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Gengsheng Zhang Monique Y. Leclerc Anandakumar Karipot Henrique F. Duarte Erich Mursch-Radlgruber Henry L. Gholz 《Theoretical and Applied Climatology》2011,106(3-4):511-521
The influence of a freshly logged area in a managed pine forest on the flow field is investigated by comparing sodar wind profile data over the forest canopy with the synoptic wind field extracted from North American Regional Reanalysis, National Centers for Environmental Prediction. As a consequence of the pressure gradient arising from the sharp temperature difference between the clearcut and the surrounding uncut forests, the local wind direction over the forest measured with the sodar departs dramatically from the prevailing synoptic wind direction when the latter is transverse to the clearcut-sodar direction. Sodar measurements also indicate systematic strong updrafts during daytime followed by nighttime downdrafts with wind coming from the logged area. This suggests the presence of horizontal advection carrying daytime warm air (or nighttime cool air) from the clearcut to the forested area. This paper also examines the influence of wind velocity, clearcut fetch, and solar radiation on locally generated circulations and advection. The presence of local circulations arising from contrasting neighboring surface characteristics well outside the footprint is of particular relevance for atmospheric flux sites where robust surface?Catmosphere exchange values are sought. This study highlights the high level of circumspection required at the time of identifying locations for flux sites. It also suggests vigilant monitoring of the surrounding landscape during eddy?Cflux measurements particularly in actively managed landscapes. 相似文献
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Louis M. Barbier Robert Smith Scott Murphy Eric R. Christian Rodger Farley John F. Krizmanic John W. Mitchell Robert E. Streitmatter Eugene C. Loh Stephen Stochaj 《Astroparticle Physics》2005,22(5-6):439-449
We have designed and built an instrument to measure and monitor the “nightglow” of the Earth’s atmosphere in the near ultraviolet (NUV). In this paper we describe the design of this instrument, called NIGHTGLOW. NIGHTGLOW is designed to be flown from a high altitude research balloon, and circumnavigate the globe. NIGHTGLOW is a NASA, University of Utah, and New Mexico State University project. A test flight took place from Palestine, Texas on July 5, 2000, lasting about 8 h. The instrument performed well and landed safely in Stiles, Texas with little damage. The resulting measurements of the NUV nightglow are compared with previous measurements from sounding rockets and balloons. 相似文献
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G. Cayrel de Strobel Y. Lebreton C. Soubiran E.D. Friel 《Astrophysics and Space Science》1999,265(1-4):345-352
The authors of this paper try to disentangle the many problems arisen from a new enlarged sample of nearby low-mass,metal-rich-stars.
These stars have reliable absolute magnitudes, deduced from Hipparcos parallaxes, precise bolometric corrections, effective
temperatures and metal abundances from high resolution detailed spectroscopic analyses. Their ages have been derived from
a grid of isochrones calculated with up to date physics. The main goal of this paper is to determine the ages of the slightly
evolved SMR stars. Among those with well determinated ages about 80% of them have intermediate ages of (2 to 5 Gyr), but only
20% have ages of 8 Gyr or more. Nevertheless, the existence of very old metal-rich stars is confirmed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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T.?P.?WagnerEmail author C.?O.?McKee J.?Kuduon R.?Kombua 《International Journal of Earth Sciences》2003,92(3):405-406
The south crater wall of a Quaternary tephra cone in the Highlands of Papua New Guinea collapsed on 20 April 1999 and sent a 150,000-m 3 landslide into its lake. Displacing 5–10% of the lake's volume, the landslide induced a 15-m-high wave which flattened vegetation throughout the crater interior, and broke over a low saddle in the crater's east rim where it destroyed two houses and injured 11 people, killing one. 相似文献
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RodrIguez Carolina; Selles Daniel; Dungan Michael; Langmuir Charles; Leeman William 《Journal of Petrology》2007,48(11):2033-2061
