Vibrational nitrogen concentration in the ionosphere and its dependence on season and solar cycle     

A. E. Ennis  G. J. Bailey  R. J. Moffett 《Annales Geophysicae》1995,13(11):1164-1171

A fully time-dependent mathematical model, SUPIM, of the Earth’s plasmasphere is used in this investigation. The model solves coupled time-dependent equations of continuity, momentum and energy balance for the O⁺, H⁺, He⁺, N⁺₂, O⁺₂, NO⁺ ions and electrons; in the present study, the geomagnetic field is represented by an axial-centred dipole. Calculation of vibrationally excited nitrogen molecules, which has been incorporated into the model, is presented here. The enhanced model is then used to investigate the behaviour of vibrationally excited nitrogen molecules with F10.7 and solar EUV flux, during summer, winter and equinox conditions. The presence of vibrational nitrogen causes a reduction in the electron content. The diurnal peak in electron content increases linearly up to a certain value of F10.7, and above this value increases at a lesser rate, in agreement with previous observations and modelling work. The value of F10.7 at which this change in gradient occurs is reduced by the presence of vibrational nitrogen. Vibrational nitrogen is most effective at F-region altitudes during summer daytime conditions when a reduction in the electron density is seen. A lesser effect is seen at equinox, and in winter the effect is negligible. The summer reduction in electron density due to vibrational nitrogen therefore reinforces the seasonal anomaly.  相似文献   

Alternating field characteristics of pseudo-single-domain (2–14 μm) and multidomain magnetite     

Monika E. Bailey  David J. Dunlop 《Earth and Planetary Science Letters》1983,63(3):335-352

We report normalized AF demagnetization curves of anhysteretic remanences (ARM's) produced by 1-, 10- and 40-Oe steady fields and of saturation isothermal remanence (IRM_s) in a suite of dispersed, unannealed magnetite powders with median sizes of 2, 4, 6, 10 and 14 μm (pseudo-single-domain or PSD size range) and 100 μm (multidomain or MD size). Interpreted in the light of the domain structure test first proposed by Lowrie and Fuller [12], the relative stability trend of curves for the 2 μm sample is of single-domain (SD) type, the 1-Oe ARM being most resistant to demagnetization followed by the 10-Oe and 40-Oe ARM's and IRM_s. For the 100-μm sample, the trend is exactly reversed and is of MD-type. In the 4–14 μm samples, hitherto undescribed transitional trends between SD-type and MD-type occur. At 6 μm, 1-Oe, 10-Oe and 40-Oe ARM's preserve an SD-type trend but for all AF's > 75 Oe, IRM_s is more resistant than any of these remanences. At 10 μm, this trend is unmistakable, and only at 14 μm do the 1-Oe, 10-Oe and 40-Oe ARM curves merge. We conclude (1) that the Lowrie-Fuller test distinguishes between small MD grains enhanced by PSD remanence and large MD grains lacking PSD remanence, rather than between SD and MD structures per se, and (2) that in the PSD transition region from 6 to 14 μm in magnetite, IRM_s changes over to MD-type relative stability around 6 μm, whereas 10-Oe and 40-Oe ARM's achieve an MD-type trend around 14 μm, in accord with the predicted field dependence of the PSD threshold size.Our theoretical interpretation assumes that the intrinsic (internal field) coercive force spectra of weak-field and strong-field remanences are identical but that the observed (external field) spectrum is shifted to lower fields as a result of the internal demagnetizing field — NJ_r of the remanence J_r. The effect is slight for weak-field J_r's but substantial for IRM_s. Since all coercivities, high as well as low, are shifted, the result of the Lowrie-Fuller test is determined simply by the shape of the intrinsic coercivity spectrum or the corresponding AF demagnetization curve. Depending on the model of self-demagnetization used, either subexponential or sublinear AF decay curves of weak-field remanence will automatically lead to an MD-type trend, whereas by either model the decay curves that characterize SD and PSD remanences (decaying slowly initially and then more rapidly) will always produce and SD-type trend.  相似文献   

Formation and pathways of North Atlantic Deep Water in a coupled ice–ocean model of the Arctic–North Atlantic Oceans     

