Publications

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2007
Bais, AF, Lubin D, Arola A, Bernhard G, Blumthaler M, Chubarova N, Erlick C, Gies HP, Krotkov NA, Lantz K, Mayer B, Mckenzie RL, d. Piacentini R, Seckmeyer G, Slusser JR, Zerefos CZ.  2007.  Surface Ultraviolet Radiation: Past, Present, and Future. Scientific assessment of ozone depletion: 2006. ( Organization W, Ed.)., Geneva, Switzerland: World Meteorological Organization Abstract
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2006
McComiskey, A, Ricchiazzi P, Gautier C, Lubin D.  2006.  Assessment of a three dimensional model for atmospheric radiative transfer over heterogeneous land cover. Geophysical Research Letters. 33   10.1029/2005gl025356   AbstractWebsite

A three-dimensional (3D) atmospheric radiative transfer model that explicitly represents surface albedo heterogeneity is tested against a one-dimensional model and surface irradiance observations in a polar region where land cover heterogeneity is high. For observations located near high latitude coastlines, the contrast between the highly absorbing ocean and reflective snow surface creates spatial heterogeneity, or a 3D effect, around the observation site. The resulting effect on radiation at the sensor should be taken into account when using a solar radiative transfer model to interpret measurements. This assessment shows that better closure is obtained with a three-dimensional model (<= 5%) versus a plane-parallel model (<= 7%). The importance of the surface 3D effect increases with aerosol or cloud optical depth and with surface albedo contrast. The model used here can be implemented at any surface site given the surrounding land cover properties.

Lubin, D, Vogelmann AM.  2006.  A climatologically significant aerosol longwave indirect effect in the Arctic. Nature. 439:453-456.   10.1038/nature04449   AbstractWebsite

The warming of Arctic climate and decreases in sea ice thickness and extent(1,2) observed over recent decades are believed to result from increased direct greenhouse gas forcing, changes in atmospheric dynamics having anthropogenic origin(3-5), and important positive reinforcements including ice - albedo and cloud - radiation feedbacks(6). The importance of cloud - radiation interactions is being investigated through advanced instrumentation deployed in the high Arctic since 1997 (refs 7, 8). These studies have established that clouds, via the dominance of longwave radiation, exert a net warming on the Arctic climate system throughout most of the year, except briefly during the summer(9). The Arctic region also experiences significant periodic influxes of anthropogenic aerosols, which originate from the industrial regions in lower latitudes(10). Here we use multisensor radiometric data(7,8) to show that enhanced aerosol concentrations alter the microphysical properties of Arctic clouds, in a process known as the 'first indirect' effect(11,12). Under frequently occurring cloud types we find that this leads to an increase of an average 3.4 watts per square metre in the surface longwave fluxes. This is comparable to a warming effect from established greenhouse gases and implies that the observed longwave enhancement is climatologically significant.

Lubin, D, Massom R, SpringerLink.  2006.  Polar Remote Sensing Volume I: Atmosphere and Oceans. , Berlin, Heidelberg: Praxis Pub., Chichester, UK Abstract
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Massom, R, Lubin D, SpringerLink.  2006.  Polar Remote Sensing Volume II: Ice Sheets. , Berlin, Heidelberg: Praxis Pub., Chichester, UK Abstract
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2005
Kirkman, D, Tytler D, Suzuki N, Melis C, Hollywood S, James K, So G, Lubin D, Jena T, Norman ML, Paschos P.  2005.  The HI opacity of the intergalactic medium at redshifts 1.6 < z < 3.2. Monthly Notices of the Royal Astronomical Society. 360:1373-1380.   10.1111/j.1365-2966.2005.09126.x   AbstractWebsite

We use high-quality echelle spectra of 24 quasi-stellar objects to provide a calibrated measurement of the total amount of Ly alpha forest absorption (DA) over the redshift range 2.2 < z < 3.2. Our measurement of DA excludes absorption from metal lines or the Ly alpha lines of Lyman-limit systems and damped Ly alpha systems. We use artificial spectra with realistic flux calibration errors to show that we are able to place continuum levels that are accurate to better than 1 per cent. When we combine our results with our previous results between 1.6 < z < 2.2, we find that the redshift evolution of DA is well described over f1.6 < z < 3.2 as A (1 +z)(gamma), where A = 0.0062 and gamma = 2.75. We detect no significant deviations from a smooth power-law evolution over the redshift range studied. We find less H i absorption than expected at z = 3, implying that the ultraviolet background is similar to 40 per cent higher than expected. Our data appears to be consistent with an H i ionization rate of Gamma similar to 1.4 x 10(-12) s(-1).

