The sensitivity of supercritical atmospheric boundary-layer flow along a coastal mountain barrier     

MICHAEL TJERNSTRÖm 《地球，A辑:动力气象学与海洋学》1999,51(5):880-901

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Regional aerosol optical depth characteristics from satellite observations: ACE‐1, TARFOX and ACE‐2 results     

P. A. Durkee  K. E. Nielsen  P. J. Smith  P. B. Russell  B. Schmid  J. M. Livingston  B. N. Holben  C. Tomasi  V. Vitale  D. Collins  R. C. Flagan  J. H. Seinfeld  K. J. Noone  E. Öström  S. Gassó  D. Hegg  L. M. Russell  T. S. Bates  P. K. Quinn 《Tellus. Series B, Chemical and physical meteorology》2000,52(2):484-497

Analysis of the aerosol properties during 3 recent international field campaigns (ACE‐1, TARFOX and ACE‐2) are described using satellite retrievals from NOAA AVHRR data. Validation of the satellite retrieval procedure is performed with airborne, shipboard, and land‐based sunphotometry during ACE‐2. The intercomparison between satellite and surface optical depths has a correlation coefficient of 0.93 for 630 nm wavelength and 0.92 for 860 nm wavelength. The standard error of estimate is 0.025 for 630 nm wavelength and 0.023 for 860 nm wavelength. Regional aerosol properties are examined in composite analysis of aerosol optical properties from the ACE‐1, TARFOX and ACE‐2 regions. ACE‐1 and ACE‐2 regions have strong modes in the distribution of optical depth around 0.1, but the ACE‐2 tails toward higher values yielding an average of 0.16 consistent with pollution and dust aerosol intrusions. The TARFOX region has a noticeable mode of 0.2, but has significant spread of aerosol optical depth values consistent with the varied continental aerosol constituents off the eastern North American Coast.  相似文献   

Molecular Absorption in Cen a on Vlbi Scales     

Huib Jan Van Langevelde  Ylva PihlstrÖm  Anthony Beasley 《Astrophysics and Space Science》2005,295(1-2):249-255

Centaurus A, the nearest AGN shows molecular absorption in the millimeter and radio regime. By observing the absorption with VLBI, we try to constrain the distribution of the gas, in particular whether it resides in the circumnuclear region. Analysis of VLBA observations in four OH and two H₂CO transitions is presented here, as well as molecular excitation models parameterized with distance from the AGN. We conclude that the gas is most likely associated with the tilted molecular ring structure observed before in molecular emission and IR continuum. The formaldehyde absorption shows small-scale absorption which requires a different distribution than the hydroxyl.  相似文献   

Primary production of Inner Mongolia, China, between 1982 and 1999 estimated by a satellite data-driven light use efficiency model   总被引：2，自引：0，他引：2  

Sara Brogaard  Micael Runnstrm  Jonathan W. Seaquist 《Global and Planetary Change》2005,45(4):313

Declining biological production as a part of an ongoing land degradation process is considered a severe environmental problem in the dry northern and northwestern regions of China. The aim of this study is to develop and adapt a satellite data-driven gross primary production model called Lund University light use efficiency model (LULUE) to temperate conditions in order to map gross primary production (GPP) for the Grasslands of Inner Mongolia Autonomous Region (IMAR), China, from 1982 to 1999. The water stress factor included in the original model has been complemented with two temperature stress factors. In addition, algorithms that allocate the proportions of C3/C4 photosynthetic pathways used by plants and that compute temperature-based C3 maximum efficiency values have been incorporated in the model.The applied light use efficiency (LUE) model is using time series of the Normalized Difference Vegetation Index (NDVI), CLouds from AVHRR (CLAVR) from the 8-km resolution NOAA Pathfinder Land Data Set (PAL). Quasi-daily rainfall and monthly minimum and maximum temperatures, together with soil texture information, are used to compute water limitations to plant growth. The model treats bare soil evaporation and actual transpiration separately, a refinement that is more biophysically realistic, and leads to enhanced precision in our water stress term, especially across vegetation gradients.Based on ground measurements of net primary production (NPP) at one site, the LULUE reproduces the variability of primary production better than CENTURY or NDVI alone. Mean annual GPP between 1982 and 1999 range from about 100 g/m² in desert regions in the west to about 4000 g/m² in the northeast of IMAR, and the coefficient of variation for GPP is highest near the margins of the deserts in the west where rainfall is erratic. Linear trends fitted through the 18-year time series reveal that the western regions have encountered no change, while a large area in the center of the IMAR shows marked increases in GPP. In the northeast, negative trends in GPP are noted and coincide with rainfall trends. Though the high inter-annual variability in primary production undermines the identification of significant trends, we could not isolate any general decline in grassland primary production.  相似文献   

