On the coupling between vegetation and the atmosphere     

Isabella M. Angelini  Michael Garstang  Robert E. Davis  Bruce Hayden  David R. Fitzjarrald  David R. Legates  Steven Greco  Stephen Macko  Vickie Connors 《Theoretical and Applied Climatology》2011,105(1-2):243-261

Recent studies suggest that vegetation can drive large-scale atmospheric circulations and substantially influence the hydrologic cycle. We present observational evidence to quantify the extent of coupling between vegetation and the overlying atmosphere. Within the context of vegetation–atmospheric interactions, we reanalyze existing climatological data from springtime leaf emergence, emissivity, dew point temperatures, and historical records of precipitation and forest coverage. We construct new rainfall transects based on a robust global climatology. Using isotopic analysis of precipitation, we find that rain in Amazonia comes primarily from large-scale weather systems coupling interior regions to the ocean and is not directly driven by local evaporation. We find that changes in vegetative cover and state influence the temperature and moisture content of the surface and atmospheric boundary layer but are not reflected in observable precipitation changes. This analysis reaffirms the view that changes in precipitation over continental reaches are a product of complex processes only partly influenced but not controlled by local water sources or vegetation.  相似文献   

Trace element partitioning in the Fe-S-C system and its implications for planetary differentiation and the thermal history of ureilites     

Leslie A. Hayden  James A. Van Orman  Cyrena A. Goodrich 《Geochimica et cosmochimica acta》2011,75(21):6570-6583

Element partitioning in metal-light element systems is important to our understanding of planetary differentiation processes. In this study, solid-metal/liquid-sulfide, liquid-metal/liquid-sulfide and solid-metal/troilite partition coefficients (D) were determined for 18 elements (Ag, As, Au, Co, Cr, Cu, Ge, Ir, Ni, Os, Pd, Pt, Mo, Mn, Re, Ru, Se and W) in the graphite-saturated Fe-S-C system at 1 atm. Compared at the same liquid S concentration, the solid/liquid partition coefficients are similar to those in the Fe-S system, but there are systematic differences that appear to be related to interactions with carbon dissolved in the solid metal. Elements previously shown to be “anthracophile” generally have larger solid/liquid partition coefficients in the Fe-S-C system, whereas those that are not have similar or smaller partition coefficients in the Fe-S-C system. The partitioning of trace elements between C-rich and S-rich liquids is, in most cases, broadly similar to the partitioning between solid metal and S-rich liquid. The highly siderophile elements Os, Re, Ir and W are partitioned strongly into the C-rich liquid, with D ? 100. The partition coefficients for Pt, Ge and W decrease significantly at the transition to liquid immiscibility, while the partition coefficient for Mo increases sharply. The bulk siderophile element patterns of ureilite meteorities appear to be better explained by separation of S-rich liquid from residual C-rich metallic liquid at temperatures above the silicate solidus, rather than by separation of S-rich liquid from residual solid metal at lower temperatures.  相似文献   

Regional 500 mb heights and U.S. 1 000-500 mb thickness prior to the radiosonde era     

P. J. Michaels  D. E. Sappington  D. E. Stooksbury  B. P. Hayden 《Theoretical and Applied Climatology》1990,42(3):149-154

Summary We developed a statistical model relating cyclone track eigenvectors over the U.S., southern Canada, and nearby oceans to a record of mean annual 500 mb heights. The length of the cyclone track record allowed us to calculate mean heights back to 1885. Use of mean annual surface pressure data allowed us to estimate the mean 1 000-500 mb thickness, which was related to mean annual temperature. This temperature calculation is unique in that it cannot suffer from urban or site bias. We find a warming of 1.5°C from the late 19th century to 1955, followed by a drop of 0.7° to 1980. By 1987, the calculated temperatures were 0.3° above the mean for 103 years of record.As an example of regional application, we examine results over the southwestern U.S.With 8 Figures  相似文献   

Geomorphological controls on coastal vegetation at the Virginia Coast Reserve     

Bruce P. Hayden  Marcio C. F. V. Santos  Guofan Shao  R. Craig Kochel 《Geomorphology》1995,13(1-4)

The establishment and succession of vegetation on migrating, low-profile barrier islands is greatly affected by the physical hydrogeomorphological processes that regulate island topography, saline and fresh groundwater table surfaces. Apart from the physical destruction of plants by overwash processes, fluctuations in water table elevations and variations in groundwater salinity, both spatially and temporally, also appear to have significant impact on the nature and distribution of vegetation on these islands. Species composition, community structure and biodiversity on the Virginia barrier islands are controlled by the same processes that give rise to landforms and maintain their form. These processes include marine water inundations, groundwater salinity variations and changes in depth to the fresh-water table. Land surface elevation, landform morphology and position on the barrier island determine exposure to high tides, storm surges, sand burial, and the extent of the fresh-water reserves.In this article, the underpinnings of a Long-term Ecological Research Program in which 25 geologists, geomorphologists, climatologists, and ecologists have a common research plan is presented and several examples of the product of this research partnership dealing with geomorphological and hydrologic controls on vegetation dynamics are detailed. Among the aspects of ecological dynamics examined in terms of geomorphological processes are vegetation zonation, succession, disturbance, and ecosystem state change.  相似文献   

