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

S Kirkwood,M Smirnova,E Belova

doi:10.5194/angeo-30-457-2012

S Kirkwood, M Smirnova + Show 1 more

Open Access

https://doi.org/10.5194/angeo-30-457-2012

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Journal: Annales Geophysicae	Publication Date: Mar 1, 2012
Citations: 31	License type: CC BY 3.0

Affiliation: Swedish Institute of Space Physics

Abstract

Abstract. Aspect sensitivities of polar mesosphere summer echoes (PMSE) measured with the ESRAD 50 MHz radar in 1997–2010 are studied using the full correlation analysis technique. Half of PMSE detected each year are found to be highly aspect sensitive. Yearly median values of the aspect sensitivity parameter θs, characterising the half-width of the scatterers' polar diagram, are 2.9–3.7° depending on the year. The other half of the PMSE have θs values larger than 9–11° and cannot be evaluated using the ESRAD vertical beam only. PMSE aspect sensitivity reveals an altitude dependence, namely, the scatter becomes more isotropic with increasing height. This result is consistent with that reported in other studies. No dependence of PMSE aspect sensitivity on backscattered power for any year was identified. In the paper the limitations of the in-beam and off-vertical beam methods for estimation of PMSE aspect sensitivity are discussed. We conclude that both methods should be combined in order to get complete information about PMSE aspect sensitivity and to estimate correctly PMSE absolute strength.

Highlights

Polar Mesosphere Summer Echoes (PMSE) are extremely strong radar echoes observed from altitudes of 80–95 km at high latitudes in the Northern and Southern Hemispheres during summer
Zecha et al (2001) used both DBS and full correlation analysis (FCA) methods in the same PMSE experiment using the ALOMAR SOUSY VHF radar. They found that the DBS method yields higher values of θs for the same PMSE layer than the spaced antennas (SA) method. (This should be borne in mind for the results presented in Sect. 4.) The authors argued that these two methods evaluate aspect sensitivity at different spatial scales and PMSE is strongly anisotropic within a radar beam but more isotropic on larger distances
The results show that 50 %–52 % of data are represented by the distributions in Fig. 3, i.e. half of all PMSE observed with ESRAD are highly aspect sensitive

Summary

Introduction

Polar Mesosphere Summer Echoes (PMSE) are extremely strong radar echoes observed from altitudes of 80–95 km at high latitudes in the Northern and Southern Hemispheres during summer. Aspect sensitivity is a property of the scatterers which describes the variation of scattered power in respect of incident angle It is quantified in terms of the half width θs of the angular polar diagram of backscatter (Hocking et al, 1986). The early measurements of aspect sensitivity of PMSE by Czechowsky et al (1988) showed that PMSE are highly aspect sensitive with typical θs of 5◦–6◦ at altitudes of 85–86 km Further works on this subject reported a variety of values of θs in this altitude range: e.g. 12◦–13◦ (Huaman and Balsley, 1998), 3.5◦ and 7◦–10◦ (Zecha et al, 2001), 11◦–15◦ (Swarnalingam et al, 2011). This implies that PMSE can be specular (or due to anisotropic turbulence) as well as rather isotropic

Results

Discussion

Conclusion