Add 6-hourly ERA-Interim winds (for now)

ERAIN_SFC00_6H/meta.yaml

+repo_name: ERAIN_SFC00_6H
+
+people:  Willi Rath (<wrath@geomar.de>)
+
+http_path_remote: https://git.geomar.de/data/ERAIN_SFC00_6H
+
+git_path_remote: git@git.geomar.de:data/ERAIN_SFC00_6H
+
+repo_description: |
+    ERA-Interim surface 00_6H
+    <https://cera-www.dkrz.de/WDCC/ui/cerasearch/entry?acronym=ERAIN_SFC00_6H>
+
+    **_Note_** _that we did not yet download all the fields from this
+    experiment.  If you need more than the fields given here, file an issue or
+    let us know in any different way._
+
+citations:
+    - text: "ECMWF (2008). ERA-Interim surface 00_6H. World Data Center for
+        Climate (WDCC) at DKRZ.
+        http://cera-www.dkrz.de/WDCC/ui/Compact.jsp?acronym=ERAIN_SFC00_6H"
+      doi: "---"
+
+known_issues: |
+    ### Land-Sea Mask
+
+    To derive an ocean mask, you can use the land-sea fraction given in
+    `ERAIN_SFC00_6H_LSM_172`.
+
+prefixes: data doc
+
+credential_files:
+    - "${HOME}/.data_repo_creds/ERAIN_SFC12_MM.cred"
+
+data:
+
+    - prefix: data
+      username_var: CERA_USER
+      password_var: CERA_PWD
+      method: !!python/name:data_repo_renderer.JblobCred
+      max_dl_time: 100
+      cera_data_sets:
+        - ERAIN_SFC00_6H_10U_165
+        - ERAIN_SFC00_6H_10V_166
+        - ERAIN_SFC00_6H_LSM_172
+
+doc:
+
+    - url: "https://cera-www.dkrz.de/WDCC/ui/cerasearch/entry?acronym=ERAIN_SFC12_MM"
+      file_name: cera_ERAIN_SFC12_MM.html
+      prefix: doc
+      method: !!python/name:data_repo_renderer.CurlSingleFile
+
+post_processing:
+
+    - util/convert_to_netcdf.sh

ERAIN_SFC00_6H/util/convert_to_netcdf.sh

+#!/bin/bash
+
+function convert_grb_to_netcdf {
+    grb_file=$1
+    nc_file="$(echo ${grb_file} | rev | cut -d. -f2- | rev)".nc
+    tmp_nc_file=${nc_file}_tmp
+    cdo -r -t ecmwf -f nc -copy ${grb_file} ${tmp_nc_file}
+    nccopy -7 -d1 -s ${tmp_nc_file} ${nc_file}
+    rm -f ${tmp_nc_file}
+}
+export -f convert_grb_to_netcdf
+
+rm -f data/grb/* data/nc/*
+find data -iname \*.grb -print0 | \
+    xargs -0 -n1 -P4 -I {} bash -c "convert_grb_to_netcdf {}"
+
+mkdir -p data/grb data/nc
+mv data/*.grb data/grb
+mv data/*.nc data/nc