Suzuki, N, Tytler D, Kirkman D, O'Meara JM, Lubin D.  2005.  Predicting QSO continua in the Ly alpha forest. Astrophysical Journal. 618:592-600.   10.1086/426062   AbstractWebsite

We present a method to make predictions with sets of correlated data values, in this case QSO flux spectra. We predict the continuum in the Lyalpha forest of a QSO, from 1020 to 1216 8, using the spectrum of that QSO from 1216 to 1600 Angstrom. We find correlations between the unabsorbed flux in these two wavelength regions in the Hubble Space Telescope (HST) spectra of 50 QSOs. We use principal component analysis to summarize the variety of these spectra, relate the weights of the principal components for 1020-1600 Angstrom to the weights for 1216-1600 Angstrom, and apply this relation to make predictions. We test the method on the HST spectra and find an average absolute flux error of 9%, with a range of 3%-30%, where individual predictions are systematically too low or too high. We mention several ways in which the predictions might be improved.

2004
Tytler, D, O'Meara JM, Suzuki N, Kirkman D, Lubin D, Orin A.  2004.  The Kast ground-based ultraviolet spectral survey of 79 quasi-stellar objects at redshift 2 for Ly alpha forest and metal absorption. Astronomical Journal. 128:1058-1077.   10.1086/423293   AbstractWebsite

We present spectra of 79 bright QSOs obtained with the Kast spectrograph on the 3 m Shane Telescope at Lick Observatory. The QSOs have emission redshifts 1.89 - 2.45, and most are near the mean value of z(em) = 2.17. Two of them, one a new discovery, are broad absorption line QSOs. The spectra have similar to250 km s(-1) resolution, and they cover 3175 - 5880 Angstrom with signal-to-noise ratios of 6 - 20 per 1.13 Angstrom pixel in the Lyalpha forest between Lyalpha and Lybeta. We show the continuum levels that we used in a previous paper to make a calibrated measurement of the amount of absorption in the Lyalpha forest at z = 1.9. We measure redshifts for 140 absorption-line systems, and we list the metal ions that we see in each system. We identify 526 emission lines and list their observed wavelengths, which we use to obtain new emission redshifts. We find that three emission lines, or line blends, in the forest have mean rest wavelengths of 1070.95 +/- 1.00, 1123.13 +/- 0.51, and 1175.88 +/- 0.30 Angstrom.

Lubin, D, Arrigo KR, van Dijken GL.  2004.  Increased exposure of Southern Ocean phytoplankton to ultraviolet radiation. Geophysical Research Letters. 31   10.1029/2004gl019633   AbstractWebsite

Satellite remote sensing of both surface solar ultraviolet radiation (UVR) and chlorophyll over two decades shows that biologically significant ultraviolet radiation increases began to occur over the Southern Ocean three years before the ozone "hole'' was discovered. Beginning in October 1983, the most frequent occurrences of enhanced UVR over phytoplankton-rich waters occurred in the Weddell Sea and Indian Ocean sectors of the Southern Ocean, impacting 60% of the surface biomass by the late 1990s. These results suggest two reasons why more serious impacts to the base of the marine food web may not have been detected by field experiments: ( 1) the onset of UVR increases several years before dedicated field work began may have impacted the most sensitive organisms long before such damage could be detected, and ( 2) most biological field work has so far not taken place in Antarctic waters most extensively subjected to enhanced UVR.

