HF Doppler observations of 23 October, 1976 total solar eclipse over south-eastern Australia

Observations of the Doppler shift of HF transmissions on 2.5 MHz and 4.5 MHz propagated via the ionosphere during the 23 October, 1976 eclipse over south-eastern Australia are reported. The 4.5 MHz signal, reflected from the F-region, showed the characteristic frequency shift attributable to recombination and/or motion of the reflection height after first contact. Spreading of the Doppler signal occurred after totality. Some wave activity was present in the record which is normal for this time of day. The 2.5 MHz observations showed little activity up to totality when sporadic E conditions set in, masking the detection of the response of the normal E-region to the eclipse.     

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.     

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.     

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].     

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.     

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.     

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.     

Lower ionosphere effect observed during the 30 June 1992 total solar eclipse

VLF radio signals (12.9 kHz) transmitted from Ω-Argentina (43°12′S, 65°24′W) were received in Atibaia, Brazil (23°11 'S, 46°33'W) during the total solar eclipse of 30 June 1992. The surface path of the totality crossed the VLF propagation path in the sunrise transition period causing a phase delay of 6.4 μs and an amplitude change of 1.3 dB. The ionospheric response to the Sun's obscuration was compared with the phase delays reported for several solar eclipses that occurred from 1966 to 1979. The results are mainly discussed in terms of the length of VLF propagation path affected. Some similarities between a sudden phase anomaly and a reversed eclipse effect are also raised.     

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.     

Modification of the strato-mesospheric temperature and wind structure resulting from the 26 February 1979 solar eclipse

Temperature and wind behavior observed during the February 1979 solar eclipse shows significant change immediately following and up to one hour after totality. Statospheric and mesospheric data obtained from Fort Churchill, Manitoba, indicate quite clearly a cooling trend between 50–60 kilometers with the maximum temperature decrease of approximately 10°C evident above 52 kilometers. This temperature perturbation was accompanied by an amplification of the meridional wind speed of 20–30 mps near 60 kilometers. These results are essentially in agreement with those obtained at Wallops Island during the March 1970 solar eclipse. Although the stratosphere was under the large-scale influence of a stratospheric warming, the short-term perturbations caused by radiative changes as a result of the solar eclipse did not appear to be masked.     

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.     

A search for a solar cycle-temperature relationship in the middle atmosphere over Volgograd

The variation of temperature in the middle atmosphere (15–80 km) at Volgograd (49°N, 44°E) during an 11-year solar cycle (1971–1982) has been studied. The temperature of the stratosphere did not show any significant influence of the sunspot cycle, but the temperatures of the mesosphere showed a strong in-phase relationship with the solar cycle. Computed correlation and regression coefficients were positive and highly significant in this region. At 60 and 70km the temperature variations were almost linearly related to the sunspot number. Seasonal studies indicated that solar activity has a much stronger influence on temperature during the winter than during the summer.     

Radar and optical observations of mesospheric wave activity during the lunar eclipse of 6 July 1982

Simultaneous measurements were made using a 2.66 MHz interferometer radar, infrared photometers, and imaging systems during the total lunar eclipse of 6 July 1982. The radar data showed that a series of six discrete scatterers passed overhead at 103 km with an average spacing of 54 min, and two passed overhead at 88 km, also 54 min apart. The 88 km events were approximately 27 min out of phase with those at 103 km. One of the 88 km events was examined in detail; the radar returns appeared to come from a single scatterer or a few clustered scatterers, with a velocity of 135 m s⁻¹ almost due south, at 6° below the horizontal. The speed and period give a horizontal wavelength of 440 km, and the phase shift between 88 and 103 km activity suggests a 30 km vertical wavelength, in agreement with values for typical medium-scale traveling ionospheric disturbances (TIDs). Infrared images were made in the near infrared, and photometric measurements were made on and off the 8−3 band of OH. These observations, made from one site near the radar and a second site 575 km south, showed wavelike structures appearing first over the radar, then further south until they filled most of the sky. The speed of development of the infrared structure pattern in the sky is consistent with the 135 m s⁻¹ southward wave speed observed by the radar, but the structures themselves appeared in place, then drifted slowly northward at 10 m s⁻¹. The photographically determined wavelengths were 30–60 km, considerably shorter than the 440 km determined with the radar.     

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.     

Climatology of the middle atmosphere of the Southern hemisphere

Main features of spatial distribution and time variations of meteorological parameters in the Southern hemisphere at altitudes 25–80 km are reviewed on the basis of zonal empirical models revised in 1982. Meridional distribution and seasonal variations are analysed. For comparison purposes with the Northern hemisphere, a model developed by Cole and Kantor in 1978 is used. It is revealed that the compilation of new models of the Southern hemisphere atmosphere has not resulted in substantial revision of hemispheric-structure outlined earlier in studies conducted in the Central Aerological Observatory. Meridional distribution of the parameters in summer is characterized by higher values of temperature, pressure and density gradients in the stratosphere of the Southern hemisphere than in that of the Northern hemisphere. This resulted in greater advancement of the core of the summer-time easterly (low towards the equator in the Southern hemisphere than in its northern counterpart. In winter, meridional temperature gradients in the middle stratosphere are greater in the Southern hemisphere than those in the Northern hemisphere, however, rapid attenuation of the gradients with height is observed in the Southern hemisphere, and above 35–40 km they become negative near 50–60°S, in contrast to positive values typical for the Northern hemisphere stratosphere. In the wind field, specific features of the Southern hemisphere westerly flow are high intensity and relatively low altitude of the maximum speed (as compared to the Northern hemisphere).The phases of the annual temperature wave at low latitudes are similar south and north of the equator; south of 30°S a reversal of the phase is observed. The semi-annual oscillation of temperature and wind is less pronounced in middle and high latitudes of the Southern hemisphere than in the Northern hemisphere.The origin of the primary differences between the hemispheres is related mainly to lower intensity of large-scale stratospheric processes in the Southern hemisphere as compared to those in the Northern hemisphere, which is confirmed by values of the standard deviation of the parameters in the two hemispheres.In summer, temperature and pressure fields based on satellite data are symmetric relative to the poles in both hemispheres. In winter, the distortion of the mean pressure field in the mesosphere may be as great in the Southern as in the Northern hemisphere.     

The response of geomagnetic spectral composition to solar wind during storm time

In this paper 16 geomagnetic storms in 1968–1978 recorded at 8 magnetic observatories located from polar to equatorial regions in the λ= 120°E longitudinal zone and its vicinity have been analysed. The horizontal component H traces of 27 h intervals have been sampled once every 1.5 min. The time sequences of the data thus obtained have been processed by the method of digital filtering and maximum entropy spectral analysis (MESA).The results of the analysis are compared with the associated solar wind parameters. It confirms that the geomagnetic disturbances are controlled by the solar wind in several ways, i.e. geomagnetic disturbances respond differently to various solar wind parameters or to the different ranges of them. The north-south component of the interplanetary magnetic field (IMF) B_z., the IMF latitude θ and the solar wind velocity V play the most important part in inducing geomagnetic storms.