Estimates of fluvial sediment discharge from in situ instruments are an important component of large‐scale sediment budgets that track long‐term geomorphic change. Suspended sediment load can be ...reliably estimated using acoustic or physical sampling techniques; however, bedload is difficult to measure directly and can consequently be one of the largest sources of uncertainty in estimates of total load. We propose a physically informed predictive empirical model for bedload sand flux as a function of variables that are measured using existing acoustic or physical sampling techniques. This model depends on the assumption that concentration and grain size in suspension are in equilibrium with reach‐averaged boundary conditions. Bayesian inference is used to fit model parameters to data from eight sand‐bed rivers and to simulate bedload flux over the available gage record at one site on the Colorado River in Grand Canyon National Park. We find that the cumulative bedload flux during the 9 year period from 2008 to 2016 was 5% of the cumulative suspended sand load; however, instantaneous bedload flux ranged from as little as 1% of instantaneous suspended sand load to as much as 75% of instantaneous suspended sand load due to fluctuations in flow strength and sediment supply. Changes in bedload flux at a constant discharge are indicative of short‐term sediment supply enrichment and depletion. Long‐term average bedload flux cannot be expected to remain constant in the future as the river adjusts to changes in sediment runoff and the dam‐regulated discharge regime.
Key Points
Bedload flux is predicted from variables that are measured at acoustic suspended sediment monitoring stations
Bayesian modeling extends the utility of this approach to a wide range of conditions and rivers
Predicted bedload flux provides an indicator of short‐term sediment supply enrichment and depletion
Spectral measurements of ultraviolet-B radiation made at Toronto since 1989 indicate that the intensity of light at wavelengths near 300 nanometers has increased by 35 percent per year in winter and ...7 percent per year in summer. The wavelength dependence of these trends indicates that the increase is caused by the downward trend in total ozone that was measured at Toronto during the same period. The trend at wavelengths between 320 and 325 nanometers is essentially zero.
SCISAT‐1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earth's atmosphere. It was launched into low Earth circular orbit ...(altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm−1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750–4400 cm−1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285–1030 nm and spectral resolution of 1–2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10–100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results.
Dobson and Brewer spectrophotometer and filter ozonometer data available from the World Ozone and Ultraviolet Data Centre (WOUDC) were compared with satellite total ozone measurements from TOMS ...(onboard Nimbus 7, Meteor 3, and Earth Probe satellites), OMI (AURA satellite) and GOME (ERS‐2 satellite) instruments. Five characteristics of the difference with satellite data were calculated for each site and instrument type: the mean difference, the standard deviation of daily differences, the standard deviation of monthly differences, the amplitude of the seasonal component of the difference, and the range of annual values. All these characteristics were calculated for five 5‐year‐long bins and for each site separately for direct sun (DS) and zenith sky (ZS) ozone measurements. The main percentiles were estimated for the five characteristics of the difference and then used to establish criteria for “suspect” or “outlier” sites for each characteristic. About 61% of Dobson, 46% of Brewer, and 28% of filter stations located between 60°S and 60°N have no “suspect” or “outlier” characteristics. In nearly 90% of all cases, Dobson and Brewer sites demonstrated 5‐year mean differences with satellites to be within ±3% (for DS observations). The seasonal median difference between all Brewer DS measurements at 25°–60°N and GOME and OMI overpasses remained within ±0.5% over a period of more than 10 years. The satellite instrument performance was also analyzed to determine typical measurement uncertainties. It is demonstrated that systematic differences between the analyzed satellite instruments are typically within ±2% and very rarely are they outside the ±3% envelope. As the satellite instrument measurements appear to be better than ±3%, ground‐based instruments with precision values worse than ±3% are not particularly useful for the analyses of long‐term changes and comparison with numerical simulations.
The twenty-second Quadrennial Ozone Symposium (QOS) was held in Toronto in August 2012, a year that marked a number of anniversaries of events related to the study of ozone and connected to Canada. ...These include the 50-year anniversary of the founding of the World Ozone Data Centre (now he World Ozone and Ultraviolet radiation Data Centre: WOUDC, by Environment Canada scientist Carleton Mateor, the 30-year anniversary of the delivery of the first commercial Bremer Ozone Spectrophotometer to Thessaloniki in Greece: the 25-year anniversary of the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer (a protocol to the Vienna Convention for the Protection of he Ozone Layer) in Montreal: and the 20 year anniversary of the introduction of the Ultraviolet (UV) index in Canada, These anniversaries speak to the strong commitment that Canada has had to ozone measurement and ozone science.
