On the tropospheric origin of Mesosphere Lower Thermosphere region intraseasonal wind variability
On the tropospheric origin of Mesosphere Lower Thermosphere region intraseasonal wind variability
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中层低热层区季节内风变率的对流层起源
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
R. Rajaram
中科院分区：
文献类型：
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作者：
K. K. Kumar;T. M. Antonita;G. Ramkumar;Vinay Deepa;S. Gurubaran;R. Rajaram
[1]2004年2月至2005年5月期间(486天)在提鲁内尔维利(8.7°N，77.8°E)对中间层低热层(MLT)区域风进行的连续中频雷达观测显示，82至94公里高度区域存在季节内振荡。两个明显的周期为50-70天和20-40天的振荡主要出现在纬向风中。由于众所周知，这些振荡在时间上是非平稳的和局部性的，所以用小波分析来研究这些振荡的时间演化。分析表明，MLT区域的50-70天振荡峰值出现在6-10月，20-40天振荡峰值出现在1-3月。为了追溯这些振荡的起源，在同一时期，我们利用出射长波辐射(OLR)观测研究了对流层ISO。本文使用的OLR是雷达站5-10°N，70-80°E附近低层大气对流活动的指标。OLR的小波分析表明，50-70天的振荡与MLT区的振荡同时达到峰值。这几个月的OLR资料没有观测到短周期(20-40天)的振荡，其峰值出现在MLT区的1-3月。然而，对水汽的分析表明，在与MLT区域相同的时间内，水汽是潮汐激发的主要候选者，存在20至40天的振荡。在本研究中，通过重力波激发的低层大气对流活动和通过潮汐强迫的水汽解释了MLT地区观测到的ISO。本文结果的意义在于显示了OLR和MLT区域纬向风的高度相干振荡。根据现有的机制，对中低大气ISO之间的耦合进行了广泛的讨论。
[1] Continuous medium frequency radar observations of mesosphere lower thermosphere (MLT) region winds during February 2004–May 2005 (486 days) over Tirunelveli (8.7°N, 77.8°E) revealed intraseasonal oscillations (ISOs) in the 82- to 94-km height region. Two distinct oscillations with periods 50–70 and 20–40 days are noticed predominantly in zonal winds. As it is well established that these oscillations are nonstationary and localized in time, wavelet analysis has been employed to study the time evolution of these oscillations. The analysis showed that 50- to 70-day oscillation peaks during June-October and 20- to 40-day oscillation peaks during January-March in the MLT region. To trace back the origin of these oscillations, the tropospheric ISO has been studied for the same period using outgoing long-wave radiation (OLR) observations. The OLR, which is the proxy for convective activity in the lower atmosphere, around the radar site 5–10°N, 70–80°E is used for the present analysis. The wavelet analysis of OLR showed the 50- to 70-day oscillation peaking at the same time as in the MLT region. The shorter period oscillation (20–40 days), which showed its peak during January-March in the MLT region, is not observed in the OLR data during these months. However, the analysis of water vapor, which is the prime candidate for excitation of tides, showed the 20- to 40-day oscillation during the same time as in the MLT region. In the present study, the lower atmospheric convective activity through gravity wave excitation and water vapor through tidal forcing are accounted for the observed ISO in the MLT region. The significance of present results lies in showing the highly coherent oscillations in OLR and MLT region zonal winds. The coupling between the lower and middle atmospheric ISO is extensively discussed in the light of existing mechanisms.