lack of anticyclones Where's Our Anticyclones?

[ZONE 51]

 

An anticyclone is a strong area of high pressure centered over a large area, under this the weather is dry with clear blue skies during the day and starry nights but sometimes with mist and fog, usually the wind is light or calm in general, although sea breezes can develop during the day. We are having high pressure there is dry and sometimes calm conditions but it seems that there is always cloud and quite often windy, this is because the high pressure is either in weaker form or being on the edge or the high pressure making things more windy, the cloud is probably stratus and flat cumulus, the cumulus is not allowed to build up high is squashed into a thin layer and as this happens the cloud becomes more flat and wide instead of going up and rising.

There's my explanation of an anticyclone and the changes we have and are experiencing especially over the last several years.

 

Below is some info from an article.

In Britain in summer an anticyclone will mean heat waves during the day. At night, however, as there are no clouds, heat will be quickly lost.  The ground will cool sufficiently to cause condensation of water vapour in the descending warm air and mist or heavy dew may form. This will clear quickly in the morning sun. After a few days, a layer of hot air builds up at ground level, which eventually will give rise to thunderstorms, ending the anticyclone.

 

In winter the longer nights combined with clear skies leads to intense cooling of the land. There is an increased risk of dew, frost and thicker, more extensive fog patches which may be slow to clear or even persist.

 

Under very calm conditions, both frost and fog may persist for several days. An anticyclone's very stable conditions and little air movement means that pollution is trapped at low levels, resulting in very poor air quality such as smogs.

 

http://www.coolgeography.co.uk/A-level/AQA/Year%2013/Weather%20and%20climate/British%20Isles/British-Anticyclones.htm

 

So that's what an anticyclone is and it's affects on our weather, but why is there less of these, what could be the causes and are they going to return?

Edited June 26, 2013 by ElectricSnowStorm

[BornFromTheVoid]

The first step would be to demonstrate that we are, in fact, having less anticyclones. Because I'm sure different parts of the UK, and Ireland, will have experienced difference conditions and have different opinions on the topic

Do you mean, specifically, summer anticyclones/high pressure?

[ZONE 51]

Mostly it is summer anticyclones I am seeing the lack of (as most are), in winter there is quite usually ridges of high pressure giving clear frosty nights between weather systems, but there is definitely less long spells of clear weather especially in summer, they where more usual around and before 7-8 years ago. There is not spells of 2 - 3 weeks of clear blue skies and a few cumulus, also don't seem to be much very deep blue skies.

Edited June 26, 2013 by ElectricSnowStorm

[BornFromTheVoid]

Mostly it is summer anticyclones I am seeing the lack of, in winter there is quite usually ridges of high pressure giving clear frosty nights between weather systems, but there is definitely less long spells of clear weather especially in summer, they where more usual 7-8 years ago. There is not spells of 2 - 3 weeks of clear blue skies and a few cumulus, also don't see much very deep blue skies either.

 

Ah right. I guess near Heathrow, your weather will often be a bit different to the majority of the UK/British Isles, being down the the SE corner of England. For Ireland, we got lucky at the end of May and early June and had (for much of the country anyway) a 2 week dry and sunny period, that was cool in the first half and warm in the second half

 

With regard to recent summers, Greenland has been hogging our anticyclones That's why most recent summer have had -ve NAOs and it's partly why we've heard reports of the record breaking melting on the Greenland ice sheet, as the clear skies and warmth really accelerates the summer melt there. That blocking high pressure has sent the jet stream south into the Atlantic, below the British Isles in recent summers, leaving us in the upper trough with mainly cool and wet conditions. The slower and more meandering jet stream of recent years has meant that weather patterns have become more "stuck", often for weeks on end

 

Although the slow and meandering jet stream continues, this summer has been different so far, with lower pressure across Greenland and a stronger Azores high pressure. The jet stream has also moved closer to the British Isles, allowing for more ridging from the south. Hopefully this trend can continue and bring some widespread summery weather during July

[ZONE 51]

BFTV good post. I know the Jet stream is the major player, but we don't know why exactly it has changed pattern, these days we don't seem to get strong highs that change the Jet? the blocking is preventing it's normal northerly movement, but the angles and strange behavior of the Jet stream through the seasons is also caused by something else I think. Usually strong areas of high pressure move up from the Azores into S-UK at least and hold stay for a few weeks, it was spring/summer 2010 the last long clear hot spell I remember which was the Azores high. There is more interest in the general public now as it is affecting out door activities(climate change)

 

Those that remember the 80s for example would remember long hot summers clear sky for weeks with deep blue sky so deep almost dark blue, this was anticyclonic high pressures, sat over the whole of or large areas of the BI.

