I think my question is similar so I’m posting it here instead of creating a new thread.
I’m coming from the position of having done some analyses using ERA5 data and now trying to use daily forecast data for some interpretations/inferences based on the ERA5 analysis.
So, for accumulated parameters like “total precipitation” and “solar surface radiation downwards”, from what I understood from the documentation, the ERA5 data corresponds to something akin to
ssrd(t=(2024/1/2 - 14:00), x, y) → total shortwave radiation that hit the area located around point (x,y) from t=(2024/1/2 - 13:00) to (2024/1/2 - 14:00).
Is this correct? Please feel free to correct me here if I am wrong.
Now, imagine we are getting data from the daily forecasts and we want to do some kind of inference and we are at t=(2024/2/1). If we want to do the inference for t=(2024/2/2 14:00), we could think about using the following IFS files corresponding to the 12z calculation:
20240201120000-24h-oper-fc.grib2
20240201120000-27h-oper-fc.grib2
Because our target time point is found at 26=12+14, is this correct?
Now, following the same logic, if we want data that is equivalent to the ERA5 format, how can we get it for this case? I am imagining we would actually need three files instead of two for a simple interpolation. We would need:
The documentation you linked to confirms that the accumulated variables on ERA5 reanalysis (hourly data) are indeed accumulated over the hour, and I believe it confirm my previous interpretation. I do not want to convert them from their provided format, I want to keep these hourly accumulation values. The values being provided in [m] vs [mm] is irrelevant for this case.
I’m still confused about the part of converting the usual daily open (operational?) data forecasts to the format of ERA5’s hourly accumulation, since that was the main point of my question. I want to get (for example) the total precipitation for an hour [m] from the IFS Open Data that is updated on a daily basis, not from the ERA5 data.
The accumulations (over the accumulation/processing period) in the short forecasts (from 06 and 18 UTC) of ERA5 are treated differently compared with those in ERA-Interim and operational data (where the accumulations are from the beginning of the forecast to the validity date/time). In the short forecasts of ERA5, the accumulations are since the previous post processing (archiving), so for:
So does the where the accumulations are from the beginning of the forecast to the validity date/time bit confirm my example calculation? I just would like to see a more formal or quantitative example like the one in the ERA5 link you provided, hence why my previous post was written with such an attempt at an example. Having this information in prose makes it more confusing to me, and hence I like the format of the ERA5 relevant page, I would just like a similar source for the operational data.
For a little more context, the reason I am asking this particular question is because applying the methodology I described is giving me negative values for surface solar radiation downwards when interpolating around 11pm to 1am in a specific region’s local time. For the same date, the corresponding ERA5 reanalysis values have a minimum of zero.
" Occasionally, we receive reports of negative precipitation totals being computed from IFS output encoded in GRIB. Although such reports often refer to “negative precipitation accumulation”, the same issue can affect any field accumulated from the start of the forecast and small but spurious positive accumulations are also possible. Positive accumulations can lead to small increases in, say, solar radiation during night time hours when a zero increase is expected. This document explains both why this happens and the circumstances in which it occurs…"