Add AO_index (#56)

input_data/SAM_index/meta.yaml

+repo_name: SAM_index
+
+people:  Willi Rath (<wrath@geomar.de>)
+
+http_path_remote: https://git.geomar.de/data/SAM_index
+
+git_path_remote: git@git.geomar.de:data/SAM_index
+
+repo_description: |
+    Marshall Southern Annular Mode (SAM) Index (Station-based)
+
+    <https://climatedataguide.ucar.edu/climate-data/marshall-southern-annular-mode-sam-index-station-based>
+
+prefixes: data doc
+
+data:
+
+    - url: "http://www.nerc-bas.ac.uk/public/icd/gjma/newsam.1957.2007.txt"
+      prefix: data
+      file_name: sam.1957.current.txt
+      method: !!python/name:data_repo_renderer.CurlSingleFile
+
+doc:
+
+    - url: "https://climatedataguide.ucar.edu/climate-data/marshall-southern-annular-mode-sam-index-station-based"
+      file_name: climatedataguide.ucar.edu_climate-data_marshall-southern-annular-mode-sam-index-station-based.html
+      prefix: doc
+      method: !!python/name:data_repo_renderer.CurlSingleFile
+
+    - url: "http://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%282003%29016%3C4134%3ATITSAM%3E2.0.CO%3B2"
+      file_name: Marshall_2003.pdf
+      prefix: doc
+      method: !!python/name:data_repo_renderer.CurlSingleFile