skyscapes.physical_model.exojax.psg_xs

skyscapes.physical_model.exojax.psg_xs#

PSG cross-section opacity adapter.

The PSG (NASA’s Planetary Spectrum Generator) hosts pre-computed absorption cross-sections in a uniform ASCII format for many atmospheric gases that ExoJAX’s line-by-line machinery (MdbHitran/OpaPremodit) cannot consume directly – either because the band is an electronic continuum (e.g. O3 Chappuis, SO2 in the UV) or because HITRAN has no entries in the desired wavelength range. This module ships an Opa-shaped adapter that loads any such PSG cross-section file and exposes the same xsmatrix(Tarr, pressure) -> (n_layers, n_nu) contract as ExoJAX’s line-list opa engines.

Format details (PSG xuv linelists):

Header lines start with #. The #TEMP: line lists one or more reference temperatures [K] (e.g. 1 column for many molecules, 11 columns for O3’s Serdyuchenko set). Data rows are wavelength_um  sigma_T1  sigma_T2 ... with cross-sections in cm^2/molecule. See https://psg.gsfc.nasa.gov/helpatm.php for the full catalog of available molecules.

Classes#

PsgCrossSectionOpacity

Cross-section-backed opacity from any PSG xs file.

Functions#

fetch_psg_xs(url, cache_filename[, cache_dir])

Download a PSG cross-section file once and cache it locally.

_load_psg_xs_table(path)

Parse a PSG cross-section ASCII file.

Module Contents#

skyscapes.physical_model.exojax.psg_xs.fetch_psg_xs(url, cache_filename, cache_dir=None)[source]#

Download a PSG cross-section file once and cache it locally.

Idempotent: if the cached file already exists it is returned without re-downloading.

Args:

url: PSG download URL. cache_filename: Name to give the cached file under

cache_dir.

cache_dir: Directory to cache into. Defaults to

~/.cache/skyscapes/ if None.

Returns:

Absolute path to the cached file.

Parameters:
Return type:

pathlib.Path

skyscapes.physical_model.exojax.psg_xs._load_psg_xs_table(path)[source]#

Parse a PSG cross-section ASCII file.

The PSG format begins with #-prefixed header lines including a #TEMP: row listing the temperature axis [K] (one or more values), followed by data rows of wavelength_um  sigma_T1  sigma_T2 ... sigma_TN with cross-sections in cm^2/molecule.

Args:

path: Path to the PSG ASCII file.

Returns:

Tuple of (wavelength_um, T_grid_K, sigma) where sigma has shape (n_wavelengths, n_temperatures) in cm^2/molecule.

Parameters:

path (str | pathlib.Path)

Return type:

tuple[numpy.ndarray, numpy.ndarray, numpy.ndarray]

class skyscapes.physical_model.exojax.psg_xs.PsgCrossSectionOpacity(name, url, molmass, nu_grid, cache_dir=None, xs_table_path=None, cache_filename=None)[source]#

Cross-section-backed opacity from any PSG xs file.

Quacks like ExoJAX’s OpaPremodit: exposes xsmatrix(Tarr, pressure) -> (n_layers, n_nu) and a molmass attribute, so it slots into the same opa_engines tuple as the line-list-backed opacity engines.

Pressure broadening is ignored. The PSG cross-section files describe electronic-continuum / pre-broadened absorption; the pressure-dependence at typical atmospheric pressures is below the photon-noise floor for HWO contrast levels. Temperature interpolation is linear against the file’s temperature axis, with out-of-range temperatures clamped to the nearest endpoint.

For files with a single temperature column the cross-section is returned independent of layer temperature.

Attributes:

name: Molecule name (e.g. "O3", "SO2"). molmass: Molar mass [g/mol]. Caller supplies; used by

opacity_profile_xs to convert mmr to column density.

nu_grid: Wavenumber grid [cm^-1] this adapter was built for.

Parameters:
name#
molmass#
nu_grid#
_T_grid#
_sigma_at_nu#
xsmatrix(Tarr, pressure)[source]#

Cross-section matrix at the requested layer temperatures.

pressure is accepted for interface parity with OpaPremodit but is unused.

Args:

Tarr: Layer temperatures [K], shape (n_layers,). pressure: Layer pressures [bar], shape (n_layers,);

ignored.

Returns:

Cross-section matrix [cm^2/molecule], shape (n_layers, n_nu). Temperatures outside the PSG file’s range clamp to the nearest endpoint cross-section. For single-temperature files the returned matrix is constant in T.

Parameters:

  • Tarr (jaxtyping.Array)

  • pressure (jaxtyping.Array)

Return type:

jaxtyping.Array