Aspect sensitivity measurements of polar mesosphere summer echoes using coherent radar imaging

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.

Aspect sensitivity of polar mesosphere summer echoes based on ESRAD MST radar measurements in Kiruna, Sweden in 1997–2010

“…A similar height dependence of PMSE aspect sensitivity has been reported in other studies (Czechowsky et al, 1988;Zecha et al, 2001;Chilson et al, 2002). Long-term aspect sensitivity measurements of PMSE at Resolute Bay by Swarnalingam et al (2011) revealed that, for strong and moderate PMSE, the median aspect angles at 84 km are by 2-4 • smaller than those at 88 km.…”

“…These show that turbulence occurrence rates start to grow from 80 km and maximise at about 88 km (Rapp and by Lübken, 2003). Chilson et al (2002) and Zecha et al (2001) noticed the enhanced aspect sensitivity at the lower edges of PMSE sublayers. Similar features are seen in our Fig.…”

“…The second and fourth panels: number N of data points contributing to each altitude interval for 1998 and 2010, respectively. al. (2001) and Chilson et al (2002). Here we discuss limitations related to a finite radar beam-width only.…”

“…Hobbs et al (2001) described both methods and their limitations resulting from the theoretical assumptions and experimental configurations. Chilson et al (2002) pointed out that in an application to the mesosphere a disadvantage of the DBS method is in the long distance between the radar sampling volumes because large off-zenith angles are used. We will discuss more limitations for both methods later in this paper.…”

“…Chilson et al (2002) applied CRI technique to PMSE and related the angular brightness distribution to aspect sensitivity. Zecha et al (2001) used both DBS and FCA methods in the same PMSE experiment using the ALOMAR SOUSY VHF radar.…”