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在地转风中，科里奥利效应/力与压力梯度力趋于相互平衡的机制是什么?

我明白是这样的可能的为科里奥利效应和压力梯度力(PGF)相互抵消，但它似乎是一个趋势(而不仅仅是一种可能性)。这背后的机制是什么?

我知道，当风被弯曲时，科里奥利效应的部分/向量与PGF直接相反。但是一旦风被弯曲，使其平行于等压线，为什么科里奥利效应(有倾向)会在那一点上与PGF相似?

这是因为1)只要以小于90°的角度向下移动，风的速度就会加快，2)风速的增加会增加科里奥利效应?所以总是会有一个时刻，科里奥利力的增长等于PGF(在这一点上，风将停止加速，因为它平行于等压线)?

回答

是的，这是因为:1 -只要风与压力梯度的角度小于90°，它就必须加快速度。这是因为它在运动方向上有一个合力，F=ma，所以它有向低压方向的加速度。而科里奥利“力”总是与运动90°，这意味着它不能加速/影响大小，只能改变方向。2 -科里奥利是$f\乘以v$，这意味着科里奥利力确实随着速度的增加而增加。随着过程的继续，方向的改变意味着PGF作为改变速度大小的成分越来越少，越来越多的是正常运动……和科里奥利家族对立。如果当包裹到达与PGF的90°时，它们没有相互抵消，那么包裹仍然会有一个定向加速度……这意味着它不再与PGF成90°。如果PGF更强/它与PGF的夹角小于90°，它的速度会进一步加速，从而进一步增加科里奥利…然后再回到垂直方向。 If Coriolis were somehow stronger/it somehow got beyond 90°, the PGF would then start to have a component that decelerates the velocity. Which would decrease the Coriolis counteracting it, and so pull it back (left in the NH) towards perpendicular. So the situation is entirely restorative/stable. It can only be at balance when they cancel each other out, and the motion is at that 90° angle (unless there are additional forces). When it somehow isn't in that balanced situation, the forces work to accelerate/push it back towards that situation. With a "sudden" low pressure, nearby parcels would not have the time/distance to undergo this process and accelerate/change direction enough before reaching the low. But typically atmospheric pressure changes are gradual changes, so basically the change in motion are so gradual that the motion at any time is essentially geostrophic at any moment. Rapid pressure changes can and do still lead to local ageostrphic motion, where the change is of such speed and magnitude that the Coriolis Force hasn't responded yet and so there is a more meaningful component of motion out of balance (and so the motion is more non-perpendicular to the PGF). And other forces... in particular friction at lower levels of the atmosphere... do alter the balance. Friction continually decelerating motion leads to a result where the path is consistently a bit less than 90°, towards the low pressure, which leads (apart from other factors) to filling of the low pressure over time. Particularly strong persistent low pressure can also result in a flow nearby that must turn so rapidly that there is a significant centrifugal "force" as well... this extra force isn't degenerative like friction is, but leads to a different balance instead, the [gradient wind balance][1], with a somewhat lower velocity compared to geostrophic balance. [1]: https://www.theweatherprediction.com/habyhints3/743/#:~:text=The%20gradient%20wind%20is%20a,centrifugal%20(outward%20fleeing)%20force.

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