| The CPC/ACDB environment
data set was used to generate the sample trajectories
shown on this website. The raw stratospheric data (70
- 0.4 mb) in the CPC/ACDB data set are produced by the
NCEP Climate Prediction Center (CPC) from satellite
retrievals. Analysis of the raw stratospheric data is
accomplished by a successive corrections method. The
analyses represent daily (12Z) "snapshots"
of the state global atmosphere. Winds are derived from
geopotential heights using a balanced wind approximation.
The analyses provided in the CPC/ACDB data set are
not "assimilations," i.e., they are not generated
in conjunction with a running General Circulation Model
(GCM).
The atmospheric parameters pressure, temperature, zonal
wind, and meridional wind are given on a three-dimensional
global grid (5 deg. longitude X 2 deg. latitude X 18
vertical levels) that extends from the surface to 0.4
hPa.
We selected a subset of the environment data for the
example trajectories shown on these pages. The selected
dates provide both winter and summer trajectories during
periods where there are no gaps in the data set. The
selected year (1981) is one of the first available years
in the data set. In time, we will investigate trajectories
for later dates.
At any given postion in the atmosphere that does not
fall exactly on a CPC/ACDB data set gridpoint, there
are eight surrounding data points. The TrajSim software
interpolates the CPC/ACDB model environment in four
dimensions.
Spatially, temperature and wind values are interpolated
linearly to the surrounding gridpoints with weighting
factors calculated from the distance between the desired
position and eight surrounding data set gridpoints.
Pressure is interpolated in the vertical dimension,
appropriately, logarithmically. Temporally, all quantities
are interpolated linearly.
Future TrajSim work will use higher-resolution data
from two sources: the NASA/GSFC/Data Assimilation Office
(DAO) and the United
Kingdom Meteorological Office (UKMO). Both organizations
use general circulation models and data assimilation
systems to produce near-real-time "snapshots"
of the state of the atmosphere. Forecasting capabilities
are available from both organizations.
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