Abstract
Abstract. An advanced hodograph-based analysis technique to derive gravity-wave (GW) parameters from observations of temperature and winds is developed and presented as a step-by-step recipe with justification for every step in such an analysis. As the most adequate background removal technique the 2-D FFT is suggested. For an unbiased analysis of fluctuation whose amplitude grows with height exponentially, we propose applying a scaling function of the form exp (z∕(ςH)), where H is scale height, z is altitude, and the constant ς can be derived by a linear fit to the fluctuation profile and should be in the range 1–10. The most essential part of the proposed analysis technique consists of fitting cosine waves to simultaneously measured profiles of zonal and meridional winds and temperature and subsequent hodograph analysis of these fitted waves. The linear wave theory applied in this analysis is extended by introducing a wave packet envelope term exp(-(z-z0)2/2σ2) that accounts for limited extent of GWs in the observational data set. The novelty of our approach is that its robustness ultimately allows for automation of the hodograph analysis and resolves many more GWs than can be inferred by the manually applied hodograph technique. This technique allows us to unambiguously identify upward- and downward-propagating GWs and their parameters. This technique is applied to unique lidar measurements of temperature and horizontal winds measured in an altitude range of 30 to 70 km.
Highlights
It is generally accepted that atmospheric gravity waves (GWs) produce global effects on the atmospheric circulation from the surface up to the mesosphere and lower thermosphere (MLT) region (e.g., Fritts and Alexander, 2003; Alexander et al, 2010; Becker, 2017)
In our analysis technique we focus solely on such fluctuations which are generated by GWs
In this paper we describe a newly developed analysis technique which allows for derivation of GW parameters such as vertical wavelength, the direction of propagation, phase speed, kinetic and potential energy, and momentum flux from the advanced lidar measurements
Summary
It is generally accepted that atmospheric gravity waves (GWs) produce global effects on the atmospheric circulation from the surface up to the mesosphere and lower thermosphere (MLT) region (e.g., Fritts and Alexander, 2003; Alexander et al, 2010; Becker, 2017). Our knowledge about gravity-wave parameters can be improved by means of high-resolution measurements of atmospheric GWs. Ideally, the measurement range should cover the entire path of the waves, starting from their sources in the troposphere to the level of their dissipation that is up to the MLT region. The new Doppler Rayleigh Iodine Spectrometer (DoRIS) in addition to the established lidar temperature measurements yields simultaneous, commonvolume measurements of winds (Baumgarten, 2010; Lübken et al, 2016) This combination of capabilities makes the lidar data unique. All those quantities, i.e. winds and temperature, when measured with high temporal and spatial resolution, reveal structuring at scales down to minutes and hundreds of meters.
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