import pandas as pd
from glob import glob

data = sorted(glob("data_U10*.csv"))

for i in data:
    print(i)
    du = pd.read_csv(i)
    dv = pd.read_csv(i.replace('U10', 'V10'))
    dw = du
    dw['obs'] = (du.obs**2 + dv.obs**2)**0.5
    dw['his'] = (du.his**2 + dv.his**2)**0.5
    dw['bc'] = (du.bc**2 + dv.bc**2)**0.5
    dw.index = du.index
    dw.to_csv(i.replace('U10', 'WND'))