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Fabry–Perot interferometric (FPI) measurements of thermospheric zonal neutral winds at Arequipa, Peru ( 16.7° S , 71.5° W , −2.7° dip ), and Carmen Alto, Chile ( 23.1° S , 69.4° W , −10.2° dip ), were collected during the solar minimum periods of September–October 1996 and 1997. The data set included 39 nights from Arequipa and 14 nights for Carmen Alto, with 8 nights of simultaneous observations. Analysis of averaged results found the peak evening zonal neutral wind speed of ∼127±15 m / s eastward for the Arequipa observatory, which is located near the magnetic equator, to occur between 21:30 and 22:30 LT. In contrast, the peak evening zonal winds of ∼100±10 m / s eastward observed from Carmen Alto, which is located near the crest of the equatorial ionization anomaly (EIA), occurred ∼0.5– 1 h later. These measurements represent the first case of groundbased FPI observations of the so called equatorial temperature and wind anomaly (ETWA) over such a small latitude range in the same longitude sector. This reduction in speed of ∼20–25% at Carmen Alto relative to Arequipa is attributed to increased ion drag at Carmen Alto caused by the higher electron density within the EIA region at altitudes of 220– 300 km . Model studies were conducted using electron density and neutral atmosphere parameters form the parameterized ionospheric model (PIM) and the mass spectrometer incoherent scatter (MSIS) models, respectively, to calculate the ratio of ion–neutral collision frequencies at the two sites. We found that the increase in electron density within the EIA was sufficient to account for the observed reduction in the zonal wind. Thus, this analysis confirms the dominant role of ion drag in modulating thermospheric dynamics at equatorial latitudes. A comparison of the FPI results with the predictions by two current neutral wind models, the Horizontal Wind Model-90 and the NCAR Thermospheric Ionosphere Electrodynamics General Circulation Model (TIEGCM), reveals that neither is able to reproduce accurately the latitude dependence reported here. Model refinements for electrodynamics and improved resolution are suggested.

The determination of the physical processes that cause the day-to-day variability of equatorial spread F (ESF) has long been one of the outstanding problems in terrestrial space physics. Within the context of the Rayleigh-Taylor instability model for ESF, mechanisms that either enhance or inhibit the growth of a seed perturbation offer potential sources of variability that can be tested. In this study the hypothesis that enhanced thermospheric meridional winds play a critical role in suppressing ESF is examined during the Multi-Instrumented Studies of Equatorial Thermospheric Aeronomy (MISETA) campaign of September 1998. New, high-time-resolution Fabry-Perot interferometer (FPI) observations at 6300-A nightglow made at Arequipa (Peru) provided the neutral wind measurements during the critical postsunset hours that had been sampled only sparsely in earlier morphology studies. Evidence of local ESF activity was obtained using GPS-based observations of phase fluctuations (Fp) and 6300-A all-sky optical images from the same site. Additional GPS measurements of Fp and total electron content (TEC) from Bogota (Colombia) and Santiago (Chile) were used to determine the full flux tube development of ESF plumes and to characterize the F region morphology of the interhemispheric Appleton anomaly. Correlative studies between the nightly magnitudes of the meridional winds (Um), ESF activity (Fp), and indices describing the strength (Is) and asymmetry (Ia) of the Appleton anomaly offered no convincing evidence for the wind suppression mechanism. The best available precursor for premidnight ESF appeared to be the strength of the electrodynamically driven Appleton anomaly pattern at sunset. If one assumes that the required seed perturbation for ESF onset is essentially always available, then for all practical purposes, the magnitude of the eastward electric field that causes upward drift is both the necessary and sufficient parameter to forecast ESF with reasonable success. These results reconfirm 60 years of study pointing to the dominance of electrodynamical processes in the onset and growth of plasma instabilities at low latitudes.

Thermospheric winds have been systematically determined at Arequipa, Peru, and Arecibo, Puerto Rico, from Fabry-Perot interferometer measurements of Doppler shifts in the nightglow 630 nm line. The wind databases (1983 - 1990 at Arequipa and 1980 - 1990 at Arecibo) have been edited to eliminate measurements during geomagnetically disturbed conditions, then sorted by season and solar flux level. Following this, they were averaged to obtain the climatological behavior of the nighttime wind variations at the two locations. A new averaging technique, multivariate regression analysis, has been applied to the data, and the results compared to our prior binning averages. The observed wind behaviors at the Arequipa and Arecibo Observatories, which are at equal geographic latitudes on opposite sides of the equator, are contrasted to establish the seasonal flow patterns. The regression analysis results have then been compared with the predicted behavior provided by the National Center for Atmospheric Research's Thermosphere-lonosphere-Electrodynamics General Circulation Model. In many cases, qualitative agreement between measurements and predictions is found as to wind directions and temporal variations, with differences in magnitude of - 0-50 m/s. However, some striking differences are found that may arise from ionosphere-thermosphere coupling effects. The overall results provide an important step in establishing the climatology of the thermospheric winds at equatorial and low-latitude sites.

Fabry-Perot interferometric observations at 630 nm of equatorial thermospheric winds and temperatures in the four cardinal directions and zenith from Arequipa, Peru, during local winter for moderate and high solar fluxes showed elevated temperatures over the Andes Mountains that persisted through the night. The difference in temperature between east and west observations was typically ∼100 to 200 K for moderate flux values and as high as 400 K at solar maximum. Correlated with these localized heating regions were differences in the zonal thermospheric wind of 50 to 70 m/s for observations to the west and to the east of the Arequipa observatory. Also noted in these periods for the region over the Andes was the increased variance of the temperature values above the measurement error. These effects of increased variability and localized heating were not observed at solar minimum. The lack of a significant local time dependence in the diurnal variation of the temperature enhancements suggests that the origin of the heating cannot be related to the coupling of the electrodynamics of the ionosphere to the thermosphere. Instead the hypothesis is advanced that gravity wave energy from the surface penetrates into the thermosphere, where viscous dissipation causes the heating. Such wave activity would also explain the increased variability of the temperatures for the thermosphere regions over mountainous terrain.

