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Wilson, A, Scott RC, Cadeddu MP, Ghate V, Lubin D.  2018.  Cloud optical properties over West Antarctica from shortwave spectroradiometer measurements during AWARE. Journal of Geophysical Research-Atmospheres. 123:9559-9570.   10.1029/2018jd028347   AbstractWebsite

A shortwave spectroradiometer was deployed on the West Antarctic Ice Sheet (WAIS) as part of the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program ARM West Antarctic Radiation Experiment (AWARE). This instrument recorded 1-min averages of downwelling hemispheric spectral irradiance covering the wavelength range 350-2,200nm with spectral resolution 3 and 10nm for wavelengths shorter and longer than 1,000nm, respectively. Using simultaneous micropulse lidar data to identify the thermodynamic phase of stratiform clouds, a radiative transfer algorithm is used to retrieve optical depth and effective droplet (or particle) size for single-phase liquid water and ice water clouds. The AWARE campaign on the WAIS first sampled typical climatological conditions between 7 December 2015 and 9 January 2016 and then a much warmer air mass with more moisture associated with a surface melt event between 10 and 17 January 2016. Before the melt event most liquid cloud effective droplet radii were consistent with pristine polar maritime clouds (mode radius 13.5m) but showed a second local maximum in the distribution (at 8m) consistent with colder, moisture-limited conditions. Most ice clouds sampled occurred before the melt event (mode optical depth 4 and effective particle size 19m). During the melt event liquid water cloud optical depth nearly doubled (mode value increasing from 8 to 14). AWARE therefore sampled on the WAIS two cases relevant to climate model simulations: typical current climatological conditions, followed by warmer meteorology possibly consistent with future increasing surface melt scenarios.

Mulmenstadt, J, Lubin D, Russell LM, Vogelmann AM.  2012.  Cloud properties over the North Slope of Alaska: Identifying the prevailing meteorological regimes. Journal of Climate. 25:8238-8258.   10.1175/jcli-d-11-00636.1   AbstractWebsite

Long time series of Arctic atmospheric measurements are assembled into meteorological categories that can serve as test cases for climate model evaluation. The meteorological categories are established by applying an objective k-means clustering algorithm to 11 years of standard surface-meteorological observations collected from 1 January 2000 to 31 December 2010 at the North Slope of Alaska (NSA) site of the U.S. Department of Energy Atmospheric Radiation Measurement Program (ARM). Four meteorological categories emerge. These meteorological categories constitute the first classification by meteorological regime of a long time series of Arctic meteorological conditions. The synoptic-scale patterns associated with each category, which include well-known synoptic features such as the Aleutian low and Beaufort Sea high, are used to explain the conditions at the NSA site. Cloud properties, which are not used as inputs to the k-means clustering, are found to differ significantly between the regimes and are also well explained by the synoptic-scale influences in each regime. Since the data available at the ARM NSA site include a wealth of cloud observations, this classification is well suited for model observation comparison studies. Each category comprises an ensemble of test cases covering a representative range in variables describing atmospheric structure, moisture content, and cloud properties. This classification is offered as a complement to standard case-study evaluation of climate model parameterizations, in which models are compared against limited realizations of the Earth atmosphere system (e.g., from detailed aircraft measurements).

Lubin, D, Vogelmann AM.  2011.  The influence of mixed-phase clouds on surface shortwave irradiance during the Arctic spring. Journal of Geophysical Research-Atmospheres. 116   10.1029/2011jd015761   AbstractWebsite

The influence of mixed-phase stratiform clouds on the surface shortwave irradiance is examined using unique spectral shortwave irradiance measurements made during the Indirect and Semi-Direct Aerosol Campaign (ISDAC), supported by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program. An Analytical Spectral Devices (ASD, Inc.) spectroradiometer measured downwelling spectral irradiance from 350 to 2200 nm in one-minute averages throughout April-May 2008 from the ARM Climate Research Facility's North Slope of Alaska (NSA) site at Barrow. This study examines spectral irradiance measurements made under single-layer, overcast cloud decks having geometric thickness <3000 m. Cloud optical depth is retrieved from irradiance in the interval 1022-1033 nm. The contrasting surface radiative influences of mixed-phase clouds and liquid-water clouds are discerned using irradiances in the 1.6-mu m window. Compared with liquid-water clouds, mixed-phase clouds during the Arctic spring cause a greater reduction of shortwave irradiance at the surface. At fixed conservative-scattering optical depth (constant optical depth for wavelengths lambda < 1100 nm), the presence of ice water in cloud reduces the near-IR surface irradiance by an additional several watts-per-meter-squared. This additional reduction, or supplemental ice absorption, is typically similar to 5 W m(-2) near solar noon over Barrow, and decreases with increasing solar zenith angle. However, for some cloud decks this additional absorption can be as large as 8-10 W m(-2).

