*** The official frost hollow thread ***
Mar 20, 2018 18:35:33 GMT -5
boombo, Donar, and 10 more like this
Post by rozenn on Mar 20, 2018 18:35:33 GMT -5
Let's share our fascination for these climatic anomolies.
Let's begin with an example, the Darbounouze closed frost hollow in the Vercors massif near Grenoble:
And its temps from last montt (not sure how close to the bottom the weather station is):
You'll notice that the so-called "Beast from the East", although noticeable when it comes to the highs, didn't bring the coldest low. That -34.6°C low on Feb 13 was all about indigenous cold.
Looking at the Google relief map, the bottom of the frost hollow is below 1,300 m, while the col a couple km north of it is more than 1,360 m asl. This means that on calm, starry nights, cold air will have nowhere to escape and will accumulate until it reaches the col, hence the closed frost hollow moniker (not sure how to call it in English actually). A cold air lake more than 60 m deep can form on such nights, the closer to the bottom the colder. This is only possible in limestone regions, where water can infiltrate into the soil. Otherwise, a water lake wil form instead of a cold air lake.
Looking at the satellite view, one can't help but notice the lack of trees at the bottom of the cold hollow and the relatively sparse vegetation at any altitude lower than the col. This is due to the fact that summer nighttime temps aren't conductive to tree growth, unlike in the surroundings. As an extreme example, on July 20, 2016, the max/min there were 27.8/-3.3°C.
Look at the stunted trees down there:
goo.gl/maps/Eq6EUJAv5sj
Either stunted or dwarf trees, like at the treeline several hundred meters higher up. In fact it's called an inverted treeline.
Beautiful!
goo.gl/maps/t4Riiced5J72
Fascinating innit?
Let's begin with an example, the Darbounouze closed frost hollow in the Vercors massif near Grenoble:
And its temps from last montt (not sure how close to the bottom the weather station is):
You'll notice that the so-called "Beast from the East", although noticeable when it comes to the highs, didn't bring the coldest low. That -34.6°C low on Feb 13 was all about indigenous cold.
Looking at the Google relief map, the bottom of the frost hollow is below 1,300 m, while the col a couple km north of it is more than 1,360 m asl. This means that on calm, starry nights, cold air will have nowhere to escape and will accumulate until it reaches the col, hence the closed frost hollow moniker (not sure how to call it in English actually). A cold air lake more than 60 m deep can form on such nights, the closer to the bottom the colder. This is only possible in limestone regions, where water can infiltrate into the soil. Otherwise, a water lake wil form instead of a cold air lake.
Looking at the satellite view, one can't help but notice the lack of trees at the bottom of the cold hollow and the relatively sparse vegetation at any altitude lower than the col. This is due to the fact that summer nighttime temps aren't conductive to tree growth, unlike in the surroundings. As an extreme example, on July 20, 2016, the max/min there were 27.8/-3.3°C.
Look at the stunted trees down there:
goo.gl/maps/Eq6EUJAv5sj
Either stunted or dwarf trees, like at the treeline several hundred meters higher up. In fact it's called an inverted treeline.
Beautiful!
goo.gl/maps/t4Riiced5J72
Fascinating innit?
