Lori K Fenton , Stephen M. Metzger , Tim I. Michaels , Stephen P. Scheidt , Taylor C. Dorn , Lynn D.V. Neakrase , Banner Cole , Owen Sprau
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引用次数: 2
Abstract
We present initial results of an investigation into meteorological and geological controls on the formation of dust devils (i.e., dust-filled vortices formed in the daytime dry convective boundary layer). During a 2-week field campaign in June 2019 at Smith Creek Valley (SCV), Nevada, USA, we conducted automated time-lapse stereo imaging of dust devils (DDs), while monitoring local meteorological conditions with a broad suite of instruments. Counts of imaged dust devils from two near-cloudless days were compared with a standard suite of atmospheric measurements from a weather tower, eddy correlation flux measurements, and ceilometer backscatter returns. DDs forming in moderate winds (5–8.5 m/s) were more likely to be relatively wide and disorganized, with qualitatively low dust opacity, whereas those forming in weaker winds were more likely to be coherent, dusty, well-formed conical or cylindrical structures. The daily maximum DD counts at SCV occurred shortly after their onset in late morning (11:00–12:00 local time), coinciding with a surge in CBL growth that was likely delayed by the thermal properties of the playa. This late morning peak contrasts with previous studies conducted elsewhere that typically observed peak DD counts in the afternoon. As observed in previous field studies, DDs formed in highly convective conditions, when the heat flux () and friction velocity () were elevated and the convective ratio exceeded ∼ 4 (i.e., exceeded ∼ 25). However, values of>4 also occurred in mid-morning, prior to DD formation and CBL growth, suggesting that this metric is not the sole condition required for DD generation. Aside from the late morning maxima, DD counts fluctuated considerably throughout the afternoon at timescales of 0.5–2 h–correlating poorly with fluctuations in and , and not at all with either or the Monin-Obukhov length (). Several factors, such as local variations in surface thermal properties and meteorology, may be responsible for these short-term fluctuations.
我们提出了对尘卷风形成的气象和地质控制的初步调查结果(即在白天干对流边界层中形成的充满灰尘的涡旋)。2019年6月,在美国内华达州史密斯溪谷(Smith Creek Valley, SCV)为期两周的野外活动中,我们对沙尘暴(dd)进行了自动定时立体成像,同时使用一系列仪器监测当地气象条件。在两个几乎无云的日子里拍摄的尘卷图像的数量与一套标准的大气测量数据进行了比较,这些数据来自气象塔、涡流相关通量测量和ceilometer的反向散射返回。在中等风速(5-8.5 m/s)下形成的坑道更有可能相对较宽且杂乱无章,粉尘不透明度较低,而在较弱风速下形成的坑道更有可能是连贯的、多尘的、形状良好的圆锥形或圆柱形结构。SCV的每日最大DD计数发生在上午晚些时候(当地时间11:00-12:00)开始后不久,与CBL增长的激增相吻合,这可能是由于playa的热性质延迟的。这个上午晚些时候的峰值与之前在其他地方进行的研究形成鲜明对比,这些研究通常在下午观察到DD的峰值。在以往的野外研究中观察到,当热流密度(H)和摩擦速度(u∗)升高,对流比w∗/u∗超过4(即-h/L超过~ 25)时,dd形成于强对流条件下。然而,>4w∗/u∗的值也出现在上午中期,在DD形成和CBL生长之前,这表明该指标不是DD产生所需的唯一条件。除了上午晚些时候的最大值外,DD数在整个下午在0.5-2 H的时间尺度上波动很大,与H和u∗的波动相关性很差,与w∗/u∗或莫宁-奥布霍夫长度(L)完全无关。一些因素,如地表热特性和气象学的局部变化,可能是这些短期波动的原因。
期刊介绍:
The scope of Aeolian Research includes the following topics:
• Fundamental Aeolian processes, including sand and dust entrainment, transport and deposition of sediment
• Modeling and field studies of Aeolian processes
• Instrumentation/measurement in the field and lab
• Practical applications including environmental impacts and erosion control
• Aeolian landforms, geomorphology and paleoenvironments
• Dust-atmosphere/cloud interactions.