摘要:

Data from the solar wind spectrometer on the Ulysses spacecraft are used to study the differential streaming between the alpha particles and protons in the solar wind over the heliographic distance range of 1.3 to 5.4 AU and latitudes from 0° to ±80° during the period December 1990 through September 1995. The study is based on 6‐hour averages of the parameterVαp= |Vα‐Vp| whereVαandVpare the vector velocities of the alpha particles and protons, respectively. It is found thatVαpdecreases with increasing distance from the Sun and with decreasing solar wind speed. The distance and velocity dependencies can be combined into a single dependence on travel timeTfrom the Sun to the point of observation, withVαpdeclining, on the average, asT−0.70±0.07. After normalization by this travel time factor, there is no residual dependence ofVαp, on heliographic latitude thus ruling out any rotational effects on either the acceleration or deceleration of the alphas relative to the protons. There is also no significant difference in the normalized values ofVαpbetween quasi‐stationary and transient (coronal mass ejection) flows. The ratiosVαp/VA, whereVAis the Alfvén speed, andVαp/Vwave, whereVwaveis the observed propagation speed of Alfvénic fluctuations, both decline with increasing distance from the Sun, butVαp/Vwaveremains in the range of 1.0 to 1.5 out to a travel time of 5 or 10 days. There are weak correlations between the normalized value ofVαpand the amplitudes of fluctuations in both the magnitude and the direction of the interplanetary magnetic field. AlthoughVαpanticorrelates strongly with the ratio of the Coulomb collision time to the solar wind expansion time, it is believed that the correlation is not evidence of a cause and effect relation between those two parameters over much of the solar wind regime observed by Ulysses. Where comparisons are possible, the Ulysses data closely agree with extrapolations of the Helios data t

ISSN:0148-0227    

DOI:10.1029/96JA01406

年代:1996

数据来源: WILEY

摘要:

We present a study of 153 fast shock waves and their relation to other large‐scale features in the solar wind: corotating interaction regions (CIRs), interplanetary counterparts of coronal mass ejections (ICMEs), and the magnetic sector structure, observed by Ulysses from October 1990 to the south solar polar pass in the summer of 1994. This is a comprehensive statistical study of interplanetary shock waves and their possible causes between 1 and 5.4 AU, in particular, out of the ecliptic. We identify six different heliographic intervals with distinct dynamic characteristics and shock wave populations (transient and corotating shocks). We present maps of large‐scale features, which provide a general context to studies of particular events observed by Ulysses and a comparison of Ulysses observations with results from other missions. From our analysis of the associations between interplanetary shocks and their possible causes we find that the strongest in‐ecliptic shock waves were leading CIRs about 4–5 AU. The strongest out‐of‐ecliptic shock waves were attributed to diverse causes at about 20° south. We observed many quasi‐parallel (θBn<45°) corotating shocks; in fact, most of the corotating reverse shocks detected during the in‐ecliptic trajectory were quasi‐parallel. The correlation between transient forward shocks and ICMEs (ejecta signatures) is similar to previous results within 1 AU: during the in‐ecliptic trajectory Ulysses detected 25 ICMEs and 31 transient forward shocks, 13 of which were associated with ICMEs. The out‐of‐ecliptic results show an analogous correlation. After the Jupiter flyby we observed a significant number of nonrecurrent reverse shocks that do not show any association with ICMEs. This type of shock, instead of being driven by supermagnetosonic plasma clouds, might be produce

ISSN:0148-0227    

DOI:10.1029/96JA00685

年代:1996

数据来源: WILEY

摘要:

A brief review of the simultaneous observations of solar total irradiance performed by the UARS ACRIM II (upper atmosphere research satellite active cavity radiometer irradiance monitor), EURECA SOVA 1 and SOVA 2 (European retrievable carrier platform solar variability experiments), ERBS ERBE (Earth Radiation Budget Satellite Earth Radiation Budget Experiment), Nimbus 7 ERB, and Atlas 1 and 2 in 1992–1993 (a period characterized as the declining phase of solar cycle 22), is presented in this paper. Statistical comparison of the irradiance values and the linear relationships among the time series are examined for the overlap period August 1992 to May 1993. The mean irradiance at 1 astronomical unit (AU) observed by the UARS ACRIM II, EURECA SOVA 1, EURECA SOVA 2, and ERBS ERBE is within the range of 1365.5–1366.9 W m−2, and high correlation (r2= 0.94) exists among the time series. Linear regression models based on the measurements are used in estimating the observed irradiance and predicting the missing values. The challenge in establishing a homogeneous long‐term database from the independent observations of shorter duration requires a clear understanding of the compatibility of the data sets and any instrument‐related drift or de

ISSN:0148-0227    

DOI:10.1029/96JA01405

年代:1996

数据来源: WILEY

摘要:

