Global Snow Mass Measurements and the Effect of Stratigraphic Detail on Inversion of Microwave Brightness Temperatures     

Mark Richardson  Ian Davenport  Robert Gurney 《Surveys in Geophysics》2014,35(3):785-812

Snow provides large seasonal storage of freshwater, and information about the distribution of snow mass as snow water equivalent (SWE) is important for hydrological planning and detecting climate change impacts. Large regional disagreements remain between estimates from reanalyses, remote sensing and modelling. Assimilating passive microwave information improves SWE estimates in many regions, but the assimilation must account for how microwave scattering depends on snow stratigraphy. Physical snow models can estimate snow stratigraphy, but users must consider the computational expense of model complexity versus acceptable errors. Using data from the National Aeronautics and Space Administration Cold Land Processes Experiment and the Helsinki University of Technology microwave emission model of layered snowpacks, it is shown that simulations of the brightness temperature difference between 19 and 37 GHz vertically polarised microwaves are consistent with advanced microwave scanning radiometer-earth observing system and special sensor microwave imager retrievals once known stratigraphic information is used. Simulated brightness temperature differences for an individual snow profile depend on the provided stratigraphic detail. Relative to a profile defined at the 10-cm resolution of density and temperature measurements, the error introduced by simplification to a single layer of average properties increases approximately linearly with snow mass. If this brightness temperature error is converted into SWE using a traditional retrieval method, then it is equivalent to ±13 mm SWE (7 % of total) at a depth of 100 cm. This error is reduced to ±5.6 mm SWE (3 % of total) for a two-layer model.  相似文献   

The submillimetre revolution     

Ian Robson 《Experimental Astronomy》2009,26(1-3):65-78

Although this is a personal reflection of the rise of submillimetre and far-infrared astronomy I will attempt to cover all the major events and players. The review will be restricted to continuum techniques and will principally cover ground-based telescopes. Balloon-based platforms will also be discussed but airborne platforms will be covered by George Rieke. It is always important to remember that a telescope is only as good as the instrumentation it supports, and because there have been few true submillimetre telescopes constructed to date, this review will devote significant time to the instrumentation and technical developments that have been the underpinning of the submillimetre revolution.  相似文献   

RAT J1953+1859: a dwarf nova discovered through high amplitude QPOs in quiescence     

Gavin Ramsay  Pasi Hakala  Thomas Barclay  Peter Wheatley  George Marshall  Harry Lehto  Ralf Napiwotzki  Gijs Nelemans  Stephen Potter  Ian Todd 《Monthly notices of the Royal Astronomical Society》2009,398(3):1333-1338

We report the discovery of an accreting binary, RAT J1953+1859, made during the RApid Temporal Survey (RATS) on the Isaac Newton Telescope. It showed high amplitude (0.3 mag) quasi-periodic oscillations on a time-scale of ∼20 min. Further observations made using the Nordic Optical Telescope showed it to be ∼4 mag brighter than in the discovery images. These photometric observations, together with radial velocity data taken using the William Herschel Telescope, point to an orbital period of ∼90 min. These data suggest that RAT J1953+1859 is a dwarf novae of the SU UMa type. What makes RAT J1953+1859 unusual is that it is the first such system to be discovered as a result of high amplitude QPOs during quiescence. This suggests that high-cadence wide-field surveys could be another means to discover cataclysmic variables as a result of their short period variability.  相似文献   

Future cereal production in China: The interaction of climate change,water availability and socio-economic scenarios   总被引：4，自引：0，他引：4  

Xiong Wei  Conway Declan  Lin Erda  Xu Yinlong  Ju Hui  Jiang Jinhe  Holman Ian  Li Yan 《Global Environmental Change》2009,19(1):34-44

