Evolution of cool skin and direct air-sea gas transfer coefficient during daytime     

Alexander V. Soloviev  Peter Schlüssel 《Boundary-Layer Meteorology》1996,77(1):45-68

Absorption of solar radiation within the thermal molecular sublayer of the ocean can modify the temperature difference across the cool skin as well as the air-sea gas transfer. Our model of renewal type is based on the assumption that the thermal and diffusive molecular sublayers below the ocean surface undergo cyclic growth and destruction, the heat and gas transfer between the successive burst events are performed by molecular diffusion. The model has been upgraded to include heating due to solar radiation. The renewal time is parameterized as a function of the surface Richardson number and the Keulegan number. A Rayleigh number criterion characterizes the convective instability of the cool skin under solar heating. Under low wind speed conditions, the solar heating can damp the convective instability, strongly increasing the renewal time and correspondingly decreasing the interfacial gas exchange. In the ocean, an additional convective instability caused by salinity flux due to evaporation becomes of importance in such cases. The new parameterization is compared with the cool skin data obtained in the western equatorial Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment in February 1993. In combination with a model of the diurnal thermocline it describes main features of the field data both in nighttime and daytime. Under low wind speed conditions (< 5 m s^-1) diurnal variations of the sea surface temperature due to the formation of a diurnal thermocline were substantially larger than those across the cool skin. Under wind speeds > 5 m s^-1, diurnal variations of the surface temperature due to the variations of the thermal molecular sublayer become more important.  相似文献   

On AGV's navigation in 3-dimensional space     

Jürgen Kusche 《Journal of Geodesy》1996,70(4):183-187

This paper deals with position estimation and path control for Autonomous Guided Vehicles (AGV). To enable a vehicle or a mobile robot in following a continuous virtual path without human control, these techniques play an important role. The relationship between the vehicle's motion in 3-dimensional space and the shape of a curved surface is described. In particular, the introduction of a digital terrain model in dead reckoning is considered. Moreover, a possible nonlinear control is developed based on curvilinear path coordinates, and the proof for global stability is given. To achieve general validity, these topics are treated here independently of the cart's special mechanization (the configuration of steered wheels and driven wheels). Simulation studies are presented to illustrate the investigations.  相似文献   

Multiple outlier detection by evaluating redundancy contributions of observations   总被引：3，自引：0，他引：3  

X. Ding  R. Coleman 《Journal of Geodesy》1996,70(8):489-498

When applying single outlier detection techniques, such as the Tau () test, to examine the residuals of observations for outliers, the number of detected observations in any iteration of adjustment is most often more numerous than the actual number of true outliers. A new technique is proposed which estimates the number of outliers in a network by evaluating the redundancy contributions of the detected observations. In this way, a number of potential outliers can be identified and eliminated in each iteration of an adjustment. This leads to higher efficiency in data snooping of geodetic networks. The technique is illustrated with some numerical examples.  相似文献   

Megamaser galaxies     

R. A. Kandalian 《Astrophysics》1996,39(3):237-244

An analysis of a sample of OH megamaser galaxies is presented. It is shown that the dependence of L_OH on L_FIR (far infrared) is not quadratic, as previously assumed, but closer to linear. In megamaser galaxies, L_C (radio continuum) L_FIR1. Analysis of the data also shows that as the OH emission line width decreases, the absolute values of the pumping efficiency and maser amplification coefficient increase. The radio luminosity of the central component in these galaxies increases with a decrease in the ratio L_FIR/L_C, whereas the FIR luminosity remains constant. These results will, in all probability, force a reexamination of the questions of pumping and maser emission mechanisms in megamaser galaxies.Translated fromAstrofizika, Vol. 39, No. 3, pp. 417–429, July–September, 1996.  相似文献   

The Taconite Inlet Lakes Project: a systems approach to paleoclimatic reconstruction     

R. S. Bradley  M. J. Retelle  S. D. Ludlam  D. R. Hardy  B. Zolitschka  S. F. Lamoureux  M. S. V. Douglas 《Journal of Paleolimnology》1996,16(2):97-110

