Observations of volcanic cloud heights and ash-atmosphere interactions

We discuss two related problems of critical importance to the International Airways Volcano Watch: the accuracy of cloud height observations, and the variation of volcanic cloud height with differing atmospheric conditions. Both affect the accuracy of volcanic ash dispersion forecasts. Ground, air, and, to a lesser extent, satellite based cloud height observations are subject to a high degree of error which creates a great deal of uncertainty and contributes to substantial over/under warning on occasion, and increased costs and risks to the aviation industry. Reporting can be improved and increased with appropriate education and by providing suitable techniques to observers. The effect of atmospheric conditions on volcanic cloud height can be extreme, and we show examples from Sakurajima (Japan), and Pinatubo (Philippines) of atmospheric convection that leads to radically higher ash transport than would otherwise be the case. To account for these effects, meteorological forecasting techniques should be used to predict the likely altitude of ash in strongly convective situations, and warning strategies adjusted to suit