On modelling the seasonal thermodynamic cycle of sea ice in studies of climatic change   总被引：1，自引：0，他引：1  

Albert J. Semtner Jr. 《Climatic change》1984,6(1):27-37

Recent work in modelling climatic changes due to increased atmospheric CO₂ has shown the maximum change to occur in the polar regions as a result of seasonal reductions in sea ice coverage. Typically, sea ice thermodynamics is modelled in a very simple way, whereby the storage of both sensible and latent heat within the ice is ignored, and the effects of snow cover on conductivity and on surface albedo and of oceanic heat flux on bottom ablation may also be neglected. This paper considers whether omission of these processes is justified within the context of quantitatively determining regional climatic changes. A related question, whether omission of ice dynamics can be justified, is not considered.Relatively complete one-dimensional models of sea-ice thermodynamics have previously been developed and tested for a variety of environmental conditions by Maykut and Untersteiner (1969, 1971) and by Semtner (1976). A simpler model which neglects the storage of sensible and latent heat is described in the Appendix to Semtner (1976). In that model, the errors in annual-mean ice thickness which would arise from neglect of heat storage can be compensated by increases in albedo and in conductivity. Here we examine the seasonal cycle of ice thickness predicted by such a model and find significant errors in phase (one month lead) and in amplitude (50% overestimate). The amplitude errors are enhanced as snowfall and oceanic heat flux diminish (or are neglected). This suggests that substantial errors may occur in climate simulations which use very simple formulations of sea ice thermodynamics, whereby early and excessive melting exaggerates the seasonal disappearance of sea ice.To illustrate the above point, two models are configured to examine the local response of Arctic sea ice to a quadrupling of atmospheric CO₂. The first model neglects a number of physical processes and mimics the behavior of sea ice found in Manabe and Stouffer (1980), both for present and enhanced levels of CO₂. The more complete second model gives a better simulation of Arctic ice for the present level of CO₂ and shows a reduced response to CO₂ quadrupling relative to that in Manabe and Stouffer (1980). In particular, the change in surface temperature is cut by a factor of two. In view of this result, a more complete treatment of sea ice thermodynamics would seem warranted in further studies of climate change. Only a minor computational increase is required.A portion of this study is supported by the U.S. Department of Energy as a part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

Late glacial and late Holocene moraines in the Cerros Cuchpanga, central Peru     

H. E. Wright  Jr. 《Quaternary Research》1984,21(3)

Small ice fields on the western cordillera northeast of Lima were expanded to three times their present size in the recent past, and the regional snow line was probably about 100 m lower than it is today. Outwash from the expanded glaciers formed deltas of silt in valley-bottom lakes. When the ice lobes retreated, the reduced outwash was trapped behind recessional moraines, and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools. The delta surfaces then became covered with peat, and radiocarbon dates for the base of the peat (1100 ± 70 and 430 ± 70 yr B.P. for two different deltas) indicate that the maximum ice advance was older than those dates and, thus, older than the Little Ice Age of many north-temperate regions. Much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys, which had previously been inundated by the cordilleran ice field. The cordilleran deglaciation and this expansion of local glaciers probably occurred between 12,000 and 10,000 yr ago, on the basis of slightly contradictory radiocarbon dates.  相似文献   

THE GATE SQUALL LINE OF 9－10 AUGUST 1974     

Wei Tongjian  Robert A. Houze  Jr. 《大气科学进展》1987,4(1):85-92

A tropical squall line that passed over the ship array of the Global Atmospheric Research Programme’s Atlantic Tropical Experiment (GATE) on 9－10 August 1974 is analyzed. This squall line was similar to squall systems that passed over the GATE ship array on four other days. It began as a purely convective cloud line, then developed an associated stratiform cloud and precipitation area. The stratiform rain built up to a maxi-mum amount over a period of 8 h, then gradually diminished over a 6 h period. This stratiform rain is esti-mated to have accounted for 32% of the squall system’s total precipitation. As in other GATE squall lines, the upper-level cloud shield from which the stratiform rain fell, was advected slowly forward of the line during the system’s lifetime, the leading line of corrective clouds consisted of transient smaller-scale convective elements, which lent the line an irregular shape and pulsatory movement, and the stratiform portion of the system was characterized by the development of a mid-level mesoscale vortex similar to that seen in other GATE eases.  相似文献   

Fresh water on the Louisiana and Texas shelf     

S.P. Dinnel  W.J. Wiseman  Jr 《Continental Shelf Research》1986,6(6)

Hydrographic data collected on monthly cruises over the West Louisiana and Texas shelf from 1963 to 1965 were analyzed and the volume of fresh water on the shelf was estimated for each data set. The freshwater volume exhibits an annual cycle that is dominated by the spring flood of the Mississippi and Atchafalaya rivers. During the winter, shelf freshwater content is low, with the highest content appearing as a discontinuous band along the inner shelf. In summer an isolated high-content region is present in the center of the shelf. This high-content region dissipates and the pattern migrates toward the southeast in the late summer. By late fall the winter distribution is again present.A fill time for the freshwater volume on the shelf was also estimated for each cruise. The freshwater volume appears, in most cases, to have originated near the time of the previous spring flood.Two of the study years had river discharges well below the long-term mean, while the third-year discharge approximated the long-term mean. These results, then, may not be applicable to large-discharge years.  相似文献   

Pressure dependence of melt viscosities on the join diopside-albite     

Mark Brearley  James E. Dickinson  Jr.  Christopher M. Scarfe 《Geochimica et cosmochimica acta》1986,50(12):2563-2570

The pressure dependence of melt viscosities on the join diopside-albite has been studied using falling-sphere viscometry. The five melt compositions investigated are: diopside, Ab₂₅Di₇₅, Ab₅₀Di₅₀, Ab₇₅Di₂₅ and albite. Experiments were performed at 1500° and 1600°C and at pressures of 5, 10, 15, 20 and 25 kbar. The positive and negative pressure dependence of the viscosity of diopside and albite, respectively, were confirmed. All intermediate compositions show an initial decrease in viscosity with increasing pressure; however, melt of Ab₂₅Di₇₅ composition passes through a minimum viscosity at approximately 12 kbar and 1600°C. This behavior is analogous to the variation in the viscosity of water with pressure at low temperature.

