ERA5 mean evaporation rates data - Why is that negative? Please, let me know if this question is too technical/specific for Earth Science. In case, I will remove it and eventually post it elsewhere.

I am processing some data extracted from ERA5 to set up a large scale hydrological model. We are calculating the evapotranspiration using the typical P-M formula, using as input the usual variables: wind speed, solar radiation, temperature, pressure, relative humidity and so on. In order to check the consistency of our calculations with the  variables provided by the ECMWF, I downloaded also some evaporation related variables. I'm struggling to understand the data related to the mean evaporation rate variable data. ERA5 are available at hourly time steps at ~0.28 degrees spatial resolution. For the mean evaporation rate, Minimum, Mean, and Maximum values are provided expressed in kg x sqmt x sec-1. Data look like this:



The ncdump is the following:



and plotting the mean values for a hour during the day, would look like this:



What looks not clear to me is why the mean evaporation rate is negative: I would expect a positive value in the wet regions and zero over the deserts. I tried to look at the ERA5 data documentation, but the issue is not addressed there. Am I misinterpreting something?
Just leaving this for future readers. I finally found in some ECMWF documentation (referring to a different variable) that: "The ECMWF Integrated Forecasting System convention is that downward fluxes are positive. Therefore, negative values indicate evaporation and positive values indicate condensation". This applies also to other variables.
Thanks to Daniel and Spencer for their help.