<p><a href="http://glossary.ametsoc.org/wiki/Inertial_flow" rel="nofollow noreferrer">Inertial flow</a> is given by the balance between Coriolis and centrifugal forces. A <a href="http://glossary.ametsoc.org/wiki/Geostrophic_flow" rel="nofollow noreferrer">geostrophic flow</a> is given by a balance between Coriolis and the gradients of pressure. The frequency of the inertial flow is the Coriolis frequency (at 43.5N, the Coriolis frequency is <span class="math-container">$10^{−4}$</span> <span class="math-container">$s^{−1}$</span>, which is equivalent to an inertial period of 17.4h). To me this is just the time that a particle takes to perform a full rotation around its center of rotation. Why does this peak shows up in plot like <a href="https://earthscience.stackexchange.com/a/8074/15547">this</a>? Is it because is carrying around a flow field at a certain smaller scale? In a perfect Inertial gyro, since it is at steady state, if you sample in one point you get always the same velocity, right? A perfect geostrophic balance does not have rotation, and I understand that in that case we would have frequency=0. But a little departure from that could give rise to large scale geostrophic gyro (like low pressure systems in the athmosphere). Would not that gyro be associated with a frequency, in the same way the inertial gyro has a frequency?  Why it is common to say the geostrophic flows do not have a frequency? For a geostrophic gyro it still takes a certain time to rotate around a center of rotation.</p>

CC BY-SA 4.0
2019-03-30T02:43:32.343Z
In inertial flows the only frequency is associated with the Coriolis effect. Meanwhile, in geostrophic balance, the Coriolis is balanced by the pressure gradient. What is the frequency of the pressure gradient? That is the issue.
arkaia
CC BY-SA 4.0
2019-03-30T14:54:11.613Z
I fell bad being such a pain about it. No need. It just leads to misconceptions.
arkaia
<geophysics><oceanography><ocean-currents><coriolis>
Why an inertial gyro has a frequency and a geostrophic gyro does not?
Millemila
# Why an inertial gyro has a frequency and a geostrophic gyro does not?

(Asked by: username_0 on 2019-03-30)

[Inertial flow](http://glossary.ametsoc.org/wiki/Inertial_flow) is given by the balance between Coriolis and centrifugal forces. A [geostrophic flow](http://glossary.ametsoc.org/wiki/Geostrophic_flow) is given by a balance between Coriolis and the gradients of pressure. The frequency of the inertial flow is the Coriolis frequency (at 43.5N, the Coriolis frequency is $10^{−4}$ $s^{−1}$, which is equivalent to an inertial period of 17.4h). To me this is just the time that a particle takes to perform a full rotation around its center of rotation. Why does this peak shows up in plot like [this](https://earthscience.stackexchange.com/a/8074/15547)? Is it because is carrying around a flow field at a certain smaller scale? In a perfect Inertial gyro, since it is at steady state, if you sample in one point you get always the same velocity, right? A perfect geostrophic balance does not have rotation, and I understand that in that case we would have frequency=0. But a little departure from that could give rise to large scale geostrophic gyro (like low pressure systems in the athmosphere). Would not that gyro be associated with a frequency, in the same way the inertial gyro has a frequency? Why it is common to say the geostrophic flows do not have a frequency? For a geostrophic gyro it still takes a certain time to rotate around a center of rotation.

**Tags:** geophysics, oceanography, ocean-currents, coriolis

> **Comments:**
> **username_1**: In inertial flows the only frequency is associated with the Coriolis effect. Meanwhile, in geostrophic balance, the Coriolis is balanced by the pressure gradient. What is the frequency of the pressure gradient? That is the issue.  
> **username_1**: I fell bad being such a pain about it. No need. It just leads to misconceptions.  

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## 0 answers

