摘要:

The mass independent isotopic fractionation in O3formation from O2photolysis has been investigated as a function of pressure (2.1‐760 Torr), UV wavelength and differing third body. In the low pressure regime (⪝ 200 Torr room temp., ⪝ 10 Torr liquid nitrogen), O3decomposition occurs, resulting in a secondary, mass‐dependent isotopic fractionation. It is demonstrated that wall effects produce O3in a mass‐dependent fashion, thus indicating the involvement of rotational states in the mass independent fractionation process. For pressures in the intermediate range, to ∼600 Torr, a single‐stage fractionation is observed, presumably with δ17O≅δ18O≅85‐100‰, though secondary effects may be operative also. At pressures above 450 Torr, the δ18O of O3decreases to 87‰ at 760 Torr. The fractionation process appears to be independent of UV wavelength and third body composition; photolysis of air produces O3isotopically similar to pure O2photolys

ISSN:0094-8276    

DOI:10.1029/GL015i007p00639

年代:1988

数据来源: WILEY

摘要:

Recent observations of bipole patterns of CG lightning strokes at ground level are interpreted in terms of the production of charge centers in a model cell of a Florida thunderstorm, and in the subsequent histories of these centers following collapse of the updraft that generated the centers.

ISSN:0094-8276    

DOI:10.1029/GL015i007p00643

年代:1988

数据来源: WILEY

摘要:

We present the channel geometries and vertical profiles of tortuosity for five natural lightning flashes and seven triggered flashes photographed in Florida. The tortuosity variation with height was quantified using the tortuosity measurement method of Hill applied over successive 200 m vertical sections. Total channel lengths analyzed were between 1 km and 1.5 km. The triggered channels often show a significant reduction of tortuosity with height; the natural flashes show no apparent trend of tortuosity variation with height. A time‐resolved record of one of the triggered flashes reveals an abrupt doubling in speed of the upward leader associated with a sharp reduction in channel tortuosity. This observation suggests that positive lightning leaders may manifest decreased tortuosity when driven by larger field

ISSN:0094-8276    

DOI:10.1029/GL015i007p00645

年代:1988

数据来源: WILEY

摘要:

Pulses with periods of nearly two years are known to influence weather and climate. The underlying mechanism of this phenomenon has remained elusive. In this report we show that the time series of air temperature, air pressure, and ocean temperature calculated in a coupled ocean‐atmosphere general circulation model display quasi‐biennial oscillations. The amplitude of the oscillation generally increases with latitude although its magnitude relative to the annual cycle decreases with latitude. The general circulation model we have studied does not incorporate the tropical stratosphere; this implies that tropospheric quasi‐biennial oscillations originate within the troposphere‐ocean

ISSN:0094-8276    

DOI:10.1029/GL015i007p00649

年代:1988

数据来源: WILEY

摘要:

Simulations obtained with a three dimensional primitive equation model in the tropical Atlantic ocean are compared with observations made during the FOCAL and SEQUAL experiments in 1984. In many respects the results are encouraging; notably, the most characteristic aspects of the 1984 warm event are correctly represented by the simulations. As part of the TOGA program, it is planned to run such a model operationally in the tropical Atlantic ocean. An improvement in the simulation is expected from a regular reinitialization of the model using observations. The quality of the forcing functions, especially the wind stress, will be improved by using a high frequency wind field provided operationally by the European Center for Medium range Weather Forecasting (ECMWF).

