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Atmospheric data

This page describes the atmospheric input data used by JURASSIC, typically provided in a file named atm.tab. The atmospheric data file defines the thermodynamic and compositional state of the atmosphere used for radiative transfer and retrieval calculations.

In JURASSIC, the atmospheric data represent the model state, while observation geometry and radiances are handled separately (see Observation and radiance files).

Purpose of the atmospheric data file

The atmospheric data file provides vertical profiles of:

  • pressure
  • temperature
  • trace gas volume mixing ratios
  • optional aerosol or cloud extinction parameters

These profiles are assumed to be horizontally homogeneous along each ray path. They are interpolated internally to the ray-tracing grid during radiative transfer calculations.

File format selection

The format of the atmospheric data file is selected via the control parameter:

  • ATMFMT

The description below refers to the default ASCII format, typically used with:

ATMFMT = 1

This is the format used in the example projects distributed with JURASSIC.

General format rules

  • The file is a plain-text ASCII table.
  • Columns are separated by spaces or tabs.
  • Header lines are optional; if present, they must not start with a valid numeric value in the first column.
  • Each row corresponds to one vertical grid point.

Units and conventions

The default atmospheric reader expects the following units:

Quantity Unit
time s
altitude (z) km
longitude, latitude deg
pressure (p) hPa
temperature (t) K
volume mixing ratio mol/mol
extinction (k) km⁻¹

These conventions are consistent with the internal JURASSIC data structures and example workflows.

Column layout (default ASCII format)

For each vertical level, the atmospheric file contains the following columns:

  1. time
  2. z – altitude
  3. lon – longitude
  4. lat – latitude
  5. p – pressure
  6. t – temperature
  7. q[0] ... q[NG-1] – volume mixing ratios for each emitter
  8. k[0] ... k[NW-1] – extinction coefficients for each spectral window

The total number of columns is therefore:

6 + NG + NW

where:

  • NG is the number of emitters defined via EMITTER[i],
  • NW is the number of spectral windows.

Trace gas volume mixing ratios

The number and order of trace gas columns must match the emitters defined in the control file:

NG = 2
EMITTER[0] = CO2
EMITTER[1] = H2O

In this case, the atmospheric file must contain exactly two VMR columns, in the same order.

Aerosol and cloud extinction

Extinction coefficients are provided per spectral window. If aerosol or cloud extinction is not used, the corresponding columns should still be present and set to zero.

Extinction values are assumed to be vertically distributed and are applied along the ray path during radiative transfer calculations.

Optional: cloud layer parameters

Some workflows support simplified cloud-layer representations defined by a small set of parameters. If enabled via the control file, the first atmospheric level only may include additional columns such as:

  • cloud-layer altitude
  • cloud-layer thickness
  • cloud extinction coefficients

If these options are not used, the corresponding parameters should be disabled in the control file and omitted from the atmospheric data.

Optional: surface parameters

Surface-related parameters (e.g. surface temperature or emissivity) may also be specified in the atmospheric data file for certain applications.

When enabled, these parameters are expected in the first row only. If surface effects are not required, the default configuration should be used and these fields omitted.

Example (schematic)

For NG = 2 emitters and NW = 1 spectral window, a single profile row might look like:

time   z    lon   lat    p      t      q_CO2      q_H2O      k_win0
0.0    0.0  0.0   50.0   1013.0  288.0  4.2e-4    7.0e-3     0.0

Consistency requirements

When preparing atmospheric data files, ensure that:

  • the number of gas columns matches NG,
  • the number of extinction columns matches NW,
  • units are consistent with the lookup tables,
  • the vertical range covers all ray paths used in the simulation.

Inconsistent atmospheric input is a common source of runtime errors or unexpected results.

Summary

The atmospheric data file (atm.tab) defines the thermodynamic and compositional state of the atmosphere used by JURASSIC. It is independent of the observation geometry and radiance data and should be prepared carefully to ensure physically meaningful and numerically stable results.