GO-ESSP Paris, Day 1 Jonathan Gregory Walker Institute, University of Reading

1. GO-ESSP Paris, Day 1 Jonathan Gregory Walker Institute, University of Reading and Met Office Hadley Centre

2. Proposed procedure for changes to conventions • New proposal made on trac, using the template, including exactly what has to be written in the standard document and the conformance document. • Moderator volunteers. • Discussion begins. trac or email list? How to encourage engagement? • Moderator periodically summarises discussion on trac, keeps it moving forward, tries to achieve a consensus. It should be expected that everyone with an interest will contribute to the discussion and consensus during this stage. • After four weeks from the proposal, or two weeks of no contributions, whichever is longer, moderator winds up the discussion: No outstanding objection Accept proposal Near consensus Accept if 2/3 of conventions committee votes in favour Not near consensus No change

3. Proposed procedure for changes to conventions • If a change is accepted, the standard document should be updated, the CF convention version number incremented, and the conformance document updated. • At this point, the change is shown in the document as provisional, but it will not be revoked unless subsequent testing shows it to be flawed. Provisional status lasts until the CF checker has successfully interpreted some data following the new convention. • Once this has been done, the document should again be updated to remove the provisional status, and the version number incremented again. • All versions of the standard and conformance document should be available online, together with a history of changes and the trac tickets they relate to. • Several changes previous agreed on email list should be reproposed this way.

4. Forecast time coordinates A forecast run with multiple forecast periods (12 h, 24 h, 36 h, etc.) from a single analysis: Single-valued analysis time (forecast_reference_time) and separate validity time (time) axis. If the “since” time in the validity time units is the analysis time, the values of the validity time = the forecast period. double atime atime:standard_name = "forecast_reference_time" ; atime:units = "hours since 1999-01-01 00:00" ; double time(time); time:standard_name = "time" ; time:units = "hours since 1999-01-01 00:00" ; float data_variable(time,lat,lon); data_variable:coordinates = "atime" ; A set of forecasts for the same validity time from different analyses: Single-valued validity time and separate analysis time axis. Multiple analysis times with multiple validity times or forecast periods, whether or not all combinations exist: Index dimension with one-dimensional auxiliary coordinate variables for analysis time, forecast time and/or forecast period. Not proposing two multivalued axes.

5. 2003 Jan 1 12:00 analysis (at 00hr) and 12hr,36hr forecasts 2003 Jan 1 00:00 6hr,12hr,18hr,24hr forecasts 2003 Jan 1 06:00 analysis and 18hr forecast variables: double reftime(record); time1:standard_name = "forecast_reference_time" ; time1:units = "hours since 2003-01-01 00:00" ; double valtime(record); time2:standard_name = "time" ; time2:units = "hours since 2003-01-01 00:00" ; double forecast_period(record); // = valtimereftime forecast_period:standard_name = “forecast_period" ; forecast_period:units = "hours" ; float temp(record,level,lat,lon); temp:standard_name = "air_temperature" ; temp:units = "K" ; temp:coordinates = "valtime reftime forecast_period" data: reftime = 12., 12., 12., 0., 0., 0., 0., 6., 6. ; valtime = 12., 24., 48., 6., 12., 18., 24., 6., 24. ; forecast_period = 0, 12, 36, 6, 12, 18, 24, 0, 18;

6. A2 A1 Q exists Means and subgrid variation Ambiguity about the area-mean for intensive quantities which do not “exist” everywhere e.g. atmosphere_cloud_liquid_water_content, sea_ice_area_fraction, sea_ice_ thickness, ocean_mixed_layer_thickness and how this relates to where e.g. surface_net_ downward_radiative_flux_where_land and coordinate variable of surface_type. Area-mean = Q  A1  A2 • The (default) point interpretation of cell_methods is well-defined. • Indicate A1 in standard names by where for common cases, otherwise by a (string-valued) coordinate variable of surface_type (sea_ice, forest, etc.). • Indicate A2 in cell_methods. • Recommend that cell_methods be included if standard_name is present. • Introduce cell_methods syntax “area:method”, in particular “area: mean” as an alternative to e.g. “lat: lon: mean”. • Unqualified “area: mean” implies A2 is the entire gridbox. • New "overtype" qualifiers to indicate A2 in cell_methods e.g. “area: mean where_sea_ice”. • A2 is irrelevant if extensive e.g. sea_ice_volume, precipitation_amount.

7. Anomaly modifier Define a new standard_name modifier of anomaly_from_climatology, to indicate that the data values indicate the departure from the climatological values (representative over some years) of the same statistic and quantity e.g. standard_name="air_temperature anomaly_from_climatology". No method currently proposed to indicate the climatology.