There
are four steps to assimilate SWE
observation at a given time step:
(1) Forecasting step: the SWE states evolve nonlinearly according to model dynamics;
its covariances are propagated linearly with time.
(2) Updating step: the SWE of
each layer is updated using the Kalman filter equations.
(3) Analysis step: Snow depth and heat content
are calculated using SWE, snow density and snow
temperature. When the model predicts no snow and the updated
SWE being non-zero, snow density is 150 km/g3 and the air temperature
at 2 m is assigned to snow
temperature. Otherwise, snow density and temperature predicted by model are used.
(4) Repartition
step: At this step, the total snow
depth is evaluated and the thickness of each layer is reassigned to ensure a layer
1 thickness of 5 cm. The SWE and heat content are calculated
accordingly.