SALT LAKE CITY — Have you noticed over the past few days that sunrises and sunsets across northern Utah look a bit different than normal? That’s because the upper level winds in the atmosphere is moving wildfire smoke from California and Oregon across our patch of sky.
As can be seen in the satellite image below from the National Oceanic and Atmospheric Association, large parts of northern Utah had smoke overhead as of Tuesday morning, but the sky over the rest of the state was relatively free of smoke.
This is because the way the upper level winds are moving and winds are dipping through the Wasatch Front up through southern Idaho.
For the past several mornings, Utahns been able to witness hazy, reddish, but somewhat dull sunrises; the result of wildfire smoke. But why is the smoke making the sunrises and sunsets look a bit different than normal?
Light moves in waves as it travels from the source, and every shade of color the human eye can see has a different wavelength. Reds and oranges have a longer wavelength than shades of blue or violet.
Light from the sun looks white, but it’s actually a combination of all visible colors. As light moves to our eyes, it’s going to interact with different particles in our atmosphere and scatter. Most of the gas molecules and particles in our atmosphere are small, so you get what is called Rayleigh scattering when the light interacts with the small particles.
When the air is clear and clean, and the sun is overhead, light only has to travel through the smaller particles and at a shorter distance, too. As a result, the sky appears blue because the wavelength of blue light is scattered efficiently by our atmospheric particles, but not so much that we can’t see it. This is where we turn to our sunrises and sunsets.
Sunrises and sunsets tend to be on the more reddish side because the sun angle is lower. This means light travels further through more atmospheric particles. The result is violets and blues getting scattered out completely, making the yellows, oranges and reds more visible.
So, where does the wildfire smoke come into play?
When you introduce smoke particles, some of them can be larger than the wavelengths coming in. When a larger particle scatters light, it’s known as Mie scattering. This type of scattering leads to longest of wavelengths being scattered best. This is why you end up with very reddish sunrises and sunsets when there is wildfire smoke aloft.
If there’s enough smoke in the sky, this effect can happen all day, blocking out the blue sky and leaving behind the red of the sun!
