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31.
We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have used ring-diagram analysis to analyze Dopplergrams obtained with the Michelson Doppler Imager (MDI) Dynamics Program, the Global Oscillation Network Group (GONG), and the Helioseismic and Magnetic Imager (HMI) instrument. We combined the zonal and meridional flows from the three data sources and scaled the flows derived from MDI and GONG to match those from HMI observations. In this way, we derived their temporal variation in a consistent manner for Solar Cycles 23 and 24. We have corrected the measured flows for systematic effects that vary with disk positions. Using time-depth slices of the corrected subsurface flows, we derived the amplitudes and times of the extrema of the fast and slow zonal and meridional flows during Cycles 23 and 24 at every depth and latitude. We find an average difference between maximum and minimum amplitudes of \(8.6 \pm0.4~\mbox{m}\,\mbox{s}^{-1}\) for the zonal flows and \(7.9 \pm0.3~\mbox{m}\,\mbox{s}^{-1}\) for the meridional flows associated with Cycle 24 averaged over a depth range from 2 to 12 Mm. The corresponding values derived from GONG data alone are \(10.5 \pm0.3~\mbox{m}\,\mbox{s}^{-1}\) for the zonal and \(10.8 \pm0.3~\mbox{m}\,\mbox{s}^{-1}\) for the meridional flow. For Cycle 24, the flow patterns are precursors of the magnetic activity. The timing difference between the occurrence of the flow pattern and the magnetic one increases almost linearly with increasing latitude. For example, the fast zonal and meridional flow appear \(2.1 \pm 0.6\) years and \(2.5\pm 0.6\) years, respectively, before the magnetic pattern at \(30^{\circ}\) latitude in the northern hemisphere, while in the southern hemisphere, the differences are \(3.2 \pm 1.2\) years and \(2.6 \pm 0.6\) years. The flow patterns of Cycle 25 are present and have reached \(30^{\circ}\) latitude. The amplitude differences of Cycle 25 are about 22% smaller than those of Cycle 24, but are comparable to those of Cycle 23. Moreover, polynomial fits of meridional flows suggest that equatorward meridional flows (counter-cells) might exist at about \(80^{\circ}\) latitude except during the declining phase of the solar cycle. 相似文献
32.
For a number of social and cultural reasons, labor force participation rates of Australian women are low. One reason not previously investigated is the problem of geographic accessibility to employment, especially for suburban women. Results from journey-to-work studies show that females either work locally or in the central-city area, whereas males travel to more dispersed locations. Further investigation of female travel patterns from each of fifty-five suburban local government areas shows that the socioeconomic status of an area, together with its job mix, explains much variety in female work travel and suggests that workforce participation rates depend in part on local job availability. The research contributes to an understanding of the nature of occupational and geographical disaggregation of the Melbourne metropolitan labor market. 相似文献
33.
Remediation of U-contaminated sites relies upon thermodynamic speciation calculations to predict U(VI) movement in the subsurface. However, reliability and applicability of geochemical speciation and reactive transport models may be limited by determinate (model) errors and random (uncertainty) errors in the equilibrium speciation calculations. This study examines propagated uncertainty in two types of subsurface calculations: I. Dissolved U(VI) speciation based on measured analytical constraints and solution phase equilibria and II. Overall U(VI) speciation which combined the dissolved phase equilibria with previously published adsorption reactions. Three levels of uncertainty, instrumental uncertainty, temporal variation and spatial variation across a site, were investigated using first-derivative sensitivity calculations and Monte Carlo simulations. Dissolved speciation calculations were robust, with minimal amplification of uncertainty and normal output distributions. The most critical analytical constraints in the dissolved system are pH, DIC, total U and total Ca, with some effect from dissolved . When considering adsorption equilibria, calculations were robust with respect to adsorbed U(VI) concentration prediction, but bimodal distributions of dissolved U(VI) concentrations were observed in simulations with background levels of total U(VI) and higher (spatial and temporal variability) estimates of input uncertainty. Consequently, sorption model predictions of dissolved U(VI) may not be robust with respect these higher levels of uncertainty. 相似文献
34.
