The thermal and dynamical state of the atmosphere during polar mesosphere winter echoes
The thermal and dynamical state of the atmosphere during polar mesosphere winter echoes
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极地中间层冬季回波期间大气的热力和动力状态
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
M. Friedrich
中科院分区：
文献类型：
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作者：
F. Lübken;B. Strelnikov;M. Rapp;W. Singer;R. Latteck;A. Brattli;U. Hoppe;M. Friedrich
2005 年 1 月，总共 18 枚火箭从挪威北部的安多亚火箭靶场（北纬 69 度）发射到被称为“极地中间层冬季回波”（PMWE）的强 VHF 雷达回波中。在太阳质子通量较大时，在中层和中层下部观察到了回波。一般来说，与夏季对应的 PMSE 相比，PMWE 的发生率要少得多（69 N 时的典型发生率分别为 1-3% 和 80%）。我们通过落球、箔条和仪表有效载荷进行的现场测量提供了有关大气热和动态状态的详细信息，因此可以对 PMWE 期间的背景大气进行前所未有的研究。有许多独立的观察结果表明中性空气湍流引起了 PMWE。离子密度波动显示 PMWE 内有湍流谱，外部没有波动。在 PMWE 附近观察到接近绝热梯度的温度递减率，表明存在持续的湍流混合。雷达回波的频谱展宽与湍流速度波动一致。湍流也解释了PMWE的平均出现高度（68-75公里）：粘度随着高度的增加而迅速增加，破坏了上层中间层的任何小尺度波动，而下层中间层的电子密度通常太低，无法引起显着的反向散射。低层中间层回波的季节性变化与早期探空火箭飞行得出的湍流气候学一致。我们进行了模型计算来研究中性空气湍流引起的等离子体波动引起的雷达反向散射。我们发现 PMWE 期间观察到的体积反射率与理论在数量上一致。除了湍流之外最关键的要求对应于：F.-J。 PMWE 的 Lüubken 是足够多的电子，例如由太阳质子事件产生的电子。我们研究了雷达回波强度对各种参数的敏感性，最重要的是电子数密度和湍流强度。我们的观测和理论考虑并没有提供任何证据表明需要带电气溶胶粒子来解释 PMWE，这与夏季回波的存在形成鲜明对比，夏季回波的存在归因于带电冰粒子。
In January 2005, a total of 18 rockets were launched from the Andoya Rocket Range in Northern Nor- way (69 N) into strong VHF radar echoes called "Polar Mesosphere Winter Echoes" (PMWE). The echoes were ob- served in the lower and middle mesosphere during large so- lar proton fluxes. In general, PMWE occur much more sel- dom compared to their summer counterparts PMSE (typical occurrence rates at 69 N are 1-3% vs. 80%, respectively). Our in-situ measurements by falling sphere, chaff, and in- strumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and there- fore allow an unprecedented study of the background at- mosphere during PMWE. There are a number of indepen- dent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Tem- perature lapse rates close to the adiabatic gradient are ob- served in the vicinity of PMWE indicating persistent tur- bulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE ( 68- 75 km): viscosity increases rapidly with altitude and de- stroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sound- ing rocket flights. We have performed model calculations to study the radar backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement Correspondence to:F.-J. L ¨ ubken for PMWE is a sufficiently large number of electrons, for ex- ample produced by solar proton events. We have studied the sensitivity of the radar echo strength on various parameters, most important electron number density and turbulence in- tensity. Our observational and theoretical considerations do not provide any evidence that charged aerosol particles are needed to explain PMWE, in contrast to the summer echoes which owe their existence to charged ice particles.