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Industry advances have greatly reduced the cost and size of ground-based shortwave (SW) sensors for the ultraviolet, visible, and near-infrared spectral ranges that make up the solar spectrum, while simultaneously increasing their... more
Industry advances have greatly reduced the cost and size of ground-based shortwave (SW) sensors for the ultraviolet, visible, and near-infrared spectral ranges that make up the solar spectrum, while simultaneously increasing their ruggedness, reliability, and calibration accuracy needed for outdoor operation. These sensors and collocated meteorological equipment are an important part of the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) User Facility, which has supported parallel integrated measurements of atmospheric and surface properties for more than two decades at fixed and mobile sites around the world. The versatile capability of these ground-based measurements includes 1) rich spectral information required for retrieving cloud and aerosol microphysical properties, such as cloud phase, cloud particle size, and aerosol size distributions, and 2) high temporal resolution needed for capturing fast evolution of cloud microphysical properties in response t...
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This book is a comprehensive discussion of the applications of both satellite remote sensing and advanced ground-based remote sensing as related to polar science and operations. It discusses the various passive and active remote sensor... more
This book is a comprehensive discussion of the applications of both satellite remote sensing and advanced ground-based remote sensing as related to polar science and operations. It discusses the various passive and active remote sensor types before concentrating on specific geophysical applications. Its interdisciplinary approach - including atmospheric chemistry, meteorology, climate and radiation balance, sea-ice studies, physical oceanography, glaciology, ecology and hydrology - means that major advances and publications are highlighted, together with the state of the art in each area.
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Research Interests: Environmental Science, Geology, Multidisciplinary, Indian Ocean, Atmospheric sciences, and 15 moreAerosol, Relative Humidity, Geophysical, Radiative Transfer, Acoustic Radiative Transfer Model, Boundary Layer, Plume, Growth Factor, Radiative Forcing, Global Climate Model, Shortwave Radio, Outgoing Longwave radiation (OLR), Troposphere, downwelling, and Discrete Ordinates
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Humidity profiles retrieved from a ground-based millimeter-wave radiometer located at McMurdo Station, Antarctica, and the West Antarctica Ice Sheet Divide are presented, and their suitability to study the humidity of the polar climate is... more
Humidity profiles retrieved from a ground-based millimeter-wave radiometer located at McMurdo Station, Antarctica, and the West Antarctica Ice Sheet Divide are presented, and their suitability to study the humidity of the polar climate is assessed. The dry conditions of the Antarctic winter and spring are ideal for ground-based millimeter-wave measurements, and the retrievals appear to realistically reproduce the spatial and temporal variabilities of humidity at both sites. The radiometer has the ability to capture the daily variability of very low humidity (0.5–4 g/kg) in the low-to-mid troposphere with an uncertainty of 10%–20% during the Antarctic winter, spring, and summer. Despite the coarse vertical resolution (200–600 m in the first 4 km), the retrievals provide additional information with respect to the European Centre for Medium Range Weather Forecasts (ECMWF) profiles used as background information. The radiometer is also able to realistically identify the location and frequency of supersaturated layers with respect to ice in the mid troposphere. The occurrence of supersaturated layers is correlated with the occurrence of ice clouds identified by a cloud mask. Overall, results show that ground-based microwave and millimeter-wave radiometry is a viable complement to satellite observations to provide continuous information on the thermodynamic state of the low-to-mid troposphere at high latitudes.
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The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE) performed comprehensive meteorological and aerosol measurements and ground-based atmospheric remote sensing at two Antarctic... more
The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE) performed comprehensive meteorological and aerosol measurements and ground-based atmospheric remote sensing at two Antarctic stations using the most advanced instrumentation available. A suite of cloud research radars, lidars, spectral and broadband radiometers, aerosol chemical and microphysical sampling equipment, and meteorological instrumentation was deployed at McMurdo Station on Ross Island from December 2015 through December 2016. A smaller suite of radiometers and meteorological equipment, including radiosondes optimized for surface energy budget measurement, was deployed on the West Antarctic Ice Sheet between 4 December 2015 and 17 January 2016. AWARE provided Antarctic atmospheric data comparable to several well-instrumented high Arctic sites that have operated for many years and that reveal numerous contrasts with the Arctic in aerosol and cloud microphysical...
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Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying... more
Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events.
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The Western Antarctic Peninsula (WAP) is a region that has undergone significant climate change. The WAP region has experienced the largest regional climate warming over the past half century. There has been a concomitant trend in the... more
The Western Antarctic Peninsula (WAP) is a region that has undergone significant climate change. The WAP region has experienced the largest regional climate warming over the past half century. There has been a concomitant trend in the Southern Annular Mode (SAM) toward a positive polarity: several modeling studies have revealed that a combination of springtime ozone depletion and greenhouse gas increases are primarily responsible. Here we investigate possible linkages with mesoscale cyclone activity in the WAP region, as a potential climate system feedback mechanism. We have analyzed 7066 satellite images from the U.S. Antarctic Program satellite tracking facility at Palmer Station, Antarctica, comprising between 2-14 overpasses per day during 1991-94 (a time interval of large SAM variability). These images allow us to reliably identify and track mesoscale cyclones. The frequency of mesoscale cyclones in the WAP region during is found to be correlated with the SAM index, most strong...
