Question on gen_be_v3 Output Files and Their Physical Meaning

[taytaytay]

Hi all,

I’m currently running gen_be_v3 in WRFDA to generate background error statistics, and I would like to better understand the outputs.

After running, I obtained the following types of files for multiple variables (e.g., PSFC, T, RH, U, V, W, QCLOUD, etc.):

• be_*.dat
• EV_*.dat
• Bv_*.txt
• sl_*.txt

For example:

• be_T.dat, EV_T.dat, Bv_T.txt, sl_T.txt
• and similarly for other variables like PSFC, RH, QCLOUD, etc.

I have a few questions:

1. What does each of these file types represent physically and mathematically?
   
   • be_*.dat → background error variance/covariance?
   • EV_*.dat → EOFs / eigenvectors?
   • Bv_*.txt → vertical covariance?
   • sl_*.txt → spatial length scales?
2. What exactly is stored inside each file (e.g., variance profiles, covariance matrices, EOF modes)?
3. What are the units of these quantities for different variables (e.g., T, RH, hydrometeors)?
4. How are these files used later by WRFDA in the 3D-Var system?

If anyone has a clear explanation or reference (documentation/paper), I would really appreciate it.

Thanks in advance!