QBO amplitude

[lee1043]

1. Implement QBO amplitude diagnostics from E3SM Diags

a. The time series of stratospheric zonal wind between 5S and 5N is plotted. QBO amplitude (zonal wind) is compared against ERA-interim. QBO spectra is plotted compared with ERA-interim.
b. Starting point: E3SM Diags QBO driver, QBO plot generation
c. cdutil to xcdat conversion needed
d. Detailed description for the diagnostics: here

Example diagnostics output

2. Define metrics from the diagnostics

From the diagnostics, it is needed to define proper metrics.