. It seems possible that there may be many sources for these waves distributed in latitude and that the observed locations are controlled by the filtering effects of F region winds.