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1988
Frederick, JE, Lubin D.  1988.  The Budget of Biologically-Active Ultraviolet-Radiation in the Earth-Atmosphere System. Journal of Geophysical Research-Atmospheres. 93:3825-3832.   10.1029/JD093iD04p03825   AbstractWebsite

This study applies the concept of a budget to describe the interaction of solar ultraviolet (UV) radiation with the Earth-atmosphere system. The wavelength ranges of interest are the biologically relevant UV-B between 280 and 320 nm and the UV-A from 320 to 400 nm. The Nimbus 7 solar backscattered ultraviolet (SBUV) instrument provides measurements of total column ozone and information concerning cloud cover which, in combination with a simple model of radiation transfer, define the fractions of incident solar irradiance absorbed in the atmosphere, reflected to space, and absorbed at the ground. Results for the month of July quantify the contribution of fractional cloud cover and cloud optical thickness to the radiation budget's three components. Scattering within a thick cloud layer makes the downward radiation field at the cloud base more isotropic than is the case for clear skies. For small solar zenith angles, typical of summer midday conditions, the effective path length of this diffuse irradiance through tropospheric ozone is greater than that under clear-sky conditions. The result is an enhanced absorption of UV-B radiation in the troposphere during cloud-covered conditions. Major changes in global cloud cover or cloud optical thicknesses could alter the ultraviolet radiation received by the biosphere by an amount comparable to that predicted for long-term trends in ozone.

Frederick, JE, Lubin D.  1988.  Possible Long-Term Changes in Biologically-Active Ultraviolet-Radiation Reaching the Ground. Photochemistry and Photobiology. 47:571-578.   10.1111/j.1751-1097.1988.tb08846.x   AbstractWebsite

Three scenarios for long-term changes in atmospheric ozone over the time period 1960 to 2030 lead to different projections for the ultraviolet radiation flux at the earth's surface. Biologically effective fluxes for damage to DNA and generalized damage to plants vary by a factor of 10 or more with latitude and season irrespective of possible changes in ozone. The natural latitudinal gradient in radiation corresponds to spatial changes in biologically effective fluxes which are large compared to temporal changes expected from trends in ozone over the time period analyzed. In an extreme scenario of ozone change, based on an assumed increase in chlorofluorocarbon release rates of 3% per year after 1980, the annually integrated effective flux for damage to DNA increases by 13.5% at latitude 40°N between 1960 and 2030. With chlorofluorocarbon release rates held fixed at their 1980 values, the corresponding radiation increase is only 2.3%. In a scenario where atmospheric chlorine remains fixed at its 1960 value, trends in atmospheric methane and nitrous oxide imply a decrease in biologically effective flux at 40°N of 5.3% between 1960 and 2030.

1989
Lubin, D, Frederick JE, Booth CR, Lucas T, Neuschuler D.  1989.  Measurements of Enhanced Springtime Ultraviolet-Radiation at Palmer-Station, Antarctica. Geophysical Research Letters. 16:783-785.   10.1029/GL016i008p00783   AbstractWebsite

Measurements of ultraviolet solar spectra from Palmer Station, Antarctica have defined the surface radiation environment of the region during the Austral spring of 1988. At wavelengths where absorption by ozone is negligible, 335–345 nm, the noontime irradiances show the expected gradual increase from the first day of measurements, 19 September, through 21 December. Large variations related to cloudiness are imposed on this background. At wavelengths less than 310 nm the influence of the 1988 ozone “hole” is apparent. The noontime irradiance observed in the wavelength band 295–305 nm on 19 October, two months prior to summer solstice, exceeded any value measured through 21 December.

