6
$\begingroup$

I've read that cold air moves faster than hot air, for example in an occluded front. But in case of anti-cyclone encountering a cyclone it appears that the cold air of the anti-cyclone moves very slowly.

So why these differences and what causes this?

Improve this question
$\endgroup$
2
  • 1
    $\begingroup$ I live in an area where we get a lot of occluded fronts and I am really curious as to the answers you might get. Perhaps it has to do with the air density of the colder air retaining its momentum better? $\endgroup$ – user824 Jan 3 '18 at 18:26
  • $\begingroup$ Dave Schultz did a good summary of governing processes. Diabatic processes such as secondary circulation and rain-induced cooling in front of the front are especially interesting. $\endgroup$ – milancurcic Jan 26 '18 at 22:22
2
$\begingroup$

I do not think that there is a general relation between the temperature of an airflow and its velocity in meteorology.

There are several physical processes that need to be considered when thinking about the surface winds in occluding cyclones or fronts. A possible mechanism that I could think of explaining the stronger winds in the cold air compared to the warm air is the difference in vertical stability. The colder air is often characterized by steeper lapse rates (a stronger decrease in temperature with height). This leads to more exchange of momentum between the near-surface air layer and the so-called free troposphere air aloft. This exchange accelerates the surface winds compared to a situation where there is less exchange (as is the case for the warm air in an occluding front).

In a (wintertime) anti-cyclone, the cold air establishes itself mainly close to the surface due to radiative cooling. This leads to a very stable vertical profile, meaning that there is not much exchange of momentum between the near-surface layer and the air aloft. In such a situation, one can say that the surface layer is decoupled from the free troposphere. When a front moves in, it will simply move over the cold layer at the surface without disturbing it too much initially. The cold air indeed moves only slowly in this case.

Hope this explains at least a part of your question.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Interesting thoughts :-) The sentence "the colder air is often characterized by steeper lapse rates" seems challenging... pretty sure the strongest lapse rates and vertical motion are typically ahead of a cold front. But you're still on to something in thinking about stability... because the greatest cold air amount and thus greatest stability is after more advection has occurred, and thus nearer the anticyclone. If I get together an answer, it'll probably be more about the shapes of such systems, and thus pressure gradient -> wind -> advection rate, but they're both important ideas :-) +1 $\endgroup$ – JeopardyTempest Sep 22 '18 at 16:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.