Relationships between the H i 21-cm line strength, Mg ii equivalent width and metallicity in damped Lyman α absorption systems     

S. J. Curran  P. Tzanavaris  Y. M. Pihlström  J. K. Webb 《Monthly notices of the Royal Astronomical Society》2007,382(3):1331-1341

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Identifying burdens of coping with climate change: A typology of the duties of climate justice     

Göran Duus-Otterström  Sverker C. Jagers 《Global Environmental Change》2012,22(3):746-753

One of the central questions in climate change debates concerns fair burden-sharing, i.e. justice in the distribution of costs of undertaking climate-managing policies. In this paper it is argued that in order to distribute such costs justly, it is necessary to have a nuanced understanding of what types of burdens they represent. Climate managing policies are usually divided into responses that seek to reduce the concentration of greenhouse gases in the atmosphere (mitigation) and responses that seek to prevent harm arising from a changing climate (adaptation). Some have argued that there are normatively significant differences between mitigation and adaptation: that the two responses adhere to different logics and evoke different patterns of burden-sharing. This paper argues that the relevant distinction is instead between m>negativem> and m>positivem> climate duties, i.e. whether an agent has a duty to undertake climate-managing policies on account of the harm its excessive emissions are causing or simply on account of its ability to assist those in need. The paper offers a typology of the different mitigation and adaptation responses that can be sorted under the negative/positive distinctions. This way of conceptualizing the issue not only enables us to better address the burden-sharing question, offering a more nuanced understanding of the types of climate burdens that are ascribable to agents and pointing out the appropriate roles of contributory responsibility and ability. It also clarifies aspects of the climate negotiations, and explains why it matters whether adaptation finance transferred to vulnerable countries is portrayed as compensation for harmful emissions or simply as donor countries discharging their humanitarian duties.  相似文献   

Planetary ENA imaging: Effects of different interaction models for Mars     

H. Gunell  M. Holmström  E. Kallio  A.F. Nagy 《Planetary and Space Science》2006,54(2):117-131

We present and compare energetic neutral atom (ENA) images that are calculated from plasma parameters given by three different simulation models of the interaction between the solar wind and Mars. The images are calculated by combining a model for the ion flow with a model of the neutral atmosphere using the cross-sections for the charge exchange collisions. The three ion models are: an empirical model that is based on Phobos 2 measurements; a three-dimensional hybrid simulation; and a three-dimensional MHD simulation. For the empirical and MHD models the images are obtained by integration of the ENA emission along lines of sight to a virtual ENA instrument. In the case of the hybrid model images are obtained by summing the contributions from all ions, whose positions, velocities, and weights are saved in files at regular intervals.Differences between the models can be detected in the images, for example the hybrid model produces ENA emissions from a larger region than the MHD model does. An asymmetry in the oxygen ion density develops in the hybrid model and can be seen in the oxygen ENA images. The images are influenced by finite gyro radius effects, which are included in the hybrid model but not in the other two. The total production rates of hydrogen ENAs are mg height="16" border="0" style="vertical-align:bottom" width="92" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0032063305000516-si118.gif">, mg height="16" border="0" style="vertical-align:bottom" width="91" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0032063305000516-si119.gif">, and mg height="16" border="0" style="vertical-align:bottom" width="92" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0032063305000516-si120.gif"> for the empirical, hybrid and MHD models respectively.This study shows the importance of considering both the type of simulation model used and the proper inclusion of relevant physical phenomena and boundary conditions, when modelling the interaction between planets and the solar wind. Although the different models agree fairly well in terms of macroscopic plasma parameters they produce ENA images that differ substantially.  相似文献   

