Atmospheric Sciences Letters

doi:10.1006/asle.2000.0001 the satellite Meteosat. The cloud head is the overall cloud system occupying much of the left-hand (western) half of the figure. The larger cloud system with colder (higher) cloud tops, occupying the right-hand (eastern) half of the figure is the polar front cloud band. The term cloud head was first used by Böttger et al. (1975) who recognized it as it as a feature that frequently precedes a period of rapid cyclonic development. The relationship of cloud heads to the overall structure and dynamics of the associated cyclone is described in Browning and Roberts (1994) and Bader et al. (1995). Cloud heads have been shown to be prominent features of several notable cyclones, a memorable one in north-west Europe being the Great Storm of October 1987 (Shutts, 1990). The identification of cloud heads in satellite imagery now plays an important role in operational forecasting practice (e.g. Young and Grahame 1999). The particular feature of the cloud head in Figure 1 that will be stressed in the present study is the series of striations in cloud-top height (temperature). Striations in cloud heads were first mentioned by Shutts (1990) and Norris and Young (1991); the striations described by Shutts had a characteristic wavelength of 10 km, whereas the wavelength of those described by Norris and Young, like those in the present study, are much longer. Five of the striations are labelled A, B, C, D and E and four canThe mystery of striated cloud heads in satellite imager