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    A Simplified Model for Intermittent Turbulence in the Nocturnal Boundary Layer

    Source: Journal of the Atmospheric Sciences:;2011:;Volume( 068 ):;issue: 008::page 1714
    Author:
    Costa, Felipe D.
    ,
    Acevedo, Otávio C.
    ,
    Mombach, José C. M.
    ,
    Degrazia, Gervásio A.
    DOI: 10.1175/2011JAS3655.1
    Publisher: American Meteorological Society
    Abstract: model for the exchange between the surface and the atmosphere under stable conditions is proposed. It is based on the classical scheme first suggested by Blackadar and comprises prognostic equations for the wind components and air and ground temperature. The main difference from previous works consists in the fact that the turbulent intensity is determined by a prognostic equation for turbulent kinetic energy (TKE), rather than by using stability functions that arbitrarily relate it to atmospheric stability. Results show that the model reproduces the condition of connection and disconnection between the surface and upper levels. Furthermore, it leads to periodic turbulence bursts when one level within the stable boundary layer (SBL) is considered and the use of additional levels increasingly leads to more complex solutions, characterizing the occurrence of global intermittency. Such turbulence bursts occur in the disconnected state and cause large fluctuations of the variables near the surface. The boundary layer height plays a role in the sense that for the same geostrophic winds, connection is favored for shallower layers. Although playing a role in the intermittency characteristics, soil type is not determinant to their existence, as the bursts occur even for very high values of heat capacity. Vertical profiles for both the intermittent and connected state are analyzed and in general agree with observations. It is shown that, near the surface, weak turbulence bursts favor the exchange between the air and the cooler ground, leading to a local temperature decrease, while stronger events that mix the air deeper in the SBL cause an average warming tendency. An opposite pattern occurs at the upper SBL. Intermittency is favored over a range of low geostrophic winds and clear skies, in agreement with previous suggestions. The vertical structure of the intermittent events is analyzed, and it shown that they are generated at the surface by a local shear increase above a threshold, propagating upward through the turbulence transfer term in the TKE equation. It is proposed that such events constitute a natural characteristic of the disconnected SBL, which occurs along with low large-scale winds and clear skies.
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      A Simplified Model for Intermittent Turbulence in the Nocturnal Boundary Layer

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    contributor authorCosta, Felipe D.
    contributor authorAcevedo, Otávio C.
    contributor authorMombach, José C. M.
    contributor authorDegrazia, Gervásio A.
    date accessioned2017-06-09T16:39:31Z
    date available2017-06-09T16:39:31Z
    date copyright2011/08/01
    date issued2011
    identifier issn0022-4928
    identifier otherams-71711.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4213633
    description abstractmodel for the exchange between the surface and the atmosphere under stable conditions is proposed. It is based on the classical scheme first suggested by Blackadar and comprises prognostic equations for the wind components and air and ground temperature. The main difference from previous works consists in the fact that the turbulent intensity is determined by a prognostic equation for turbulent kinetic energy (TKE), rather than by using stability functions that arbitrarily relate it to atmospheric stability. Results show that the model reproduces the condition of connection and disconnection between the surface and upper levels. Furthermore, it leads to periodic turbulence bursts when one level within the stable boundary layer (SBL) is considered and the use of additional levels increasingly leads to more complex solutions, characterizing the occurrence of global intermittency. Such turbulence bursts occur in the disconnected state and cause large fluctuations of the variables near the surface. The boundary layer height plays a role in the sense that for the same geostrophic winds, connection is favored for shallower layers. Although playing a role in the intermittency characteristics, soil type is not determinant to their existence, as the bursts occur even for very high values of heat capacity. Vertical profiles for both the intermittent and connected state are analyzed and in general agree with observations. It is shown that, near the surface, weak turbulence bursts favor the exchange between the air and the cooler ground, leading to a local temperature decrease, while stronger events that mix the air deeper in the SBL cause an average warming tendency. An opposite pattern occurs at the upper SBL. Intermittency is favored over a range of low geostrophic winds and clear skies, in agreement with previous suggestions. The vertical structure of the intermittent events is analyzed, and it shown that they are generated at the surface by a local shear increase above a threshold, propagating upward through the turbulence transfer term in the TKE equation. It is proposed that such events constitute a natural characteristic of the disconnected SBL, which occurs along with low large-scale winds and clear skies.
    publisherAmerican Meteorological Society
    titleA Simplified Model for Intermittent Turbulence in the Nocturnal Boundary Layer
    typeJournal Paper
    journal volume68
    journal issue8
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/2011JAS3655.1
    journal fristpage1714
    journal lastpage1729
    treeJournal of the Atmospheric Sciences:;2011:;Volume( 068 ):;issue: 008
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
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