Calculate the taug coefficient

def _calc_taug(w, aod700, p):
    """Calculate the taug coefficient"""
    p0 = 101325.
    tg1 = 1.24 + 0.047*np.log(w) + 0.0061*np.log(w)**2
    tg0 = 0.27 + 0.043*np.log(w) + 0.0090*np.log(w)**2
    tgp = 0.0079*w + 0.1
    taug = tg1*aod700 + tg0 + tgp*np.log(p/p0)

    return taug