Readme of GOCART Data
Data Description:
This is the gridded monthly averaged data of aerosol optical depth at 550nm from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model (collection c3.1). The original data format of GOCART is ASCII with a resolution of 2.5x2 degrees. The data were provided by Dr. Mian Chin in Atmospheric Chemistry and Dynamic Branch (Code 613.3) and Dr. Hongbin Yu in Climate and Radiation Branch (Code 613.2), Laboratory for Atmospheres, GSFC/NASA. Details of the GOCART model and related references can be found at http://code916.gsfc.nasa.gov/People/Chin/aot.html
The GOCART data in the GES-DISC Interactive Online Visualization and ANalysis Infrastructure (Giovanni) were processed from the original ASCII data into two different resolutions. The 2.5x2 degree resolution data were simply converted from the original ASCII format into a flat binary format. The 1x1 degree resolution data were calculated from the original 2.5x2 degree data using a simple bi-linear interpolation in order to match the resolution of MODIS aerosol products for making inter-comparison. The bi-linear interpolation software used is called regrid2, a user defined function in Grid Analysis and Display System (GrADS).
A total of 12 atmospheric aerosol components and cloud fraction are included in Giovanni. These are:
BC - black carbon optical depth at 550 nm
OC - organic carbon optical depth at 550 nm
SU - sulfate optical depth at 550 nm
DU - dust optical depth at 550 nm
SS - sea-salt optical depth at 550 nm
OCn - natural organic carbon optical depth at 550 nm
DUa - accumulation-mode (diameter less than 1µm) dust optical depth at 550 nm
SSa - accumulation-mode (diameter less than 1µm) sea-salt optical depth at 550 nm
SUn - natural sulfate optical depth at 550 nm
tot - total optical depth at 550 nm
fine - fine-mode aerosol optical depth at 550 nm
ant - anthropogenic aerosol optical depth at 550 nm
FRC_cld - total cloud fraction from the assimilated meteorological fields in the Goddard Earth Observing System Data Assimilation System (GEOS-DAS) version 3.
Where tot, fine, and ant are composite of specific aerosol components. They are defined as:
tot = BC + OC +SU + SS + DU
fine = BC + OC + SU + DUa + SSa
ant = BC + OC + SU - OCn - SUn
The data collection c3.1 reflects the use of GEOS-3 version of the meteorological data and the collection 1 for all the GOCART aerosols: v15 (SU, SUn, OC, OCn, BC, DUa, SSa), v17 (SS), and v20 (DU), where v* is the GOCART running version number.
Data Filename Convention:
2.5x2 degree flat binary files:
TAU550_param_collection_YYYYMM.dat
FRC_cld_geos3_YYYYMM.dat
Where:
param - atmospheric aerosol components
collection - GOCART data collection number
YYYYMM - year and month
1x1 degree flat binary files:
TAU550_param_collection_1d_YYYYMM.dat
FRC_cld_geos3_YYYYMM.dat
Where:
param - atmospheric aerosol components
collection - GOCART data collection number
YYYYMM - year and month
Data Structure:
2.5x2 degree flat binary files:
Horizontal resolution: 2.5 deg longitude by 2 deg latitude except the two polar grid boxes which are in 1 deg latitude.
Dimensions: 144x91
First point: (-180, -89.5)
Details of center longitudinal and latitudinal grid box can be found in: http://code916.gsfc.nasa.gov/People/Chin/gocart.latlon
1x1 degree flat binary files:
Horizontal resolution: 1deg longitude by 1 deg latitude
Dimensions: 360x180
First point: (-179.5, -89.5)
Sample Images:
GOCART total aerosol optical depth at 550nm of resolution 2.5x2 degree for January 2001
GOCART total aerosol optical depth at 550nm of resolution 1x1 degree for January 2001
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