Impact of mesoscale vegetation heterogeneities on the dynamical and thermodynamic properties of the planetary boundary layer
Impact of mesoscale vegetation heterogeneities on the dynamical and thermodynamic properties of the planetary boundary layer
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DOI：
10.1029/2009jd012811
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发表时间：
2010-02-03
影响因子：
4.4
通讯作者：
Murphy, Jennifer G.
中科院分区：
文献类型：
--
作者：
Garcia-Carreras, Luis;Parker, Douglas J.;Murphy, Jennifer G.
本研究利用非洲季风多学科分析（AMMA）项目在贝宁共和国上空的飞机观测资料，研究植被非均质性对行星边界层内动力学的影响，如对流、输送和混合。异戊二烯是一种主要由木本植被排放的生物源性挥发性有机化合物，被用作运输的示踪剂，将陆地表面与边界层性质联系起来。与植被边界的行星边界层（PBL）温度梯度相关，观测到持续的中尺度风组织控制了积云的形成模式。发现PBL温度、经向风速、异戊二烯浓度和森林或灌木覆盖比例之间有很强的关系，证实了观测到的动态的陆地表面强迫。观测结果表明，辐合带倾向于出现在暖面和大气异常的南缘。偏北的天气风增加了中尺度气流南部的连贯性，使辐合带向南移位。PBL势温与经向风和异戊二烯浓度的关系分别在10 km和8 km波段具有空间相干。可见卫星数据的季节气候学显示，下午农田上空的云量增加，这表明所提供的结果不仅限于本案例研究，而且对该地区具有气候学意义。
This study uses aircraft observations over the Republic of Benin from the African Monsoon Multidisciplinary Analyses (AMMA) campaign to investigate the impact of vegetation heterogeneities on the dynamics within the planetary boundary layer, such as convection, transport, and mixing. Isoprene, a biogenic volatile organic compound emitted primarily by woody vegetation, was used as a tracer for transport to link the land surface to the boundary layer properties. Associated to planetary boundary layer (PBL) temperature gradients at vegetation boundaries, a persistent mesoscale organization of the winds which controlled patterns in the formation of cumulus congestus clouds was observed. A strong relationship among PBL temperatures, meridional wind velocity, isoprene concentrations, and fraction of forest or shrub cover was found, corroborating the land surface forcing of the observed dynamics. The observations show that the convergence zones tended to occur on the southern edge of warm surface and atmospheric anomalies. The northerly synoptic wind appears to have increased the coherency of the southerly part of the mesoscale flow and displaced the convergence zones southward. The relationships between the PBL potential temperatures and the meridional wind and isoprene concentrations were spatially coherent down to wavelengths of 10 and 8 km, respectively. A seasonal climatology of visible satellite data shows enhanced cloud cover in the afternoon over cropland, suggesting that the results presented are not limited to this case study but are of climatological significance in the region.