Forcings in GISS Climate Model

Stratospheric Aerosol Optical Thickness

Stratospheric aerosol optical thicknesses used in GISS climate simulations are given here. Discussions of the data are given in the references below. The datasets are updated when additional data or improvements become available. We welcome comments or suggestions regarding these data.

Optical Depth at 550 nm

The first figure is of the global and hemispheric mean stratospheric optical depths.

Line plot of global and hemispheric mean stratospheric optical depths, 1850-2012

+ Download ASCII text dataset (65 kB).

The second figure is of the zonal mean stratospheric optical depths.

Keogram plot of zonal mean stratospheric optical depths, 1850-2012

+ Download netCDF dataset (942 kB)
+ Download ASCII text dataset (gzipped, 137 kB)
+ View plot PDF (144 kB)

The optical depths are organized into four altitude levels (15-20 km, 20-25 km, 25-30 km, 30-35 km). The netCDF data file also includes a variable that vertically sums across the four levels.

The above optical depth data were updated 2012-12-13. The netCDF version was added 2016-11-14.

Effective Particle Radius

The effective radius of the aerosol particles is defined as

reff = 0.20 (in the state with small optical thickness)
reff = 0.20 + taumax(latitude)0.75 × f(t-t0) (µm) (for large volcanoes)

where f(t-t0) is a function of time derived from the observed reff for Pinatubo, while keeping the observed values for El Chichon and Pinatubo.

The next figure is of the global and hemispheric mean effective aerosol particle radii.

Line plot of lobal and hemispheric mean effective aerosol particle radii, 1850-1999

+ Download ASCII data (52 kB)
+ View plot PDF

The final figure is of the zonal effective aerosol particle radii for selected short time periods.

+ Download netCDF dataset (191 kB)
+ Download ASCII data (gzipped, 22 kB)
+ View plot PDF

The above particle radius data were updated 2005-09-22. The netCDF version was added 2016-11-08.

The relation between the optical thickness and the forcings are roughly (See "Efficacy ..." below):

  • instantaneous forcing Fi (W/m2) = -27 τ
  • adjusted forcing Fa (W/m2) = -25 τ
  • SST-fixed forcing Fs (W/m2) = -26 τ
  • effective forcing Fe (W/m2) = -23 τ


April 1995: Data around the period of El Chichon eruption (January 1982 to December 1984) were multiplied by 1.1 uniformly in all latitude zones so that the global mean optical depths match better with an analysis provided by Jim Pollack in April 1994.

Data for January 1991 to December 1994 were added. These optical thickness at 550 nm were derived by Andrew Lacis from SAGE data supplied by Larry Thomason of Langley Research Center (cf. Hansen et al., reference below).

Background aerosols with an optical thickness 0.0001 were added as a lower limit for aerosol amount at all times.

June 1999: Data for January 1995 to October 1997 were updated using Dr. Larry Thomason's SAGE data. The data were extended through December 1999 assuming that the optical thickness decreases exponentially with a one year decay constant.

For the period prior to 1985, the same time constant (one year) was used to smooth noisy data, preserving the integral of optical depth over several years around time of a given volcano.

April 2002: Data for Krakatoa and Santa Maria were modified. The optical thickness for Krakatoa is 1.1 times that for Pinatubo, based on three-year integration of pyrheliometer data, with the spatial distribution based on Pinatubo but with the two hemispheres switched. The optical thickness for Santa Maria (0.55 times that of Pinatubo) has comparable aerosol amount in both hemispheres based on ice core data.

December 2012: OSIRIS time series dataset provided by Dr. Adam Bourassa was used, interpolating linearly for the missing data, converting from 750 nm to 550 nm assuming 1/wavelength relation. The dataset starts within a few months from October 2001, and the initial Bourassa data were used as background aerosol optical depth following the Pinatubo decay.

See volcano list table (2012-12-13): PDF or Word DOC.

November 2016: We have added netCDF versions of the gridded data to the download links. There is otherwise no change or addition to the stratospheric aerosol data available here.


Please address scientific inquiries about these data to Dr. Makiko Sato.

Also participating in this research were Drs. Andrew Lacis, James Hansen, and Larry Thomason.


Bourassa, A.E., A. Robock, et al. 2012: Large volcanic aerosol load in the stratosphere linked to Asian monsoon transport. Science 337, 78-81, doi:10.1126/science.1219371.

Hansen, J., et al. 1996: A Pinatubo climate modeling investigation. In The Mount Pinatubo Eruption: Effects on the Atmosphere and Climate (G. Fiocco, D. Fua, and G. Visconti, Ed.). NATO ASI Series Vol. I 42, pp. 233-272. Springer-Verlag. Heidelberg, Germany.

Hansen, J., M. Sato, R. Ruedy, L. Nazarenko, A. Lacis, G.A. Schmidt, G. Russell, et al. 2005: Efficacy of climate forcings. J. Geophys. Res., 110, D18104, doi:10.1029/2005/JD005776.

Haywood, J.M., et al. 2010: Observations of the eruption the Sarychev volcano and simulations using the HadGEM2 climate model. J. Geophys. Res. 115, D21212 doi:10.1029/2010JD014447.

Sato, M., J.E. Hansen, M.P. McCormick, and J.B. Pollack 1993: Stratospheric aerosol optical depth, 1850-1990. J. Geophys. Res. 98, 22987-22994.

Thomason, L., 1998: SAGE II Stratospheric Aerosol Data Products. Dataset formerly available at More recent versions found at SAGE II V6.20 and V7 available via the NASA Langley Atmospheric Science Data Center (site accessed 2016-11-02).

Vernier, J.-P., L.W. Thomason, et al. 2011: Major influence of tropical volcanic eruptions on the stratospheric aerosol layer during the last decade. Geophys. Res. Lett., 38, no. 12, L12807, doi:10.1029/2011GL047563.

Note: PDF documents require the free Adobe Reader or compatible viewing software to be viewed.

This page was written by Dr. Makiko Sato.

Data last updated: 2012-12-14 — Page last updated: 2016-11-08.

+ Return to Model Forcings Homepage