Tidal signatures in temperatures derived from daylight lidar soundings above Kühlungsborn (54°N, 12°E)

Abstract

We have developed a new Rayleigh–Mie–Raman (RMR) lidar at the mid-latitude station in Kühlungsborn (54°N, 12°E) for analyzing geophysical phenomena at day and night, e.g., temperature tides and Noctilucent Clouds. For this study we have used about 3100h of data since April 2011 with additional data from summer 2010. The RMR lidar was in operation day and night in addition to the existing daylight-capable potassium resonance lidar. We show for the first time an overview of the altitude structure and seasonal variation of temperature tides, observed with lidars between 40 and 100km altitude at a mid-latitude site. There is a gap around 80km altitude due to a decreasing signal-to-noise ratio during the day. We derive mean tidal amplitudes and phases with 24-, 12-, and 8-h period. In most of the months, the diurnal component dominates the other tidal components with mean amplitudes of 1–2K in the stratopause region (45–55km altitude), where it is up to three times higher than semidiurnal and terdiurnal tidal amplitudes. The diurnal tide is damped at ∼60km altitude. In the mid-mesosphere (65–70km) diurnal, semidiurnal, and terdiurnal tidal components have comparable mean amplitudes of about 1–1.5K, except around the equinoxes. Around the mesopause the diurnal tide dominates again, with mean amplitudes of about 4K, but with a large variability. The seasonal variation shows a conspicuous structure below ∼65km altitude with tidal amplitudes small in summer and large around the equinoxes. This structure vanishes above ∼65km. There, the amplitude increases in summer. The measured tidal amplitudes and phases are compared with the MERRA (Modern Era Retrospective analysis for Research and Applications) reanalysis data. Repeated soundings in subsequent years allow to examine the year-to-year variation. The data from March in both 2012 and 2013 show a prominent diurnal tide at around 45km altitude with amplitudes about three times larger than in the other months. The short-term variability can be examined from continuous lidar operations during clear-sky periods. In a case study we show a large variability of the tidal amplitudes, especially the 8-h variation. This can only be examined due to a good temporal coverage of the lidar data.