It is suggested that the three-dimensional, fully polymerized, albite structure dominates flow at low pressures. With increasing pressure, disruption of this structure and decrease in the average size of the flow units leads to domination by the diopside structure. The variation in viscosity with composition along the join at one atmosphere can be adequately modelled using the and (1965) configurational entropy model with an additional two-lattice configurational entropy of mixing term. The pressure dependence of viscosity in the diopside-albite system, however, cannot be predicted by the model, because there is an absence of information on the pressure dependence of the model parameters.

It is probable that relatively polymerized magmas (e.g. rhyolites to SiO₂-saturated basalts) show a negative pressure dependence of viscosity to depths where they originate in the lower crust or upper mantle. In contrast, the most depolymerized, naturally-occurring melts, such as strongly SiO₂-undersaturated basalts and picrites, may exhibit a viscosity minimum. The viscosity of these melts may be sufficiently high at depths within the upper mantle to inhibit their segregation, rise and eventual eruption at the surface.  相似文献   

Slug Tests in Unconfined Formations: An Assessment of the Bouwer and Rice Technique   总被引：3，自引：0，他引：3  

Z. Hyder  J. J. Butler  Jr. 《Ground water》1995,33(1):16-22

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Applications of Universal Kriging to an Aquifer Study in New Jersey   总被引：1，自引：0，他引：1  

Amleto A. Pucci  Jr.  Jo Ann E. Murashige 《Ground water》1987,25(6):672-678

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SPECTROPHOTOMETRIC DETERMINATION OF FERROUS IRON IN EIGHTEEN UNITED STATES GEOCHEMICAL REFERENCE STANDARDS     

Charles B. Bruce  Jr.  Nathan W. Bower 《Geostandards and Geoanalytical Research》1987,11(1):41-42

Iron (II) oxide in 50 mg samples of silicate rocks, deposits, and soils is measured after digestion with HF and HCl in the presence of ICl. The iodine produced is measured spectrophotometrically. Results are presented for the eighteen available USGS geochemical reference standards including the GXR series.  相似文献   

On the relationship of thunderstorm ice hydrometeor characteristics and total lightning measurements   总被引：1，自引：0，他引：1  

Wiebke Deierling  John Latham  Walter A. Petersen  Scott M. Ellis  Hugh J. Christian  Jr.   《Atmospheric Research》2005,76(1-4):114

Satellite-borne and ground-based devices for the detection of lightning offer the opportunity to explore relationships–on all significant scales up to global–between lightning frequency, f, and other thundercloud parameters. Calculations predict that f is proportional to the product of the downflux p of solid precipitation and the upward mass flux, I, of ice crystals. This prediction has received support from limited computational studies. The physical reasons for such a relationship are explained in terms of the paramount role of ice in the electrification of thunderstorms. Herein, this prediction is subjected to further, preliminary examination through analysis of lightning and dual-polarimetric radar data collected during the STERAO experiment conducted in Northern Colorado during the summer of 1996. The analysis has yielded some highly provisional support for this flux hypothesis. Computed trends of radar derived hydrometeor fractions of solid precipitation and small ice show correlation to the total lightning frequency and raise the possibility of determining values of p and/or I from lightning measurements.It is shown that the extent to which the observed correlations between f and both solid precipitation and small ice trends are or are not strong can provide an indication as to whether the lightning activity is limited by the available concentrations of precipitating or non-precipitating ice in the upper regions of the charging zone of the thundercloud, where most of the charge transfer occurs. It is demonstrated that the most accurate determinations of precipitation rate p from measurements of lighting frequency f are likely to be for conditions where the field-growth is limited by the availability of graupel pellets. It is shown that the simultaneous time variations of f and solid precipitation trends of the type obtained in the STERAO experiment could enable us to determine the nature of the dominant glaciation process operative in the thunderclouds studied.  相似文献   

Current-scattered (?) detrital remanence directions in the Zn-rich Pennsylvanian Stark black shale, USA     

K. Kawasaki  D. T. A. Symons  R. M. Coveney Jr  . 《Geophysical Journal International》2007,171(2):594-602

Palaeomagnetic results are reported from the metalliferous Stark black shale in the Upper Pennsylvanian (Missourian/Kasimovian) Kansas City Group. Palaeomagnetic analysis of 400 specimens from 28 sites gives a characteristic remanent magnetization in 17 sites of the shale that yields a Late Mississippian to Middle Pennsylvanian palaeopole at 32.2°N 128.5°E (dp = 4.7° and dm = 8.8°). The observed palaeomagnetic age is slightly older than the host rock, indicating that the mineralization of the Stark Shale has, excluding recent alteration, a primary sedimentary or syngenetic origin. The reason for the slightly older age is likely due to trace modern hematite that slightly steepens the remanence inclination. The large oval of 95 per cent confidence is interpreted to be caused by clay–magnetite aggregates that formed during sediment transport and the biasing effect of the gentle palaeocurrent at each site acting on the large aggregates. Therefore, the scattered distribution of the site mean remanence declinations found for the Stark Shale is evidence of a detrital remanent magnetization that is formed by primary sedimentary processes with an enriched metallic content and not remagnetization with mineralization by secondary hydrothermal processes.  相似文献