Characteristics of Nocturnal Low-Level Jets Observed in the North Florida Area
Characteristics of Nocturnal Low-Level Jets Observed in the North Florida Area
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DOI：
10.1175/2009mwr2705.1
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发表时间：
2009-08
影响因子：
3.2
通讯作者：
A. Karipot;M. Leclerc;Gengsheng Zhang
中科院分区：
文献类型：
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作者：
A. Karipot;M. Leclerc;Gengsheng Zhang
利用跨越540个夜晚的声雷达测量结果研究了佛罗里达北部地区夜间低空急流的季节和年际变化。平均而言，喷射存在于62%的夜间时段检查。所观察到的射流速度范围在3和21 m s 21之间，高度在80和700 m之间。观测结果表明，低空急流在11月至2月较冷的月份发生得更频繁（占夜间时段的70%），而在6月至8月较温暖的月份（占47%）。在夏季，偏南的急流占主导地位，而偏北的急流在冬季更频繁。寒冷的月份经常会出现速度超过14 m s 21的喷流，通常与锋面系统的通过有关。利用北美区域再分析（NARR）风廓线资料观测的4年期间的年际变化表明，急流特征的差异很小。急流高度与NARR行星边界层高度的比较表明，佛罗里达北部的急流经常发生在行星边界层内。观测到的低空急流的发生和速度与陆地-海洋温度对比以及该地区表面压力梯度的强度和方向有关。使用希尔伯特-黄变换分析表明，在喷流高度附近出现了大约24小时周期的大振幅振荡，这表明惯性振荡是佛罗里达北部喷流形成的一个可能原因。
The seasonal and interannual variability of the nocturnal low-level jets over the north Florida region are investigated using sodar measurements spanning 540 nights. On average, jets are present in 62% of the nocturnal periods examined. The observed jet speeds range between 3 and 21 m s 21 and heights are between 80 and 700 m. Observations show that the low-level jet occurs more frequently (70% of the nocturnal periods) during the colder months November‐February in contrast with the warmer months June‐August (;47%). The presence of southerly jets dominates the summer months, whereas northerly jets are more frequent during winter. Colder months frequently exhibit jets with speeds exceeding 14 m s 21 , often associated with the passage of frontal systems. The interannual variability observed using the North American Regional Reanalysis (NARR) wind profile data during a 4-yr period shows only minimal differences in jet characteristics.A comparison of jet heights with NARR planetary boundary layer heights suggests that jets at the north Florida location frequently occur within the planetary boundary layer. The occurrence and speed of observed low-level jets are linked to both the land‐ocean temperature contrast and to the strength and orientation of surface pressure gradients over the region. A high occurrence of large-amplitude oscillations with approximately a 24-h period near the jet height is shown using the Hilbert‐Huang transform analysis, suggesting that inertial oscillations are one possible cause of jet formation in north Florida.