Exploring Kootenay Lake

Snow falls off trees (move cursor over image; wait; move cursor off image; repeat).

The outbreak of cold air following a cold front set the stage for today’s events. the Lake had:

• Steam fog—a crowd of evanescent sprites that raced across the water surface.
• Steam devils—whorl winds that towered over the fog (same link as steam fog).
• Sun dogs—parhelia, a type of halo caused by sunlight and ice crystals.

This morning’s steam fog was as grand as one gets; the steam devil (below) was nice but not as grand as those of last December (but, then the season is still young). The sun dog was almost as nice as any I have seen around the Lake, especially as a portion of the parhelic circle extended from it to the left (see the discussion under haloes).

All in all, a lovely brisk morning for watching the Lake.

Steam fog over the Lake as seen from Duhamel (Nelson is in the background).

An acceptable, but not superb, steam devil (rising out of the steam fog) at Crescent Bay.

A sun dog and parhelic circle seen from Crescent Bay (with steam fog below).

In early November, snow is high in the mountains; by late November, it has descended to lake level. Between those occasions, the mountainside presents a canvas upon which two distinctly different patterns of white are painted.

Rime on the mountainside (first picture below) presents a sharp transition—white above the 0°C isotherm, dark below. The stratus cloud which left this pattern will have extended both above and below the transition, but the rime only forms when the temperature is less than 0°C and supercooled cloud drops freeze onto the trees. Although this pattern is often supposed to result from snow, it does not.

Falling snow leaves a gradual transition between white and dark on the mountainside (second picture). For various reasons, the snow does not melt instantly when it falls below the 0°C isotherm, but only gradually makes the transition into a rain shower. The pattern on the mountainside reflects this and is clearly different than that produced by rime.

These issues are explored in greater depth and with more pictures on the Kootenay Lake website on a page entitled, Snow level, Rime, and Virga.

Rime on a mountainside presents a sharp transition

Snow on the same mountainside presents a gradual transition

Long parallel lines of bubbles are often seen on the lake surface when the wind speed exceeds about 11 km/hr but is less than about 45 km/hr (when the pattern breaks up). Judging by the sparcity of white caps in the pictures, below, the wind speed was likely between 20 to 30 km/hr.

The wind drags on the surface waters of the lake and causes helical rolls to form in the upper layers of the lake. The axes of these rollers lie more or less along the wind direction. Pairs of rollers turn in opposite directions rather like the wringers on old–fashioned washing machines. Surface water flows inward and sinks between a pair of adjacent rollers, but the bubbles (and other floating debris) are left as lines on the surface.

This pattern of wind–driven helical rolls in the surface waters of the lake is called a Langmuir Circulation, after Irving Langmuir who first explained its structure after observing similar lines of seaweed during an ocean crossing in 1938.

A good place to observe Langmuir Circulation on Kootenay Lake is from the Nelson Bridge during a brisk westerly wind.

There is a time in the Fall when the view of Sphinx (over 2800 m. in the Purcell Mountains) as seen from the West Arm presents an irresistible combination of water, trees, and snow—well worth a fanciful interpretation.

The Kootenay-Lake Website offers a discussion and more pictures of local fall colours.