Poor Patrick Moore. I have a book of his, A Passion for Astronomy, which contains an illustration captioned "The author's main telescope - a 15-inch reflector with octagonal wooden tube and massive fork mounting, set up at Selsey." And a most impressive instrument it looks. But the evening before last a tornado invaded Selsey from the sea, and by all accounts the observatory in Moore's garden was severely damaged.
Selsey lies on the south coast of England, near the Isle of Wight, and the tornado was the most vicious to have been experienced in Britain for some time. It seems to have begun as a "waterspout" at sea, and then moved eastwards across the headland known as Selsey Bill as a tornado, leaving a two-mile trail of unprecedented destruction in its wake.
The tornado is the enfant terrible of meteorology. It is quite different from the relatively minor "wind-devils" or "dust-devils" that occur from time to time on hot sunny afternoons in summer, well known to farmers as the impish scatterers of new-mown hay. The tornado, although also small-scale and very localised, is the most violent of all windstorms - a fierce maelstrom of swirling air with a life span of anything from a few minutes to perhaps an hour.
The essential requirement for the formation of a tornado is the presence of strong persistent updraughts in the atmosphere, and the availability of plenty of moisture near the ground. It so happens that these same conditions facilitate the development of thunderstorms, hail and heavy showers, so a tornado often coincides with these phenomena.
In such conditions, the anomalous buoyancy of the air at lower levels causes it to rise; as it ascends it is forced to "turn" because of variations in the strength and direction of the wind with height - a phenomenon known to meteorologists as vertical wind shear - and sometimes this turning motion rapidly accelerates, and the result is a tornado.
We think of tornadoes as nasty foreign things, common perhaps in the blazing sunshine of Great Plains of the US, or on the deserted pampas of the Argentine. But they can, and do, occur anywhere in the middle latitudes. Every year there are about 100 to 150 tornadoes in the south of England, and now and then they occur in Ireland, too.
The frequency here is significantly less - probably fewer than 10 a year; moreover, Irish tornadoes, and indeed their British counterparts, are considerably less vicious than their transatlantic cousins, but when they come, they can still leave an impressive trail of damage in their wake.