Lubin, D, Frederick JE, Krueger AJ.  1989.  The Ultraviolet-Radiation Environment of Antarctica - Mcmurdo Station During September-October 1987. Journal of Geophysical Research-Atmospheres. 94:8491-8496.   10.1029/JD094iD06p08491   AbstractWebsite

The large depletions in column ozone observed over Antarctica during spring imply enhanced levels of solar ultraviolet radiation at the Earth's surface. Daily data from the Nimbus 7 Total Ozone Mapping Spectrometer were combined with a model of atmospheric radiative transfer to compute the time evolution of ultraviolet irradiance, at wavelengths from 290 to 350 nm, incident on McMurdo Station during September-October 1987. Large changes in column ozone occur as the polar vortex moves over the site. This is accompanied by correspondingly large variations in ultraviolet radiation at the Earth's surface. At a wavelength near 305 nm, the irradiance in early October exceeds values appropriate to an unperturbed ozone layer by a factor of 5–6. As December 21 approaches, the noontime ultraviolet irradiance increases, irrespective of changes in ozone. Any lengthening of the period of ozone depletion toward summer solstice will have a substantial impact on the ultraviolet irradiance received by the Antarctic surface.

1990
Lubin, D, Frederick JE.  1990.  Observations of ozone and cloud properties from NSF ultraviolet-monitor measurements at Palmer Station, Antarctica. Antarctic Journal of the United States, Washington, DC. 25:241-242. AbstractWebsite

The National Science Foundation scanning spectroradiometer at Palmer Station provides hourly ground-based measurements of solar ultraviolet irradiance. In addition to defining the ultraviolet radiation environment of the region, these measurements allow the derivation of the column density of atmospheric ozone above the station nearly every daylight hour. This hourly time resolution, not generally available from other methods of monitoring Antarctic ozone abundances, enables the detection of large and rapid changes in total column ozone and ultraviolet surface irradiance associated with the dynamics of the polar vortex. In conjunction with a daily record of sky conditions and radiative transfer modeling, the ultraviolet-monitor measurements permit a quantitative understanding of the role of cloud cover in regulating ultraviolet radiation levels at the Antarctic Earth surface.

Lubin, D, Frederick JE.  1990.  Column Ozone Measurements from Palmer-Station, Antarctica - Variations During the Austral Springs of 1988 and 1989. Journal of Geophysical Research-Atmospheres. 95:13883-13889.   10.1029/JD095iD09p13883   AbstractWebsite

The National Science Foundation scanning spectroradiometer at Palmer Station, Antarctica (64°46′S, 64°04′W), provides hourly ground-based measurements of solar ultraviolet (UV) irradiance. In addition to defining the UV radiation environment of the region, these measurements allow the derivation of the column density of atmospheric ozone above the station nearly every daylight hour. This hourly time resolution, not generally available from other methods of monitoring Antarctic ozone abundances, enables the detection of large and rapid changes in total column ozone and UV surface irradiance associated with the dynamics of the polar vortex. Column ozone abundance is derived from a ratio of measured irradiances at 300 and 313.5 nanometers (nm) by means of theoretical calculation of this ratio as a function of total ozone amount. Noontime ozone abundances over Palmer Station obtained from this method agree with those obtained by the Total Ozone Mapping Spectrometer (TOMS) instrument aboard Nimbus 7 to within about 10% throughout the austral spring of 1988. Ozone recovery at Palmer Station, associated with the breakup of the polar vortex as indicated by TOMS satellite ozone observations, occurred rapidly within a 24-hour period beginning in midafternoon on November 15. Over the Antarctic Peninsula, the 1989 ozone depletion was slightly greater than in 1988, the minimum noontime ozone abundances over Palmer Station as measured by the spectroradiometer being 194 and 166 Dobson units for October 14, 1988, and October 14, 1989, respectively. The 1989 ozone depletion however ended by November 5 over the Antarctic Peninsula, 10 days earlier than the 1988 event.

1991
Lubin, D, Frederick JE.  1991.  The Ultraviolet-Radiation Environment of the Antarctic Peninsula - the Roles of Ozone and Cloud Cover. Journal of Applied Meteorology. 30:478-493.   10.1175/1520-0450(1991)030<0478:tureot>2.0.co;2   AbstractWebsite