Food production in China is a fundamental component of the national economy and driver of agricultural policy. Sustaining and increasing output to meet growing demand faces significant challenges including climate change, increasing population, agricultural land loss and competing demands for water. Recent warming in China is projected to accelerate by climate models with associated changes in precipitation and frequency of extreme events. How changes in cereal production and water availability due to climate change will interact with other socio-economic pressures is poorly understood. By linking crop and water simulation models and two scenarios of climate (derived from the Regional Climate Model PRECIS) and socio-economic change (downscaled from IPCC SRES A2 and B2) we demonstrate that by the 2040s the absolute effects of climate change are relatively modest. The interactive effects of other drivers are negative, leading to decreases in total production of ?18% (A2) and ?9% (B2). Outcomes are highly dependent on climate scenario, socio-economic development pathway and the effects of CO₂ fertilization on crop yields which may almost totally offset the decreases in production. We find that water availability plays a significant limiting role on future cereal production, due to the combined effects of higher crop water requirements (due to climate change) and increasing demand for non-agricultural use of water (due to socio-economic development). Without adaptation, per capita cereal production falls in all cases, by up to 40% of the current baseline.By simulating the effects of three adaptation scenarios we show that for these future scenarios China is able to maintain per capita cereal production, given reasonable assumptions about policies on land and water management and progress in agricultural technology. Our results are optimistic because PRECIS simulates much wetter conditions than a multi-model average, the CO₂ crop yield response function is highly uncertain and the effects of extreme events on crop growth and water availability are likely to be underestimated.  相似文献   

Performance and Sustainability of District-Scale Ground Coupled Heat Pump Systems     

Ayşe Özdoğan Dölçek  Ian Atkins  Matthew K. Harper  James M. Tinjum  Christopher Y. Choi 《Geotechnical and Geological Engineering》2017,35(2):843-856

This study proposes a solution to the problem of maintaining the performance and sustainability of district-scale, cooling-dominated ground coupled heat pump (GCHP) systems. These systems tend to overheat because heat dissipates slowly in relation to the size of the borefields. To demonstrate this problem, a 2000-borehole field is considered at a district-scale GCHP system in the Upper Midwest, US. The borefield’s ground and fluid temperature responses to its design heating and cooling loads are simulated using computational fluid dynamics implemented by applying the finite volume method. The ground temperature is predicted by applying the thermal loads uniformly over the borefield and simulating heat dissipation to the surrounding geology through conduction coupled with advection due to groundwater flow. The results show that a significant energy imbalance will develop in the ground after the first few years of GCHP operation, even with high rates of groundwater flow. The model presented in this study predicts that the temperature at the center of the borefield will reach 18 °C after 5 years and approximately 50 °C after 20 years of operation in the absence of any mitigation strategies. The fluid temperature in the boreholes is then simulated using a single borehole model to estimate the heat pump coefficient of performance, which decreases as the modeled system heats up. To balance the energy inputs/outputs to the ground—thus maintaining the system’s performance—an operating scheme utilizing cold-water circulation during the winter is evaluated. Under the simulated conditions, this mitigation strategy carries the excess energy out of the borefield. Therefore, the proposed mitigation strategy may be a viable measure to sustaining the operating efficiency of cooling-dominated, district-scale borefields in climates with cold winters.  相似文献   

Individual lava flow thicknesses in Oceanus Procellarum and Mare Serenitatis determined from Clementine multispectral data   总被引：1，自引：0，他引：1  

Shoshana Z. Weider  Ian A. Crawford  Katherine H. Joy 《Icarus》2010,209(2):323-336

We use multispectral reflectance data from the lunar Clementine mission to investigate the impact ejecta deposits of simple craters in two separate lunar mare basalt regions, one in Oceanus Procellarum and one in Mare Serenitatis. Over 100 impact craters are studied, and for a number of these we observe differences between the TiO₂ (and FeO) contents of their ejecta deposits and the lava flow units in which they are located. We demonstrate that, in the majority of cases, these differences cannot plausibly be attributed to uncorrected maturity effects. These observations, coupled with morphometric crater relationships that provide maximum crater excavation depths, allow the investigation of sub-surface lava flow stratigraphy. We provide estimated average thicknesses for a number of lava flow units in the two study regions, ranging from ∼80 m to ∼600 m. In the case of the Serenitatis study area, our results are consistent with the presence of sub-surface horizons inferred from recent radar sounding measurements from the JAXA Kaguya spacecraft. The average lava flow thicknesses we obtain are used to make estimates of the average flux of volcanic material in these regions. These are in broad agreement with previous studies, suggesting that the variation in mare basalt types we observe with depth is similar to the lateral variations identified at the surface.  相似文献   

Asteroseismology of solar and stellar models     

Ian W. Roxburgh 《Astrophysics and Space Science》2010,328(1-2):3-11

I discuss several asteroseismology diagnostic techniques that can be applied to the high quality data on stellar oscillations obtained, and to be obtained in the future, from ground based and space based experiments. In particular I discuss techniques using the representation of oscillation frequencies in terms of inner and outer phase shifts which can be used both for model fitting and inversion procedures to probe the inner structure of stars, and hence to test and improve our modelling.  相似文献   

