WRF DFI setting for Twice DFI (TDFI)

[JiaWang]

In the WRF guide, it states "dfi_cutoff_seconds = 3600 (should not be longer than the filter window)"
In the TDFI, WRF integrates backward from 0 to -2T, and then integrates forward from -T to T. Then what is the filter window, T or 2T?
In the Peckham et. al. (2016) paper, they set T=20min, and the cutoff frequency to be 1h. Do these numbers make sense given "should not be longer than the filter window"?

 

[JiaWang]

PS: in the above derivation, r~0.1.

If the "dfi_cutoff_seconds = 3600" which means tau=1h, then it will correspond to a minimum time span of 0.5788h (35min) in the case of TDFI.

Correction: Peckham et. al. (2016) set T=10min, which is equivalent to a time span of 20min.

I am not sure the effect of using a short time span (20min) that is smaller than the required minimum time span (35min).

 

[JiaWang]

My understanding is that, by using a time span less than the required minimum time span (T_minimum), it leads to less effective damping of high frequency waves