QBO形成过程中重力内波的活动特征

Features of Internal Gravity Waves during the QBO′s Generation

本文利用一个沿赤道的经度－高度二维原始方程模式，在下边界处采用一个东传、波数为１（波１Ｅ）和一个西传、波数为２（波２Ｗ），相速度绝对值均为３１ｍ·ｓ－１的两个波作为强迫波，对赤道平流层低层的大尺度运动进行了模拟，再现了平均纬向流的准两年周期振荡（ＱＢＯ）式变化，振荡周期约为３６个月，东西风带的最大风速达４８ｍ·ｓ－１，远远超过两个强迫波的相速度。波动分析表明，通过波与波的非线性相互作用，产生了许多新波，新波中波数为１的西传波（波１Ｗ）和波数为２的东传波（波２Ｅ）在ＱＢＯ形成过程中起了一定的重要作用，强迫波１Ｅ和２Ｗ可分别将西风带和东风带加速到３１ｍ·ｓ－１，对于东风带，相速度约为９１ｍ·ｓ－１的波１Ｗ可进一步加速平均流到４８ｍ·ｓ－１；而对于西风带，波２Ｅ在２０ｋｍ以下对平均流有一定的加速作用。

A two-dimensional model in the equatorial zonal-vertical plane was applied to study the internal gravity waves during the QBO′s generation in the lower equatorial stratosphere. Two monochromatic waves are steadily forced at the bottom boundary. One is the eastward-propagating wave with wavenumber 1 (wave 1E) and the other is the westward-propagating wave with wavenumber 2 (wave 2W). Their absolute phase velocities are about 31 m·s -1 . The model successes in reproducing the QBO-like oscillations of the zonal mean flow and the oscillation period is about 36 months. However, the maximum absolute wind speeds of both easterlies and westerlies are about 48 m·s -1 which is much larger than the absolute phase velocities of the two forced waves. Wave analysis shows that many new waves are generated through nonlinear wave-wave interactions. In newly generated waves, the westward-propagating wave with zonal wavenumber 1 (wave 1W) and eastward-propagating waves with zonal wavenumber 2 (wave 2E) take some important roles in the QBO′s generation. The forced wave 1E and 2W can accelerate westerlies and easterlies to about 31 m·s -1 , respectively. For easterlies, the newly generated wave 1W, whose phase velocity is about 91 m·s -1 , may further accelerate the zonal mean flow up to 48 m·s -1 . But for westerlies, the newly generated wave 2E can accelerate the zonal mean flow only under 20 km and the excessive acceleration of the zonal mean flow is likely due to the self-acceleration of wave 1E.