The thermometer on my Subaru measured -14 deg F and was dropping quickly. Was this a good decision to get up at dawn and drive north into the San Luis Valley of Colorado for some winter photography?
Blanca Peak,14,351-foot (4,374 m) rises above the cold air (-11 deg F) of the San Luis Valley, Colorado. Blanca Peak, Tsisnaasjiní, is the sacred mountain of the East to the Navajo, marking the eastern boundary of the traditional Navajo homeland.
Northward I drove. My destination in the San Luis Valley of Colorado would be even colder. A recent snowstorm blanketed the mountains and the valley they towered above. The white landscape reflected any heat directed at it, while any heat it held radiated into the cold sky.
This immense valley floor reaches 122 miles north-to-south and about 80 miles at its widest east-to-west dimension. I can see forever here.
Wildlife was sparse. Who in their right mind would hang out here?
As I traversed this winter wonderland, I did see an occasional Rough-legged hawk. The snowy fields here are similar to their home ranges in the Arctic.
Rough-legged hawks migrate to the San Luis Valley on some winters. They hunt the open country for voles and small birds. Note the feathered “leggings” that help keep them warm in the icy habitats they occupy.
Sub-zero temperatures prevailed even in the intense sunlight. The sunlight warmed air above a ground layer of bitterly cold still air. This created a strong temperature inversion. Normally cold air resides above warmer air at ground level. Today it was the opposite. Optical turbulence was obvious from the inhomogeneous mixing of cold and warm air cells.
The warmth of my car added to the turbulence challenges. Swirls of warm air escaped the open window into the freezing air, blurring my vision. Light rays originating from my photography subjects were diverted en route to my camera.
When I researched optical turbulence in my past life, I likened these warm/cold air cells to lumps found in tapioca pudding.
Normally this kind of optical turbulence is associated with looking across the ground of a hot desert. In the heat of a summer day, hot air rises from the ground and interacts with cooler air above. Pockets of hot and cold air refract rays of light differently. What once was a light ray traveling straight through uniform temperature air was now diverted each time it encountered an air cell with a different temperature.
The resulting optical effect is much like looking through privacy glass used in showers – the image of the subject is blurred since there is no longer a one-to-one mapping from a point on the subject (scene) to a point on the camera sensor or my pupil. This makes photography challenging. It is impossible to get a sharp image. Atmospheric turbulence can blur photos and our vision in hot and cold environments.
I had experienced this effect photographing wolves in Yellowstone. It was a sunny day and no wind; the air temperature never rose above -27 deg F. I almost threw my new camera in the trash since it would not acquire a sharp focus. It was not an issue with the camera, though.
Another temperature inversion effect caused some bizarre optical effects in the frigid San Luis Valley.
Light rays from the lower slopes of San Antonio Mountain (10,912 ft (3,326 m)), New Mexico, are refracted (bent) downwards from warmer air toward the colder air at the ground level. This creates a superior mirage effect, known as Fata Morgana, which can be observed when looking at distant objects through a temperature inversion. The distant mountain, 47 miles (76 km), appears to be “raised” vertically from the refracted light rays. Look closely at the symmetrical patterns in the lower part of the mirage. The image is inverted due to light rays from the bottom of the mountain crossing, due to refraction, light rays from higher portions of the mountain. Trees on the horizon are stretched vertically.
Light rays from the distant San Antonio Mountain refract along curved paths in the temperature inversion. The light rays bend down towards the colder air by the ground. When we observe these rays of light, the image we see of the mountain appears elevated, and in places where light rays cross, the observed image is inverted. This drawing exaggerates the effect I observed in San Luis Valley. The lower part of the distant mountain’s image is inverted, as evidenced by the symmetrical patterns on the mountain’s lower slopes seen in the next photo.
A tighter crop view of the Fata Moranga mirage of San Antonio Mountain. The mirage image shows a “lifted” mountain, along with what appears to be an inversion of some parts of the mountain in the mirage. Also, notice the distortion of the trees.
Whereas the previous discussion described how intermixed pockets of warm and cold air scrambled light rays’ directions, resulting in a blurry image, the strong temperature inversion caused superior mirages to occur.
Known as Fata Morgana, these mirages “lift” distant mountains into the air, sometimes creating multiple inverted images above the real image.
The term Fata Morgana is the Italian name for “Morgan the Fairy”, a sorceress of medieval legends and sister of King Arthur. The legendary Fata Morgana has been blamed for causing complex mirages over bodies of water, especially in the Strait of Messina.
My trip into the deep freeze of San Luis Valley was otherwordly. Life feels delicate in these arctic conditions. The raptors I saw hung onto every calorie they could, resting on telephone poles to save their precious energy to stay warm and only fly when they saw prey down below.
Observing the bending of light rays in the extreme temperature inversion made me think about what I was seeing. It triggered memories of seeing snowy peaks dancing above the San Luis Valley floor, far north of Taos. Without the extreme temperature inversion, I cannot see these distant peaks.
It feels good to be home safely by the woodstove after my winter voyage!