https://hdl.handle.net/1721.1/97457 2026-04-04T20:50:24Z 2026-04-04T20:50:24Z Evans, J. V. Holt, J. M. Oliver, W. L. Wand, R. H. https://hdl.handle.net/1721.1/97679 2019-04-12T12:52:35Z 1982-09-01T00:00:00Z

Studies of the Midlatitude and High Latitude Ionosphere from Millstone Hill during Solar Maximum Conditions Evans, J. V.; Holt, J. M.; Oliver, W. L.; Wand, R. H. This report summarizes the work carried out at the Millstone Hill radar from April 1979 through March 1982 in studies of the earth's upper atmosphere and ionosphere with the support furnished by the National Science Foundation (Grant ATM-79-09189). Most notable were new studies of the auroral and subauroral regions of the ionosphere using a scanning technique in which the 1° beam of the UHF steerable radar is scanned at a fixed elevation (typically 4°) through 180° or 360° azimuth. This technique provides maps of the electron density, electron and ion temperatures and line-of-sight drifts at fixed altitudes as functions of invariant latitude and local time. These show a rich variety of behavior depending upon magnetic activity and season. In particular, the nighttime trough frequently is found to appear first in mid-afternoon at latitudes where the ion drift is high and sunward. Later the trough usually is found equatorwards of regions of fast convection. It is suggested that troughs may be manufactured in regions of rapid flow during substorms and then corotate with the earth as 'fossils' once the electric fields have diminished. Other studies reported herein include the analysis of the daily mean temperature, and the semidurnal temperatures and winds in the lower thermosphere as well as studies of the exospheric temperature. The report includes a detailed account of the improvements made in both the hardware and the software at the radar during the three-year period.

1982-09-01T00:00:00Z Evans, J. V. Holt, J. M. https://hdl.handle.net/1721.1/97678 2019-04-12T13:25:13Z 1982-01-01T00:00:00Z

Millstone Hill Thomson Scatter Results for 1974 Evans, J. V.; Holt, J. M. During 1973, the vertically-directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperature and vertical ion velocity in the F-region over periods of 24 hours one or two times per month. The observations spanned the height interval 200-900 km approximately, and achieved a time resolution of about 30 minutes. This report presents the results of the measurements made using single long pulses in a set of contour diagrams. The behavior observed during these observations is discussed briefly in terms of the diurnal, seasonal, sunspot cycle, and magnetic disturbance variations reported previously and which now are believed to be largely understood.

1982-01-01T00:00:00Z Evans, J. V. Babcock, R. R., Jr. Holt, J. M. https://hdl.handle.net/1721.1/97677 2019-04-11T10:23:06Z 1979-10-22T00:00:00Z

Millstone Hill Thomson Scatter Results for 1973 Evans, J. V.; Babcock, R. R., Jr.; Holt, J. M. During 1973, the vertically-directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperature and vertical ion velocity in the F-region over periods of 24 hours one or two times per month. The observations spanned the height interval 200-900 km approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams. For a number of the days, the results have been used to derive the diurnal variation of the temperature of the neutral atmosphere above 300 km (the exospheric temperature) as well as the speed of the neutral wind in the magnetic meridian plane at this altitude. These results were used to define a model for the pressure variation in the thermosphere over Millstone whose E-W variation is set by the observed temperature variation, and whose N-S variation was adjusted to reproduce the observed winds calculated by solving momentum equations for the neutral air. These results, together with similar results obtained using data gathered over the six-year period 1970-1975 have been used in a study of the seasonal and sunspot cycle variation of the mean meridional and zonal winds. Also reported are the results of a study of the effect of magnetic storms on the thermospheric winds observed over Millstone Hill.

1979-10-22T00:00:00Z Evans, J. V. Holt, J. M. Oliver, W. L. Wand, R. H. https://hdl.handle.net/1721.1/97676 2019-04-12T13:25:13Z 1979-09-01T00:00:00Z

Studies of the Midlatitude and High Latitude Ionosphere from Millstone Hill April 1976 - March 1979 Evans, J. V.; Holt, J. M.; Oliver, W. L.; Wand, R. H. During the period 1 April 1976 through 31 March 1979, the Millstone Hill radar facility in Westford, Massachusetts (42° N, 71.5° W) was supported for incoherent scatter studies of the earth's upper atmosphere and ionosphere by the National Science Foundation under Grant ATM 75-22193. This report describes the work carried out under this grant.