First ENA observations at Mars: ENA emissions from the martian upper atmosphere     

Y. Futaana  S. Barabash  M. Holmström  E. Kallio  H. Gunell  R. Lundin  M. Yamauchi  J.D. Winningham  J.R. Sharber  A.J. Coates  D.O. Kataria  P. Riihelä  H. Koskinen  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  A. Fedorov  S. Orsini  M. Maggi  P. Bochsler  N. Krupp  M. Fränz  C. Dierker 《Icarus》2006,182(2):424-430

The neutral particle detector (NPD) on board Mars Express has observed energetic neutral atoms (ENAs) from a broad region on the dayside of the martian upper atmosphere. We show one such example for which the observation was conducted at an altitude of 570 km, just above the induced magnetosphere boundary (IMB). The time of flight spectra of these ENAs show that they had energies of 0.2-2 keV/amu, with an average energy of ∼1.1 keV/amu. Both the spatial distribution and the energy of these ENAs are consistent with the backscattered ENAs, produced by an ENA albedo process. This is the first observation of backscattered ENAs from the martian upper atmosphere. The origin of these ENAs is considered to be the solar wind ENAs that are scattered back by collision processes in the martian upper atmosphere. The particle flux and energy flux of the backscattered ENAs are mg height="15" border="0" style="vertical-align:bottom" width="156" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0019103505004707-si1.gif"> and mg height="15" border="0" style="vertical-align:bottom" width="161" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0019103505004707-si2.gif">, respectively.  相似文献   

Monument-antenna effects on GPS coordinate time series with application to vertical rates in Antarctica     

Matt?A.?KingEmail author  Michael?Bevis  Terry?Wilson  Bjorn?Johns  Frederick?Blume 《Journal of Geodesy》2012,86(1):53-63

We examine the electromagnetic coupling of a GPS antenna–monument pair in terms of its simulated affect on long GPS coordinate time series. We focus on the Earth and Polar Observing System (POLENET) monument design widely deployed in Antarctica and Greenland in projects interested particularly in vertical velocities. We base our tests on an absolute robot calibration that included the top ~0.15 m of the monument and use simulations to assess its effect on site coordinate time series at eight representative POLENET sites in Antarctica over the period 2000.0–2011.0. We show that the neglect of this calibration would introduce mean coordinate bias, and most importantly for velocity estimation, coordinate noise which is highly sensitive to observation geometry and hence site location and observation period. Considering only sub-periods longer than 2.5 years, we show vertical site velocities may be biased by up to ±0.4 mm/year, and biases up to 0.2 mm/year may persist for observation spans of 8 years. Changing between uniform and elevation-dependent observation weighting alters the time series but does not remove the velocity biases, nor does ambiguity fixing. The effect on the horizontal coordinates is negligible. The ambiguities fixed series spectra show noise between flicker and random walk with near-white noise at the highest frequencies, with mean spectral indices (frequencies <20 cycles per year) of approximately −1.3 (uniform weighting) and −1.4 (elevation-dependent weighting). While the results are likely highly monument specific, they highlight the importance of accounting for monument effects when analysing vertical coordinate time series and velocities for the highest precision and accuracy geophysical studies.  相似文献   

Orbit determination of the Lunar Reconnaissance Orbiter   总被引：3，自引：1，他引：2  

Erwan?MazaricoEmail author  D.?D.?Rowlands  G.?A.?Neumann  D.?E.?Smith  M.?H.?Torrence  F.?G.?Lemoine  M.?T.?Zuber 《Journal of Geodesy》2012,86(3):193-207

We present the results on precision orbit determination from the radio science investigation of the Lunar Reconnaissance Orbiter (LRO) spacecraft. We describe the data, modeling and methods used to achieve position knowledge several times better than the required 50–100 m (in total position), over the period from 13 July 2009 to 31 January 2011. In addition to the near-continuous radiometric tracking data, we include altimetric data from the Lunar Orbiter Laser Altimeter (LOLA) in the form of crossover measurements, and show that they strongly improve the accuracy of the orbit reconstruction (total position overlap differences decrease from ~70 m to ~23 m). To refine the spacecraft trajectory further, we develop a lunar gravity field by combining the newly acquired LRO data with the historical data. The reprocessing of the spacecraft trajectory with that model shows significantly increased accuracy (~20 m with only the radiometric data, and ~14 m with the addition of the altimetric crossovers). LOLA topographic maps and calibration data from the Lunar Reconnaissance Orbiter Camera were used to supplement the results of the overlap analysis and demonstrate the trajectory accuracy.  相似文献