46 research outputs found
Radio propagation study Semiannual progress report, 1 Jun. - 30 Nov. 1965
Ionospheric studies using radio signals received from SYNCOM 3, Polar Ionosphere Beacon, and 20 Mc/s satellite
Direct Manual Calculations of Ionospheric Parameters Using a Single-polynomial Analysis
Ionospheric parameter calculations using single polynomial analysis to determine variation of electron density with heigh
Investigations of the ionospheric using radio signals from artificial satellites
The occurrence and characteristics of ionospheric irregularities in medium latitudes and in polar regions were measured using radio signals from artificial satellites. Ionospheric changes during quiet and disturbed conditions were also measured. Electron density, elevation angle, and amplitude and frequency of these high frequency signals were determined as well as the direction of their arrival
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Ionospheric origin of magnetospheric O+ ions
Flows of thermal atomic oxygen (O+) ions are deduced from topside ionospheric plasma density profiles. The mean flux within most of the polar cap is of the order of 10^12 m^{−2} s^{−1}, a figure which is consistent with both theoretical and experimental estimates of the light ion polar wind at greater altitudes. Larger flows (up to 6 × 10^12 m^{−2} s^{−1}) are observed near the poleward edge of the night-side statistical auroral oval, a feature not reproduced in the light ion flux. The implication is one of a low altitude acceleration mechanism, acting upon the O+ ions at these latitudes and at heights above that at which the fluxes are observed. Such a process would enable ions to escape from the ionosphere because they do not exchange charge with neutral hydrogen. The observations are in general agreement with energetic O+ ions as previously observed in various parts of the magnetosphere
The low latitude ionospheric effects of the April 2000 magnetic storm near the longitude 120°E
Plasmaspheric electron content in the GPS ray paths over Japan under magnetically quiet conditions at high solar activity
First limits on the 21 cm power spectrum during the Epoch of X-ray heating
We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). 3 h of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1–3 h of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 104 mK on comoving scales k ~< 0.5 h Mpc−1. This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12~< z ~< 18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window
Model results for the ionospheric E region: solar and seasonal changes
A new, empirical model for NO densities is
developed, to include physically reasonable variations with local time, season,
latitude and solar cycle. Model calculations making full allowance for secondary
production, and ionising radiations at wavelengths down to 25 Ã…, then give
values for the peak density NmE that are only 6% below the
empirical IRI values for summer conditions at solar minimum. At solar maximum
the difference increases to 16%. Solar-cycle changes in the EUVAC radiation
model seem insufficient to explain the observed changes in NmE,
with any reasonable modifications to current atmospheric constants. Hinteregger
radiations give the correct change, with results that are just 2% below the IRI
values throughout the solar cycle, but give too little ionisation in the E-F
valley region. To match the observed solar increase in NmE,
the high-flux reference spectrum in the EUVAC model needs an overall increase of
about 20% (or 33% if the change is confined to the less well defined radiations
at λ NmE show a
seasonal anomaly, at mid-latitudes, with densities about 10% higher in winter
than in summer (for a constant solar zenith angle). Composition changes in the
MSIS86 atmospheric model produce a summer-to-winter change in NmE
of about –2% in the northern hemisphere, and +3% in the southern hemisphere.
Seasonal changes in NO produce an additional increase of about 5% in winter,
near solar minimum, to give an overall seasonal anomaly of 8% in the southern
hemisphere. Near solar maximum, reported NO densities suggest a much smaller
seasonal change that is insufficient to produce any winter increase in NmE.
Other mechanisms, such as the effects of winds or electric fields, seem
inadequate to explain the observed change in NmE. It therefore
seems possible that current satellite data may underestimate the mean seasonal
variation in NO near solar maximum. A not unreasonable change in the data, to
give the same 2:1 variation as at solar minimum, can produce a seasonal anomaly
in NmE that accounts for 35–70% of the observed effect at all
times