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DOI | 10.5194/acp-18-1241-2018 |
The early summertime Saharan heat low: sensitivity of the radiation budget and atmospheric heating to water vapour and dust aerosol | |
Alamirew, Netsanet K.1; Todd, Martin C.1; Ryder, Claire L.2; Marsham, John H.3,4; Wang, Yi1 | |
2018-01-31 | |
发表期刊 | ATMOSPHERIC CHEMISTRY AND PHYSICS |
ISSN | 1680-7316 |
EISSN | 1680-7324 |
出版年 | 2018 |
卷号 | 18期号:2页码:1241-1262 |
文章类型 | Article |
语种 | 英语 |
国家 | England |
英文摘要 | The Saharan heat low (SHL) is a key component of the west African climate system and an important driver of the west African monsoon across a range of timescales of variability. The physical mechanisms driving the variability in the SHL remain uncertain, although water vapour has been implicated as of primary importance. Here, we quantify the independent effects of variability in dust and water vapour on the radiation budget and atmospheric heating of the region using a radiative transfer model configured with observational input data from the Fennec field campaign at the location of Bordj Badji Mokhtar (BBM) in southern Algeria (21.4 degrees N, 0.9 degrees E), close to the SHL core for June 2011. Overall, we find dust aerosol and water vapour to be of similar importance in driving variability in the top-of-atmosphere (TOA) radiation budget and therefore the column-integrated heating over the SHL (similar to 7 W m(-2) per standard deviation of dust aerosol optical depth - AOD). As such, we infer that SHL intensity is likely to be similarly enhanced by the effects of dust and water vapour surge events. However, the details of the processes differ. Dust generates substantial radiative cooling at the surface (similar to 11 W m(-2) per standard deviation of dust AOD), presumably leading to reduced sensible heat flux in the boundary layer, which is more than compensated by direct radiative heating from shortwave (SW) absorption by dust in the dusty boundary layer. In contrast, water vapour invokes a radiative warming at the surface of similar to 6 W m(-2) per standard deviation of column-integrated water vapour in kg m(-2). Net effects involve a pronounced net atmospheric radiative convergence with heating rates on average of 0.5 K day(-1) and up to 6 K day(-1) during synoptic/mesoscale dust events from monsoon surges and convective cold-pool outflows ("haboobs"). On this basis, we make inferences on the processes driving variability in the SHL associated with radiative and advective heating/cooling. Depending on the synoptic context over the region, processes driving variability involve both independent effects of water vapour and dust and compensating events in which dust and water vapour are co-varying. Forecast models typically have biases of up to 2 kg m(-2) in column-integrated water vapour (equivalent to a change in 2.6 W m(-2) TOA net flux) and typically lack variability in dust and thus are expected to poorly represent these couplings. An improved representation of dust and water vapour and quantification of associated radiative impact in models is thus imperative to further understand the SHL and related climate processes. |
领域 | 地球科学 |
收录类别 | SCI-E |
WOS记录号 | WOS:000423701200002 |
WOS关键词 | WEST-AFRICAN MONSOON ; CONVECTION-PERMITTING SIMULATIONS ; COLD POOL OUTFLOWS ; MINERAL DUST ; OPTICAL-PROPERTIES ; SAHEL RAINFALL ; DIURNAL CYCLE ; CMIP5 SIMULATIONS ; MOIST CONVECTION ; FIELD CAMPAIGN |
WOS类目 | Environmental Sciences ; Meteorology & Atmospheric Sciences |
WOS研究方向 | Environmental Sciences & Ecology ; Meteorology & Atmospheric Sciences |
引用统计 | |
文献类型 | 期刊论文 |
条目标识符 | http://119.78.100.173/C666/handle/2XK7JSWQ/16141 |
专题 | 地球科学 |
作者单位 | 1.Univ Sussex, Dept Geog, Brighton, E Sussex, England; 2.Univ Reading, Dept Meteorol, Reading, Berks, England; 3.Univ Leeds, Sch Earth & Environm, Leeds, W Yorkshire, England; 4.NCAS, Leeds, W Yorkshire, England |
推荐引用方式 GB/T 7714 | Alamirew, Netsanet K.,Todd, Martin C.,Ryder, Claire L.,et al. The early summertime Saharan heat low: sensitivity of the radiation budget and atmospheric heating to water vapour and dust aerosol[J]. ATMOSPHERIC CHEMISTRY AND PHYSICS,2018,18(2):1241-1262. |
APA | Alamirew, Netsanet K.,Todd, Martin C.,Ryder, Claire L.,Marsham, John H.,&Wang, Yi.(2018).The early summertime Saharan heat low: sensitivity of the radiation budget and atmospheric heating to water vapour and dust aerosol.ATMOSPHERIC CHEMISTRY AND PHYSICS,18(2),1241-1262. |
MLA | Alamirew, Netsanet K.,et al."The early summertime Saharan heat low: sensitivity of the radiation budget and atmospheric heating to water vapour and dust aerosol".ATMOSPHERIC CHEMISTRY AND PHYSICS 18.2(2018):1241-1262. |
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