According to a snippet in the Daily Telegraph , a study published in a recent issue of Neurology , the scientific journal of the American Academy of Neurology, concludes that Chinook winds can trigger migraine.
The study, apparently, looked at the diaries of 75 migraine patients aged 16 to 65 over two years. Thirty-two of these patients were found to be more likely to experience migraines during Chinook conditions than at other times. And one has to say, this comes as no surprise.
The Chinook is a warm dry wind that sweeps down the eastern side of the Rocky Mountains into Wyoming, Colorado and Montana in the early spring. It is named after the Chinook Indians, because it blew from "over the Chinook camp", and it is a specific case of the fohn , the generic name by which the phenomenon is known worldwide.
If moist air is forced upwards by rising ground, its moisture is often extracted in the form of rain on windward slopes. The stream of air which then flows down the leeward side is therefore relatively dry, and for complex reasons related to its dryness its temperature increases very rapidly with the increasing atmospheric pressure on the descent.
The population downwind of the mountain range then experiences the warm dry wind of the fohn - or on the Great Plains of the United States, the Chinook.
It is well known than many residents of regions prone to winds like these know precisely when a fohn is imminent. For many of them it is preceded by a range of symptoms known collectively as "fohn disease", whose sufferers experience headache, nausea and sleeplessness, together with irritability, depression and a general feeling of debility.
Medical examination reveals an increased pulse rate and a fall in blood pressure - and no doubt it can bring on attacks of migraine as well in those susceptible.
Nobody knows exactly what causes fohn disease. For many years it was believed it might be associated with a characteristic oscillation in atmospheric pressure which often precedes the warm wind, a variation of several hectopascals over a few minutes.
But such pressure changes are now regularly experienced in lifts and aeroplanes with no ill-effects, even in the case of persons with a history of fohn disease. More recently, there has been a tendency to blame the condition on positive ions, tiny air particles with a small positive electrical charge which are more than usually prevalent in such circumstances and known to have adverse effects of the kind described on those susceptible.
But no one really knows. Fohn disease remains one of the unsolved mysteries of bio-meteorology.