On an instrumented rocket payload flown through the polar ionospher.•, large-amplitude electrostatic ELF waves have been measured in the unstable E region. Using three-axis instantaneous measurements of the electric vector of the wave field, it was possible to confirm the electrostatic nature of the waves and to make a direct determination of the full k vector as a function of altitude during upleg and downleg passages through the E region. Simultaneous measurements were made of electron density and temperature, dc electric field, and ac and dc magnetic field. This allows comparisons to be made with theories of the crossed field two-stream instability, the conditions for which were well satisfied. The direction of propagation and the frequency range are in agreement with theory, but the phase velocity is lower than predicted, being only about one third of the electron drift velocity. In a short communication [Olesen et al., 1976] we reported observations of an ionospheric plasma instability both from the ground and locally from a rocket launched from Sfindre Strfimfjord, Greenland (75.0 ø invariant latitude) on July 8, 1974, at 15.19 UT. In the present paper a thorough analysis is presented on the ELF waves in the E region, but first the ground-based ionospheric measurements are recapitulated. Then data from the rocket are presented for the upleg and downleg traversals of the E layer, followed by the analysis of the electrostatic waves. GEOPHYSICAL CONDITIONS DURING THE FLIGHT Figure 1 shows the general situation during the rocket flight. Ground-based ionosondes at Sfindre Strfimfjord and Godhavn and a 12.7-MHz backscatter radar at Sfindre Strfimfjord were used to detect the presence of a widespread ionosph•eric E region plasma instability [see Olesen et al., 1976]. As shown in that paper the Godhavn ionograms displayed a very intense slant E condition (SEC) with a strong slant Es trace, which is interpreted as backsatter signals from irregularities in the E region. The ionosonde measuring technique used selects the irregularity wavelength versus range in the way shown in Figure 1. This does not, however, exclude a wide irregularity spectrum at each range. The ionosonde cannot determine the azimuthal distribution, but the backscatter radar measures echoes at the positions shown in Figure 1, in good agreement with the Godhavn ionograms. The Kp index was greater than 5, corresponding to an average position of the equatorward boundary of the cleft lower than 72 ø invariant latitude [Pike, 1972]. This supports our assumption that the rocket ascended and descended in the polar cap ionosphere. The horizontal magnetic perturbations at Godhavn (77.5 ø invariant latitude) and Unmanak (78.5 ø invariant latitude) were fairly constant around 300 ? (nT) during the whole flight. At Sfindre Strfimfjord the magnetic perturbation decreased from around 200 ? at the time of the upleg passage of the E region to a very small value at the time of the downleg passage. The direction was at all locations very nearly geomagnetic south. Th...
The polar Slant-E-Condition (SEC) has been investigated using the incoherent scatter radar (ISR) facility installed at Sdr. Strømfjord, Greenland (inv. lat. = 74°) along with co-located and remote ionosondes, riometers, magnetometers and other equipment. SEC events are characterized by the occurrence of diffuse, slanted backscatter traces (slant Es) in ionograms and abnormally high attenuation (lacuna) of the ionosonde return signals at frequencies close to the E-region plasma frequency.The ISR observations of E-region electron densities, electron and ion temperatures and plasma convection velocities have shown, that SEC occurs during events of substantially elevated electron temperatures related to the occurrence of plasma instabilities driven by strong horizontal electric fields. A self-consistent model for electron heating in an unstable plasma has been applied to the observations and very good agreement was found between observed and calculated electron temperature profile shapes and values of peak temperatures. There was fair agreement between observed and calculated height ranges for the heated electrons. These results and the consequences of the fictitious electron-plasma wave collision term used in the electron heating model are discussed.
This paper presents initial results from the first comprehensively instrumented rocket flown through a Farley‐unstable polar cap E‐region. Groundbased ionosondes and magnetometers at two locations and HF radar backscatter at the launch site were used to determine the presence of a geographically widespread ionospheric plasma instability. The observed wave direction, electric field, and current density fit the predictions of the linear theory of the Farley instability, whereas the gradient‐drift instability seems to be excluded by the geometry of the observations.
Acid treatment of an iridoid glycoside results in the cleavage of the acetal bond between the sugar unit and the monoterpenoid aglycon. Iridoids possessing non‐conjugated enol ether systems, however, undergo the hydration of the iridoid enol ether functionality in acid medium, as well as the hydrolysis of the bond. We examined the acid rearrangement of secoiridoids such as oleuropein (1) and secologanin (2) and their reduction products oleuropeinol (3) and secologaninol (4), to examine whether similar behaviour also occurs in this case. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The slant E condition (SEC) on polar cap ionograms is shown to be a signature for the Farley instability in the polar cap E region. A correlation is found between the sign of the azimuthal component of the interplanetary magnetic field and the SEC occurrence in the cap, By > 0 (By < 0) corresponding to peak SEC occurrence in the northern polar cap dawn (dusk) sector.
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