A comprehensive study of meteorological, hydrological, limnological and sedimentological conditions in the watersheds of density-stratified (meromictic) lakes around Taconite Inlet, Northern Ellesmere Island, N.W.T., Canada was carried out from 1990–1992. Lakes C1 and C2 contain seawater trapped by isostatic uplift as the former embayments became isolated from the sea. These lakes, and Lake C3, contain varved sediments which provide an annually resolvable paleoclimatic record. By studing the major systems influencing sedimentation in one of these lakes (Lake C2) a better understanding of the climatic controls on varve formation, and hence on the paleoclimatic signal in the varved sediment record, was obtained. The varves of Lake C2 provide a proxy record of summer temperature for the region.This is the first in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

Emigration,return, immigration: a review and evaluation of Greece's postwar experience of international migration     

Fakiolas R  King R 《International journal of population geography : IJPG》1996,2(2):171-190

"This paper offers a review and evaluation of the Greek experience of international migration.... The analysis is based partly on available published data, and partly on qualitative appraisals. Three major international migration phases are analysed--emigration, return migration and immigration--and the main socio-economic and cultural effects of these migration trends are discussed. The paper pays particular attention to the recent mass immigration movements, noting their heterogeneity...and describing their impact on the Greek labour market. The article concludes with some comments on the difficulties of formulating a Greek migration policy in the light of the country's location, open borders and internationalized economy."  相似文献   

Imaging coronal emission lines under high sky-background conditions     

C. U. Keller  R. N. Smartt 《Solar physics》1996,166(2):311-315

We have obtained images in solar coronal emission lines under high sky-background conditions by making precise differential measurements between the coronal emission line and the near-by continuum, which is primarily due to scattered light from the solar disk. Chopping between the two wavelengths was performed at 100 kHz to avoid artifacts from fast-flying dust particles and other aerosols, and also from seeing effects. The differential signal was detected with a novel CCD camera that demodulates signals up to 100 kHz. These preliminary observations show coronal emission at the 0.2% level of the scattered-light background and pave the way to efficient and precise imaging of coronal emission features under less than ideal coronal-sky conditions.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.  相似文献   

The effects of solar and ionospheric parameters on seasonal variation of 6300 Å line emission at Calcutta     

S. K. Midya  R. Chattopadhyay 《Earth, Moon, and Planets》1996,74(2):123-129

The purpose of this paper is to find correlation between OI 6300 Å line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained:

(i)	Solar flare index plays more important role for the emissions of 6300 Å line than other solar parameters.
(ii)	Intensity of 6300 Å line increases linearly with the increase of solar flare index.
(iii)	Virtual height plays more important role than critical frequency for the emission of 6300 Å line-intensity.
(iv)	Possible explanation of this type of variation is also presented.

  相似文献   

Sediment oxygen profiles in a super-oxygenated antarctic lake     

Wharton RA  Meyer MA  McKay CP  Mancinelli RL  Simmons GM 《Limnology and oceanography》1994,39(4):839-853

Perennially ice-covered lakes are found in the McMurdo Dry Valleys of southern Victoria Land, Antarctica. In contrast to temperate lakes that have diurnal photic periods, antarctic (and arctic) lakes have a yearly photic period. An unusual feature of the antarctic lakes is the occurrence of O2 at supersaturated levels in certain portions of the water column. Here we report the first sediment O2 profiles obtained using a microelectrode from a perennially ice-covered antarctic lake. Sediment cores collected in January and October 1987 from Lake Hoare in Taylor Valley show oxygenation down to 15, and in some cases, 25 cm. The oxygenation of sediments several centimeters below the sediment-water interface is atypical for lake sediments and may be characteristic of perennially ice-covered lakes. There is a significant difference between the observed January and October sediment O2 profiles. Several explanations may account for the difference, including seasonality. A time-dependent model is presented which tests the feasibility of a seasonal cycle resulting from the long photoperiod and benthic primary production in sediments overlain by a highly oxygenated water column.  相似文献   

A rural “eye” in the Capital: Tuti Island,Khartoum, Sudan     

H. R. J. Davies 《GeoJournal》1994,33(4):387-392

Islands at strategic points have often become the core of a modern city, or have been developed as historic heritage sites. This has been especially true when the settlers have been strangers in the land. This paper examines why such a situation has not occurred with Tuti Island at the confluence of the White and Blue Niles in the centre of Sudan's Three Towns capital, even though the first permanent inhabitants at the confluence were strangers and chose Tuti Island for their first settlement. The paper questions whether Tuti can survive as a green eye in its present form with the increasing pressures from the urban areas surrounding it.  相似文献