Abstract. As part of the NSF/CEDAR program (Coupling Energetics, and Dynamics of Atmospheric Regions) in Multi-Instrumented Studies of Equatorial Thermospheric Aeronomy (MISETA), an all-sky CCD airglow imaging system has been in operation in Arequipa, Peru, since October 1993. Here we report on the first such use of a wide-field imager to document the optical signature and variability of a brightness feature associated with the so-called midnight temperature maximum (MTM). While the observational driver of this study is a 'rightness wave" (BW) seen in 6300 A and 5577 } airglow images, detailed case studies are conducted during two campaign periods when Fabry-Perot interferometer (FPI) and digital ionosonde data were also available. During the passage of a BW, the FPI observed enhancements in thermospheric temperatures, reversals (from equatorward to poleward) of the meridional neutral winds, and local minima in the zonal neutral winds. The ionosonde recorded decreases in the height of the F- layer during BW events. This lends support to the concept that the poleward winds generated by the MTM pressure bulge cause the lowering of the F- layer to regions of enhanced loss (h < 300 km) and corresponding airglow production. The two- dimensional field -of-view of the imager allows identification of the geographical orientation of the BW pattern. We use the orientation angle of the BW as an indicator of the geographical orientation of the MTM. Significant day-to-day variability in these patterns suggest a complex mix of tidal mode interactions that lead to the overall MTM phenomena.

An equatorial campaign was conducted during September 25 to October 7, 1994, to investigate the neutral and plasma dynamics in the equatorial ionosphere after sunset in relation to the day-to-day variability of the occurrence of equatorial spread F (ESF). The campaign was organized under the auspices of National Science Foundation's Multi-Instrumented Studies of the Equatorial Thermosphere Aeronomy program (MISETA), which included the Jicamarca radar, spaced-antenna satellite scintillation, digisonde, all-sky imager, and Fabry-Perot interferometer (FPI) measurements near the magnetic equator in Peru. During a part of the period September 27 to October 3, the Geophysics Directorate of Phillips Laboratory performed measurements away from the magnetic equator at Aguaverde, Chile (magnetic latitude: 11°S) located 800 km to the east of the Jicamarca meridian using geostationary and GPS satellite scintillation, digisonde and all-sky imager systems. The incoherent scatter radar results indicate that the postsunset enhancement of upward plasma drift, even though of the order of only 20 m s−1 during the solar minimum period, is a necessary condition for the generation of ESF. In view of the extreme difficulty of determining the neutral wind speed during the early evening hours by the FPI due to low airglow intensity, it was not possible to unequivocally associate the observed postsunset enhancements with strong eastward neutral winds. However, considering a few observations contiguous to the campaign period, it appears that such a causal relationship may exist. The scintillation drift measurements in Peru and Chile indicated that the zonal irregularity drift was smaller away from the magnetic equator, implying a variation of neutral wind with latitude. This is reproduced in the altitude variation of zonal drift observed by the Jicamarca radar. During a magnetic storm, scintillation measurements indicated that eastward drifts near the magnetic equator are accompanied by westward drifts near the anomaly peak, which is consistent with the effects of a disturbance dynamo. The campaign results indicate that in order to resolve the variability of ESF, a careful probing of neutral dynamics as a function of latitude needs to be undertaken during the postsunset period.

Fabry Perot interferometer observations of equatorial 630 nm airglow thermospheric winds and temperatures were made at Arequipa, Peru (16.5 S, 71.5 W) during the solar maximum years of 1989 and 1990. Examination of the thermospheric winds measured from Doppler shifts of the 630 nm airglow emission in the two directions east and west of Arequipa shows that the zonal wind is often significantly weaker over the Andes (east) than over the Pacific (west) in winter. Between 19 LT and 24 LT, the typical reductions in speed found were ∼40 to 70 m/s. In the same time period the temperature results show elevated values of ∼200-500 K for the three directions (north, east, and zenith) over mountainous terrain compared with those of the two directions (west and south) over water. This effect fades near equinoctial periods. Examination of the standard deviation of the temperature ohservations for the five directions showed an increase in this value above the measurement error hy a factor of three for the direction toward the Andes (East) but not for the direction over water (South) ; this elevation is consistent with wave activity as a source of the heating. Viscous dissipation of waves propagating into the thermosphere region from below is suggested as an explanation for the localized regions of heating.

Monostatic and bistatic measurements of thermospheric winds have been made with Fabry-Perot Interferometers at the Millstone Hill and Laurel Ridge Observatories. Synchronized observing sequences have been chosen to enable the determination of vertical winds from the measurements. The vertical winds are found to be significant on some nights with velocities of tens of m/s. For geomagnetically quiet nights, the averaged values for eight samples in the July–October 1992 period show little variation during the night, averaging ∼10 m/s downward. The average for three geomagnetically disturbed nights oscillates from a downward maximum of ∼50 m/s at ∼02 UT to an upward maximum of ∼20 m/s at ∼07 UT. Temporal variations in the vertical motions suggest oscillatory behavior with periods of ∼0.7, ∼1.8 and ∼3.4 h, respectively, on three quiet nights, possibly associated with gravity wave or tidal-harmonic effects.

