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The impact of meteorology on smoke a...

Adebiyi, Adeyemi A.

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The impact of meteorology on smoke and low-level clouds over the southeast Atlantic.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	The impact of meteorology on smoke and low-level clouds over the southeast Atlantic./
作者:	Adebiyi, Adeyemi A.
面頁冊數:	243 p.
附註:	Source: Dissertation Abstracts International, Volume: 78-03(E), Section: B.
Contained By:	Dissertation Abstracts International78-03B(E).
標題:	Meteorology. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10154833
ISBN:	9781369099256

The impact of meteorology on smoke and low-level clouds over the southeast Atlantic.
Adebiyi, Adeyemi A.

The impact of meteorology on smoke and low-level clouds over the southeast Atlantic. - 243 p.

Source: Dissertation Abstracts International, Volume: 78-03(E), Section: B.

Thesis (Ph.D.)--University of Miami, 2016.

In this dissertation, we use radiosondes and satellite observation, reanalysis datasets, as well as radiative and trajectory models to document the relationship between the low-level clouds, smoke and meteorology over the southeast Atlantic. The southeast Atlantic presents a natural environment with one of the world's largest marine low-level clouds, occurring along with the largest consumption of biomass fire over the adjacent southern African continent. This combination results in an extensive region of above-cloud biomass burning aerosols (predominantly smoke) over the marine low-level clouds, whereby the elevated smoke could lead to the stabilization of the lower troposphere, reduction of the cloud-top entrainment, and the build-up of water vapor within the boundary layer, which may eventually lead to increases in cloud fraction and decreases in cloud-top heights, in a process called semi-direct aerosol effect. The smokes are transported at a preferred altitude (&sim;750h Pa -- 550hPa) by a background easterly winds between July and October. During the same period, strong surface winds and ocean-influenced cold surface temperature characterize the meteorology within the boundary layer. The marine low-level cloud region is also associated with strong climatological subsidence above it, and cloud-top temperature inversion layer. The meteorological variations occurring above and below the low-level clouds are capable of influencing the cloud properties, and therefore may confound with the aerosol effects, making the separation of the aerosol and meteorological influences, on the low-level cloud, a very difficult challenge. We address this problem by identifying the dynamical and thermodynamical variations above the low-level clouds during the the peak aerosol months (July--October). Specifically, three areas are explored in this dissertation: the convolution of the dynamical and moisture effects with shortwave-absorbing aerosols over the low-level clouds; the role of the mid-tropospheric easterly-transporting system on both the elevated smoke and the low-level cloud environments; and the synoptic-scale sensitivity of the low-level clouds to a range of interacting meteorological conditions, with and without the presence of the elevated smoke.

ISBN: 9781369099256Subjects--Topical Terms:

542822
Meteorology.

The impact of meteorology on smoke and low-level clouds over the southeast Atlantic.
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245 1 4 $a The impact of meteorology on smoke and low-level clouds over the southeast Atlantic.
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500 $a Source: Dissertation Abstracts International, Volume: 78-03(E), Section: B.
500 $a Adviser: Paquita Zuidema.
502 $a Thesis (Ph.D.)--University of Miami, 2016.
520 $a In this dissertation, we use radiosondes and satellite observation, reanalysis datasets, as well as radiative and trajectory models to document the relationship between the low-level clouds, smoke and meteorology over the southeast Atlantic. The southeast Atlantic presents a natural environment with one of the world's largest marine low-level clouds, occurring along with the largest consumption of biomass fire over the adjacent southern African continent. This combination results in an extensive region of above-cloud biomass burning aerosols (predominantly smoke) over the marine low-level clouds, whereby the elevated smoke could lead to the stabilization of the lower troposphere, reduction of the cloud-top entrainment, and the build-up of water vapor within the boundary layer, which may eventually lead to increases in cloud fraction and decreases in cloud-top heights, in a process called semi-direct aerosol effect. The smokes are transported at a preferred altitude (&sim;750h Pa -- 550hPa) by a background easterly winds between July and October. During the same period, strong surface winds and ocean-influenced cold surface temperature characterize the meteorology within the boundary layer. The marine low-level cloud region is also associated with strong climatological subsidence above it, and cloud-top temperature inversion layer. The meteorological variations occurring above and below the low-level clouds are capable of influencing the cloud properties, and therefore may confound with the aerosol effects, making the separation of the aerosol and meteorological influences, on the low-level cloud, a very difficult challenge. We address this problem by identifying the dynamical and thermodynamical variations above the low-level clouds during the the peak aerosol months (July--October). Specifically, three areas are explored in this dissertation: the convolution of the dynamical and moisture effects with shortwave-absorbing aerosols over the low-level clouds; the role of the mid-tropospheric easterly-transporting system on both the elevated smoke and the low-level cloud environments; and the synoptic-scale sensitivity of the low-level clouds to a range of interacting meteorological conditions, with and without the presence of the elevated smoke.
520 $a First, the analysis of the radiosondes at St. Helena Island, a small island located approximately 1800 km offshore of continental Africa (15.9°S, 5.6°W), shows the presence of mid-tropospheric moisture within the smoke layer, and above the low-level clouds. The smoke layer has previously been associated with hot and dry layer, perhaps in analogy to the Saharan air layer. The mid-tropospheric moisture over the south-east Atlantic has not been previously documented, and it occurs more than 70% of the time between September and October. During the same months, as the aerosol loading increases, the amount of the mid-tropospheric moisture also increases. The result of the radiative transfer calculations shows that the mid-tropospheric moisture-induced longwave cooling accounts for about 30% of the aerosol-induced shortwave warming, within the smoke layer. At the cloud top, increased mid-tropospheric moisture could increase cloud-top heights by enhancing the downwelling longwave radiation at the cloud top, and potentially reducing the turbulent mixing within the boundary layer, which may ultimately reduce the cloud fraction. This process essentially opposes the cloud-thickening semi-direct aerosol effect due to the elevated smoke alone.?
520 $a By isolating the independent effects of selected above-cloud and surface-based meteorological influences during July--October period, it is shown that increases in lower tropospheric stability (LTS, defined as theta800 hPa -- theta1000 hPa), cold surface advection and warm 800 hPa horizontal temperature advection, all lead to increases in marine low-level cloudiness over the southeast Atlantic. In addition, the mid-tropospheric moisture is shown to independently result in reduction of cloud fraction, especially in the near- coastal region. Enhanced subsidence independently leads to increased cloudiness north of 20°S, but decreased cloudiness south of 20°S. The subsidence-induced reduction in cloudiness, south of 20°S, contributes significantly to counteracting the stability-induced increases in cloudiness over the same region. When aerosol is present north of 20°S, the effect of LTS on the low-level cloud is increased by about 13% over the region where the elevated aerosols are more likely separated from the underlying clouds, and by about 32% when the aerosols are more likely in contact with the underlying cloud layer.
520 $a The results of this dissertation provide a detailed, useful meteorological context, highlighting new information, for the several multi-national upcoming field campaigns planned over the southeast Atlantic region. It also provides a useful understanding of the background dynamics and basic physical connections between the aerosols, the low-level clouds and the meteorology over the southeast Atlantic, that can be used in future studies involving aerosol-cloud-radiation interactions, and ultimately in numerical climate models to improve the estimation of climate sensitivity to subtropical low-level clouds. (Abstract shortened by ProQuest.).
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