1979-09-01T00:00:00Z Oliver, W. L. Salah, J. E. Wand, R. H. Evans, J. V. https://hdl.handle.net/1721.1/97675 2019-04-12T13:25:10Z 1979-02-23T00:00:00Z

Incoherent Scatter Measurements of E- and F-Region Density, Temperatures, and Collision Frequency at Millstone Hill Oliver, W. L.; Salah, J. E.; Wand, R. H.; Evans, J. V. The Millstone Hill incoherent (Thomson) scatter radar system has been operated since 1963 to perform a synoptic study of F2-region electron densities, and electron and ion temperatures. These measurements have been conducted by transmitting single long pulses and performing digital sweep integration and spectrum analysis of the reflected signals. This report describes changes made to the system in 1969 to permit extensions of the measurements to altitudes below 200 km (i.e., the E- and F1-regions). These changes include modifications to the radar timing equipment to permit the transmission of close-spaced pairs of pulses from which the echo autocorrelation function can be determined in the computer by processing appropriately spaced pairs of echo samples. By operating the radar coherently, it has also been possible to subtract the unwanted (stronger) clutter signals from the ionospheric echoes. Samples are presented of the results that can now be obtained from these programs.

1979-02-23T00:00:00Z Evans, J. V. Holt, J. M. https://hdl.handle.net/1721.1/97674 2019-04-12T13:25:09Z 1978-09-18T00:00:00Z

Millstone Hill Thomson Scatter Results for 1972 Evans, J. V.; Holt, J. M. During 1972, the vertically directed incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure electron density, electron and ion temperatures, and vertical ion velocity in the F-region over periods of 24 hours, one or two times per month. The observations spanned the height interval 200 to 900 km, approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams. For a number of the days, the spectra of the signals gathered at altitudes between 450 and 1125 km have been the subject of further analysis in an effort to determine the percentage of H[superscript +] ions present over Millstone. The results suggest that H[superscript +] ions are escaping from the F-region to the magnetosphere at a value close to the theoretical limiting flux during the daytime in all seasons. At night the flux becomes downward commencing near midnight in winter, but may remain upward throughout the night in summer.

1978-09-18T00:00:00Z Evans, J. V. Emery, B. A. Holt, J. M. https://hdl.handle.net/1721.1/97673 2019-04-12T13:25:13Z 1978-03-24T00:00:00Z

Millstone Hill Thomson Scatter Results for 1971 Evans, J. V.; Emery, B. A.; Holt, J. M. During 1971, the incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure the electron density, electron and ion temperatures, and the vertical velocity of the 0[superscript +] ions in the F-region over periods of 24 hours on 20 days. The observations spanned the height interval 200 to 900 km, approximately, and achieved a time resolution of about 30 minutes. This report presents these results, after smoothing as a set of machine-drawn contour plots. The report discusses the behavior observed in 1971 in light of that seen in previous years. A significant number of days appear to have been disturbed by large traveling ionospheric disturbances. Results for the average exospheric temperature, the mean meridional, and zonal winds for 1970and 1971 derived from these incoherent scatter measurements in a separate study by B.A. Emery are summarized here for completeness. The results appear to confirm the mean wind behavior that would be predicted by the recent Mass-Spectrometer, Incoherent-Scatter (MSIS) global model for the thermosphere and support the view that interhemispheric transport of light neutral constituents (e.g., atomic oxygen) gives rise to tie anomalous seasonal behavior of the ionosphere at midlatitudes.

1978-03-24T00:00:00Z Evans, J. V. Holt, J. M. https://hdl.handle.net/1721.1/97672 2019-04-11T04:32:21Z 1976-05-11T00:00:00Z

Millstone Hill Thomson Scatter Results for 1970 Evans, J. V.; Holt, J. M. During 1970, the incoherent scatter radar at Millstone Hill (42.6°N, 71.5°W) was employed to measure the electron density, electron and ion temperatures, and vertical velocity of the ions in the F-region over periods of 24 hours on an average of twice per month. The observations spanned the height interval 200 to 900 km, approximately, and achieved a time resolution of about 30 minutes. This report presents the results of these measurements in a set of contour diagrams. Commencing with the data presented in this report, a method of data reduction has been used which supersedes the older one of constructing the contour diagrams by hand. In the new method the set of points for any given parameter is matched by a two-dimensional polynomial surface in a least-squares fit. The program that carries this out is described fully in the report. By obtaining a continuous analytical description of the data with respect to height and time, machine-drawn contouring becomes possible and is now employed. The new program also provides a means of transferring the results to other users in machine-readable form. In addition, the new program yields a more repeatable smoothing of the data with respect to height and time, thereby allowing parameters that depend upon gradients (e.g., heat and particle fluxes) to be estimated more accurately.