The National Science Foundation scanning spectroradiometer at Palmer Station, Antarctica (64-degrees-46'S, 64-degrees-04'W) provides hourly ground-based measurements of solar ultraviolet (UV) irradiance at the earth's surface. These measurements define the UV radiation environment of the region and, in conjunction with a daily record of sky conditions and radiative transfer modeling, permit a quantitative understanding of the role of cloud cover in regulating UV radiation levels at the Antarctic surface, including the period of the springtime ozone depletion. The transmission properties of cloud types over the Antarctic Peninsula are quantified by taking the ratio of UV-A irradiances measured under them to UV-A irradiances calculated for clear skies and the same solar zenith angle, and the results are then generalized to the UV-B. Under the average overcast sky in the region, UV irradiance at all wavelengths is slightly greater than half of the value for clear skies. Under the thickest overcast layers, UV irradiance at all wavelengths is roughly 20% what it would be if the sky were clear. In a seasonally averaged sense cloudiness has no effect on the percentage enhancement in UV-B surface irradiance that results from the springtime ozone depletion. However, when considering time scales of hours to several days, an increase in cloud cover can be discussed in terms of its ability to attenuate the solar irradiance; in some cases giving a surface UV-B level comparable to that found under an unperturbed ozone column and clear skies. Depending on the amount of ozone depletion and the type of cloud cover, there will always be a wavelength below which surface radiation levels are excessive during spring.

1992
Lubin, D, Gautier C.  1992.  Fourier transform infrared spectroradiometer measurements of atmospheric longwave emission over Palmer Station, spring 1991. Antarctic Journal of the United States. 27:276. Abstract

Presents the results of Fourier Transform Infrared spectroradiometer measurements of atmospheric longwave emission from the zenith sky over Palmer Station in Antarctica. Overcast as the most common sky condition in the area; Definition of longwave cloud forcing at the earth's surface.

Lubin, D, Mitchell BG, Frederick JE, Alberts AD, Booth CR, Lucas T, Neuschuler D.  1992.  A Contribution toward Understanding the Biospherical Significance of Antarctic Ozone Depletion. Journal of Geophysical Research-Atmospheres. 97:7817-7828.   10.1029/91JD01400   AbstractWebsite

Measurements of biologically active UV radiation made by the National Science Foundation (NSF) scanning spectroradiometer (UV-monitor) at Palmer Station. Antarctica, during the Austral springs of 1988, 1989, and 1990 are presented and compared. Column ozone abundance above Palmer Station is computed from these measurements using a multiple wavelength algorithm. Two contrasting action spectra (biological weighting functions) are used to estimate the biologically relevant (dose from the spectral measurements: a standard weighting function for damage to DNA, and a new action spectrum representing the potential for photosynthesis inhibition in Antarctic phytoplankton. The former weights only UV-B wavelengths (280-320 nm) and gives the most weight to wavelengths shorter than 300 nm, while the latter includes large contributions out to 355 nm. The latter is the result of recent Antarctic field work and is relevant in that phytoplankton constitute the base of the Antarctic food web. The modest ozone hole of 1988, in which the ozone abundance above Palmer Station never fell below 200 Dobson units (DU), brought about summerlike doses of DNA-effective UV radiation 2 months early, but UV doses which could inhibit photosynthesis in phytoplankton did not exceed a clear-sky "maximum normal" dose for that time of year. The severe ozone holes of 1989 and 1990, in which the ozone abundance regularly fell below 200 DU, brought about increases in UV surface irradiance weighted by either action spectrum. Ozone abundances and dose-weighted irradiances provided by the NSF UV-monitor are used to derive the radiation amplification factors (RAFs) for both DNA-effective irradiance and phytoplankton-effective irradiance. The RAF for DNA-effective irradiance is nonlinear in ozone abundance and is in excess of the popular "two for one" rule, while the RAF for phytoplankton-effective irradiance approximately follows a "one for one" rule.

1993
Lubin, D, Holm-Hansen O, Helbling EW.  1993.  Ultraviolet radiation and its effects on organisms in aquatic environments. Environmental UV photobiology. ( Young AR, Ed.).:379-345., New York: Plenum Press Abstract
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Holmhansen, O, Helbling EW, Lubin D.  1993.  Ultraviolet-Radiation in Antarctica - Inhibition of Primary Production. Photochemistry and Photobiology. 58:567-570.   10.1111/j.1751-1097.1993.tb04933.x   AbstractWebsite

