Geoscience Reference
In-Depth Information
150
100
50
50
100
−1
0
50
200
40N
20N
EQ
20S
40S
60S
80E 100E 120E 140E 160E 180W160W140W120W100W 80W 60W 40W 20W
0E
20E
40E
60E
Fig. 13.9 NCODA 3DVAR analysis regions for global HYCOM. The three regions in the Atlantic,
Indian and Pacific Ocean cover the Mercator projection part of the global model grid. The three
regions in the Arctic Cap cover the irregular bi-polar part of the global grid: northern part of the
Atlantic, northern part of the Pacific, and a region covering the Arctic Ocean. A spherical grid
projection is used in the vicinity of Antarctica
available for assimilation in real-time. The delays in the altimeter data are at least
7296 h due to orbit corrections that have to be applied to improve the accuracy of
the measurements. Profile data can be delayed up to 72
h. Since ocean data are so
sparse it is important to use all of the data in the assimilation. Accordingly, in real-
time applications the 3DVAR has the capability to select data for the assimilation
based on receipt time (the time the observation is received at the center) instead
of observation time. In this way all data received since the previous analysis are
used in the next real-time run of the 3DVAR. However, data selected this way will
necessarily contain non-synoptic measurement times. This source of error in the
analysis is reduced by comparing observations against time dependent background
fields using FGAT. Hourly forecast fields are used in the FGAT for assimilation of
SST observations in order to maintain a diurnal cycle in the model. Daily averaged
forecast fields are used in FGAT for profile data types (both synthetic and real).
SSH data are assimilated in global HYCOM using the MODAS synthetic profile
approach. The 3D temperature, salinity, and u
v velocity analysis increments are
incrementally inserted into the model over a 6 h time period using the incremental
analysis update procedure ( Bloom et al. 1996 ). A separate 2D ice concentration
analysis is used to update the ice concentration in the thermodynamic ice model.
Figures 13.10 , 13.11 ,and 13.12 give time series of innovation and residual error
statistics in the Pacific domain of the hindcast run. The statistics are computed in
;
Search WWH ::




Custom Search