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What would be your guess why CARRA snow thickness (on sea ice) is usually much larger than from altimetry?

It is not clear which altimetry product the question is referring to and how accurate it is. However, a comparison study of such data with CARRA data would be of interest. The modelling of snow on sea ice in CARRA applies the SICE scheme (Batrak et al, 2018, https://doi.org/10.5194/gmd-11-3347-2018). This scheme has been shown to give advances over previous schemes, which don't attempt to take the snow on sea ice into account, however it still does not give a perfect representation of the snow on sea ice. To speculate about sources for possible biases, one could mention the absence of ice dynamics in the scheme: If there is an area of intensive snow accumulation, ice has no chance to transport this snow and it keeps piling up in the same grid cells. Also the absence of snow-ice formation in the model (even though it isn't as important in the Arctic as in the Antarctic). Additionally, the CARRA system doesn't represent the process of snow precipitation loss to the open sea portion of a grid cell when ice concentration is below 100%.


QUESTIONS RELATED TO THE CARRA DATA

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We have 2m relative and 2m specific humidity for the CARRA single level CDS entry at https://cds.climate.copernicus.eu/cdsapp#!/datasetdatasets/reanalysis-carra-single-levels?tab=formdownload.

For pressure and height levels we have only relative humidity and for model levels only specific humidity. See at 

The conversion between relative and specific humidity is therefore relevant for the pressure, height and model level CDS entries.  

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We have several radiation parameters in the CDS at the single level CARRA entry: https://cds.climate.copernicus.eu/cdsapp#!datasets/dataset/reanalysis-carra-single-levels?tab=overview

These are as follows:

  • Direct solar radiation
  • Surface latent heat flux
  • Surface net solar radiation
  • Surface net solar radiation clear sky
  • Surface net thermal radiation,
  • Surface net thermal radiation clear sky
  • Surface solar radiation downwards
  • Surface thermal radiation downwards
  • Time-integrated surface direct short wave radiation flux
  • Top net solar radiation
  • Top net thermal radiation

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This is a valid question what we are aware of. First of all we tried to speed up the access to the data, i.e. faster download speeds for the full (whole domain) data files. We think that with the migration of our archiving system to Bologna this gave some improvements. We are also planning to put the most used parts of the CARRA datasets into spinning discs instead of tapes. The next step will be to make possible for the users to have any geographic subset of the CARRA data. This is work in progress (the complications are related to the distorted Lambert projection geometry towards the Pole and the fact that the netcdf files don't have a good data compression capabilities).


When will monthly and daily means be available?

The software computing CARRA daily and monthly mean values are ready and will be deployed soon for the entire CARRA dataset. Since we need to get through the entire more than 30-year sub-daily CARRA dataset for the daily/monthly mean computations it will take a bit of time to complete the process and open the dataset for public use. Our latest estimate is that the means will be available for the users around mid-2024. We will give news on our progress in the CARRA User Forum (see at Copernicus Arctic Regional Reanalysis (CARRA)).