Accounting for Pliem-Xiu and NOAH Module to Simulate Dust: A Case of Western Areas of Ahwaz

Extended abstract 1- INTRODUCTION In the arid and semi-arid areas of Asia, dust storms occur frequently. Much progress has been made in the monitoring modeling and prediction of Asian dust storms. Dust emission is caused by wind erosion in the sensitive areas. Wind erosion is described as the transportation of soil particles by means of the wind. Soil Surface moisture is one of the most important factors that affects wind erosion. Soil Surface moisture is very low in deserts; consequently, appropriate land surface module must be used for accurate soil moisture and dust simulation. The difficulty in the initialization of soil moisture fields over mesoscale or regional domains and the inability of simple soil moisture models to track realistically the long-term evolution of soil moisture fields suggest the need for some kind of data assimilation for the dynamical adjustment of soil moisture fields. The key elements of the land surface model include soil moisture and evapotranspiration based on the ISBA model. The surface model includes a two-layer soil model with a 1-cm surface layer and a 1-m root-zone layer. 2- THEORETICAL FRAMEWORK Efforts have been made to develop integrated dust modelling systems which couple the models for atmospheric, land-surface, and aeolian processes, real-time dust observations and databases for land-surface parameters, so that the dust-storm dynamics and the environmental control factors are adequately represented. The modeling component comprises an atmospheric model and some modules for the land-surface processes, dust emission, transport, and deposition. Land-surface data are required for the atmospheric model as well as for the land-surface, dust-emission, and dust-deposition schemes. In this study, Pliem Xiu and NOAH land surface modules were used and their dust simulations were compared. 3- METHODOLOGY Land surface models are becoming increasingly common components of mesoscale meteorological models. The Pleim–Xiu land surface model has been incrementally improved by the addition of an alternative indirect data assimilation technique. The soil moisture assimilation technique developed for this model differs from the techniques used with the ISBA model in two ways. First, instead of the incremental periodic adjustments to the soil moisture, the continuous Newtonian relaxation or “nudging” was used. Second, nudging coefficients were defined according to the model parameters rather than statistical analysis. The nudging soil moisture tendencies were Soil moisture tendencies were evaluated every model time step using the current forecast values of T and RH as compared with the “observed” values interpolated from periodic (usually 3 hourly) objective analyses. When the deep soil moisture w2 exceeded the field capacity, further moistening through nudging was not permitted but drying was allowed. In a similar way, when w2 fell below the wilting point, only nudging in the moistening direction was allowed. These restrictions prevented runaway moistening or drying when model biases did not respond to the soil moisture adjustments. 4- RESULTS Results indicated that the Pliem Xiu module simulated low levels of soil surface moisture and accurate dust concentrations. The soil surface thickness of the Pliem Xiu was 1 cm and the soil surface thickness in the NOAH was 10 cm. 5- CONCLUSIONS AND SUGGESTIONS Land surface models are becoming increasingly common components of mesoscale meteorological models. It seems that lower thickness in Pliem Xiu caused faster response of the soil surface moisture to atmosphere forces and more accurate soil surface moisture. The third level of soil moisture was daily used to assess the data schema produced from the radar satellite. Key Words: wind erosion, Pleim Xiu module, NOAH module, soil surface moisture.