Berque, J, Lubin D, Somerville RCJ.  2004.  Infrared radiative properties of the Antarctic plateau from AVHRR data. Part I: Effect of the snow surface. Journal of Applied Meteorology. 43:350-362.   10.1175/1520-0450(2004)043<0350:irpota>2.0.co;2   AbstractWebsite

The effective scene temperature, or "brightness temperature," measured in channel 3 (3.5-3.9 m m) of the Advanced Very High Resolution Radiometer (AVHRR) is shown to be sensitive, in principle, to the effective particle size of snow grains on the Antarctic plateau, over the range of snow grain sizes reported in field studies. In conjunction with a discrete ordinate method radiative transfer model that couples the polar atmosphere with a scattering and absorbing snowpack, the thermal infrared channels of the AVHRR instrument can, therefore, be used to estimate effective grain size at the snow surface over Antarctica. This is subject to uncertainties related to the modeled top-of-atmosphere bidirectional reflectance distribution function resulting from the possible presence of sastrugi and to lack of complete knowledge of snow crystal shapes and habits as they influence the scattering phase function. However, when applied to NOAA-11 and NOAA-12 AVHRR data from 1992, the snow grain effective radii of order 50 mum are retrieved, consistent with field observations, with no apparent discontinuity between two spacecraft having different viewing geometries. Retrieved snow grain effective radii are 10-20-mum larger when the snow grains are modeled as hexagonal solid columns rather than as spheres with a Henyey-Greenstein phase function. Despite the above-mentioned uncertainties, the retrievals are consistent enough that one should be able to monitor climatically significant changes in surface snow grain size due to major precipitation events. It is also shown that a realistic representation of the surface snow grain size is critical when retrieving the optical depth and effective particle radius of clouds for the optically thin clouds most frequently encountered over the Antarctic plateau.

Lubin, D.  2004.  Thermodynamic phase of maritime Antarctic clouds from FTIR and supplementary radiometric data. Journal of Geophysical Research-Atmospheres. 109   10.1029/2003jd003979   AbstractWebsite

A Fourier Transform Infrared (FTIR) spectroradiometer was deployed at Palmer Station, Antarctica, from 1 September to 17 November 1991. This instrument is similar to the Atmospheric Emitted Radiance Interferometer (AERI) deployed with the U. S. Department of Energy Atmospheric Radiation Measurement (ARM) program. The instrument measured downwelling zenith radiance in the spectral interval 400 2000 cm(-1), at a resolution of 1 cm(-1). The spectral radiance measurements, which can be expressed as spectral brightness temperature T-b(nu), contain information about cloud optical properties in the middle infrared window (800-1200 cm(-1) 1, 8.3-12.5 mm). In this study, this information is exploited to (1) provide additional characterization of Antarctic cloud radiative properties, and (2) demonstrate how multisensor analysis of ARM data can potentially retrieve cloud thermodynamic phase. Radiative transfer simulations demonstrate how T-b(nu) is a function of cloud optical depth tau, effective particle radius r(e), and thermodynamic phase. For typical values of tau and r(e), the effect of increasing the ice fraction of the total optical depth is to flatten the slope of T-b(nu) between 800 1000 cm(-1). For optically thin clouds (tau similar to 3) and larger ice particles (re(ice) > 50 mm) the behavior of T-b(nu) in this interval switches from a decrease with increasing wavenumber n to an increase with nu, once the ice fraction of the total optical depth exceeds similar to0.7. The FTIR spectra alone cannot be interpreted to obtain thermodynamic phase, because a relatively small slope in T-b(nu) between 800-1000 cm(-1) could represent either an optically thin cloud in the ice or mixed phase, or an optically thick cloud radiating as a blackbody. Sky observations and ancillary radiometric data are needed to sort the FTIR spectra into categories of small cloud optical depth, where the mid-IR window data can be interpreted; and larger cloud optical depth, where the FTIR data contain information only about cloud base temperature. Spectral solar ultraviolet (UV) irradiance measurements from the U. S. National Science Foundation's UV Monitor at Palmer Station are used to estimate area-averaged effective cloud optical depth tau(sw), and these estimates are used to sort the FTIR data. FTIR measurements with colocated tau(sw) < 16 are interpreted to estimate cloud thermodynamic phase. Precipitating cloud decks generally show flatter slopes in T-b(ν), consistent with the ice or mixed phase. Altostratus decks show a larger range in T-b(ν) slope than low cloud decks, including increasing slopes with ν, suggesting a more likely occurrence of the ice phase. This study illustrates how cloud thermodynamic phase can be defensibly retrieved from FTIR data if high quality shortwave radiometric data are also available to sort the FTIR measurements by cloud opacity, and both data types are available at the ARM sites.

