摘要:

The fast particles in the electron foreshocks propagate along the magnetic field lines, so that the effect of low frequency magnetic fluctuations is to create both a broadening and a fine structure of the foreshock upstream boundary. This is studied by means of a 3‐D numerical simulation of turbulent magnetic fields. Applications to Venus, Earth, and Mars magnetic foreshocks are done. It is found that a spacecraft can be magnetically connected to the bow shock even when it is upstream of the nominal magnetic foreshock boundary, and that the mixing of magnetic field lines can give an explanation for the broadband bursty electrostatic noise observed within the electron foreshoc

ISSN:0094-8276    

DOI:10.1029/96GL00660

年代:1996

数据来源: WILEY

摘要:

It is demonstrated that large‐amplitude low‐frequency waves (LFW) can generate lower hybrid waves (LHW) in the auroral zone and ring current region. The LHW could then heat the ions. The ion energization due to the LHW may be comparable with that produced by the ponderomotive force of the

ISSN:0094-8276    

DOI:10.1029/96GL00844

年代:1996

数据来源: WILEY

摘要:

Short intervals (<2.5 hrs) of dense (≥10 cm−3), cold (≤ 10 eV) plasmaspheric plasma are observed at synchronous orbit in association with the growth phase of geomagnetic substorms. We interpret the strong correlation between these phenomena in terms of the reconfiguration of the duskside/nightside magnetosphere during the growth phase of geomagnetic substorms. This reconfiguration moves plasmaspheric plasma outward to synchronous orbit, occasionally even in the midnight r

ISSN:0094-8276    

DOI:10.1029/95GL03663

年代:1996

数据来源: WILEY

摘要:

In October/November 1993 DOAS measurements of total columns of NO2and O3were performed on a ship cruise from Germany to South Africa. The results are compared to data collected during an earlier campaign with a similar setup [Kreher et al. 1995], which took place in 1990, before the eruption of the Pinatubo volcano. Overall no general trend for NO2in 1993 in comparison to 1990 could be detected.The O3vertical column densities in 1993 are mostly around 280 Dobson Units, showing a significant increase to over 330 DU south of 25°S, and significantly lower O3values south of 50°S. The height of the NO2concentration maximum was calculated from the NO2am/pm ratio and data from ozonesondes. The resulting heights are mostly round 29 km, except in the region (south of ≈ 45°S) where the lowest ozone column densities occurred, there the calculated height is ≈

ISSN:0094-8276    

DOI:10.1029/96GL00852

年代:1996

数据来源: WILEY

摘要:

Observations of a developing reverse convection cell on September 23, 1986 are examined using auroral images acquired with the UV imager on board the Viking Spacecraft. The cell possesses a counter‐clockwise rotational sense and evolves on the duskside of the northern auroral distribution between the duskside oval and a complex duskside transpolar arc system. As the structure evolves, it grows and appears to displace the transpolar arc toward the dawn. We interpret these observations in terms of a model proposed by Burch et al., [1992] in which open field lines produced by merging on the high latitude magnetopause produce reverse convection cells between the oval and the transpolar arcs associated with horse‐collar or teardrop auroral patte

ISSN:0094-8276    

DOI:10.1029/96GL00619

年代:1996

数据来源: WILEY

摘要:

Measurements with an airborne lidar performed during the Arctic winter 1994/95 show, that the ozone mixing ratio declined by about 50% throughout the polar vortex in the period from the beginning of February to mid of March in a sharp defined altitude band from 420 K to 520 K potential temperature. The simultaneous detection of the stratospheric aerosol density provides evidence that this depletion was not caused by dynamical processes but by chemical reactions.

ISSN:0094-8276    

DOI:10.1029/96GL00772

年代:1996

数据来源: WILEY

摘要:

The global ocean/atmosphere flux of methyl bromide has been estimated from shipboard measurements of the saturation anomaly. When such data are extrapolated globally on the basis of constant saturation anomaly, the ocean is a net sink for methyl bromide [Lobert et al, 1995]. The same data can also be extrapolated on the basis of steady‐state production rate of methyl bromide in the water column, allowing regional and seasonal variations in temperature to affect the saturation anomaly. We have carried out this type of extrapolation, and we found that the oceans are a strong net source of methyl bromide to the atmosphere. The difference arises mainly due to slow degradation rates in water of higher latitudes. A reduction of the applied production rate by more than 35% is needed in order to switch the ocean from a source to a sink of methyl bromide. These results demonstrate the sensitivity of current estimates of oceanic flux to assumptions about methyl bromide production and destruction in the water colum

ISSN:0094-8276    

DOI:10.1029/96GL00424

年代:1996

数据来源: WILEY

摘要:

Along Track Scanning Radiometer (ATSR) data from the ERS 1 satellite mission are used in a global analysis of the surface temperature of the oceans. The data are the low resolution 0.5° by 0.5° average temperatures and cover about 24 months. At global scales a significant seasonal variability is found. On each of the hemispheres the surface temperatures reach their maximum after summer heating. The seasonal sea level variability, as observed from TOPEX/POSEIDON, reaches its maximum 1.1–1.4 months la

ISSN:0094-8276    

DOI:10.1029/96GL00618

年代:1996

数据来源: WILEY

摘要:

The extreme dryness of the lower stratosphere is believed to be caused by freeze‐drying of air as it enters the stratosphere through the cold tropical tropopause. Previous investigations have been focused on dehydration occurring at the tops of deep convective cloud systems. However, recent observations of a ubiquitous stratiform cirrus cloud layer near the tropical tropopause suggest the possibility of dehydration as air is slowly lifted by large‐scale motions. In this study, we have evaluated this possibility using a detailed ice cloud model. Simulations of ice cloud formation in the temperature minima of gravity waves (wave periods of 1–2 hours) indicate that large numbers of ice crystals will likely form due to the low temperatures and rapid cooling. As a result, the crystals do not grow larger than about 10 µm, fallspeeds are no greater than a few cm‐s−1, and little or no precipitation or dehydration occurs. However, ice clouds formed by large‐scale vertical motions (with lifetimes of a day or more) should have fewer crystals and more time for crystal sedimentation to occur, resulting in water vapor depletions as large as 1 ppmv near the tropopause. We suggest that gradual lifting near the tropical tropopause, accompanied by formation of thin cirrus, may account for the

ISSN:0094-8276    

DOI:10.1029/96GL00722

年代:1996

数据来源: WILEY

摘要:

Recent attempts to estimate the contribution of clouds to absorption of solar radiation by the atmosphere have been based on the difference between measurements of solar flux at the top‐of‐the‐atmosphere, or in the atmosphere above cloud level, and measurements of solar flux at the surface, or in the atmosphere below cloud level. One problem with this approach is that fluxes below cloud level depend on the position of the clouds relative to the sun, which is not the case for measurements above cloud level. For example, at any point in the atmosphere below cloud level, the net downward flux varies considerably, depending on whether or not the clouds block the direct rays of the sun. As a result, the net downward flux above cloud level is generally a maximum for clear‐sky conditions, but not so for the net downward flux below cloud level. This effect, if not taken into account, would bias the methods used to infer the contribution of clouds to atmospheric absorption, and lead to an overestimate of the contr

ISSN:0094-8276    

DOI:10.1029/96GL00775

年代:1996

数据来源: WILEY