McFarquhar, GM, Ghan S, Verlinde J, Korolev A, Strapp JW, Schmid B, Tomlinson JM, Wolde M, Brooks SD, Cziczo D, Dubey MK, Fan JW, Flynn C, Gultepe I, Hubbe J, Gilles MK, Laskin A, Lawson P, Leaitch WR, Liu P, Liu XH, Lubin D, Mazzoleni C, Macdonald AM, Moffet RC, Morrison H, Ovchinnikov M, Shupe MD, Turner DD, Xie SC, Zelenyuk A, Bae K, Freer M, Glen A.  2011.  Indirect and semi-direct aerosol campaign: The impact of Arctic aerosols on clouds. Bulletin of the American Meteorological Society. 92:183-+.   10.1175/2010bams2935.1   AbstractWebsite

INDIRECT AND SEMI-DIRECT AEROSOL CAMPAIGN (ISDAC): THE IMPACT OF ARCTIC AEROSOLS ON CLOUDS A comprehensive dataset of microphysical and radiative properties of aerosols and clouds in the boundary layer in the vicinity of Barrow, Alaska, was collected in April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC). ISDAC's primary aim was to examine the effects of aerosols, including those generated by Asian wildfires, on clouds that contain both liquid and ice. ISDAC utilized the Atmospheric Radiation Measurement Pro-gram's permanent observational facilities at Barrow and specially deployed instruments measuring aerosol, ice fog, precipitation, and radiation. The National Research Council of Canada Convair-580 flew 27 sorties and collected data using an unprecedented 41 state-of-the-art cloud and aerosol instruments for more than 100 h on 12 different days. Aerosol compositions, including fresh and processed sea salt, biomass-burning particles, organics, and sulfates mixed with organics, varied between flights. Observations in a dense arctic haze on 19 April and above, within, and below the single-layer stratocumulus on 8 and 26 April are enabling a process-oriented understanding of how aerosols affect arctic clouds. Inhomogeneities in reflectivity, a close coupling of upward and downward Doppler motion, and a nearly constant ice profile in the single-layer stratocumulus suggests that vertical mixing is responsible for its longevity. observed during ISDAC. Data acquired in cirrus on flights between Barrow and Fairbanks, Alaska, are improving the understanding of the performance of cloud probes in ice. Ultimately, ISDAC data will improve the representation of cloud and aerosol processes in models covering a variety of spatial and temporal scales, and determine the extent to which surface measurements can provide retrievals of aerosols, clouds, precipitation, and radiative heating.

Lubin, D, Vogelmann AM.  2007.  Expected magnitude of the aerosol shortwave indirect effect in springtime Arctic liquid water clouds. Geophysical Research Letters. 34   10.1029/2006gl028750   AbstractWebsite

Radiative transfer simulations are used to assess the expected magnitude of the diurnally-averaged shortwave aerosol first indirect effect in Arctic liquid water clouds, in the context of recently discovered longwave surface heating of order 3 to 8 W m(-2) by this same aerosol effect detected at the Barrow, Alaska, ARM Site. We find that during March and April, shortwave surface cooling by the first indirect effect is comparable in magnitude to the longwave surface heating. During May and June, the shortwave surface cooling exceeds the longwave heating. Due to multiple reflection of photons between the snow or sea ice surface and cloud base, the shortwave first indirect effect may be easier to detect in surface radiation measurements than from space.

Morrow, E, Scheeres DJ, Lubin D.  2001.  Solar sail orbit operations at asteroids. Journal of Spacecraft and Rockets. 38:279-286.   10.2514/2.3682   AbstractWebsite

The inherent capabilities of solar sails and that they need no onboard supplies of fuel for propulsion make them well suited for use in long-term, multiple-objective missions. They are especially well suited for the exploration of asteroids, where one spacecraft could rendezvous with a number of asteroids in succession. The orbital mechanics of solar sail operations about an asteroid, however, have not yet been studied in detail. Building an previous studies, we find both hovering points and orbiting trajectories about various sized asteroids using equations of motion for a solar sail spacecraft. The orbiting trajectories are stable and offer good coverage of the asteroid surface, although restrictions on sail acceleration are needed for smaller asteroids.

