Ordinarily classic summer sea breeze session at CBK Beach, Hayling Island, south coast of England Photo: Sam Light
A regular column to enhance our understanding of the wonderful world of wind by iKitesurf meteorologist, Shea Gibson. This issue we get super topical and look at the current alarming weather patterns
WORDS: iKitesurf meteorologist Shea Gibson
USA PACIFIC NORTHWEST HEATWAVES AND THE UK’S LACK OF SEA BREEZES - IS THERE A CONNECTION?
The western USA and western Canada have been experiencing some massive heat waves with many records being broken this summer. Although many parts of these areas still hold the records from the 1930’s due to the Dust Bowl and other contributors, these heat waves are becoming more common. The heat waves are caused by blocking features in the atmosphere, which allow for large surges of hot air to rise from the equator into latitudes far north. Many folks up in these areas do not have air conditioning and aren’t equipped to deal with extreme heat in these normally pleasant summer climates. It has caused a lot of problems to many peoples’ health and well-being, and even led to several businesses having to shut down (not to mention proliferated the rapid spread of multiple wildfires).
So now we look at the UK and how this has affected the local weather patterns. Specifically, where have the sea breezes in southern England gone this summer and will they pick back up?
As we have discussed in our other articles, the northern hemisphere is known for its Coriolis Effect, which keeps weather systems steering from west-to-east. So where we see one blocking pattern, we can expect free or rapid flow to the next blocking pattern mainly in the mid to upper level of the atmosphere. We tend to call this ‘teleconnection’ – the down-wind effects of one system to another. To understand this we need to know about transport method and recent conditions over the North Atlantic. The subtropical jet stream is responsible for much of the transfer of moisture aloft up over the North Atlantic in the summer. Looking over the entire Atlantic Basin, we have the well-know Bermuda-Azores High, which is a blocking pattern in-of-itself and tends to dominate with a few fluctuations during the warmer month. This also helps set up high pressures over the UK to deliver the summer southwesterly sea breezes. The subtropical jet usually rides up and over it at around ~ 11 kilometres aloft to deliver moisture across the North Atlantic and at times throws it towards Europe. Now let’s think of this as the prime delivery system in between the blocking pattern between the NW USA and UK and, from what we have seen, the eastern side of the Bermuda-Azores High has broken down quite a few times. But wait, we have one more topic to factor in here. The NAO (North Atlantic Oscillation) also plays into this heavily. In simple terms, this atmospheric feature has been in positive status, which leads to a series of upper lows and domes of high pressure north of the UK and western Europe as a whole. This translates to more N/NE wind events with cooler air and above average precipitation for many areas. Popular kiteboarding spots in the southwestern UK in Cornwall have had more SW/WSW sea breeze days than most other locales, just by position alone, out in the Atlantic. However, as we head east and north we find that has not been the case and we have seen more N/NE events kill off the diurnal sea breezes, which are more typical this time of the year. Downward dives in the jet stream and wrap-around flow from upper low pressure systems and temporary blocking highs to the north have occurred more frequently than normal. Sea Breezes feed off of warm air and dry slotting at the coast, so when we have gloomy/overcast skies and showers or storms, then we can rule the sea breeze out. So will the pattern reset with more high pressure doming over eastern Europe and the UK? Much will depend on if the NAO stays positive and the Bermuda-Azores High can expand and hold across the entire Atlantic Basin. It does look like the first two weeks of July have held positive, and we are just waiting for the Bermuda Azores High to expand east and create the ridging process up across western Europe. This would be the favorable setup to bring those diurnal Sea Breezes back. It is never set in stone for long term outlooks, but we can look for the pattern which provides us more wind. Going from mesoscale (larger area) to microscale (local level) is tough to think about in terms of all these factors, but the main things you need to know about sea breezes in warmer months is that they feed off of stronger synoptic flow, dry air slotting at the coast and can be significantly enhanced by troughing and/or storming well inland. When a normal pattern is disrupted upstream on a large scale, it has affects downstream. Keep that in mind as we all remain students and stewards of our atmosphere. Stay safe and stay in the wind! Shea Gibson
RECAP OF TERMS:
BLOCKING PATTERN: A setup where High or Low pressure sets up for not allowing other systems through. Can last for short or long periods of time. The Bermuda-Azores High is a well-known blocking pattern for example. TELECONNECTION: Climate anomalies being related to each other at large distances, typically thousands of kilometres. UPPER LOW: An area of low pressure that forms at the mid level or higher altitudes of the atmosphere by warm air occluding from the cold air. JET STREAM: Fast moving belts of air driven by both the equator and the polar ice caps. The polar jet brings the colder air and the subtropical jet brings the warmer air. SYNOPTIC FLOW: Flow limited to smaller areas of the world within usually ~1000 kilometres in which local climate can influence the mean or given ‘synoptic’ flow.
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