An efficient, all-sky input optical system has been mated to a 100-mm-aperture Fabry–Perot interferometer that employs a cooled (−150 °C) CCD as a photon detector to create an all-sky Doppler interferometer. The instrument is capable of simultaneously measuring Doppler shifts and widths of nightglow emission lines from many different points in the sky, thereby providing determinations of upper-atmosphere neutral wind and temperature fields over a large region (to ≈2000 km in extent). For OI 630-nm (thermosphere) and OH 799.6-nm (mesopause) nightglow emissions, exposure times of 5–15 min provide good-quality interferometric images. The capability of the all-sky Doppler interferometer is illustrated by examples of thermospheric wind and temperature fields measured over Millstone Hill, Massachusetts.

Near-equatorial thermospheric wind velocities at Arequipa, Peru, are determined over about two-thirds of a solar cycle using Fabry-Perot interferometer measurements of Doppler shifts in the nightglow 630-nm emission line. Mean monthly nocturnal variations in the meridional and zonal wind components are calculated from the nightly data to remove short-term (day-to-day) variability as well as any additional changes introduced by the progression of the solar cycle. For most of the years, at the winter solstice, there is a weak (more than 100 m/s) transequatorial flow from the summer to the winter hemisphere in the early and the late night, with essentially zero velocities in between. At the equinoxes, an early-night poleward (southward) flow at solar minimum (1986) is replaced by an equatorward (northward) flow at solar maximum (1989-1990).

Measurements of zonal irregularity drifts were made by the spaced receiver scintillation and radar interferometer techniques from Huancayo and Jicamarca, respectively. The Fabry-Perot Interferometer operated at Arequipa provided the zonal neutral winds. These simultaneous measurements were performed during evening hours in the presence of equatorial spread- F on three nights in October 1988. The zonal drift of 3-m irregularities obtained with the 50-MHz radar showed considerable variation as a function of altitude. The drift of hundreds of m-scale irregularities obtained by the scintillation technique agreed with the drift of 3-m irregularities when the latter were measured near the F -peak. The neutral winds, on the other hand, sometimes exceeded the irregularity drifts by a factor of two. This is a possible result of the partial reduction of the vertical polarization electric field in the F -region caused by the effects of integrated Pedersen conductivity of the off-equatorial night-time E -region coupled to the F -region at high altitudes above the magnetic equator.

[1] A study of the midnight temperature maximum (MTM) climatology has been made for the low-latitude station at Arequipa, Peru (16.2°S, 71.5°W) using Fabry-Perot measurements for the period 1997–2001. Examination of the Arequipa nighttime temperature data after removal of the nocturnal cooling (as represented by the semiempirical NRLMSISE-00 model) shows a Gaussian-like time dependence with amplitudes between 20 and 200 K centered on 0400–0600 UT. A typical value of 50 to 75 K was found for data averaged over the nights from late March to early October, cloudy skies preventing measurements during summer months (November–February). These data show the MTM activity to fluctuate sporadically throughout the austral winter. Also evident are large variations of the offset between the observed temperatures and the MSIS model, with individual nightly offsets between ±200 K. Averaging these offsets over all nights for any 1 year and for all 5 years reduces the offset to a value of ∼20 K. The observed time for the occurrence of the MTM peak amplitude exhibits a seasonal variation; during winter solstice the peak typically occurs between 0500 and 0700 UT, later than during the fall and spring equinoxes, when the peak occurs between 0300 and 0500 UT. The variation of the MTM amplitude with day number shows a weak semiannual oscillation with peak values of 150–200 K near equinoxes and a small secondary maximum of 50 to 70 K near the winter solstice. Examination of the variation of the yearly-averaged MTM amplitude between solar minimum and solar maximum show a slight trend featuring a ∼20 K reduction.

An account is given of laboratory studies made over 50 years ago that revealed a very fast electron-ion recombination process and the subsequent experiments that established the underlying mechanism. These studies were facilitated by development during World War II of major new technologies such as microwaves and fast electronics. Many of these developments took place at MIT in its classified Radiation Laboratory. In 1946, these extensive facilities were converted to the Research Laboratory for Electronics, where Physics Professors W. P. Allis and S. C. Brown formed the Microwave Discharge Group, initially with four graduate student experimenters.

[1] The response of a ground-based Fabry-Perot interferometer (FPI) to predicted non-Maxwellian energy distributions of atomic oxygen in the F region is calculated. Analysis of the simulated profiles shows that the high-energy component of the non-Maxwellian profiles has a modest effect on ground-based measurements, raising the temperature derived from the Doppler-broadened profiles above that of the thermosphere in the 630 nm emission region. The effect is small compared to the uncertainties for an individual measurement but could be significant when large numbers of profiles are averaged in an attempt to reduce uncertainties in the determinations. However, the effect cannot account for the >100 K difference between the FPI determinations and values derived from empirical models such as the Mass Spectrometer Incoherent Scatter model.

A novel design of a rf afterglow source of the oxygen forbidden lines at 630.0 and 557.7 nm for use in thermospheric dynamics studies is presented. With a repetitive discharge-afterglow excitation cycle, the source yields adequate afterglow intensities of the OI lines that are sufficiently free of background continuum for use in Fabry-Perot interferometer measurements of spectral line profiles. These lines provide accurate zero-velocity references in Fabry-Perot determinations of Doppler shifts in the OI thermospheric lines. The design considerations for the rf source are described, together with its preparation and filling by an ultrahigh-vacuum gas-handling system. Examples are given of the source's output spectrum, as measured by a grating spectrometer, and its spectral line profiles, as determined by a Fabry-Perot interferometer. Comparative interferometry between the OI afterglow source lines and nearby (within approximately 0.01-0.02-nm) lines from hollow-cathode sources illustrates the means of establishing secondary reference sources in cases in which the primary OI afterglow source is not available.

