Characteristics of the D region winter anomaly are examined, by using ionospheric data along a meridian chain of stations near Japan. The data were obtained by means of long-distance VLF radio wave propagation and HF radio wave vertical sounding. Interesting features are the equatorward extension of the anomaly and the variability of its duration. These features are further discussed in comparison with radiance data measured by pressure modulator radiometer channel 3000 (maximum weight near 80-km altitude in the mesosphere) on board Nimbus 6 during two winters, 1975/1976 and 1976/1977. Meteorological conditions during these winters were quite different, a major stratospheric sudden warming taking place during the latter winter but not during the former winter. The key result of this study is that the occurrence of the winter anomaly is basically associated with the amplification of a planetary-scale wave with zonal wave number 1 in the mesosphere. At the same time we find that the local appearance of the anomaly near Japan is controlled by the movement and latitudinal structure of the excited wave 1. It is further indicated that the increase in mesospheric local temperature is not always associated with the occurrence of the anomaly, suggesting that another dynamical effect of planetary-scale waves is important for the occurrence of the anomaly.