1976-05-11T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97671 2019-04-11T07:52:43Z 1974-07-23T00:00:00Z

Millstone Hill Thomson Scatter Results for 1969 Evans, J. V. This report summarizes the results for the electron-density distribution, electron and ion temperatures, and vertical ionization fluxes in the F-region obtained during 1969 using the Millstone Hill (42.6°N, 71.5°W) Thomson (incoherent) scatter radar system. These data, for the height interval approximately 200 to 900 km, were gathered over 24-hour observing periods, roughly twice per calendar month. The time resolution to obtain results over this entire height interval was either 30 or 45 minutes, depending upon which of two operating modes was employed. The results for the diurnal variation of the electron density and temperature exhibit the characteristic summer and winter patterns discussed previously. The transition between the two takes place in April and October. Two cases of overhead auroral precipitation were observed during the year as a consequence of efforts to observe a stable red arc. Other instances of geomagnetically disturbed behavior were infrequent. Vertical fluxes of ionization were measured, and the flux escaping to the magnetosphere near midday was found to have an average value of ~5 x 10[superscript 7] el/cm[superscript 2]/sec. Near midnight, the magnetosphere appears to supply the local ionosphere with a flux of about half this amount..

1974-07-23T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97670 2019-04-11T10:23:05Z 1973-01-23T00:00:00Z

Millstone Hill Thomson Scatter Results for 1968 Evans, J. V. This report summarizes the results for the electron density distribution, electron and ion temperatures in the F-region obtained during 1968 using the Millstone Hill (42.6°N, 71.5°W) Thomson (incoherent) scatter radar system. These data, for the height interval approximately 200 to 800 km, were gathered over 24-hour observing periods, roughly twice per calendar month. The time required to obtain a complete electron density and temperature profile over this height interval was usuaIly 30 minutes. During 1968 the apparatus employed to measure the frequency spectrum of the reflected signals vs altitude, which in turn yields the estimates of the electron and ion temperatures, was rebuilt permitting the measurements at all altitudes to be made in real time, and with greater accuracy than heretofore. In addition, the new spectrum analyzer permitted the first measurements at Millstone Hill of the vertical drift of the plasma. These results, which are difficult to condense into summary form, are not included in the report. The density and temperature results show that the separate clear patterns of summer and winter diurnal behavior, recognized at sunspot minimum, can still be discerned at sunspot maximum on all but very disturbed days. A number of disturbance patterns observed previously were again detected in 1968, albeit on fewer occasions than in 1967. Apparently, by chance, the days selected for observation in 1968 contained fewer instances of magnetic disturbance than in 1967. The average heat flux from the magnetosphere has been investigated. While there appears to be a clear dependence on solar flux (as defined by the 10.7-cm radio emission), there remains a summer-to-winter variation of 5 to 7 that cannot be easily explained.

1973-01-23T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97669 2019-04-10T18:06:48Z 1971-07-22T00:00:00Z

Millstone Hill Thomson Scatter Results for 1967 Evans, J. V. This report summarizes results for the electron density distribution and electron temperature of the F-region obtained during 1967 using the Millstone Hill (42.6“N, 71.5°W) Thomson (incoherent) scatter radar system. These data, for the height interval of approximately 200 to 800 km, were gathered over 24-hour observing periods twice per calendar month. The time required to obtain a complete electron density and temperature profile over this height interval was 30 minutes. The results show a far wider range of behavior than that encountered in previous years. This is attributed to the increase in magnetic activity as sunspot maximum is approached. On magnetically quiet days, the characteristic behavior observed previously for electron density manifests itself. Winter days exhibit a maximum at all levels near noon and a weaker maximum at the layer peak in the early morning (0200 to 0400 EST), while summer days exhibit a maximum near sunset and only a small day-to-night change in density near the layer peak. Two days exhibited a pattern of behavior, first noted in 1965, that appears characteristic of many storms. This consists of an increase in density on the afternoon of the first day of the storm followed by a marked decrease the next morning. Other days show instances of nocturnal heating and erratic behavior of the F-region electron density at night. We believe that on several occasions in 1967 the plasmapause boundary moved south of Millstone giving rise to a rapid fall in f[subscript o]F2 and to much of the irregular behavior observed at night.

