What is the soil temperature variable over the oceans in IFS and ERA5?

Datasets and Usage
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1

Hello,

I am using soil temperature data (stl, or sot depending on the age of the data) from the IFS and ERA5, and can’t work out what the data over the oceans for this variable is.

Given the ocean is not land (obviously) I would have thought it would be nans, but it’s not - it looks like its related to the sea surface temperature. I know it’s not skin temperature because it varies with ‘soil level’ but I can’t find anywhere in the documentation which describes it. Is it ocean temperature at ocean levels matching the soil level depths? Or something else?

Note that I do need this data so I don’t want to replace it with nans - I just want to understand exactly what it is.

Thanks in advance!

Cat

2

Dear Catherine,

Thanks for your request!

All forecast and analysis fields are gapless with real values everywhere (so no NaN values). In terms of soil moisture, for example, values over the ocean are simply set to zero. In contrast, for soil temperature, fields are a composite of soil temperature over land, sea surface temperature over the ocean and ice temperature over sea ice. The increments of soil temperature layer 1 (stl1) over the ocean are effectively the sea surface temperature increments, while ice temperature is not analysed in the system - meaning that the analysis fields are equal to the forecast fields. Soil temperature layer 1 over land physically represents the temperature of the first 7 cm soil and does not match any ocean levels.

Cheers,

Christoph