With the seasonal formation of the ozone hole over Antarctica, there is much concern regarding the effects of increased solar UV-B radiation (280-320 nm) on the marine ecosystem in the Southern Ocean. In situ incubations of natural phytoplankton assemblages in antarctic waters indicate that under normal ozone conditions UV-B radiation is responsible for a loss of approximately 4.9% of primary production in the euphotic zone, whereas UV radiation with wavelengths between 320 and 360 nm causes a loss of approximately 6.2%. When combined with data on the action spectrum for photoinhibition by UV radiation, our data suggest that the enhanced fluence of UV-B radiation under a well-developed ozone hole (1 50 Dobson units) would decrease daily primary productivity by an additional amount of less-than-or-equal-to 53.8%. Calculations that take into consideration the extent and duration of low stratospheric ozone concentrations during September to November indicate that the decrease in total annual primary production in antarctic waters due to enhanced UV-B radiation would be less-than-or-equal-to 0.20%.

1994
Lubin, D, Ricchiazzi P, Gautier C, Whritner R.  1994.  A method for mapping Antarctic surface ultraviolet radiation using multispectral satellite imagery. Antarctic Research Series. 62:53-81.   10.1029/AR062p0053   Abstract

Satellite-tracking facilities recently deployed at U.S. Antarctic research stations provide an extensive data set for studying the atmospheric radiation budget. Images from the advanced very high resolution radiometers (AVHRR) aboard the National Oceanic and Atmospheric Administration polar orbiters can be used in conjunction with data from the Nimbus 7 total ozone mapping spectrometer (TOMS) to construct maps of biologically active ultraviolet irradiance at the Antarctic Earth surface. We have developed a method to perform this mapping which involves refinements to the satellite data as well as detailed radiative transfer theory. We recalibrate the AVHRR data to account for sensor deterioration in orbit, and we remove bidirectional reflectance effects where possible. A surface albedo map can be constructed for the region and time period of interest by compositing as many cloud-free AVHRR images as are available. The optical depth of clouds over the open ocean can be estimated from AVHRR visible channel imagery by direct application of a delta-Eddington radiative transfer model. Over snow and ice, radiative transfer limitations require the use of an empirical parameterization for cloud optical depth as a function of the brightness temperature difference between AVHRR thermal channels 3 and 4. This parameterization is derived for cloud fields over the ocean and applied to nearby cloud fields over snow and ice. Once each pixel in a satellite image has an associated estimate of total ozone, cloud optical depth, and surface albedo, a delta-Eddington radiative transfer model is used to calculate the surface irradiance at any ultraviolet, visible, or near-infrared wavelength. Estimates of cloud optical depth and surface irradiance can be validated by ground-based radiometers, including the NSF UV monitor.

Holm-Hansen, O, Lubin D.  1994.  Solar ultraviolet radiation: effect on rates of CO2 fixation in marine phytoplankton. Regulation of atmospheric CO2 and O2 by photosynthetic carbon metabolism. ( Tolbert NE, Preiss J, Eds.).:55-74., New York; Oxford: Oxford University Press Abstract
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Lubin, D.  1994.  Infrared Radiative Properties of the Maritime Antarctic Atmosphere. Journal of Climate. 7:121-140.   10.1175/1520-0442(1994)007<0121:irpotm>2.0.co;2   AbstractWebsite

The longwave radiation environment of the Antarctic Peninsula and Southern Ocean has been investigated using radiometric Fourier Transform Infrared (FTIR) measurements of atmospheric emission in conjunction with detailed radiative transfer theory. The California Space Institute FTIR Spectroradiometer was deployed at Palmer Station, Antarctica (64 degrees 46'S, 64 degrees 04'W), where it made zenith sky emission measurements several times daily between 25 August 1991 and 17 November 1991. Emission spectra covered the entire middle infrared (5-20 mu m) with one inverse centimeter spectral resolution. For FTIR data obtained under cloudy skies, a least-squares algorithm is used to match the emission spectra with discrete-ordinate radiative transfer calculations that are based on marine cloud microphysics. This algorithm provides a determination of cloud emissivity, and useful estimates of cloud optical depth and equivalent radius of the droplet size distribution. Temperatures in the lower troposphere between 259 K and 273 K diminish the radiative importance of water vapor and enhance the importance of clouds and CO2 relative to midlatitudes. Springtime variability in stratospheric temperature and ozone abundance has a small but noticeable impact of about 1.0 W m(-2) on surface longwave flux under clear skies. The mid-IR window emissivities of low stratiform clouds are most often between 0.90 and 0.98, with few as large as unity. Most low stratiform clouds appear to have moderate mid-IR optical depth (5-10), but relatively large equivalent radius (9-11 mu m). However, clouds with base height between 1 and 2 km have noticeably smaller emissivities and optical depths. The emissivity of maritime antarctic clouds is determined to be smaller for a given liquid water path than the parameterization used in the NCAR Community Climate Model (CCM1), and an appropriate mass absorption coefficient for antarctic clouds is 0.065 m(2) g(-1) for the mid-IR window.

