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Scott, RC, Lubin D.  2016.  Unique manifestations of mixed-phase cloud microphysics over Ross Island and the Ross Ice Shelf, Antarctica. Geophysical Research Letters. 43:2936-2945.   10.1002/2015gl067246   AbstractWebsite

Spaceborne radar and lidar observations from the CloudSat and CALIPSO satellites are used to compare seasonal variations in the microphysical and radiative properties of clouds over Ross Island, Antarctica, with two contrasting Arctic atmospheric observatories located in Barrow, Alaska, and Summit, Greenland. At Ross Island, downstream from recurrent intrusions of marine air over the West Antarctic Ice Sheet and eastern Ross Ice Shelf, clouds exhibit a tendency toward the greatest geometrical thickness and coldest temperatures in summer, the largest average ice water content, IWC, at low altitude during summer and autumn, the most abundant IWC at cold mixed-phase temperatures (-40 degrees C

Lubin, D, Kahn BH, Lazzara MA, Rowe P, Walden V.  2015.  Variability in AIRS-retrieved cloud amount and thermodynamic phase over west versus east Antarctica influenced by the SAM. Geophysical Research Letters. 42:1259-1267.   10.1002/2014gl062285   AbstractWebsite

In a sample of summertime cloud retrievals from the NASA Atmospheric Infrared Sounder (AIRS), a positive Southern Annular Mode (SAM) index polarity is associated with greater cloud frequency and larger effective cloud fraction over West Antarctica compared with a negative SAM index polarity. The opposite result appears over the high East Antarctic Plateau. Comparing AIRS-retrieved cloud fraction with Antarctic Automatic Weather Station 2 m air temperature data, a positive and significant correlation is found over most of West Antarctica, signifying a longwave heating effect of clouds. Over East Antarctica correlations between Sun elevation and 2 m air temperature are strongest, consistent with lower cloud amount.

Lubin, D, Simpson AS.  1997.  Measurement of surface radiation fluxes and cloud optical properties during the 1994 Arctic Ocean Section. Journal of Geophysical Research-Atmospheres. 102:4275-4286.   10.1029/96jd03215   AbstractWebsite

During a voyage to the north pole from Alaska by the icebreakers USCGC Polar Sea and Canadian CGC Louis S. St.-Laurent (the 1994 Arctic Ocean Section, July 24 to September 3) an atmospheric radiation and remote sensing experiment measured downwelling shortwave and longwave radiation reaching the sea ice surface. The experiment included a Fourier transform infrared (FTIR) spectroradiometer which measured zenith radiance at 1 cm(-1) resolution in the middle infrared wavelength range 5-20 mu m, an Eppley pyranometer measuring most of the downwelling shortwave flux (0.28-2.80 mu m), an Eppley pyranometer measuring the downwelling near-infrared flux (0.78-2.80 mu m), and an Eppley pyrgeometer measuring the downwelling longwave flux. In conjunction with a discrete-ordinates radiative transfer model, the FTIR emission spectra are used to estimate 8-12 mu m cloud emissivity and effective radius of the cloud droplet size distribution. The broadband shortwave flux measurements are used to estimate shortwave cloud scattering optical depth. Most of the FTIR emission spectra recorded under overcast skies are consistent with cloud effective radius in the range 10-12 mu m, but 27% of the spectra are more consistent with the range 4-6 mu m, suggesting an occasional continental aerosol influence to Arctic cloud microphysics. The average daily shortwave cloud-scattering optical depth ranged from 2 to 46, which is similar to a range inferred from radiometer data recorded at Barrow, Alaska, during the same season. The downwelling shortwave flux measurements and estimates of net surface flux are generally consistent with a four-decade Russian climatology but also suggest that the frequency of cloud cover sampled during the 1994 Arctic Ocean Section was somewhat larger than the climatological average. These radiation measurement data from the 1994 Arctic Ocean Section should be useful for examining the treatment of atmospheric radiation and surface energy input in Arctic climate model simulations.

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.