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首页> 外文期刊>Journal of Geophysical Research, D. Atmospheres: JGR >The low-level jet dust emission mechanism in the central Sahara: Observations from Bordj-Badji Mokhtar during the June 2011 Fennec Intensive Observation Period
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The low-level jet dust emission mechanism in the central Sahara: Observations from Bordj-Badji Mokhtar during the June 2011 Fennec Intensive Observation Period

机译：撒哈拉中部的低空喷射尘埃排放机制：2011年6月芬尼茨密集观测期期间Bordj-Badji Mokhtar的观测

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摘要

This paper presents the first detailed analysis of low-level jets (LLJs) in the central Sahara from ground-based observations at Bordj-Badji Mokhtar, Algeria, and addresses their operation as a dust emission mechanism. On LLJ mornings, composite wind speeds in the core (300 m aboveground level) reach 13.5 m s~(-1) at 0400. Surface temperatures increase from 0545 (30 min after sunrise), and jet decay begins around 0600. Ten meter winds lag those in the core by 5 h; peak 10 m wind speed, 7.5 m s~(-1), occurs at 0900. Only the deepest and strongest LLJs lead to dust emission. At 0600, these five LLJs have core wind speeds ≥16 m s~(-1), below-core wind shear ≥ 0.6 m s~(-1)/30m, and wind shear between the core and 500 m above the core ≤-1.8 m s~(-1). On these occasions, momentum mixes down from the LLJ after surface heating, leading to emission. On nondusty LLJmornings, the convective boundary layer is 100 m shallower, and the LLJ is too weak to provide enough momentum to be mixed down for emission. LLJs are most frequently embedded in the monsoon flow or in the Harmattan; there is a clear association with the Saharan Heat Low. ERA-Interim reanalysis underestimates both Harmattan and monsoon LLJ core winds (by 4ms~(-1) and 6m s~(-1), respectively). The Met Office Africa Limited Area Model underestimates Harmattan LLJ core winds by only 0.2 m s~(-1). Monsoon LLJ core winds, however, are underestimated by 8.5 m s~(-1). Surface winds at 0900 are underestimated in both cases by up to 6 m s~(-1).
机译：本文根据阿尔及利亚Bordj-Badji Mokhtar的地面观测资料，对撒哈拉中部的低空急流（LLJ）进行了首次详细分析，并阐述了其作为扬尘排放机制的作用。在LLJ早晨，0400时岩心（地上300 m）的复合风速达到13.5 ms〜（-1）。地表温度从0545（日出后30分钟）开始升高，并且射流衰减开始于0600左右。滞后十米5小时内到达核心最高风速10 m为7.5 m s〜（-1），发生在0900。只有最深和最强的LLJ才会导致扬尘。在0600，这五个低空急流的风速≥16ms〜（-1），岩心下方风切变≥0.6 ms〜（-1）/ 30m，岩心与岩心以上500 m之间的风切变≤-1.8毫秒〜（-1）。在这些情况下，表面加热后动量会从LLJ混合下来，从而导致排放。在非尘埃LLJmornings上，对流边界层浅100 m，并且LLJ太弱，无法提供足够的动量以进行向下混合以排放。 LLJ最常嵌入季风流或Harmattan中。与撒哈拉低地热有明显的联系。 ERA-Interim重新分析低估了Harmattan和季风LLJ核心风（分别为4ms〜（-1）和6m s〜（-1））。非洲气象局有限区域模型仅将Harmattan LLJ核心风低估了0.2 m s〜（-1）。然而，季风LLJ核心风被低估了8.5 m s〜（-1）。在两种情况下，在0900处的地面风都低估了6 m s〜（-1）。

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