adding GSGI

[btupper]

GSGI data through 2019 are available here.

https://www2.whoi.edu/staff/ykwon/data/

Obtain the data like this...

$ wget https://www2.whoi.edu/staff/ykwon/wp-content/uploads/sites/27/2023/02/NOAA_OISST_GS_dSST_index_monthly_1993_2019_release.mat.zip

Here's what we get when we unpack the .mat matlab formatted file.

List of 7
 $ LON1          : num [1, 1] 285
 $ LON2          : num [1, 1] 309
 $ SST.N.deseason: num [1:324, 1] -0.731 0.377 0.554 0.893 0.205 ...
 $ SST.S.deseason: num [1:324, 1] -0.291 -0.35 -0.358 -0.29 -0.331 ...
 $ YR            : num [1, 1:27] 1993 1994 1995 1996 1997 ...
 $ dSST.deseason : num [1:324, 1] -0.44 0.726 0.911 1.184 0.536 ...
 $ readme        : chr [1, 1] "dSST=SST_N minus SST_S"
 - attr(*, "header")=List of 3
  ..$ description: chr "MATLAB 5.0 MAT-file, Platform: MACI64, Created on: Wed May 19 14:40:12 2021                                         "
  ..$ version    : chr "5"
  ..$ endian     : chr "little"

Presumably the dSST.deseason is the gradient index

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And the paper https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL100914

But is this the same as the "GSI"?

[btupper]

No - GSI seems to be a location index, but GSGI is a SST gradient index