[1] Measurements of the thermospheric neutral wind at Arequipa, Peru, and observations of the drift of the irregularities at Ancon, Peru, are used to study the coupling that exists between ions and neutrals at equatorial latitudes and the variability of this coupling as a function of the occurrence of scintillations. This study is based on data collected at the Arequipa and Ancon stations between 1996 and 1998. Our comparative analysis indicates that the relative wind-drift values vary depending on season and the solar flux level. We found that during the equinoxes and low solar flux values, the averaged zonal drift is larger than the wind by 15 m s−1, but for solar flux values above 130 units, the average wind exceeds the drift values by 10 to 20 m s−1. We suggest that the occurrence of larger equinoctial drifts can be explained by the existence of altitude gradients in the zonal wind during that season. During the June solstice the zonal wind seems to exceed the irregularity drift by ∼10–20 m s−1 independent of the solar flux. We also find that the meridional wind shows a modest dependence on the scintillation activity during the June solstice. During scintillation events and between 2000 and 2400 LT the averaged meridional wind observed to the south and north of Arequipa exceeds their corresponding no-scintillation values by 20 m s−1. We present likely explanations of this effect.

A novel all-sky Doppler interferometer (ASDI) has been used to measure Doppler shifts and widths of nightglow emission lines from the upper atmosphere, thereby permitting determination of the neutral wind and temperature fields over regions up to 2000 km in diameter. The ASDI instrument consists of efficient all-sky (160 degree(s) field-of-view) input optics, a 100 mm aperture Fabry-Perot interferometer and output optics which focus 5 orders of the interference ring pattern superposed on the sky image onto a 512 X 512 pixel, LN2-cooled (-150 degree(s)C) CCD detector. Good quality CCD images of the midlatitude nightglow oxygen 630.0 nm red line (approximately equals 300 km altitude) and 557.7 nm green line (approximately equals 105 km altitude) and the OH 799.4 nm line (approximately equals 86 km altitude) are obtained in 5 - 15 min exposures. The image signal-to-noise ratio is sufficient for division of the 5 circular interference rings into 24 equal azimuthal sectors, so that Doppler shifts and widths for 120 distinct regions of the sky can be obtained from one exposure. Wind and temperature fields derived from the ASDI nightglow 630 nm measurements are compared for observations following the autumnal and the vernal equinoxes.

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground-based incoherent scatter radar and Fabry-Perot optical interferometers to generate a revision (HWM90) of the HWM87 empirical model and extend its applicability to 100 km. Comparison of the various data sets with the aid of the model shows in general remarkable agreement, particularly at mid and low latitudes. The ground-based data allow modeling of seasonal/diurnal variations, which are most distinct at mid latitudes. While solar activity variations are now included, they are found to be small and not always very clearly delineated by the current data. They are most obvious at the higher latitudes. The model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below. Significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of Fabry-Perot observations.

A Fabry-Perot interferometer has been gathering F region wind data at Millstone Hill routinely since mid-1988. A total of 27 nights of optical data have been collected with simultaneous incoherent scatter radar data. Data for 22 nights (of which 10 were geomagnetically quiet and 12 were unsettled) have been used to evaluate the O+-O collision frequency. Our data show that the collision frequency based on Dalgarno's adjusted theoretical value (Dalgarno, 1964) that was used at Millstone Hill Observatory before 1988 should be increased by a factor of 1.9±0.15.

Midlatitude F-region neutral winds and temperatures determined from Fabry-Perot interferometer measurements of the doppler shifts and widths of nightglow 630.0 nm line profiles are presented for the priority regular world day 14 August 1980. They exhibit, in many respects, the observed behavior for other summer, geomagnetically quiet nights at solar maximum. The neutral temperature decreases from ∼ 1500°K after sunset (21 h LT) to a minimum of ~ 1200°K before dawn (05 h LT), except to the north of the observatory. The zonal winds are eastward at sunset at ∼ 50 m/sec, decrease to zero at ∼ 02 h LT and are westward just before dawn. The meridional winds are zero just after sunset and reach a maximum equatorward value of ∼ 50–70 m/sec at local midnight but do not decrease as predicted; instead, they remain at roughly these values towards dawn. The NCAR thermospheric general circulation model (TGCM) is used to predict the global upper atmospheric temperature and circulation patterns for this world day. The model predictions agree with the measured neutral temperatures and exhibit qualitative similarities to the measured neutral winds. It is concluded that inclusion in the model of ion drift at midlatitudes should improve the agreement with observations.

Three‐body association coefficients for the conversion of atomic He+, Ne+, and Ar+ ions to molecular ions have been determined using drift‐tube mass‐spectrometer techniques at gas temperatures from 78 to 300 K. The 300 K results for the conversion of He+ to He2+ agree well with those obtained by other investigators using various techniques; however at 78 K, our results disagree strongly with one of the previous determinations. In the cases of conversion of Ne+ to Ne2+ and Ar+ to Ar2+, the rate coefficients differ substantially for ground state ions in their 2P3/2 and 2P1/2 fine structure states; also, the temperature dependence of this effect is distinctly different for the two gases. It does not appear that available theories give an adequately quantitative description of these association processes.

