Calculate Nino4 index
Added by John Taylor about 3 years ago
I am interested in calculating the Nino4 index over the full span of the ERA5 data. However, the ERA5 data set wraps at the international dateline making it difficult to extract the Nino4 grid cells using selindexbox or selatlonbox.
As I need to calculate the index over a large number of data files I was wondering if there is a nice solution to this problem using CDO?
Thank you for your assistance!
John
Replies (5)
RE: Calculate Nino4 index - Added by Ralf Mueller about 3 years ago
hi John!
sorry, I don't get the point with ERA5 problems. Could your upload a singe timestep maybe? sellonlatbox work also with triangular grid, so I think it should work, but without the input it's hard to tellRE: Calculate Nino4 index - Added by John Taylor about 3 years ago
I have uploaded a file as requested.
The region I am interested in as follows:
Niño 4 (5N-5S, 160E-150W): The Niño 4 index captures SST anomalies in the central equatorial Pacific.
Here is a plot of the region:- http://www.bom.gov.au/climate/enso/indices/about.shtml
using sellonlatbox causes the model to go the long way round, ie 1241 longitude values instead of 200, so you get all longitudes except the 160E-150W region.
cdo sellonlatbox,-150,160,-5,5 sst_era5_moda_sfc_19790101-19790131.nc outfile.nc
RE: Calculate Nino4 index - Added by Ralf Mueller about 3 years ago
cdo -sellonlatbox,160,-150,-5,5 ...worked for me. the order of longitudes given to the operator determines the size of the box, i.e. the small nino4 box or its complement.
hth
ralf
RE: Calculate Nino4 index - Added by John Taylor about 3 years ago
Thank you for your help much appreciated!
That makes sense as the default increment is positive, although the longitudes are now on a different 0-360 scale.
longitude = 160, 160.25, 160.5, 160.75, 161, 161.25, 161.5, 161.75, 162,
162.25, 162.5, 162.75, 163, 163.25, 163.5, 163.75, 164, 164.25, 164.5,
164.75, 165, 165.25, 165.5, 165.75, 166, 166.25, 166.5, 166.75, 167,
167.25, 167.5, 167.75, 168, 168.25, 168.5, 168.75, 169, 169.25, 169.5,
169.75, 170, 170.25, 170.5, 170.75, 171, 171.25, 171.5, 171.75, 172,
172.25, 172.5, 172.75, 173, 173.25, 173.5, 173.75, 174, 174.25, 174.5,
174.75, 175, 175.25, 175.5, 175.75, 176, 176.25, 176.5, 176.75, 177,
177.25, 177.5, 177.75, 178, 178.25, 178.5, 178.75, 179, 179.25, 179.5,
179.75, 180, 180.25, 180.5, 180.75, 181, 181.25, 181.5, 181.75, 182,
182.25, 182.5, 182.75, 183, 183.25, 183.5, 183.75, 184, 184.25, 184.5,
184.75, 185, 185.25, 185.5, 185.75, 186, 186.25, 186.5, 186.75, 187,
187.25, 187.5, 187.75, 188, 188.25, 188.5, 188.75, 189, 189.25, 189.5,
189.75, 190, 190.25, 190.5, 190.75, 191, 191.25, 191.5, 191.75, 192,
192.25, 192.5, 192.75, 193, 193.25, 193.5, 193.75, 194, 194.25, 194.5,
194.75, 195, 195.25, 195.5, 195.75, 196, 196.25, 196.5, 196.75, 197,
197.25, 197.5, 197.75, 198, 198.25, 198.5, 198.75, 199, 199.25, 199.5,
199.75, 200, 200.25, 200.5, 200.75, 201, 201.25, 201.5, 201.75, 202,
202.25, 202.5, 202.75, 203, 203.25, 203.5, 203.75, 204, 204.25, 204.5,
204.75, 205, 205.25, 205.5, 205.75, 206, 206.25, 206.5, 206.75, 207,
207.25, 207.5, 207.75, 208, 208.25, 208.5, 208.75, 209, 209.25, 209.5,
209.75, 210 ;
RE: Calculate Nino4 index - Added by Ralf Mueller about 3 years ago
which makes the whole thing more clear, right. no more jumping around from -179 to +180