Diadromy and longitudinal patterns of upstream penetration of freshwater fish in Taranaki,New Zealand     

Michael K. Joy  Ian M. Henderson  Russell G. Death 《新西兰海洋与淡水研究杂志》2013,47(3):531-543

Diadromous fish species dominate the New Zealand freshwater fish fauna and make up 15 of the 17 native fish species found on the Taranaki Ring Plain. Trajectories of occurrence in relation to elevation and distance from the sea are described for 11 diadromous and 2 non‐diadromous species using data from the New Zealand Freshwater Fish Database and data collected over the summer of 1997/ 98. Distinctive distributions were found for most of the species related to their differing migratory strategies and abilities. The species were ranked based on components of these trajectories to compare their penetrative ability. Comparison of the ranking methods used revealed they produced similar results. The ranking of the 11 diadromous species in Taranaki relative to each other revealed similar rankings to those for the same species from the West Coast of the South Island. The non‐migratory native fish, Cran's bully (Gobiomorphus basalis), was not found on the western side of the mountain. This distribution is thought to be the result of the local extinction of non‐migratory species in high gradient or unstable streams.  相似文献   

Sea Surface Height Variability in the Indian Ocean from TOPEX/POSEIDON Altimetry and Model Simulations     

Bulusu Subrahmanyam  Ian S. Robinson 《Marine Geodesy》2013,36(3):167-195

Sea Surface Height (SSH) variability in the Indian Ocean during 1993-1995 is studied using TOPEX/POSEIDON (T/P) altimetry data. Strong interannual variability is seen in the surface circulation of the western Arabian Sea, especially in the Somali eddy structure. During the Southwest (SW) monsoon, a weak monsoon year is characterized by a single eddy system off Somalia, a strong or normal monsoon year by several energetic eddies. The Laccadive High (LH) and Laccadive Low (LL) systems off southwest India are observed in the altimetric SSH record. The variability of the East India Coastal Current (EICC), the western boundary current in the Bay of Bengal, is also detected. Evidence is found for the propagation of Kelvin and Rossby waves across the northern Indian Ocean; these are examined in the context of energy transfer to the western boundary currents, and associated eddies. A simple wind-driven isopycnal model having three active layers is implemented to simulate the seasonal changes of surface and subsurface circulation in the North Indian Ocean and to examine the response to different wind forcing. The wind forcing is derived from the ERS-1 scatterometer wind stress for the same period as the T/P altimeter data, enabling the model response in different (active/weak) monsoon conditions to be tested. The model output is derived in 10-day snapshots to match the time period of the T/P altimeter cycles. Complex Principal Component Analysis (CPCA) is applied to both altimetric and model SSH data. This confirms that long Rossby waves are excited by the remotely forced Kelvin waves off the southwest coast of India and contribute substantially to the variability of the seasonal circulation in the Arabian Sea.  相似文献   

Wind-Direction Effects on Urban-Type Flows   总被引：2，自引：2，他引：0  

Jean Claus  O. Coceal  T. Glyn Thomas  S. Branford  S. E. Belcher  Ian P. Castro 《Boundary-Layer Meteorology》2012,142(2):265-287

Practically all extant work on flows over obstacle arrays, whether laboratory experiments or numerical modelling, is for cases where the oncoming wind is normal to salient faces of the obstacles. In the field, however, this is rarely the case. Here, simulations of flows at various directions over arrays of cubes representing typical urban canopy regions are presented and discussed. The computations are of both direct numerical simulation and large-eddy simulation type. Attention is concentrated on the differences in the mean flow within the canopy region arising from the different wind directions and the consequent effects on global properties such as the total surface drag, which can change very significantly—by up to a factor of three in some circumstances. It is shown that for a given Reynolds number the typical viscous forces are generally a rather larger fraction of the pressure forces (principally the drag) for non-normal than for normal wind directions and that, dependent on the surface morphology, the average flow direction deep within the canopy can be largely independent of the oncoming wind direction. Even for regular arrays of regular obstacles, a wind direction not normal to the obstacle faces can in general generate a lateral lift force (in the direction normal to the oncoming flow). The results demonstrate this and it is shown how computations in a finite domain with the oncoming flow generated by an appropriate forcing term (e.g. a pressure gradient) then lead inevitably to an oncoming wind direction aloft that is not aligned with the forcing term vector.  相似文献