An important part of global air motion in the mid-latitudes of the Earth normally takes the form of waves wandering around the planet, oscillating between the tropical and the Arctic regions.

The waves travel from west to east and often call on the northern and northwestern parts of India, which we know as western disturbances.

These waves have quite in the news in recent years - down to this year, as recently as last week, when they set off an unprecedented late-spring snowstorm over northwestern Europe.

Earlier in February, a train of western disturbances rolling into Northwest India had ventured unusually south of their usual paths to dip into Central and adjoining Peninsular India to create freaky weather – hailstorm in Central India and untimely string of thundershowers all over the place.

Now, there is study material available that seeks to link the sudden change in weather – snowing wet or bone dry – from scientists of Potsdam Institute for Climate Impact Research.

They have attributed it to fluctuations in the course of the ‘atmospheric rivers’ that flow around the northern latitudes and close to polar region.

The world suffered from severe regional weather extremes in recent years - a heat wave in the US in 2011 preceded by the one in Russia 2010. To complete the riddle, the latter coincided with an unprecedented Pakistan flood.

The Potsdam study suggests that man-made climate change repeatedly disturbs the patterns of atmospheric flow around the globe’s Northern hemisphere through a subtle resonance mechanism.

So when they swing up, these waves suck warm air from the tropics to Europe, Russia, or the US, and when they swing down, they do the same thing with cold air from the Arctic, lead researcher Vladimir Petoukhov said.

During several recent extreme weather events these planetary waves almost freeze in their tracks for weeks.

“So instead of bringing in cool air after having brought warm air in before, the heat just stays. We observed a strong amplification of the usually weak, slowly moving component of these waves,” says Petoukhov.

Time is critical here: two or three days of 30 degrees Celsius are no problem, but 20 or more days lead to extreme heat stress.

Since many ecosystems and cities are not adapted to this, prolonged hot periods can result in a high death toll, forest fires, and dramatic harvest losses.

Climate change caused by greenhouse-gas emissions from fossil-fuel burning does not mean uniform global warming – in the Arctic, the relative increase of temperatures amplified by the loss of snow and ice is higher than on average.

This in turn reduces temperature difference between the Arctic and, for example, Europe: Temperature differences are a main driver of air flow.

Additionally, continents generally warm and cool more readily than the oceans. “These two factors are crucial for the mechanism we detected,” says Petoukhov.

They result in an unnatural pattern of the mid-latitude air flow, so that for extended periods the slow waves get trapped.