摘要:

A tailward‐moving plasmoid was observed at the GEOTAIL satellite at a GSM position (−73.3, 18.1, −1.1)REon September 16, 1993, at 0417 UT, when the IMP 8 satellite was at (−37.5, −2.5, 1.7)REat the midnight plasma sheet/lobe interface. The first indication of the plasmoid formation a few minutes after the negative bay onset of a small, localized auroral substorm was the onset of tailward beams of energetic ions and electrons at GEOTAIL well within the plasma sheet. Earthward‐streaming energetic ions observed at IMP 8 a few minutes later suggest that the plasmoid evolved from within the plasma sheet to encompass the flux of nearly the entire thickness of the plasma sheet. The opposite direction of the anisotropies at IMP 8 and GEOTAIL suggest that the particle acceleration region was betweenX=−37.5 and −73REat that time. The isolated substorm associated with this plasmoid started equatorward of 67° latitude at a location which we map to near‐Earth nightside plasma sheet (|X|<15RE) based on ground observations of a field line resonance. The active electrojet did not expand poleward until at least 10 min after the detection of the acceleration region tailward of IMP 8 and at least several minutes after the core of the plasmoid had moved tailward of GEOTAIL. These observations reinforce by means of in situ, concurrent, multipoint measurements the attitude expressed recently by several researchers that the locations of lobe reconnection and equatorial projection of electrojet intensification during substorm expansion are distinctly differe

ISSN:0094-8276    

DOI:10.1029/95GL03133

年代:1995

数据来源: WILEY

摘要:

An analysis is performed on the heating of electrons in the lower ionosphere due to the electromagnetic radiation from vertical and horizontal lightning discharges. Disturbances of the electron temperature in the daytime ionosphere may exceed 50°Kfor vertical strokes and 100°Kfor horizontal lightning discharges. The association of this analysis to some other related phenomena, is finally discusse

ISSN:0094-8276    

DOI:10.1029/95GL01982

年代:1995

数据来源: WILEY

摘要:

A new all‐sky imaging Fabry‐Perot (ASIFP) spectrometer has been developed for ground‐based mapping of upper atmospheric wind and temperature fields in the auroral zone. Although several other ASIFP spectrometers exist for atmospheric studies [Rees et al., 1984; Sekar et al., 1993; Biondi et al., 1995] these instruments have all operated with etalons of fixed optical gap, a method potentially subject to errors in the presence of auroral intensity gradients. In this instrument the etalon plate spacing is scanned periodically over one order of interference and each photon detected is assigned to a wavelength interval which is determined from both its arrival location on the detector and the etalon plate spacing prevailing at the detection time. Spectra accumulated this way are not distorted by spatial intensity gradients. Preliminary λ630 nm observations were made during the winter of 1994/95 from Poker Flat Research Range, Alaska. To illustrate some of the features we have observed in this study we present line‐of‐sight wind estimates derived for the night of December 7, 1994. The background wind matches averages presented previously by Sica et al. [1986]and is consistent with winds driven principally by momentum deposition from ionospheric plasma convection through ion‐drag. Smaller scale curvature and divergence features are also discernable and a

ISSN:0094-8276    

DOI:10.1029/95GL02437

年代:1995

数据来源: WILEY

摘要:

The discovery of a cellular structure in the high latitude thermospheric (120–350 km) neutral density provides a new framework in which to interpret high latitude density data. During geomagnetically active times, above about 170 km, the cells consist of density enhancements near noon and midnight and depletions near dawn and dusk. In this paper, a previously unexplained observation is presented and interpreted in terms of the cells. In general the high latitude neutral density is expected to increase during magnetically active conditions. On the contrary, the SETA‐1 satellite measured a 40% density decrease near 200 km during the geomagnetic storm of April 3, 1979. In the past, such ‘anomalous’ observations have often been attributed to the inseparability of density and winds in accelerometer measurements. We first show that the depletion cannot be caused by winds, and then show that the depletion is a natural consequence of the cellular structure inherent in the mass density at

ISSN:0094-8276    

DOI:10.1029/95GL02226

年代:1995

数据来源: WILEY

摘要:

A realistic parameterization scheme for the deposition of gravity‐wave momentum in the middle atmosphere has been incorporated into the 2D version of a global‐scale Numerical Spectral Model of the Earth's middle atmosphere. Here we present early results, obtained with only the simplest assumptions for the incident gravity‐wave spectrum—that it is azimuthally isotropic (i. e., identical flux in the four cardinal directions), globally uniform, and unchanging with season—and with essentially “untuned” values of tunable parameters. This model reproduces reasonably well the observed anomalous latitudinal temperature distribution and the zonal circulation of the upper mesosphere during solstice, just as other models do. It also produces relatively large oscillations in the mean zonal circulation of the middle atmosphere at low latitudes, descending in altitude with time. In the mesosphere and upper stratosphere, the dominant period is semi‐annual and the maximum amplitude is about 20 m/s near a height of 50 km. At lower levels, the dominant period is about 20 months and the maximum amplitude is about 8 m/s near 25 km. These values resemble those associated with the observed Semi‐Annual Oscillation and Quasi‐Biennial Oscillation, respectively, leading us to conclude that small scale gravity waves may contribute si

