UKC

We seem to be getting loads of pictures in the gallery this winter showing cloud inversions. Lots of them are brilliant photos, especially when seen full screen.

Are we actually having more inversions this winter, or is it just luck that more people are getting above the clouds and snapping away (not me unfortunately ☹️).

Definitely more inversions, and these often solid persistent inversions lasting several days. These were caused by a slow moving intense area high pressure, over Scotland in December, and England and Wales in January.

It's not uncommon to get the odd few days giving good cloud inversions in winter (the colder ground temps allow the fog or low cloud to persist after sunrise unlike in the summer). What has been a bit unusual is the persistence of these fairly intense high pressure systems with mean sea level pressure often around 1040 hPa. With these more intense highs there's often a greater chance of getting a strong low level temperature inversion. However, you still need sufficient moisture to form the cloud below the inversion, so river valleys or low lying marshy ground are often the best places to find a cloud inversion. A gentle onshore flow can sometimes help too by bringing in more moisture from the sea.

As I understand it, another factor in the formation of significant temperature inversions is the part played by cold air draining down mountainsides. The calm conditions associated with anticyclones helps with this, as if there are even quite gentle winds the layers of cold air forming at ground level at night become mixed with warmer air not in contact with the cold ground and so the cold air is less likely to drain down into the valleys. If one is in the right place at the right time - possibly in a gill running down a steep hillside just after sunset or later one can feel the cold air forming a katabatic wind running down the slope. It can be a very striking experience.

You're quite right, cold air called katabatic drainage will flow down a slope under calm clear conditions overnight, strengthening the temperature inversion in hollows such as deep cories or cwms where the cold air pools. You still need sufficient moisture though, so tarns or lochans can help with this. As an interesting aside, these katabatic winds rarely exceed around 15 mph in the UK, but can reach speeds of 100 mph in Antarctica during the winter as they hurtle down the massive glaciers!

One common misconception around fog is that it is much harder for fog to form in completely still conditions. Basically as the layer at the surface cools, any moisture condensed isn't replaced from above so you end up with a very dry layer at the surface, perhaps a few patches of thin shallow fog. A slight breeze (3-5 mph) helps mix this up and draw more moisture down to the surface, aiding fog formation and better cloud inversion conditions.

Actually Michael, gravity is getting much stronger* and pulling all the mountains up higher and higher - in many cases above the clouds

*why? 5G, Planet X, Brexit, and millions of Black OP satellites swirling above us

It fascinates me that there’s no consensus on if Earth’s gravity is getting stronger or weaker; this comes down to the planetary mass balance” - do the losses from the launch rate of space rockets and the boil off of our atmosphere exceed the accretion of micrometeorites etc onto the planet?  One of life’s mysteries.

I think it's a fascinating thing, gravity. (My post just above was silly as usual, helps me get through the day, through life). The more I read about gravity (in an amateur way, in magazines like Nature and Scientific American and even the occasional book) the more interesting and mind-boggling it gets