A case study on variational soil moisture analysis from atmospheric observations

Using a stand-alone 1-dim soil and atmospheric boundary layer model, the fe asibility of off-line variational soil moisture analysis by assimilation of near-surface atmospheric observations is investigated. The experiments are performed using the soil module and boundary layer formulation taken from the regional forecast model of the German Weather Service. Assimilation exp eriments indicate that atmospheric information allows to initialize soil hu midity to realistic values. Sensitivity studies using an adjoint code show that proper modeling of the soil moisture signal propagation into the atmos phere is crucial for the algorithm. An assessment of errors corrupting the fit resulting from erroneous cloud-cover specification is performed. The er rors are found to be small for the case considered thus confirming the usef ulness of assimilation of soil moisture for short-term weather forecasts ev en under non-perfect conditions. (C) 1998 Elsevier Science B.V. All rights reserved.