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51.
Snow accumulation and melt were observed at shrub tundra and tundra sites in the western Canadian Arctic. End of winter snow water equivalent (SWE) was higher at the shrub tundra site than the tundra site, but lower than total winter snowfall because snow was removed by blowing snow, and a component was also lost to sublimation. Removal of snow from the shrub site was larger than expected because the shrubs were bent over and covered by snow during much of the winter. Although SWE was higher at the shrub site, the snow disappeared at a similar time at both sites, suggesting enhanced melt at the shrub site. The Canadian Land Surface Scheme (CLASS) was used to explore the processes controlling this enhanced melt. The spring‐up of the shrubs during melt had a large effect on snowmelt energetics, with similar turbulent fluxes and radiation above the canopy at both sites before shrub emergence and after the snowmelt. However, when the shrubs were emerging, conditions were considerably different at the two sites. Above the shrub canopy, outgoing shortwave radiation was reduced, outgoing longwave radiation was increased, sensible heat flux was increased and latent flux was similar to that at the tundra site. Above the snow surface at this site, incoming shortwave radiation was reduced, incoming longwave radiation was increased and sensible heat flux was decreased. These differences were caused by the lower albedo of the shrubs, shading of the snow, increased longwave emission by the shrub stems and decreased wind speed below the shrub canopy. The overall result was increased snowmelt at the shrub site. Although this article details the impact of shrubs on snow accumulation and melt, and energy exchanges, additional research is required to consider the effect of shrub proliferation on both regional hydrology and climate. Copyright 2010 John Wiley & Sons Ltd and Crown in the right of Canada. 相似文献
52.
2016年7月18—22日在华北地区发生了一次极端强降水事件,其中19—20日降水较为集中,20日降水最强。本文利用NCEP/NCAR再分析逐日风场资料和国家级地面气象站基本气象要素日值数据集,研究了本次事件的Rossby波活动及能量变化,结果表明:本次极端强降水事件持续时间约5 d,雨带呈西南—东北走向。华北地区受对流层中低层的气旋性异常环流和对流层上层反气旋性异常环流的控制,水汽则主要源于孟加拉湾和中国南海地区。发生极端降水期间,波扰动能量在对流层低层主要呈经向传播而在对流层上层呈纬向传播,对流层低层的波扰动能量对华北地区的影响比上层更为明显。涡动动能在华北地区的增强和维持主要是涡动非地转位势通量散度项、涡动有效位能和涡动动能的斜压转换项以及其他剩余部分与摩擦耗散引起的能量损耗之和的共同作用,涡动动能在19日增强、20日维持,随后减弱。涡动热量通量变化显示低层有暖湿空气向北输送,高层有干冷空气向南输送,支持了正压和斜压转换,而华北地区上空涡动动量通量的变化则使得基本气流中的涡动动能增强,这些变化影响到极端降水事件的发生发展。 相似文献