The D-region winter anomaly and dynamical effects of atmospheric planetary-scale waves.

Abstract

A study is presented of the D-region winter anomaly, observed by ground based measurements of long-distance VLF radio wave propagation and HF radio wave vertical sounding at several stations located in and near Japan over 3 winters from 1974 to 1977. These winters have different meteorological conditions (i.e., a major stratospheric sudden warming in the winter 1976/77, a minor warming in 1974/75 and no warmings in 1975/76). The activity of the anomaly is compared with that of planetary-scale waves using atmospheric data in the lower stratosphere and radiance data in the upper stratosphere and mesosphere obtained by the PMR (Pressure Modulator Radiometer) on board Nimbus 6 satellite. The latitudinal extent and duration of the anomaly are shown to be primarily controlled by the amplification of planetary-scale wave with zonal wavenumber 1. When a major warming took place as a result of an unusual amplification of wave 1, an intense event of the anomaly was observed for a long time. However,

On the Use of VLF Narrowband Measurements to Study the Lower Ionosphere and the Mesosphere–Lower Thermosphere

“…He concluded that the D-region electron density at 75-90 km is enhanced during SSW events, resulting in a notable lowering of the VLF nighttime reflection height. Subsequent studies [e.g., Muraoka, 1985;Muraoka et al, 1986] strengthened these findings, while noting that the winter anomaly occurrence is associated with a mesospheric planetary wave with zonal wave number 1.…”