摘要:

Global images of Earth's ultraviolet dayglow as gained with an imaging photometer on board Dynamics Explorer 1 exhibit transient decreases, or atmospheric holes, in the dayglow intensities over areas with diameters ∼50 km. Features of these atmospheric holes include (1) preferential motion in the east‐to‐west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meteors, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes when the spacecraft approaches Earth during its perigee passes. A significantly less extensive series of images of Earth's ultraviolet dayglow with the Viking spacecraft also provides evidence of these atmospheric holes. The atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere. Supporting evidences for the existence of these small comets are given by telescopic sighting of these objects at greater altitudes before disruption and the detection of water bursts in Earth's upper atmosphere. We summarize the current status of this small‐comet hypothesis and its relationship to conventional wisdom concerning geophysical, lunar, and interplanetary ph

ISSN:8755-1209    

DOI:10.1029/92RG02316

年代:1993

数据来源: WILEY

摘要:

A new, speculative, and, we hope, provocative summary of the North Atlantic circulation is described, including both horizontal currents (wind‐driven) and the primarily (thermohaline) meridional flows that involve the transformation of warm to cold water at high latitudes. Our picture is based on a synthesis of a variety of independent investigations that are contained in the literature as opposed to a presentation of the results of one technique or the point of view of one author. We describe a thermohaline cell (the so‐called thermohaline conveyor belt) that is concentrated within the Atlantic and Southern oceans (rather than essentially global), with the most important upwelling sites being in the circumpolar and the equatorial current regimes. We concentrate on deep water formation and its replacement relative to intermediate‐water formation. It has been pointed out recently that the formation of 13 Sv (1 Sv = 106m³ s−1) of southward flowing North Atlantic Deep Water is compensated for in the upper ocean by northward cross‐equatorial transport. We suggest that this thermocline layer flow passes through the Straits of Florida, transits the Gulf Stream system on its inshore side, and exits through the North Atlantic Current system after recirculation and modification. There is now a clear observational basis for the structure of recirculating gyres on the southern and northern sides of the Gulf Stream. We suggest a recirculation for the North Atlantic Current as well. We also describe a C‐shaped component to the southern Gulf Stream recirculation and identify a roughly 10‐Sv circulation in the eastern North Atlantic associated with the Azores Current. Recirculations play an important role in deep boundary current regimes and in water mass formation and modification. The transport of the deep western and northern boundary currents in the North Atlantic Ocean may be boosted (roughly doubled or tripled) by counterclockwise recirculating gyres and by additions of modified bottom or intermediate water. While the North Atlantic is the most completely observed ocean, there are still significant gaps in our knowledge of i

ISSN:8755-1209    

DOI:10.1029/92RG02583

年代:1993

数据来源: WILEY

摘要:

This is a review of quantum chemical, statistical‐mechanical, electrostatic, and crystal chemical studies of phyllosilicates. Atomic‐level studies have examined the structure and bonding within phyllosilicate layers, the effects of cation substitution on bonding and charge distribution, the structure of water, and the distribution of cations in the interlayer, and the bonding between phyllosilicate layers. The major needs for future research are statistical‐mechanical simulations of ion exchange reactions, electron transport in transition‐metal‐containing phyllosilicates, structure and bonding at phyllosilicate edges, and mechanisms of crystal growth and di

ISSN:8755-1209    

DOI:10.1029/92RG01823

年代:1993

数据来源: WILEY

摘要:

Net organic metabolism (that is, the difference between primary production and respiration of organic matter) in the coastal ocean may be a significant term in the oceanic carbon budget. Historical change in the rate of this net metabolism determines the importance of the coastal ocean relative to anthropogenic perturbations of the global carbon cycle. Consideration of long‐term rates of river loading of organic carbon, organic burial, chemical reactivity of land‐derived organic matter, and rates of community metabolism in the coastal zone leads us to estimate that the coastal zone oxidizes about 7 × 1012moles C/yr. The open ocean is apparently also a site of net organic oxidation (∼16 × 1012moles C/yr). Thus organic metabolism in the ocean appears to be a source of CO2release to the atmosphere rather than being a sink for atmospheric carbon dioxide. The small area of the coastal ocean accounts for about 30% of the net oceanic oxidation. Oxidation in the coastal zone (especially in bays and estuaries) takes on particular importance, because the input rate is likely to have been altered substantially by human activities

ISSN:8755-1209    

DOI:10.1029/92RG02584

年代:1993

数据来源: WILEY