E-region nitric oxide concentrations inferred from the 26 February 1979 eclipse expedition

Nitric oxide (NO) concentrations have been determined from the analysis of positive ion composition data obtained by AFGL for eclipse and post-eclipse conditions near Red Lake, Canada. Values of about 3 × 10⁸ cm⁻³ for 105–110 km and about 3 × 107 cm⁻³ for 90 km have been established. A residual ion-pair production rate of about 50 cm⁻³ s⁻¹ is estimated for eclipse totality at 110 km. A factor of two uncertainty is thought to be appropriate for all deduced values. The calculated NO concentrations appear to be within the range of typical variations for this season (late winter) and latitude (51°N).     

26 February 1979 total solar eclipse induced LF (60 kHz) phase retardation

The LF phase retardation induced by the total solar eclipse of Monday, 26 February 1979 and observed by monitoring the 12.5 km path length 60 kHz WWVB transmission from Fort Collins, U.S.A., to Calgary, Canada, as the path of totality at the 80 km height of the D-layer swept over Billings, Montana, U.S.A., near the midpoint of this transmission path is reported.     

Positive and negative ion composition measurements in the D- and E-regions during the 26 February 1979 solar eclipse

Two rockets bearing quadrupole mass spectrometers capable of measuring both positive and negative ion composition were launched from Red Lake, Canada, during the solar eclipse. Both instruments had liquid helium cryopumps and shock-attaching conical samplers. The payloads also contained two Gerdien condensers to measure total positive and negative ion concentrations and ion mobilities. Attitude control systems aligned the payloads with the velocity vector throughout ascent and descent. The first rocket was launched so that the D-region was in darkness 35 ± 8 s on the upleg and about 150 ± 15 s on the downleg for the study of ionospheric decay processes. The second rocket was fired after totality into 75% solar illumination for the study of ionospheric recovery. The positive ion composition above 105 km exhibited a strongly increasing NO⁺/O₂⁺ ratio with time after second contact due to O₂⁺ charge transfer with NO and a sharply diminished ionization rate. However, in both nights, the ionization below 105 km was created mainly by energetic particle deposition as exemplified by the increased ion concentrations and the composition signatures of a particle event: asignificant enhancement of O₂⁺ below 105 km and large amounts of H₅O₂⁺ ions in the D-region which result from the O₂⁺ clustering scheme. H₅O₂ was the major ion in the upper D-region while H₇O⁺₃, H₉O₄⁺ and H₅O₂⁺ were dominant ions at lower altitudes. Numerous minor species were also detected. The negative ion distributions in both flights exhibited a distinct shelf at 83 ± 2 km, decreasing by more than an order of magnitude by 90 km and with minima near 75 km. In the 75–90 km range, a significant percentage of the negative ions had masses exceeding 160 a.m.u. Comparisons are made with prior negative ion measurements during similar daytime auroral zone absorption (AZA) events. Two striking characteristics of the precipitating particles were apparent from these and past observations in daytime AZA events: there is a near absence of low energy electrons capable of ionizing above about 105 km and there is'a significant spatial and/or temporal variability in the electron flux. This paper is devoted principally to a presentation of the ion composition measurements and associated uncertainties.     

A model of the lower ionosphere above Red Lake,Canada, during the 26 February 1979 solar eclipse

Measurements of ionization sources, ionization profiles and minor atmospheric constituents were conducted during the 26 February 1979 solar eclipse above Red Lake, Canada. A model of the lower thermosphere has developed to describe the D- and E-regions of the ionosphere for this case with the model being guided by the measurements. During the eclipse a rather intense particle precipitation event was in progress. For this reason, an auroral deposition code was coupled to a chemical-kinetics code to calculate degraded primary and secondary electron fluxes, ionization rates, positive ion and electron densities. The model was calibrated with the experimental measurements of electron flux below 100 km and electron density between 70 and 150 km. This calculation not only satisfactorily described the ionization in the E-region but also the gross electron density characteristics of the D-region. Bursts in the observed electron flux were also simulated with the model to give electron density profiles that were remarkably consistent with small perturbations seen in the electron density measurements.     