ISSN:0094-8276    

DOI:10.1029/95GL03059

年代:1995

数据来源: WILEY

摘要:

Rapid temperature fluctuations are shown to cause liquid H2SO4/HNO3/H2O stratospheric aerosols to depart considerably from thermodynamic equilibrium. While HNO3uptake by larger droplets is diffusively hindered, small droplets can approach the composition of a pure binary HNO3/H2O solution with up to 52 wt% HNO3, 48 wt% H2O and very small amounts of H2SO4. The stoichiometry of these droplets is close to that of nitric acid trihydrate (NAT) and freezing experiments suggest that this could be a suitable pathway for the formation of frozen polar stratospheric clouds (PSCs) of type‐I

ISSN:0094-8276    

DOI:10.1029/95GL03056

年代:1995

数据来源: WILEY

摘要:

Model calculations suggest that the ozone decrease observed a few years after the eruptions of Mt. Pinatubo and El Chichon may have been unique in the Earth's history, and is directly linked to the emission in the atmosphere of industrially manufactured chlorofluorocarbons. For chlorine loadings typical of the pre‐1980 period, the ozone column abundance should have increased after a large volcanic eruption. After 1980, as a result of growth in chlorine loading, the response of ozone became negative in winter at mid‐ and high latitudes. In the future, the response of ozone is expected to become positive again, if the production of chlorofluorocarbons is sufficiently reduced. The calculations also show that, under low chlorine loadings, the response of ozone is insensitive to the magnitude of the eruption, while, under present conditions (high chlorine loading), the ozone depletion increases with the amount of SO2injected in the stratosphere by the volc

ISSN:0094-8276    

DOI:10.1029/95GL03057

年代:1995

数据来源: WILEY

摘要:

Aerosol particles were collected during the dry season in the amazonian forest and in African and Brazilian savannas. Sampling was performed inside the plumes of vegetation fires and in the local background atmosphere. Samples were analysed for their elemental composition by Particle Induced X‐Ray Emission (PIXE). Enrichment factors relative to the local background were calculated. Savanna fire aerosols are characterised by enrichments in elements like K, P, Cl, Zn, and Br, whereas forest fire emissions are enriched in Si and Ca. The unexpected low potassium enrichment factor for the forest fires could be due to the prevailing smoldering conditions, whereas the high values of potassium enrichment factor during savanna fires could be associated with the predominant flaming conditions. This result indicates that potassium may be considered a good tracer of the flaming phase of fires only. Emission factors of P, S, Cl, K, Ca, Mn, Zn, Br and total particulate matter were calculated for African savanna fires. Our estimates of the annual potassium and zinc emissions by tropical savanna fires indicate that the contribution of this source should be taken into account to understand the biogeochemical cycle of these element

ISSN:0094-8276    

DOI:10.1029/95GL03170

年代:1995

数据来源: WILEY

摘要:

Mass accommodation coefficients on aqueous droplets have been measured for two substituted aromatic compounds using a droplet train apparatus and detection in the gas phase by laser induced fluorescence. Values of (1.8±0.5) × 10−2and (2.7±0.5) × 10−2have been obtained at 283 K for aniline and phenol, respectively. Mass accommodation of toluene was below the limit of detection of 1.0 × 10−3. Phenol and aniline are chosen as models for polar and oxygenated species formed as Cyintermediates in the oxidation of less soluble aromatic hydrocarbon precursors. The measurements indicate that mass accommodation of such species could be a significant pathway for the removal of tropospheric hy

ISSN:0094-8276    

DOI:10.1029/95GL02944

年代:1995

数据来源: WILEY

摘要:

A transient CO2experiment has been performed with the BMRC coupled atmosphere ocean General Circulation Model (GCM). No flux corrections were used in the experiment. A roughly linear temporal increase in global surface temperature is found in response to the CO2increase. The rate of increase is consistent with the (relatively low) equilibrium response found previously using the Atmospheric GCM and a simple ocean. Ocean surface temperatures increase more at mid latitudes than at high northern or southern latitudes where heat is sequestered into the deep ocean. Despite the secular climate drift which occurs in the model, the major patterns of atmospheric and oceanic temperature change are similar to changes noted elsewhere (from flux corrected models). This adds further support to the main conclusions drawn from transient CO2experiments performed elsewhere with coupled GCMs.

ISSN:0094-8276    

DOI:10.1029/95GL01727

年代:1995

数据来源: WILEY