Seasonal variation of gravity wave parameters using different filter methods with daylight lidar measurements at midlatitudes

Abstract

The daylight‐capable Rayleigh‐Mie‐Raman (RMR) lidar at the midlatitude station in Kühlungsborn (54°N, 12°E) is in operation since 2010. The RMR lidar system is used to investigate different fractions of atmospheric waves, like gravity waves (GW) and thermal tides (with diurnal, semidiurnal, and terdiurnal components) at day and night. About 6150 h of data have been acquired until 2015. The general challenge for GW observations is the separation of different wave contributions from the observed superposition of GW, tides, or even longer periodic waves. Unfiltered lidar data always include such a superposition. We applied a Butterworth filter to separate GW and tides by vertical wavelength with a cutoff wavelength of 15 km and by observed periods with a cutoff period of 8 h. GW activity and characteristics are derived in an altitude range between 30 and 70 km. The retrieved vertically filtered temperature deviations contain GW with small vertical wavelengths over a broad range of periods, while only a small range of periods is included in the temporally filtered temperature deviations. We observe an annual variation of the wave activity for unfiltered and vertically filtered data, which is caused from tides and inertia gravity waves. In contrast to that, filtering in time leads to a weak semiannual variation for gravity waves with periods of 4–8 h, especially in higher altitudes. During summer, these waves have the half of the total amount of the potential energy budget compared to the unfiltered data. This shows the importance of waves with periods smaller than 8 h.

Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding

“…But it is reliable that after this wind reversal the gravity waves become important, especially those with periods <8 h. This indicates a difference for either the vertical propagation conditions for these waves from the same source or a better oblique propagation of gravity waves from different sources. The first mechanism leads to the exact same behavior which was already observed in the seasonal variation of these waves during summer in the study by Baumgarten et al (2017). In the summer the waves with periods less than 8 h can propagate to higher altitudes than inertia gravity waves.…”

“…Most other multi-day lidar studies are done with resonance lidars in an altitude range of 80-110 km because technologies for daylight suppression have been available for many years for these types of lidars (e.g., States and Gardner, 2000;Fricke-Begemann and Höffner, 2005;Yuan et al, 2010;Cai et al, 2017). Another 3-day study for the middle atmosphere was performed by Baumgarten et al (2015) using an RMR lidar but at high latitudes. They investigated only inertia gravity waves in temperature data with combined wind measurements without looking at the tidal variations.…”

“…The cutoff parameter are chosen as 15 km and 8 h for the vertical and the temporal filtering, respectively. A further description of the method can be found in Baumgarten et al (2017). In addition, a composite analysis of the lidar data as described in Kopp et al (2015) is used to investigate mean amplitudes of tidal waves.…”

Winds and temperatures of the Arctic middle atmosphere during January measured by Doppler lidar

“…7a. When comparing absolute values of GWED to previous studies, it is necessary to keep in mind that GWEDs depend on season, locally different wave sources, and data analysis procedures (e.g., Baumgarten et al, 2017). Nevertheless, studies by Alexander et al (2011) andMzé et al (2014) at Antarctic and midlatitude stations, respectively, found quantitatively similar results for potential GWEDs averaged over multiple years.…”

“…Therefore, wind measurements in the middle atmosphere with reasonable temporal and vertical resolution are of special interest (Meriwether and Gerrard, 2004;Drob et al, 2008). Not only do wind measurements provide additional information about atmospheric stability, together with temperature observations they also offer more sophisticated studies of gravity waves (e.g., Eckermann et al, 1995;Zink and Vincent, 2001;Placke et al, 2013;Bossert et al, 2014;Baumgarten et al, 2015) than studying gravity waves solely from temperature measurements (e.g., Chanin and Hauchecorne, 1981;Whiteway and Carswell, 1995;Alexander et al, 2011). In a recent study, Dörnbrack et al (2017) point out that information about background wind is essential to correctly interpret ground-based gravity wave observations, specifically regarding identified phase lines and the vertical propagation direction.…”