A microwave-afterglow mass-spectrometer apparatus has been used to determine the dependence on electron temperature T/sub e/ of the recombination coefficients ..cap alpha.. of the hydronium-series ions H/sub 3/O/sup +/ x (H/sub 2/O)/sub n/. For n = 1--3, we find ..cap alpha.. (37/sup +/) = (2.5 +- 0.5) x 10/sup -6/ (300/T/sub e/ (K))/sup 0.08/, ..cap alpha.. (55/sup +/) = (3.0 +- 0.6) x 10/sup -6/ (300/T/sub e/ (K))/sup 0.08/, and ..cap alpha.. (73/sup +/) = (3.6 +- 0.7) x 10/sup -6/ (300/T/sub e/ (K))/sup 0.00/ cm/sup 3//sec over the range 300--400 K < or = T/sub e/ < or = 6000--8000 K and T/sub gas/ = T/sub +/ = 300--400 K. For n = 4 and 5, ..cap alpha.. (91/sup +/) approx. = ..cap alpha.. (109/sup +/) approx. 5 x 10/sup -6/ cm/sup 3//sec, with no apparent dependence on T/sub e/. These results for the higher hydrates differ somewhat from those obtained by Leu, Biondi, and Johnsen. The very weak dependence of ..cap alpha.. on T/sub e/ is quite similar to the behavior noted for the NH/sub 4//sup ts+/ x (NH/sub 3/)/sub n/ cluster ions.

The electron-temperature dependence of the recombination of mass-identified N${\mathrm{O}}^{+}$ ions with electrons is studied by means of a microwave-afterglow/mass-spectrometer apparatus employing microwave heating of the electrons. Under conditions where the N${\mathrm{O}}^{+}$-ion wall current satisfactorily tracks the volume electron density decay, the electron decay data indicate that the recombination coefficient, $\ensuremath{\alpha}(\mathrm{N}{\mathrm{O}}^{+})$, decreases as ${T}_{e}^{\ensuremath{-}(0.37\ifmmode\pm\else\textpm\fi{}0.03)}$ over the range $380\ensuremath{\le}{T}_{e}\ensuremath{\le}5470$ K with ${T}_{+}={T}_{n}=380$ K. The values of $\ensuremath{\alpha}(\mathrm{N}{\mathrm{O}}^{+})$ obtained at ${T}_{e}={T}_{+}={T}_{n}=300 \mathrm{and} 380$ K are (${4.3}^{7}$\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ and (${3.5}^{0}$\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec, respectively. These values apply to N${\mathrm{O}}^{+}$ ions in their ground electronic and probably the $v=1 or 0$ vibration state, and are in good agreement with previous afterglow measurements. Our ${T}_{e}^{\ensuremath{-}0.37}$ variation agrees qualitatively with theoretical predictions of a $\ensuremath{\sim}{T}_{e}^{\ensuremath{-}0.5}$ variation, but is not in agreement with the $\ensuremath{\sim}{T}_{e}^{\ensuremath{-}0.83}$ variation obtained for N${\mathrm{O}}^{+}$ ($v=0$) ions using ion-storage techniques. We are unable to account for the discrepancies in the energy dependences obtained in the two measurements.

Recent observations have shown that, prior to the onset of equatorial spread-F, there exists an altitude modulation in bottomside F-region electron density contours. It has generally been accepted that such a modulation is caused by internal-gravity waves propagating upward from below. In this brief note we suggest that gravity waves may be generated in situ, via the wind shear mechanism. Theoretical calculations and some observations indicate that large wind shears can occur during early evening hours in the low latitude thermosphere. We show that the wind shear may possibly generate gravity waves with horizontal wavelengths on the order of a few hundred kilometers, which is the scale of the observed electron density modulation.

Nightglow 6300-A intensity suppression and enhancement transients have been observed in conjunction with heating of the F region ionospheric electrons in Arecibo ionospheric modification experiments (IME). Ohmic heating of the electrons during X mode propagation of the heating wave results in a ∼1.3% suppression of intensity, in semiquantitative agreement with the suppression predicted for ΔTe ≃ 130°K (measured by the backscatter radar). The 6300-A intensity enhancements (∼6 R) associated with O mode propagation of the heating wave are far too large to be produced by ohmic heating (a value ΔTe ∼ 900°K, about 5 times larger than the backscatter measured value, would be required), suggesting electron acceleration by strong plasma waves that are generated by the heating RF wave. The O(¹D) lifetimes determined from the time constants of the 6300-A intensity enhancement transients yield an F region quenching coefficient k(N2) ≃ 6 to 8 × 10−11 cm³/s, in good agreement with the Platteville IME and with laboratory results.

The paper examines the recombination of electrons with ammonium-series cluster ions, NH4(+)-(NH3)n, for two reasons: (1) NH4(+) may be a significant ion in the lower atmospheres of the earth and the outer planets, and (2) to investigate the weak temperature dependence of the cluster ion's recombination coefficient. A microwave afterglow mass spectrometer was used to determine the recombination coefficients for the first five members of the ammonium series, (18+) through (86+), at temperatures between 200 and 410 K. The electron temperature dependence of the recombination coefficient was determined for (35+) and (52+), the n = 1 and 2 cluster ions, over the temperature range 300-3000 K.

Drift tube-mass spectrometer measurements of several ion-molecule reactions believed to be prominent in the hydrogen-helium upper atmosphere of Jupiter are described. The total rate constant at 300 K of the reaction of He(+) with H2 is about 1.1 x 10 to the neg 13 cu cm/sec. The reaction proceeds mainly by dissociative charge transfer to produce H(+), with a small portion going by charge transfer to H2(+) and by atom rearrangement to HeH(+). The rate coefficient increases slowly with ion mean energy to a value of 2.8 x 10 to the neg 13 at 0.18 eV. The rate of the corresponding reaction with deuterium, He(+) + D2, has the rate coefficient of about 5 x 10 to the neg 14 at 300 K. Measurements of the three-body reaction of H' and the two-body reaction of HeH' with H2 to form H3(+) ions are described.

