Negative values in significant height of total swell

Hi all,

I'm new to using the ERA5 datasets and had a question about the significant height of total swell. I'm working on a research project where we want to model the effects of wind and waves on an outcome. Since local wind speed and direction impact wave height, I decided to use the data for total swell since it does not include parts of the wave spectrum identified as windsea. This is primarily to break up the correlation between wind and local waves vs swells. 

So, I went ahead and downloaded the data and I'm looking at it in R and the data seems to be giving me negative values. Am I supposed to standardize the data somehow? Does the negative mean anything? Any help for this newbie would be much appreciated!!

Also, as an aside: any thoughts on using significant height of a total swell vs. significant height of combined wind waves and swell would also be appreciated!!

Hi  Thamanna

what format did you download the data in? (netCDF?) 


Yes, netCDF and then used the netCDF packages in R to work with it.


Just a thought - did you try unpacking the netCDF before working with the files? (use 'ncpdq' from NCO). Is it possible you are seeing the packed values in the netCDF file?



That's entirely possible. I use the raster brick function in R. I can try using the scale_factor and add_offset to address this. I guess I wasn't sure if there was a technical reason this might be happening (ie wasn't sure if it was actually possible for swell heights to be negative). 

Thanks for the help!

Hi Thamanna,

I think unpacking the files before you use them ( and I suggest using 'ncpdq' rather than doing it manually!) would remove one possible cause of the issue.