Isotopic Determination of Food Web Origins in Restoring and Ancient Estuarine Wetlands of the San Francisco Bay and Delta 总被引:1,自引:0,他引:1
We compared the extent to which ancient and restoring wetlands in three estuary regions of San Francisco Bay support estuarine
ecosystems through food web contributions. In comparison to mature marshes, we hypothesized that food webs of increasingly
younger restoration sites would display increased dependency upon allochthonous subsidies due to nominal internal production.
Using multiple stable isotopes (δ13C, δ15N, δ34S) in a mixing model, we traced links among primary producers and estuarine consumers. Results indicate that food webs of
estuarine marshes are heavily dependent upon autochthonous marsh materials (76 ± 17%), even within the youngest restoration
marshes (11 years). Nearly all sampled organisms relied upon autochthonous marsh materials, with the exception of Neomysis kadiakensis, a mysid shrimp, which derived the majority of its support from freshwater-produced phytoplankton. Marsh-derived organic
matter (OM) support was consistent both temporally throughout the year and spatially along the three estuary regions, but
evidence suggests that the specific type of OM supporting estuarine consumers depends on position along the estuarine gradient
and on seasonal shifts in freshwater flow. These results indicate that wetland restoration rapidly provides important contributions
to marsh consumers and potentially bolsters food web linkages in shallow-water ecosystems. 相似文献
35.
R.A. GarcÍa T. Corbard W.J. Chaplin S. Couvidat A. Eff-Darwich S.J. Jiménez-Reyes S.G. Korzennik J. Ballot P. Boumier E. Fossat C.J. Henney R. Howe M. Lazrek J. Lochard P.L. Pallé S. Turck-Chièze 《Solar physics》2004,220(2):269-285
In the modern era of helioseismology we have a wealth of high-quality data available, e.g., more than 6 years of data collected
by the various instruments on board the SOHO mission, and an even more extensive ground-based set of observations covering
a full solar cycle. Thanks to this effort a detailed picture of the internal rotation of the Sun has been constructed. In
this paper we present some of the actions that should be done to improve our knowledge of the inner rotation profile discussed
during the workshop organized at Saclay on June 2003 on this topic. In particular we will concentrate on the extraction of
the rotational frequency splittings of low- and medium-degree modes and their influence on the rotation of deeper layers.
Furthermore, for the first time a full set of individual |m|-component rotational splittings is computed for modes ℓ≤4 and 1<ν<2 mHz, opening new studies on the latitudinal dependence
of the rotation rate in the radiative interior. It will also be shown that these splittings have the footprints of the differential
rotation of the convective zone which can be extremely useful to study the differential rotation of other stars where only
these low-degree modes will be available. 相似文献
36.
When properly calibrated, Holocene pollen data provide an important source of quantitative information about Holocene climates. Multiple linear regression of modern climate and pollen data allows the development of statistical calibration functions that transform percentages of certain pollen types into quantitative estimates of climatic variables, and these functions, when applied to Holocene pollen data, yield estimates of climatic variables for past times. Confidence intervals for the climatic variables provide estimates of the statistical errors. These interval estimates are based upon the following statistical assumptions: (1) the regression model is appropriate; (2) the errors in measuring the climate variables are independent, normally distributed and have constant variance; and (3) no outliers are present. We outline the steps to be followed in calculating calibration functions, including (1) selecting the calibration region; (2) selecting a pollen sum; (3) analyzing scatter diagrams of a given climate variable against each pollen type; (4) deleting outliers and transforming pollen data; (5) performing the regression; and (6) testing the appropriateness of the statistical assumptions. We used available computer programs for most of this study. In addition, we developed new software to compute the Moran statistic to test for spatial autocorrelation among the regression residuals, using the dual of the Voronoi diagram to describe the spatial relationships among the sites. In order to illustrate the sequence of procedures, we used data from the lower peninsula of Michigan to develop a calibration function for July mean temperature and then used Holocene pollen data from central lower Michigan to estimate past temperatures. 相似文献
37.
C. S. Baldner S. Basu R. S. Bogart O. Burtseva I. González Hernández D. Haber F. Hill R. Howe K. Jain R. W. Komm M. C. Rabello-Soares S. Tripathy 《Solar physics》2013,287(1-2):57-69
Ring-diagram analysis is a helioseismic tool useful for studying the near-surface layers of the Sun. It has been employed to study near-surface shear, meridional circulation, flows around sunspots, and thermal structure beneath active regions. We review recent results obtained using ring-diagram analysis, state some of the more important outstanding difficulties in the technique, and point out several extensions to the technique that are just now beginning to bear fruit. 相似文献
38.
