G. Rose

Ionospheric modification experiments with the Tromsø heating facility

Abstract The experiments performed up to mid 1984 with the heating facility at Ramfjordmoen near Tromso, Norway, are summarized. These experiments comprise D -region modification, polar electrojet modulation at VLF, ELF and ULF frequencies, excitation of E -region small-scale irregularities and of F -region small- and large-scale irregularities, anomalous absorption of HF wave on long and short time scales, excitation of incoherent backscatter plasma and ion lines, stimulated radio wave emission and F -region in situ measurements.

Relationships between the local dynamical structure of the atmosphere and ionospheric absorption during the Western European Winter Anomaly Campaign 1975/76

During the period December 1975–mid-February 1976 of the Western European Winter Anomaly Campaign, the local dynamical and thermal structure of the stratosphere and mesosphere was determined by some 31 rocket launches at El Arenosillo, Spain, while the mesospheric thermal structure in the winter (northern) hemisphere was derived from Nimbus 6 satellite observations. An analysis of these data is presented here. As determined by the A3 technique and the parameter Ld[= L0(n +1)], ionospheric absorption is significantly correlated with many features of the dynamical and thermal structure of the atmosphere. The strongest correlations are, on this occasion, with local winds, at a level between 85 and 92 km altitude, the sense being that high absorption corresponds to northward and eastward wind tendencies, while low absorption corresponds to southward and westward wind tendencies. Additionally, there is a significant correlation with local temperature above 60 km, high absorption corresponding to high mesospheric temperatures. These local variations are corroborated by data obtained from the PMR 3000 channel of the Nimbus 6 satellite (centred about 80km). A trivariate analysis of absorption (Ld), temperature (40° latitude) and meridional temperature gradient along the 0° longitude meridian, which corresponds to the pressure gradient driving a ‘geostrophic’ zonal wind, shows extremely high significance. High ionospheric absorption in Spain is associated with disruption of the normally strong winter vortex around a warm winter mesospheric pole. As the polar temperature decreases, temperatures at low- and mid-latitudes increase and, responding to a decrease of meridional temperature gradient, the mid-latitude zonal and meridonal wind regime changes. Disturbances of the winter mesospheric polar vortex are triggered by the upward propagation of earlier perturbations within the troposphere and/or stratosphere. Delays of 2–4 days are indicated between the onset of stratospheric circulation disturbances, perturbation of the mesospheric polar vortex, and the consequent dynamical and thermal effects in the mid-latitude mesosphere which are associated with anomalously high ionospheric absorption.

Electron densities during winter anomalous absorption of different intensity observed at 37.1°N, 6.73°W, during winter 1975/76—I

Abstract The results of in situ measurements of electron concentration in the D-region of the ionosphere obtained with different probe techniques during the Western European Winter Anomaly Campaign 1975/76 are described. Electron density profiles were measured on fifteen days when the amount of absorption was low, medium or winter-anomalous at time of launch. In agreement with earlier results and with those gathered by other authors, the electron density was found to be increased between about 75 and 95km when winter-anomaly was present. One probe technique allowed measurements of ionization also at heights well below the D-region where the number density of free electrons is very small compared with that of negative ions. On four flights of this probe, electrons could be distinguished from ions in the probe records at heights between 58 and 62 km, in one case even from 38 km upwards. This means that λ, the ratio between the number density of negative ions and that of free electrons had changed in favour of electrons in this height region when these launches took place. Further, significant increases of ion density by a factor of 14–20 at a height of 40 km and a different scale height of ionization between 40 and 70 km was observed on three flights. Two events of this kind were observed when λ was small at heights below 70 km. This increase of ionization at 40 km was neither related to air temperatures measured with a different instrumentation flown on small meteorological rockets shortly after the launch of the guard ring probes, nor to cosmic ray intensity measured on the ground.

Electron densities during winter anomalous absorption of different intensity—II

Abstract Electron density profiles mainly gathered between 70 and 100 km from 19 rocket flights during the Western Europe Winter Anomaly Campaign 1975/76 are presented. After suitable normalization these profiles can be arranged vs A3 absorption enhancement and provide an electron density history for the time period of the campaign.

The seasonal variation of radio wave absorption in Europe

Abstract The seasonal variation of radio wave absorption of three mid-latitudes is calculated using an atmospheric model and compared to measurements of two winters and one summer. From the correlations of the absorption patterns of three A3 paths, velocities of these patterns are derived and the relevance of such velocities to enhanced absorption is examined.

On the existence of anomalous radio wave absorption during winter in 40° northern latitude

Abstract Fieldstrength records on 2.8 Mc/s between Sardinia and Italy have shown that the winter anomaly of ionospheric absorption still exists at 40° northern latitude but is less pronounced and of shorter duration than at 52°N.

Interplanetary magnetic field polarity changes and D-region radio wave absorption

Abstract A significant correlation has been found between interplanetary magnetic field polarity changes and the short wave radio wave absorption of the D -region. The results support the explanation that the galactic cosmic rays are one of the most important transfer agents of sun-weather relationships.

An experimental contribution to the question of transient couplings of tropospheric planetary pressure waves and changes in the short wave radio wave absorption in the D-region of the ionosphere

Abstract Quasi-periodic oscillations with periods ranging from days to several weeks can clearly be traced in tropospheric parameters and parameters of relevance to the mesosphere and to the D -region of the ionosphere like short wave radio wave absorption data, but a permanent upward propagation of these planetary-scale waves does not seem to exist. The transition of the summer atmosphere into a winter atmosphere however, as is seen at the bottom of the troposphere as an increase of the sum of the annual and half annual Fourier components of air pressure (which begins in September and lasts until midwinter) is accompanied by a parallel change of the ionospheric D -region, namely: the increase of short wave radio wave absorption, well known as the winter-anomaly.