Wang Jingfeng, Chagnon Frédéric J F, Williams Earle R, Betts Alan K, Renno Nilton O, Machado Luiz A T, Bisht Gautam, Knox Ryan, Bras Rafael L
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Proc Natl Acad Sci U S A. 2009 Mar 10;106(10):3670-4. doi: 10.1073/pnas.0810156106. Epub 2009 Feb 23.
Shallow clouds are prone to appear over deforested surfaces whereas deep clouds, much less frequent than shallow clouds, favor forested surfaces. Simultaneous atmospheric soundings at forest and pasture sites during the Rondonian Boundary Layer Experiment (RBLE-3) elucidate the physical mechanisms responsible for the observed correlation between clouds and land cover. We demonstrate that the atmospheric boundary layer over the forested areas is more unstable and characterized by larger values of the convective available potential energy (CAPE) due to greater humidity than that which is found over the deforested area. The shallow convection over the deforested areas is relatively more active than the deep convection over the forested areas. This greater activity results from a stronger lifting mechanism caused by mesoscale circulations driven by deforestation-induced heterogeneities in land cover.
浅云容易出现在森林砍伐后的地表上空，而深云出现的频率远低于浅云，它们更倾向于出现在有森林覆盖的地表上空。在朗多尼亚边界层实验（RBLE - 3）期间，对森林和牧场站点进行的同步大气探测，阐明了造成观测到的云与土地覆盖之间相关性的物理机制。我们证明，由于森林覆盖地区的湿度高于森林砍伐地区，其大气边界层更不稳定，且具有更大的对流有效位能（CAPE）值。森林砍伐地区的浅层对流相对比森林覆盖地区的深层对流更为活跃。这种更强的活动是由森林砍伐引起的土地覆盖异质性驱动的中尺度环流所导致的更强抬升机制造成的。