We study the temporal variation of subsurface flows of 828 active regions and 977 quiet regions. The horizontal flows cover
a range of depths from the surface to about 16 Mm and are determined by analyzing Global Oscillation Network Group high-resolution Doppler data with ring-diagram analyses. The vertical velocity component is derived from the divergence of
the measured horizontal flows using mass conservation. For comparison, we analyze Michelson Doppler Imager (MDI) Dynamics Run data covering 68 active regions common to both data sets. We determine the change in unsigned magnetic
flux during the disk passage of each active region using MDI magnetograms binned to the ring-diagram grid. We then sort the
data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. We find that
emerging flux has a faster rotation than the ambient fluid and pushes it up, as indicated by enhanced vertical velocity and
faster-than-average zonal flow. After active regions are formed, downflows are established within two days of emergence in
shallow layers between about 4 and 10 Mm. Emerging flux in existing active regions shows a similar scenario, where the upflows
at depths greater than about 10 Mm are enhanced and the already established downflows at shallower depths are weakened. When
active regions decay, the corresponding flow pattern disappears as well; the zonal flow slows down to values comparable to
that of quiet regions and the upflows become weaker at deeper layers. The residual meridional velocity is mainly poleward
and shows no obvious variation. The magnitude of the residual velocity, defined as the sum of the squares of the residual
velocity components, increases with increasing magnetic flux and decreases with decreasing flux. 相似文献
39.
Lunar X-ray fluorescence observations by the Chandrayaan-1 X-ray Spectrometer (C1XS): Results from the nearside southern highlands 总被引:1,自引:0,他引:1
S. Narendranath P.S. Athiray B.J. Kellett C.J. Howe M. Grande I.A. Crawford S. Lalita S.Z. Weider L.R. Nittler D. Rothery N. Bhandari M.A. Wieczorek the CXS team 《Icarus》2011,214(1):53-66
The Chandrayaan-1 X-ray Spectrometer (C1XS) flown on-board the first Indian lunar mission Chandrayaan-1, measured X-ray fluorescence spectra during several episodes of solar flares during its operational period of ∼9 months. The accompanying X-ray Solar Monitor (XSM) provided simultaneous spectra of solar X-rays incident on the Moon which are essential to derive elemental chemistry. In this paper, we present the surface abundances of Mg, Al, Si, Ca and Fe, derived from C1XS data for a highland region on the southern nearside of the Moon. Analysis techniques are described in detail including absolute X-ray line flux derivation and conversion into elemental abundance. The results are consistent with a composition rich in plagioclase with a slight mafic mineral enhancement and a Ca/Al ratio that is significantly lower than measured in lunar returned samples. We suggest various possible scenarios to explain the deviations. 相似文献
40.
S.Z. Weider B.J. Kellett B.M. Swinyard I.A. Crawford K.H. Joy M. Grande C.J. Howe J. Huovelin S. Narendranath L. Alha M. Anand P.S. Athiray N. Bhandari J.A. Carter A.C. Cook L.C. d'Uston V.A. Fernandes O. Gasnault M. Wieczorek 《Planetary and Space Science》2012,60(1):217-228
We present X-ray fluorescence observations of the lunar surface, made by the Chandrayaan-1 X-ray Spectrometer during two solar flare events early in the mission (12th December 2008 and 10th January 2009). Modelling of the X-ray spectra with an abundance algorithm allows quantitative estimates of the MgO/SiO2 and Al2O3/SiO2 ratios to be made for the two regions, which are in mainly basaltic areas of the lunar nearside. One of these ground tracks includes the Apollo 14 landing site on the Fra Mauro Formation. Within the 1σ errors provided, the results are inside the range of basaltic samples from the Apollo and Luna collections. The Apollo 14 soil composition is in agreement with the results from the January flare at the 1σ uncertainty level. Discrepancies are observed between our results and compositions derived for the same areas by the Lunar Prospector gamma-ray spectrometer; some possible reasons for this are discussed. 相似文献