摘要:

The vast ice sheet of Antarctica is isolated geographically but not meteorologically from the rest of the planet. Tropospheric aerosols in or near the accumulation mode size, around a half micron diameter, reside in the atmosphere for tens of days and teleconnect Antarctica with other regions by transport that reaches planetary scales of distances. The aerosol on the ice sheet, therefore, at any time and place represents “memory modules” of events that took place at regions separated from Antarctica by tens of thousands of kilometers. Scientific attention to this collective aerosol system provides insight into long‐range atmospheric transport. Investigations of particles in the ultraclean air over Antarctica were slow to get going mainly because of a failure to recognize the possibility of semiglobal transport of “dust”; as a result, this field is very young, having gone through its “romantic period” of exploratory studies in the late 1960s and entered into a time of synthesis and paradigm building only in the mid‐1970s. An important recent discovery is that the aerosol number concentration (the condensation nuclei (CN)) over this distant ice sheet undergoes a regular, methodical and predictable seasonal variation, nearly disappearing around winter solstice but being relatively robust (i.e., comparable to what one finds over mid‐oceans) in summer. A weakened seasonal modulation of CN is found at coastal sites. Circumstantial evidence indicates that the CN over the ice are produced from gas photolytically. Thus the tiniest particles over Antarctica are products of a slow “chemical” conversion within the atmosphere itself. A major discovery with numerous possible deep geobiological ramifications is that the aerosol over the ice sheet is by mass 70–90% sulfate, in the molecular form of hydrated droplets of sulfuric acid, except during transient events of a few days duration when atmospheric transport forces warm, moist air from the oceans into the interior continental regions. These events are most frequent in late winter‐early spring, accompanying the breakdown of the circumpolar vortex. These “sodium storms” transport large quantities of sea salt to the central ice sheet sporadically. Chemical studies of the submicron ice cap aerosols indicate that there is a uniquely winter and uniquely summer “crustal,” insoluble aerosol that represents<5% of aerosol mass but which has provided an interesting long‐term permanent record of itself going back 2 × 105years in the ice. In terms of aerosol mass, the aerosol is composed of crustal products (<5%), transported sea‐salt residues (highly variable but averaging ∼ 10%), Ni‐rich meteoric material, and anomalously enriched material with an unknown origin. Most of the Antarctic aerosol, however, is the “natural acid sulfate aerosol” apparently deriving from biological pr

ISSN:8755-1209    

DOI:10.1029/RG026i001p00089

年代:1988

数据来源: WILEY

摘要:

Although trace stratospheric gases such as ozone have been measured in Antarctica from the surface since 1957 and from balloons since 1966 and stratospheric aerosols have been measured routinely by balloon‐borne particle counters since 1972, only recently has any real interest in these measurements developed. This new awareness is directly related to the realization, in 1985, that springtime Antarctic total ozone had declined about 50% since about 1977. Such an unprecedented, unpredicted change understandably created a great deal of interest in past Antarctic ozone‐related measurements. Early theories of this phenomenon included both chemical and dynamical ozone depletion mechanisms. Chemical theories generally utilized stratospheric particles (created in the low‐temperature environment of the Antarctic stratosphere) to enhance chemical conversion of reservoir chlorine compounds to active ozone‐destroying chlorine heterogeneously. Dynamic models utilized particle heating to lift the polar vortex air mass in spring and cause reductions in ozone. Thus these theories generated an interest not only in ozone measurements but also in stratospheric particulates (aerosols) and in measurements of trace gases which could be used as tracers of atmospheric motions, for example, nitrous oxide. In 1986 the first major field studies, in the National Ozone Expedition, were directed at this problem. In the following review of in situ balloon‐borne measurements of aerosols and trace gases the limited amounts of data prior to 1986 are summarized. The new measurements of 1986 have revealed much concerning the nature of the ozone depletion mechanism. While the steady decline in ozone in the 12‐ to 20‐km region in September can probably only be explained by fast chemistry, the phenomenon appears to be shaped spatially and temporally by dynamical phenomena. The next several years will see expanded research in this area, not only in Antarctica but also in other regions in an attempt to detect reductions in ozone which may occur at th

