Abstract
Abstract. The Esrange VHF radar (ESRAD), located in northern Sweden (67.88° N, 21.10° E), has been used to investigate polar mesosphere summer echoes (PMSE). During July and August of 1998, coherent radar imaging (CRI) was used to study the dynamic evolution of PMSE with high temporal and spatial resolution. A CRI analysis provides an estimate of the angular brightness distribution within the radar’s probing volume. The brightness distribution is directly related to the radar reflectivity. Consequently, these data are used to investigate the aspect sensitivity of PMSE. In addition to the CRI analysis, the full correlation analysis (FCA) is used to derive estimates of the prevailing three-dimensional wind associated with the observed PMSE. It is shown that regions within the PMSE with enhanced aspect sensitivity have a correspondingly high signal-to-noise ratio (SNR). Although this relationship has been investigated in the past, the present study allows for an estimation of the aspect sensitivity independent of the assumed scattering models and avoids the complications of comparing echo strengths from vertical and off-vertical beams over large horizontal separations, as in the Doppler Beam Swinging (DBS) method. Regions of enhanced aspect sensitivity were additionally shown to correlate with the wave-perturbation induced downward motions of air parcels embedded in the PMSE.Key words. Ionosphere (polar ionosphere) Meteorology and Atmospheric Dynamics (middle atmosphere dynamics) Radio Science (Interferometry)
Highlights
Ecklund and Balsley (1981) announced the surprising existence of layers of strong VHF backscatter originating from the northern polar mesopause region
There are many intriguing aspects of polar mesosphere summer echoes (PMSE); here we focus on regions within the echoing layers that are aspect sensitive when probed with VHF radars
We have demonstrated that these features are possibly related through the interaction of atmospheric wave oscillations within the upper mesosphere and lower thermosphere
Summary
Ecklund and Balsley (1981) announced the surprising existence of layers of strong VHF backscatter originating from the northern polar mesopause region. Aspect sensitivity estimates are obtained by comparing the echo strengths from vertical and off-vertical radar beams. This method has been used in the mesosphere for the study of PMSE, it suffers from the disadvantage of large horizontal separations of the radar sampling volumes at such heights. It is possible to make in-beam estimates of the aspect sensitivity of PMSE by using the full correlation analysis (FCA) technique (Zecha et al, 2001). Similar to FCA, CRI enables in-beam calculations of various atmospheric parameters through the use of data from spatially separated receiving antennas. By using FCA and CRI, it is shown that atmospheric waves play a role in establishing regions of enhanced aspect sensitivity within PMSE. The radar beam was directed vertically during all measurements. (See Yu (2000) and Yu et al (2001) for additional information on the configuration of the radar.)
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