Solar wind structure sources and periodicities of auroral electron power over three solar cycles     

Barbara A. Emery  Ian G. Richardson  David S. Evans  Frederick J. Rich 《Journal of Atmospheric and Solar》2009,71(10-11):1157-1175

We assess the contributions of various types of solar wind structures (transients, coronal hole high-speed streams (HSS), and slow-speed wind) to hourly average auroral electron power (P_e). The time variation of the solar wind velocity (V_sw) and P_e are determined by HSS, which contribute ～47% to P_e and V_sw. Transients contribute ～42% of P_e in solar maxima, and ～6% in solar minimum. Cross-correlations of P_e with V_sw|B| for negative B_z are significant. P_e exhibits solar rotational periodicities similar to those for V_sw, with strong 7- and 9-day periodicities in 2005–2008 and equinox semiannual periodicities in 1995–1999.  相似文献   

Tsunamis on the Pacific Coast of Canada Recorded in 1994–2007     

Frederick E. Stephenson  Alexander B. Rabinovich 《Pure and Applied Geophysics》2009,166(1-2):177-210

In the last 15 years there have been 16 tsunami events recorded at tide stations on the Pacific Coast of Canada. Eleven of these events were from distant sources covering almost all regions of the Pacific, as well as the December 26, 2004 Sumatra tsunami in the Indian Ocean. Three tsunamis were generated by local or regional earthquakes and two were meteorological tsunamis. The earliest four events, which occurred in the period 1994–1996, were recorded on analogue recorders; these tsunami records were recently re-examined, digitized and thoroughly analysed. The other 12 tsunami events were recorded using digital high-quality instruments, with 1-min sampling interval, installed on the coast of British Columbia (B.C.) in 1998. All 16 tsunami events were recorded at Tofino on the outer B.C. coast, and some of the tsunamis were recorded at eight or more stations. The tide station at Tofino has been in operation for 100 years and these recent observations add to the dataset of tsunami events compiled previously by S.O. Wigen (1983) for the period 1906–1980. For each of the tsunami records statistical analysis was carried out to determine essential tsunami characteristics for all events (arrival times, maximum amplitudes, frequencies and wave-train structure). The analysis of the records indicated that significant background noise at Langara, a key northern B.C. Tsunami Warning station located near the northern end of the Queen Charlotte Islands, creates serious problems in detecting tsunami waves. That station has now been moved to a new location with better tsunami response. The number of tsunami events observed in the past 15 years also justified re-establishing a tide gauge at Port Alberni, where large tsunami wave amplitudes were measured in March 1964. The two meteorological events are the first ever recorded on the B.C. coast. Also, there have been landslide generated tsunami events which, although not recorded on any coastal tide gauges, demonstrate, along with the recent investigation of a historical catastrophic event, the significant risk that landslide generated tsunami pose to coastal and inland regions of B.C.  相似文献   

Time-transgressive cryoplanation terrace development through nivation-driven scarp retreat     

Kelsey E. Nyland  Frederick E. Nelson 《地球表面变化过程与地形》2020,45(3):526-534

Cryoplanation terraces are elevated bedrock features resembling giant staircases, with alternating steep scarps and shallow sloping treads. These landscape-scale features have long been associated with periglacial environments, but the processes involved in their formation remain vaguely specified and contentious. The two leading hypotheses for the formation of cryoplanation terraces are centered on: (1) geologic structure; and (2) nivation-driven scarp retreat. The nivation-formation hypothesis invokes scarp retreat under erosion processes associated with late-lying snowbanks. To test whether cryoplanation terraces develop through scarp retreat, six relative weathering indices (fracture counts, Cailleux roundness, Cailleux flatness, Krumbein sphericity, rebound, and weathering rind thickness) were measured across well-developed terraces in unglaciated eastern Beringia (central and western Alaska) at Mt Fairplay, Eagle Summit, and Skookum Pass. Statistically significant differences in relative weathering indices detected through chi-square and multiple-comparison procedures indicate that material is less weathered closer to scarps, i.e. that these areas were more recently exposed than those distant from the scarp. Based on these findings, a refined model of time-transgressive cryoplanation terrace development through nivation-driven scarp retreat is proposed. This new qualitative model addresses the removal of weathered material from terrace treads down side slopes through piping and gravity-driven mass-wasting processes. © 2019 John Wiley & Sons, Ltd.  相似文献   

Development of an adaptive disturbance rejection system for the rapidly deployable stable platform—Part 2: Controller design and closed loop response     

Tannen S. VanZwieten  James H. VanZwieten  Mark J. Balas  Frederick R. Driscoll 《Ocean Engineering》2010,37(14-15):1367-1379

