Pk = Ak + Bk * Ps
    Ps = surface pressure
    k = 1..65
    Pk = pressure at level k
    https://www.gfdl.noaa.gov/fv3/fv3-key-components/

    Note: not clear from the above URL, but the pressure should be the 
    hydrostatic pressure.

 ak =
  20, 64.247, 137.79, 221.958, 318.266, 428.434, 554.424, 698.457, 863.058, 
    1051.08, 1265.752, 1510.711, 1790.051, 2108.366, 2470.788, 2883.038, 
    3351.46, 3883.052, 4485.493, 5167.146, 5937.05, 6804.874, 7777.15, 
    8832.537, 9936.614, 11054.853, 12152.937, 13197.065, 14154.316, 
    14993.074, 15683.489, 16197.967, 16511.736, 16611.603, 16503.144, 
    16197.315, 15708.893, 15056.342, 14261.435, 13348.671, 12344.49, 
    11276.348, 10171.712, 9057.051, 7956.908, 6893.117, 5884.206, 4945.029, 
    4086.614, 3316.217, 2637.553, 2051.15, 1554.789, 1143.988, 812.489, 
    552.72, 356.223, 214.015, 116.899, 55.712, 21.516, 5.741, 0.575, 0, 0 ;

 bk =
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
    3.697e-05, 0.00043106, 0.00163591, 0.00410671, 0.00829402, 0.01463712, 
    0.02355588, 0.03544162, 0.05064684, 0.06947458, 0.09216691, 0.11881219, 
    0.14926877, 0.18329624, 0.22057019, 0.26068545, 0.30316412, 0.34746849, 
    0.39301826, 0.4392108, 0.48544331, 0.53113482, 0.57574665, 0.61879962, 
    0.65988704, 0.69868292, 0.73494523, 0.76851468, 0.79930974, 0.82731884, 
    0.85259067, 0.8752236, 0.89535499, 0.913151, 0.92879731, 0.94249106, 
    0.95443411, 0.96482757, 0.9738676, 0.98174229, 0.9886266, 0.99467119, 1 ;

obtained from fv_core.res.tile4.nc.