# Disk space requirements¶

The following sections will help you assess how much disk space you will need on your server to store GEOS-Chem Classic input data and output data.

## Space for GEOS-Chem Classic input data¶

The data format used by GEOS-Chem Classic is COARDS-compliant netCDF. This is a standard file format used for Earth Science applications. See our netCDF guide for more information.

### Meteorology fields¶

The amount of disk space that you will need depends on two things:

1. Which type of met data you will use, and

Disk space needed for 1-year of MERRA-2 data

Resolution

Type

Size GB/yr

$$1^{\circ}{\times}1.25^{\circ}$$

Global

~30

$$2^{\circ}{\times}2.5^{\circ}$$

Global

~110

$$0.5^{\circ}{\times}0.625^{\circ}$$

Nested Asia (aka AS)

~115

$$0.5^{\circ}{\times}0.625^{\circ}$$

Nested Europe (aka EU)

~58

$$0.5^{\circ}{\times}0.625^{\circ}$$

Nested North America (aka NA)

~110

Disk space needed for 1-year of GEOS-FP data

Resolution

Type

Size GB/yr

$$1^{\circ}{\times}1.25^{\circ}$$

Global

~30

$$2^{\circ}{\times}2.5^{\circ}$$

Global

~120

$$0.25^{\circ}{\times}0.3125^{\circ}$$

Nested Asia (aka AS)

~175

$$0.25^{\circ}{\times}0.3125^{\circ}$$

Nested Europe (aka EU)

~175

$$0.25^{\circ}{\times}0.3125^{\circ}$$

Nested North America (aka NA)

~175

### Obtaining emissions data and met fields¶

There are several ways to obtain the input data required for GEOS-Chem classic. These are described in more detail in the following sections.

1. Perform a GEOS-Chem dry-run simulation;

3. Transfer data with Globus GEOS-Chem data (WashU) endpoint>.

Also see our Input data for GEOS-Chem Classic for more data download options.

## Space for data generated by GEOS-Chem Classic¶

### Monthly-mean output¶

We can look to the GEOS-Chem Classic full-chemistry benchmark simulations for a rough upper limit of how much disk space is needed for diagnostic output. The GEOS-Chem 13.0.0 vs. 12.9.0 1-month benchmark simulation generated approximately 837 MB/month of output. Of this amount, diagnostic output files accounted for ~646 MB and restart files accounted for ~191 MB.

We say that this is an upper limit, because benchmark simulations archive the “kitchen sink”–all species concentrations, various aerosol diagnostics, convective fluxes, dry dep fluxes and velocities, J-values, various chemical and meteorological quantities, transport fluxes, wet deposition diagnostics, and emissions diagnostics. Most GEOS-Chem users would probably not need to archive this much output.

GEOS-Chem Classic specialty simulations–simulations for species with first-order loss by prescribed oxidant fields (i.e. Hg, CH4, CO2, CO)–will produce much less output than the benchmark simulations. This is because these simulations typically only have a few species.

### Reducing output file sizes¶

You may subset the horizontal and vertical size of the diagnostic output files in order to save space. For more information, please see our section on GEOS-Chem History diagnostics.

Furthermore, since GEOS-Chem 13.0.0, we have modified the diagnostic code so that diagnostic arrays are only dimensioned with enough elements necessary to save out the required output. For example, if you only wish to output the SpeciesConc_O3 diagnostic, GEOS-Chem will dimension the relevant array with (NX,NY,NZ,1) elements (1 because we are only archiving 1 species). This can drastically reduce the amount of memory that your simulation will require.

### Timeseries output¶

Archiving hourly or daily timeseries output would require much more disk space than the monthly-mean output. The disk space actually used will depend on how many quantities are archived and what the archival frequency is.