Dear Jono & Amitava,


I hope this email finds you well.


We have finally completed our non-linear test-field 
analysis of kinetically and magnetically forced shear 
flows with a setup similar to Jono's 2015 ApJ paper, 
Fig. 9. The paper has been submitted to ApJ, and should 
appear in arXiv on Tuesday.

In summary: we find a shear-current effect (that is, a 
small but a negative eta_{yx}) in kinetically forced 
cases, and, with ease, also an exponentially growing 
dynamo instability. Inspection of a simplified 0D system, 
however, reveals that the dynamo is not driven by the SC 
effect, as the contribution from the incoherent effects 
is much more important. The existence of a coherent 
SC effect might contribute to the dynamo action, but 
the evidence of this is not fully conclusive. In the 
magnetically forced case, we have trouble seeing a 
dynamo with the standard forcing function, and measure 
a positive eta_{yx}, but according to our 0D analysis, 
dynamo instability should be seen nevertheless. Hence, 
we tried out a different kind of forcing function, where 
we removed the lowest wavevectors (up to k=3). With this 
forcing function, we see the dynamo instability, while 
the TF measurements do not change. As eta_{yx} remains 
positive with all shear rates investigated, and becomes 
increasingly more positive with the aspect ratio of 
the box being increased, we conclude that the magnetic 
SC effect cannot occur in simplified MHD (magnetised 
burgulence, as we call it).

With all this trouble with the forcing function, our 
next milestone is to employ the NLTFM with density 
fluctuations accounted for, to full MHD with naturally 
driven SSD. Only then we can give a definite answer to 
the existence of the MSC effect.

If you have any comments or other feedback, we would be 
very interested in hearing about them.

Best regards, Maarit, Axel, ...