The mid-Holocene eruptive products of Nevado de Longavívolcano (36·2°S, Chile) are the only reported occurrenceof adakitic volcanic rocks in the Quaternary Andean SouthernVolcanic Zone (33–46°S). Dacites of this volcano arechemically distinct from other evolved magmas of the regionin that they have high La/Yb (15–20) and Sr/Y (60–90)ratios and systematically lower incompatible element contents.An origin by partial melting of high-pressure crustal sourcesseems unlikely from isotopic and trace element considerations.Mafic enclaves quenched into one of the dacites, on the otherhand, constitute plausible parental magmas. Dacites and maficenclaves share several characteristics such as mineral chemistry,whole-rock isotope and trace element ratios, highly oxidizingconditions (NNO + 1·5 to >NNO + 2, where NNO is thenickel–nickel oxide buffer), and elevated boron contents.A two-stage mass-balance crystal fractionation model that matchesboth major and trace elements is proposed to explain magmaticevolution from the least evolved mafic enclave to the dacites.Amphibole is the main ferromagnesian phase in both stages ofthis model, in agreement with the mineralogy of the magmas.We also describe cumulate-textured xenoliths that correspondvery closely to the solid assemblages predicted by the model.We conclude that Nevado de Longaví adakitic dacites arethe products of polybaric fractional crystallization from exceptionallywater-rich parent magmas. These basaltic magmas are inferredto be related to an exceptionally high, but transient inputof slab-derived fluids released from serpentinite bodies hostedin the oceanic Mocha Fracture Zone, which projects beneath Nevadode Longaví. Fractional crystallization that is modallydominated by amphibole, with very minor garnet extraction, isa mechanism for generating adakitic magmas in cold subductionzones where a high flux of slab-derived fluids is present. KEY WORDS: adakite; amphibole; Andes; differentiation; Southern Volcanic Zone 相似文献
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《Journal of Atmospheric and Solar》2002,64(16):1745-1754
The ionosphere often becomes turbulent and develops electron density irregularities. These irregularities scatter radio waves to cause amplitude and phase scintillation and affect satellite communication and GPS navigation systems. The effects are most intense in the equatorial region, moderate at high latitudes and minimum at middle latitudes. The thermosphere and the ionosphere seem to internally control the generation of irregularities in the equatorial region and its forcing by solar transients is an additional modulating factor. On the other hand, the irregularity generation mechanisms in the high-latitude ionosphere seem to be driven by magnetospheric processes and, therefore, high-latitude scintillations can be tracked by following the trail of energy from the sun in the form of solar flares and coronal mass ejections. The development of a global specification and forecast system for scintillation is needed in view of our increased reliance on space-based communication and navigation systems, which are vulnerable to ionospheric scintillation. Such scintillation specification systems are being developed for the equatorial region. An equatorial satellite equipped with an appropriate suite of sensors, capable of detecting ionospheric irregularities and tracking the drivers that control the formation of ionospheric irregularities, has also been planned for the purpose of specifying and forecasting equatorial scintillations. In the polar region, scintillation specification and forecast systems are yet to emerge although modeling and observations of polar cap plasma structures, their convection and associated irregularities have advanced greatly in recent years. Global scintillation observations made during the S-RAMP Space Weather Month in September 1999 are currently being analyzed to study the effects of magnetic storms on communication and navigation systems. 相似文献
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A generalized frontogenesis function and its application 总被引：3，自引：0，他引：3
With the definition of generalized potential temperature, a new generalized frontogenesis function, which is expressed as the Lagrangian change rate of the magnitude of the horizontal generalized potential temperature gradient, is derived. Such a frontogenesis function is more appropriate for a real moist atmosphere because it can reflect frontogenesis processes, in which the atmosphere in a frontal zone is typically characterized by neither completely dry nor uniform saturation. Furthermore, by derivation, the expression of generalized frontogenesis function includes both temperature and humidity gradients, which is different from and superior to the traditional frontogenesis function in moist processes, which also uses equivalent potential temperature. Diagnostic studies of real cases are performed and show that the generalized frontogenesis function in non- uniformly saturated moist atmosphere indeed provides a useful tool for frontogenesis, compared to using the traditional frontogenesis function. The new frontogenesis function can be used in situations involving either a strong temperature or moisture gradient and is closely correlated with precipitation. 相似文献