The region around
the Karakoram mountain range is a very puzzling one. Not only does it have some
of the highest and most glacierized mountains in the world, the glaciers there
are also not shrinking, like they do in the rest of world. In close-by mountain
ranges, such as the Kunlun Shan, glaciers are actually growing on average. This
has caused quite some headaches for climate and cryosphere scientists.
solution was found in the atmosphere: when the Karakoram was colder, the air
around it spun more in one direct. When it was warmer, the air around the
Karakoram spun more in the other direction. This behaviour was dubbed the
‘Western Tibetan Vortex’, and it showed that there was a region of cooling in
the Karakoram, which may have caused the glaciers to grow.
But is it really
the vortex that is causing the temperatures to change, or are temperature
changes the cause of the vortex? We now argue that it is the latter. First of
all, we found that such vortex-like is exactly what you expect from atmospheric
theory: if you change the temperature in a region, the wind field will change
around it. There never really is a vortex in the atmosphere though.
We confirmed that
this theoretical behaviour is also happening in the real atmosphere. Another
thing we checked is the role of warming compression of the air from (adiabatic
heating). This was suggested to be the main driver of temperatures for the
Karakoram glaciers, but we found it to have very little influence. Although
adiabatic heating is important higher in the atmosphere, we found the surface
temperature mainly to be determined by the amount of sunlight that reaches the
An interesting implication of our findings is that temperature changes cause vortex-like behaviour almost everywhere. So, the methods that have been used before to study the Western Tibetan Vortex can also be used in other regions.
de Kok, R.J. & Immerzeel, W.W.: “The Western Tibetan Vortex as an emergent feature of near‐surface temperature variations”, Geophysical Research Letters.
Download full (open access) paper here
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