摘要:

One of the most striking features discovered during the encounter of space probe ICE and comet Giacobini‐Zinner was the presence of intensive MHD turbulence even at large distances from the comet. In this paper it is shown that the mass loading of the solar wind with cometary ions can cause such a phenomeno

ISSN:0094-8276    

DOI:10.1029/GL013i002p00085

年代:1986

数据来源: WILEY

摘要:

IUE observation of Uranian emissions in hydrogen Lyman alpha (H Ly‐α over, the past four years have recently been summarized by Clarke et al. [1985]. Over this time period they find an average H Ly‐α brightness of 1260 R which they estimate is composed of 200 R of solar scattered radiation and 1060 R from a collisional source. A third component, not considered by previous authors, is the reflection of H Ly‐α emissions from the interstellar wind. Hydrogen in the interstellar wind forms an extended source of H Ly‐α whose importance relative to the solar flux increases with distance from the sun. We demonstrate that scattering of interstellar H Ly‐α is more important than scattering of solar H Ly‐α for reasonable values of H column abundance and, in fact, may make up 10 ‐ 40% of the observed signal. Large H column abundances are still required to explain the H Ly‐α brightness solely on the basis of resonant scattering; therefore it is likely that the emissions are due in part to collisional sources and in part to the scattering of interstellar H Ly‐α with solar scatte

ISSN:0094-8276    

DOI:10.1029/GL013i002p00089

年代:1986

数据来源: WILEY

摘要:

Voyager IRIS brightness temperature measurements of Titan at a wavelength of 530 cm−1are crudely indicative of ground or lower tropospheric temperatures and indicate 93 K for the equator and 91 K for both northern and southern high latitudes. The symmetry between north and south is unexpected for the time of Voyager encounter (Northern Titan spring). We show that this near‐symmetry can arise naturally in a model where the poles are "pinned" year‐round at the dew point of CH4‐N2lakes or, more probably, a CH4‐N2rich surface layer on a deep ethane‐rich ocean. For a polar temperature of 91 K, the model implies that the atmosphere contains somewhat less than 8% mole frac

ISSN:0094-8276    

DOI:10.1029/GL013i002p00093

年代:1986

数据来源: WILEY

摘要:

The results of a theoretical investigation of the generation of broadband electrostatic noise (BEN) by an ion beam in the Earth's magnetotail are presented. It is shown that at low beam temperatures an ion beam can generate BEN at wave normal angles (θ) between zero and 80°, with the maximum growth occurring at θ = 0° when the beam velocity is small and at large θ (∼ 70°) for higher beam velocities. It is also shown that two types of instability are responsible for the wave amplification. One is the ion acoustic instability associated with the electron‐ion beam relative drift, and the other is the ion‐ion instability. The broad frequency and angular spectra of BEN can be explained by the presence of the two instabilities. These instabilities are shown to be insensitive to the presence of a background mag

ISSN:0094-8276    

DOI:10.1029/GL013i002p00097

年代:1986

数据来源: WILEY

摘要:

Preliminary results are presented on the nature of a distinct class of sub‐km high latitude irregularities which can create localized regions of near saturated VHF and fairly intense UHF scintillations in the nighttime auroral F‐region. The unique feature of this class of irregularities is that it is associated not with large scale (several tens of km) organized density gradients in the F‐region but with velocity shears with shear gradient scale lengths ∼10km. The presence of velocity shears was established by EISCAT ion drift measurements, continuous STARE measurements of electron drift and the in‐situ ion drift measurements from the HILAT satellite. Analytical and numerical simulation studies of velocity shear driven Kelvin‐Helmholtz type plasma instabilities are necessary to elucidate the generation mechanism of this class of irr

ISSN:0094-8276    

DOI:10.1029/GL013i002p00101

年代:1986

数据来源: WILEY

摘要:

The data obtained from the Intercosmos‐Bulgaria‐1300 Satellite have shown that during strong magnetic storms a halo of suprathermal electrons with number density equal to 0, 1% of the ionospheric plasma density with effective transverse temperature of the order of several eV appeared in the region of the intense small‐scale (1 km) field‐aligned currents. These electrons are believed to be the main carriers of narrow field‐aligned currents. The observed approach to isotropy of the electron flux is interpreted in terms of Coulomb scattering, although it is hard to explain the electric fields necessary for the electron acceleration without the presence of anomalous r

ISSN:0094-8276    

DOI:10.1029/GL013i002p00105

年代:1986

数据来源: WILEY

摘要:

A comparison of satellite mass spectrometer data from Dynamics Explorer‐2 and Atmosphere Explorer‐C and ‐D provides new evidence supporting the hypothesis that NO2is the source of the observed continuum glow near ram‐facing surfaces of the space shuttle. Surface reactions of thermospheric N and O in mass spectrometer ion sources produce NO and NO2in amounts highly dependent on surface temperature and composition, with direct exposure of ion source surfaces to rammed gas a necessary condition for the production of large amounts of NO2. Initial orbit data indicate that a period of surface conditioning is necessary before these odd nitrogen molecules can be produced effi

ISSN:0094-8276    

DOI:10.1029/GL013i002p00109

年代:1986

数据来源: WILEY

摘要:

Measurements of NO2, HNO3, and PAN, as well as O3were made in March 1985 at Alert, N.W.T., Canada. The observations show that PAN is by far the dominant NOyspecies at this Northern location at the onset of spring. Surface loss of HNO3and possibly O3seemed to occur over the snowy surface, but no loss of PAN was apparent. The observations are further evidence for the importance of PAN as a major carrier of the oxides of nitrogen in the clean troposphere. Although concurrently measured light hydrocarbons would appear to be sufficient for local formation of PAN, it is suggested that this did not take place but rather that long range transport from more southerly regions was responsible for the observed PAN levels.

ISSN:0094-8276    

DOI:10.1029/GL013i002p00113

年代:1986

数据来源: WILEY

摘要:

The kinetics of the reaction of chlorine nitrate (ClONO2) with water vapor have been investigated in large‐volume (2500‐L and 5800‐L) Teflon or Teflon‐coated environmental chambers to assess the importance of this reaction as a loss process for odd nitrogen in the stratosphere. These data show that the upper limit rate constant for the homogeneous gas phase reaction between ClONO2and H2O is<2 × 10−21cm³ molecule−1s−1at 298 ± 1 K. With this rate constant, the homogeneous reaction of ClONO2with water vapor will be of negligible importance under stratosp

ISSN:0094-8276    

DOI:10.1029/GL013i002p00117

年代:1986

数据来源: WILEY

摘要:

The origin of water precipitating in different geographic regions is investigated with the NASA/GISS GCM. Water evaporating from various source regions is "tagged" and then followed as a tracer in four model simulations, one for each season. The contributions of source region evaporations to simulated rainfall at specific locations is tabulated. The results show that in the summer, water vapor for midlatitude and high latitude precipitation tends to be recycled locally, whereas low latitude continental precipitation is more dependent on oceanic moisture sources.

ISSN:0094-8276    

DOI:10.1029/GL013i002p00121

年代:1986

数据来源: WILEY