Podgorny, I, Lubin D.  1998.  Biologically active insolation over Antarctic waters: Effect of a highly reflecting coastline. Journal of Geophysical Research-Oceans. 103:2919-2928.   10.1029/97jc02763   AbstractWebsite

Near an Antarctic coastline or sea ice edge, multiple reflection of photons between the high-albedo surface and a cloud will increase the downwelling surface insolation not only over the high-albedo surface itself but also out over the adjacent open water. This insolation enhancement is examined with a Monte Carlo radiative transfer model. The insolation enhancement extends to a typical distance of 4 km out to sea, with the most important effects being within 2 km of the coastline. The strength of the multiple reflection effect depends primarily on cloud base height and cloud optical depth and only slightly on cloud geometrical thickness. The insolation enhancement is also a function of wavelength, being larger for ultraviolet wavelengths than for the visible. This is due to a slightly greater contribution from Rayleigh scattering at the shorter wavelengths, although at ultraviolet wavelengths where ozone absorption is strong, tropospheric ozone absorption can offset the Rayleigh scattering contribution at larger cloud optical depths. On the basis of the limited range of the multiple reflection effect (2-4 km out to sea) the insolation enhancement due to the high-albedo coastline is unlikely to be a major influence on the primary productivity of all Antarctic waters; however, it may influence phytoplankton blooms near the coast and photobiological experiments carried out at coastal research stations. Also, the insolation enhancement may have significance in sea ice leads and polynyas.

Lubin, D, Garrity C, Ramseier RO, Whritner RH.  1997.  Total sea ice concentration retrieval from the SSM/I 85.5 GHz channels during the Arctic summer. Remote Sensing of Environment. 62:63-76.   10.1016/s0034-4257(97)00081-3   AbstractWebsite

During the 1994 Arctic Ocean Section, a joint voyage across the Arctic Ocean, by the U.S. Coast Guard Cutter Polar Sea and the Canadian Coast Guard Ship Louis S. St.-Laurent, telemetry from the Defense Meteorological Satellite Program (DMSP) polar orbiters was tracked by a shipboard antenna. Special Sensor Microwave Imager (SSM/I) data was used to generate maps of total sea. ice concentration, using the NASA Team algorithm with the 19 GHz and 37 GHz channels, and using a polarization-based algorithm with the 85.5 GHz channels. When compared with shipboard ice observations, the total sea ice concentration estimated from the 85.5 GHz algorithm are at least as accurate as those from the algorithm that uses only the lower SSM/I frequencies, despite the potential for greater difficulty in dealing with cloud liquid water contamination in the 85.5 GHz signal during the Arctic summer. Near the edge of the ice pack, the 85.5 GHz algorithm often provided more accurate estimates of total ice concentration when compared with surface observations, most likely because of the finer grid spacing at 85.5 GHz (12.5 km vs. 25 km for 37 GHz). However, when using the 85.5 GHz algorithm over regions of lower ice concentration, the reference polarizations in a given image must be chosen with care because over lower sea ice concentration the polarization-based algorithm is more sensitive to cloud opacity and can easily and substantially underestimate the ice concentration. The 85.5 GHz total sea ice retrievals are compared with in situ snow wetness measurements. This comparison suggests that, despite the higher atmospheric opacity at 85.5 GHz, information about sea ice surface properties that affect emissivity can be obtained from these SSM/I channels. (C) Elsevier Science Inc., 1997.

Lubin, D, Chen JP, Pilewskie P, Ramanathan V, Valero FPJ.  1996.  Microphysical examination of excess cloud absorption in the tropical atmosphere. Journal of Geophysical Research-Atmospheres. 101:16961-16972.   10.1029/96jd01154   AbstractWebsite

To investigate the excess shortwave absorption by clouds, a numerical cloud generation model has been coupled to a plane-parallel discrete ordinates radiative transfer model. The former was used in a time-dependent fashion to generate a cumulonimbus turret and three types of cirrus anvil (precipitating, extended, detached) representing three stages of cloud evolution outward from the turret. The cloud particle size distributions, as a function of altitude, were used as input to the radiative transfer model using indices of refraction for pure water and pure ice and equivalent sphere Mie theory. The radiative transfer model was used to calculate the ratio of cloud forcing at the surface to cloud forcing at the top of the atmosphere, both for the broadband shortwave and as a function of wavelength. Recent empirical studies have placed this cloud forcing ratio at around 1.5, and our coupled model results approach this value for small solar zenith angles, when the cloud contains large (>100 mu m) ice particles that absorb significantly in the near infrared (primarily the 1.6-mu m window). However, the empirical studies are based on diurnal averages, and our plane-parallel radiative transfer model yields an area and diurnally averaged cloud forcing ratio of only 1.18 for a tropical cumulonimbus and cirrus anvil system, primarily because of the rapid decrease of the ratio with solar zenith angle. The ratio decreases because of the increase in albedo with solar zenith angle, which is a characteristic feature of plane-parallel clouds. Adding dust or aerosol to the cloud layers, to make them absorb at visible wavelengths, makes the instantaneous cloud forcing ratio larger for an overhead Sun but also makes the solar zenith angle dependence in the cloud forcing ratio more pronounced. These two effects cancel, eliminating interstitial aerosol as a possible explanation for the excess cloud absorption in plane-parallel radiative transfer modeling. The strong dependence of the surface/top of the atmosphere cloud forcing ratio on solar zenith angle may be a fundamental defect with the plane-parallel approach to solar radiative transfer in a cloudy atmosphere.