A microwave afterglow-mass spectrometer apparatus is used to determine the dissociative recombination coefficients for capture of electrons by H3(+) and H5(+) ions as a function of electron temperature. At an ion and neutral temperature of 240 K, the coefficient for H3(+) is found to vary slowly with the electron temperature at first, decreasing from 1.6 x 10 to the -7th cu cm/s at an electron temperature of 240 K to 1.2 x 10 to the -7th cu cm/s at an electron temperature of 500 K; at electron temperatures ranging from 500 to 3000 K, the coefficient falls as the reciprocal of the electron temperature. It is noted that the results, which have an uncertainty of + or - 20 percent, agree satisfactorily over the common energy range (0.03-0.36 eV) with the recombination cross sections determined in merged beam measurements by Auerbach et al. (1977). Attention is also given to the implication of the results for modeling planetary atmospheres and interstellar clouds.

A sky-mapping filter photometer has been used to determine the 630.0 nm airglow enhancement produced by explosive release of 3 × 10 26 CO 2 molecules into the F-region at 320 km altitude on 8 September 1982 as part of project BIME. The enhancement is produced when COg molecules engage in atom transfer with the F-region O + ions to form O 2 + ions, which subsequently dissociatively recombine with the ambient electrons to produce O( 1 D) atoms to yield the 630.0 nm radiation. The morphology of the enhanced airglow region has been traced in a series of 630.0 nm intensity contour maps as a function of time, the enhancement reaching a central brightness of approximately 400 R about 2 min after release and a diameter of ∼ 250 km some 3 min after release. The measurements of central intensity and enhanced region radius as a function of time are compared with model calculations by Mendillo and Herniter of diffusive expansion of CO 2 molecules from either a point release or from an initial, extended volume. While peak intensities are reasonably reproduced, the measured decay of the 630.0 nm intensity and the growth in size of the enhanced region are rather different from the model predictions. The measured 200 m/s drift southeastward of the enhanced region is consistent with the motion of the neutral thermosphere determined from optical doppler shifts less than an hour earlier.

Fabry-Perot interferometer measurements of the Doppler shifts and widths of the nightglow 630.0 nm line at Laurel Ridge Observatory, Pennsylvania are presented for the period 1975 to 1979, covering both solar minimum and solar maximum conditions. The F-region neutral wind vectors v n and temperatures T n deduced from these measurements show both day-to-day changes and overall seasonal patterns in the nocturnal variations during geomagnetically quiet conditions. Divergence in both the meridional and zonal horizontal flow is noted on occasion. The v n results are compared with models including only solar EUV heating and those with EUV plus a high latitude heat source. The aggregate v n data for solar cycle minimum conditions agree best with model predictions for winter zonal and equinoctal meridional winds and worst for winter meridional and summer zonal winds. At solar cycle maximum the predicted, rapid transition at equinox from summer to winter wind patterns and vice-versa is observed. The T n data are in reasonable agreement with the MSIS model predictions.

A drift-tube\char22{}mass-spectrometer apparatus has been used to determine the mobilities of mass-identified atomic ions in the noble gases as a function of $\frac{E}{p}$ (drift field/gas pressure) at $T=295$ K. The measured values of the reduced mobilities ${\ensuremath{\mu}}_{0}$ of ${\mathrm{He}}^{+}$ in He, ${\mathrm{Ne}}^{+}$ in Ne, and ${\mathrm{Ar}}^{+}$ in Ar are in agreement with earlier investigations that did not employ mass identification. The measured value at $\frac{E}{p}=O$, ${\ensuremath{\mu}}_{0}({H}^{+} \mathrm{in}\mathrm{He})=({31.0}_{\ensuremath{-}1.0}^{+0.5})$ ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, is in good agreement with quantum-mechanical calculations, but the observed decrease of ${\ensuremath{\mu}}_{0}$ with ion energy is somewhat slower than that predicted by theory. The measured mobility of each of the noble-gas ions ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$, ${\mathrm{Kr}}^{+}$, and ${\mathrm{Xe}}^{+}$ in He is found to be $\ensuremath{\sim}(6\ensuremath{-}12)%$ lower than that of the corresponding alkali-metal ion (as determined by Tyndall's group).

Radiative charge-transfer coefficients for single-electron transfer between doubly or singly charged noble-gas ions and noble-gas atoms have been determined at thermal energy using a drift-tube mass-spectrometer apparatus. At 300 K, $k({\mathrm{He}}^{2+}+\mathrm{He})=(4.8\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{3}$/sec, with slightly smaller coefficients for the reactions ${\mathrm{Ne}}^{2+}$ + Ne, ${\mathrm{Ar}}^{2+}$ + Ar, ${\mathrm{Kr}}^{2+}$ + Kr, and ${\mathrm{Xe}}^{2+}$ + Xe. Differences in reactivity are found for the different, low-lying $^{1}S$, $^{1}D$, and $^{3}P$ states of the doubly charged ions. A three-body contribution to the radiative process is noted, with rate coefficients ranging between ${10}^{\ensuremath{-}31}$ and ${10}^{\ensuremath{-}30}$ ${\mathrm{cm}}^{6}$/sec at 300 K for the different noble-gas systems. The radiative charge-transfer coefficients for singly ionized ions are somewhat smaller, $k({\mathrm{He}}^{+}+\mathrm{Ne})\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{3}$/sec and $k({\mathrm{Ne}}^{+}+\mathrm{Ar})\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{3}$/sec at 300 K. The measured value of $k({\mathrm{He}}^{2+}+\mathrm{He})$ is in reasonable agreement with the very recent theoretical calculations of Cohen and Bardsley.

