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The Landscape Reconstruction Algorithm (LRA) overcomes some of the fundamental problems in pollen analysis for quantitative reconstruction of vegetation. LRA first uses the REVEALS model to estimate regional vegetation using pollen data from large sites and then the LOVE model to estimate vegetation composition within the relevant source area of pollen (RSAP) at small sites by subtracting the background pollen estimated from the regional vegetation composition. This study tests LRA using training data from forest hollows in northern Michigan (35 sites) and northwestern Wisconsin (43 sites). In northern Michigan, surface pollen from 152-ha and 332-ha lakes is used for REVEALS. Because of the lack of pollen data from large lakes in northwestern Wisconsin, we use pollen from 21 hollows randomly selected from the 43 sites for REVEALS. RSAP indirectly estimated by LRA is comparable to the expected value in each region. A regression analysis and permutation test validate that the LRA-based vegetation reconstruction is significantly more accurate than pollen percentages alone in both regions. Even though the site selection in northwestern Wisconsin is not ideal, the results are robust. The LRA is a significant step forward in quantitative reconstruction of vegetation. 相似文献
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Fischer-Tropsch catalysis, which converts CO and H2 into CH4 on the surface of iron catalyst, has been proposed to produce the CH4 on Titan during its formation process in a circum-planetary subnebula. However, Fischer-Tropsch reaction rate under the conditions of subnebula have not been measured quantitatively yet. In this study, we conduct laboratory experiments to determine CH4 formation rate and also conduct theoretical calculation of clathrate formation to clarify the significance of Fischer-Tropsch catalysis in a subnebula. Our experimental result indicates that the range of conditions where Fischer-Tropsch catalysis proceeds efficiently is narrow (T∼500-600 K) in a subnebula because the catalysts are poisoned at temperatures above 600 K under the condition of subnebula (i.e., H2/CO = 1000). This suggests that an entire subnebula may not become rich in CH4 but rather that only limited region of a subnebula may enriched in CH4 (i.e., CH4-rich band formation). Our experimental result also suggests that both CO and CO2 are converted into CH4 within time significantly shorter than the lifetime of the solar nebula at the optimal temperatures around 550 K. The calculation result of clathration shows that CO2-rich satellitesimals are formed in the catalytically inactive outer region of subnebula. In the catalytically active inner region, CH4-rich satellitesimals are formed. The resulting CH4-rich satellitesimals formed in this region play an important role in the origin of CH4 on Titan. When our experimental data are applied to a high-pressure model for subnebula evolution, it would predict that there should be CO2 underneath the Iapetus subsurface and no thick CO2 ice layer on Titan's icy crust. Such surface and subsurface composition, which may be observed by Cassini-Huygens mission, would provide crucial information on the origin of icy satellites. 相似文献
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Radiometric surface temperatures, derived from measurements by the AVHRR instrument aboard the NOAA-9 and the NOAA-11 polar orbiting satellites, were used in combination with wind velocity and temperature profiles measured by radiosondes, to calculate surface fluxes of sensible heat. The measurements were made during FIFE, the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment, in a hilly tall grass prairie area of northeastern Kansas. The method of calculation was based on turbulent similarity formulations for the atmospheric boundary layer. Good agreement (r = 0.7) was obtained with reference values of sensible heat flux, taken as arithmetic means of measurements with the Bowen ratio method at six ground stations. The values of evaporation (latent heat fluxes), derived from these sensible heat fluxes by means of the energy budget, were also in good agreement (r = 0.94) with the corresponding reference values from the ground stations. 相似文献
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T. Sugita Y. Kondo M. Koike M. Kanada N. Toriyama H. Nakajima T. Deshler R. Imasu 《Journal of Atmospheric Chemistry》1999,32(1):183-204
A new balloon-borne optical particle counter has been developed to make in situ measurements of stratospheric aerosols. The intensity of light scattered at 60° from the forward direction by individual particles is measured. Aerosol number concentrations in seven size channels can be inferred. The counter has been calibrated using polystyrene and polyvinyl toluene latex spheres. There is good agreement between measured and calculated individual pulse intensities for aerosol with radii from 0.16 to 2.6 µm. The size resolution is limited by broadening of the pulse count/pulse height spectrum, arising mainly from the photoelectron statistics of photomultipliers. Stratospheric aerosol measurements have been made using this instrument at Kiruna (68°N, 21°E), Sweden, in February 1995, and at Aire sur l'Adour (44°N, 0°W), France, in 1992, 1993, and 1994. The uncertainties in the measurements are discussed. The retrieved aerosol concentrations and size distributions are presented, and shown to be broadly consistent with measurements made by the University of Wyoming optical particle counter. 相似文献
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Peng K. Hong Seiji Sugita Yasuhito Sekine Naruhisa Takatoh Tetsuharu Fuse Hideyo Kawakita Eliot F. Young Kosuke Kurosawa Junichi Haruyama Toshihiko Kadono Shunichi Kamata Tomohiko Sekiguchi Hirotomo Noda 《Icarus》2011,214(1):21-29
