One step closer to solving the mystery of Noctilucent cloud voids?
Jacek Stegman at the Department of Meteorology at Stockholm University has placed a camera on the roof of the Department to take photos of noctilucent clouds during the short summernights of Stockholm. Going through the material he found a perfect set of photos of noctilucent clouds with an unusual feature called "ice void". These photos has led him to dismiss previous theories of how the void in the clouds
− With our ordinary camera we take photos every 30 seconds. So we could follow the void, how it appears and how it behaves until it disappears. In these photos it does not behave the way that would support earlier speculations based on satellite observations. Rather the opposite. It stays put in one spot and while the noctilucent clouds pass through it, the void seems to swallow or melt the ice contained in the cold cloud air that passes it, says Jacek Stegman.
Noctilucent clouds appear high in the atmosphere, about 80 km above the summer pole. Noctilucent clouds, also known as polar mesospheric clouds, have been extensively observed and characterized from the ground since their first identification in 1885. It has been argued that these clouds first appeared at this time following the eruption of the Krakatau vulcano and that they are important indicators for atmospheric changes. Noctilucent clouds were first detected from space by an instrument on the OGO‐6 satellite in 1972.
Recently, a satellite borne instrument discovered nearly circular ice‐free regions within the clouds, denoted as “ice voids.” The origin of these voids is a mystery since it is not known what causes the clouds to disappear in large circular areas.
Unique observations
Since the voids have been observed from satellites which only can take pictures of the clouds once every one and a half hours the whole life range of a void has not been photographed before. This means that until now we completely lack observations of the development and disappearance of the voids. Until MISU researchers now have presented the first full temporal development of a void observed by a ground‐based camera.
There has been several theories on why these voids appear. Some have suggested that it is ice and some that it has to do with meteorites.
− To our surprise the void did not drift with the wind as cloud features around it. It remained stationary for around one hour. These observations give important clues to help us solve the mystery of the origin of these voids—they suggest a steady local heating of the atmosphere as the cause, says Jacek Stegman.
− We will continue studying these phenomena. We still do not know why they appear and how it is linked to climate change.
Jacek Stegman and Linda Megner at MISU got an article about these findings published in AGU 100, Advancing earth and space science.
Noctilucent cloud void (4248 Kb)