Thursday, October 27, 2011

So Autumn

The fall glow in the Range of Light is especially remarkable in Yosemite Valley these days. We are at that point in the sun's apparent migration in the sky when it sets very low in the west, in the skyline notch that is the Merced River Canyon. It's the analog sunset point to that which produces the 'firefall effect' at Horsetail Fall. That photogenic phenomenon happens about 7-8 weeks after Winter Solstice; we are now 7-8 weeks before solstice. The low sunset lets a more colorful sunlight into the Valley at the end of the day. (Horsetail Fall is just trickling now so won't produce the volume of mist/water that catches the light in February.)
In mid-summer the sun sets well to the north of the Merced's exit point, so is high over the canyon rim; in winter it sets high over the canyon wall to the south - in both cases setting when the sunlight is still whiter.
During the day, the sun is traversing a lower angle than in summer, too, but still reaches more of the Valley floor than it does in mid-winter. The Valley's deciduous plants are ending their growing season with the decay of chorophyll that allows other leaf pigments to shine before leaves drop to the ground. Big-leaf maples put on the biggest color display now, and these bands of yellow highlight their preferred wetter, shady habitat in ways that may not have been apparent all summer. The one sugar maple in Old Yosemite Village turned more yellow than red this year, and the afternoon up-canyon breezes have this tree already about 20% bare now. Black oaks are going brown-yellow but many leaves have dropped from some. Dogwoods are still largely green, but showing their startling pink in places. Black cottonwoods are mostly bare now. The brightest plant in the Valley now is dogbane or Indian hemp (Apocynum) - their radiant gold almost hurts one's eyes.
The meadows are a light brown, the fallen pale leaves cover darker ground, more sunshine reaches the ground through branches that are baring. Even ponderosas participate in this season, browning and shedding some of their needles after the dry summer. It all adds up to a lighter albedo. Though the days are shorter and the sun is lower, Yosemite Valley is reflecting more light and is brighter than it is all summer. Only the winter snow will raise the Valley's albedo beyond this dreamy, pale glow of autumn.
Incense cedars are raining their helicopter seeds now. Gray squirrels have been shredding pine cones for a few weeks and their litter of cone scales is everywhere. Been seeing more chickarees than usual in the Valley, also working over the ponderosa cones. Down canyon a bit, Torreya has been dropping its strange green fruits.
The Merced is running at about 80 cfs at Pohono Bridge and dropping since our last storm on 5 October (average for this date is around 33 cfs). Last evening the Valley rim was entirely mantled in a cloud layer that built just at sunset.

Friday, October 14, 2011

Foliage change

Rain ten days ago really swelled the Merced River. The historical average flow for last week was below 30 cfs. It had been running closer to 100 cfs, then leapt to over 600 after the rain. That the high country got snow showed in the nice 24-hour cycle of melt ebb and flow shortly after the storm. Our waterfalls are again looking exceptional for this time of year.
Ladybird beetles are on the move in this warm (moist) weather, with many swarming in El Portal the past couple of days.
A red-shouldered hawk, and a pair of great horned owls were heard in the volunteer campground in Yosemite Valley. A Say's phoebe was seen in Rancheria Flat.
Orion and Canis Major dominate the morning skies if you're out early and have a view to the south.
The sugar maple in old Yosemite Village has just started to show a tiny touch of color. At the Valley elevation, other than dogbane and some bracken, most color has not yet appeared. Alders skip the show and just start dropping their green leaves into the river when they're done, which is now.
Higher up you'll find aspen and bilberry being more colorful now. It should be a good weekend for getting out in the park.
Half Dome cables are down for the winter, Backpackers, Yosemite Creek and Crane Flat Campgrounds are closed for the season now.