Xiong, XZ, Storvold R, Stamnes K, Lubin D.  2004.  Derivation of a threshold function for the Advanced Very High Resolution Radiometer 3.75 mu m channel and its application in automatic cloud discrimination over snow/ice surfaces. International Journal of Remote Sensing. 25:2995-3017.   10.1080/01431160310001619553   AbstractWebsite

The distinct contrast between the reflectance of solar radiation in Advanced Very High Resolution Radiometer (AVHRR) channel 3 (3.75 mum) by clouds and by bright surfaces provides an effective means of cloud discrimination over snow/ice surfaces. A threshold function for the top-of-atmosphere (TOA) albedo in channel 3 (r(3)) is derived and used to develop an improved method for cloud discrimination over snow/ice surfaces that makes explicit use of TOA r(3) . Corrections for radiance anisotropy and temperature effects are required to derive accurate values of r(3) from satellite measurements and to utilize the threshold function. It has been used to retrieve cloud cover fractions from National Oceanic and Atmospheric Administration (NOAA)-14 AVHRR data over the Arctic Ocean and over the North Slope of Alaska (NSA) Atmospheric Radiation Measurement (ARM) site in Barrow, Alaska. The retrieved cloud fractions are in good agreement with SHEBA (Surface HEat Budget of the Arctic Ocean) surface visual observations and with NSA cloud radar and lidar observations, respectively. This method can be utilized to improve cloud discrimination over snow/ice surfaces for any satellite sensor with a channel near 3.7 mum.

2003
Arrigo, KR, Lubin D, van Dijken GL, Holm-Hansen O, Morrow E.  2003.  Impact of a deep ozone hole on Southern Ocean primary production. Journal of Geophysical Research-Oceans. 108   10.1029/2001jc001226   AbstractWebsite

[1] Field studies show that photosynthesis by Antarctic phytoplankton is inhibited by the increased ultraviolet radiation (UVR) resulting from springtime stratospheric ozone (O-3) depletion. To extend previous observations, a numerical model utilizing satellite-derived distributions of O-3, clouds, sea ice, surface temperature, and phytoplankton biomass was developed to study the hemispheric-scale seasonal effects of a deep Antarctic O-3 hole on primary production in the Southern Ocean. UVR-induced losses of surface phytoplankton production were substantial under all O-3 conditions, mostly due to UVA. However, when integrated to the 0.1% light depth, the loss of primary production resulting from enhanced fluxes of UVB due to O-3 depletion was <0.25%. The loss of primary production is minimized by the strong attenuation of UVR within the water column and by sea ice which is at its peak extent at the time of the most severe O-3 depletion.

Lubin, D, Lynch S, Clarke R, Morrow E, Hart S.  2003.  Increasing reflectivity of the Antarctic ocean-atmosphere system: Analysis of Total Ozone Mapping Spectrometer (TOMS) and passive microwave data for 1979-1994. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd002702   AbstractWebsite

Measurements of Lambert equivalent reflectance at 380 nm from the Total Ozone Mapping Spectrometer (TOMS) instrument have shown increases in reflectivity between 1979 and 1994 over much of the Southern Ocean, encompassing 280degrees in longitude. These trends represent a possible change in the state of the Antarctic ocean-atmosphere system related to recent climate warming. To determine if these reflectivity trends are due to changes in cloud cover or sea ice, or both, the TOMS data were collocated with a contemporaneous passive microwave satellite data set from the scanning multichannel microwave radiometer and the Special Sensor Microwave Imager. The passive microwave data sets specify total sea ice concentration, retrieved by a uniform method for all years using the NASA Team algorithm. To first order the locations of TOMS reflectivity increases coincide with regions where sea ice concentration has increased over the past 2 decades, signifying that the TOMS trends are the result of trends in underlying sea ice and not cloud cover. However, when the TOMS reflectivity measurements are sorted into fixed sea ice concentration bins of 0.1 width, the TOMS data also show increasing reflectivity trends in regions where sea ice extent has been decreasing (Amundsen and Bellingshausen Seas and the Western Antarctic Peninsula). Over open water, TOMS reflectivity trends are less convincing and may be artifacts related to uncertainties in passive microwave sea ice identification. These results suggest that a significant component of the Southern Ocean TOMS reflectivity trends may be a gradual increase in the albedo of the underlying sea ice. This could be caused by a gradual lengthening of the sea ice season, with a concomitant increase in the persistence of dry snow on the sea ice cover.