Spectrometers are designed to isolate particular wavebands and suppress light from wavelengths outside the band of interest. However, a small amount of undesired light will always enter the detector, ...not through the designed optical path, but through random scattering from the instrument optical components, housing, and dust particles. Every spectrophotometer has stray light coming from outside the nominal measurement waveband. For Dobson spectrophotometers and single monochromator Brewer spectrophotometers, which are basic instruments in the World Meteorological Organization (WMO) ozone and ultraviolet (UV) monitoring network, the error introduced by stray light is substantial when the ozone slant path becomes very large because of high solar zenith angles and a thick ozone layer. These are common conditions during Arctic spring. To study the issue, a long ozone slant path Intercomparison/Calibration campaign for Nordic Brewers and Dobsons was held at Sodankylä 8-24 March 2011 and a follow-up campaign to extend calibrations to shorter ozone slant paths took place at Izaña observatory, Tenerife, between 28 October and 18 November 2011. These campaigns were part of the Committee on Earth Observation Satellites (CEOS) Intercalibration of Ground-based Spectrometers and Lidars project funded by the European Space Agency (ESA), intended to permit the homogenization of ozone data from the European ozone ground-truthing network. During the active intercomparison periods, measurements were taken only when good conditions for sun or moon observations existed. Laboratory measurements using calibration lamps and helium-cadmium (HeCd) lasers were an essential part of both campaigns. The campaigns produced a high-quality database of total ozone and UV measurements and an accurate, up-to-date calibration and characterization of participating Brewers and Dobsons against the European standard instruments from the Regional Dobson Calibration Centre-Europe (RDCC-E) and the Regional Brewer Calibration Centre-Europe (RBCC-E). In the present work we focus on single monochromator Brewers and present a physics-based method to compensate for the stray-light effects in ozone retrieval using laboratory characterizations and radiative transfer modelling. The method was tested with independent data from the campaign.
We report the pressure dependence of the Néel temperature TN up to P≈27 GPa for the recently discovered itinerant antiferromagnet (IAFM) TiAu. The TN(P) phase boundary exhibits unconventional ...behavior in which the Néel temperature is enhanced from TN≈33 K at ambient pressure to a maximum of TN≈35 K occurring at P≈5.5 GPa. Upon a further increase in pressure, TN is monotonically suppressed to ∼22 K at P≈27 GPa. We also find a crossover in the temperature dependence of the electrical resistivity ρ in the antiferromagnetic (AFM) phase that is coincident with the peak in TN(P), such that the temperature dependence of ρ=ρ0+AnTn changes from n≈3 during the enhancement of TN to n≈2 during the suppression of TN. Based on an extrapolation of the TN(P) data to a possible pressure-induced quantum critical point, we estimate the critical pressure to be Pc≈45 GPa.
The Brewer reference triad Fioletov, V. E.; Kerr, J. B.; McElroy, C. T. ...
Geophysical research letters,
October 2005, Letnik:
32, Številka:
20
Journal Article
Recenzirano
It has been more than 20 years since the Brewer reference triad was established by Environment Canada at Toronto. The triad serves as a reference for traveling standard instruments that are used to ...calibrate Brewer spectrophotometers around the world. The members of the triad are calibrated on a regular basis at Mauna Loa, Hawaii. Regular tests made with an internal quartz halogen lamp make it possible to track the instrument response between the calibrations. A new analysis of available column ozone data records indicates that the uncertainty in the daily values derived from each instrument is approximately 0.6%. The random errors of individual observations are within ±1% for 90% of all measurements. Sources of potential errors in the individual Brewer measurements as well as quality control tools are also discussed.
During the Arctic polar springtime, dramatic ozone losses occur not only in the stratosphere but also in the underlying troposphere. These tropospheric ozone loss events have been observed over large ...areas, in the planetary boundary layer (PBL) throughout the Arctic. They are associated with enhanced concentrations of halogen species and are probably caused by catalytic reactions involving bromine monoxide (BrO) and perhaps also chlorine monoxide (ClO). The origin of the BrO, the principle species driving the ozone destruction, is thought to be the autocatalytic release of bromine from sea salt accumulated on the Arctic snow pack, followed by photolytic and heterogeneous reactions which produce and recycle the oxide. Satellite observations have shown the horizontal and temporal extent of large BrO enhancements in the Arctic troposphere, but the vertical distribution of the BrO has remained uncertain. Here we report BrO observations obtained from a high-altitude aircraft that suggest the presence of significant amounts of BrO not only in the PBL but also in the free troposphere above it. We believe that the BrO is transported from the PBL into the free troposphere through convection over large Arctic ice leads (openings in the pack ice). The convective transport also lifts ice crystals and water droplets well above the PBL, thus providing surfaces for heterogeneous reactions that can recycle BrO from less-reactive forms and thereby maintain its ability to affect the chemistry of the free troposphere.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A new algorithm to retrieve nitrogen dioxide (NO2) column densities using MKIV ("Mark IV") Brewer spectrophotometers is described. The method includes several improvements, such as a more recent ...spectroscopic data set, the reduction of measurement noise, interference by other atmospheric species and instrumental settings, and a better determination of the zenith sky air mass factor. The technique was tested during an ad hoc calibration campaign at the high-altitude site of Izaña (Tenerife, Spain) and the results of the direct sun and zenith sky geometries were compared to those obtained by two reference instruments from the Network for the Detection of Atmospheric Composition Change (NDACC): a Fourier Transform Infrared Radiometer (FTIR) and an advanced visible spectrograph (RASAS-II) based on the differential optical absorption spectrometry (DOAS) technique. To determine the extraterrestrial constant, an easily implementable extension of the standard Langley technique for very clean sites without tropospheric NO2 was developed which takes into account the daytime linear drift of stratospheric nitrogen dioxide due to photochemistry. The measurement uncertainty was thoroughly determined by using a Monte Carlo technique. Poisson noise and wavelength misalignments were found to be the most influential contributors to the overall uncertainty, and possible solutions are proposed for future improvements. The new algorithm is backward-compatible, thus allowing for the reprocessing of historical data sets.
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