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Long-term variability in the mesosphere and lower thermosphere and its relation with the lower atmsophere

中层和低层热层的长期变化及其与低层大气的关系

基本信息

批准号：
15540420
负责人：
MIYOSHI Yasunobu
金额：
$ 1.47万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15540420/
关键词：
atmospheric coupling process below and above long-term variability general circulation general circulation model atmospheric tides Kelvin wave 惑星波大気重力波大気の長周期振動

项目摘要

A new general circulation model (GCM) which contains the region from the ground surface to the exobase has been developed, and used to investigate behavior of the migrating diurnal tide for equinox condition. We studied day-to-day variations of migrating diurnal and semidiurnal tides in the mesosphere and thermosphere and their relation with migrating diurnal tides generated in the lower atmosphere. For example, fluctuations of the migrating diurnal amplitude with periods of 17-18 and 25 days are found in the height range from 20 to 300 km, indicating dynamical coupling between the mesosphere and thermosphere and the lower atmosphere.By using the GCM, excitation mechanism of intraseasonal oscillation of the zonal mean zonal wind in the equatorial mesosphere and lower thermosphere (MLT) were investigated. Wave-mean flow interaction with ultra fast Kelvin waves and diurnal tides is important for driving the intraseasonal oscillation. Not only the migrating diurnal tide but also the non-migrating diurnal tide plays an important role in excitation of the intraseasonal oscillation. Intraseasonal variations of amplitudes of the ultra fast Kelvin waves and the diurnal tides are found at height range from 20 to 90 km heights. Intraseasonal variations of amplitudes of these waves are closely related with variations of the moist convective activity.Interannual variation of the semiannual oscillation in the equatorial MLT was investigated. Upward propagating gravity waves in the MLT are modulated by interannual variation of the zonal wind in the lower stratosphere associated with the Quasi-Biennial Oscillation. This QBO modulated gravity wave activity in the MLT produces interannual variation of the semiannual oscillation.

本文提出了一个新的包含从地面到外底区域的大气环流模式，并用于研究昼夜分点条件下的迁移日潮行为。本文研究了中层和热层中迁移性日潮和半日潮的逐日变化及其与低层大气中迁移性日潮的关系。例如，在20~300 km高度范围内，纬向平均纬向风的日振幅有17-18天和25天的周期波动，表明中层、热层和低层大气之间存在动力耦合。波平均流与超快开尔文波和日潮汐的相互作用对驱动季节内振荡很重要。不仅迁移日潮对季节内振荡的激发起重要作用，非迁移日潮也起重要作用。在20~90km高度范围内，超快Kelvin波和日潮振幅存在季节内变化。这些波动振幅的季节内变化与湿对流活动的变化密切相关。MLT中向上传播的重力波受平流层下部纬向风年际变化的调制，而纬向风的年际变化与准两年振荡有关。这种QBO调制的MLT重力波活动产生了半年振荡的年际变化。