Results from a fully time dependent three‐dimensional gasdynamic model of the interaction of the solar wind with the local interstellar medium are presented. Both subsonic and supersonic interstellar winds are considered, while the mediating effects of interstellar neutrals, magnetic fields, and cosmic rays are ignored. In accord with solar minimum observations by Ulysses, the solar wind properties are assumed to depend on heliolatitude. Two large, long‐lived polar coronal holes, one in the northern and the other in the southern hemisphere, are assumed to produce a hot, low‐density, high‐speed wind which bounds a cooler, higher‐density, low‐speed ecliptic wind. The solar wind boundary conditions for the simulation are drawn directly from published Ulysses data [Phillips et al., 1995, 1996]. Results from these calculations are compared to simulations which adopt isotropic solar wind conditions. For the parameters used in these simulations (which correspond to a solar wind ram pressure increase of 1.5 from the ecliptic plane to solar pole), the termination shock is found to be elongated along the solar polar axis and weakly time dependent. The elongation results in an increased flow in the ecliptic plane compared to that over the solar poles. With the increased flow in the ecliptic plane comes enhanced pressure and density gradients which leads to the generation and amplification of turbulent vortices in the heliotail. The rotational axes of the heliotail vortices are perpendicular to the ecliptic plane. Overall, it is found that a modest increase in solar wind ram pressure with heliolatitude has a pronounced effect on the global structure of the termination shock and

ISSN:0148-0227    

DOI:10.1029/96JA01298

年代:1996

数据来源: WILEY

摘要:

On the basis of transport theories appropriate to a radially expanding solar wind, new results for the evolution of the energy density in solar wind fluctuations at MHD scales are derived. The models, which represent a departure from the well‐known WKB description, include the effects of “mixing”, driving by stream‐stream interactions (compression and shear) and interstellar pick‐up ions as well as non‐isotropic MHD turbulence. Magnetometer data from Voyager 1 and 2 and Pioneer 11 are compared to the turbulence‐based models and close agreement is found between theory and data for a reasonable choice

ISSN:0148-0227    

DOI:10.1029/96JA01275

年代:1996

数据来源: WILEY

摘要:

The dissipative, mass‐loading, multifluid model, developed byZank et al. [1993, 1994] to describe the structurally complex bow shocks observed at comets, has been extended to include the effects of a magnetic field. After describing the model, the shock structure problem associated with the one‐dimensional, steady state conservation equations is solved. The solutions are compared to those obtained from previous cold and warm gasdynamic models. The characteristic speeds of the system are calculated, and it is found that the physically relevant solutions correspond to fast magnetosonic shocks. The extended multifluid model is used to explore a new type of wave, called an “MHD draping shock,” which was proposed byNeubauer et al.[1990] to explain the unusual behavior of the magnetic field across the outbound Halley bow shock. It is found that mass loading induces switch‐on behavior at quasi‐parallel shocks, even in a high plasma beta environment. Across quasi‐parallel shocks we find switch‐on rotations as large as 30° in the cold solar wind case. This value decreases with increasing solar wind plasma beta, to a value of 16° at a value of βsw= 1. We do not find rotations large enough to explain the 69° twist in the field observed by Giotto, nor do we find any cases where the perpendicular component of the

ISSN:0148-0227    

DOI:10.1029/96JA00749

年代:1996

数据来源: WILEY

摘要:

Results from time‐dependent two‐dimensional hydrodynamic simulations of the global heliosphere suggest that drag between the plasma ions and the interstellar neutrals, caused by charge‐exchange collisions, may cause the heliopause to be hydrodynamically unstable. Both ions and neutrals are treated as fluids coupled by charge‐exchange collisions. The neutral‐ion drag is proportional to the plasma density and introduces an effective gravity in the direction of the neutral flow, which, because the interstellar plasma is much denser than the heliosheath plasma, causes a Rayleigh‐Taylor‐like instability to develop. The heliopause is unstable only near the stagnation point at the “nose” of the heliosphere. In the simulations, the heliopause is seen to oscillate nonlinearly about its equilibrium position with a timescale of the order of a hundred years and amplitudes of tens of AUs. Growth rates from the simulations are in reasonable agreement with theoretical estimates. The possible stabilizing influence of energetic solar wind neutrals, neglected in the present model, is discussed. Implications of this instability on the interpretation of the Voyager 2–3 kHz emissions

ISSN:0148-0227    

DOI:10.1029/96JA00606

年代:1996

数据来源: WILEY

摘要:

The rotational distribution of the “thermal” emission from the v = 1 vibrational level of NO, resulting from impacts of NO in the ground vibrational level (v=0) with oxygen atoms, is examined using the cryogenic infrared radiance for shuttle (CIRRIS‐1A) database. A block of NO quiescent (nonauroral) nighttime limb radiances observed by the CIRRIS ‐1A interferometer and radiometer around 5.3 μm are inverted to obtain the local rotational envelopes of the 1→0 vibrational transition as functions of altitude for both spin components. It is found possible to describe these local rotational envelopes by Maxwell‐Boltzmann distributions and to obtain rotational temperatures for each spin component of the vibrationally excited NO. The two spin components, within the accuracy of the measurements, are described by the same rotational temperature, which differs, however, from the mass spectrometer incoherent scatter (MSIS) model temperature at most altitudes. At low altitudes (≤110 km), the rotational temperature and the temperature describing the relative population of the spin states of the vibrationally excited NO approach each other, indicating the onset of thermodynamic equilibrium for the spin and the rotational degr

ISSN:0148-0227    

DOI:10.1029/96JA01250

年代:1996

数据来源: WILEY

摘要:

The neutral wind field effects on the development of the equatorial plasma bubbles have been simulated by a two‐dimensional time‐dependent model similar to that developed by Zalessak and Ossakow. The results indicate that when there exists no neutral wind, any perturbation on the bottom‐side of the ionosphere density profile will be amplified by the gravitational Rayleigh‐Taylor (GRT) instability and an upwelling bubble will form as expected. When a zonal neutral wind field exists, the uplift velocity of the bubble will be enhanced by a uniform neutral wind, but suppressed by vertical shear of the wind field. Secondary structures called plumes will grow out from the side walls of the primary bubble if some secondary perturbation signal with vertical structure is seeded. We notice that patches and multiple plume structures have been observed in the mid‐latitude and low‐latitude ionosphere. So we have developed a two‐dimensional local theory of the generalized GRT instability to calculate the growth rate of a small‐scale perturbation signal in the vicinity of the primary bubble and found that the growth rate increases with time along with the growth of the bubble. It is proved that the irregularities generated by some of our simulations should be able to cascade into observable (e.g., by radar) turbulence in a reasonable period of time after their generation. Similar to the effect on the growth of the primary bubble, a strong uniform wind field may enhance the growth rate of a perturbation signal in the vicinity of the bubble, while a strong vertical wind shear will suppress the growth rate. The main point of this theory is that the growth rate of the GRT instability is controlled by the density gradients and the magnitudes of the velocity of the plasma motion relative to the neutral wind in both directions. In addition, our simulations have proved that a seeding wave with phase velocity matching the background wind speed will generate the fastest growing bubble, disapproving the theory of sp

ISSN:0148-0227    

DOI:10.1029/96JA01404

年代:1996

数据来源: WILEY

摘要:

Ionospheric disturbances associated with low‐latitude auroral events that occurred during geomagnetic storms on October 21, 1989, and May 10, 1992, are investigated from measurements of the total electron content (TEC) by the U.S. Navy Navigation Satellite System (NNSS) and ionosonde data from the Japanese meridian chain. Features of the ionospheric disturbances are then associated with the progression of geomagnetic disturbances during the storms. After the onset of the main phase of each storm, anomalous TEC distributions characterized by depressed TEC distributions on the high‐latitude side (>35° geographic latitude) and an enhanced equatorial ionization anomaly (EIA) on the low‐latitude side (<35° geographic latitude) were observed over Japan both by the NNSS and by the meridian chain of ionosonde stations. This enhancement of the EIA suggests the penetration of magnetospheric electric fields during the storms. Corresponding to the anomalous TEC decreases in the northern part of Japan, ionosonde stations in this region observed specific disturbances of ionospheric variation characterized by simultaneous decreases of ƒ0F2and increases ofh′F. These features of ionospheric variations on the high‐latitude side can be attributed to the upward escape of ionospheric plasma caused by the heating and evacuation mechanisms, which are induced by depletion of the plasmasphere and the resulting access of ring current particles to low latitudes. After the appearance of the characteristic ionospheric variations mentioned above, low‐latitude aurorae were observed at the maximum development stage of theDst, associated with the recovery of midlatitude geomagnetic horizontal (H) components. Prior to the appearance of the low‐latitude aurorae, magnetic disturbances in the auroral region increased with the decrease of midlatitudeHcomponents, as a natural consequence of magnetic storms. However, they showed a recovery before the start of the low‐latitude aurorae, while the magnitude of the low‐latitude magnetic field continued to decrease. These observed features of the magnetic disturbances suggest that the position of the auroral oval shifted toward the equator before the appearance of the low‐latitude aurorae. Consequently, these observations are consistent with the plasmapause and auroral zone moving toward the equator before the onset of low‐latitude aurorae. We conclude that the convection electric field penetrating toward low latitudes causes the enhancement of the EIA, the shrinkage of the plasmasphere, and the penetration of high‐energy particles towa

ISSN:0148-0227    

DOI:10.1029/96JA00832

年代:1996

数据来源: WILEY