The Lunar Crater Observation and Sensing Satellite (LCROSS) mission was an impact exploration searching for a volatile deposit in a permanently shadowed region (PSR) by excavating near-surface material. We conducted infrared spectral and imaging observations of the LCROSS impacts from 15 min before the first collision through 2 min after the second collision using the Subaru Telescope in order to measure ejecta dust and water. Such a ground-based observation is important because the viewing geometry and wavelength coverage are very different from the LCROSS spacecraft. We used the Echelle spectrograph with spectral resolution λ/Δλ ∼ 10,000 to observe the non-resonant H2O rotational emission lines near 2.9 μm and the slit viewer with a K′ filter for imaging observation of ejecta plumes. Pre-impact calculations using a homogeneous projectile predicted that 2000 kg of ejecta and 10 kg of H2O were excavated and thrown into the analyzed area immediately above the slit within the field of view (FOV) of the K′ imager and the FOV of spectrometer slit, respectively. However, no unambiguous emission line of H2O or dust was detected. The estimated upper limits of the amount of dust and H2O from the main Centaur impact were 800 kg and 40 kg for the 3σ of noise in the analyzed area within the imager FOV and in the slit FOV, respectively. If we take 1σ as detection limit, the upper limits are 300 kg and 14 kg, respectively. Although the upper limit for water mass is comparable to a prediction by a standard theoretical prediction, that for dust mass is significantly smaller than that predicted by a standard impact theory. This discrepancy in ejecta dust mass between a theoretical prediction and our observation result suggests that the cratering process induced by the LCROSS impacts may have been substantially different from the standard cratering theory, possibly because of its hollow projectile structure. 相似文献
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Potential temperature, specific humidity and wind profiles measured by radiosondes under unstable but windy conditions during FIFE in northeastern Kansas were analyzed within the framework of Monin-Obukhov similarity. Around 86% of these profiles were found to have a height range over which the similarity, formulated in terms of the Businger-Dyer functions, is valid and for which the resulting surface fluxes are in good agreement with independent measurements at ground stations. When scaled with the surface roughness z
0
= 1.05 m and the displacement height d
0
= 26.9 m, for the potential temperature this height range was 45 (±31) (z – d
0
)/z
0
104 (±54) and the comparison of the profile-derived surface fluxes with the independent measurements gave a correlation coefficient of r = 0.96. For the specific humidity these values are 42 (±29) (z – d
0
)/z
0
96 (±38) and r = 0.94. In terms of the height of the bottom of the inversion H
i
, in the morning hours the upper limit of (z – d
0
) in the Monin-Obukhov layer is approximately 0.3H
i
, whereas for a fully developed ABL it is closer to 0.1H
i
. Probably, as a result of the short sampling times and perhaps also of the small gradients under the windy conditions, the exact height range of validity was difficult to establish from a mere inspection of these profiles. 相似文献
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An update is presented for the functionC in the heat transfer equation and for the functionB
w in the momentum transfer equation of the bulk similarity approach for the atmospheric boundary layer (ABL). Motives for this update are recent developments in the formulation of Monin-Obukhov functions for the surface layer, and the availability of the new data set of FIFE-89, the 1989 phase of the First ISLSCP Field Experiment, which took place over the same hilly prairie terrain in north-eastern Kansas as the 1987 phase, i.e., FIFE-87. Functional forms developed in earlier studies are considered. In addition, a new form is derived based on a simple dual structure of the ABL. The functions are calibrated with the data set obtained during FIFE-87; the results are then verified with the independent data set acquired during FIFE-89.Formerly at Cornell University. 相似文献
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Pollen accumulation rates (PARs) provide a potential proxy for quantitative tree volume (m3 ha?1) reconstruction with reliable absolute pollen productivity estimates (APPEs). We obtained APPEs for pine, spruce and birch at their range limits in northern Finland under two temperature periods (‘warm’ and ‘cold’) based on long‐term pollen trap and tree volume records within a 14‐km radius of each trap. APPEs (mean ± SE; × 108 grains m?3 a?1) tend to be higher for the ‘warm’ periods (pine 123.8 ± 24.4, birch 528.0 ± 398.4, spruce 434.3 ± 113.7) compared with the ‘cold’ periods (pine 95.5 ± 37.3, birch 317.3 ± 282.6, spruce 119.6 ± 37.6), although the difference is only significant for spruce. Using an independent temperature record and the APPEs obtained, we reconstruct a low‐frequency record of pine volume changes over the last 1000 years at Palomaa mire, where a high‐resolution record of Pinus PARs is available. Five phases are distinguished in the reconstruction: moderate pine volume, AD 1080–1170; high volume, AD 1170–1340; low volume, AD 1340–1630; very low volume, AD 1630–1810; and rising pine volume, AD 1810–1950. These phases do not coincide with periods of high or low June–July–August temperatures, and thus appear to reflect regional variations in tree volume, while high‐frequency changes within each time‐period block show variations in PARs in response to temperature. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献