摘要:

Using data from the drift meter and magnetometer on board the HILAT satellite, we have examined fluctuations in high latitude electric and magnetic fields at scale sizes between 80 km and 3 km. A comparison of data from summer and winter allows us to assess the impact of changing ionospheric conductivity on the magnetospheric generator. We find that, at these scale sizes, the magnetosphere tends to behave as a constant current source that is independent of ionospheric conductivity. This characteristic was noted on both open and closed field lines. The electric field pattern, on the other hand, is much more highly structured in the winter than in the summer. This behavior implies scale size dependent potential drops on closed field lines.

ISSN:0094-8276    

DOI:10.1029/GL013i006p00495

年代:1986

数据来源: WILEY

摘要:

Recent measurements of the rates for reactions of NaO2and NaOH with HCl and of the photoabsorption cross section of NaCl allow for realistic estimates of the impact of sodium chemistry on chlorine partitioning in the upper stratosphere. When sodium chemistry is incorporated into our one‐dimensional model of the upper atmosphere, the results indicate that the calculated ClO concentrations near 50 km could increase by up to a factor of two with a corresponding decrease in calculated O3abundances of as much as 15 percent. The impact on ClO and O3depends crucially on the assumed meteoritic source of sodium, on transport from the mesosphere, and on transformation and removal of gaseous sodium in the stratosphere. Since the fluctuations in the abundance of gaseous sodium could induce O3variations comparable to those caused by changes in temperature and solar UV, consideration of the chemistry of sodium and other metals may be an important element in efforts toward early detection of trends in upper stratospheric O3. Future increases in stratospheric chlorine will magnify the impact of sodium species on ozon

ISSN:0094-8276    

DOI:10.1029/GL013i006p00499

年代:1986

数据来源: WILEY

摘要:

When the ionosphere is illuminated with two strong HF signals, nonlinear mixing processes can take place near the region of reflection. The first direct experimental evidence of such processes occurring in ionospheric plasma are presented in this paper. The experiments were performed at Arecibo, where the HF ionospheric modifier was split to operate as two pure isolated and independent pumps over the frequency range of 3‐8 MHz and the frequency difference between the two pumps was varied between a fraction of a Hz and several kHz. The purity of the trans‐ mitted signals was always ensured. Strong nonlinear effects were observed when the frequency difference was several Hz. Specifically, the HF signal from the ionosphere contained sidebands which were separated by multiples of the difference (Δf) between the two pumping frequencies. The first sidebands were typically 20‐40 db below the pump signal. The strengths of the first sidebands increased, when the difference (Δf) between the two pumping frequencies decreased. Below about 5‐10 Hz, the power in the first sidebands varied almost in Δf−nfashion, with n between 1 and 2. The power in the sidebands was also a strong nonlinear function of the incident pump field strength, showing the presence of a threshold. It is suggested that studies of such nonlinear mixing processes would be valuable both for diagnostic and practical usage of ionosp

ISSN:0094-8276    

DOI:10.1029/GL013i006p00503

年代:1986

数据来源: WILEY

摘要:

We have measured the cross section for the dissociative excitation of the forbidden OI(2p4¹D—3s³S, λ1641.3 Å) transition by electron impact on O2. At 100 eV, we find a cross section value of 1.22 × 10−23cm² ±35%. This result is consistent with recent estimates of this branching ratio from theoretical calculations and aeronomical observations and supports the suggestion by Meier et al. [1985] that observation of the OI λ1641.3 Å line would be useful for remote monitoring of atomic oxygen in the uppe

ISSN:0094-8276    

DOI:10.1029/GL013i006p00506

年代:1986

数据来源: WILEY

摘要:

Visible imagery from Space Shuttle mission STS‐9 (Spacelab 1) has been analysed for the ram angle effect and the absolute intensity of glow. The data are compared with earlier measurements and the anomalous high intensities at large ram angles are confirmed. Absolute intensities of the ram glow on the shuttle tile, at 6563 Å, are observed to be ˜20 times more intense than those measured on the AE‐E spacecraft. Implications of these observations for an existing theory of glow involving NO2are pres

ISSN:0094-8276    

DOI:10.1029/GL013i006p00509

年代:1986

数据来源: WILEY

摘要:

Magnetic field observations from the JPL vector helium magnetometer on the ISEE‐3/ICE spacecraft are used to investigate long term temporal variations in the interplanetary magnetic field during solar cycle 21. As reported by previous studies, IMF intensity exhibited a broad decrease during the last sunspot minimum with average values of only 4.7 nT being measured in mid‐1976. It is shown in this study that IMF magnitude peaked in late 1982 at 9.0 nT, or approximately twice its solar minimum intensity. The strength of the interplanetary field decreased rapidly during 1983 and 1984 to a value of 6.2 nT in early 1985. Comparison with the auroral AE index indicates that the post‐maximum peak in IMF strength in 1981‐83 was associated with a ∼50% increase in mean substorm activity levels. This is the first time that a long term variation in the IMF has been observed to produce an increase in geomagnetic activity comparable to, or greater than the enhancements accompanying the well known declining phase high speed streams. A marked decrease in Parker spiral angle, which indicated the presence of high speed streams in 1973‐75 during the declining phase of solar cycle 20, is also observed 11 years later in 1984‐85. The variations in the intensity of the interplanetary magnetic field, and its components, are shown to be only moderately correlated with the Mt. Wilson magnetograph measurements of full disk magnetic flux, i.e., linear correlation coefficients of 0.5 to 0.7. The implications of these results for the long term evolution of the interplanetary magnetic field and its effects on geomagnetic activity

ISSN:0094-8276    

DOI:10.1029/GL013i006p00513

年代:1986

数据来源: WILEY

摘要:

A model is presented for radial diffusion and charge state partitioning of sulfur and oxygen ions in the Io torus, including effects of electron impact and charge exchange. When applied to Voyager 1 radial profiles of total ion flux tube content, the model shows that the ion residence time in the torus,τD, as defined in spectroscopic studies of ion partitioning, is related to the radial diffusion coefficient,DLL, atL= 7 byτD≈ 8/DLL(7). This result appears to bring spectroscopic estimates of the ion residence time (τD≳ 60 to 100 days) into reasonable agreement with estimates ofDLLfrom magnetospheric diffusion studies,DLL≈

ISSN:0094-8276    

DOI:10.1029/GL013i006p00517

年代:1986

数据来源: WILEY

摘要:

We report evidence for superrotation of plasma in the pre‐dawn magnetosphere of Jupiter during the outbound segments of the Voyager 1 and 2 encounters. The evidence consists of a forward spiral of magnetic field lines crossing the equatorial plasma sheet, as distinct from the more typical backward spiral associated with subcorotational flow. (The Voyager plasma instruments were not pointed favorably for measurement of the azimuthal flow component during the outbound trajectories.) The limited available statistics indicate that superrotational flow is restricted in local time to the night side, and also restricted in system III longitude to the hemisphere opposite the active sector of the magnetic‐anomaly model. The results are thus compatible with the planetary‐wind concept in general and with the corotating convection model in parti

ISSN:0094-8276    

DOI:10.1029/GL013i006p00521

年代:1986

数据来源: WILEY

摘要:

We report the results of determinations of tidal periods from spectral analysis of the voltage induced across an unpowered length of the TAT‐7 telecommunications cable in the North Atlantic Ocean over an approximately 19 day interval. Particularly prominent spectral components are observed at several frequencies, including those identified as corresponding to the diurnal declination luni‐solar (K1), semi‐diurnal principal solar (S2), semidiurnal principal lunar (M2), and monthly lunar (Mm), components. In addition, a large amplitude spectral component of high statistical significance was observed at a frequency of 3.0051 cpd, approximately one‐third the sidereal day. This component does not appear to be related to the solar component S3and possibly corresponds to a declination luni‐solar K3frequency, although the amplitude is very much larger than that which might be expected. Other common lunar tides appear to be a minor component of the data. Such cable data can be used for studies and refinement on a global scale of large‐scale tidal (ocean and ionosph

ISSN:0094-8276    

DOI:10.1029/GL013i006p00525

年代:1986

数据来源: WILEY

摘要:

Carbon‐14 radiotracer experiments at 10 kbar (1 GPa) and 1000°‐1200°C reveal that, due to low diffusivity or low solubility (or both), carbon is immobile in the grain boundary regions of natural dunite. Within the resolution of the beta‐track mapping technique, grain boundary diffusion of carbon from a pure graphite source is not detectable in experiments of up to 10 days duration at 1200°C, even though measurable volume diffusion profiles are generated at these conditions (D ∼ 3‐4 × 10−10cm²/s, in agreement with previous estimates). The documented immobility of carbon in dunite grain boundaries precludes development of a continuous carbon film by diffusion from an initially localized source. If such a film is the cause of the mantle high‐conductivity layer, it probably originated by a process involving fluid (CO/CO2) infiltration and su

ISSN:0094-8276    

DOI:10.1029/GL013i006p00529

年代:1986

数据来源: WILEY