The solar eclipse of 26 February 1979: analysis and modelling of primary pair production,electron density and ionic composition

The solar eclipse of 26 February 1979 was observed from Red Lake, Canada, (52 °N, 91 °W) where totality occurred at about 1053 local time. Several research groups and government agencies participated in an extensive ground- and rocket-based observational program directed at the middle atmosphere. At the time of the eclipse, an extensive geomagnetic storm was in progress and the middle atmosphere was undergoing temperature and circulation changes associated with a stratospheric warming. Concurrent observations of atmospheric constituents, solar radiation, electron flux and other middle atmosphere parameters were obtained as inputs for a D-region predictive chemical computer code, DAIRCHEM, tailored to eclipse conditions. Ion pair production rates were computed by an E-region infrared radiance model and were used as necessary source function input values for DAIRCHEM computations. The computations yielded predictions of electron and total positive ion densities about totality. The positive ion measurements of a supersonic Gerdien condenser and a subsonic blunt probe during the eclipse were in agreement with the model computations and provided normalizing summations of total positive ions for the interpretation of mass spectrometer measurements. The chemical computer code identified principal routes for increase and removal of key species such as O₂⁺, NO⁺, hydrated clusters and negative ions. The dominant precursor ion for pair production hydrates was O₂⁺ and the chemistry was characteristic of the disturbed D-region.     

HF Doppler observations of gravity waves during the 16 February 1980 solar eclipse

Observations by the HF Doppier technique of the ionospheric effects of the 16 February 1980 solar eclipse in Africa are presented. Some oscillations which are detected at two stations can be attributed to a travelling coherent structure. Its characteristics are consistent with a gravity wave generated by the eclipse.     

Ionospheric electron content observations during the total solar eclipse of February 16, 1980

Observations on the Faraday rotation of a transionospheric VHF signal obtained from a network of four stations near the path of totality during the total solar eclipse of 16 February 1980 are reported. A small decrease of 3–4% in the total ionization has been obtained around the time of totality. Absence of any periodic structure following the eclipse indicates that the TIDs are not of significant amplitude in the present case to be detected by the Faraday rotation technique.     

Upper atmosphere wind observations over Southern Australia during the total solar eclipse of 23 October 1976

Observations of winds in the 80–100 km height region were made at three locations in South Australia during the total solar eclipse of 23 October 1976. One station (Tantanoola) was located in the eclipse path while the others (Adelaide and Woomera) were situated several hundred kilometers north of the path of totality. Wind variations caused either directly by cooling of the 90 km region or by the propagation of a bow wave generated in the lower atmosphere were searched for but no events were found that could be ascribed unambiguously to the eclipse.     

Differential Doppler measurements of the ionosphere during a solar eclipse

The effects of the solar eclipse of 26 February 1979 on the ionosphere were measured using differential Doppler techniques. Nayy navigation satellite passes were monitored at 12 sites located across the North American continent. These data yield a measurement of the vertical columnar electron content along a north-south line. Different sites monitoring the same pass provide simultaneous observations of ionospheric variations along different longitude lines. Two satellite passes occurred during or just after the eclipse. These data show a shoulderjust northward of the umbra region and a trough just behind the umbra containing large horizontal gradients. This sharp trough recovered quickly with a half-life of about 10 min.     

Shadow bands during the total solar eclipse of 3 November 1994

We recorded shadow bands just before and just after the total phase of the solar eclipse of 3 November 1994. The recordings were made using two broad-band silicon photodiodes separated by 100 mm. They were mounted on a plate that faced the eclipsed Sun, which was at an altitude of 32.4° as seen from our observing site 4500 m above sea level between Putre and Lake Chungara in northern Chile. The irradiance fluctuations associated with the shadow bands were around 0.008 W m⁻² rms on a background of about 2–8 W m⁻². The cross-correlation function indicates that the shadow bands were moving at a speed of about 1.8 m s⁻¹ perpendicular to their extent. The power spectral density functions are in accord with the shadow band theory of Codona (1986). We carried out a similar experiment in Baja California during the eclipse of 11 July 1991. In spite of teh considerable differences between the two circumstances, our results on the two occasions are broadly similar.     

Shadow bands during the total solar eclipse of 11 July 1991

We recorded shadow bands just before and just after the total phase of the solar eclipse of 11 July 1991. The recordings were made using two broad band silicon photodiodes separated horizontally by 100 mm. They faced the zenith, near to where the eclipsed Sun lay as seen from our observing site close to San José del Cabo in Baja California. The irradiance fluctuations associated with the shadow bands were around 0.04 W m⁻² peak to peak on a background of 1–3 W m⁻². The cross-correlation function indicates that the shadow bands were moving at about 1.8 m s⁻¹ perpendicular to their extent. The power spectral density functions are in accord with the shadow band theory of Codona [(1986), Astron. Astrophys. 164, 415–427].     

