Showing papers on "Total electron content published in 1981"

Generation of kilometer scale irregularities during the midnight collapse at Arecibo

Abstract: Coordinated observations of the incoherent scatter radar at Arecibo, Puerto Rico, and total electron content/scintillation measurements made by using the 137-MHz transmissions from the geostationary satellite SMS 1 from the nearby station of Ramey are studied to determine the background ionospheric conditions necessary for the generation of kilometer scale irregularities in the midlatitude ionosphere It is found that the well-known midnight descent or collapse of the F region known to occur in this part of the world is sometimes associated with increases in the bottomside electron content, as well as large scintillation events (∼10 dB) From a measurement of vector ion velocities and electron densities during such events, it is determined that the scintillations occur in a region of eastward and northward electric fields coupled with a northward directed density gradient caused by the northward propagation of the midnight collapse The role of possible plasma instability mechanisms, specifically the E × B gradient drift instability and the Perkins instability, is discussed in the formation of the kilometer scale irregularities giving rise to VHF scintillations

Use of Faraday-rotation data from beacon satellites to determine ionospheric corrections for interplanetary spacecraft navigation

Abstract: Faraday-rotation data from the linearly polarized 137-MHz beacons of the ATS-1, SIRIO, and Kiku-2 geosynchronous satellites are used to determine the ionospheric corrections to the range and Doppler data for interplanetary spacecraft navigation. The JPL operates the Deep Space Network of tracking stations for NASA; these stations monitor Faraday rotation with dual orthogonal, linearly polarized antennas, Teledyne polarization tracking receivers, analog-to-digital converter/scanners, and other support equipment. Computer software examines the Faraday data, resolves the pi ambiguities, constructs a continuous Faraday-rotation profile and converts the profile to columnar zenith total electron content at the ionospheric reference point; a second program computes the line-of-sight ionospheric correction for each pass of the spacecraft over each tracking complex. Line-of-sight ionospheric electron content using mapped Faraday-rotation data is compared with that using dispersive Doppler data from the Voyager spacecraft; a difference of about 0.4 meters, or 5 x 10 to the 16th electrons/sq m is obtained. The technique of determining the electron content of interplanetary plasma by subtraction of the ionospheric contribution is demonstrated on the plasma torus surrounding the orbit of Io.

The E and F region ionospheric response to solar flares: 1. Effects of approximations of solar flare EUV fluxes

Abstract: SOLRAD and many other satellite systems have provided a large data base showing the time-dependent behavior of broadband solar fluxes in the X ray and EUV spectral regions. These bands are broad in the sense that one band may contain many ionospherically important spectral lines. We present results of tests performed to determine how this information can best be used to predict the effects of a solar flare on the ionosphere. Our approach has been to first adopt a model of the spectral line and continuum enhancements based on a synthesis of many types of flare observations. This detailed spectral model is used in a time-dependent ionosphere model to calculate the response of the electron and ion density profiles. Then the spectral model is mathematically filtered to show how it would appear to the SOLRAD EUV detectors, and this degraded information is used in the ionosphere model. Comparison of the two ionosphere calculations shows that the two spectra produce changes in the total electron content in the ionosphere that differ by only a few percent. Thus, given the present uncertainty in our knowledge of solar flare EUV spectra, SOLRAD broadband EUV solar flux measurements can be used to calculate the ionospheric effects of EUV flare enhancements. Significant changes due to the flare which occur in the individual species densities are described.

Time cells for adaptive prediction of total electron content

Abstract: Adaptive procedures, using multiplicative and additive prediction functions of the standard deviation of the observations, are analyzed to estimate and compare their effectiveness in correcting for ionospheric variability in time delay and range measurements The adaptive algorithms use real time measurements to reduce rms errors in ionospheric predictions Total electron content data from Hamilton, Massachusetts, for 1969–1976 are used to evaluate diurnal, seasonal, and solar cycle impact on radar, navigation, and communication systems Time cells are defined from the growth rate of rms residual error Significant reductions in rms error are achieved in daytime, at solar maximum, when time delay and range errors are greatest, using a multiplicative prediction function

Analysis of nuclear propagation effects utilizing wideband satellite data. Final report, 14 January 1980-30 January 1981

Abstract: Previous analyses of the Wideband Satellite data have emphasized the scale-size regime between 500 m and several tens of kilometers. In this report we describe the results of a detailed analysis of the auroral and equatorial total electron content (TEC) structure associated with the various scintillation phenomena. A nighttime equatorial anomaly was a prominent feature in the equatorial data, particularly as the solar cycle maximum approached. In the auroral data we found that an enhanced F region is the primary contributor to steep latitudinal TEC gradients. Because recent data have shown an abrupt steepening of the irregularity spectral density function near 500 m, a careful analysis of the mutual coherence function was performed to see if this feature could be detected in the Wideband scintillation data. The analysis did indeed reveal such a feature, which is evidently a permanent characteristic of the most severely disturbed equatorial irregularity continuum.

Ionosphere layer shape from second‐order ATS 6 measurements

Abstract: The carrier phase at 40 MHz on the ATS 6 to Boulder beacon experiment is found to be sufficiently well resolved to allow the measurement of the second-order term as well as the first-order total electron content value. The second-order component of phase path is primarily due to a truncation of the expansion for refractive index when the satellite is within about 45° of zenith, but it is dominated by ray path bending when the satellite is outside that zone. The second-order value is used to derive scale height at the peak of the F layer for one day of data with absolute accuracy of about ±10% during the daytime, when the plasma densities are generally high. The scale height determined at the peak differs from that derived from ionograms for the underside of the peak and also differs from that of the α-Chapman layer fitted to total content and peak density. The main advantage of the second-order evaluation of scale height is its spatial coincidence with total content and F factor observations.

Analysis of Nuclear Propagation Effects Utilizing Wideband Satellite Data.

Abstract: : Previous analyses of the Wideband Satellite data have emphasized the scale-size regime between 500 m and several tens of kilometers. In this report we describe the results of a detailed analysis of the auroral and equatorial total electron content (TEC) structure associated with the various scintillation phenomena. A nighttime equatorial anomaly was a priminent feature in the equatorial data, particularly as the solar cycle maximum approached. In the auroral data we found that an enhanced F region is the primary contributor to steep latitudinal TEC gradients. Because recent data have shown an abrupt steepening of the irregularity spectral density function near 500 m, a careful analysis of the mutual coherence function was performed to see if this feature could be detected in the Wideband scintillation data. The analysis did indeed reveal such a feature, which is evidently a permanent characteristic of the most severely disturbed equatorial irregularity continuum. (Author)