Comparison of mesospheric VHF radar echoes and rocket probe electron concentration measurements

Abstract

Refractive index irregularities in the equatorial mesosphere have been investigated using both the Jicamarca VHF radar and a rocket‐borne Langmuir probe launched from Punta Lobos, Peru. On February 27, 1983, a single layer of turbulence was observed in the upper mesosphere by both experiments. There is very good agreement between the observed radar echo power and the radar scattering cross section calculated from the rocket data when these are interpreted in the context of isotropic turbulence. The inner and outer scales of turbulence have been calculated from both the radar and the rocket data, and good agreement is found. The radar data show indications of large‐scale vortices in the layer of irregularities. Rocket data show that the inner scale of turbulence in the upper mesosphere is a few tens of meters and that the Jicamarca radar Bragg wavelength (3 m) is well within the viscous subrange of turbulence in this altitude range. The spectral index in the inertial subrange is close to −5/3, changing to about −7 at higher wave numbers. Energy dissipation rate in the layer was calculated to be 0.05 W kg−1, in good agreement with previous estimates.

Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes

“…We follow Røyrvik and Smith (1984) who derived a relation between radar reflectivity and the power spectral densities of measured electron number density fluctuations at the radar Bragg scale. Essentially, the radar reflectivity η is proportional to the power spectral density (PSD) of the absolute electron number density fluctuations at the radar half wavelength, i.e., η ∝η e = P SD( N e , λ/2),…”

Rocket measurements of mesospheric ionization irregularities

“…This irregularity is thoroughly investigated by Royrvik and Smith ( 1984) and is compared to simultcneous coherent scatter measurements at J'icamarca. A spectrum of this irregularity is shown iu Figure 5.8.…”

“…These fluctuations have been observed to occur in layers with a wide range of thicknesses ranging from the order of tens of meters (Rastogi and Bowhil'l, 1976) to the order of kilometers (Royrvik and Smith, 1984;Rottger et al, 1979). Isotropic turbulence is generally believed to cause these layers (Hocking and Vincent, 1982;Thrane and Grandal, 1981;Royrvik and Smith, 1984).…”

“…These fluctuations have been observed to occur in layers with a wide range of thicknesses ranging from the order of tens of meters (Rastogi and Bowhil'l, 1976) to the order of kilometers (Royrvik and Smith, 1984;Rottger et al, 1979). Isotropic turbulence is generally believed to cause these layers (Hocking and Vincent, 1982;Thrane and Grandal, 1981;Royrvik and Smith, 1984). Some radar investigations have indirated very narrow angular spectra for layers below 75 km (Fukao et al, 1980), suggesting very flat structures with horizontal scales greater than one Fresnel zone (Hocking and Vincent, 1982), making turbulence an unlikely mechanism for generating such layers.…”

“…The radar thus provides insight into the shape of the spectrum at wave numbers above the inertial range. The combination of radar and rocket measurements is used by Royrvik and Smith (1984) to compare measurements of an irregularity from the 27 February 1983 Peru flight with coincident radar measurements at Jicamarca. Radar can also measure aspect sensitivity of an irregularity, an indication of anisotropy.…”