Rocket measurements of positive ions during polar mesosphere winter echo conditions

Abstract

Abstract. On 18 January 2005, two small, instrumented rockets were launched from Andøya Rocket Range (69.3 • N, 16 • E) during conditions with Polar Mesosphere Winter Echoes (PMWE). Each of the rockets was equipped with a Positive Ion Probe (PIP) and a Faraday rotation/differential absorption experiment, and was launched as part of a salvo of meteorological rockets measuring temperature and wind using falling spheres and chaff. Layers of PMWE were detected between 55 and 77 km by the 53.5 MHz ALWIN radar. The rockets were launched during a solar proton event, and measured extremely high ion densities, of order 10 10 m −3 , in the region where PMWE were observed. The density measurements were analyzed with the wavelet transform technique. At large length scales, ∼10 3 m, the power spectral density can be fitted with a k −3 wave number dependence, consistent with saturated gravity waves. Outside the PMWE layers the k −3 spectrum extends down to approximately 10 2 m where the fluctuations are quickly damped and disappear into the instrumental noise. Inside the PMWE layers the spectrum at smaller length scales is well fitted with a k −5/3 dependence over two decades of scales. The PMWE are therefore clearly indicative of turbulence, and the data are consistent with the turbulent dissipation of breaking gravity waves. We estimate a lower limit for the turbulent energy dissipation rate of about 10 −2 W/kg in the upper (72 km) layer.

Statistical characteristics of PMWE observations by the EISCAT VHF radar

“…Large ε values during PMWE events have been repeatedly observed (e.g. Collis et al, 1992;Lübken et al, 2007;Kirkwood et al, 2006b;Brattli et al, 2006). Note also that Lübken et al (2006) reported smaller spectral widths (their Fig.…”

“…Previous investigations of PMWE also noted the requirement of very strong turbulence inside the layers in order to explain such strong radar return (Stebel et al, 2004;Brattli et al, 2006 Another question that we would like to address here is the applicability of Eq. (6) to the measured spectral width.…”

Dust charging and density conditions deduced from observations of PMWE modulated by artificial electron heating

“…For this to be the case, the ion density would have to be increased by a factor of 10, to a value ∼3 × 10 10 m −3 , which we find to be unrealistic. This value is several times larger than the ion densities measured during a very strong proton event on January 18, 2005 [ Brattli et al , 2006] where the plasma densities at PMWE heights were exceptionally large [ Lübken et al , 2006]. We will consider two other mechanisms by which the PMWE signal can relax to the undisturbed PMWE value: (I) The effect of neutral winds at the PMWE heights, and (II) the effect of photo‐detachment [e.g., Weingartner and Draine , 2001; Havnes and Kassa , 2009; Rapp , 2009].…”

Height and time characteristics of seasonal and diurnal variations in PMWE based on 1 year observations by the PANSY radar (69.0°S, 39.6°E)

“…It is well known as a plausible explanation that PMWE are caused by fluctuations in the refractive index due to neutral turbulence associated mainly with breaking of atmospheric gravity waves [ Czechowsky et al , ; Brattli et al , ; Lübken et al , ]. This idea is common for most mesosphere echoes and not limited to the polar region [ Czechowsky et al , ; Zeller et al , ].…”