Happy September equinox, everyone.

One of the cool things about this day is that it has a fairly high profile on the common, demi-Gregorian calendar, the equinoxes perhaps figuring even larger than solstices in my casual surveys. Another one is that it is only the autumnal equinox if you live north of the equator: otherwise, it is the vernal kind.

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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.

Here’s something to try: go to Flickr’s map feature at search “Mauna Kea.” Or “duluth, mn.” Or “coldfoot, ak.” Pretty cool, if you ask me. Particularly since there are now a couple of GPS-enabled camera phones. I think I’ll wait for the price to come down a little bit (from $750-$1000, according to reports) before I think about it, though.

A very fun morning discovering many cartographic links and projects today.

Whether you are a book snob, an Australian firefighter, a map junkie, or a mushing groupie, there are web-based maps for you.

Coming soon is a post about the variety of ways (cartographic and otherwise) to represent the Sun and Moon.

I recieved an email from my friend Rod Floro, a science teacher at Kea’au Middle School who is spending the next several weeks at sea as a crew member on the Alingano Maisu. As with any trip, Rod experienced problems with the airlines and new language at the destination when he flew from Hawai`i Island to Majuro in the Marshall Islands.

According to the PVS website, the voyage from Kealakekua Bay to Majuro lagoon was about 2200 miles and 26 days. One of the first actual signs of land (other than the knowledge of the navigators) was a sighting of birds (manu o ku or white terns) which can range out about a hundred miles from land during the day. Also, Google Maps has much better pictures of Majuro available than they did a couple of days ago.

Below the fold is a bit of Rod’s email–enjoy.

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Grateful for the wind

13 February 2007

The weather has been wierd for the last couple of days, like the wind switch is stuck between ‘Trades,’ and ‘Kona.’ Aside from plenty of vog succeeded by plenty of rain, this just kind of makes everybody uneasy.

So it’s nice to see somebody enjoying the weather. As I was leaving campus on my way downtown today, I saw an `io looping gracefully on a thermal just across Lanikaula St. Unfortunately, by the time I parked and got the camera out, it had soared a few hundred yards farther away and I couldn’t get a picture.

A while ago, somebody told me about a nesting pair near Kukahau`ula, the Institute for Astronomy headquarters building. I wonder if this was one of those birds, though I have also seen a pair up by the hospital. I wonder how big the `io population on the island is?

Here’s a new tracking map for Ku Holo La Komohana, via Google Maps. Still not a lot of detail, but that has a lot to do with the emptiness of the ocean in that neighborhood. There is, however much more color, and as they head South, there will be more to see.

On Tuesday 6 February, the canoes passed Johnston Atoll–an island so small and isolated that it nearly defies description. As a natural counterpart to its status as a National Wildlife Refuge (dedicated in 1926), since 1962 Johnston has also been a high-altitude nuclear weapon test site and a storage depot for many of the US’s nastiest chemical WMDs. Come on, they’re good for the coral.

At any rate, there are also many more pictures on the Polynesian Voyaging Society blog. Many mahalos to the crew for putting the time in on that stuff, when they have so many other demands on their time.