  A High-performance Atmospheric Radiation Package (HARP) is developed for
studying multiple-scattering planetary atmospheres. HARP is an open-source
program written in C++ that utilizes high-level data structure and
parallel-computing algorithms. It is generic in three aspects. First, the
construction of the model atmospheric profile is generic. The program can
either take in an atmospheric profile or construct an adiabatic thermal and
compositional profile, taking into account the clouds and latent heat release
due to condensation. Second, the calculation of opacity is generic, based on
line-by-line molecular transitions and tabulated continuum data, along with a
table of correlated-k opacity provided as an option to speed up the calculation
of energy fluxes. Third, the selection of the solver for the radiative transfer
equation is generic. The solver is not hardwired in the program. Instead, based
on the purpose, a variety of radiative transfer solvers can be chosen to couple
with the atmosphere model and the opacity model.
  We use the program to investigate the radiative heating and cooling rates of
all four giant planets in the Solar System. Our Jupiter's result is consistent
with previous publications. Saturn has a nearly perfect balance between the
heating rate and cooling rate. Uranus has the least radiative fluxes because of
the lack of CH4 and its photochemical products. Both Uranus and Neptune suffer
from a severe energy deficit in their stratospheres. Possible ways to resolve
this issue are discussed. Finally, we recalculate the radiative time constants
of all four giant planet atmospheres and find that the traditional values from
(Conrath BJ, Gierasch PJ, Leroy SS. Temperature and Circulation in the
Stratosphere of the Outer Planets. Icar. 1990;83:255-81) are significantly
overestimated.