 

Q: Do the high and low pressure systems affect where the jet stream runs, or does the jet stream affect where these systems will go?

A: This is one of those "which came first, the chicken or the egg" questions. Briefly, jet streams are located over boundaries of warm and cold air. A USA TODAY Online graphic shows how this works. You'll find links to more about jet streams at the bottom of the text with the graphic. But, jet streams also help determine the locations of high and low pressure areas, which in turn help create flows of warm and cool air that set up the boundaries. The links from the graphic will lead you to several other graphics on these topics. Also, chapters 3 and 4 of my USA TODAY Weather Book has a lot more detail about all of this (10-18-98)

http://usatoday30.usatoday.com/weather/resources/askjack/waskjet.htm

Edited June 26, 2013 by ElectricSnowStorm

[BornFromTheVoid]

It's true that we don't know the exact reasons for the change. Natural variability, and I suppose luck, will play a large role on where the jet stream goes.

If I go into detail on certain other reasons for the jet stream behaviour (e.g. climate change causing reductions to Arctic summer snow cover and sea ice- reducing the temperature gradient, blah blah blah!) I'll likely get shouted at by the mods and have my post deleted, as it will attract those who don't believe the climate and/or the Arctic is changing or has an influence on the jet stream, and all kind of silly arguments will break out

Let's just say, it's complicated!

[ZONE 51]

It is complicated and makes good discussion.  When it come to anticyclones then the jet stream and other things need to be talked about too. We need the Jet stream to bring our rains(moslty)especially winter rain I would think, but it is out of pattern bringing the wrong seasonal weather.

Edited June 26, 2013 by ElectricSnowStorm

[Terminal Moraine]

Those that remember the 80s for example would remember long hot summers clear sky for weeks with deep blue sky so deep almost dark blue, this was anticyclonic high pressures, sat over the whole of or large areas of the BI.

I think you're either getting your decades mixed up or looking at the past through rose tinted spec's.Only 1989 and 1983 produced the sort of spells you're talking of with any frequency; all the other summers in the 80s were the sort I like.Long anticyclonic spells in summer were far more prevalent between about 1993 and 2006 but this was an anomalous period and almost any other decade in the last 200 years would fail to live up to it.

[TonyH]

1984 was sunny and dry?

[hillbilly]

1984 was at least as good as 83 if not better in these parts with drought conditions and weeks of lovely sunny weather but as for anticyclonic conditions in summer periods we deffinately get less .When was the last time we saw a big high pressure over the uk in summer with good weather to go with it?

[ZONE 51]

I think you're either getting your decades mixed up or looking at the past through rose tinted spec's.

Only 1989 and 1983 produced the sort of spells you're talking of with any frequency; all the other summers in the 80s were the sort I like.

Long anticyclonic spells in summer were far more prevalent between about 1993 and 2006 but this was an anomalous period and almost any other decade in the last 200 years would fail to live up to it.

 

I said this - Those that remember the 80s for example would remember long hot summers clear sky for weeks with deep blue sky so deep almost dark blue, this was anticyclonic high pressures, sat over the whole of or large areas of the BI.

 

I did say example on the 80s, but as you say more anticyclonic spells were 1993 - 2006 with the last date here was very long went on from May until July was remarkable and drought then ended with a severe cold front storm.  1990? sure that was a scorcher with long hot clear spells.

[ZONE 51]

1984 was at least as good as 83 if not better in these parts with drought conditions and weeks of lovely sunny weather but as for anticyclonic conditions in summer periods we deffinately get less .When was the last time we saw a big high pressure over the uk in summer with good weather to go with it?

Exactly, as you say big high pressure, if one of these covered a large area of hundreds of km wide each way and centered right over the UK then everyone would get the nice weather at once. Heat highs (Azores high..) don't get much far north these days, the south UK usually sits on the edge and becomes windy. When do we see a 1040mb summer high centered over us these days?

Edited June 26, 2013 by ElectricSnowStorm

[ZONE 51]

Example image of strong summer high pressure (not for early next week as says on image! for those hoping it is for next week!)

 

Found summer high for June 2005 below:

Edited June 26, 2013 by ElectricSnowStorm

[hillbilly]

Example image of strong summer high pressure (not for early next week as says on image! for those hoping it is for next week!)

I am hoping it will turn up in 2 weeks time and last right through till September 5th