Seasonal Cycle of Gravity Wave Potential Energy Densities from Lidar and Satellite Observations at 54° and 69°N

Abstract

We present gravity wave climatologies based on seven years (2012–2018) of lidar and SABER temperatures and reanalysis data at Kühlungsborn (54°N) and at ALOMAR(69°N) in the altitude range 30–70 km. 9452 (5044) hours of lidar observations at Kühlungsborn (ALOMAR) were used. Filtering according to vertical wavelength (λz <15 km) or period (τ <8 h) is applied. Gravity wave potential energy densities (GWPED) per unit volume (EpV) and per unit mass (Epm) are derived. GWPED from reanalysis are smaller compared to lidar. The difference increases with altitude in winter and reaches almost two orders of magnitude around 70 km. A seasonal cycle of EpV with maximum values in winter is present at both stations in nearly all lidar/SABER measurements and in reanalysis data. For SABER and for lidar (with λ <15 km) the winter/summer ratios are a factor of ~2–4, but are significantly smaller for lidar with τ <8 h. The winter/summer ratios are nearly identical at both stations and are significantly larger for Epm compared to EpV. Lidar/SABER observations show that EpV is larger by a factor of ~2 at Kühlungsborn compared to ALOMAR, independent of season and altitude. Comparison with mean background winds shows that simple scenarios regarding GW filtering etc. cannot explain the Kühlungsborn/ALOMAR differences. EpV decreases with altitude in nearly all cases. Corresponding EpV scale heights from lidar are generally larger in winter compared to summer. Above ~55 km, EpV in summer is almost constant with altitude at both stations. The winter/summer difference of EpV scale heights is much smaller or absent in SABER and in reanalysis data.

High‐Cadence Lidar Observations of Middle Atmospheric Temperature and Gravity Waves at the Southern Andes Hot Spot

“…If chosen too large, background features like tides and PWs are taken for GWs. For the following analysis the cutoff wavelength is defined as km, a value used in multiple studies (Baumgarten et al., 2017; Bramberger et al., 2017; Kaifler et al., 2017; Rapp et al., 2018; Strelnikova et al., 2021). Given that seasonal oscillations exhibit vertical scales in the order of ∼70 km, the prior subtraction of them has a negligible effect on the scale separation of the Butterworth filter.…”

Role Of the Sun and the Middle atmosphere/thermosphere/ionosphere In Climate (ROSMIC): a retrospective and prospective view

“…On the other hand, in situ observations with a super-pressure balloon can provide a horizontal distribution of the GW activity and its momentum flux for the entire (intrinsic) frequency band at a single altitude (Vincent and Hertzog 2014;Jewtoukoff et al 2015). Lidar observations of gravity waves are now available (both day and night) of suitable quality and resolution for mean wave characteristics to be derived and compared with models (Baumgarten et al 2017;Strelnikova et al 2020). A recent gravity wave climatology at 54 • N and 69 • N based on nearly 15,000 h of lidar measurements has some similarity to reanalysis models but also significant discrepancies (Strelnikova et al 2020).…”

“…Lidar observations of gravity waves are now available (both day and night) of suitable quality and resolution for mean wave characteristics to be derived and compared with models (Baumgarten et al 2017;Strelnikova et al 2020). A recent gravity wave climatology at 54 • N and 69 • N based on nearly 15,000 h of lidar measurements has some similarity to reanalysis models but also significant discrepancies (Strelnikova et al 2020). It is now generally accepted that simple gravity wave parametrization scenarios such as those being used in several GCMs, cannot cover all aspects of the physical processes related to gravity waves, i.e., their observed spatial and temporal intermittency and their interaction with tides (Baumgarten et al 2018).…”

VAHCOLI, a new concept for lidars: technical setup, science applications, and first measurements

“…For Doppler-resonance the laser must be tunable to an atomic absorption line. We have developed a highly efficient, narrowband, diode-pumped alexandrite ring laser in cooperation with the Fraunhofer Institute for Laser Technology in Aachen (Höffner et al, 2018;Strotkamp et al, 2019). The laser head includes various subsystems such as a Q-switch driver, cavity control, power measurement, and a beam expansion telescope, all of which are placed in a sealed housing for touch-free operation over long periods.…”

“…VAHCOLI may also be extended to other wavelengths relevant for thermospheric or space applications (Höffner et al, 2018;Munk et al, 2018;Höffner et al, 2019). Due to its compact design and autonomous operation a VAHCOLI unit may also be of interest for measurements from satellites (Strotkamp et al, 2019). The final aim is to further improve the VAHCOLI units and to develop a cost-effective multi-purpose lidar with several systems that may be employed at various locations and be operated quasiautonomously.…”