# A Geostationary Instrument Simulator for Aerosol Observing System Simulation Experiments
## 2 Methodology and Data
### GEOS-5 Nature Run Aerosol Simulation  
The GEOS-5 Nature Run (GSNR) is a 2-year (May 2005-May 2007) global 7 km non-hydrostatic mesoscale simulation based on the Ganymed version of GEOS-5, the NASA GMAO Earth system model. The Goddard Chemistry, Aerosol, Radiation, and Transport model (GOCART, [19]) was run online with coupling to the GEOS-5 radiation code [20], and handled the sources, sinks, and chemistry of dust, sulfate, sea salt, black carbon (BC), and organic carbon (OC) aerosols. The model tracked the total mass of sulfate, two modes (hydrophobic and hydrophilic) of organic and black carbon aerosol, and the particle size distributions of dust and sea salt resolved across five non-interacting size bins for each. The G5 NR simulation was driven by the following prescribed parameters: (1) sea surface temperature and sea-ice, (2) daily sources of volcanic and biomass burning aerosols and trace gases, (3) high-resolution anthropogenic aerosol and trace gas emissions, (4) sinks of aerosols and trace gases, and (5) biogenic sources and sinks of CO\({}_{2}\).  
Besides a full meteorological description of the atmosphere, the G5 NR outputs contain vertical profiles (72 layers from the surface to 0.01 hPa) of concentrations of the 15 aerosol tracers, as well as O\({}_{3}\), CO, and CO\({}_{2}\) at 30 min time intervals. As the aerosol mass mixing ratios were initialized at zero at the start of the G5 NR time period, the first 6 months of the simulation were taken as spin-up in order for aerosol mass mixing ratios to reach equilibrium in the stratosphere. Figure 2 shows an example of the simulated instantaneous concentrations of sea salt, black and organic carbon, dust, and sulfate, and illustrates the high spatial resolution of the G5 NR.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & **TEMPO** & **GEMS** & **SENTINEL-4** \\ \hline Satellite Longitude & \(-100^{\circ}\) & \(128.2^{\circ}\) & \(0^{\circ}\) \\ Number of Pixels East -West & \(1250\) & \(700\) & \(570\) \\ Number of Pixels North-South & \(2000\) & \(2000\) & \(530\) \\ East-West Field of Regard & & & \\  & Top & \(-166^{\circ}\) to \(-33^{\circ}\) & \(55^{\circ}\) to \(145^{\circ}\) & \(-21^{\circ}\) to \(61^{\circ}\) \\  & Bottom & \(-123^{\circ}\) to \(-65^{\circ}\) & \(87^{\circ}\) to \(139^{\circ}\) & \(-9^{\circ}\) to \(39^{\circ}\) \\ North-South Field of Regard & Left & \(18^{\circ}\) to \(63^{\circ}\) & \(-5^{\circ}\) to \(42^{\circ}\) & \(30^{\circ}\) to \(66^{\circ}\) \\  & Right & \(18^{\circ}\) to \(52^{\circ}\) & \(-5^{\circ}\) to \(-45^{\circ}\) & \(31^{\circ}\) to \(53^{\circ}\) \\ Spectral Range & & \(290\)–\(690\) nm & \(300\)–\(500\) nm & \(305\)–\(500\) nm \& \(750\)–\(775\) nm \\ Spectral Resolution & & \(0.6\) nm & \(0.6\) nm & \(0.5\) nm \& \(0.12\) nm \\ \hline \hline \end{tabular}
\end{table}
Table 1: Instrument specifications for the geostationary constellation.  
Figure 2: The 7 km G5 NR aerosol simulation for 27 July 2006 at 12 Z. Blue shading corresponds to sea salt concentration, green shading corresponds to black and organic carbon concentrations, red-orange shading corresponds to dust, and white shading corresponds to sulfate.