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Blogs > loveisamyth > loveisamyth, stars are forever


loveisamyth 68M
849 posts
5/25/2016 4:14 am

Last Read:
5/27/2016 4:29 am
POLAR MESOSPHERIC SUMMERTIME ECHOS
Noctilucent clouds aren't the only sign of Arctic summer. So are polar mesospheric summertime echos (PMSEs). Arctic researchers who monitor VHF radio receivers sometimes pick up late night signals from distant transmitters. These strange "echos" occur during the months from May through August, the same as noctilucent cloud season. On May 14th, Rob Stammes of Laukvik, Lofoten, Norway, may have recorded the first PMSEs of 2016.



"I use my VHF receiving system generally for signals from auroras and meteors," says Stammes. "This couldn't have been auroras, because aurora activity was low. Plus, there is a big difference between the sound from aurora echoes and the sound of other reflection mechanisms. This event was much more like a PMSE, which I have detected many times in previous seasons."

PMSEs are radio waves reflected from an altitude of 80 km to 90 km. That part of Earth's upper atmosphere is called the "mesosphere." It is, coincidentally, the same place noctilucent clouds are found. The exact cause of PMSEs is not yet known; theorists have proposed explanations ranging from steep electron density gradients and "dressed aerosols" to gravity waves and turbulence. The echoes are often accompanied by visible NLCs, but not always.



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