A. V. da Rosa

Response of the ionospheric electron content to fluctuations in solar activity

Abstract An investigation is made of the influence of the solar activity on the ionospheric electron content. Both the long and short term effects are studied. It is shown that a linear relationship exists between the value of the daily mean electron content and the solar radio flux at 2.8 GHz. The coefficients of the linear regression between these two variables are dependent on the day of the year, showing marked annual variation. The sensitivity of the ionosphere seems to be the same for both short period and long term fluctuations of solar radio flux. A delay of between 1 and 3 days is found between the fluctuations in microwave flux and corresponding changes in the ionosphere. Delays observed in Hawaii were longer than those at Stanford. Using the linear relationship between solar radio noise and the mean electron content, it is possible to prognosticate with reasonable accuracy the mean daily value of the electron content.

A global response of the total electron content of the ionosphere to the magnetic storm of 17 and 18 June 1972

Abstract A global study is made of the response of the total electron content of the ionosphere to the sudden commencement (S.C.) geomagnetic storm of 17 June 1972. Using data from 18 sites, a comparison is made of the seasonal differences between this storm and the 17 December 1971 ionospheric storm studied on a similar global basis by Schodel et al . (1974). When storm induced total electron content enhancements occur, they generally occur within 24 h of the S.C. and they tend to be larger in the winter hemisphere; subsequent depletions are generally more severe in the summer hemisphere. The best-defined storm effect is the positive phase evening enhancements seen in the American longitude sector. The local times of the peak enhancements show a coupled seasonal/longitudinal/latitudinal pattern with latitude being the clearest ordering parameter. The magnitudes of the subsequent negative phase depletions show a longitudinal gradient from east to west.

A global description of the F-region during the ionospheric storm of 17 December 1971

Abstract Total electron content data—observed continuously by means of geostationary radio beacons—provide a good means to study the ionosphere during severe ionospheric storms. Data of 20 sites were collected in order to study the ionospheric storm of 17 December 1971. A remarkable increase in the total electron content occurred at midlatitude stations throughout the northern hemisphere. Stations at auroral and equatorial latitudes also showed sharp increases which were both LT and latitude dependent whereas both sites in the southern hemisphere showed substantial depletions in the total electron content.

ENHANCEMENT OF IONIZING RADIATION DURING A SOLAR FLARE

Measurements of electron concentrations in the ionosphere, between 100 and 250 km altitude, were used to compute the increase in solar ionizing radiation during two flares on 21 and 23 May 1967. Since the altitude of maximum absorption of the solar energy (approximately unit optical depth) depends on the wavelength of the radiation, it is possible to estimate separately the energy enhancement in different portions of the spectrum. An ionizing energy flux increase of nearly 5 erg cm−2 sec−1 was observed on 21 May, while on the 23rd, the increase was over 7 erg cm−2 sec−1. In both flares, most of the absolute increase occurred in the 20–205 Å region of the spectrum, although the relative increase was much larger at the shorter wavelengths.

Determination of the columnar electron content and the layer shape factor of the plasmasphere up to the plasmapause

Abstract Measurements of the total columnar electron content of the plasmasphere up to the plasmapause have been made using the beacon transmitters aboard the geostationary satellite ATS-III. The technique employed is a combination of the differential Doppler frequency and the Faraday rotation angle methods. Such a combination permits the determination of the integration constant necessary to convert differential Doppler data into information about the absolute value of the columnar content. A ‘layer shape factor’ defined as the ratio between the Faraday rotation angle and the columnar content is also determined. The diurnal behavior of this factor can yield information on the exchange of ionization between the ionosphere and the protonosphere. This paper describes the analysis used to obtain both the absolute value of content and the shape factor.

Propagation errors in VHF satellite-to-aircraft ranging

An airplane navigation system based on the measurement, at very-high frequency, of the range between the aircraft and a geostationary satellite is under development by NASA. An examination is made of the errors resulting from the unknown propagation characteristics of the signal through the ionosphere. These errors are found to be a function of the distance between subaircraft and subsatellite points. At short distances unfavorable geometry causes small ranging errors to be translated into large position errors. As the distance increases, the errors become smaller, until a minimum is reached at some 5000 km. At even larger distances the errors again increase due to the greater path length of the signal in the ionosphere. Completely disregarding ionospheric effects leads to position errors of some 5 km at a 5000-km distance during the midday period near the solar cycle maximum. By using good predictions of the ionospheric electron content, it may be possible to reduce such errors to 1 km on a representative day. Since the errors are proportional to the columnar electron content, they become correspondingly smaller at night and decrease by, roughly, a factor of 3 during the sunspot minimum period.

Zonal drifts of irregularities imparted by meridional winds

Abstract In a uniform ionosphere, meridional winds cause only meridional motions of irregularities. It is shown, however, that if one considers F-region irregularities in a real ionosphere in which there is a highly conductive E-layer, zonal motions occur. During the day a substantial westward drift takes place while at night the drift is eastward but smaller owing to the much smaller E-layer conductivity. Thus, the effect of meridional winds is to impart a net westward drift to small irregularities in the ionization, provided such irregularities persist long enough.

NEUTRAL WINDS IMPLIED BY ELECTRON CONTENT OBSERVATIONS DURING THE 7 MARCH 1970 SOLAR ECLIPSE.

Abstract Measurements of columnar electron content using geostationary satellite signals were made at several of our observatories throughout the U.S., during the 7 March 1970 solar eclipse. The ionospheric response to the solar eclipse was simulated in a computer. Discrepancies between observed and simulated electron content behaviours can be greatly reduced by assuming the existence of plausible neutral winds originated by the eclipse in the F-region heights.