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This study has used a combination of ocean color, backscattered ultraviolet, and passive microwave satellite data to investigate the impact of the springtime Antarctic ozone depletion on the base of the Antarctic marine food web - primary... more
This study has used a combination of ocean color, backscattered ultraviolet, and passive microwave satellite data to investigate the impact of the springtime Antarctic ozone depletion on the base of the Antarctic marine food web - primary production by phytoplankton. Spectral ultraviolet (UV) radiation fields derived from the satellite data are propagated into the water column where they force physiologically-based numerical models of phytoplankton growth. This large-scale study has been divided into two components: (1) the use of Total Ozone Mapping Spectrometer (TOMS) and Special Sensor Microwave Imager (SSM/I) data in conjunction with radiative transfer theory to derive the surface spectral UV irradiance throughout the Southern Ocean; and (2) the merging of these UV irradiances with the climatology of chlorophyll derived from SeaWiFS data to specify the input data for the physiological models.
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The quasars in our sample were originally selected and observed in a survey aimed at measuring the deuterium-to-hydrogen abundance ratio (D/H) in the Ly{alpha} forest. The observations were carried out with Keck HIRES through a... more
The quasars in our sample were originally selected and observed in a survey aimed at measuring the deuterium-to-hydrogen abundance ratio (D/H) in the Ly{alpha} forest. The observations were carried out with Keck HIRES through a 1.14" slit resulting in a velocity resolution of ~8km/s (FWHM). The spectra were extracted by the automated program, MAKEE, written by Tom Barlow. (2 data
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ABSTRACT
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ABSTRACT
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We use spectra of the 310 QSOs which include 140 pairs and 10 triplets. We use spectra that we obtained with LRIS on the Keck I telescope, the Kast spectrograph on the Lick 3-m Shane telescope and from CTIO and KPNO. We also use spectra... more
We use spectra of the 310 QSOs which include 140 pairs and 10 triplets. We use spectra that we obtained with LRIS on the Keck I telescope, the Kast spectrograph on the Lick 3-m Shane telescope and from CTIO and KPNO. We also use spectra from the SDSS data release 5 (DR5). We obtained spectra with LRIS from 2001 to 2004 September. (2 data files).
The first large sample of absorption lines in the spectra of pairs of QSOs that are close in the sky contains some surprises. The absorbers in the paired QSOs have very similar redshifts, within 200 km/s, as if the absorption is from slow... more
The first large sample of absorption lines in the spectra of pairs of QSOs that are close in the sky contains some surprises. The absorbers in the paired QSOs have very similar redshifts, within 200 km/s, as if the absorption is from slow moving blue and not red galaxies. The absorption is not from winds flowing out of galaxies at high velocities, suggesting that the metals entered the intergalactic medium at earlier times. We see no change in the absorption from neutral hydrogen in front of QSOs, and an increase in absorption to 6 Mpc behind QSOs. Either the QSO UV is emitted from the side facing us only, or these low luminosity QSOs emit for under 1 Myr at the intensity we seen. Supported by the NSF.
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We are using a new method to measure the amount of gas flowing out of galaxies in high velocity winds. We measure the small-scale clustering of QSO metal line absorption systems in 3D. We find that when one QSO shows an absorption system,... more
We are using a new method to measure the amount of gas flowing out of galaxies in high velocity winds. We measure the small-scale clustering of QSO metal line absorption systems in 3D. We find that when one QSO shows an absorption system, the spectrum of a second QSOs near in the sky often shows another absorption system within 200
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The climate responses to the sustained multi-decadal total solar irradiance (TSI) decrease in the pre-industrial era and global warming scenario are examined using the NCAR Community Atmosphere Model version 3 (CAM3) coupled with a... more
The climate responses to the sustained multi-decadal total solar irradiance (TSI) decrease in the pre-industrial era and global warming scenario are examined using the NCAR Community Atmosphere Model version 3 (CAM3) coupled with a mixed-layer slab ocean model. Both global average and regional surface air temperature (SAT) changes simulated by the model in the pre-industrial era are similar to that derived from diverse proxy data, indicating the model captures the influence of solar change on climate in the past and is useful for projecting the impact of solar variation on future climate. Diagnostic analysis demonstrates that TSI reduction shifts the AO/NAO state to a more negative index, resulting in observed regional SAT change in the model. In addition, the positive sea ice-solar radiation feedback amplifies the surface cooling due to the TSI decrease. The global annual average cooling effect induced by the TSI decrease in the global warming scenario is reduced by about 27% relat...
