摘要:

Langmuir wave packets with low frequency modulations (or beats) have been observed in the Jovian foreshock. Here it is argued that these modulations are direct evidence for the Langmuir wave decayL→L′ +S. In this decay, ‘pump’ Langmuir wavesL, driven by an electron beam, produce backscattered product Langmuir wavesL′ and ion sound wavesS. TheLandL′ waves beat at the frequency and wavevector of theSwaves, thereby modulating the wave packets. Electron beam speeds are deduced from the observed modulations, thereby providing testable predictions for the theory. Beam speeds calculated using the modulated Jovian wave packets (1) are reasonable, at 4 – 10 times the electron thermal speed, (2) are consistent with theoretical limits on the decay process, and (3) decrease with increasing foreshock depth, as expected theoretically. These results strongly support the theory. The modulation depth of some wave packets suggests saturation by the decayL→L′ +S. Applications to modulated Langmuir packets in the Venusian and terrestrial foreshocks and in a type III radio source are proposed, and future te

ISSN:0094-8276    

DOI:10.1029/92GL02632

年代:1992

数据来源: WILEY

摘要:

We study the waves within, and upstream of, the density enhancements in front of the magnetopause using magnetic field and plasma measurements from ISEE 1 and 2. The waves upstream of the density enhancements are most likely to be mirror modes and are convected with the magnetosheath flow. Within the density enhancements there is additional wave power at lower frequencies. These low frequency waves appear to be slow modes propagating sunward and quasi‐standing in the flow. These observations lend support to the contention that the outer edge of the density enhancement is a slow mode wave front which marks the greatest distance that slow modes can propagate upstream into the solar win

ISSN:0094-8276    

DOI:10.1029/92GL02499

年代:1992

数据来源: WILEY

摘要:

A magnetotail‐like structure is modelled using a 2‐dimensional, single‐ion species, electromagnetic, Darwin (no displacement current), particle‐in‐cell (PIC) code, which is a modified version of that described by Hamilton and Eastwood [1982]. The modifications include new boundary conditions for the magnetic fields which allow a non‐symmetrical topology to be modelled.The work presented here is aimed at the construction and testing of a self‐consistent ‘steady‐state’ model. It is found that the model supports significant magnetic perturbations, arising as a consequence of cyclotron resonance interactions with ion beam‐like features. When subjected to transient changes in the convection electric field, the model also exhibits field reconfiguration and particle responses reminiscent of near‐E

ISSN:0094-8276    

DOI:10.1029/92GL02097

年代:1992

数据来源: WILEY

摘要:

The two‐dimensional nonlinear evolution of the ionization‐driven adiabatic auroral arc instability has been studied for the first time. We find: (1) the adiabatic auroral arc instability can fully develop on time scales of tens to hundreds of seconds and on spatial scales of tens to hundreds of kilometers, (2) the evolution of this instability leads to nonlinear “hook‐shaped” conductivity structures, (3) this instability can lead to parallel current filamentation over a wide range of scale sizes from kΛ01 where k is the wavenumber and Λ0is the initial arc width perpendicular to the geomagnetic field, and (4) the k‐spectra of the density, electric field, and parallel current develop into inverse power laws in agreement with satellite observations. Comparison with mesoscale auroral phenomenology and current filamentation str

ISSN:0094-8276    

DOI:10.1029/92GL02491

年代:1992

数据来源: WILEY

摘要:

Since October 1991, the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) on board the Upper Atmosphere Research Satellite (UARS) has been measuring the solar spectral irradiance from 120 to 400 nm with low (5 nm) and moderate (1.1 nm) resolution on a daily basis. By scaling the modulation measured over four solar rotations to proxy indicators of solar activity, we estimate the amplitude of the solar ultraviolet irradiance variation during the 11‐year activity cycle, extending the wavelength coverage of existing empirical variability models to 120 nm and distinguishing the variability of the emission lines from that of the underlying solar continuum. These estimates are compared with results from another empirical variability model and from direct measurement

ISSN:0094-8276    

DOI:10.1029/92GL02656

年代:1992

数据来源: WILEY

摘要:

A physical mechanism for in situ forcing of the Venus thermospheric superrotation is developed, which is in accord with the bulk of the constraining observations. Saturation of small‐ to medium‐scale internal gravity waves in the thermosphere can supply the necessary accelerations of the mean flow if the waves have predominantly large westward phase speeds, characteristic of the wind speeds in the upper clouds. Several scenarios for wave forcing are examined, and the Lindzen‐Holton parameterization is used to derive wave‐induced accelerations of the mean flow. The results are compared to the VTGCM, which uses a similar wave drag parameterization with an ad hoc (empirically based) asymmetry parameter to model the superr

ISSN:0094-8276    

DOI:10.1029/92GL02110

年代:1992

数据来源: WILEY

摘要:

Although it is well known that temperature affects the heterogeneous reaction probability (γ) of ClONO2and H2O on suite acid aerosol surfaces by determining the amount of water which will co‐condense with H2SO4vapor, the effect of the ambient water‐vapor concentration, which also affects the aerosol composition, has not been investigated in detail. A nearly constant stratospheric water vapor mixing ratio dictates that the water vapor partial pressure vary proportional to atmospheric pressure and thus increase rapidly in the lower stratosphere. In addition, the water vapor mixing ratio increases dramatically in the lower stratosphere following tropospheric‐stratospheric exchange. The increase in water vapor partial pressure results in a large increase in γ and may be a factor contributing to ozone destruction in the lower stratosphere. Comparison of the lifetime of ClONO2to heterogeneous reactions with that expected from gas phase photochemistry is used to estimate the relative importance of these processes and indicates that winter and spring polar regions are the most likely to be a

ISSN:0094-8276    

DOI:10.1029/92GL02493

年代:1992

数据来源: WILEY

摘要:

A long path FTIR‐based product study was carried out by the visible (λ>400 nm) photolysis of mixtures containing CF3NO, NO and ethane or propane (in mtorr range) in 700 torr of synthetic air at 297 ± 2 K. Kinetic and spectroscopic evidence has been obtained for the reaction (1), CF3O + RH → CF3OH + R (RH = C2H6or C3H8). Using the reaction (2), CF3O + NO → CF2O + FNO as the reference reaction, values for the relative rate constants k2/k1were determined to be 50 ± 15(σ) and 20 ± 5(σ) for C2H6and C3H8, respectively. These results suggest that the hydrocarbon reactions may provide a significant pathway for the tropospheric degradation of HFCs and HCFCs containing

ISSN:0094-8276    

DOI:10.1029/92GL02496

年代:1992

数据来源: WILEY

摘要:

Eastern Asia contains many large pollution sources whose emissions can be transported over large areas of North Pacific. In order to characterize this transport, we collected a sixty‐day series of daily aerosol samples concurrently from Sapporo, Japan and Vladivostok, CIS from April to May, 1991. These were analyzed for non‐sea‐salt (nss) sulfate and nitrate. The arithmetic mean concentrations of nss‐sulfate (4.66 ± 2.68 μg m−3) and nitrate (2.58 ± 1.62 μg m−3) in Vladivostok were 70% and 40% higher than the corresponding concentrations of nss‐sulfate (2.69 ± 2.06 μg m−3) and nitrate (1.86 ± 1.42 μg m−3) in Sapporo. Several episodic peaks of nss‐sulfate and nitrate in Vladivostok corresponded to the peaks observed in Sapporo, which is located approximately 700 km east of Vladivostok. About 40% and 25% of the variance in the nss‐sulfate and nitrate concentrations at the two sites could be explained by the large‐scale transport of substances under the strong winds from the west and southwest This suggests that the high concentrations are associated with strong regional sources located to windward of these cities and that the concentrations that we measured are probably representative of a large area of the coas

ISSN:0094-8276    

DOI:10.1029/92GL02639

年代:1992

数据来源: WILEY

摘要:

The partial pressure of CO2in surface seawater and in air were continuously measured during the cruise ALIZE II (January 1991–March 1991) in the equatorial Pacific from Panama to Nouméa via Tahiti. It provides a large set of data for estimating the air‐sea CO2flux in the equatorial Pacific. An average flux is calculated between 2.5N and 2.5S. This estimation ranges from 5 to 8.5 mmol m−2d−1according to the CO2exchange coeffici

ISSN:0094-8276    

DOI:10.1029/92GL02501

年代:1992

数据来源: WILEY