Satheesh, SK, Lubin D.  2003.  Short wave versus long wave radiative forcing by Indian Ocean aerosols: Role of sea-surface winds. Geophysical Research Letters. 30   10.1029/2003gl017499   AbstractWebsite

[1] Recent observations over the Indian Ocean have demonstrated aerosol short wave absorption as high as 20 to 25 W m(-2). The aerosol net radiative forcing reduces substantially while considering the broad spectrum including the long wave region (due to large infrared forcing which is opposite in sign). At highwinds, presence of large amounts of sea-salt aerosols (absorbing in infrared) enhances the infrared forcing; hence reduces the net radiative forcing. In this paper, we examine the role of sea-surface winds (which enhance sea-salt aerosols) on long wave aerosol forcing. Even at moderate winds (6-10 m s(-1)), the short wave forcing reduces by similar to45% due to the dominance of sea-salt aerosols. At high winds (>10 m s(-1)), a major fraction of the long wave forcing is contributed by sea-salt (more than 70%). Our studies show that neglecting aerosol long wave radiative forcing can cause large errors in climate models.

Garrity, C, Lubin D, Kern S, Pedersen LT.  2003.  Linescan camera evaluation of SSM/I 85.5 GHz sea ice retrieval (vol 83, pg 472, 2002). Remote Sensing of Environment. 84:321-321.   10.1016/s0034-4257(02)00180-3   AbstractWebsite
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2002
Xiong, XZ, Li W, Lubin D, Stamnes K.  2002.  Evaluating the principles of cloud remote sensing with AVHRR and MAS imagery over SHEBA. Journal of Geophysical Research-Oceans. 107   10.1029/2000jc000424   AbstractWebsite

[1] A rigorous discrete ordinates radiative transfer formulation has been applied to two Advanced Very High Resolution Radiometer (AVHRR) images extracted from telemetry collected by the CCGS Des Groseilliers satellite tracking system during SHEBA to estimate cloud optical depth and effective radius of the cloud droplet size distribution. The two cases, from 2 and 3 June 1998, were chosen for analysis because (1) the images contained mostly liquid water clouds and (2) contemporaneous MODIS Airborne Simulator (MAS) overflight imagery was available for these AVHRR overpasses. The objective is to apply the same detailed radiative transfer formulation to both the MAS and AVHRR data so that the quality of the retrievals from the latter can be evaluated. Retrievals of cloud optical properties from MAS are assumed to be more reliable, because (1) all MAS channels have direct radiometric calibration, (2) the higher spatial resolution of MAS (50 m nadir versus 1.1 km nadir with AVHRR) should yield smaller uncertainties related to partially cloudy pixels in a given study area, and (3) effective droplet radius can be retrieved directly from the MAS 1.62-mum m channel without additional uncertainties involved with subtracting a thermal radiance component. Examination of the retrievals from both sensors in these two cases reveals considerable spatial variability (more than a factor of 2) in cloud optical depth, on a variety of scales ranging from tens of meters to tens of kilometers, even for relatively uniform liquid water clouds. Retrievals of cloud effective droplet radius from AVHRR are generally consistent with those from MAS, suggesting that AVHRR can be reliably used to estimate this quantity. However, AVHRR-based retrievals of cloud optical depth are subject to large errors that result from small uncertainties in the absolute radiometric calibration of AVHRR channel 2. Using recalibration coefficients from one of the more robust AVHRR postlaunch calibration efforts, the cloud optical depths that we retrieved from NOAA 14 AVHRR channel 2 are consistently 30-50% larger than those obtained from MAS. The intercomparison of MAS and AVHRR retrievals of cloud optical depth also revealed errors with AVHRR due to partial cloud cover, and these errors are not immediately apparent when examining the AVHRR retrievals alone. If the AVHRR retrievals are averaged to spatial resolutions of order 10-30 km, they appear to become more stable for use in applications such as atmospheric energy budget calculations.