Comments on Spaulding's report on overkill     

Julian D. Hayden 《Quaternary Research》1984,22(1):140-141

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A polarimetric spectral imager using acousto-optic tunable filters     

WM. Hayden Smith  K. M. Smith 《Experimental Astronomy》1990,1(5):329-343

We report laboratory and telescopic observations with a polarimetric spectral imager based on an acousto-optic tunable filter (AOTF) where we demonstrate simultaneous acquisition of orthogonally polarized images at a spectral resolving power on the order of 103 and at a Rayleigh criterion spatial resolution of 100 line pairs per mm. This matches the spatial resolution of most digital arrays. An AOTF is shown to be usable as a fast shutter with a contrast of over 10⁴ on a sub-millisecond time scale while providing an high transmittance of about 75% (both polarizations summed) when illuminated by white light. The polarization contrast between the orthogonally polarized images exceeds 10⁴ across the field of view, permitting accurate measurement of the polarization parameters of incident light. These characteristics are now being used in a program of high spatial resolution imaging in narrow spectral bands. Some peculiarities and limitations of AOTFs are indicated.This research was supported by NASA under Grant NAGW-122 and under contract with the Jet Propulsion Laboratory under NASA grant NAS 7-918.Visiting Astronomer, Mauna Kea Observatory.  相似文献   

High-resolution observations of the 6815-Å band of methane in the major planets     

Kevin H. Baines  William V. Schempp  William Hayden Smith 《Icarus》1983,56(3):534-542

High-resolution (0.1-Å) spectra of the 6815-Å band of methane are presented for Jupiter, Saturn, Uranus, and Neptune. Spectra for Uranus, Neptune, and the equatorial region of Saturn were acquired with the SPIFI (W. H. Smith, T. R. Hicks, and J. P. Born (1978). Proceedings of the 4th International Colloquium on Astrophysics, Triest, July 3–7, 1978. pp. 593–599) at the 2.2-m telescope of the Mauna Kea Observatory during May and June 1980. Additional spectra were obtained for Jupiter and the northern temperate and polar regions of Saturn in December 1980 and January 1981 from Kitt Peak National Observatory's McMath Solar Telescope. The spectra show a dichotomy in strength of methane absorption between Jupiter-Saturn and Uranus-Neptune. A simple model analysis, based on homogeneous scattering models, is unable to resolve whether this dichotomy is due to an actual increase in the methane mixing ratio with solar distance or to the temperature dependence of line strengths and absorption pathlengths in these atmospheres. If the rotational quantum number for the prominent 6818.9-Å feature is J < 4, then significant aerosol extinction must exist within the visibly accessible portion of Uranus' atmosphere for the methane mixing ratio to be greater than the solar value.  相似文献   

On the ortho-para equilibrium of H2 in the atmospheres of the Jovian planets     

William Hayden Smith 《Icarus》1978,33(1):210-216

The ratio for the equivalent widths for the unsaturated H₂ quadrupole transitions observed in the Jovian planets is calculated and compared with a large number of observations. The comparison indicates that equilibrium hydrogen may be present in Jupiter and Saturn, while Uranus and Nepture exhibit ratios not in accord with equilibrium hydrogen. Observations which can differentiate among the possible states of H₂ are proposed.  相似文献   

Doing community supported agriculture: Tactile space,affect and effects of membership     

Jennifer Hayden  Daniel Buck 《Geoforum》2012,43(2):332-341

Community supported agriculture (CSA) is a direct-marketing food network that has the potential to decommmodify food and support farmers while providing consumers with sustainably raised, seasonal, local food. Through an ethnographic exploration of one CSA, we describe the processes, practices, affect and effects of consumer membership within the context of non-representational theory. Carolan (2007) suggests that when non-representational ways of knowing are fostered through long-term embodied involvement in “tactile space,” “deep commitments” to the environment and others are encouraged. This study augments understandings of tactile space. Findings show that members engage in the tactile spaces of CSA (e.g. attending distribution, cooking more), but with varied effects: leading one member to voice compassion for the farmer which “is something you don’t feel in a supermarket” while another admits feeling “like I’ve been conned.” In spite of mixed experiences and affects, on balance we conclude that CSA membership does affect environmental ethics.  相似文献   

A Wind-Tunnel Artificially-Thickened Simulated Weakly Unstable Atmospheric Boundary Layer     

P. E. Hancock  S. Zhang  P. Hayden 《Boundary-Layer Meteorology》2013,149(3):355-380

A wind-tunnel simulation of an atmospheric boundary layer, artificially thickened as is often used in neutral flow wind-loading studies, has been investigated for weakly unstable stratification, including the effect of an overlying inversion. Rather than using a uniform inlet temperature profile, the inlet profile was adjusted iteratively by using measured downstream profiles. It was found that three cycles are sufficient for there to be no significant further change in profiles of temperature and other quantities. Development to nearly horizontally-homogeneous flow took a longer distance than in the neutral case because the simulated layer was deeper and therefore the length scales larger. Comparisons show first-order and second-order moments quantities are substantially larger than given by ‘standard forms’ in the mixed layer but are close in the surface layer. Modified functions, obtained by matching one to the other, are suggested that amount to an interpolation in the mixed layer between the strongly unstable and the weakly unstable cases.  相似文献