Patches of polar mesospheric summer echoes characterized from radar imaging observations with MAARSY

Abstract

Abstract.A recent study has hypothesized that polar mesospheric summer echoes (PMSEs) might consist mainly of localized isotropic scattering. These results have been inferred from indirect measurements. Using radar imaging with the Middle Atmosphere Alomar Radar System (MAARSY), we observed horizontal structures that support our previous findings. We observe that small-scale irregularities, causing isotropic scattering, are organized in patches. We find that patches of PMSEs, as observed by the radar, are usually smaller than 1 km. These patches occur throughout the illuminated volume, supporting that PMSEs are caused by localized isotropic or inhomogeneous scattering. Furthermore, we show that imaging can be used to identify side lobe detections, which have a significant influence even for narrow beam observations. Improved spectra estimations are obtained by selecting the desired volume to study parameters such as spectral width and to estimate the derived energy dissipation rates. In addition, a combined wide beam experiment and radar imaging is used to resolve the radial velocity and spectral width at different volumes within the illuminated volume.

Enhancing the spatiotemporal features of polar mesosphere summer echoes using coherent MIMO and radar imaging at MAARSY

“…Based on recent multibeam observations as well as radar imaging, Sommer and Chau (2016) have concluded that the PMSEs are not as aspect-sensitive as previously reported, and instead, most of the time they are organized in kilometerscale spatial structures drifting across the observing beams. Such results have been independently verified with bistatic observations at VHFs, where PMSEs were observed with small systems at zenith angles close to 30 • (e.g., Chau et al, 2018).…”

“…PMSEs present strong radar cross sections (RCSs) that allow them to be observed with less transmitting power, which is the case when using MIMO. Previous efforts to study their spatial structure have been limited to a few kilometers' spatial resolution and a few minutes' temporal resolution (e.g., Latteck et al, 2012a;Stober et al, 2013;Sommer and Chau, 2016). Recently, Stober et al (2018) have presented many examples of monochromatic gravity waves (GWs) and Kelvin-Helmholtz instabilities (KHIs) using 9 days of multibeam PMSE observations with MAARSY.…”

“…The results of Sommer and Chau (2016) were obtained with MAARSY using the whole antenna array for transmitting and an antenna compression approach, i.e., a wide beam by properly phasing the antennas (e.g., Woodman and Chau, 2001) and a multiple-receiver configuration. The spatial structures were obtained using the Capon technique due to its implementation simplicity and its relatively fast processing speed.…”

“…Given that PMSEs are highly associated with noctilucent clouds (NLCs) (e.g., Hoppe et al, 1990;Stebel et al, 2000;Kaifler et al, 2011), spatial structures ranging from a few hundreds of meters to a few tens of kilometers observed in NLCs (e.g., Baumgarten and Fritts, 2014) are expected to be observed also in PMSEs. Indeed this is the case, PMSE structures of a few kilometers have been already reported by Sommer and Chau (2016) and structures of a few tens of kilometers have been reported by Chau et al (2018).…”

Spectral Observation Theory and Beam Debroadening Algorithm for Atmospheric Radar

“…They assumed that the radar beam is rotationally symmetric and that the beam pattern (e.g., the polar gain diagram) is characterized simply by the beamwidth θ beam with no sidelobes. Recently, the impact of neglecting the sidelobes in estimating the strength of the turbulence is evaluated by Sommer and Chau [5]. They concluded therein that even the standard sidelobe level (∼−18 dB) for circular aperture should be taken into account for evaluating turbulence.…”