ISSN:0094-8276    

DOI:10.1029/GL015i007p00653

年代:1988

数据来源: WILEY

摘要:

We measured noble gases in amorphous silica of geothermal origin. These samples were formed by precipitation from geothermal water in neutral pH, and by the leaching of rocks in acid hot springs. The concentration of132Xe has a negative correlation with the temperature of geothermal water although36Ar and84Kr show no such correlation. The relationship between132Xe content A (×10−8cm³STP/g) and temperature T(°C) is approximated by the equation A=−(4.5×10−3)T +0.50. The obtained equation should be useful for estimating the silica‐forming temperature that cannot be easily measured by ot

ISSN:0094-8276    

DOI:10.1029/GL015i007p00657

年代:1988

数据来源: WILEY

摘要:

A close relationship between geophysical activity (seismicity and ground deformation) and chemical changes in volcanic reservoirs has been proposed several times in active volcanic areas. In Campi Flegrei caldera, especially during the bradyseismic crisis which occurred between 1982‐1984, this correlation was never clearly demonstrated because of the high rate of occurrence of earthquakes and the small number of gas samples.After at least two years of both geochemically and geophysically quiescent period, a swarm of 50 earthquakes, felt in the area of the Solfatara crater with 2.0 maximum magnitude, occurred on the 10thof April 1987. At about the same time (before and after), several geochemical parameters showed important changes in concentration. These include water vapour, nitrogen, hydrogen, methane and to a lesser extent hydrogen sulfide in fumarolic gases from Bocca Grande fumarole in the Solfatara crater and the radon content in water wells situated far from the swarm epicentral area. In our opinion, the processes causing the geochemical changes are linked to aseismic creeping mechanisms, which leads to an easier rising of fluids in fumaroles (H2O, N2, H2and CH4) and in the superficial water table (Rn).The subsequent seismicity could be related to consequent local stress accumulation on gas reservoir rocks induced by creepin

ISSN:0094-8276    

DOI:10.1029/GL015i007p00661

年代:1988

数据来源: WILEY

摘要:

A very slow earthquake or crustal deformation with a rise time longer than the period of the free oscillation of the Earth is difficult to observe on seismograms. However, we show that it can be detected from tide gauge records, because the free oscillation of an ocean basin such as the Japan Sea contains longer eigenperiods than those of the solid Earth. Actually, such an oscillation was excited by the Niigata earthquake of 1964 and recorded on tide gauges. Comparison of the tide gauge spectra of the free oscillation with the noise spectra shows that the free oscillation of the Japan Sea excited by a magnitude 7 class earthquake can be detected in the present tide gauge observation system. Further, a simulation for a very slow earthquake with a source process time of 1 hour shows that the slow event, which cannot be detected on seismograms, is detectable on tide gauges. However, the smaller the slip, the more difficult it is to detect the movement because of the limited dynamic range of the existing tide gauge system. If a slow deformation precedes a large earthquake, tide gauge records would be useful for earthquake prediction, so improvements in the observation system are desirable.

ISSN:0094-8276    

DOI:10.1029/GL015i007p00665

年代:1988

数据来源: WILEY

摘要:

Underside P‐reflections at mantle discontinuities are difficult to observe directly on seismograms mainly because of their low amplitude. It is shown that stacking seismograms obtained at several epicentral distances but having their PP bounce points in the same region, enables the identification of such phases. This method is applied to data from Japanese and Taïwan events recorded by the NARS array and other broadband European stations; discontinuities at about 670 and 300 km are revealed beneath Northern Euras

ISSN:0094-8276    

DOI:10.1029/GL015i007p00669

年代:1988

数据来源: WILEY

摘要:

Seismic anomalies which are interpreted as midcrustal magma bodies are present in several areas in the Basin and Range province of the western United States. In general, the upper boundaries of these inferred magma bodies coincide in depth with prominent midcrustal increases in P‐wave velocity. Crustal density profiles calculated from measured P‐wave velocity profiles indicate that near‐liquidus basalts should be less dense than the crust below the midcrustal velocity increases, and more dense above them. This implies that rising mafic magmas are trapped where they lose buoyancy at midcrustal density discontinuities. Buoyant trapping may generate large silicic magma systems by focussing ascending mafic magmas into a small depth interval in the

ISSN:0094-8276    

DOI:10.1029/GL015i007p00673

年代:1988

数据来源: WILEY