Valentin

Why is it hot in Europe this week? Well, it has to do with the “omega block” in the jet stream. Omega blocks get their name because they resemble the Greek uppercase letter omega, Ω. You can see that in the synoptic setup. The map below on the left shows the 500 mb geopotential height anomaly at 18z. The contour lines resemble the Ω shape due to an enormous high-pressure ridge in the mid-troposphere that is sandwiched between two low-pressure systems to its east and west. Hot Saharan air has been advected—that is, horizontally transported—northward into western Europe due to anticyclonic (clockwise) airflow, and as that air mass moves north, it is compressed adiabatically beneath the ridge where air is sinking. This process is natural and has nothing whatsoever to do with climate change or greenhouse gas emissions. In fact, there are quite a few studies suggesting that reduced latitudinal baroclinicity (north-to-south temperature gradient) caused by Arctic amplification could reduce the frequency of mid- and high-latitude blocking events (e.g., Hassanzadeh et al., 2014; Woollings et al., 2018). 🔗 agupubs.onlinelibrary.wiley.com/doi/10.1002/20… 🔗 link.springer.com/article/10.100… There is, however, debate about this. Europe has seen an unusual amount of these extreme heat events since 2019, but most other areas of the globe have not. The notable exception was the June–July 2021 Pacific Northwest heatwave in North America, but even that wasn’t as rare as previously thought. 🔗 sciencedirect.com/science/articl… The most likely explanation for this boils down to a combination of two things: 1️⃣ Undiagnosed changes in atmospheric circulation patterns. 2️⃣ Increased absorbed solar radiation at the surface due to reduced stratiform low- and mid-level cloud cover (increased sunniness), some of which is likely due to reduced atmospheric aerosol concentrations from the EU’s strict pollution regulations. The overall increase in the “global mean temperature” (which mostly affects overnight lows) has very little to do with this event. Even in a “pre-industrialized” climate, a record-breaking heatwave would still be happening. Heck, the “global mean temperature” fell today despite the heat cranking up in Europe. This is mostly weather systems moving around. When you have a chaotic system with two turbulent fluids interacting with each other (the atmosphere and ocean), wild things can happen. Get your weather information from real meteorologists, not sensationalistic clickbait news outlets like BBC News or the Daily Mail.