Currently, both military and civilian operations that require at-sea cargo transfers are severely limited by environmental conditions and loading forces that induce vessel motions. To increase the robustness of at-sea cargo transfer to these environmental conditions and loading forces, efforts have recently been made toward an actively controlled, rapidly deployable stable platform (RDSP). The purpose of the research presented here is to implement an output feedback adaptive controller and adaptive disturbance rejection scheme that will mitigate the effect of environmental conditions and reject disturbances caused by various loading situations. Because of the controller's distinct ability to adapt to various operating conditions, anticipate and reject load disturbances of unknown magnitude, and adjust to stay within input saturation constraints, the framework is a good fit for the RDSP. Three missions are considered using a previously developed 3 degree of freedom simulation of a 1/10th scale RDSP prototype. Results show successful mitigation of load disturbances and a significant reduction in pitch motions using a control command that remains within the given amplitude and rate constraints. In the case of cargo transfer operations, the adaptive control system is able to significantly increase the cargo throughput by rejecting the disturbances before they are able to cause large pitching dynamics.  相似文献   

Development and validation of harmonic wave group single-run procedure for RAO with comparison to regular wave and transient wave group procedures using URANS     

S. Maysam Mousaviraad  Pablo M. Carrica  Frederick Stern 《Ocean Engineering》2010,37(8-9):653-666

A harmonic wave group single run seakeeping procedure is developed, validated and compared with regular wave and transient wave group procedures, using an unsteady Reynolds averaged Navier–Stokes solver, although all procedures can be also implemented using experiments or potential flow. Incoming waves are generated by linear superposition of potential solution for a number of component waves. The regular wave procedure requires multiple runs, whereas single run procedures obtain the response amplitude operators (RAO) for a range of frequencies at a fixed speed, assuming linear ship response. The transient wave group procedure provides continuous RAO curves, while the harmonic wave group procedure obtains discrete transfer functions without focusing. Results are presented for heave and pitch response amplitudes and phases for the DTMB model 5512 in head waves. Verification and validation studies are performed for the transient wave group procedure. Validation is achieved at the average interval of 9.54 (%D). Comparisons of the procedures show that the harmonic wave group procedure is the most efficient, saving 75.8% on the computational cost compared with the regular wave procedure. Error values from all procedures are similar at 4 (%D). Harmonic wave group results are validated for a wide range of the Froude numbers, with satisfactory results.  相似文献   

Change in Extent of Meadows and Shrub Fields in the Central Western Cascade Range,Oregon∗     

Sadao Takaoka  Frederick J. Swanson 《The Professional geographer》2013,65(4):527-540

We examined change in areal extent of mountain meadows and fields of deciduous shrubs and conifer saplings in the central western Cascade Range of Oregon, based on analysis of aerial photographs taken in 1946 and 2000. These nonforest vegetation patches are distinctive habitats in dominantly forested landscapes, such as the Cascades, and change in extent of these habitats is of interest to scientists and land managers. We mapped and dated even-aged forest stands of probable postfire origin around the nonforest patches, using tree-ring analysis and interpretation of aerial photographs. We used these and archival data to interpret possible influences of past wildfire and sheep grazing on the extent of nonforest patches. The total area of nonforest vegetation patches decreased from 5.5 percent of the study area in 1946 to 2.5 percent in 2000. Significantly more cases of contracted patches were observed for mesic and xeric meadows which have adjacent forest established after wildfire in the approximately 150 years preceding 1946. A higher proportion of mesic (47 percent, n = 47) than xeric (17 percent, n= 115) meadows contracted between 1946 and 2000. Broad-leaved shrub fields were unchanged, probably because of topo-edaphic controls, dense cover of shrubs, and snow effects; but all fields of conifer saplings underwent succession to forest. We observed no strong influences of sheep grazing on the extent of meadows.  相似文献   

Far ultraviolet spectral properties of Saturn’s rings from Cassini UVIS     

E. Todd Bradley  Joshua E. Colwell  Jeffrey N. Cuzzi  Lindsey Chambers 《Icarus》2010,206(2):458-466

Spectra taken by the Cassini Ultraviolet Imaging Spectrograph (UVIS) of Saturn’s C ring, B ring, Cassini Division, and A ring have been analyzed in order to characterize ring particle surface properties and water ice abundance in the rings. UVIS spectra sense the outer few microns of the ring particles. Spectra of the normalized reflectance (I/F) in all four regions show a characteristic water ice absorption feature near 165 nm. Our analysis shows that the fractional abundance of surface water ice is largest in the outer B ring and decreases by over a factor of 2 across the inner C ring. We calculate the mean path length of UV photons through icy ring particle regolith and the scattering asymmetry parameter using a Hapke reflectance model and a Shkuratov reflectance model to match the location of the water ice absorption edge in the data. Both models give similar retrieved values of the photon mean length, however the retrieved asymmetry (g) values are different. The photon mean path lengths are nearly uniform across the B and A rings. Shortward of 165 nm the rings exhibit a slope that turns up towards shorter wavelengths, while the UV slope of 180/150 nm (reflectance outside the water absorption ratioed to that inside the absorption band) tracks I/F with maxima in the outer B ring and in the central A ring. Retrieved values of the scattering asymmetry parameter show the regolith grains to be highly backscattering in the FUV spectral regime.  相似文献   

