Summer 2024 - General Discussion

Was the summer of 1988 a bad one?

Without a doubt it is real. The first part of it is related to the variation of the stratospheric polar vortex where we see a deceleration in the strength of the zonal westerlies in the stratosphere through the spring as the Arctic gradually warms up decreasing the temperature contrast that leads to a powering up of the jet stream every autumn/winter.

The second part is related to the increased heat reservoir over the continent with atmospheric pressure falling leading to airflows from sea to land. In turn this leads to enhanced westerly winds after a period of increased frequency of easterly winds through mid-spring to early summer. This explains why May is the sunniest month on average in Ireland with all places seeing a decrease as the summer progresses even though June and July have a higher potential (for example 53N has a maximum potential of 486 hrs through May whilst July has a maximum potential of 499 hrs). Ireland of course does not get even close to these potential totals with the country only receiving between 25 and 35% of the potential on average. All of this is in spite of zonal westerlies aloft still being easterly and do not reverse back to westerly until the final days of August.

There is a misconception that some people think this European monsoon phenomenon is nonsense because July is one of the driest months of the year, especially in southeast England but monsoon doesn't mean increase in rainfall necessarily, it refers to a significant change in the prevailing wind.

There is evidence that Hadley Cell expansion related to climate change is also enhancing this "European monsoon" phenomenon with increased high pressure into Iberia which in turn results in less easterly winds. When you deduct the 500mb geopotential height anomalies for July/August of 1991-20 versus 1961-90, the change to enhanced westerlies is clear as day in these months.

Even 2024 has seen this phenomenon in action. The second half of April 2024 was northerly after an unusually westerly first half that led to a lot of rainfall. May 2024 was easterly but often with low pressure close to the south drawing in humid easterly winds and sometimes volatile so quite cloudy. There was quite a bit of northerly winds through the first half of June but then they veered more northwesterly through into July rather than direct northerly. The "monsoon" is well clear between the summer and mid to late spring.

Warm and sunny this afternoon with a lovely breeze. Swim time.