Lubin, D, Simpson AS.  1994.  The Longwave Emission Signature of Urban Pollution - Radiometric Ftir Measurement. Geophysical Research Letters. 21:37-40.   10.1029/93gl03374   AbstractWebsite

Air pollutants trapped beneath frequent temperature inversions in the Los Angeles basin bring about surface radiance enhancements of up to fifty percent in the middle-infrared window (8-12 microns). This constitutes an anthropogenic modification to the downwelling longwave flux which can be as large as 9 W/m2. A Fourier Transform Infrared (FTIR) spectroradiometer has been used to measure middle-infrared atmospheric emission spectra under Los Angeles smog, and these 1 cm-1 resolution spectra demonstrate that both anthropogenic aerosols and increased tropospheric ozone abundance contribute to enhancements in surface longwave radiation.

Lubin, D.  1994.  The Role of the Tropical Super Greenhouse-Effect in Heating the Ocean Surface. Science. 265:224-227.   10.1126/science.265.5169.224   AbstractWebsite

Measurements made by a Fourier transform infrared (FTIR) spectroradiometer operating in the middle infrared (5 to 20 micrometers, with a spectral resolution of one inverse centimeter) imply that there is an anomalously large greenhouse effect over equatorial oceans that is caused by water vapor. As sea-surface temperature increased from 297 to 303 degrees kelvin, the net infrared cooling at the surface decreased by 30 to 50 watts per square meter. Thus, according to the FTIR data, the super greenhouse effect that had been inferred from satellite measurements contributes directly to radiative heating of the sea surface. The data demonstrate that most of this heating occurs in the middle infrared by means of the continuum emission window of water vapor and that tropical deep convection contributes substantially to this super greenhouse effect.

1995
Lubin, D, Holm-Hansen O.  1995.  Atmospheric ozone and the biological impact of solar ultraviolet radiation. Encyclopedia of environmental biology. Vol. 1, A-E. 1( Nierenberg WA, Ed.).:147-168.: Academic Press Abstract
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Lubin, D, Cutchin D, Conant W, Grassl H, Schmid U, Biselli W.  1995.  Spectral Longwave Emission in the Tropics - Ftir Measurement at the Sea-Surface and Comparison with Fast Radiation Codes. Journal of Climate. 8:286-295.   10.1175/1520-0442(1995)008<0286:sleitt>2.0.co;2   AbstractWebsite

Longwave emission by the tropical western Pacific atmosphere has been measured at the ocean surface by a Fourier Transform Infrared (FTIR) spectroradiometer deployed aboard the research vessel John Vickers as part of the Central Equatorial Pacific Experiment. The instrument operated throughout a Pacific Ocean crossing, beginning on 7 March 1993 in Honiara, Solomon Islands, and ending on 29 March 1993 in Los Angeles, and recorded longwave emission spectra under atmospheres associated with sea surface temperatures ranging from 291.0 to 302.8 K. Precipitable water vapor abundances ranged from 1.9 to 5.5 column centimeters. Measured emission spectra (downwelling zenith radiance) covered the middle infrared (5-20 mu m) with one inverse centimeter spectral resolution. FTIR measurements made under an entirely clear field of view are compared with spectra generated by LOWTRAN 7 and MODTRAN 2, as well as downwelling flux calculated by the NCAR Community Climate Model (CCM-2) radiation code, using radiosonde profiles as input data for these calculations. In the spectral interval 800-1000 cm(-1), these comparisons show a discrepancy between FTIR data and MODTRAN 2 having an overall variability of 6-7 mW m(-2) sr(-1) cm and a concave shape that may be related to the representation of water vapor continuum emission in MODTRAN 2. Another discrepancy appears in the spectral interval 1200-1300 cm(-1), where MODTRAN 2 appears to overestimate zenith radiance by 5 mW m(-2) sr(-1) cm. These discrepancies appear consistently; however, they become only slightly larger at the highest water vapor abundances. Because these radiance discrepancies correspond to broadband (500-2000 cm(-1)) flux uncertainties of around 3 W m(-2), there appear to be no serious inadequacies with the performance of MODTRAN 2 or LOWTRAN 7 at high atmospheric temperatures and water vapor abundances. On average, CCM-2 flux calculations agree to within 1 W m(-2) with downwelling flux estimates from the FTIR data over all sea surface temperatures, although this result has a scatter of +/-12 W m(-2) at high sea surface temperatures.

