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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Abnormal Circulation Changes in the Winter Stratosphere, Detected Through Variations of D Region Ionospheric Absorption

A method to detect stratospheric warmings using ionospheric absorption records obtained by an Absorption Meter (method A3) is introduced. The activity of the stratospheric circulation and the D region ionospheric absorption as well as other atmospheric parameters during the winter anomaly experience an abnormal variation. A simultaneity was found in the beginning of abnormal variation in the mentioned parameters, using the absorption records for detecting the initiation of the stratospheric warming. Results of this scientific experience of forecasting in the El Arenosillo Range, are presented.

Delamorena, B. A.↗
NASA NTRS1984

Autumn and Winter Anomalies in Ionospheric Absorption as Measured by Riometers

Seasonal variations of ionospheric absorption were studied using riometer (A2) measurements over a wide latitude range. In agreement with the results of earlier studies of A1 radiowave absorption, equinoctial maxima of approximately equal amplitude are observed in the auroral zone and near the equator. However, at intermediate latitudes riometer absorption maximizes during the fall season, whereas the A1 data show a semi-annual variation with maxima occurring in summer and winter. The autumn anomaly in riometer absorption is observed at much higher geographic latitude in the Southern Hemisphere, but at comparable geomagnetic latitudes in both hemispheres. The winter anomaly was seen only in absorption values calculated at constant solar zenith angle.

Ranta, H.↗
NASA NTRS1989

Dynamics of the middle atmosphere in winter (Dynamics). Interrelation between the different variations of turbulent diffusion and ionospheric absorption originating in the middle atmosphere

The turbulent diffusion coefficient was computed from the parameters of sporadic E layers using the wind shear theory of midlatitude sporadic E and models of the ionosphere as well as that of the neutral upper atmosphere. The turbulent diffusion coefficient obtained for the period of circulation disturbances associated with stratospheric warmings and for the intervals of the winter anomaly indicate changes similar to the ionospheric absorption of radio waves, in the former case decreased, in the latter case increased values. This may hit at the role of turbulent transport in the formation of these anomalies. On the basis of these findings, a seasonal variation of the turbulent diffusion coefficient having a minimum in summer and an increase of this parameter with increasing geomagnetic activity are anticipated.

Bencze, P.↗
NASA NTRS1989

Positive ion composition in the polar D and E regions measured during moderate ionospheric absorption

During the MAC/Epsilon campaign a mass spectrometer probe was flown on a rocket launched from Andoya (Norway) on 12 November 1987 at 0021 UT providing partial ion density profiles in the altitude range between less than 50 to 125 km. Due to the short sampling period of 0.17 seconds structural features could be observed at approx. 150 m height resolution in the regimes where metal ions occur and where cluster ions are dominant. The observations were made during stable ionospheric absorption of 1 to 1.5 dB. Preliminary results are presented and discussed.

Laemmerzahl, P.↗
NASA NTRS1972

Equatorial ionospheric absorption during half a solar cycle (1964-1970)

An extensive series of vertical incidence absorption measurements made at an equatorial station is analyzed in detail for a better understanding of the lower ionosphere. A quantitive empirical relationship is derived between absorption and 1 to 8 A solar flux for moderate levels of solar activity. It is shown that the threshold flux for D region modification, at a solar zenith angle of 10 deg, is approximately 0.0005 erg/sq/cm/sec. Attention is drawn to the incidence of days of high absorption even in the absence of solar X-ray activity. Available evidence points to variability of the order of 10 to 40% in the intensity of the solar Lyman alpha radiation as the most likely cause of these unusual, though infrequent, enhancements in absorption.

Gnanalingam, S.↗
NASA NTRS1974

Equatorial ionospheric absorption during half a solar cycle /1964-1970/

An extensive series of vertical incidence absorption measurements made at an equatorial station is analyzed in detail to provide information which will lead to a better understanding of the lower ionosphere. A quantitative empirical relationship is derived between absorption and 1-8 A solar flux for moderate levels of solar activity. It is shown that the threshold flux for D-region modification, at a solar zenith angle of 10 deg, is approximately 0.0005 erg per sq cm per sec. Attention is drawn to the incidence of days of high absorption even in the absence of solar X-ray activity. Available evidence points to variability of the order of 10-40 per cent in the intensity of the solar Lyman-alpha radiation as the most likely cause of these unusual, though infrequent, enhancements in absorption.

Gnanalingam, S.↗
NASA NTRS1977

The 5-day wave and ionospheric absorption

In a previous paper, Fraser and Thorpe (1976) indicated that the average partial-coherence spectra for three summers and the average for three winters at a southern mid-latitude site had a dominant peak at a period of about six days. This peak in coherence between absorption and temperature is anomalous, and the present paper explains how some of the unexpected coherence features can be explained by the five-day wave described by Geisler and Dickinson (1976) and whose existence in the upper stratosphere was discussed by Rodgers (1976).

Fraser, G. J.↗
NASA NTRS1984

Ionospheric Absorption on 1539 Khz in Relation to Solar Ionizing Radiation

Radio wave absorption data on 1539 kHz for the summer period of 1978 to 1980 are considered in relation to variations of solar X-ray and L-alpha radiation. It is shown that under non-flare conditions L-alpha dominates in controlling absorption and that X-rays contribute about 10% to the total absorption. Optimum regression equations show that absorption is proportional to the m-th power of ionizing flux where m 1. The role of correcting L-alpha values, measured by the AE-E satellite, is discussed.

Boska, J.↗
NASA NTRS1975

Effect of small ionospheric irregularities on radio wave absorption

The ionospheric absorption of a radio wave caused by small-scale irregularities with a gaussian autocorrelation function is calculated for various values of the linear scale height, the radio frequency, the scale size of the irregularities, and the mean-square fractional electron density fluctuations. The absorption is due to scattering of the radio wave into plasma oscillations by the irregularities. It is concluded that the absorption due to such irregularities with a mean-square fractional electron density deviation greater than about 0.000001 exceeds the normal collisional height-integrated absorption. Absorption of this type could play a significant part in heating experiments or in an ionosphere containing naturally occurring irregularities.

Chen, H. C.↗
NASA NTRS1964

Aerospace group

Rocket measurements of ionospheric absorption and Faraday rotation for determination of D layer electron collision frequency

FARADAY ROTATION↗