Simultaneous observations of NLCs and MSEs at midlatitudes: implications for formation and advection of ice particles

Gerding, Michael; Zöllner, Jochen; Zecha, Marius; Baumgarten, Kathrin; Höffner, Josef; Stober, Gunter; Lübken, Franz-Josef

We combined ground-based lidar observations of noctilucent clouds (NLCs) with collocated, simultaneous radar observations of mesospheric summer echoes (MSEs) in order to compare ice cloud altitudes at a midlatitude site (Kühlungsborn, Germany, 54inline-formula N, 12inline-formula E). Lidar observations are limited to larger particles (inline-formula>10 nm), while radars are also sensitive to small particles (inline-formula<10 nm), but require sufficient ionization and turbulence at the ice cloud altitudes. The combined lidar and radar data set thus includes some information on the size distribution within the cloud and through this on the “history” of the cloud. The soundings for this study are carried out by the IAP Rayleigh–Mie–Raman (RMR) lidar and the OSWIN VHF radar. On average, there is no difference between the lower edges (inline-formula M5inlinescrollmathml z normal NLC normal low 24pt17ptsvg-formulamathimgd54facfdece002a70b6dfff074d09f59 acp-18-15569-2018-ie00001.svg24pt17ptacp-18-15569-2018-ie00001.png and inline-formula M6inlinescrollmathml z normal MSE normal low 25pt17ptsvg-formulamathimg821deb5ca4a0cea3a940d1ecbf3aa272 acp-18-15569-2018-ie00002.svg25pt17ptacp-18-15569-2018-ie00002.png ). The mean difference of the upper edges inline-formula M7inlinescrollmathml z normal NLC normal up 24pt17ptsvg-formulamathimg188e2ad1bf0b4bb317f3be26ab360067 acp-18-15569-2018-ie00003.svg24pt17ptacp-18-15569-2018-ie00003.png and inline-formula M8inlinescrollmathml z normal MSE normal up 25pt17ptsvg-formulamathimg12fec26ac7b4a9c5b0bef8fd389d5d4c acp-18-15569-2018-ie00004.svg25pt17ptacp-18-15569-2018-ie00004.png is inline-formula∼500inline-formulam, which is much less than expected from observations at higher latitudes. In contrast to high latitudes, the MSEs above our location typically do not reach much higher than the NLCs. In addition to earlier studies from our site, this gives additional evidence for the supposition that clouds containing large enough particles to be observed by lidar are not formed locally but are advected from higher latitudes. During the advection process, the smaller particles in the upper part of the cloud either grow and sediment, or they sublimate. Both processes result in a thinning of the layer. High-altitude MSEs, usually indicating nucleation of ice particles, are rarely observed in conjunction with lidar observations of NLCs at Kühlungsborn.

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Gerding, Michael / Zöllner, Jochen / Zecha, Marius / et al: Simultaneous observations of NLCs and MSEs at midlatitudes: implications for formation and advection of ice particles. 2018. Copernicus Publications.

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