1971-07-22T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97668 2019-04-11T04:30:36Z 1971-01-19T00:00:00Z

Millstone Hill Thomson Scatter Results for 1966 Evans, J. V. This report presents F-region electron densities and electron temperatures observed during the year 1966 at the Millstone Hill Radar Observatory (42.6°N, 71.5°W) by the UHF Thomson (incoherent) scatter radar. The measurements were usually made for periods of 24 hours twice per month, and covered the altitude range 150 to 750 km approximately. The time required to collect all the measurements spanning this height interval was 30 minutes, i.e., half that of previous years. The results exhibit a greater amount of random time variation than seen heretofore, partly as a result of the better time resolution achieved and partly because each day has been analyzed individually, i.e., we have discontinued the practice of computing only the monthly mean behavior. We believe, however, that the largest part of the random variation is real and results from fluctuations in the solar EUV flux, which increase in magnitude as the sunspot number rises. Also, we expect a growing incidence of fluctuations produced by large-scale traveling ionospheric disturbances as we approach sunspot maximum. Despite this variability, the characteristics “winter” and “summer” type behavior reported for Millstone in previous years is clearly recognizable. On four days in which pronounced effects due to geomagnetic storms are evident, the layer rose to great heights in the late afternoon and achieved an abnormally high density (and lower-than-normal temperature). The reverse behavior was encountered the next morning. This sequence is similar to that first seen in June 1965, and its interpretation in terms of current ideas is summarized.

1971-01-19T00:00:00Z Evans, J. V. Julian, R. F. Reid, W. A. https://hdl.handle.net/1721.1/97667 2019-04-12T13:25:09Z 1970-02-06T00:00:00Z

Incoherent Scatter Measurements of F-Region Density, Temperatures, and Vertical Velocity at Millstone Hill Evans, J. V.; Julian, R. F.; Reid, W. A. The Millstone Hill Thomson (incoherent) scatter radar system has been operated routinely since 1963 to perform a synoptic study of F-region electron densities, and electron and ion temperatures. This report describes system changes made in 1968 which considerably increased the accuracy of the measurements and allowed their extension to higher altitudes. These changes have also made it impossible to measure the vertical velocity of the plasma over the altitude range 450 to 900 km to an accuracy on the order of 5 to 10 m/sec, depending upon altitude and time of day. Of even greater significance, complete machine reduction of the results is now possible so that considerable savings in time and effort have been secured in analyzing the data. The new system permits all the radar data to be gathered in the digital computer in real time, thereby eliminating the need for post real-time processing of magnetic-tape recordings of the signals. Furthermore, it is now possible to transmit the data to other workers in computer-usable form. This report describes the main functions of the computer program required to analyze the measurements, and lists the times of all measurements made with the new system prior to 1 January 1970. Examples of these results are presented and discussed.

1970-02-06T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97666 2019-04-12T13:25:08Z 1969-12-08T00:00:00Z

Millstone Hill Thomson Scatter Results for 1965 Evans, J. V. This report presents F-region electron densities, and electron and ion temperatures observed during the year 1965 at the Millstone Hill Radar Observatory (42.6°N. 71.5“W) by the UHF Thomson (incoherent) scatter radar. The measurements were made over 48-hour periods that were usually scheduled to include the International Geophysical World days near the center of each month. Geomagnetic storm sudden commencements occurred during two of the observing periods, but do not appear to have given rise to marked variation of the densities or temperatures. On the other band, measurements made during the progress of a major storm (15-19 June 1965) exhibit large changes compared with the behavior observed in the following month. The remaining months were magnetically quiet, and the density and temperature behavior were similar to those observed in 1964. Millstone is a midlatitude station exhibiting a characteristic “winter” and "summer” daytime density variation. The transition between these two types occurs rapidly around equinox, without any corresponding seasonal change in the F-region thermal structure. Current ideas concerning the mechanisms responsible for this and other features of diurnal and seasonal variations arc discussed.

