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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Observing clouds in 4D with multi-view stereo photogrammetry

We report that newly installed stereo cameras ringing the Southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site in Oklahoma are providing a 4D gridded view of shallow clouds. Six digital cameras have been installed in pairs at a distance of 6 kilometers from the site and with a spacing of 500 meters between cameras in a pair. These pairs of cameras provide stereoscopic views of shallow clouds from all sides; when these data are combined, they allow for a complete stereo reconstruction. The result – the Clouds Optically Gridded by Stereo (COGS) product – is a 4D grid of cloudiness covering a 6 km × 6 km × 6 km cube at a spatial resolution of 50 meters and a temporal resolution of 20 seconds. This provides an unprecedented set of data on the sizes, lifetimes, and lifecycles of shallow clouds. Lastly, this type of information is critical for developing cloud macrophysical schemes for the next generation of weather and climate models.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Formation and fractionation of CO (carbon monoxide) in diffuse clouds observed at optical and radio wavelengths

We modeled H{sub 2} and CO formation incorporating the fractionation and selective photodissociation affecting CO when A{sub V} ≲ 2 mag. UV absorption measurements typically have N({sup 12}CO)/N({sup 13}CO) ≈ 65 that are reproduced with the standard UV radiation and little density dependence at n(H) ≈ 32–1024 cm{sup −3}: densities n(H) ≲ 256 cm{sup −3} avoid overproducing CO. Sightlines observed in millimeter wave absorption and a few in UV show enhanced {sup 13}CO by factors of two to four and are explained by higher n(H) ≳ 256 cm{sup −3} and/or weaker radiation. The most difficult observations to understand are UV absorptions having N({sup 12}CO)/N({sup 13}CO) > 100 and N(CO) ≳ 10{sup 15} cm{sup −2}. Plots of W{sub CO} versus N(CO) show that W{sub CO} remains linearly proportional to N(CO) even at high opacity owing to sub-thermal excitation. {sup 12}CO and {sup 13}CO have nearly the same curve of growth so their ratios of column density/integrated intensity are comparable even when different from the isotopic abundance ratio. For n(H) ≳ 128 cm{sup −3}, plots of W{sub CO} versus N(CO) are insensitive to n(H), and W{sub CO}/N(CO) ≈ 1 K km s{sup −1}/(10{sup 15} CO cm{sup −2}); this compensates for small CO/H{sub 2} to make W{sub CO} more readily detectable. Rapid increases of N(CO) with n(H), N(H), and N(H{sub 2}) often render the CO bright, i.e., a small CO-H{sub 2} conversion factor. For n(H) ≲ 64 cm{sup −3}, CO enters the regime of truly weak excitation, where W{sub CO} ∝ n(H)N(CO). W{sub CO} is a strong function of the average H{sub 2} fraction and models with W{sub CO} = 1 K km s{sup −1} fall in the narrow range of 〈f{sub H{sub 2}}〉 0.65–0.8 or 〈f{sub H{sub 2}}〉 0.4–0.5 at W{sub CO} 0.1 K km s{sup −1}. The insensitivity of easily detected CO emission to gas with small 〈f{sub H{sub 2}}〉 implies that even deep CO surveys using broad beams may not discover substantially more emission.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Intercomparison of observed cloud radiative forcing - A zonal and global perspective

Cloud radiative forcing determined by the Earth Radiation Budget Experiment (ERBE) scene identification method and two regression methods is compared using identical data sources and the same analysis periods. Results confirm that from the global perspective the increased reflection of SW radiation induced by clouds is greater than outgoing longwave energy trapped by clouds. The estimates of net effect obtained from the three methods are found to be in good agreement (within 3.5 W/sq m). It is concluded that differences in published global mean values of net cloud radiative forcing are mainly due to different data sources and analysis periods. The best estimated annual mean among all previous estimates is considered to be the ERBE measurement (-17.3 W/sq m).

Sohn, Byung-Ju↗