David A. Bailey  Peter B. Rhines  Sirpa Häkkinen 《Climate Dynamics》2005,25(5):497-516

We investigate the formation process and pathways of deep water masses in a coupled ice–ocean model of the Arctic and North Atlantic Oceans. The intent is to determine the relative roles of these water masses from the different source regions (Arctic Ocean, Nordic Seas, and Subpolar Atlantic) in the meridional overturning circulation. The model exhibits significant decadal variability in the deep western boundary current and the overturning circulation. We use detailed diagnostics to understand the process of water mass formation in the model and the resulting effects on the North Atlantic overturning circulation. Particular emphasis is given to the multiple sources of North Atlantic Deep Water, the dominant deep water masses of the world ocean. The correct balance of Labrador Sea, Greenland Sea and Norwegian Sea sources is difficult to achieve in climate models, owing to small-scale sinking and convection processes. The global overturning circulation is described as a function of potential temperature and salinity, which more clearly signifies dynamical processes and clarifies resolution problems inherent to the high latitude oceans. We find that fluxes of deep water masses through various passages in the model are higher than observed estimates. Despite the excessive volume flux, the Nordic Seas overflow waters are diluted by strong mixing and enter the Labrador Sea at a lighter density. Through strong subpolar convection, these waters along with other North Atlantic water masses are converted into the densest waters [similar density to Antarctic Bottom Water (AABW)] in the North Atlantic. We describe the diminished role of salinity in the Labrador Sea, where a shortage of buoyant surface water (or excess of high salinity water) leads to overly strong convection. The result is that the Atlantic overturning circulation in the model is very sensitive to the surface heat flux in the Labrador Sea and hence is correlated with the North Atlantic Oscillation. As strong subpolar convection is found in other models, we discuss broader implications.  相似文献   

Lightning optical pulse statistics from storm overflights during the Altus Cumulus Electrification Study   总被引：2，自引：0，他引：2  

D.M. Mach  R.J. Blakeslee  J.C. Bailey  W.M. Farrell  R.A. Goldberg  M.D. Desch  J.G. Houser 《Atmospheric Research》2005,76(1-4):386

The Altus Cumulus Electrification Study (ACES) was conducted during the month of August 2002 in an area near Key West, Florida. One of the goals of this uninhabited aerial vehicle (UAV) study was to collect time resolved optical pulse data from thunderstorms. During the month long campaign, we acquired 5256 lightning generated optical pulses. Most of these observations were made while quite close to the top of the storms. We divided our data into two amplitude groups based on prior NASA U2 aircraft optical data and the pulse characteristics. The group of strong pulses with radiance greater than 2.1 mW m^{− 2} sr^{− 1} had mean and median 10–10% optical pulse widths of 770 and 740 μs, respectively, 50–50% pulse widths of 399 and 355 μs, respectively, and 10–90% risetimes of 292 and 260 μs. These values are very similar to the previous U2 based optical results The other group of pulses consisting of slightly more than a quarter of the total pulses observed had radiances less than the minimum values detected in the U2 study. These weak pulses were narrower than the strong pulses with 50–50% mean and median values of 199 and 160 μs, respectively. Only 12% of the flashes observed contained only weak pulses. The source of these weak pulses is unknown, but we suspect that some are artifacts of the close proximity of the aircraft to cloud top.  相似文献   

Mapping the Globalization of the Temporary Staffing Industry*     

Neil M. Coe  Jennifer Johns  Kevin Ward 《The Professional geographer》2007,59(4):503-520

Very little is currently known about the globalization of the temporary staffing industry, a strategically significant sector given its role in promulgating wider labor market flexibility. This article starts to rectify this research lacuna in four ways: by conceptualizing the international expansion of temporary staffing and comparing it to other business service sectors, by identifying and mapping the top twenty transnational staffing agencies, by offering a typology of the leading transnational agencies based on their functional and geographic characteristics, and by charting a research agenda for future work on this sector.  相似文献   

Religion, Violence and Political Mobilisation in South Asia – Edited by Ravinder Kaur     

