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A Study of the Influences of Aerosol...

Zhang, Wei.

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A Study of the Influences of Aerosol on Boundary Layer Clouds Using Large-Eddy Simulations.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	A Study of the Influences of Aerosol on Boundary Layer Clouds Using Large-Eddy Simulations./
作者:	Zhang, Wei.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	135 p.
附註:	Source: Dissertations Abstracts International, Volume: 80-06, Section: B.
Contained By:	Dissertations Abstracts International80-06B.
標題:	Atmospheric sciences. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10932114
ISBN:	9780438693418

A Study of the Influences of Aerosol on Boundary Layer Clouds Using Large-Eddy Simulations.
Zhang, Wei.

A Study of the Influences of Aerosol on Boundary Layer Clouds Using Large-Eddy Simulations. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 135 p.

Source: Dissertations Abstracts International, Volume: 80-06, Section: B.

Thesis (Ph.D.)--State University of New York at Stony Brook, 2018.

This item must not be sold to any third party vendors.

Aerosols act as cloud condensation nuclei (CCN) and ice nuclei (IN), and affect the climate by changing the cloud characteristics in many ways. A Large Eddy Simulation (LES) model coupled with comprehensive microphysics is applied to the study of aerosols' effect on marine boundary layer clouds. This thesis includes results from two research projects: the first one has explored how the morphological, microphysical, dynamical and radiative properties of marine shallow cumuli respond to aerosol perturbation; the second one has quantified the potential of increased aerosol number concentration to inhibit precipitation in marine stratocumulus clouds through the investigation of precipitation susceptibility. The simulations of shallow cumulus clouds include several baseline and sensitivity test runs with different initial aerosol loadings to represent clean or polluted environment, different control of coagulation process to restrain or permit precipitation, and different choice of microphysical scheme to use explicit bin or bulk microphysical scheme. The results show stronger evaporation and enhanced suppression of precipitation in the polluted runs. These two mechanisms act in opposite directions to modify the cloud water content. The final change of liquid water path (LWP) depends on the dominating mechanism which may differ in different environmental conditions. The change of cloud effective radius is robust due to the Twomey effect, while the variation of cloud fraction is more complex. The diagnosed shortwave forcing is controlled by the change in cloud fraction, suggesting the importance of cloud fraction change in the prediction of shortwave cloud radiative forcing and climate change. The cloud drops size distribution and relative dispersion are examined as functions of distance to cloud edges at various heights above the cloud base. The overall relative dispersion is smaller in polluted cases due to their weaker coagulation and stronger updraft. For bin simulations, an algorithm is developed to calculate the coagulation rate based on the cloud drops spectrum and the coagulation kernel. It shows that, although the relative dispersion is relatively large in the entrainment zone near cloud edge, the cloud drops there are too small to collide. Thus, the rain drops prefer to form in more adiabatic regions such as cloud core. Additionally, there are some differences between the results in bin and bulk simulations, particularly in the prediction of cloud fraction and shortwave forcing, which requires further work to evaluate the performance of different microphysical schemes. Four simulations with different initial CCN concentration have been applied to the study of drizzling stratocumulus using LES with explicit bin microphysics. The precipitation susceptibility (S0) is calculated to quantify the decrease in the surface precipitation rate by the increase in cloud drop number concentration. The behavior of S0 under different LWP conditions and the corresponding controlling factors are explored. The results show that the potential of increasing CCN to suppress precipitation highly depends on the growth state of rain/drizzle drops and the cloud drop size distribution. The ratio of autoconversion rate over accretion rate is a good indicator for the behavior of S0 in LWP bins. Besides, the proportion of drops with radii smaller than 6 μm has large impact on S0 too.

ISBN: 9780438693418Subjects--Topical Terms:

3168354
Atmospheric sciences.

A Study of the Influences of Aerosol on Boundary Layer Clouds Using Large-Eddy Simulations.
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506 $a This item must not be sold to any third party vendors.
520 $a Aerosols act as cloud condensation nuclei (CCN) and ice nuclei (IN), and affect the climate by changing the cloud characteristics in many ways. A Large Eddy Simulation (LES) model coupled with comprehensive microphysics is applied to the study of aerosols' effect on marine boundary layer clouds. This thesis includes results from two research projects: the first one has explored how the morphological, microphysical, dynamical and radiative properties of marine shallow cumuli respond to aerosol perturbation; the second one has quantified the potential of increased aerosol number concentration to inhibit precipitation in marine stratocumulus clouds through the investigation of precipitation susceptibility. The simulations of shallow cumulus clouds include several baseline and sensitivity test runs with different initial aerosol loadings to represent clean or polluted environment, different control of coagulation process to restrain or permit precipitation, and different choice of microphysical scheme to use explicit bin or bulk microphysical scheme. The results show stronger evaporation and enhanced suppression of precipitation in the polluted runs. These two mechanisms act in opposite directions to modify the cloud water content. The final change of liquid water path (LWP) depends on the dominating mechanism which may differ in different environmental conditions. The change of cloud effective radius is robust due to the Twomey effect, while the variation of cloud fraction is more complex. The diagnosed shortwave forcing is controlled by the change in cloud fraction, suggesting the importance of cloud fraction change in the prediction of shortwave cloud radiative forcing and climate change. The cloud drops size distribution and relative dispersion are examined as functions of distance to cloud edges at various heights above the cloud base. The overall relative dispersion is smaller in polluted cases due to their weaker coagulation and stronger updraft. For bin simulations, an algorithm is developed to calculate the coagulation rate based on the cloud drops spectrum and the coagulation kernel. It shows that, although the relative dispersion is relatively large in the entrainment zone near cloud edge, the cloud drops there are too small to collide. Thus, the rain drops prefer to form in more adiabatic regions such as cloud core. Additionally, there are some differences between the results in bin and bulk simulations, particularly in the prediction of cloud fraction and shortwave forcing, which requires further work to evaluate the performance of different microphysical schemes. Four simulations with different initial CCN concentration have been applied to the study of drizzling stratocumulus using LES with explicit bin microphysics. The precipitation susceptibility (S0) is calculated to quantify the decrease in the surface precipitation rate by the increase in cloud drop number concentration. The behavior of S0 under different LWP conditions and the corresponding controlling factors are explored. The results show that the potential of increasing CCN to suppress precipitation highly depends on the growth state of rain/drizzle drops and the cloud drop size distribution. The ratio of autoconversion rate over accretion rate is a good indicator for the behavior of S0 in LWP bins. Besides, the proportion of drops with radii smaller than 6 μm has large impact on S0 too.
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