Winds, waves, clouds & meteors in the mesosphere

中间层是位于大约50到100公里高度的大气层的一部分。与低层大气不同，中间层的一般环流是由大气波驱动的。这些波是在低层大气中产生的，从那里它们上升到中间层并破裂，就像波浪在海滩上破裂一样。这些波的破裂将能量和动量转移到中间层，并驱动一种独特的大气环流。在这种环流中，空气在地球的夏季极地上空升起，越过赤道，然后在相反的冬季极地汇合和下降。整个中间层下降的空气最终进入平流层，携带着流星沉积的化学物质和“烟雾”粒子--从而将中间层与底层平流层和对流层直接连接起来。“流星烟雾”看起来像是核，凝结了夏季高海拔极地中间层云(也称为夜光云)的冰晶。然而，这些云也需要低于150K(-123摄氏度)的非常低的温度才能形成。这些较低的温度只是由于在波浪驱动的环流中上升到夏季极地地区的空气冷却的结果。然后，更大规模的波浪和大气层潮汐调制了这种环流，从而调制了云的发生。这意味着风、浪、极地中间层云和流星都是紧密相连的，而试图理解其中一种就意味着理解其他。该项目将使用先进的流星雷达和气辉相机来调查中间层的波浪和潮汐，并研究它是如何耦合到大气层底层的。从技术上讲，这些相机是“气辉成像器”，记录了中间层微弱辉光层的排放。这些层中明亮的涟漪图案揭示了大气波的存在。这些相机是由犹他州立大学运营的，所以我们的项目是一个跨大西洋的合作项目。流星雷达将测量流星携带的漂移，从而揭示中间层的风、大范围的海浪和潮汐。雷达还将测量流星进入大气层的流量，甚至可以测量大气温度。我们的目标是发现大尺度的海浪和潮汐如何与驱动环流的小尺度海浪相互作用。这些波是否调制了波浪驱动过程，如果是的话，又是如何调制的？这些观测将在两个截然不同的地点进行。一个是南极的Rothera，另一个是美国的熊湖。这两个地点大气的对比行为将有助于揭示极地大气与地球其他地方的不同之处。我们的结果将被伦敦大学学院的同事使用，他们正在开发一个大气的数学模型。我们将与NASA AIM(中间层冰的大气)卫星合作进行测量，以研究南极上空的极地中间层云，并调查波浪和潮汐如何改变这些神秘云的出现、亮度和可变性。这颗卫星定于2006年底发射。我们还将与美国、阿根廷和加拿大的团队合作，在阿根廷安装一种新型流星雷达。这一新雷达将被优化，以直接测量中间层的波动驱动。最后，我们将把我们在南极进行的测量与在北极完全相同纬度的相同雷达进行的测量进行比较。这些测量将有助于揭示两个极地地区的中间层如何以及为什么不同。

The mesosphere is that part of the atmosphere at heights of about 50 to 100 km. Unlike the lower atmosphere, the general circulation of the mesosphere is powered, or 'driven' by atmospheric waves. These waves are generated in the lower atmosphere, from where they ascend into the mesosphere and break, rather like waves breaking on a beach. The breaking of these waves transfers energy and momentum into the mesosphere and drives a unique atmospheric circulation. In this circulation, air rises over the summer polar regions of the Earth, crosses the equator and then converges and descends over the opposite, winter, pole. The entire descending air of the mesosphere eventually ends up in the stratosphere, carrying with it chemicals and 'smoke' particles deposited by meteors - thus connecting the mesosphere very directly to the underlying stratosphere and troposphere. The 'meteor smoke' appears to act as the nuclei on which condense the ice crystals of ghostly high-altitude summertime polar mesospheric clouds (also known as noctilucent clouds). However, the clouds also require very cold temperatures of below 150 K (- 123 degrees C) in order to form. These low temperatures are only achieved as a result of the cooling of the air as it rises over the summer polar region in the wave-driven circulation. Larger-scale waves and atmospheric tides then modulate this circulation and so modulate the occurrence of the clouds. This means that winds, waves, polar mesospheric clouds and meteors are all intimately connected, and that attempts to understand one mean understanding the others. This project will use sophisticated meteor radars and airglow cameras to investigate the waves and tides of the mesosphere and to study how it couples to the underlying layers of the atmosphere. The cameras, technically 'airglow imagers', record the emissions from faintly glowing layers in the mesosphere. Bright ripple patterns in these layers reveal the presence of atmospheric waves. The cameras are operated by Utah State University and so our project is a trans-Atlantic collaboration. The meteor radars will measure the drifting of meteors carried by the flow and so reveal the winds, large-scale waves and tides of the mesosphere. The radars will also measure the flux of meteors into the atmosphere and can even measure the temperature of the atmosphere. Our goal is to discover how the large-scale waves and tides interact with the small-scale waves responsible for driving the circulation. Do these waves modulate the wave driving process, and if so how? These observations will be carried out at two very different sites. One is Rothera in the Antarctic and the other is Bear Lake in the USA. The contrasting behaviour of the atmosphere over these two site will help reveal how the polar atmosphere differs from elsewhere on the Earth. Our results will be used by colleagues at University College London who are developing a mathematical model of the atmosphere. We will make collaborative measurements with the NASA AIM (Aeronomy of Ice in the Mesosphere) satellite to study polar mesospheric clouds over the Antarctic and to investigate how waves and tides modify the occurrence, brightness and variability of these mysterious clouds. This satellite is due to launch in late 2006. We will also work in a collaborative project with groups from the USA, Argentina and Canada to install a new type of meteor radar in Argentina. This new radar will be optimised to directly measure the wave driving of the mesosphere. Finally, we will compare our measurements made in the Antarctic to measurements made by an identical radar at exactly the same latitude in the Arctic. These measurements will help reveal how and why the mesosphere differ over the two polar regions.