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The 1994 Arctic Ocean Section (AOS) and the 1997-98 Surface Heat Budget of the Arctic (SHEBA) experiments pioneered the deployment of advanced spectroradiometers for studies of clouds and climate, including Fourier Transform Infrared... more
The 1994 Arctic Ocean Section (AOS) and the 1997-98 Surface Heat Budget of the Arctic (SHEBA) experiments pioneered the deployment of advanced spectroradiometers for studies of clouds and climate, including Fourier Transform Infrared (FTIR) instruments. This type of instrumentation is now operating routinely at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) North Slope of Alaska (NSA) site, and the multiyear time series of these measurements is now revealing key optical and microphysical properties of the pervasive cloud cover over the Arctic Ocean, as they influence the surface energy budget. The most recent analysis has confirmed an indirect effect of anthropogenic aerosol (Arctic "haze") on the radiation balance, through its influence on the size distribution of liquid and ice particles in clouds. The detection of this aerosol indirect effect in FTIR data, and its implications for the budget of shortwave and longwave radiation at the Arctic Ocean ...
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Page 1. CHAPTER 5 Surface Ultraviolet Radiation: Past and Future Lead Authors: JB Kerr G. Seckmeyer Coauthors: AF Bais G. Bernhard M. Blumthaler SB Diaz N. Krotkov D. Lubin RL McKenzie AA Sabziparvar J. Verdebout ...
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ABSTRACT Distinct cloud regimes exist locally and globally that have been identified commonly through the use of objective classification methods. Such classification helps identify the meteorological conditions that are closely... more
ABSTRACT Distinct cloud regimes exist locally and globally that have been identified commonly through the use of objective classification methods. Such classification helps identify the meteorological conditions that are closely associated with specific cloud regimes, and facilitates evaluation of cloud parameterizations. This study focuses on cloud regime classification using k-means clustering for the Atmospheric Radiation Measurement Program's cloud observations at South Great Plain site, along with coincident satellite cloud measurements. Two approaches will be used and compared: cluster analysis using mean cloud statistics, coupled with a set of meteorological parameters; and cluster analysis using pixel-level cloud properties. The scale dependence of the classified cloud properties derived from the two clustering approaches will be investigated, with an aim of evaluating the scale dependent cloud parameterization for future high-resolution climate models. Cloud life cycle is also introduced in the classification process using the sequencing of the clusters and the evolution stage of typical synoptic weather patterns. For heavily precipitating clouds, cloud tracking of mesoscale convective systems and cyclone tracking of synoptic weather patterns will be employed to determine the evolution stage of clouds. Single column model results will be evaluated for different cloud regimes.
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In anticipation that unmanned aerial vehicles (UAVs) will have a useful role in atmospheric energy budget studies over sea ice, a Monte Carlo model is used to investigate three-dimensional radiative transfer over a highly inhomogeneous... more
In anticipation that unmanned aerial vehicles (UAVs) will have a useful role in atmospheric energy budget studies over sea ice, a Monte Carlo model is used to investigate three-dimensional radiative transfer over a highly inhomogeneous surface albedo involving open water, sea ice, and melt ponds. The model simulates the spatial variability in 550-nm downwelling irradiance and albedo that a UAV would measure above this surface and underneath an optically thick, horizontally homogeneous cloud. At flight altitudes higher than 100 m above the surface, an airborne radiometer will sample irradiances that are greatly smoothed horizontally as a result of photon multiple reflection. If one is interested in sampling the local energy budget contrasts between specific surface types, then the UAV must fly at a low altitude, typically within 20 m of the surface. Spatial upwelling irradiance variability in larger open water features, on the order of 1000 m wide, will remain apparent as high as 500...
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Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium (D or 2H), 3He, 4He and 7Li during the first few minutes of the universe. In this review we concentrate on recent data which give the primordial deuterium (D)... more
Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium (D or 2H), 3He, 4He and 7Li during the first few minutes of the universe. In this review we concentrate on recent data which give the primordial deuterium (D) abundance.We have measured the primordial D/H in gas with very nearly primordial abundances. We use the Lyman series absorption lines seen in the spectra of quasars. We have measured D/H towards three QSOs, while a fourth gives a consistent upper limit. All QSO spectra are consistent with a single value for D/H: 3.325+0.22−0.25X10−5. From about 1994 − 1996, there was much discussion of the possibility that some QSOs show much higher D/H, but the best such example was shown to be contaminated by H, and no other no convincing examples have been found. Since high D/H should be much easier to detect, and hence it must be extremely rare or non-existent.The new D/H measurements give the most accurate value for the baryon to photon ratio, η, and hence the ...