Lubin, D, Ricchiazzi P, Payton A, Gautier C.  2002.  Significance of multidimensional radiative transfer effects measured in surface fluxes at an Antarctic coastline. Journal of Geophysical Research-Atmospheres. 107   10.1029/2001jd002030   AbstractWebsite

[1] At a coastal high-latitude site, multiple reflection of photons between the high albedo surface and an overlying cloud can enhance the downwelling shortwave flux out over the adjacent open water to a distance of several kilometers. This coastal albedo effect has been predicted by theoretical radiative transfer studies and has also been measured under ideal conditions. In this study, three multispectral solar ultraviolet radiometers were deployed in the vicinity of Palmer Station, Antarctica (64degrees 46'S, 64degrees 04'W) to determine the prevalence of the coastal albedo effect under the region's natural variability in cloud cover. One radiometer was deployed near the base of a glacier, and the other two radiometers were deployed on Janus Island and Outcast Island, islets similar to2.8 km (1.5 nautical miles) and 5.6 km (3 nautical miles) distant from Palmer Station, respectively. The radiometers were operated simultaneously for 16 days during late December 1999 and January 2000. Under all cloudy sky conditions sampled by this experiment the coastal albedo effect is seen in the data 60% of the time, in the form of a decreasing gradient in surface flux from Palmer Station through Janus and Outcast Islands. During the other 40% of the cloudy sky measurements, local cloud inhomogeneity obscured the coastal albedo effect. The effect is more apparent under overcast layers that appear spatially uniform and occurs 86% of the time under the low overcast decks sampled. The presence of stratus fractus of bad weather, under higher overcast layers, obscures the coastal albedo effect such that it occurs only 43% of the time. A wavelength dependence is noted in the data under optically thin cloud cover: the ratio of a flux measured at an islet to that measured at the station increases with wavelength. This wavelength dependence can be explained by plane-parallel radiative transfer theory.

Xiong, XZ, Lubin D, Li W, Stamnes K.  2002.  A critical examination of satellite cloud retrieval from AVHRR in the Arctic using SHEBA data. Journal of Applied Meteorology. 41:1195-1209.   10.1175/1520-0450(2002)041<1195:aceosc>2.0.co;2   AbstractWebsite

This study examines the validity and limitations associated with retrieval of cloud optical depth tau and effective droplet size r(e) in the Arctic from Advanced Very High Resolution Radiometer ( AVHRR) channels 2 (0.725-1.10 mum), 3 (3.55-3.93 mum), and 4 (10.3-11.3 mum). The error in r(e) is found to be normally less than 10%, but the uncertainty in tau can be more than 50% for a 10% uncertainty in the satellite- measured radiance. Model simulations show that the satellite- retrieved cloud optical depth tau(sat) is overestimated by up to 20% if the vertical cloud inhomogeneity is ignored and is underestimated by more than 50% if overlap of cirrus and liquid water clouds is ignored. Under partially cloudy conditions, tau(sat) is larger than that derived from surface-measured downward solar irradiance (tau(surf)) by 40%-130%, depending on cloud-cover fraction. Here, tau(sat) derived from NOAA-14 AVHRR data agrees well with tau(surf) derived from surface measurements of solar irradiance at the Surface Heat Budget of the Arctic Ocean (SHEBA) ice camp in summer, but tau(sat) is about 2.3 times tau(surf) before the onset of snowmelt. This overestimate of tau(sat) is mainly due to the high reflectivity in AVHRR channel 2 over snow/ ice surfaces, the presence of partial cloud cover, and inaccurate representation of the scattering phase function for mixed-phase clouds.