Jennifer Hyndman 《Singapore journal of tropical geography》2007,28(2):239-240

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Spatial variability of liquefaction potential in regional mapping using CPT and SPT data   总被引：5，自引：0，他引：5  

Jennifer A. Lenz  Laurie G. Baise   《Soil Dynamics and Earthquake Engineering》2007,27(7):690-702

Cone penetration test (CPT) and standard penetration test (SPT) are widely used for the site specific evaluation of liquefaction potential and are getting increased use in the regional mapping of liquefaction hazard. This paper compares CPT and SPT-based liquefaction potential characterizations of regional geologic units using the liquefaction potential index (LPI) across the East Bay of the San Francisco Bay, California, USA and examines the statistical and spatial variability of LPI across and within geologic units. Overall, CPT-based LPI characterizations result in higher hazard than those derived from the SPT. This bias may result from either mis-classifications of soil type in the CPT or a bias in the CPT simplified procedure for liquefaction potential. Regional mapping based on cumulative distribution of LPI values show different results depending on which dataset is used. For both SPT and CPT-based characterizations, the geologic units in the area have broad LPI distributions that overlap between units and are not distinct from the population as a whole. Regional liquefaction classifications should therefore give a distribution, rather than a single hazard rating that does not provide for variability within the area. The CPT-based LPI values have a higher degree of spatial correlation and a lower variance over a greater distance than those estimated from SPTs. As a result, geostatistical interpolation can provide a detailed map of LPI when densely sampled CPT data are available. The statistical distribution of LPI within specific geologic units and interpolated maps of LPI can be used to understand the spatial variability of liquefaction potential.  相似文献   

Direct measurements of volume transports through Fram Strait   总被引：9，自引：1，他引：9  

Eberhard Fahrbach  Jens Meincke  Svein Østerhus  Gerd Rohardt  Ursula Schauer  Vigdis Tverberg  Jennifer Verduin 《Polar research》2001,20(2):217-224

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.  相似文献   

The Holocene paleohydrology and climatic history of the northern great sandy desert - fitzroy trough: With special reference to the history of the northwest Australian monsoon     

Karl-Heinz Wyrwoll  Jennifer Hopwood  N. L. McKenzie 《Climatic change》1992,22(1):47-65

The Holocene history of the northwest Australian monsoon is considered in the light of new stratigraphic findings from the southern margin of the monsoon regime. A discussion of the present-day climatology of northwestern Australia and synoptic controls on precipitation in the areas at the southern margin of the monsoon regime is given as background information for the interpretation of stratigraphic findings from swamp and alluvial sequences. The stratigraphic findings point to little change in the intensity of the northwest Australian monsoon since ca. 6.5 ka. A more tentative inference drawn from the field evidence is that the monsoon activity may well have been reduced in this region during the Early Holocene; during this time insolation levels were also reduced. The possible relationship of the northwest Australian monsoon to insolation levels is explored. It is clear that monsoon behavior cannot be accounted for as a simple linear response of monsoon intensity to variations in insolation. Possible controls are discussed with particular emphasis on the plausibility of changes in the damping of convective motions providing the mechanism. Gill's model of heat-induced circulation is used to provide some evidence in favour of this conjecture.  相似文献   

EVALUATION OF MODELS FOR ESTIMATION OF NET RADIATION FOR ALPINE SLOPING SURFACES          下载免费PDF全文

Huo Zonghui  W. G. Bailey 《Acta Meteorologica Sinica》1992,6(2):189-197

This paper describes and tests two models for estimating net radiation(or the radiation balance)on sloping surfacesof alpine environments.They are an empirical method based on the linear relationship between net radiation and globalsolar radiation and a flux-by-flux method involving the estimation of all the individual components of radiation budgetindependently.The results show that the empirical method is capable of predicting hourly net radiation on sloping sur-faces to within about±53 W m~(-2) under all sky conditions.During clear sky conditions,it could predict net radiation onslopes to within±58 W m~(-2) or 16% of the measured values.The flux-by-flux method,although it did not perform aswell as the empirical method,performed adequately and could give estimates of net radiation on slopes with root meansquare error of less than 74 W m~(-2)(20%)and a mean bias error of 27 W m~(-2)(7%).  相似文献