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Stratocumulus Cloud-Top Height Estimates and Their Climatic Implications Public Deposited

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  • A depth-dependent boundary layer lapse rate was empirically deduced from 156 radiosondes released during six month-long research cruises to the southeast Pacific sampling a variety of stratocumulus conditions. The lapse-rate dependence on boundary layer height is weak, decreasing from a best fit of 7.6 to 7.2 K km⁻¹ as the boundary layer deepens from 800 m to 2 km. Ship-based cloud-base heights up to 800 m correspond well to lifting condensation levels, indicating well-mixed conditions, with cloud bases >800 m often 200–600 m higher than the lifting condensation levels. The lapse rates were combined with Moderate Resolution Imaging Spectrometer 11-μm-derived cloud-top temperatures and satellite microwave-derived sea surface temperatures to estimate stratocumulus cloud-top heights. The October-mean cloud-top height structure of the southeast Pacific was then spatially and diurnally characterized. Coastal shoaling is apparent, but so is a significant along-coast cloud-top height gradient, with a pronounced elevation of the cloud-top heights above the Arica Bight at ~20°S. Diurnal cloud-top height variations (inferred from irregular 4-times-daily sampling) can locally reach 250 m in amplitude, and they can help to visualize offshore propagation of free-tropospheric vertical motions. A shallow boundary layer associated with the Chilean coastal jet expands to its north and west in the afternoon. Cloud-top heights above the Arica Bight region are depressed in the afternoon, which may mean that increased subsidence from sensible heating of the Andes dominates an afternoon increase in convergence/upward motion at the exit of the Chilean coastal jet. In the southeast Atlantic during October, the stratocumulus cloud-top heights are typically lower than those in the southeast Pacific. A coastal jet region can also be identified through its low cloud-top heights. Coastal shoaling of the South Atlantic stratocumulus region is mostly uniform with latitude, in keeping with the more linear Namibian/Angolan coastline. The southeast Atlantic shallow cloudy boundary layer extends farther offshore than in the southeast Pacific, particularly at 15°S.
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  • Zuidema, Paquita, David Painemal, Simon de Szoeke, Chris Fairall, 2009: Stratocumulus Cloud-Top Height Estimates and Their Climatic Implications. Journal of Climate, 22, 4652–4666.
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  • Support from the NOAA Climate Program for the Prediction of the Americas (CPPA Grant NA06OAR4310056) for PZ and DP, and CPPA Grants GC07-095 and GC06-087 for SdS and CF, is gratefully acknowledged.
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  • description.provenance : Submitted by Deborah Campbell (deborah.campbell@oregonstate.edu) on 2012-04-18T20:44:42Z No. of bitstreams: 1 deSzoekeSimon.CEOAS.StratocumulusCloudTop.pdf: 3778068 bytes, checksum: 554a69977368a4d2ef9fdd1b1e295c70 (MD5)
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