Garrity, C, Lubin D, Kern S, Pedersen LT.  2002.  Linescan camera evaluation of SSM/I 85.5 GHz sea ice retrieval. Remote Sensing of Environment. 83:472-487.   10.1016/s0034-4257(02)00063-9   AbstractWebsite

Retrievals of total sea ice concentration from four algorithms using the 85.5 GHz vertically and horizontally polarized channels of the Special Sensor Microwave Imager (SSM/I) over the marginal ice zone in the Barents and Greenland Seas are compared with retrievals of total sea ice concentration from helicopter-borne linescan camera observations made during a cruise of the R/V Polarstern during May-June 1997. The goals are to evaluate (1) SSM/I 85.5 GHz retrievals of total sea ice concentration for climatological purposes, and (2) the ability of 85.5 GHz data to show the sea ice edge through cloud cover, for operational purposes. The SSM/I 85.5 GHz channels offer a spatial resolution of 12.5 km, which is sufficient to resolve ice edge features and small polynyas; however, there is generally more atmospheric contamination of the sea ice signal at 85.5 GHz than at the lower frequencies (19 and 37 GHz) traditionally used for sea ice remote sensing. A self-adjusting algorithm that performs a nonlinear correction for atmospheric moisture, without explicit atmospheric input data, yields the best accuracy over total sea ice concentrations greater than 30%. However, this algorithm can misclassify clouds over open water as sea ice, and is therefore unreliable for locating the sea ice edge. The best algorithm for locating the sea ice edge is found to be the SEA LION algorithm, which explicitly uses meteorological reanalysis data to correct for atmospheric contamination. For total sea ice concentrations in the range 20-70%, empirical 85.5 GHz hybrids of lower-frequency algorithms developed at the NASA Goddard Space Flight Center can improve the accuracy of these algorithms. (C) 2002 Elsevier Science Inc. All rights reserved.

Lubin, D, Satheesh SK, McFarquar G, Heymsfield AJ.  2002.  Longwave radiative forcing of Indian Ocean tropospheric aerosol. Journal of Geophysical Research-Atmospheres. 107   10.1029/2001jd001183   AbstractWebsite

A spectrally resolved discrete-ordinates radiative transfer model is used to calculate the change in downwelling surface and top-of-the-atmosphere (TOA) outgoing longwave (3.9-500 mum) radiative fluxes induced by tropospheric aerosols of the type observed over the Indian Ocean during the Indian Ocean Experiment (INDOEX). Both external and internal aerosol mixtures were considered. Throughout the longwave, the aerosol volume extinction depends more strongly on relative humidity than in most of the shortwave (0.28-3.9 mum), implying that particle growth factors and realistic relative humidity profiles must be taken into account when modeling the longwave radiative effects of aerosols. A typical boundary layer aerosol loading, with a 500-nm optical depth of 0.3, will increase the downwelling longwave flux at the surface by 7.7 W m(-2) over the clean air case while decreasing the outgoing longwave radiation by 1.3 W m(-2). A more vertically extended aerosol loading, exhibiting a high opacity plume between 2 and 3 km above the surface and having a typical 500-nm optical depth of 0.7, will increase the downwelling longwave flux at the surface by 11.2 W m(-2) over the clean air case while decreasing the outgoing longwave radiation by 2.7 W m(-2). For a vertically extended aerosol profile, approximately 30% of the TOA radiative forcing comes from sea salt and approximately 60% of the forcing comes from the combination of sea salt and dust. The remaining forcing is from anthropogenic constituents. These results are for the external mixture. For an internal mixture, TOA longwave forcings can be up to a factor of two larger. Therefore, to complete our understanding of this region's longwave aerosol radiative properties, more detailed information is needed about aerosol mixing states. These longwave radiative effects partially offset the large shortwave aerosol radiative forcing and should be included in regional and global climate modeling simulations.

