摘要:

The heating of the bulk of the incident ions at low Mach number quasi‐perpendicular collisionless shocks is observed to take place very rapidly, within the shock ramp. In this paper we show that the trajectories of ions passing through the shock ramp lead to a dispersion in phase space resulting in an effective increase in ion temperature. The main heating is predicted to take place in the second half of the ramp. We present results of self‐consistent computer simulations which confirm this predict

ISSN:0094-8276    

DOI:10.1029/96GL01108

年代:1996

数据来源: WILEY

摘要:

Quasi‐electrostatic (QE) thundercloud fields are proposed to maintain the ionospheric electrons at a persistently heated level well above their ambient thermal energy. Changes in the thundercloud charge (e.g., in lightning discharges) lead to heating/cooling above/below this quiescent level, and are registered as sudden (i.e., ‘fast’<20 ms) subionospheric VLF signal changes, occurring simultaneously (i.e., ‘early’,<20 ms) with lightning discharges, and referred to as early/fast VLF events [Inan et a

ISSN:0094-8276    

DOI:10.1029/96GL01360

年代:1996

数据来源: WILEY

摘要:

Night‐time measurements of the hydroxyl Meinel (3, 1) rotational band were used to infer the mesospheric temperature over Scandinavia from June through August, 1992. The resulting temperature time series showed spectrally‐distinct, statistically‐significant fluctuations with periods between 2 and 16 days, although only the 16‐day oscillation will be discussed here. The period, amplitude and temporal history of this wave agree with model predictions and radar wind measurements of the (1, 3) Rossby normal mode, and are therefore consistent with its identification as the temperature signature of this mode. The relationship of these summer temperature oscillations and the occurrence of noctilucent clouds is di

ISSN:0094-8276    

DOI:10.1029/96GL01068

年代:1996

数据来源: WILEY

摘要:

During the ECHO‐94 campaign PMSE have been observed with the ALOMAR‐SOUSY radar on 53.5 MHz at Andenes (69.28°N; 16.02°E) and with the EISCAT‐VHF radar on 224 MHz at Tromsø (69.58°N; 19.21°E). Comparisons of simultaneous measurements demonstrate generally good agreement between PMSE structures derived by both equipments. A detailed comparison shows differences caused by the mesospheric mean wind field as well as differences of the local dynamic or thermodynamic state at both measur

ISSN:0094-8276    

DOI:10.1029/96GL01107

年代:1996

数据来源: WILEY

摘要:

Simultaneous and co‐located measurements of mesospheric winds near South Pole, by high‐resolution optical and meteor radar methods, show that these two methods determine very similar motions at slightly different heights of observation. The measured atmospheric motions by the two techniques show that a) The mean wind during 12 days in June, 1995 was found to have a 7 m/s amplitude flowing towards the 5°E longitude direction. The latter direction is different from the 30E° direction found earlier during August 1991 and 1992. b) The observed dominant oscillations in the wind at both heights of observation are those of zonal wavenumber one character. Westward phase propagation was determined for the observed short‐period (∼0 hours) oscillations and eastward phase propagation for the longer‐period (∼3 days) oscillations, respectively. Because of the neighboring heights of observation by the optical and meteor radar methods, thein situvertical wavelengths of propagation of the observed waves have been determined to be greater than 100 km for the 10‐hr oscillations and near 65 km for the longer period oscillations. With this new information we are able to independently establish the earlier assignment of the nearly 10‐hr oscillations as the different meridional modes of a zonal wavenumber one Lamb wave. The determined vertical wavelength and eastward phase progression of the longer periodicity waves indicate these oscillations are likely to be the gravest inertio‐gravity wave, which has the appropriate equivalent depths at these periods of oscillation. The simultaneous absence of statistically significant kinetic temperature and optical‐tracer emission rate oscillations at the frequencies corresponding to the wind motions, provides independent support to the earlier deductions on the ability of the atmosphere near the rotational poles to support only certain zonal c

ISSN:0094-8276    

DOI:10.1029/96GL01193

年代:1996

数据来源: WILEY

摘要:

Application of detailed balance permits estimation of the rate coefficients for the reaction of highly vibrationally excited O2with ambient O2to yield odd oxygen, a process of potential importance in the stratosphere, O2(υ=26, 27) + O2→ O3+ O. The rate coefficients calculated in this manner are much smaller than those reported from experiment and below any level of atmospheric significan

