Calculate the taub coefficient

def _calc_taub(w, aod700, p):
    """Calculate the taub coefficient"""
    p0 = 101325.
    tb1 = 1.82 + 0.056*np.log(w) + 0.0071*np.log(w)**2
    tb0 = 0.33 + 0.045*np.log(w) + 0.0096*np.log(w)**2
    tbp = 0.0089*w + 0.13

    taub = tb1*aod700 + tb0 + tbp*np.log(p/p0)

    return taub