1969-12-08T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97665 2019-04-12T13:25:08Z 1967-11-15T00:00:00Z

Millstone Hill Thomson Scatter Results for 1964 Evans, J. V. Thomson scatter (incoherent backscatter) observations of the ionosphere were made at Millstone Hill at a wavelength of 68 cm during 1964, for 30-hour periods every two weeks. These data have been employed to derive the mean hourly F-region (200 to 700 km) electron density profile and electron and ion temperature curves in each month. The results are presented in this report, together with the derived seasonal variation of electron density (at 0600, 1200, 1800 and 2400 hours local time) and the average daytime (0900 to 1500) and nighttime (2100 to 0300) electron and ion temperature behavior. Separate measurements with a 23-cm radar permitted the temperature results reported to be extended to lower altitudes (~130 km) and, in addition, provided information concerning the ionic constituents between 130 and 230 km. Although 1964 was at sunspot minimum, the seasonal variation in f[subscript o]F2 was quite evident. It is shown that this feature is strictly associated with the peak of the layer and that densities above 400-km altitude are highest at the equinoxes. No seasonal variations of temperature are found which might be large enough to account for the phenomenon. At night the peak densities are highest in summer, and the temperatures at all altitudes highest in winter. This last effect is believed largely due to heat conducted from the protonosphere, which in winter continues to be heated by photoelectron escape from the conjugate ionosphere which remains sunlit throughout the night.

1967-11-15T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97664 2019-04-11T10:23:02Z 1965-01-22T00:00:00Z

Ionospheric Backscatter Observations at Millstone Hill Evans, J. V. Studies of the electron-density, eIectron and ion temperatures in the F-region were mode by means of ground-based radar observations at the MilIstone Hill Radar Observatory. A 70-meter parabolic antenna directed vertically and a 2.5-Mw pulse radar operating at 440 Mcps were employed for these measurements which were conducted for periods of 30 hours at approximately weekly intervals throughout 1963. Examination of the echo power as a function of height leads to a profile of electron density with height, provided the electron and ion temperatures are the same (T[subscript e] = T[subscript i]). Additional measurements of the spectra of the signals corresponding to different heights permit the ratio T[subscript e]/T[subscript i] to be determined and, where this is different from unity, the observed profile can then be corrected for the effect on the scattering introduced by the inequality in temperature. Results of observations extending over a period of one year from February 1963 to January 1964 are presented. The ratio T[subscript e]/T[subscript i] achieved a maximum value ~2.0 to 2.6 at a height of about 300 km soon after dawn, irrespective of the season. There was Iittle change in height dependence in this ratio throughout the daylight hours, and at sunset the ratio felI with a time constant of the order of an hour. At night T[subscript e]/T[subscript i] was occasionally close to unity, but more often a significant difference remained in the temperatures at all heights. Ion temperature increased with height at all times, but above 500 km this may be due in part to the presence of an unknown amount of He[superscript +] ions, which considerably affects the interpretation of the signal spectra. Electron temperatures were largely independent of height above about 300 km. Evidence is presented of ionospheric heating during magnetically disturbed conditions, but it is shown that this is only of great importance at night.

1965-01-22T00:00:00Z Evans, J. V. https://hdl.handle.net/1721.1/97662 2019-04-12T12:50:45Z 1962-07-24T00:00:00Z

Studies of the F-Region by the Incoherent Backscatter Method Evans, J. V. The Millstone Hill radar facility operated by M.I.T. Lincoln Laboratory has made measurements of the distribution of electrons in the F-region of the ionosphere by observing the weak incoherent backscatter signal. These measurements were first made early in 1960 and were continued throughout 1961 on a routine basis at least once a week. This report presents alI the electron density profiles measured up to the end of 1961. Results of spectral analyses of the signals made early in 1962 are also given. The distribution of electrons above the peak of the F-region has been a subject of special study. On the basis of the results obtained to date the conclusions reached are: (a) the scale height of the electron density increases with height, (b) the ion temperature is not very dependent on height, though it does show a marked diurnal variation, (c) the election-to-ion temperature ratio is 1:1 during the hours of darkness, but during the daytime it increases too peak value ~1.6:1 around noon and (d) the scattering cross section for the electrons is close to the expected value when alIowance is made for (c).

1962-07-24T00:00:00Z