Cool weather mirage

[capona]

What causes mirage in cooler temps?
Went shooting today , 50 degrees . Had a lot of mirage. In the heat I can understand why.
But I don't think I've had it before in cooler temps. What gives?

 

[LaHunter]

I live in Louisiana and we have mirage all the time where I shoot, whether its cool or hot after about 9:00 am.
I am speculating, but I am thinking the air humidity along with the moisture in the ground play a role. Also, as the sun warms the ground, the moisture begins to evaporate at a high rate.

 

[Huntnful]

I have the same thing here in California. I shoot right near the delta, which is basically sea level with a shallow water table. Even on cool days, there is a haze to the air. I don't quite consider it mirage though for some reason. There's no movement to it. It's just a continuous distortion in the air. Some days it's not bad and some days it really bad. I think it's just moisture or something. Basically I have no answer, but know exactly what you're referring to.

 

[capona]

It could be the humidity coming out of the ground. We have had a lot of snow this winter.

 

[Tiny Tim]

Its a relativity thing. Dark surfaces absorb heat more than white/reflective surfaces do. for example, I've looked through scopes in below zero weather over snow covered fields. But a large herd of cattle, a barn or large areas of uncovered gravel or an area covered in manure or uncovered earth will result in significant mirage. When I flew as a pilot, you could tell the difference between flying over a corn field vs a hay field vs a blacktopped city. Wherever you have differences of heat absorption and reflection, mirage is possible.

 

[capona]

Thanks Tim. That explains it well for me.

 

[DJ Fergus]

What causes mirage in cooler temps?
Went shooting today , 50 degrees . Had a lot of mirage. In the heat I can understand why.
But I don't think I've had it before in cooler temps. What gives?

I had some mirage in 50 degree weather a few days back. I think it's the sunlight hitting the cold damp ground causing evaporation of the moisture on the ground.

 

[cjuve]

I have seen this on the last couple mornings here. Heavy vertical mirage just prior to sun breaking the ridge, temps sub 30 degrees. As the sun started warming the ground the mirage dissipates. Vertical compensation was as much as 1.5 MOA from prior known dope at 600 yds. I thought I was loosing zero at first but after watching the shifting POI on several rifles and paying close attention to mirage density it pretty much correlated.

 

[LaHunter]

I have seen this on the last couple mornings here. Heavy vertical mirage just prior to sun breaking the ridge, temps sub 30 degrees. As the sun started warming the ground the mirage dissipates. Vertical compensation was as much as 1.5 MOA from prior known dope at 600 yds. I thought I was loosing zero at first but after watching the shifting POI on several rifles and paying close attention to mirage density it pretty much correlated.

During the heavy vertical mirage, were your POI low or high? I have heard / read reports of both low & high impacts, curious to hear what you experienced?

 

[cjuve]

Initial POI was high, first sighter failed to hit the target out of two different rifles. Second sighters out of the same two different rifles impacted 6-8" high of POA at same elevations for both rifles. I made the same turret adjustment for both rifles down 1.5 MOA, first rifle hit at expected impact elevation. It is at this time that the mirage cleared enough so see bullet holes in target. Second rifle group impact 1.5 MOA low. Fired 3 shot group out of first rifle group landed 1.5 MOA low as well.
I actually returned a Mark 5 HD to Leupold last week after experiencing the same thing last weekend, it never occurred to me that the mirage would have that large of an impact. If I had not had two rifles side by side shooting them one after the other I might still be scratching my head. There was also a little horizontal shift with it as well.

I can guarantee 100% that it was not the loads or heat stress in the rifles.

 

[cjuve]

I believe that there was a pretty good temperature differential between the ground(warmer) and air(cooler) that was causing the mirage.

 

[243winchester]

Yes I can agree with that up here in Minnesota.