摘要:

We have studied steady convection with adiabatic and viscous heating for variable viscosity in the Boussinesq limit using the mean‐field theory. A strong nonlinear coupling is found between the thermodynamic constants governing adiabatic heating and the rheological parameters. We have established the range of rheological values for which adiabaticity would occur throughout the mantle. Too large an activation volume, greater than 6 cm³/mol for the cases examined here, would produce unreasonably high temperature at the bottom of the mantle (>6000 K) and superadiabatic gradients, especially in the lower mantle. Radiogenic heating plays a profound role in controlling dynamically mantle temperatures. Present values for the averaged mantle heat production would yield objectionably high temperatures in the lower mant

ISSN:0094-8276    

DOI:10.1029/GL013i001p00038

年代:1986

数据来源: WILEY

摘要:

The role of capillarity is potentially important for determining heat transfer in hydrothermal regions. Capillarity allows mixing of phases in liquid/vapor systems and results in enhanced two‐phase convection. Comparisons involving a numerical model with capillarity and analytical models without indicate that heat transfer can be enhanced by about an order of magnitude. Whether capillarity can be important for a particular hydrothermal region will depend on the nature of mineral precipitation as well as pore and fracture size distribution

ISSN:0094-8276    

DOI:10.1029/GL013i001p00042

年代:1986

数据来源: WILEY

摘要:

The Jakobshavns Effect may have been a significant factor in hastening the collapse of palaeo ice sheets with the advent of climatic warming after 18,000 years ago and may precipitate partial collapse of the present‐day Greenland and Antarctic Ice Sheets following CO2‐induced climatic warming in the decades ahead. The Jakobshavns Effect is observed today on Jakobshavns Glacier, which is located at 69°10′N on the west coast of Greenland. The Jakobshavns Effect is a group of positive feedback mechanisms which allow Jakobshavns Glacier to literally pull ice out of the Greenland Ice Sheet at a rate exceeding 7 km/a across a floating terminus 800 m thick and 6 km wide. The pulling power results from an imbalance of horizontal hydrostatic forces in ice and water columns at the grounding line of the floating terminus. Positive feedback mechanisms that sustain the rapid ice discharge rate are ubiquitous surface crevassing, high summer rates of surface melting, extending creep flow, progressive basal uncoupling, progressive lateral uncoupling, and rapid iceberg c

ISSN:0094-8276    

DOI:10.1029/GL013i001p00046

年代:1986

数据来源: WILEY

摘要:

New isolation and detection methods were developed to measure dimethylsulfoxide (DMSO) and dimethylsulfone (DMSO2) in marine rain and marine air masses. Central equatorial Pacific rain contained 1 to 10 µg/ℓ of each of these compounds. Uncontaminated air sampled off Miami contained 2 to 6 ng/m³ of each component. These concentrations suggest that DMSO and DMSO2may be as significant as dimethylsulfide (DMS) in marine sulfur transport. In fact, DMSO was observed to undergo disproportionation in illuminated seawater or distilled water to DMS and DMSO2. This latter observation implies a partially reversible loop in the sulfur transport cycle and complicates the calculation of the flux of sulfur into the marine boundary la

ISSN:0094-8276    

DOI:10.1029/GL013i001p00049

年代:1986

数据来源: WILEY

摘要:

Analysis of northern hemisphere mid‐latitude temperature data at 30 mbar over the last 20 years suggests a long‐term negative trend of about ‐0.24 K/decade when all observations between 10°N and 90°N are considered. This stratospheric cooling which could tentatively be attributed to the increase of the carbon dioxide amount in the stratosphere is in qualitative agreement at 30 mbar with a model calculation of the historical evolution of temperature and chemical composition in the middle atm

ISSN:0094-8276    

DOI:10.1029/GL013i001p00052

年代:1986

数据来源: WILEY

摘要:

In this paper the detection of haze using satellite imagery is compared with simultaneous aircraft measurements of haze parameters. The vertical optical depths of the effective pollutant layers are compared with results from the satellite data in order to gauge a threshold for the detection of haze from satellites. This comparison indicates that in terms of the optical depth this threshold is approximately equal to 0.065. Regression analysis indicates that a ground aerosol SO4=concentration of ∼3 µgm−3may be typical of such a value of optical d

ISSN:0094-8276    

DOI:10.1029/GL013i001p00056

年代:1986

数据来源: WILEY

摘要:

Recent calculations and computer simulations of the right‐hand resonant ion beam instability have indicated that gyrophase‐bunched ion distributions may be generated as a first step in the disruption of field‐aligned beams. Theory predicts a distinct phase angle relationship between the gyrovelocity of the phase‐bunched ions and the wave magnetic field. In this paper, observations of such a relationship between gyrophase‐bunched ions and MHD‐like waves upstream from the Earth's bow shock are presented. The observed phases are in accord with the theoretical predictions of the right‐hand resonant ion bea

ISSN:0094-8276    

DOI:10.1029/GL013i001p00060

年代:1986

数据来源: WILEY

摘要:

During electron beam accelerator operation on Spacelab I, substantial fluxes of electrons were observed with energies greater than the initial beam energy. In this letter numerical calculations are performed for the emission of an unneutralized, one‐dimensional electron beam. These calculations show clearly that space charge oscillations, which are associated with the charge buildup on the emitter, strongly modify the beam and cause the returning beam particles to have a distribution of kinetic energies ranging from half to over twice the initial energ

ISSN:0094-8276    

DOI:10.1029/GL013i001p00064

年代:1986

数据来源: WILEY

摘要:

Observations of charged particle precipitation measured near Frobisher Bay by the NOAA‐7 and ‐8 satellites were compared with simultaneous photographs of auroras made by an image‐intensified, all‐sky camera located at the South Pole Station (the nominal magnetic conjugate point). The results show that auroral phenomena have a high degree of correlation between the two locations and demonstrate the expected poleward migration of the location of the auroras within each individual hemisphere during the midday hours. In addition, a systematic variation in the location of auroral phenomena in one hemisphere relative to the other is observed during the course of the day. The northern aurora moves further poleward in the noon to afternoon (magnetic local time) than does its southern counterpart. In contrast, the morning hours before 0900 MLT, show the northern features closer to the equator than the southern features. The conjugate point to the south pole, in effect, displayed a shift of approximately eight degrees during the course o

ISSN:0094-8276    

DOI:10.1029/GL013i001p00068

年代:1986

数据来源: WILEY

摘要:

On October 27th 1984, high‐latitude ionospheric convection was observed by the European incoherent scatter (EISCAT) radar. For a nine‐hour period, simultaneous observations of the interplanetary magnetic field (IMF) were obtained sunward of the Earth's bow shock. During this period, the IMF abruptly turned southward, having previously been predominantly northward for approximately three hours, and a strong enhancement in convection was observed 11 ± 1 minutes later. Using the very high time resolution of the EISCAT data, it is shown that the convection enhancement propagated eastward, around the afternoon magnetic local time sector, at a speed of the order of 1 kms−1. These results are interpreted in terms of the effects of an onset of steady IMF‐geomagnetic field merging and are the first to show how a new pattern of enhanced convection is established in the high latitude io

ISSN:0094-8276    

DOI:10.1029/GL013i001p00072

年代:1986

数据来源: WILEY