Drop a pebble in water, and ripples eventually affect water far away from where it was dropped. Likewise, weather in one region will eventually affect the weather hundreds or thousands of kilometres away—something borne out by what is currently happening in Europe.

Weather and climate do not care for geographical boundaries set by humans is ringing loud and clear from the destructive heat wave scalding the continent for more than 10 days now. Breaking out of the Iberian Peninsula (Spain and Portugal), the heat wave has reportedly killed at least 1,000 people in these two countries alone. The searing wave has since spread to the UK, Croatia, France, Germany, Greece, Ireland, Italy, Morocco, Poland and Switzerland. Climate change/warming is cited as the immediate cause, but there are other proximate causes for the record-breaking heat.

Combine system effect

The first is a combined effect of low-pressure and high-pressure systems sitting on both sides of the Atlantic. Low-pressure areas draw air (winds) from high-pressure areas across national or geographical borders. Meteorologists point to a “low” that has been locked off the coast of Portugal for days now. It has been sourcing hot and dry winds from the sunbaked Sahara desert in Africa to the south. According to meteorologists, the widespread heat wave may not relent anytime soon, with temperatures expected to hover well above the average through this week across much of Europe. But the northern part of the continent is expected to start to cool by the latter part of the week.

Not entirely unheard of

Heat waves are not entirely unheard of in Europe. Meteorologists point to the sustained episodes in 2003, 2006, and 2021, with the last one being the hottest on record. Apart from the usual suspect (climate change, which has a gradual and longer-term influence), the local circulation pattern and the oceans also play their part. For instance, the jet stream is the global belt of strong, fast winds prevailing at heights of 8–15 kilometres above the surface at speeds ranging from 129 to 225 kmph and capable of reaching up to 443 kmph. These winds help push weather systems around the globe. Closer to home, western disturbances that modulate weather over North-West India are an offshoot of the jet stream.

Jet stream frivolities

When the jet stream briefly splits in two, as it reportedly did over Europe two weeks ago, it leaves an area of weak winds and high pressure between the two branches that allows extreme weather to build. In the instant case, the “low” from its vantage point off Portugal invited hot winds from Africa, which converged over South Europe. They refused to move away since there was hardly any wind to carry them, allowing heat to build gradually.

Another reason could be warming in the Arctic, leading to a situation where the temperature differential between it and the Equator decreases. This causes wind speeds to drop, allowing time and space for weather systems to linger (semi-permanent systems) and bring sustained hot or cold weather depending on the season.

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