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Results for “Shortwave Array Spectroradiometer-Zenith”

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DOE OSTI2016

Observation of the spectrally invariant properties of clouds in cloudy-to-clear transition zones during the MAGIC field campaign

We use the spectrally invariant method to study the variability of cloud optical thickness τ and droplet effective radius reff in transition zones (between the cloudy and clear sky columns) observed from Solar Spectral Flux Radiometer (SSFR) and Shortwave Array Spectroradiometer-Zenith (SASZe) during the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign. The measurements from the SSFR and the SASZe are different, however inter-instrument differences of self-normalized measurements (divided by their own spectra at a fixed time) are small. The spectrally invariant method approximates the spectra in the cloud transition zone as a linear combination of definitely clear and cloudy spectra, where the coefficients, slope and intercept, character-ize the spectrally invariant properties of the transition zone. Simulation results from the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model demonstrate that (1) the slope of the visible band is positively correlated with the cloud optical thickness τ while the intercept of the near-infrared band has high negative cor-relation with the cloud drop effective radius reff even without the exact knowledge of τ; (2) the above relations hold for all Solar Zenith Angle (SZA) and for cloud-contaminated skies. In observations using redundant measure-ments from SSFR and SASZe, we find that during cloudy-to-clear transitions, (a) the slopes of the visible band de-crease, and (b) the intercepts of the near-infrared band remain almost constant near cloud edges. The findings in simulations and observations suggest that, while the optical thickness decreases during the cloudy-to-clear transition, the cloud drop effective radius does not change when cloud edges are approached. These results sup-port the hypothesis that inhomogeneous mixing dominates near cloud edges in the studied cases.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Cloud Edge Properties Measured by the ARM Shortwave Spectrometer Over Ocean and Land

In this paper, we use the spectrally invariant method to study the variability of cloud optical thickness (τ) and droplet effective radius (r eff ) in transition zones between the cloudy and clear-sky columns observed by Shortwave Array Spectroradiometer-Zenith at the Southern Great Plains Central Facility site (SGP C1) and during the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign. The spectrally invariant method approximates the spectra in the transition zone as a linear combination of definitely clear and definitely cloudy spectra. The slope and intercept of the linear relations characterize τ and r eff in the transition region, respectively. The radiative transfer model simulations show that that (i) the slope of the visible band is positively correlated with τ, while (ii) the intercept of the near-infrared band has a high negative correlation with r eff . We have analyzed 22 cloud edge cases from the SGP and MAGIC and found that from cloud to clear in the transitions, (a) the slopes of the visible band decrease, indicating the decrease of τ toward cloud edges, and (b) the intercepts of the near-infrared band show a much more significant increase at the SGP than from the MAGIC. The results from observed cases suggest that while τ decreases for all cases, the decrease in r eff is much more significant for cloud over land at the SGP site compared to the ocean counterpart during the MAGIC campaign.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

saszefilterbands

ARM Instrument: Shortwave Array Spectroradiometer-Zenith

54 ENVIRONMENTAL SCIENCES↗