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    What Controls Stratocumulus Radiative Properties? Lagrangian Observations of Cloud Evolution

    Source: Journal of the Atmospheric Sciences:;1997:;Volume( 054 ):;issue: 017::page 2215
    Author:
    Pincus, Robert
    ,
    Baker, Marcia B.
    ,
    Bretherton, Christopher S.
    DOI: 10.1175/1520-0469(1997)054<2215:WCSRPL>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: Marine stratocumulus clouds have a large impact on the earth?s radiation budget. Their optical properties vary on two distinct timescales, one associated with the diurnal cycle of solar insolation and another with the downstream transition to trade cumulus. Hypotheses regarding the control of cloud radiative properties fall broadly into two groups: those focused on the effects of precipitation, and those concerned with the environment in which the clouds evolve. Reconciling model results and observations in an effort to develop parameterizations of cloud optical properties is difficult because marine boundary layer clouds are not in equilibrium with their local environment. The authors describe a new technique for the observation of boundary layer cloud evolution in a moving or Lagrangian frame of reference. Blending satellite imagery and gridded environmental information, the method provides a time series of the environmental conditions to which the boundary layer is subject and the properties of clouds as they respond to external forcings. The technique is combined with in situ observations of precipitation off the coast of California and compared with the downstream evolution of cloud fraction in five cases that were observed to be precipitating with three cases that were not. In this small dataset cloud fraction remains almost uniformly high, and there is no relationship between the presence of precipitation and the evolution of cloud fraction on 1- and 2-day timescales. Analysis of a large number of examples shows that clouds in this region have a typical pattern of diurnal evolution such that clouds that are optically thicker than about 10 during the morning are unlikely to break up over the course of the day but will instead show a large diurnal cycle in optical depth. Morning cloud optical thickness and the resultant susceptibility to breakup have a much larger impact on diurnally averaged cloud radiative forcing than do diurnal variations in cloud properties. Cloud response is significantly correlated with lower tropospheric temperature stratification at all times, though the best correlation exists when cloud response lags stability by at least 16 h. Sea surface temperature is also correlated with cloud properties during the period in which cloud response is measured and the 12 h prior. The authors suggest that sea surface temperature plays two competing roles in determining boundary layer cloudiness, with rapid changes in SST promoting cloudiness on short timescales but tending to lead to a more rapid transition to the trade cumulus regime.
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      What Controls Stratocumulus Radiative Properties? Lagrangian Observations of Cloud Evolution

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4158453
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    • Journal of the Atmospheric Sciences

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    contributor authorPincus, Robert
    contributor authorBaker, Marcia B.
    contributor authorBretherton, Christopher S.
    date accessioned2017-06-09T14:34:40Z
    date available2017-06-09T14:34:40Z
    date copyright1997/09/01
    date issued1997
    identifier issn0022-4928
    identifier otherams-22046.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4158453
    description abstractMarine stratocumulus clouds have a large impact on the earth?s radiation budget. Their optical properties vary on two distinct timescales, one associated with the diurnal cycle of solar insolation and another with the downstream transition to trade cumulus. Hypotheses regarding the control of cloud radiative properties fall broadly into two groups: those focused on the effects of precipitation, and those concerned with the environment in which the clouds evolve. Reconciling model results and observations in an effort to develop parameterizations of cloud optical properties is difficult because marine boundary layer clouds are not in equilibrium with their local environment. The authors describe a new technique for the observation of boundary layer cloud evolution in a moving or Lagrangian frame of reference. Blending satellite imagery and gridded environmental information, the method provides a time series of the environmental conditions to which the boundary layer is subject and the properties of clouds as they respond to external forcings. The technique is combined with in situ observations of precipitation off the coast of California and compared with the downstream evolution of cloud fraction in five cases that were observed to be precipitating with three cases that were not. In this small dataset cloud fraction remains almost uniformly high, and there is no relationship between the presence of precipitation and the evolution of cloud fraction on 1- and 2-day timescales. Analysis of a large number of examples shows that clouds in this region have a typical pattern of diurnal evolution such that clouds that are optically thicker than about 10 during the morning are unlikely to break up over the course of the day but will instead show a large diurnal cycle in optical depth. Morning cloud optical thickness and the resultant susceptibility to breakup have a much larger impact on diurnally averaged cloud radiative forcing than do diurnal variations in cloud properties. Cloud response is significantly correlated with lower tropospheric temperature stratification at all times, though the best correlation exists when cloud response lags stability by at least 16 h. Sea surface temperature is also correlated with cloud properties during the period in which cloud response is measured and the 12 h prior. The authors suggest that sea surface temperature plays two competing roles in determining boundary layer cloudiness, with rapid changes in SST promoting cloudiness on short timescales but tending to lead to a more rapid transition to the trade cumulus regime.
    publisherAmerican Meteorological Society
    titleWhat Controls Stratocumulus Radiative Properties? Lagrangian Observations of Cloud Evolution
    typeJournal Paper
    journal volume54
    journal issue17
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/1520-0469(1997)054<2215:WCSRPL>2.0.CO;2
    journal fristpage2215
    journal lastpage2236
    treeJournal of the Atmospheric Sciences:;1997:;Volume( 054 ):;issue: 017
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
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