Turbulence in the Strongly Heterogeneous Near-Surface Boundary Layer over Patchy Snow

IF 2.3 3区 地球科学 Q3 METEOROLOGY & ATMOSPHERIC SCIENCES Boundary-Layer Meteorology Pub Date : 2024-01-22 DOI:10.1007/s10546-023-00856-4
Michael Haugeneder, Michael Lehning, Ivana Stiperski, Dylan Reynolds, Rebecca Mott
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Abstract

The near-surface boundary layer above patchy snow cover in mountainous terrain is characterized by a highly complex interplay of various flows on multiple scales. In this study, we present data from a comprehensive field campaign that cover a period of 21 days of the ablation season in an alpine valley, from continuous snow cover until complete melt out. We recorded near-surface eddy covariance data at different heights and investigated spectral decompositions. The topographic setting led to the categorisation of flows into up and down valley flows, with a down valley Föhn event in the middle of the observation period. Our findings reveal that the snow cover fraction is a major driver for the structure and dynamics of the atmospheric layer adjacent to the snow surface. With bare ground emerging, stable internal boundary layers (SIBL) developed over the snow. As the snow coverage decreased, the depth of the SIBL decreased below 1 m and spectra of air temperature variance showed a transition towards turbulent time scales, which were caused by the intermittent advection of shallow plumes of warm air over the snow surface. The intermittent advection could also be observed visually with high spatio-temporal resolution measurements using a thermal infrared camera. While the shallow advection only affected the lowest measurement level at 0.3 m, the measurements above at 1 m, 2 m, and 3 m indicate that the distribution of eddy size and, thus, the turbulence structure, did not distinctly change with height.

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成片积雪上强异质近地表边界层中的湍流
山区零星积雪覆盖上方的近地表边界层的特点是各种流动在多个尺度上高度复杂的相互作用。在本研究中,我们展示了一项综合野外活动的数据,该活动覆盖了高山峡谷消融季节的 21 天,从持续积雪覆盖到完全融化。我们记录了不同高度的近地表涡度协方差数据,并研究了光谱分解。根据地形环境,我们将气流分为上谷气流和下谷气流,并在观测期间的中间出现了一次下谷弗恩事件。我们的研究结果表明,积雪覆盖率是雪面附近大气层结构和动态的主要驱动因素。随着裸露地面的出现,稳定的内部边界层(SIBL)在雪面上形成。随着积雪覆盖率的降低,稳定内边界层的深度减小到 1 米以下,空气温度变化的频谱显示出向湍流时间尺度的过渡,这是由积雪表面浅层暖空气羽流的间歇性平流造成的。通过使用热红外摄像机进行高时空分辨率测量,还可以直观地观察到间歇性平流。虽然浅层平流只影响到 0.3 米的最低测量高度,但 1 米、2 米和 3 米的测量结果表明,漩涡大小的分布以及湍流结构并没有随着高度的变化而明显改变。
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来源期刊
Boundary-Layer Meteorology
Boundary-Layer Meteorology 地学-气象与大气科学
CiteScore
7.50
自引率
14.00%
发文量
72
审稿时长
12 months
期刊介绍: Boundary-Layer Meteorology offers several publishing options: Research Letters, Research Articles, and Notes and Comments. The Research Letters section is designed to allow quick dissemination of new scientific findings, with an initial review period of no longer than one month. The Research Articles section offers traditional scientific papers that present results and interpretations based on substantial research studies or critical reviews of ongoing research. The Notes and Comments section comprises occasional notes and comments on specific topics with no requirement for rapid publication. Research Letters are limited in size to five journal pages, including no more than three figures, and cannot contain supplementary online material; Research Articles are generally fifteen to twenty pages in length with no more than fifteen figures; Notes and Comments are limited to ten journal pages and five figures. Authors submitting Research Letters should include within their cover letter an explanation of the need for rapid publication. More information regarding all publication formats can be found in the recent Editorial ‘Introducing Research Letters to Boundary-Layer Meteorology’.
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