Xiong, XZ, Stamnes K, Lubin D.  2002.  Surface albedo over the Arctic Ocean derived from AVHRR and its validation with SHEBA data. Journal of Applied Meteorology. 41:413-425.   10.1175/1520-0450(2002)041<0413:saotao>2.0.co;2   AbstractWebsite

A method is presented for retrieving the broadband albedo over the Arctic Ocean using advanced very high resolution radiometer (AVHRR) data obtained from NOAA polar-orbiting satellites. Visible and near-infrared albedos over snow and ice surfaces are retrieved from AVHRR channels 1 and 2, respectively, and the broadband shortwave albedo is derived through narrow-to-broadband conversion (NTBC). It is found that field measurements taken under different conditions yield different NTBC coefficients. Model simulations over snow and ice surfaces based on rigorous radiative transfer theory support this finding. The lack of a universal set of NTBC coefficients implies a 5%-10% error in the retrieved broadband albedo. An empirical formula is derived for converting albedo values from AVHRR channels 1 and 2 into a broadband albedo under different snow and ice surface conditions. Uncertain calibration of AVHRR channels 1 and 2 is the largest source of uncertainty, and an error of 5% in satellite-measured radiance leads to an error of 5%-10% in the retrieved albedo. NOAA-14 AVHRR data obtained over the Surface Heat Budget of the Arctic Ocean (SHEBA) ice camp are used to derive the seasonal variation of the surface albedo over the Arctic Ocean between April and August of 1998. Comparison with surface measurements of albedo by Perovich and others near the SHEBA ice camp shows very good agreement. On average, the retrieval error of albedo from AVHRR is 5%-10%.

Kerr, J, Seckmeyer G, Bais AF, Bernhard G, Blumthaler M, Diaz SB, Krotkov NA, Lubin D, Mckenzie RL, Sabziparvar AA, Verdebout J.  2002.  Surface Ultraviolet Radiation: Past and Future. Scientific assessment of ozone depletion, 2002. Executive summary. ( Organization W, Ed.).:5.1-5.46., [Washington, D.C.]; [Nairobi, Kenya]; [Geneva, Switzerland]; [Brussels, Belgium]: National Oceanic and Atmospheric Administration : National Aeronautics and Space Administration ; United Nations Environment Programme ; World Meteorological Organization ; European Commission Abstract
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2001
Kirkman, D, Tytler D, O'Meara JM, Burles S, Lubin D, Suzuki N, Carswell RF, Turner MS, Wampler EJ.  2001.  New Hubble Space Telescope spectra of QSO PG 1718+4807: No evidence for strong deuterium absorption. Astrophysical Journal. 559:23-28.   10.1086/322357   AbstractWebsite

The Z(abs) similar to 0.701 absorption system toward QSO PG 1718 + 4807 is the only example of a QSO absorption system which might have a deuterium/hydrogen ratio approximately 10 times the value found toward other QSOs. We have obtained new Space Telescope Imaging Spectrograph spectra from the Hubble Space Telescope of the Ly alpha and Lyman limit regions of the system. These spectra give the redshift and velocity dispersion of the neutral hydrogen, which produces most of the observed absorption. The Ly alpha line is too narrow to account for all of the observed absorption. It was previously known that extra absorption is needed on the blue side of the main H I near the expected position of deuterium. We do not find evidence in the current data that the extra absorption is entirely deuterium and find that it is more likely that some of the extra absorption is contaminating H. Until new data can be found that can independently constrain the line parameters of the potential contaminating H, it will not be possible to measure D/H in this system. Some uncertainty persists because we have a low signal-to-noise ratio and the extra absorption-be it deuterium or hydrogen-is heavily blended with the Ly alpha absorption from the main hydrogen absorption.

Ramanathan, V, Crutzen PJ, Lelieveld J, Mitra AP, Althausen D, Anderson J, Andreae MO, Cantrell W, Cass GR, Chung CE, Clarke AD, Coakley JA, Collins WD, Conant WC, Dulac F, Heintzenberg J, Heymsfield AJ, Holben B, Howell S, Hudson J, Jayaraman A, Kiehl JT, Krishnamurti TN, Lubin D, McFarquhar G, Novakov T, Ogren JA, Podgorny IA, Prather K, Priestley K, Prospero JM, Quinn PK, Rajeev K, Rasch P, Rupert S, Sadourny R, Satheesh SK, Shaw GE, Sheridan P, Valero FPJ.  2001.  Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze. Journal of Geophysical Research-Atmospheres. 106:28371-28398.   10.1029/2001jd900133   AbstractWebsite

Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform. observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (+/- 10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the ma or players. The dominant factor, however, is the large negative forcing (-20 +/- 4 W m(-2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.