Long-term changes of mesospheric summer echoes at polar and middle latitudes
Long-term changes of mesospheric summer echoes at polar and middle latitudes
复制标题
极地和中纬度地区中层夏季回波的长期变化
DOI：
10.1016/j.jastp.2006.02.012
复制
发表时间：
2006
影响因子：
1.9
通讯作者：
O. Zeller
中科院分区：
文献类型：
--
作者：
J. Bremer;P. Hoffmann;J. Höffner;R. Latteck;W. Singer;M. Zecha;O. Zeller
夏季月份主要在极地纬度(极地中间层夏季回波(PMSE))可以观测到较强的中间层甚高频雷达回波，但在中纬度(中间层夏季回波(MSE))回波功率也降低。这种出乎意料的强雷达回波现象与中上层和中层顶区小冰粒的存在密切相关。因此，这些回波包含有关中层温度和水蒸气含量的信息。但(P)MSE的强度还取决于入射太阳波辐射和沉淀高能粒子通量所产生的电离水平。利用1994年以来在安得内斯(69.3°N，16.0°E)和1998年以来在库伦斯伯恩(54.6°N，11.8°E)的甚高频雷达观测资料，分析了(P)MSE强度与太阳和地磁活动的关系，并得出了可能的长期变化。2002年的特殊行为与南半球冬季行星波活动增强引起的半球间耦合有关。随着雷达回波功率和(P)MSE季节持续时间的增加，有一些小趋势的迹象，这与观测到的夜光云(NLC)和极地中层云(PMC)亮度的一些变化定性一致。然而，派生趋势的显著水平很低，在大多数情况下，趋势与零没有显著不同。
Strong mesospheric VHF radar echoes can be observed during summer months mainly at polar latitudes (polar mesosphere summer echoes, PMSE) but with a reduced echo power also at middle latitudes (mesosphere summer echoes, MSE). This phenomenon of unexpected strong radar echoes is closely connected with the existence of small ice particles in the upper mesosphere and mesopause region. Therefore, these echoes contain information about the mesospheric temperature and water vapour content. But the strength of (P)MSE also depends on the level of ionisation due to incident solar wave radiation and precipitating high energetic particle fluxes. Using observations with VHF radars at Andenes (69.3°N, 16.0°E) since 1994 and at Kühlungsborn (54.6°N, 11.8°E) since 1998, the dependence of the strength of the (P)MSE on the solar and geomagnetic activity has been analysed and, in addition, possible long-term variations were derived. The special behaviour of the year 2002 is discussed in connection with an interhemispheric coupling due to enhanced planetary wave activity at the southern hemisphere winter season. There are some hints of small trends with increasing radar echo power and duration of the (P)MSE season in qualitative agreement with some changes of the observed occurrences rate of noctilucent clouds (NLC) and of the brightness of polar mesospheric clouds (PMC). However, the significance levels of the derived trends are low, and in most cases the trends are not significantly different from zero.