A computer program for flow-log analysis of single holes (FLASH)     

Day-Lewis FD  Johnson CD  Paillet FL  Halford KJ 《Ground water》2011,49(6):926-931

A new computer program, FLASH (Flow-Log Analysis of Single Holes), is presented for the analysis of borehole vertical flow logs. The code is based on an analytical solution for steady-state multilayer radial flow to a borehole. The code includes options for (1) discrete fractures and (2) multilayer aquifers. Given vertical flow profiles collected under both ambient and stressed (pumping or injection) conditions, the user can estimate fracture (or layer) transmissivities and far-field hydraulic heads. FLASH is coded in Microsoft Excel(5) with Visual Basic for Applications routines. The code supports manual and automated model calibration.  相似文献   

Influence of liquid structure on diffusive isotope separation in molten silicates and aqueous solutions     

James M. Watkins  Donald J. DePaolo  Frederick J. Ryerson  Brook T. Peterson 《Geochimica et cosmochimica acta》2011,75(11):3103-6139

Molecular diffusion in natural volcanic liquids discriminates between isotopes of major ions (e.g., Fe, Mg, Ca, and Li). Although isotope separation by diffusion is expected on theoretical grounds, the dependence on mass is highly variable for different elements and in different media. Silicate liquid diffusion experiments using simple liquid compositions were carried out to further probe the compositional dependence of diffusive isotopic discrimination and its relationship to liquid structure. Two diffusion couples consisting of the mineral constituents anorthite (CaAl₂Si₂O₈; denoted AN), albite (NaAlSi₃O₈; denoted AB), and diopside (CaMgSi₂O₆; denoted DI) were held at 1450 °C for 2 h and then quenched to ambient pressure and temperature. Major-element as well as Ca and Mg isotope profiles were measured on the recovered quenched glasses. In both experiments, Ca diffuses rapidly with respect to Si. In the AB-AN experiment, D_Ca/D_Si ≈ 20 and the efficiency of isotope separation for Ca is much greater than in natural liquid experiments where D_Ca/D_Si ≈ 1. In the AB-DI experiment, D_Ca/D_Si ≈ 6 and the efficiency of isotope separation is between that of the natural liquid experiments and the AB-AN experiment. In the AB-DI experiment, D_Mg/D_Si ≈ 1 and the efficiency of isotope separation for Mg is smaller than it is for Ca yet similar to that observed for Mg in natural liquids.The results from the experiments reported here, in combination with results from natural volcanic liquids, show clearly that the efficiency of diffusive separation of Ca isotopes is systematically related to the solvent-normalized diffusivity - the ratio of the diffusivity of the cation (D_Ca) to the diffusivity of silicon (D_Si). The results on Ca isotopes are consistent with available data on Fe, Li, and Mg isotopes in silicate liquids, when considered in terms of the parameter D_cation/D_Si. Cations diffusing in aqueous solutions display a similar relationship between isotopic separation efficiency and D_cation/D_H2O, although the efficiencies are smaller than in silicate liquids. Our empirical relationship provides a tool for predicting the magnitude of diffusive isotopic effects in many geologic environments and a basis for a more comprehensive theory of isotope separation in liquid solutions. We present a conceptual model for the relationship between diffusivity and liquid structure that is consistent with available data.  相似文献   

Climate change impacts on sugarcane attainable yield in southern Brazil     

Fabio R. Marin  James W. Jones  Abraham Singels  Frederick Royce  Eduardo D. Assad  Giampaolo Q. Pellegrino  Flávio Justino 《Climatic change》2013,117(1-2):227-239

This study evaluated the effects of climate change on sugarcane yield, water use efficiency, and irrigation needs in southern Brazil, based on downscaled outputs of two general circulation models (PRECIS and CSIRO) and a sugarcane growth model. For three harvest cycles every year, the DSSAT/CANEGRO model was used to simulate the baseline and four future climate scenarios for stalk yield for the 2050s. The model was calibrated for the main cultivar currently grown in Brazil based on five field experiments under several soil and climate conditions. The sensitivity of simulated stalk fresh mass (SFM) to air temperature, CO₂ concentration [CO₂] and rainfall was also analyzed. Simulated SFM responses to [CO₂], air temperature and rainfall variations were consistent with the literature. There were increases in simulated SFM and water usage efficiency (WUE) for all scenarios. On average, for the current sugarcane area in the State of São Paulo, SFM would increase 24 % and WUE 34 % for rainfed sugarcane. The WUE rise is relevant because of the current concern about water supply in southern Brazil. Considering the current technological improvement rate, projected yields for 2050 ranged from 96 to 129 t?ha^?1, which are respectively 15 and 59 % higher than the current state average yield.  相似文献