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The tropopause minimum acts as a barrier^ between the troposphere and stratosphere because mixing and heat transport by convection can only occur when temperature decreases with height. The troposphere - with convection allowed - is turbulent and well mixed. The stratosphere with its temperature increase with height is stable, stratified into layers and relatively poorly mixed^^.
At high latitudes the tropopause and lower stratosphere temperature can plunge to ~ -85°C to provide the conditions for PSCs, polar stratospheric clouds of which the incredibly bright and colourful nacreous clouds are a subset.
The tropopause height does not gradually drop from low to high latitudes. Rather, it drops rapidly in the area of the subtropical and polar front jets (STJ and PFJ respectively in the Figure on the left), as shown in the Palmen-Newton model of the general circulation (Fig 12.16 or Fig on left). Especially when the jet is strong and the associated front at low levels intense, then the tropopause height drops suddenly across the jet stream. Sometimes the tropopause actually folds down to 500 hPa (5.5 km) and even lower, just behind a well-defined cold front.
Siberia enjoys a well-deserved reputation as one of the coldest places on Earth. But the last time the planet got really cold, Siberia apparently didn't go along for the ride, providing animals a warm oasis from the Ice Age
originally posted by: kosmicjack
a reply to: onequestion
I'm hoping that some of our science savvy members can put this in context for us. I was bummed that the twitter post didn't link to a more comprehensive explanation.
At the same time, it is also known that greenhouse gases are increasing in concentration with each passing year. Based on the variations in solar heating and on the amount of CO
2 in the atmosphere, some calculations of future temperatures have been made. According to these estimates, the interglacial period the Earth is in now may persist for another 50,000 years if CO
2 levels increase to 750 parts per million (ppm) (the present atmospheric concentration of CO
2 is about 398 ppm by volume, but is rising rapidly as humans continue to burn fossil fuels.) If CO
2 drops instead to 210 ppm, then the next glacial period may only be 15,000 years away.
My current opinion is that we are about to hit an ice age.