Wayfinding and waves

27 April 2009

I once had a brief discussion with a much smarter fellow than myself wherein he argued that four was an arbitrary number for cardinal geographic directions. While I concede (now, as I didn’t then) that he is correct from a geometric point of view, there seems to be at least one evident physical reason for the choice: one direction each for sunrise, sunset, and halfway from each to the other.

While Guy Ottewell gives a potential (if esoteric) thesis for why A is the first letter of a couple of different alphabets, I have nothing like the speculative erudition to say whether my guess holds any water. I do know, though, that while useful direction finding tools can be simple, they can also be arbitrary. Polynesian navigators use celestial coordinate systems shaped from the rising and setting of the Sun and other stars, and these coordinate systems are sometimes symmetrical and even, but not always. Navigators also shape their course based upon other information including clouds, wind, sea critters, birds, and other factors.

One of these other factors was brought into sharper focus for me as I flew from Minneapolis to Cleveland last week, passing over Lakes Michigan and Erie on the way. As far as I’ve been able to figure, this trip was at a similar altitude to those from Hilo to Honolulu, flying at approximately 30,000 feet. What struck me as different, though, was that while I was used to seeing the Pacific Ocean with increasing complexity as more and different sets of waves gradually revealed themselves crossing and rolling on its slightly rough skin, I didn’t see any texture of swells on the two Great Lakes.

Having grown up about six blocks from the edge of Lake Superior, and spent time tagging along on boats with my father from a tender age, I can attest that the Great Lakes do possess waves of sufficient size as to be seen from the air. Those waves might not be the sixty-foot seas of the northern Pacific that cause the weather announcers to doubt their script in the middle of reading it, or even the massive rollers that create the fantastic offshore breaks at Peahi near Maui or Mavericks off California, but Great Lakes waves have sunk ships and otherwise imposed their presence in plenty of ways. In short, I was surprised that I couldn’t see anything from the air, even on a relatively calm day.

My guess as to the cause is something called fetch. In this case a noun, fetch refers to the distance across the water that a wind blowing in that direction has to build up waves. While modeling the problem quantitatively is by nature more complicated, fetch can have an effect equal to that of the speed of the wind. It is the biggest reason why small lakes don’t have big waves. Wind speed and fetch can also affect the rate at which waves come in, their period, a characteristic well known and scrutinized by surfers everywhere.

I’ll do some checking with other resources, but I would guess that the tapestry of overlaid swells that help Polynesian navigators orient themselves on the Pacific was also present on Lake Michigan a week ago, and that the chief difference in appearance wasn’t caused by a difference in height of the waves, but rather in their frequency. Lake Michigan is long and thin, perhaps 85 miles wide from Milwaukee, WI on the west side to Grand Haven, MI on the east, but 280 miles north to south from rural Summer Island on the UP to industrial Gary, Indiana. Thus, when the wind is blowing most directions, there is fairly little water to build up long distances between waves. Only if the wind blows due north or due south (winds being named for the direction they are blowing _from_, in most cases) is their enough fetch to produce swells wide enough to be seen from the air.

Any kindly contributors with more knowledge are invited to comment, particularly if you have done some calculations. I am halfway through building a KML file for the trip, and will post it to the comments when it’s finished.

Both the elliptical title of this post and the long distance from its antecedent have the same toothmarks: I’ve been reading so much, I haven’t wanted to write anything. I’ve enjoyed being both the style and the substance of The Periodic Table by Primo Levi, and read it interspersed with revisiting some Terry Pratchett and Arturo Perez-Reverte. Also slowly, slowly working my way through Borges Ficciones, wherein the most pertinent quote might be from The Library of Babel: “You, reader, are you sure you understand my language?”

I’m not sure I do, but it is wonderfully toilsome to try.

At any rate, the weather here has been early summer over the weekend–sunny and 70 degrees. The Sun is now transiting the meridian pretty high in the sky, and the skylights in our house are providing lots of light. As the Moon waxes these days, it picks up where the Sun leaves off, and it, too, illuminates our kitchen from above. We planted some roses in the backyard yesterday, and right now a delicate golden kinglet seems to be taking advantage of the legions of buds on the red maple right outside the kitchen window, making a hurried morning meal. For my own hurried morning meal, I cracked open a jar of apple butter received from one of Elle’s comrades at the university. I’m trying to use more glass jars so I can use fewer disposable containers; I’m also trying to buy as much food as possible in reusable containers.

Coffee has been a problem there, although since I buy bulk beans, I usually just end up with the strangely useless paper bags provided at the store. I also usually don’t buy expensive coffee, on the argument that if Kona estate peaberry isn’t laying around, I won’t know the difference. All of this is by way of saying that I was highly amused that Dunkin’ Donuts is marketing their coffee in grocery stores here, where I don’t think there’s an actual Dunkin’ Donuts storefront for a thousand miles: I prefer Dunkin’ Donuts to that Krispy Kreme, which we at least have in Portland. I am amused to no end that I stepped outside habit to buy a name brand product which is then not the product that gives the name. But it is pretty good coffee.

Front-page editors of various newspapers I saw yesterday seem to feel bound to report on the North Korean missle launch, and perhaps in honor of tradition to do it in the same way such things were reported during the cold war. Although I haven’t seen anybody labelled ‘Reds,’ yet. Perhaps they are referring to the limited historical and belligerent importance when they use smaller type for that headline than for budget stuff. Or perhaps they have taken notice, as Jeffrey Lewis has, that for as much as North Korea wants to impress the world by being a scary nuclear power, they are actually 0 for 3 with these kinds of things.

Sure, they did prove to their own citizens that they are still defiant, but that doesn’t seem too important right now. The NORK government is also still trying to tell everybody that they got a satellite into orbit, but people seem to be paying more attention to the statement by Obama, encouraging renewed consideration of the Comprehensive Test Ban Treaty.

That’s an unintended success.