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Re: [ferret_users] Converting Overturning circulation from depth axis to density axis



In general the ZAXREPLACE family of functions converts from depth to density coordinates.

But be careful about the meaning of a calculation in this case!

==>> A meridional streamfunction integrated zonally on depth levels, then converted to a density axis, is NOT the same as a streamfunction on density levels!

The latter would be integrated on density levels from the start, and some argue that this is the correct way to do this calculation. See a nice little paper by Hazeleger et al (2001 GRL, 28(9), 1763-1766), which explores these differences explicitly and compares the resulting streamfunctions and their interpretation. 

The calculation in density space from the start is not straightforward because isopycnals outcrop (e.g. in the Atlantic and Pacific the SST increases to the west). It's not obvious how to treat those isopycnal layers that exist in only part of the zonal span of the ocean, and this is also computationally tricky. For another, there is a lot of seasonal variability of SST, so some upper layers may outcrop only during parts of the year, and the mean fields may not represent the true surface influences felt by a particular outcropping layer.

But in any case a z-level streamfunction regridded to density is not a streamfunction in density levels.

Billy K

On May 25, 2014, at 12:02 AM, Star Physicist <couragetoknowgc@xxxxxxxxxxx> wrote:

> Dear Ferret Users,
> How can I convert my Meridional overturning stream-function from Z (depth Axis) to density space. Actually I want to get similar plot as shown in Figure 2 of attached article. For the calculation of stream-function in depth axis I am using following line:
> Let StreamFunction = ty_trans[x=@sum,z@rsum]                             !!!!!!ty_trans is T-cell y-volume transport
> 
> Regards,
> Dogar
> <AMOC_DensitySpace_Rong2010.pdf>




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