Estimating land surface energy and water fluxes by using the Land Data Assimilation System developed at the university of Tokyo (LDASUT)

Abstract

This paper reports an application of an Land Data Assimilation System developed in the University of Tokyo (LDASUT) on the Gaize PBL site at the northwest of Tibet Plateau, for the period from July to August, 2007. The objectives of this study are: (1) to validate LDASUT in bare soil field using in-situ observation, (2) to check the feasibility to estimate areal land surface variables reliably with using LDASUT driven by GCM output data. For the system validation, LDASUT was first driven by in-situ observed micrometeorological data, and simulated energy fluxes were compared to hourly direct measurements; simulated soil moisture content was compared to the in-situ soil moisture observation at the depth of 4 cm. The results show that LDAS can generally simulate those variables well and thus the capability of LDAS is validated. In order to check the possibility of applying LDAS globally and simulating surface energy and water budget worldwide, Japan Meteorology Agency (JMA) Model Output Local Time Series (MOLTS) data were used as the driven data of LDAS. Performance of LDAS was not so good when it was driven by the JMA MOLTS data. This result demonstrated that there were systemic biases lied in JMA MOLTS data in the study region and thus it can not directly apply to LSM or LDAS.