摘要:

During the Condor campaign a number of instruments were set up in Peru to support the rocket experiments. In this series of papers we report on the results of the experiments designed to study the equatorialFregion. In this overview paper we summarize the main results as well as report upon the macroscopic developments of spreadFas evidenced by data from backscatter radars, from scintillation observations, and from digital ionosonde meaurements. In this latter regard, we argue here that at least two factors other than the classical gravitational Rayleigh‐Taylor plasma instability process must operate to yield the longest‐scale horizontal organization of spreadFstructures. The horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow, although detailed comparison with theory seems to require shear frequencies a bit higher than observations indicate. On the other hand, the largest‐scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions. Using simultaneous rocket and radar data, we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over Jicamarca are primarily spatial structures advecting overhead. The detailed rocket‐radar comparison verified several other earlier results and speculations, particularly those made in the PLUMEX experiments. In particular, companion papers discuss and extend some of the PLUMEX results to include the role of anomalous diffusion (LaBelle et al., this issue) in the theory of equatorial spreadFand to shed light upon the shallow spectral form often observed in the intermediate‐scale regime (LaBelle and Kelley, th

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05487

年代:1986

数据来源: WILEY

摘要:

Two rockets launched into spreadFduring March 1983 show that the intermediate‐scale spectrum of density irregularities sometimes exhibits a knee near 1 km scale length. This result confirms previous reports which are reviewed. Two different nonlinear theories of spreadFturbulence are studied here and shown to be consistent with the experimental spectra when the knee is observed. Also, the existence or nonexistence of the knee may be effected by two linear mechanisms: the injection of kilometer scale turbulence at the steepened walls of spreadFbubbles and the nonlocal role of the compressibleEregion in the development of spreadF. This spectral feature, which seems to be associated with the most turbulent state of equatorial spreadF, has not yet been identified in computer simulation

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05504

年代:1986

数据来源: WILEY

摘要:

Two sounding rockets launched from Peru as part of Project Condor confirm and extend a number of previous rocket measurements of the wave number spectrum of equatorial spreadFirregularities. Other papers in this series present investigations of the intermediate‐ and long‐wavelength regimes; here, we concentrate on wavelengths less than 100 m. The Condor density fluctuation spectra display a break at a wavelength near 100 m, identical to that found in the PLUMEX experiment (Kelley et al., 1982b). The Condor data also confirm a subrange in which the density and the wave potential obey the Boltzmann relation—a strong indication of the presence of low‐frequency electrostatic waves with finite wavelength parallel to the magnetic field, perhaps low‐frequency drift waves as proposed by Kelley et al. (1982b). The Condor data are also consistent with the previous conjecture that drift waves only exist above 300 km altitude. To investigate the difference in spectra observed over two altitude ranges, we have fit to the data a form for the power spectrum taken from Keskinen and Ossakow (1981). The fitted spectrum, along with empirically determined growth and dissipation rates, is next used to calculate the energy pumped into the spectrum at long wavelengths as well as the energy dissipated at shorter wavelengths. It is found that the energy is balanced by classical collisional effects in the low‐altitude case, but energy balance in the high‐altitude case requires an enhanced dissipation of about 500 times that due to classical diffusion. This result again implies the existence of electrostatic waves, which cause anomalous diffusion due to two mechanisms: nonambipolar diffusion and wave‐particle interactions. We propose that the enhanced diffusion coefficient should also be consistent with a convective transport model for anomalous diffusion. In this model, the long‐wavelength portion of the spectrum consists of coherently steepened (k−2) Rayleigh‐Taylor generated structures, while the short wavelengths are a turbulent cascade of low‐frequency drift waves which cause convective transport. We have used the measured electric field spectrum in the drift wave regime to calculate the effective diffusion due to stochasticE×Bscattering. The resulting diffusion coefficient is comparable to that indicated by the observations, although its value depends on the outer scale selected for the turbulent spectrum. Furthermore, the experimental data show that the wavelength at which the drift wave cascade originates varies inversely with the power spectral density. If stochasticE×Bscattering is the dominant enhanced diffusion mechanism, then in order to duplicate the observed behavior, the turbulent portion of the spectrum must extend to longer scales than the wavelength at which the drift waves are excited. Thus the model is consistent with but does not uniquely imply an inverse cascade of drift wave turbule

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05513

年代:1986

数据来源: WILEY

摘要:

Radar backscatter at 50 MHz, rocket, and VHF/GHz scintillation measurements of spreadFirregularities at the magnetic equator in Peru were made during the Project Condor campaign in March 1983. The paper discusses the coordinated set of observations on two evenings, March 1 and March 14, 1983, when the altitude of theFregion peak differed by more than 150 km. The full complement of equatorial spreadFphenomena, namely, the occurrence of 3‐m plume structures and VHF/GHz scintillations, were recorded on both these evenings. It was found that the radar backscatter with extended plumes occurs in association with maximum 1.7‐GHz scintillations. This established that the height‐integrated rms electron density deviation of ∼200‐m scale irregularities causing 1.7‐GHz scintillations maximizes in extended 3‐m plume structures. The magnitude of 1.7‐GHz scintillations recorded at high elevation angles (∼76°) near the magnetic equator did not exceed a value ofS4= 0.2 (4 dB) in contrast to the near saturated 1.5‐GHz scintillations routinely observed at Ascension Island near the crests of the equatorial anomaly ofF2ionization. The observed scintillation magnitudes at 1.7 GHz have, however, been found to be compatible with the ambientFregion and the irregularity parameters measured by the rocket. The spectral indexnof scintillations has been found to be relatively less steep (n∼ −3) on March 1, 1983, when theFregion was high, and the index is steep (n∼ −5) on March 14, 1983, when theFregion was at a lower altitude. TheFregion rocket, however, measured nearly identical one‐dimensional spectral indices of intermediate‐scale irregularities on both evenings, compatible with the less steep spectral index of scintillations. The irregularity drift velocities measured by the spaced receiver scintillation measurements were in general agreement with the radar interferometer results except that the spaced receiver drifts were 20% higher. The zonal drift was observed to be ∼100 m/s on the night of March 1 and ∼200 m/s on the night of March 14. This result may be a consequence of the day‐to‐day variability of the measured zonal neutral winds and field

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05526

年代:1986

数据来源: WILEY

摘要:

In this paper we present and discuss equatorial spreadFdata taken with a digital ionosonde/HF radar located at Huancayo, Peru. A modified phenomenology is developed which uses the system's ability to do echo location. The onset of irregularities is seen to occur in the east and to move westward, while inside this large‐scale structure the plasma is found to drift eastward. A very curious difference has been identified between spreadFobservations with the ionosonde and with the VHF radar at Jicamarca. At VHF, spreadFonset often occurs when the ionosphere is rising, whereas in all five examples presented here, the digital ionosonde detected onset when the apparent ionosphere motion was downward. The result even held on the one night of common data taking. The effect could be instrumental but may be related to the considerable orographic differences in the two sites. Isolated scattering patches are observed and are tentatively identified as detached or “fossil” plumes. At frequencies above the nominalf0F2the system (and other ionosondes) may in fact function as a coherent radar. During one night, data were obtained simultaneously with the HF radar, a rocket, and the Jicamarca VHF radar. Comparisons of these data are discussed in detail. Finally, additional evidence is presented that acoustic gravity waves play a role in the development of equatorial spreadFand in the formation of detached plumes. To be self‐consistent, the gravity waves must come from nearby sources such as the tropical rain forest to the east of Ji

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05539

年代:1986

数据来源: WILEY

摘要:

We obtained nighttime measurements of equatorial thermospheric wind dynamics at Arequipa, Peru, with an automated field‐widened Fabry‐Perot interferometer between April 1983 and August 1983 and reduced data from 62 nights. Significant seasonal variations in both zonal and meridional components of the thermospheric neutral wind vector were observed. Near the equinox, between 2000 and 2300 LT, the zonal wind component is eastward with an amplitude between 100 and 150 m/s that gradually ebbs to zero by dawn. The meridional component is generally small throughout the night. In the winter months (May–August) and at the winter solstice the zonal wind persists eastward throughout the night with speeds between 50 and 150 m/s. The meridional component is directed poleward (southward) toward the winter hemisphere with a speed of 50–75 m/s that decays to zero by midnight. Comparison with the predictions of the National Center for Atmospheric Research thermospheric general circulation model for equinoctial and solstice conditions shows good agreement. We conclude that the observed seasonal changes are caused by the changing nature of the solar forcing function. The Arequipa results found the day‐to‐day variability in the winter thermospheric winds to be less than that found for the summer equatorial observations obtained at Kwajalein. Interferometric measurements of the 630.0‐nm intensity at equinox showed a major reduction of the emission lasting 1 or 2 hours in all directions but south shortly after evening twilight; this decrease was not observed

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05557

年代:1986

数据来源: WILEY

摘要:

The temporal characteristics of the full‐disk chromospheric EUV fluxes agree well with those of the ground‐based measurements of the chromospheric He I absorption line at 10,830 Å and differ systematically from those of the coronal EUV and 10.7‐cm flux. The ratio of the flux increase during the rise of solar cycle 21 to that during solar rotation variations is uniformly high for the chromospheric EUV and corroborating 10,830‐Å fluxes, highest for the transition region and “cool” coronal EUV fluxes (T<2×106°K), and lowest for the “hot” coronal EUV and 10.7‐cm flux. The rise and decay rates of episodes of major activity progress from those for the hot coronal EUV lines and the 10.7‐cm flux to slower values for the chromospheric H Lyman alpha line, 10,830‐Å line, and photospheric 2050‐Å UV flux. We suggest that active region remnants contribute significantly to the solar cycle increase and during the decay of episodes of major activity. The ratio of power in 13‐day periodicity to that for 27 days is high (1/3) for the photospheric UV flux, medium (1/6) for the chromospheric EUV and 10,830‐Å fluxes, and small to negligible for the hot coronal EUV fluxes. These ratios are used to estimate the dependence of active region emission on the solar central meridian distance for ch

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05567

年代:1986

数据来源: WILEY

摘要:

A new unified family of models for incompressible, steady state magnetic reconnection in a finite region is presented. They are obtained by expanding in powers of the Alfvén Mach number and may be used to elucidate some of the puzzling properties of numerical experiments on reconnection which are not present in the classical models. The conditions imposed on the inflow boundary of the finite region determine which member of the family occurs. Petscheklike and Sonneruplike solutions are particular members. The Sonneruplike regime is a special case of a weak slow mode expansion in the inflow region, and it separates two classes of members with reversed currents. These are the hybrid regime with a mixture of strong fast mode and slow mode expansions and the flux pileup regime with a strong slow mode expansion, in which the magnetic field strength increases as it approaches the diffusion region and the flow diverges. The Petscheklike regime is a singular case of a weak fast mode expansion, and it separates the hybrid regime from a regime of slow mode compressions. The hybrid expansions are fast mode in character in the center of the inflow and slow mode near the edges of the region, while the flux pileup expansions possess long thin diffusion regions and no maximum reconnection rate. The maximum rate is calculated for the other solutions as a function of the magnetic Reynolds number and compared with the classical Sweet‐Parker and Petschek rates. For the flux pileup and hybrid regimes, reconnection can be much faster than the maximum Petschek rate. Care should be taken in deciding which type of reconnection is operating in a numerical experiment. Indeed, no experiment to date has used boundary conditions appropriate for demonstrating steady state Petschek reconnecti

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05579

年代:1986

数据来源: WILEY

摘要:

We report the first major statistical investigation of the far wake of an unmagnetized object embedded in the solar wind. The investigation is based on Pioneer Venus Orbiter magnetometer data from 70 crossings of the Venus wake at altitudes between 5 and 11 Venus radii during reasonably steady IMF conditions. We find that Venus has a well‐developed tail, flaring with altitude and possibly broader in the direction parallel to the IMF cross‐flow component. Tail lobe field polarities and the direction of the cross‐tail field are consistent with tail accretion from the solar wind. Average values for the cross‐tail field (2 nT) and the distant tail flux (3 MWb) indicate that most distant tail field lines close across the center of the tail and are not rooted in the Venus ionosphere. We illustrate our findings in a three‐dimensional

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05589

年代:1986

数据来源: WILEY

摘要:

A theory of medium‐energy (∼ keV) electrons and heavy ions in Jupiter's magnetosphere is presented. Lower hybrid waves are generated by the combined effects of a ring instability of neutral wind pickup ions and the modified two‐stream instability associated with transport of cool Iogenic plasma. The quasi‐linear energy diffusion coefficient for lower hybrid wave‐particle interactions is evaluated, and several solutions to the diffusion equation are given. Calculations based on measured wave properties show that the noise modifies substantially the particle distribution functions. The effects are to accelerate superthermal ions and electrons to keV energies and to thermalize the pickup ions on time scales comparable to the particle residence time. The [S2+]/[S+] ratio at medium energies is a measure of the relative contribution from Iogenic thermal plasma and neutral wind ions, and this important quantity should be determined from future measurements. The theory also predicts a preferential acceleration of heavy ions with an acceleration time that scales inversely with the root of the ion mass. Electrons accelerated by the process contribute to further reionization of the neutral wind by electron impact, thus providing a possible confirmation of Alfvén's critical velocity effect in the Jovian mag

ISSN:0148-0227    

DOI:10.1029/JA091iA05p05605

年代:1986

数据来源: WILEY