Lubin, D, Weber PG.  1995.  The Use of Cloud Reflectance Functions with Satellite Data for Surface Radiation Budget Estimation. Journal of Applied Meteorology. 34:1333-1347.   10.1175/1520-0450(1995)034<1333:tuocrf>2.0.co;2   AbstractWebsite

The bidirectional reflectance distribution function (BRDF) of an overcast atmosphere above an ocean surface has been calculated as a function of wavelength using a discrete-ordinates radiative transfer model. This plane-parallel BRDF appears qualitatively similar to the empirically derived angular dependence models from the Earth Radiation Budget Experiment. But when these two different BRDFs are used to estimate net shortwave flux at the ocean surface, discrepancies of 20-60 W m(-2) can occur between the respective net surface nux estimations. When using either BRDF with Advanced Very High Resolution Radiometer data for surface radiation budget estimation, this uncertainty can be minimized by restricting the satellite viewing( polar) angle to between 30 degrees and 50 degrees. Accurate measurements of the planetary BRDF would help resolve these differences.

Ricchiazzi, P, Gautier C, Lubin D.  1995.  Cloud Scattering Optical Depth and Local Surface Albedo in the Antarctic - Simultaneous Retrieval Using Ground-Based Radiometry. Journal of Geophysical Research-Atmospheres. 100:21091-21104.   10.1029/95jd01461   AbstractWebsite

We have used solar irradiance measurements from a ground-based multichannel radiometer system deployed at Palmer Station, Antarctica (64 degrees 46'S, 64 degrees 04'W), during spring 1991 to simultaneously estimate cloud scattering optical depth and surface albedo. Irradiance measurements at 410 and 630 nm, in conjunction with a discrete ordinate radiative transfer (RT) model, enable this simultaneous retrieval by exploiting the wavelength dependence in Rayleigh scattering strength. The RT model is used in an inverse mode to find the values of surface albedo and cloud optical depth that match calculated and measured irradiances at both wavelengths. Under the homogeneous stratiform cloud cover for which the technique applies, surface albedo at 630 nm was consistently retrieved at above 0.9. For most homogeneous, overcast conditions, cloud optical depth (at 630 nm) is found to be in the range 20-50, with a most probable value of 25. This measurement and retrieval technique should be useful for compiling high-latitude cloud opacity and surface albedo climatologies of interest for global change and photobiology research.

Lubin, D, Jensen EH.  1995.  Effects of Clouds and Stratospheric Ozone Depletion on Ultraviolet-Radiation Trends. Nature. 377:710-713.   10.1038/377710a0   AbstractWebsite

ANTHROPOGENIC depletion of ozone in the lower stratosphere has been of global environmental concern for two decades, but the environmentally relevant quantity-the flux of solar ultraviolet radiation (UVR) reading the Earth's surface-remains poorly quantified on a global basis. The three most important parameters governing surface UVR fluxes and trends are solar elevation, total vertically integrated ozone abundance and cloud opacity. Here we use global satellite measurements of total ozone abundance and cloud reflectance to examine how the trends in UVR resulting from established trends in total ozone abundance(1,2) compare with the potentially large natural variability in UVR that results from variations in cloud opacity. We find that throughout many temperate regions-including large parts of continental Europe, North and South America, New Zealand, Australia and southern Africa-interannual variability in cloud opacity is sufficiently small that by the end of this century, trends in summer average local-noon UVR dose rates relevant to mammalian skin cancer or plant damage should be significant with respect to cloud variability.

