Never shy of diving into controversial waters, "Weather Eye" this morning will analyse the meteorological aspects of the current deafness epidemic in the Army. It may well be that that the weather is to blame.
Impending rain, apparently, enhances sound, and so do threatened storms. The belief that sound carries particularly well in such circumstances is summed up in the old proverb:
Sounds travelling far and wide
Do a stormy day betide
And indeed the same phenomenon manifests itself in the traditional perception in many seaside places that the breaking waves make more noise before a coming storm. Since rain and storms in Ireland might be said to be perpetually "impending", the statistics of our climate may well be crucial evidence for the defence - or is it the attack?
Several factors combine to lend credence to assertions such as these. In the first place the sky is likely to be cloudy with the approach of rain. This means that the ground is protected from the direct heat of the sun, so that vertical convective currents are weak or non-existent. This reduces the level of turbulence in the atmosphere, which in more sunny conditions tends to dissipate sound.
Secondly, pre-frontal air with the approach of rain is likely to be humid. Humid air has a high water-vapour content, and this improves its capacity for carrying sound.
And a third factor concerns the thermal structure of the atmosphere. In normal day-time circumstances, air temperature falls sharply with increasing height in the first few tens of feet above the ground. This has the effect of causing sound waves originating near the earth to bend upwards as they spread out from their source - making sounds at the surface some distance away less audible than they might otherwise be.
Conversely, on a clear night, the earth loses heat by radiation, and the air temperature near the ground is usually much lower than that some distance up above; this has the effect of diverting sound waves, originally headed upwards, down again in the direction of the ground - so distant noises can be clearly heard.
With the approach of rain, however, the atmosphere normally assumes what meteorologists call a "stable" condition - the usual day-time decrease in temperature in the vertical is diminished, or perhaps even reversed. This holds the sound down near to the surface of the earth, allowing it to spread horizontally for a comparatively long distance before attenuation to inaudibility.