Seasonal variation of gravity wave activity in the lower atmosphere observed with the MU radar
Seasonal variation of gravity wave activity in the lower atmosphere observed with the MU radar
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DOI：
10.1029/94jd01717
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发表时间：
1994-11
影响因子：
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通讯作者：
Y. Murayama;T. Tsuda;S. Fukao
中科院分区：
文献类型：
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作者：
Y. Murayama;T. Tsuda;S. Fukao
本文分析了 1985 年 12 月至 1989 年 12 月期间 MU 雷达逐月观测揭示的对流层和平流层低层（5~25 km）重力波活动的季节变化。在平流层低层，周期为 5 min~21 h 的重力波引起的风速变化表现出明显的年变化，冬季最大，夏季最小，与急流强度的季节变化吻合较好。这表明重力波的激发与背景平均风的行为密切相关。短周期重力波（地基周期为5 min~2 h）的单位体积比动能在冬季和春季增强，其剖面峰值位于急流峰值（∼12 km）附近。另一方面，长周期（2-21小时）分量的动能表现出明显的年变化，在对流层中层和平流层下层出现冬季最大值和夏季最小值。平流层低层长周期分量的动能比对流层低，似乎没有穿透平流层低层。在短周期分量中，观察到急流峰值高度附近的水平与垂直风方差之比在冬季较大，在夏季较小，这可能是由于布伦特-维萨拉频率的季节性变化。冬季对流层上层和平流层下层长周期分量的风方差比大幅减小，可能是由于重力波的多普勒频移所致。 5分钟至21小时周期分量的纬向动量垂直通量在对流层上层和平流层下层显示为负值，这意味着平流层下层向上传播的重力波相对于背景风大部分向西传播。我们没有发现经向动量的垂直通量有任何显着的季节性变化。
In this paper we analyzed the seasonal variation of gravity wave activity in the troposphere and lower stratosphere (5–25 km) as revealed by monthly observations with the MU radar between December 1985 and December 1989. In the lower stratosphere, wind velocity variance due to gravity waves with periods of 5 min-21 hours showed a clear annual variation with a maximum in winter and a minimum in summer, agreeing fairly well with the seasonal variation of the jet stream intensity. This suggests that the excitation of gravity waves is closely related to the behavior of the background mean winds. The specific kinetic energy per unit volume of short-period gravity waves (ground-based period of 5 min-2 hours) was enhanced in winter and spring, its peak in the profile being located near the peak of the jet stream (∼12 km). On the other hand, the kinetic energy of the long-period (2–21 hours) component showed clear annual variation with a winter maximum and a summer minimum in the middle troposphere and lower stratosphere. The kinetic energy of the long-period component was smaller in the lower stratosphere than in the troposphere, which did ot seem to penetrate the lower stratosphere. In the short-period component the ratio of the horizontal to the vertical wind variances near the jet peak height was observed to be large in winter and small in summer, probably due to the seasonal variation of the Brunt-Vaisala frequency. The wind variance ratio for the long-period component in the upper troposphere and lower stratosphere was greatly reduced in winter, possibly due to the Doppler shifting of gravity waves. The vertical flux of zonal momentum for the 5 min- to 21-hour period component showed negative values in the upper troposphere and lower stratosphere, implying that the upward propagating gravity waves in the lower stratosphere mostly traveled westward relative to the background wind. We did not find any significant seasonal variations in the vertical flux of meridional momentum.