Ninth International Conference on Permafrost ... - IARC Research

Improve the Active Layer Temperature Profile Estimation by theData Assimilation MethodRui Jin, Xin LiCold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of SciencesIntroductionThe heat and hydrological regimes of the frozen ground,especially its active layer dynamics, have important impactson the energy and water exchange between the land andatmosphere, runoff, the carbon cycle, and crop growth.There are two methods widely used in frozen groundresearch including the physically based model and in situ/remote sensing observation. However, there are someuncertainties in the model simulation. The observation hasinstrumental and representative errors as well. The in situstations are distributed sparsely. Additionally, althoughremote sensing can provide a regional view, the directapplication of remote sensing was to detect the soil surfacefreeze-thaw status by microwave bands.Land data assimilation provides a new methodology tomerge the observations into the dynamics of the land surfacemodel for improving the estimation of land surface state (Liet al. 2007).Framework of Active Layer Data AssimilationSystemThe active layer data assimilation system comprised fourcomponents:1. Model operation: The SHAW (Simultaneous Heatand Water) (Flerchinger & Saxton 1989) model was used toprovide the dynamical framework.2. Observation operator: The microwave radiativetransfer model Tb= e⋅Teff(Liou 1998) was used toconvert the predicted model state variable to the simulatedbrightness temperature.3. Assimilation strategy: The ensemble kalman filter(Evensen 2003) is a new sequential data assimilationalgorithm, which can deal with the nonlinearity anddiscontinuity of the model.4. Dataset: It includes atmospheric forcing data, landsurface parameters, in situ SMTMS (Soil Moisture andTemperature Measurement System) observation, and SSM/Idata.The assimilation experiments were carried out at AMDO(32.2°N, 91.6°E, 4700 m) station on the Tibet plateau, whichis located in the island permafrost region.Assimilating the 4 cm depth soil temperature observationThe 4 cm depth soil temperature observation wasassimilated because it contributed to the microwave emissionand was less influenced by the environmental conditionsthan the soil surface temperature.The experiment of assimilating hourly 4 cm depth soiltemperatures showed the result matched well with theFigure 1. The assimilation result of 4 cm, 20 cm, 60 cm, and 100 cm soil temperature by introducing the 4 cm depth soil temperatureobservation: (a) the non-diagonal element equals to 0; (b) the non-diagonal element is determined by the model error and the correlationanalysis.117