ISSN:8755-1209    

DOI:10.1029/RG026i001p00113

年代:1988

数据来源: WILEY

摘要:

Total ozone levels over Antarctica have declined by about 50% over the past decade, principally during the spring seasons. This unprecedented and unanticipated change in the total ozone column has precipitated a great deal of research into the dynamics and chemistry of the Antarctic, and their contributions to the observed behavior of ozone there. Observations of the total ozone column and its vertical profile over Antarctica are reviewed. Theoretical models to explain the mysterious change in ozone abundances are described, along with observations of Antarctic temperatures. Both chemical and dynamical processes occurring in Antarctic spring may be related to polar stratospheric clouds. The radiative and chemical properties of these clouds are summarized. Available observations of other chemical species besides ozone (e.g., nitrogen dioxide, chlorine monoxide) are also discussed. The current status of the evidence supporting various theories of the behavior of ozone in the Antarctic is summarized.

ISSN:8755-1209    

DOI:10.1029/RG026i001p00131

年代:1988

数据来源: WILEY

摘要:

Precipitation over Antarctica is an important climatic variable whose study has been limited by the frequent inability to discriminate between actual snow precipitation and drifting snow. Recent advances in point precipitation measurements promise to circumvent this problem. In addition, indirect estimates based upon the atmospheric water balance equation provide seasonal precipitation amounts for areas larger than 1×106km². For broad‐scale studies in the continental interior net snow accumulation closely approximates precipitation. Annual precipitation is relatively high over the marginal ice slopes in relation to amounts in the interior. This meridional distribution is due to the orographic lifting of moist air by the ice sheet. Zonal precipitation variations are related to the quasi‐stationary cyclones in the circumpolar low‐pressure trough. Most precipitation falls in winter, when the average moisture content of the air is low. The intensity of cyclonic activity is the key factor governing the amount of precipitation and its variations. Precipitation generation in coastal regions is strongly influenced by the fact that poleward moving, moist maritime air masses are deflected by the steep marginal ice slopes to blow parallel to the terrain contours. Direct orographic lifting with accompanying adiabatic cooling is the dominant precipitation formation mechanism inland of the 1‐km elevation contour; intrusions of moist air far into the continent are accompanied by southerly winds through a deep tropospheric layer. Above 3000 m elevation where terrain slopes are gentle, radiative cooling is the primary mechanism by which saturation is maintained within moist air, and thus by which precipitation is formed. Most precipitation at these elevations falls from clear skies. This phenomenon does not differ from precipitation originating in clouds but is a direct result of the low moisture content of the air, and hence ice layers are optically too thin to be visible

ISSN:8755-1209    

DOI:10.1029/RG026i001p00149

年代:1988

数据来源: WILEY

摘要:

Surface winds over Antarctica, often classified as “katabatic,” are intimately related to the orientation and steepness of the underlying ice terrain. Such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope‐directed horizontal pressure gradient force. It is possible to diagnose the time‐averaged, near‐surface streamline patterns of cold air drainage currents using recently compiled, detailed Antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion. The resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity‐driven flows off the ice sheets. In certain interior sections, negatively buoyant air from a large catchment area drains through a restricted section of coastline. Such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds. Implications for sea ice formation ar

ISSN:8755-1209    

DOI:10.1029/RG026i001p00169

年代:1988

数据来源: WILEY

摘要:

High‐latitude ULF waves at all frequencies are reviewed with emphasis on simultaneous measurements in both hemispheres. The seasonal variation of interhemisphere high‐latitude data is valuable in helping to understand the topology of the magnetosphere. The frequent occurance of Pc 1–2 pulsations at high latitudes and in the polar cap is discussed. Evidence for ground detection of flux transfer events via magnetic pulsations is reviewed. The correlation of high‐latitude pulsation data with other ground techniques of measuring particle precipitation is presented to better define the subset of high‐latitude ULF that is produced by local current systems fed by particle precipitation and field‐aligned currents. Finally, simultaneous ground and spacecraft measurements of ULF are reviewed which provide information on the propagation of ULF across such boundaries as the magnetopause and the

ISSN:8755-1209    

DOI:10.1029/RG026i001p00181

年代:1988

数据来源: WILEY