Collaborative Experiments of Convection and Gravity Waves

1.对流层和平流层的气球观测利用1993年至1996年赤道加里曼丹每日的无线电探空资料，我们研究了大气重力波的长期变化，发现它们在对流层中的季节变化和准重力波的调制，平流层两年一次的振荡。我们进行了一次观测活动，在爪哇、2000年11月至12月，苏门答腊和加里曼丹群岛。在平流层发现了重力波，并揭示了其纬度依赖性。垂直波数谱在200 m以下出现指数为-3的拖尾。传统理论用重力波的饱和度来解释这一特征。然而，有趣的是，在观测到的平流层下部没有看到饱和。在印度尼西亚万隆郊区安装了一台全天空成像仪，用于观测投射到OH气辉上的重力波。我们已经成功地在90公里左右的高度观测到重力波，并研究了水平结构和传播。结果表明，它们的传播主要是向南的。观测将继续进行，预计将提供数据，揭示重力波的季节性和逐年变化。用中频雷达和流星雷达观测中层和低热层加里曼丹的中频雷达增加了一个新的天线，使其能够测量与低热层区域的波有关的动量通量。利用爪哇的中频雷达和流星雷达，研究了重力波和长周期行星尺度波的长期变化。从1996年开始的两年中，重力波和开尔文波的活动都很弱。还发现，30至60天周期的波与对流层季节内振荡有很好的相关性。

1. Balloon Observation of the troposphere and the stratosphereBy using daily radiosonde soundings from 1993 to 1996 in the equatorial Kalimantan, we have investigated long-term variability of atmospheric gravity waves and found their seasonal variation in the troposphere and a modulation by the Quasi-Biennial Oscillation in the stratosphere.We have conducted an observational campaign to launch radiosondes 4 times daily at three sites in each of Java, Sumatra, and Kalimantan Islands from November to December, 2000. Gravity waves were identified in the stratosphere, and their latitudinal dependence was revealed. Vertical wavenumber spectra showed tails with a -3 exponent down to the vertical wave length of 200m. Conventional theories have explained this feature in terms of saturation of gravity waves. Interestingly, however, it was shown that no saturation was seen in the observed lower stratosphere.2. Observation of gravity waves with all-sky imagersAn all-sky imager was installed in the suburb of Bandung, Indonesia to observe gravity waves projected onto OH airglow. We have successfully observed gravity waves at altitudes around 90km and studied horizontal structure and propagation. It was found that their propagation was mostly southward. The observation will be continued and is expected to provide data to reveal seasonal and year-to-year variability of the gravity waves.3. Observation of the mesosphere and lower thermosphere (MLT) by MF and meteor radarsA new antenna was added to the MF radar in Kalimantan in order to make it capable of measuring the momentum flux associated with waves in the MLT region. With the MF radar and a meteor radar in Java, long-term variation of gravity waves and long-period planetary-scale waves were investigated. Activities of gravity and Kelvin waves were found to be weak throughout two years from 1996. It was also found that waves with 30- to 60-day periods correlate well with tropospheric intra-seasonal oscillation.