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- ItemAnnual variability of ice-nucleating particle concentrations at different Arctic locations(Göttingen : Copernicus GmbH, 2019) Wex, H.; Huang, L.; Zhang, W.; Hung, H.; Traversi, R.; Becagli, S.; Sheesley, R.J.; Moffett, C.E.; Barrett, T.E.; Bossi, R.; Skov, H.; Hünerbein, A.; Lubitz, J.; Löffler, M.; Linke, O.; Hartmann, M.; Herenz, P.; Stratmann, F.Number concentrations of ice-nucleating particles (NINP) in the Arctic were derived from ground-based filter samples. Examined samples had been collected in Alert (Nunavut, northern Canadian archipelago on Ellesmere Island), Utqiagvik, formerly known as Barrow (Alaska), Nyalesund (Svalbard), and at the Villum Research Station (VRS; northern Greenland). For the former two stations, examined filters span a full yearly cycle. For VRS, 10 weekly samples, mostly from different months of one year, were included. Samples from Ny-Alesund were collected during the months from March until September of one year. At all four stations, highest concentrations were found in the summer months from roughly June to September. For those stations with sufficient data coverage, an annual cycle can be seen. The spectra of NINP observed at the highest temperatures, i.e., those obtained for summer months, showed the presence of INPs that nucleate ice up to-5 °C. Although the nature of these highly ice-active INPs could not be determined in this study, it often has been described in the literature that ice activity observed at such high temperatures originates from the presence of ice-active material of biogenic origin. Spectra observed at the lowest temperatures, i.e., those derived for winter months, were on the lower end of the respective values from the literature on Arctic INPs or INPs from midlatitude continental sites, to which a comparison is presented herein. An analysis concerning the origin of INPs that were ice active at high temperatures was carried out using back trajectories and satellite information. Both terrestrial locations in the Arctic and the adjacent sea were found to be possible source areas for highly active INPs.
- ItemOn the evaluation of the phase relation between temperature and wind tides based on ground-based measurements and reanalysis data in the middle atmosphere(Göttingen : Copernicus GmbH, 2019) Baumgarten, K.; Stober, G.The variability in the middle atmosphere is driven by a variety of waves covering different spatial and temporal scales. We diagnose the variability in the thermal tides due to changes in the background wind by an adaptive spectral filter, which takes the intermittency of tides into account. We apply this diagnostic to temperature observations from daylight-capable lidar at midlatitudes (54° N, 12° E) as well as to reanalysis data of horizontal winds from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). These reanalysis data provide additional wind information in the altitude range between 30 and 70 km at the location of the lidar as well as on a global scale. Using the global data gives information on the tidal modes seen at one location. A comparison of the temperature and wind information affirms whether there is a fixed phase relation of the tidal waves in the temperature and the wind data. We found that in general the local tidal signatures are dominated by migrating tidal modes, and the signature is weaker in temperatures than in winds. While the meridional wind tide leads the zonal wind tide by 90°, the phase relation between the temperature and the wind tide is more complex. At certain altitudes the temperature tide follows the zonal wind tide. This knowledge helps in improving the interpretation of the seasonal variation in tides from different observables, especially when only data from single locations are used. The findings provide additional information about the phase stability of tidal waves, and the results clearly show the importance of a measurement acquisition on a routine basis with high temporal and spatial resolution. © 2019 Author(s).
- ItemSimultaneous observations of NLCs and MSEs at midlatitudes: Implications for formation and advection of ice particles(Göttingen : Copernicus GmbH, 2018) Gerding, M.; Zöllner, J.; Zecha, M.; Baumgarten, K.; Höffner, J.; Stober, G.; Lübken, F.-J.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, 54° N, 12° E). Lidar observations are limited to larger particles ( > 10 nm), while radars are also sensitive to small particles ( < 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 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 (lowNLC and lowMSE). The mean difference of the upper edges upNLC and upMSE is g1/4 500 m, 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. © Author(s) 2018.