摘要:

Significant effects on the concentration and temperature of ozone in the upper atmosphere were observed during a major solar flare, and subsequent geomagnetic storm, which occurred during the interval August 6 to September 4, 1953. Ozone concentrations, as measured by the absorption of solar radiation by the 9.6 micron ozone band, decreased during the event but retuned to previous levels after the event. Temperature changes were also observed. The changes lag changes inKp, the geomagnetic activity index, by approximately 5 to 7 days.

ISSN:0148-0227    

DOI:10.1029/94JA02783

年代:1995

数据来源: WILEY

摘要:

Narrow enhancements of electron precipitation, with energy and flux well above typical values, have been observed with DE 2 in the cusp/cleft region. The electron flux in the energy range 0.2‐1 keV was 2 orders of magnitude higher in these structures than in the magnetosheath and were seen in approximately 80% of DE 2 cusp crossings at ionospheric altitudes. Typically, there was more than one electron structure in each cusp crossing. The position of these structures showed a systematic variation: for poleward ion dispersion (energy decreases with increasing latitude), electron structures were seen more often on the equatorial boundary of the cusp, while for equatorward ion dispersion (energy decreases with decreasing latitude), electron structures were more often seen on the poleward boundary. This suggests that the electron structures are associated with newly reconnected field lines. The electron spectra suggest that field‐aligned acceleration processes could produce the electron structures, first near the boundary of the cusp/cleft during the reconnection of field lines and then in the cusp/cleft during the motion of reconnected flux tubes through the polar ionosph

ISSN:0148-0227    

DOI:10.1029/94JA02307

年代:1995

数据来源: WILEY

摘要:

A one‐dimensional hybrid satellite track model has been developed to calculate the high‐latitude thermospheric/ionospheric structure below the satellite altitude using Dynamics Explorer 2 (DE 2) satellite measurements and theory. This model is based on Emery et al. (1985) satellite track code but also includes elements of Roble et al. (1987b) global mean thermosphere/ionosphere model. A number of parameterizations and data handling techniques are used to input satellite data from several DE 2 instruments into this model. Profiles of neutral atmospheric densities are determined from the MSIS‐90 model and measured neutral temperatures. Measured electron precipitation spectra are used in an auroral model to calculate particle impact ionization rates below the satellite. These rates are combined with a solar ionization rate profile and used to solve the O+diffusion equation, with the measured electron density as an upper boundary condition. The calculated O+density distribution, as well as the ionization profiles, are then used in a photochemical equilibrium model to calculate the electron and molecular ion densities. The electron temperature is also calculated by solving the electron energy equation with an upper boundary condition determined by the DE 2 measurement. The model enables calculations of altitude profiles of conductivity and Joule heating rate along and below the satellite track. In a first application of the new model, a study is made of thermospheric and ionospheric structure below the DE 2 satellite for a single orbit which occurred on October 25,1981. The field‐aligned Poynting flux, which is independently obtained for this orbit, is compared with the model predictions of the height‐integrated energy conversion rate. Good quantitative agreement between these two estimates has been reached. In addition, measurements taken at the incoherent scatter radar site at Chatanika (65.1° N, 147.4° W) during a DE 2 overflight are compared with the model calculations. A good agreement was found in lower thermospheric conductivities and Joule h

ISSN:0148-0227    

DOI:10.1029/94JA02075

年代:1995

数据来源: WILEY

摘要:

Magnetic field and particle data obtained from the Akebono satellite in the period from December 1989 to February 1990 are used for examining the relationships between electron populations and field‐aligned currents in the poleward boundary region of the nightside auroral oval. It is found that suprathermal electron beams frequently observed at the poleward boundary of the auroral oval associated with a latitudinally narrow (∼ 1°) field‐aligned current system located at the poleward edge, which has been designated as “the boundary current system” by Fukunishi et al. (1993, p. 11,250). In addition, an unstructured band of plasma‐sheet‐like electrons with isotropic pitch angle distributions except for loss cone appears through the auroral oval including the boundary current region. As a result, the electron energy spectra at the poleward boundary are characterized by a superposition of two Maxwellian functions: the isotropic high‐temperature component and the field‐aligned low‐temperature component. From the Maxwellian fitting procedure, the temperature and the density of the high‐temperature component are estimated to be 0.3 ‐ 1.7 keV and ≤ 1.0 cm−3, respectively, and those of the low‐temperature component are estimated to be 10 ‐ 80 eV and 2 ‐ 16 cm−3, respectively. An important finding is that the temperature and the density of the low‐temperature component and the density of the high‐temperature component are significantly enhanced in the upward current region occupying the equatorward portion of the boundary current system, while the temperature of the high‐temperature component is nearly constant throughout this region. These characteristics strongly suggest that the high‐temperature component originates from plasma sheet electrons, while the low‐temperature component originates from ionospheric electrons. It is likely that ionospheric thermal electrons flow away from the polewardmost downward current region into the magnetosphere and are accelerated and heated by some wave‐particle interaction p

ISSN:0148-0227    

DOI:10.1029/94JA02440

年代:1995

数据来源: WILEY

摘要:

A modulational instability of the electron Bernstein wave is studied. The process involves decay of the pump electron Bernstein wave into both a Stokes electron Bernstein sideband and an anti‐Stokes electron Bernstein sideband, together with a lower‐hybrid decay mode. The threshold field of the proposed instability for third‐harmonic resonance is found to be around 1 V/m in a height region sufficiently below the upper‐hybrid resonance layer and increases with the harmonic numberl. It is then proposed that scattering of the anti‐Stokes and Stokes sidebands of this modulational instability off field‐aligned density irregularities produces frequency‐upshifted and frequency‐downshifted sidebands constituting the broad symmetric structure in the stimulated electromagnetic emission spectrum observed in ionospheric heat

ISSN:0148-0227    

DOI:10.1029/94JA02580

年代:1995

数据来源: WILEY

摘要:

The phase velocities of 1‐m electrostatic plasma waves excited by the two‐stream instability in the ionosphericEregion were measured with a coherent radar. Simultaneously, plasma temperatures were measured with an incoherent radar inside the sampling volume of the coherent radar. The phase velocities, when measured in units of the ion acoustic velocity, were shown to decrease in magnitude from 1.0 toward 0.7 as the electron temperature of the plasma increases from 500° to 3000°K. Recent theoretical predictions are in accord with this experimental r

ISSN:0148-0227    

DOI:10.1029/94JA02727

年代:1995

数据来源: WILEY

摘要:

We have operated a very long baseline interferometer array at a northern midlatitude site, illuminated by VHF radio beacons from two geosynchronous satellites, quasi‐continuously for over a year. The array can detect and measure the trace velocity of traveling ionospheric disturbances (TIDs) via their signatures in the line‐of‐sight total electron content (TEC). The system noise level is of the order of 1013m−2in the TEC, so that even very weak perturbations can be studied. We have used the year‐long TID detection/velocimetry data set to describe local time and seasonal dependences of the wave parameters. The most striking finding is that the preferred azimuths of TIDs in the data set tend to belong to either of two modes: The first mode, strongest at midday and in the early afternoon, particularly around winter equinox, propagates southward. The second mode, strongest in the evening, especially during summer solstice through autumn equinox, propagates west‐northwestward. The two modes are disposed in local time such as to suggest the agency of clockwise rotation of the TID preferred azimuths versus time, as expected by wind filtering in the thermospheric diurnal tide. However, there is a gap between the two modes' azimuth bands. Moreover, the two modes exist in all trace‐speed quartiles of the data set TIDs, a finding which is at variance with the hypothesis of wind filtering being the primary explanation o

ISSN:0148-0227    

DOI:10.1029/94JA02663

年代:1995

数据来源: WILEY

摘要:

Total solar irradiance measurements from the 1984‐1993 Earth Radiation Budget Satellite (ERBS) active cavity radiometer and 1978‐1993 Nimbus 7 transfer cavity radiometer spacecraft experiments are analyzed to detect the presences of 11‐, 22‐, and 80‐year irradiance variability components. The analyses confirmed the existence of a significant 11‐year irradiance variability component, associated with solar magnetic activity and the sunspot cycle. The analyses also suggest the presence of a 22‐ or 80‐year variability component. The earlier Nimbus 7 and Solar Maximum Mission (SMM) spacecraft irradiance measurements decreased approximately 1.2 and 1.3 Wm−2, respectively, between 1980 and 1986. The Nimbus 7 values increased 1.2 Wm−2between 1986 and 1989. The ERBS irradiance measurements increased 1.3 Wm−2during 1986‐1989, and then decreased 0.4 Wm−2(at an annual rate of 0.14 Wm−2yr−1) during 1990‐1993. Considering the correlations between ERBS, Nimbus 7, and SMM irradiance trends and solar magnetic activity, the total solar irradiance should decrease to minimum levels by 1997 as solar activity decreases to minimum levels, and then increase to maximum levels by the year 2000 as solar activity rises. The ERBS measurements yielded 1365.4 ± 0.7 Wm−2as the mean irradiance value with measurement accuracies and precisions of 0.2% and 0.02%, respectively. The ERBS mean irradiance value is within 0.2% of the 1367.4, 1365.9, and 1366.9 Wm−2mean values for the SMM, Upper Atmosphere Research Satellite (UARS), and Space Shuttle Atmospheric Laboratory for Applications and Science (ATLAS 1) Solar Constant (SOLCON) active cavity radiometer spacecraft experiments, respectively. The Nimbus 7 measurements yielded 1372.1 Wm−2as the mean value with a measurement accuracy of 0.5%. Empirical irradiance model fits, based upon 10.7‐cm solar radio flux (F10) and photometric sunspot index (PSI), were used to assess the quality of the ERBS, Nimbus 7, SMM, and the UARS irradiance data sets and to identify irradiance variability trends which may be caused by drifts or shifts in the spacecraft sensor responses. Comparisons among the fits and measured irradiances indicate that the Nimbus 7 radiometer response shifted by a total of 0.8 Wm−2between September 1989 and April 1990 and that the ERBS and UARS radiometers each drifted approximately

ISSN:0148-0227    

DOI:10.1029/94JA02897

年代:1995

数据来源: WILEY

摘要:

The dispersion relation for waves in a cold, magnetized plasma is discussed using the potential for the longitudinal part of the electric field. This clarifies wave emission from a conductor in low Earth orbit and should be useful in considering the far field and both hot plasma and nonlinear, near‐field effects. General formulas for radiation impedance are directly obtained. For tethers a fundamental dependence on contactor size is discussed. Spherical and ellipsoidal contactors and an (anodeless) bare tether are considered. Simple arguments on nonlinear contactor effects lead to a surprisingly simple result for impedances off the Alfvén bran

ISSN:0148-0227    

DOI:10.1029/94JA02857

年代:1995

数据来源: WILEY

摘要:

The plasma motor generator (PMG) experiment, launched June 26, 1993, was a tethered system of two identical plasma contactors connected via a 500‐m conducting tether. The experiment was designed to demonstrate the ability of plasma contactors to provide a low‐impedance connection between a spacecraft and the ionosphere for both the electron emission and collection. The flight data indicate that plasma contactors enhance electron collection and emission by both neutralizing the electron space charge and scattering electrons across the geomagnetic field lines. Up to a 0.3 A steady current flowed along the tether in a circuit completed through the ionosphere. An analytical model for plasma contactor interaction with a background plasma which incorporates electron scattering by plasma waves is compared with the flight data. Good agreement between the model and the data is achieved for an effective scattering frequency equal to one twentieth of the local plasma contactor plasma freque

ISSN:0148-0227    

DOI:10.1029/94JA03142

年代:1995

数据来源: WILEY