birder
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Thunderstorms.
23 Dec 2019 at 9:52pm QuoteEditlikePost OptionsPost by birder on 23 Dec 2019 at 9:52pm
This year for the first time ever I haven't seen or heard any thunder in the UK, is this a sign of climate change?
Others have commented on this.
www.onepotscience.com/why-are-there-no-thunderstorms-in-the-uk/We had our first thunderstorm of the year on the 13th June 2020 with some others each day until the 17th, I enjoyed watching them. I presume they're caused by a change in the jetstream?
This depicts the situation quite well...
A depression parked itself south of UK and then slowly drifted, while diffusing, North to a position over the UK.
While south of us, it dragged humid air into the country where sunny conditions pushed the moisture up by convection. High pressure to the east held the depression in place with a northward drift for days so, the convection/humid air continued.
As the depression moved over the UK, It rotated a weather front pivoting in the Bristol area, this was thursday to friday. The long duration rain that occurred on these days was the same weather front circling twice over the country!
It eventually lost energy and dissipated.
With the easterly air flow and moisture, if these synoptics occurred in the winter it would possibly have been a major snow event!!
Regarding the jet, its position is determined by the location of high pressure, it must go around these. When conditions are zonal, the jet happily scurries the depression along and gives their trajectory momentum. However the jet will always deviate around a high pressure, hence when HP is in the way of the usual zonal flow it 'blocks' it.
This is what happened last week, except the blocking was to our east so the depression stalled in the proximity of the UK.
None of this has anything to do with 1.5°c increase in temperature but is highly likely a function of low solar activity.
All of the recent hot days in the past 2years were as a result of high pressure placement and the movement of air from one place to another, on very hot days the air moved from very far south to very far north!
I haven't seen lightning mentioned as a metric from any historical weather descriptions, there are however many references to great storms with large hail destroying fields of crops for miles.
Historically people weren't really concerned with measuring weather too much, but recorded events which had notable effects/destruction.
You can be 100% sure a storm which destroyed crops with hail would have been a supercell, probably with tornados.
There are many papers attributing blocking to low solar activity, scientists try to explain current weather by involving arctic ice or the fact that its hot in one place so driving synoptics in another.
It is however, the placement of high pressure which drives the synoptic pattern which results in warm/cold air going where it does.
Under 'normal' zonal conditions high pressure remains north and south if temperate areas allowing depressions to scoot in between, fueled by a jet that has clear passage.
During low solar activity, high pressure extends from the north into the temperate areas blocking the clear passage, as the jet bends around these, it has to travel in northerly/southerly directions and transports airmasses in a similar way.
Lightning requires energy difference and or convection, so where hot and cold airmasses meet, or cold air moving over hot surfaces.
These scenarios are far more likely in blocked, or meridional conditions as more mixing of airmasses occur.
In the UK however, blocking does not guarantee Lightning as can be seen by '18 & '19 which were blocked summers (last year incredibly so as demonstrated by a record-NAO period) where '19 particularly had 2 storms in my area only, whereas we had 5 consecutive days last week.
