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REWC calculate


VareKey

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Hello all,

I am using measurement data with the one-year extension, how can I calculate the generalised extreme wind climate,REWC, to use on the WASP 3.0? In the previous version, 2.0,I used the EWC estimator and convert the lib into rewc.

Thanks for your help.

VareKey
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Hi VareKey,


Unfortunately, we do not have an EWC estimator for WEng3.

The extreme-wind model in WEng3 depends on observation of extreme events rather than fitted distributions. The best way to generate this input (*.OEWC files) is with the new WACA2. You can also input WEng2-style (*.OEWC) files generated by WACA1, but if you still have the data it is better to recalculate the *.OEWC files with WACA2, as then you will model effects of terrain-induced flow direction changes more correctly. Unfortunately, the old (*.EWC) format is not supported in WEng3 and this is why you are having problems using the output from the EWC estimator or REWC files generated from this. The EWC estimator predicted extreme-wind Gumbel distributions and stored the parameters in the OEWC file instead of the observed winds required by WEng3, so to make it work we would have to make a simulation pseudo-random “observations”. It could be done, but the results would be random. I remember that we discussed the problem during the development of WEng3 and decided against it.

Maybe you need this tool because you only have a short time series available. In that case it might be a possibility to use data from a remote site and then translate that to regional statistics, see http://www.wasp.dk/Products/WEng/ExtremeWinds.aspx We are also developing a peak-over-threshold method for WEng3 and it should be available quite soon.


Cheers,
Morten
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Hi Morten,
First of all thanks for you answer. In this particular case we tried not to estimate the extreme winds, since the extension of data is inappropriate, but is sufficient to evaluate the wind shear, flow inclination and turbulence intensity.
We are using WACA 2 but since the series is less than two years OEWC cannot be calculated. So, in this case is the use the REWC files computed from NCEP/NCAR reanalysis data, and made available by RISO; a reasonable approach? Or is there a standard REWC just to evaluate the abovementioned features?
Thanks in advance.
Best regards,
VareKey
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Hi VareKey,


The REWC files derived from reanalysis data should be used with care. My colleagues working with mesoscale models warn about problems in complex terrain, very high roughness, and areas with tropical cyclones. So it is a good idea to make comparisons with statistics based on high-quality data from similar projects in the region you are operating in.


Unfortunately, the REWC file format has changed from WEng2 to WEng3. I have been assigned the task of updating our reanalysis-based REWC files to the new format but unfortunately, I have been working with other projects.


We are implementing an alternative method based on the peak-over –threshold approach for the WEng 3.1 upgrade version,which should be available very soon. This will allow you to prepare EWC statistics from time series of short duration, but the statistical uncertainty will be very high – there is no way to change that.


Best regards,
Morten
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