Rate coefficients have been determined in a drift tube‐mass spectrometer apparatus for the oxidation reactions of Ti+ and Th+ ions in O2 and NO for ion mean energies ranging from thermal (300 K) to 5 eV. Formation of the first oxides of metal ions M+ in the reactions M+ + O2 (NO) → MO+ + O (N) is found to occur with rate coefficients close to the theoretical maximum values (i.e., the ``Langevin'' limit), except for Ti+ + NO, which proceeds more slowly. Further oxidation in the reactions MO++O2 (NO)→ MO2++ O(N) has been detected only for M = Th and with small rate coefficients. The associative ionization reaction Th + O2→ ThO2+ + e has been observed to occur, although no rate coefficient can be obtained from our measurements. In addition, thermal energy ionic mobilities of thorium and titanium ions in helium are found to be μ0(Ti+) = (25.5±1) and μ0(Th+) = (15.75±0.5) cm2 V−1·sec−1 at 300 K.

The ionic mobilities of O+, O2+, O2+, and O2+2 in helium and neon have been measured using a selected‐ion drift apparatus (SIDA). It is found that the mobilities of both O+ and O+2 ions in the metastable states (2D or 4Πu) are measurably smaller than those of the same ions in their ground states. The detection and identification of metastable ions was carried out by using known, state‐selective ion–molecule reactions. A similar mobility differentiation of ground‐state and metastable ions was not observed for the O2+ and O2+2 ions.

Measurements of non-resonant charge transfer between atomic ions and atoms have been made in a drift tube/mass spectrometer apparatus as a function of E/p (drift field/gas pressure) at 295 K. Comparison of the measured rates with available theories suggests an inability to predict the moderately slow reaction rates.

Microwave afterglow and grating spectrometric apparatus are used to study dissociative recombination in krypton. Over the electron temperature range $300\ensuremath{\le}{T}_{e}\ensuremath{\le}8400$ K and with ${T}_{+}={T}_{\mathrm{gas}}=300$ K, the total rate coefficient may be represented by $\ensuremath{\alpha}[{{\mathrm{Kr}}_{2}}^{+}]=1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{[\frac{300}{{\mathrm{T}}_{e}(\mathrm{K})}]}^{0.55}$ ${\mathrm{cm}}^{3}$/sec, with an uncertainty of \ifmmode\pm\else\textpm\fi{} 10%. At thermal energy (300 K) excited states of Kr* having energies up to that of the ${\mathrm{Kr}}_{2}^{+}$ ion in its ground electronic and vibrational state are observed to result from the dissociative recombination. With microwave heating to ${T}_{e}\ensuremath{\sim}7000$ K, additional, higher-lying Kr* states (up to \ensuremath{\sim} 0.5 eV above the ${\mathrm{Kr}}_{2}^{+}$ ion ground state) are observed. In both cases the excited states most strongly populated by dissociative recombination appear to be the $5p$ states.

An investigation of the reactions of metastable O(+) ions and O2 using drift tube-mass spectrometer techniques is presented. It was shown that ordinary charge transfer is the dominant reaction branch in both cases; it occurs with large rate coefficients, k(N2) = (8 + or - 2) x 10 to the -10th cu cm/s and k(O2) = (7 + or - 2) x 10 to the -10th cu cm/s, at an effective ion temperature of about 550 K. The reaction He(+) + O2 is used as a source of metastable O(+) ions, and evidence is presented that the O(+) ions so produced are in the 2D state rather than the 2P state. The results are compared with previous measurements, and inferences drawn from ionospheric observations.

The dissociative charge transfer of He(+) ions with H2 and D2 molecules has been studied using a temperature-variable drift-tube mass-spectrometer apparatus over the temperature range 78 to 330 K. The binary rate coefficients are small at 300 K, approximately 10 to the -13th to 10 to the -14th cu cm/sec, and only slightly larger at 78 K. Termolecular contributions to the binary rate coefficients are found to be small at 330 K but increase substantially with decreasing temperature. Two-body charge transfer with D2 is found to be slower than with H2 by a factor of 10, in good agreement with recent theoretical predictions, although the measured values of the rate coefficients are larger by a factor of about 4 than the predicted values.

A microwave-afterglow mass-spectrometer apparatus employing microwave heating of the electrons has been used to determine the dependence on Te of the recombination coefficient of electrons with HCO(+) ions. By comparison of the observed electron-density decays to the computed behavior of a recombination- and ambipolar-diffusion-controlled afterglow, it is found that the Te dependence of the recombination coefficients follows a power law with an index of -0.69 + or - 0.07 over the range Te = 293-5500 K. The magnitude of the recombination coefficient is similar to that observed and calculated for simple diatomic ions, while the temperature dependence is somewhat stronger than the Te exp -0.5 dependence predicted by a simplified theory for diatomic ions.

Observing resonances in cross‐section‐versus‐energy curves has long been a way of life for nuclear and particle physicists, for whom this is often the only way to detect short‐lived quantum states. Atomic physicists, on the other hand, have traditionally used other means for observing internal energy states of atoms and molecules. But sixteen years ago a resonance in the cross section for electrons scattering off helium changed the tradition, and by now there is a long catalog of observed resonances in atoms and molecules and an accompanying body of theoretical work that seeks to account for the newly discovered states and explain their behavior.

An all-sky-mapping filter photometeer has been used to study equatorial 630.0 nm nightglow intensity depletions. A generally eastward drift of the ∼ 0m/sec. At times two airglow depletions moving at different velocities were observed simultaneously; in one case they merged. Simultaneous interferometric determinations of doppler shifts in the 630.0 nm line indicated that the velocity of the neutral atmosphere does not appear to be correlated with the drift of the airglow depletions. The results are compared with other observations.

