New monsoon sperber code in xCDAT -- PR cleaned up

[lee1043]

This PR is for monsoon_sperber code that is converted to use xcdat (update by @bosup).
A new branch is made by @lee1043 for clean up the previous PR (#1011).

[lee1043]

@bosup I found the difference in the output. Can you investigate where that is coming from and if they could be more consistent?

Metrics calculated from the previous version of the code (shown from Demo_2b_notebook):

{
  "GISS-E2-H": {
    "r1i1p1": {
      "AIR": {
        "decay_index": 53,
        "duration": 17,
        "onset_index": 37,
        "slope": 0.037490989405760906
      },
      "AUS": {
        "decay_index": 52,
        "duration": 22,
        "onset_index": 31,
        "slope": 0.028602770104420926
      },
      "GoG": {
        "decay_index": 49,
        "duration": 24,
        "onset_index": 26,
        "slope": 0.017398272573029495
      },
      "NAmo": {
        "decay_index": 64,
        "duration": 52,
        "onset_index": 13,
        "slope": 0.012011903431421198
      },
      "SAmo": {
        "decay_index": 56,
        "duration": 30,
        "onset_index": 27,
        "slope": 0.020883715095941786
      },
      "Sahel": {
        "decay_index": 47,
        "duration": 17,
        "onset_index": 31,
        "slope": 0.03490883309967567
      }
    }
  }
}

Metrics calculated from the code in this PR:

{
  "GISS-E2-H": {
    "r1i1p1": {
      "AIR": {
        "decay_index": 54,
        "duration": 20,
        "onset_index": 35,
        "slope": 0.032632458420097696
      },
      "AUS": {
        "decay_index": 54,
        "duration": 23,
        "onset_index": 32,
        "slope": 0.0272846353443767
      },
      "GoG": {
        "decay_index": 48,
        "duration": 23,
        "onset_index": 26,
        "slope": 0.01760572910784664
      },
      "NAmo": {
        "decay_index": 63,
        "duration": 51,
        "onset_index": 13,
        "slope": 0.011989028721760442
      },
      "SAmo": {
        "decay_index": 56,
        "duration": 31,
        "onset_index": 26,
        "slope": 0.020573642677988356
      },
      "Sahel": {
        "decay_index": 48,
        "duration": 18,
        "onset_index": 31,
        "slope": 0.03399930925007501
      }
    }
  }
}

[lee1043]

@bosup informed that this PR is ready for review (thanks!). @lee1043 will start reviewing it.

[lee1043]

@bosup has been working on this PR. Below is for the verification result.
monsoon_Sperber_code_conversion_comparison.pdf

[lee1043]

@acordonez I think this PR is pretty much ready. When you get a chance could you please run demo 2b with this PR to see if it runs well?

[acordonez]

@lee1043 The notebook ran with no errors. I am seeing some slight differences in the metrics but is that also expected similar to the MJO? For example, decay index of 48 vs. 47, or slope of 0.03490883309967567 vs. 0.03399930924787022.

[lee1043]

@acordonez thanks for reviewing and approving. Yes, although it would be nicer if we've got more consistency for the indices, it looks like further in depth investigation might be needed to fully address that, and I consider for now it is acceptable. I am going to merge this PR and tag v3.5.

[lee1043]

All checks passed, merging it now.