ISSN:0094-8276    

DOI:10.1029/96GL01071

年代:1996

数据来源: WILEY

摘要:

Comparisons of total column ozone measurements from three ground‐based instruments (Dobson spectrophotometer, ozonesonde, and visible wavelength grating spectrometer) and the TOMS instrument are presented for the period 1991 to 1994 at Arrival Heights/McMurdo, Antarctica. The primary purpose of these comparisons is to investigate the accuracy of the visible spectrometer, while a second aim is to compare version 6 and version 7 TOMS satellite retrievals with the ground‐based measurements. While the Dobson, TOMS and ozonesonde measurements show good agreement, there is a seasonal dependence between data from the visible wavelength spectrometer and each of the other three instruments. However, the visible spectrometer produces valuable data for the late autumn and early spring, when data are not available from the Dobson and T

ISSN:0094-8276    

DOI:10.1029/96GL01199

年代:1996

数据来源: WILEY

摘要:

Ballonborne backscatter measurements of polar stratospheric clouds (PSC) from four Arctic winters have been used together with isentropic airparcel trajectories to assess recent theories of PSC formation. Assuming unperturbed HNO3concentrations, observations performed in the month of January, reveal that PSC formation initiates 3–4 K below the nitric acid trihydrate (NAT) condensation temperature (TNAT). According to a suggested scenario for PSC formation [Tabazcdeh et al., 1995] liquid supercooled ternary solution particles may freeze upon an increase in temperature after previously being close to the ice frost point. Liquid particles, identified by the temperature histories according to this scenario, show a relatively compact relationship between measured temperature and backscatter ratio, indicating a substantial growth at 3–4 K below the NAT‐temperature as expected by ternary solution particles. Newly formed solid particles are of small size, in contrast to aged solid particles which appear to retain large sizes up to the NAT‐temperatures during evaporation and grow by condensation at temperatures slightly below TNAT, indicating the composition to

ISSN:0094-8276    

DOI:10.1029/96GL01041

年代:1996

数据来源: WILEY

摘要:

We have analyzed a full month of daily and hourly satellite infrared data covering the Central Pacific, with an eye to identifying and characterizing self‐similar behavior of the cloud variability. It is found that the cloud outgoing longwave radiation field exhibits anomalous scaling, with parameters that are quite consistent across a broad range of synoptic situations. The presence of anomalous scaling means that, although the cloud field exhibits spatially self‐similar behavior, the power spectrum alone is not sufficient to characterize the spatial structure of cloud variability. The scaling laws do not conform to what would be expected from passive scalar advection/diffusion, but they do closely resemble the scaling laws for temperature fluctuations in a turbulent convecting la

ISSN:0094-8276    

DOI:10.1029/96GL01121

年代:1996

数据来源: WILEY

摘要:

The stratosphere can be used as an archive of past tropospheric conditions. Measurements of the long‐lived trace gases CF4, C2F6, and SF6have been carried out on stratospheric air samples obtained by balloon borne cryosampling from altitudes of up to 34 km between 1987 and 1995. SF6observations were used to ‘date’ the air samples. Above 25 km height the SF6concentrations are lagging the tropospheric ones by several years: 4.5 years for the tropics, 6 years for mid‐latitudes and up to 10 years for the arctic winter vortex. The high ages of stratospheric air found inside the upper polar vortex may indicate that the lag of the peak halogen burden between the troposphere and the polar stratosphere is longer than previously assumed. The age information from SF6allows to reconstruct tropospheric trends for CF4and C2F6since 1982. Accordingly, for the period 1982 to 1995, concentrations increased from 62 to 75 ppt for CF4and from 1.5 to 2.6 ppt for C2F6. Mean increase rates of 1.00 ppt yr−1for CF4and 0.084 ppt yr−1for C2F6translate into annual injection rates of about 14,600 t yr−1and 1,900 t yr−1respectively. With aluminium production as the only major source, average emissions per ton of primary aluminium are thus calculated to be 0.77 kg for CF4and 0.10 kg

ISSN:0094-8276    

DOI:10.1029/96GL01198

年代:1996

数据来源: WILEY