Since 1999 radar continuous observations of polar mesospheric echoes have been conducted on the Norwegian island of Andøya (69.30°N, 16.04°E), with the ALWIN radar (1999–2008) and MAARSY (since 2011). Traditionally these observations have been named after their seasonal occurrence, i.e., Polar Mesosphere Summer Echoes (PMSE) and Polar Mesosphere Winter Echoes (PMWE). PMSE are much stronger than PMWE and are known to be due to contributions of charged-dust (ice) particles and turbulence. On the other hand, most PMWE are mainly due to turbulence. Both echoes depend on electron density and its gradients. The use of MAARSY, more 17 dB sensitive than the ALWIN radar, makes it possible to observe turbulence-dominated echoes, usually below 80 km, all year round with a mean seasonal occurrence frequency of about 14%. Their minimum occurrence rate is 2% in July and August, while there are two maxima, one in March/April (22%) and the second one in October (26%). On average the dust-dominated summer echoes starts on 14 May and ends on 26 August (i.e. 105 days) with an average occurrence in June/July of 95%. These summer echoes occur mainly between 80 and 90 km, and present a maximum daily occurrence around 13:00 LT. On the other hand, the turbulence-dominated winter echoes occur mainly between 55 and 80 km with maximum daily occurrence around 11:30 LT. Besides the seasonal and daily occurrence of these echoes, we present the variability of occurrence frequency rates for the summer layers since 1994. After eliminating the effects of geomagnetic and/or solar activity the occurrence of the summer dust-dominated echoes show a positive trend of about 0.32%̇/yr over the last twenty seven years which might be related to the observed negative mesospheric temperature trends at polar latitudes.

自1999年以来，在挪威的安多亚岛（北纬69.30°，东经16.04°），ALWIN雷达（1999-2008年）和MAARSY（自2011年起）以来，对雷达进行了连续的极地中层回波观测。传统上，这些观测以季节出现来命名，即极地中层夏季回波（PMSE）和极地中层冬季回波（PMWE）。PMSE比PMWE强得多，并且众所周知是由于带电灰尘（冰）颗粒和湍流引起的。另一方面，大多数PMWE主要是由于湍流。两种回波都取决于电子密度及其梯度。MAALSY的灵敏度比ALWIN雷达高17 dB，因此可以全年观测湍流为主的回波，通常低于80 km，平均季节性发生频率约为14％。它们的最小发生率在7月和8月为2％，而最大值出现在两个，一个在3月/ 4月（22％），另一个在10月（26％）。平均而言，以尘埃为主的夏季回波从5月14日开始，到8月26日（即105天）结束，6月/ 7月的平均回声为95％。这些夏季回波主要发生在80至90 km之间，并且在LT 13:00左右每天最多出现。另一方面，以湍流为主的冬季回波主要发生在55至80 km之间，而最大的每日回声发生在LT 11:30左右。除了这些回声的季节性和日常发生之外，我们还介绍了自1994年以来夏季各层的发生频率速率的变化性。在消除了地磁和/或太阳活动的影响之后，夏季以尘埃为主的回声的出现呈正趋势。大约0。