Lomax, AS, Lubin D, Whritner RH.  1995.  The Potential for Interpreting Total and Multiyear Ice Concentrations in Ssm/I 85.5 Ghz Imagery. Remote Sensing of Environment. 54:13-26.   10.1016/0034-4257(95)00082-c   AbstractWebsite

The 85.5 GHz vertically and horizontally polarized channels of the Special Sensor Microwave Inagers (SSM/1) aboard the Defense Meteorological Satellite Program (DMSP) spacecraft offer the potential to map sea ice with a spatial resolution of 12.5 km, a factor of two improvement over the popular National Aeronautics and Space Administration (NASA) Team algorithm, but with the limitation of increased atmospheric influence on the sea ice signal. Application of an algorithm for estimating total ice concentration from 85.5 GHz data, which exploits the large polarization for open water versus the small polarization for most ice types, reveals agreement with the NASA Team algorithm typically within. a standard deviation of +/- 3% for nearly cloud-free winter conditions. The uncertainty increases to a standard deviation of +/- 6% for cloudy winter conditions. In winter, volume scattering from multiyear ice has a noticeable impact on the 85.5 GHz brightness temperatures. By employing a polarization corrected temperature variable previously defined to isolate precipitation in mid-latitude DMSP imagery, it is possible to exploit the large differences in 85.5 GHz emissivity between first year and multiyear ice to interpret an 85.5 GHz image in terms of both total ice and multiyear ice concentration. Preliminary results, for nearly cloud-free winter conditions, reveal agreement between these interpretations and the NASA Team algorithm to within a standard deviation of +/- 6%, with slightly better agreement at Low multiyear ice concentration.

1996
Aagaard, K, Barrie L, Carmack E, Garrity C, Jones EP, Lubin D, Macdonald RW, Swift JH, Tucker W, Wheeler PA, Whritner R.  1996.  U.S., Canadian researchers explore Arctic Ocean. EOS, Transactions American Geophysical Union. 77:209,213.   10.1029/96EO00141   Abstract

During July–September 1994, two Canadian and U.S. ice breakers crossed the Arctic Ocean (Figure 1) to investigate the biological, chemical, and physical systems that define the role of the Arctic in global change. The results are changing our perceptions of the Arctic Ocean as a static environment with low biological productivity to a dynamic and productive system. The experiment was called the Arctic Ocean Section (AOS) and the ships were the Canadian Coast Guard ship Louis S. St.-Laurent and the U.S. Coast Guard cutter Polar Sea.

Lubin, D, Harper DA.  1996.  Cloud radiative properties over the South Pole from AVHRR infrared data. Journal of Climate. 9:3405-3418.   10.1175/1520-0442(1996)009<3405:crpots>2.0.co;2   AbstractWebsite

Over the Antarctic plateau, the radiances measured by the AVHRR middle infrared (11 and 12 mu m) channels are shown to depend on effective cloud temperature, emissivity, ice water path, and effective radius of the particle size distribution. The usefulness of these dependencies is limited by radiometric uncertainties of up to 2 K in brightness temperature and by the fact that the radiative transfer solutions are not single valued over all possible ranges of temperature, effective radius, and ice water path. Despite these limitations, AVHRR imagery can be used to characterize cloud optical properties over the Antarctic continent if surface weather observations and/or radiosonde data can be collocated with the satellite overpasses. From AVHRR imagery covering the South Pole during 1992, the mean cloud emissivity is estimated at 0.43 during summer and 0.37 during winter, while the mean summer and winter effective radii are estimated at 12.3 and 5.6 mu m, respectively. When a radiative transfer model is used to evaluate these results in comparison with surface pyrgeometer measurements, the comparison suggests that the AVHRR retrieval method captures the overall seasonal behavior in cloud properties. During months when the polar vortex persists, AVHRR infrared radiances may be noticeably influenced by polar stratospheric clouds.

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.