def pearson(obs,mod):
    """
    Pearson's correlation coefficient = mean((x-mean(x))/stddev(x) * (y-mean(y))/stddev(y))
    """
    return ((obs-obs.mean(axis=0))/obs.std(axis=0)*(mod-mod.mean(axis=0))/mod.std(axis=0)).mean(axis=0)