The relation between productivity and temperature in the Pliocene North Atlantic at the onset of northern hemisphere glaciation: a palynological study     

Gerard J.M. Versteegh  Henk Brinkhuis  Henk Visscher  Karin A.F. Zonneveld 《Global and Planetary Change》1996,11(4):155-165

High resolution palynological analysis of DSDP Cores 607/607A shows for the interval between 2.8 and 2.2 Ma B.P. (which includes the onset of major northern hemisphere glaciations) a 41 ka cyclicity characterised by much higher palynomorph concentrations for the cooler intervals than for the warmer ones. Variation in dilution and concentration of palynomorphs can neither be explained by differential input of terrigenous clastics or carbonate, nor by differences in sedimentation rate, sediment density or selective preservation of palynomorphs. Subdivision of the palynomorph record in terms of autochthonous and allochthonous components, provides a way to detect changes in open ocean productivity and transport through time. It seems that a negative correlation between productivity and temperature in the latest Pleistocene open Atlantic had already been established before the major onset of northern hemisphere glaciations. A conceptual model is proposed to explain the observed lead of the palynological record relative to the isotope and carbonate records is proposed. This early response can result from changes in North Atlantic surface ocean circulation induced by changing atmospheric circulation.  相似文献   

Solar-Cycle Variation of Subsurface Meridional Flow Derived with Ring-Diagram Analysis     

R. Komm  I. González Hernández  R. Howe  F. Hill 《Solar physics》2015,290(11):3113-3136

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Solar-Cycle Variation of Subsurface Zonal Flow     

R. Komm  R. Howe  I. González Hernández  F. Hill 《Solar physics》2014,289(9):3435-3455

We study the solar-cycle variation of the zonal flow in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm covering the period from mid-2001 to mid-2013 or from the maximum of Cycle 23 through the rising phase of Cycle 24. We have analyzed Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams with a ring-diagram analysis. The zonal flow varies with the solar cycle showing bands of faster-than-average flows equatorward of the mean latitude of activity and slower-than-average flows on the poleward side. The fast band of the zonal flow and the magnetic activity appear first in the northern hemisphere during the beginning of Cycle 24. The bands of fast zonal flow appear at mid-latitudes about three years in the southern and four years in the northern hemisphere before magnetic activity of Cycle 24 is present. This implies that the flow pattern is a direct precursor of magnetic activity. The solar-cycle variation of the zonal flow also has a poleward branch, which is visible as bands of faster-than-average zonal flow near 50° latitude. This band appears first in the southern hemisphere during the rising phase of the Cycle 24 and migrates slowly poleward. These results are in good agreement with corresponding results from global helioseismology.  相似文献   

A Full-Sun Magnetic Index from Helioseismology Inferences     

I. González Hernández  M. Díaz Alfaro  K. Jain  W. K. Tobiska  D. C. Braun  F. Hill  F. Pérez Hernández 《Solar physics》2014,289(2):503-514

Solar magnetic indices are used to model the solar irradiance and ultimately to forecast it. However, the observation of such indices is generally limited to the Earth-facing hemisphere of the Sun. Seismic maps of the far side of the Sun have proven their capability to locate and track medium–large active regions at the non-visible hemisphere. We present here the possibility of using the average signal from these seismic far-side maps, combined with similarly calculated near-side maps, as a proxy to the full-Sun magnetic activity.  相似文献   

A CH₃CN and HCO⁺ survey towards southern methanol masers associated with star formation     

C. R. Purcell  R. Balasubramanyam  M. G. Burton  A. J. Walsh  V. Minier  M. R. Hunt-Cunningham  L. L. Kedziora-Chudczer  S. N. Longmore  T. Hill  I. Bains  P. J. Barnes  A. L. Busfield  P. Calisse  N. H. M. Crighton  S. J. Curran  T. M. Davis  J. T. Dempsey  G. Derragopian  B. Fulton  M. G. Hidas  M. G. Hoare  J.-K. Lee  E. F. Ladd  S. L. Lumsden  T. J. T. Moore  M. T. Murphy  R. D. Oudmaijer  M. B. Pracy  J. Rathborne  S. Robertson  A. S. B. Schultz  J. Shobbrook  P. A. Sparks  J. Storey  T. Travouillion 《Monthly notices of the Royal Astronomical Society》2006,367(2):553-576

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A photometrically and kinematically distinct core in the Sextans dwarf spheroidal galaxy     

Jan T. Kleyna  Mark I. Wilkinson  N. Wyn Evans  Gerard Gilmore 《Monthly notices of the Royal Astronomical Society》2004,354(4):L66-L72

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Sputtering and high altitude meteors     

K. A. Hill  L. A. Rogers  R. L. Hawkes 《Earth, Moon, and Planets》2004,95(1-4):403-412

Conventional ablation theory assumes that a meteoroid undergoes intensive heating during atmospheric flight and surface atoms are liberated through thermal processes. Our research has indicated that physical sputtering could play a significant role in meteoroid mass loss. Using a 4th order Runge-Kutta numerical integration technique, we tabulated the mass loss due to the two ablation mechanisms and computed the fraction of total mass lost due to sputtering. We modeled cometary structure meteoroids with masses ranging from 10⁻¹³ to 10⁻³ kg and velocities ranging from 11.2 to 71 km s⁻¹. Our results indicate that a significant fraction of the mass loss for small, fast meteors is due to sputtering, particularly in the early portion of the light curve. In the past 6 years evidence has emerged for meteor luminosity at heights greater than can be explained by conventional ablation theory. We have applied our sputtering model and find excellent agreement with these observations, and therefore suggest that sputtered material accounts for the new type of radiation found at great heights.  相似文献   

The isolated non-circular ringlets of Saturn     

Jay Roderick Hill  D. A. Mendis 《Earth, Moon, and Planets》1982,26(2):217-226

We show that the combined effect of electrodynamic and gravitational forces can account for a number of features observed by Voyagers 1 and 2 in the isolated fine dust rings of Saturn. These include (a) the appearance and disappearnce of the braids in the F-ring, (b) the eccentricities of the F-ring and the ringlets within the Encke and Cassine divisions and a gap in the C-ring, and (c) the kinks in the eccentric Encke ring. They may also account for the very existence of these rings.  相似文献   

REPLY     

A. David Hill 《The Professional geographer》1982,34(1):92-92

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On the braids and spokes in Saturn's ring system     

Jay Roderick Hill  D. A. Mendis 《Earth, Moon, and Planets》1981,24(4):431-436

Two of the features in the Saturnian ring system recently observed by the Voyager 1 spacecraft are (a) the braiding of theF-ring and (b) the radial spokes that rotate across theB-ring. Both of these phenomena are explained by recognizing that the grains that constitute both theF-ring and the spokes are charged to high electrostatic potentials and are sufficiently small to be strongly affected by the magnetic field of the planet. Processes for the charging of the grains are also suggested.  相似文献