A few notes on R2D2's use in this repository

[guillaumevernieres]

I'm back to working on marine DA in GDASApp and I thought I would start a discussion as well as dump some of my r2d2 related thoughts here, since mental notes never work!

1. I export the R2D2_CONFIG variables after creating an r2d2_config.yaml that it points to. I don't see this being done on the atm side. Am I missing something? I'm of the opinion that the default config file should be ALWAYS over-written.

2. We need to separate the DA window with how things are stored in R2D2, for example, on the marine side we currently store observations in 10 minute and 1 day windows. We fetch the obs for the cycle from the 2 types of storage. As an example, for a 6 hour window, the 10 mn obs are concatenated, the 1 day obs are trimmed.