I have seen reference to a number of different temporal dimensions across ECMWF outputs and am having a hard time interpreting each one. This applies to ERA5 (reanalysis) and SEAS5 (seasonal forecasts) products.
Fundamentally, I want to know:
What is the time period that a reanalysis or forecast applies to? (SEAS5 and ERA5)
<xarray.Dataset> Size: 57GB
Dimensions: (number: 25, verifying_time: 18, forecastMonth: 7,
time: 12, step: 24, latitude: 23, longitude: 38,
valid_time: 18)
Coordinates:
* number (number) int64 200B 0 1 2 3 4 5 6 7 ... 18 19 20 21 22 23 24
* verifying_time (verifying_time) datetime64[ns] 144B 1990-01-01 ... 1991-...
* forecastMonth (forecastMonth) int64 56B 1 2 3 4 5 6 7
* time (time) datetime64[ns] 96B 1990-01-01 ... 1990-12-01
* step (step) timedelta64[ns] 192B 28 days 30 days ... 215 days
valid_time (time, step) datetime64[ns] 2kB ...
surface float64 8B ...
* latitude (latitude) float64 184B 37.8 37.4 37.0 ... 29.8 29.4 29.0
* longitude (longitude) float64 304B 60.0 60.4 60.8 ... 74.0 74.4 74.8
Data variables:
tprate (number, verifying_time, forecastMonth, time, step, valid_time, latitude, longitude) float32 57GB ...
Attributes:
GRIB_edition: 1
GRIB_centre: ecmf
GRIB_centreDescription: European Centre for Medium-Range Weather Forecasts
GRIB_subCentre: 0
Conventions: CF-1.7
institution: European Centre for Medium-Range Weather Forecasts
history: 2024-08-08T16:14 GRIB to CDM+CF via cfgrib-0.9.1...
time: Initial time of forecast. (1st of each month in the year)
forecastMonth: Months since forecast_reference_time (time). (1-7)
step: Time in nanoseconds since forecast_reference_time (time) - Why are there 24 step values?
verifying_time: 18 values, corresponding to the 1st of each month. All 1990 months, plus first 6 months of 1991. - What does this correspond to?valid_time: A function of time and step. Also 18 values. - What does this correspond to?
Following what we've implemented in other analyses, I would assume that all we need to care about are time and forecastMonth.
ERA5
TODO
When is a forecast issued? When does a forecast apply to?
I have seen reference to a number of different temporal dimensions across ECMWF outputs and am having a hard time interpreting each one. This applies to ERA5 (reanalysis) and SEAS5 (seasonal forecasts) products.
Fundamentally, I want to know:
Relevant links:
SEAS5
If we look at a
.grib
outputs for SEAS5, for example:Returns:
time
: Initial time of forecast. (1st of each month in the year)forecastMonth
: Months since forecast_reference_time (time
). (1-7)step
: Time in nanoseconds since forecast_reference_time (time
) - Why are there 24 step values?verifying_time
: 18 values, corresponding to the 1st of each month. All 1990 months, plus first 6 months of 1991. - What does this correspond to?valid_time
: A function oftime
andstep
. Also 18 values. - What does this correspond to?Following what we've implemented in other analyses, I would assume that all we need to care about are
time
andforecastMonth
.ERA5
TODO
When is a forecast issued? When does a forecast apply to?