Interferometric measurements of nightglow 630.0 nm doppler shifts and widths have yielded determinations of the meridional, zonal and vertical velocities and the temperature in the midlatitude thermosphere during the Priority Regular World Day 18 May 1983. Both the meridional and zonal velocities exhibit a diverging flow in the early night, changing to a converging flow in the later night. Associated with this are apparent, large vertical velocities (20-30 m/s), upward in the early night, downward in the later night and back upward at the end, which also correlate with decreases and increases in the neutral temperature. While the sense of these observed effects is in agreement with the behavior predicted by existing hydrodynamic models of thermospheric flow, the magnitudes are either much larger (vertical velocities) or much smaller (temperature changes) than the model predictions.

The mobilities of the doubly charged rare-gas ions He/sup 2 +/, Ne/sup 2 +/, Ar/sup 2 +/, Kr/sup 2 +/, and Xe/sup 2 +/ in their parent gases have been determined in a drift-tube mass-spectrometer apparatus. The finding of more than one mobility for each of the doubly charged ions (with the exception of He/sup 2 +/) is attributed to the presence of the /sup 3/P, /sup 1/D, and /sup 1/S long-lived, lowest-energy states of these ions. At 300 K the reduced mobilities (in units of cm/sup 2//V sec) extrapolated to zero field have the values ..mu../sub 0/(He/sup 2 +/ in He) = 18.3; ..mu../sub 0/(Ne/sup 2 +/ in Ne) = 6.5(/sup 1/D), 7.0(/sup 3/P), 8.5(/sup 1/S); ..mu../sub 0/(Ar/sup 2 +/ in Ar) = 2.7(/sup 3/P), approx. 2.2(/sup 1/D); ..mu../sub 0/(Kr/sup 2 +/ in Kr) = 1.11 and 1.28; ..mu../sub 0/(Xe/sup 2 +/ in Xe) = 0.65 and 0.75. The measured values are accurate to +- 3%.

Measured rates are presented for the reaction of He(+) ions with H2 (and D2) molecules to form H(+), H2(+), and HeH(+) ions, as well as for the subsequent reactions of H(+) and HeH(+) ions with H2 to form H3(+). The neutralization of H3(+) /and H5(+)/ ions by dissociative recombination with electrons is shown to be fast. The reaction He(+) + H2 is slow (k 1.1 x 10 to the minus 13th cu cm/sec at 300 K) and produces principally H(+) by the dissociative charge transfer branch. It is concluded that there may be a serious bottleneck in the conversion of two of the primary ions of the upper Jovian ionosphere, H(+) and He(+) (which recombine slowly), to the rapidly recombining H3(+) ion.

Fabry-Perot inteferometer determinations of thermospheric temperatures from 630.0-nm nightglow line-width measurements have been carried out for the period April-August 1983 from Arequipa, Peru (16.4-deg S, 71.5-deg W geographic; 4.4-deg S magnetic). The nightly variation of the thermospheric temperature T(n) measured on 62 nights is compared with MSIS model predictions and found to agree occasionally with the model but, on average, to exceed model predictions by about 180 K. The largest differences, 400-500 K, often occur during strongly increasing geomagnetic activity such as sudden commencements. The rapid increases in T(n) may result from energetic neutrals precipitating at low latitudes from the ring current or from energy carried to equatorial regions from high-latitude (auroral oval) heat sources by gravity waves and equatorward neutral winds.

The rates and energy dependences of the reactions O+ + N2 → NO+ + N and O+ + O2 → O + O2+ have been studied in a drift tube/mass spectrometer apparatus. At 300°K rate coefficients of (1.2 ± 0.2) × 10−12 and (2.0 ± 0.2) × 10−11 cm3/sec are found for the reactions with N2 and O2, respectively. The rate coefficients at 300°K and their variation with ion energy are in satisfactory agreement with previous results of flowing afterglow studies carried out at temperatures up to 600°K. At ion energies above ∼ 0.15 eV for O+ + N2 and ∼ 0.25 eV for O+ + O2 the rates are observed to increase sharply, a behavior anticipated on the basis of extrapolations to low energies of ion beam results. Both reactions are of particular importance in converting atomic O+ ions in the Earth's ionosphere (E and F regions) into molecular ions. The present measurements extend previous rate coefficient determinations to ion energies appropriate to F region conditions (500°K < T < 2000°K).

A 150 mm aperture, pressure scanned Fabry-Perot interferometer has been used to study the midlatitude twilight and nightglow sodium D-line profiles. The line width measurements during evening and morning twilight indicate that the sodium layer temperature rises to a midwinter maximum (∼230 K) and then falls to a midsummer minimum (∼150 K), in qualitative agreement with the CIRA 1972 model predictions. Nightglow intensity measurements obtained with the interferometer indicate a highly variable behaviour, ranging from near-constant intensities, to monotonically falling, and to rising and falling intensities during the night. Broadening of the nightglow line profiles yields a sodium atom dissociation kinetic energy of (46 ± 4) meV. This suggests that the Chapman NaO + O chemiexcitation process, rather than dissociative recombination of “corkscrewing” ions and electrons, gives rise to the nightglow.

Rate coefficients for several two- and three-body ion-molecule reactions involving hydrocarbons have been determined at thermal energies and above using drift tube-mass spectrometer techniques. The measured rates for clustering and breakup reactions involving CH5(+) and C2H5(+) ions in methane are found to be strongly temperature dependent in the range from 80 to 240 K. The equilibrium constants determined for these reactions differ somewhat from those of Hiraoka and Kebarle (1975). Rate coefficients for two-body reactions of CH5(+), C2H5(+), N(+), H(+), and D(+) ions with methane and/or ethane have been measured. The results indicate that the product yields of several of the fast ion-molecule reactions depend strongly on ion energy (temperature), and therefore previous room-temperature results may be of limited value for model calculations of Titan's atmosphere.