Tomographic reconstruction of atmospheric gravity wave parameters from airglow observations

Abstract

Abstract. Gravity waves (GWs) play an important role in the dynamics of the mesosphere and lower thermosphere (MLT). Therefore, global observations of GWs in the MLT region are of particular interest. The small scales of GWs, however, pose a major problem for the observation of GWs from space. We propose a new observation strategy for GWs in the mesopause region by combining limb and sub-limb satellite-borne remote sensing measurements for improving the spatial resolution of temperatures that are retrieved from atmospheric soundings. In our study, we simulate satellite observations of the rotational structure of the O 2 A-band nightglow. A key element of the new method is the ability of the instrument or the satellite to operate in so-called "target mode", i.e. to point at a particular point in the atmosphere and collect radiances at different viewing angles. These multi-angle measurements of a selected region allow for tomographic 2-D reconstruction of the atmospheric state, in particular of GW structures. The feasibility of this tomographic retrieval approach is assessed using simulated measurements. It shows that one major advantage of this observation strategy is that GWs can be observed on a much smaller scale than conventional observations. We derive a GW sensitivity function, and it is shown that "target mode" observations are able to capture GWs with horizontal wavelengths as short as ∼ 50 km for a large range of vertical wavelengths. This is far better than the horizontal wavelength limit of 100-200 km obtained from conventional limb sounding.

Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

“…3.3 are non-linear. Further, the gain matrix G(a a ) is used to calculate the influence of an arbitrary error source described by a covariance matrix S on the retrieval result G −1 S G. Covariance matrices describing different systematic error sources are assembled using an autoregressive approach with reasonable standard deviations and correlation lengths (Tarantola, 2004). The standard deviations and correlation lengths used for the different systematic errors are summarised in Table 2.…”

Effect of OH emission on the temperature and wind measurements derived from limb-viewing observations of the 1.27 µm O<sub>2</sub> dayglow

“…The schematic drawing of the limb-imaging geometry and instrument concept is shown in Fig. 4, which closely follows the WAMI concept (Ward et al, 2001). The field of view (FOV) of NWTSI is defined by the first telescope with a value of 1.5 • × 1.5 • , which allows NWTSI to cover an entire altitude range from 20 to 120 km in single images for a nominal spacecraft altitude of 410 km.…”

“…The enormous success of the Wind Imaging Inter-ferometer (WINDII) (Shepherd et al, 2012), high-resolution Doppler imager (HRDI) (Ortland et al, 1996) and TIMED Doppler interferometer (TIDI) (Killeen et al, 2006), which measured winds in the upper mesosphere and lower thermosphere using Doppler shifts in visible airglow emission lines, stimulates interest in measuring wind and temperature from limb-viewing satellites using the 1.27 µm dayglow (Wu et al, 2018). Ward et al (2001) designed a high-sensitivity interferometer, WAMI, to provide simultaneous measurements of horizontal wind and rotational temperature by using the combination of a "strong" emission line group and a "weak" group of the O 2 (a 1 g ) airglow. A similar instrument, MIMI, designed by York University, also takes advantage of strong and weak emission lines for dynamics and thermodynamics measurement.…”

“…The observing strategy of using two sets of three emission lines (as shown in Fig. 1 of Ward et al, 2001) makes it a perfect approach for WAMI and MIMI to improve our knowledge of the wind and temperature of the lower thermosphere and middle atmosphere, as well as global distribution and transport of O 3 . In recent years, measuring wind and temperature in the planetary atmosphere of Mars and Venus, for example, was also proposed by using a 1.27 µm band emission of the electronically excited O 2 (a 1 g ) state (Ward et al, 2002;Zhang et al, 2017).…”

AtmoCube A1: airglow measurements in the mesosphere and lower thermosphere by spatial heterodyne interferometry

“…Song et al 1 developed a new satellite observation strategy for the detection of gravity waves in the mesosphere and lower thermosphere (MLT) at high spatial resolution. This measurement technique requires an agile satellite platform to make multiangle observations of a specific atmospheric volume and a spectrometer particularly suited for the detection of faint emission lines.…”