AMATEUR NATURALIST

The rise of high winds and waves

Posted April 24, 2011, at 5:46 p.m.

When I was about 8, one of those menacing hurricanes with tattered clouds and surly, dangerous rain tore into Maine. I think it must have been Hurricane Esther, which reached Category 4 (131 to 155 mph winds, storm surge 13 to 18 feet) and knocked a plane out of the sky near Bermuda.

My own recollection of it is vivid: When the rain had stopped but the wind and gray sky were still lowering, I discovered I could spread my arms out and lean into the wind over the embankment beside our driveway. It was exhilarating and scary. From that time on, I kept a terrific respect and uneasiness about a gale, especially in boats and small airplanes. The wind, in my experience, has a sort of single-minded madness, as if it’s in pursuit.

Fifty years later, some Australian researchers have discovered that high wind speeds have been increasing over the past approximately 25 years. They studied satellite radar data of wind speeds and wave heights over the whole Earth, and found that between 1985 and 2008, wind speeds over most of the oceans increased by one-quarter to one-half percent each year; winds in the highest 1 percent of speed increased an average of three-quarters of 1 percent.

Wave heights also increased, though not quite as much as wind speed. The largest waves, meaning those in the top 1 percent of giantlike, increased an average of one-half percent per year, with some places showing increases of 1 percent per year. The researchers, from the Swinburne University of Technology in Melbourne, found for example that the average height of the top 1 percent of waves off southwest Australia was around 18 feet, about 3 feet higher than in 1985.

Ocean waves are set up mainly by wind, and you can see the mechanism by watching breezes riffle across calm river or lake surfaces. The higher the wind speed, the larger the waves, of course, as the energy in wind increases with the cube of its speed. So waves set up by winds blowing strong enough over an open stretch gain enough energy to turn into swells that far outdistance the wind that kicked them up.

From time to time there appears a rogue wave, which is a wave that’s significantly larger than you’d expect from the sea conditions around it. The huge wave that washed over sightseers at Acadia National Park a couple of years ago, and resulted in the death of a girl, was by this definition a rogue wave. The first scientifically measured rogue wave struck a platform in the North Sea off Norway in 1995. Waves there were frequently 39 feet, but this wave was 84 feet high. A monster, as it were.

For the record, a tsunami is not a rogue wave. It’s a wave set up by a geological event, such as the huge earthquake near Japan last month. A tsunami can be just a few inches or can be so big it takes 15 or 20 minutes to wash up and recede, as in Japan and in Indonesia in 2004. A tidal wave, or tidal bore, is something different yet, being a wave set up in a river or bay by incoming tide pushing against the outflow.

Anyway, these rising high-wind speeds may or may not be a result of global climate change. The researchers indicate that data from a longer time span are needed to sort out whether this is just a natural ebb and flow of winds, or if it’s an unusual spike that could continue to grow. If it is, there could be some concern about effects on offshore wind turbines, which have to feather their blades and shut down to avoid damage in very high winds. Interestingly, the researchers found a 5-10 percent increase in gust speeds where offshore turbines are typically placed. I could not find any reference to data from the Gulf of Maine.

We are not going to blow away, any more than we are going to bake to death in global warming. But there’s something dangerous in a gale that wiseness or foolishness fears, a sort of madness when wind and sea contend to see who is mightier. Some people love to feel the blasts in their faces. A heavy sea is “dirty” to a sailor. It still makes me uneasy.

naturalist@dwildepress.net

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