Atmospheric electricity measurements at Pune during the solar eclipse of 18 March 1988

Measurements of atmospheric electric potential gradient, conductivity of both polarities and space charge at the ground surface at Pune during the partial solar eclipse of 18 March 1988 have been made. In spite of no appreciable change in atmospheric temperature at the ground surface, all the atmospheric electric parameters showed remarkable changes during the period of eclipse. Results do not support any vertical transport of charge, either by conduction or by convection, near to the ground surface.     

Magnetic observations at the time of the 23 October 1976 solar eclipse in Australia

The solar eclipse of 23 October 1976 passed across south-east Australia in the local solar afternoon. This paper records the magnetic observations of a line of ten temporary stations stretching from a region of fifty percent obscuration to the path of totality. Magnetic conditions at the time were mildly disturbed. Analyses of the data have sought an eclipse effect in the basic quiet daily variation, and also in the disturbance variations. However, no eclipse effect in the primary ionospheric currents has been clearly distinguished above spatial uneveness, due to local differential induction, in the induced secondary currents flowing in the earth.     

Atmospheric electrical potential gradient measurements during the annular solar eclipse of 29 April 1976

This paper gives the results of measurements of the potential gradient of the electric field of the atmosphere during the annular eclipse of the sun, on 29 April 1976, on the island of Santorini. The potential gradient during the annular eclipse showed a diminution. The results of measurements of the intensity of the total solar radiation and the temperatures of the air and the earth's surface are also given.     

Penetration of solar wind plasma elements into the magnetosphere

Assuming that the solar wind is unsteady and non-uniform, it is suggested that field aligned plasma elements dent the magnetopause surface. This indentation makes the magnetopause boundary convex and therefore locally unstable with respect to flute instabilities. The intruding element is slowed down and stopped within 1 or 2 Earth radii from the magnetopause. Its excess convection kinetic energy is dissipated in the lower polar cusp ionosphere after ~ 50–500 s, depending on the value of the integrated Pedersen conductivity. Once the plasma element has been engulfed, keeping its identity, the warm plasma content is dissipated by precipitation and by drifting. The magnetosheath particles with large pitch angles are mirrored, and feed the plasma mantle flow.Several consequences of this penetration mechanism are pointed out:Ionospheric heating beneath the polar cusp;Birkeland currents on the eastward and westward edges of the plasma element;Diamagnetic field fluctuations within 1–2 R_E from the magnetopause (multiple magnetopause crossings);Oscillation of the magnetopause surface after a new element has penetrated;Exit of energetic particles out of the magnetosphere, and entry of energetic solar wind particles into the magnetosphere along the magnetic field lines of the intruding element;Subtraction of magnetic flux from the dayside magnetosphere and its addition to the geomagnetic tail when the magnetic field of the element has a southward component.     

Long-period variations of wind parameters in the mesopause region and the solar cycle dependence

A solar dependence of wind parameters below 100 km was found by Sprenger and Schminder on the basis of long-term continuous ionospheric drift measurements (D1) in the l.f. range. For winter they obtained for the prevailing wind a positive correlation with solar activity and for the amplitude of the semi-diurnal tidal wind a negative correlation. Later on this result was confirmed by radar meteor wind measurements (D2) at Obninsk and further D1 measurements at KÜhlungsborn and Collm.However, after the years 1973–1974 a change in the behaviour of the zonal prevailing wind was observed. At this time we found a significant negative correlation with solar activity with an indication of a new change after 1983. This was obtained from D1 results in Collm and D2 results in Kühlungsborn not only for winter, but also for summer and even for annual averages. We conclude that this long-term behaviour points rather to a climatic variation with an internal atmospheric cause than to a direct solar control. The negative correlation with solar activity of the semi-diurnal tidal wind in winter remained unchanged (up to 1984) and also proved to be the same in summer and for annual averages. Recent satellite data of the solar u.v. radiation and the upper stratospheric ozone have shown that the possible variation of the thermal tidal excitation during the solar cycle amounts to only a few per cent. This is, therefore, insufficient to account for the 40–70% variation of the tidal amplitudes. Some other possibilities of explaining this result are discussed.