A Weak Constraint 4D-Var Assimilation System for the Navy Coastal Ocean Model Using the Representer Method - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 372

MODAS minus FG Temperature at prf5 MODAS minus FG Salinity at prf5

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Days of August, 2003 Days of August, 2003

MODAS minus 4DVR Temperature at prf5 MODAS minus 4DVR Salinity at prf5

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Days of August, 2003 Days of August, 2003

Fig. 15.5 Same as Fig. 15.3 , except for location 5

local external/surface forcing coupled with strong mixing, and not by the short-lived
initial conditions. Nevertheless, the assimilation still significantly reduces these
discrepancies (bottom panels of Fig. 15.4 ) through the depth-time domain except
for some isolated places. Assimilation results at location 4 (south of the mouth of
the bay) are very similar to those at location 2, and therefore are not shown here.
At location 5 (north of the mouth of the bay) the maximum depth is 100 m. The
largest salinity discrepancies are in the upper 20 m during the first 5-day, as seen
in Fig. 15.5 . There are also some moderate discrepancies in the lower layers around
day 24. Temperature discrepancies are initially moderate (less than 1.5 K during
the first 5-day period) and remain low until day 20, after which they start growing
again, reaching 2 K. For most of the assimilation period these discrepancies are
significantly reduced below 0.5 K, except for some isolated locations, e.g. around
40 m depth at days 21 and 22.

15.4.3 AOSN II Data

The dataset comprises SST from satellite and aircraft, a few SSH from satellite
altimetry (due to the limited area of the model domain), vertical profiles of
temperature and salinity from Slocum and Spray gliders and two moorings (M1 and
M2) and AXBTs. All the vertical profiles are projected on a static grid of 42 levels.
Slocum glider tracks covered a portion of the bay, the mouth of the bay and
the area to the northwest of the bay, i.e. the upwelling center around Ano Nuevo.
Spray glider tracks originated from the nearshore and went offshore in transec-like
trajectories as seen in Fig. 15.6 . To avoid redundancy some of the glider data are
withheld from the assimilation and used for validation of the analyses. Withholding
the data takes into account the model grid resolution and the prescribed horizontal
decorrelation scale of the model error. The observations are assigned a constant error
of 0.5 K and 0.3psu in temperature and salinity respectively.