Four-dimensional Data Assimilation Scheme Research Articles

Impacts of LULC, FDDA, Topo-wind and UCM schemes on WRF-CMAQ over the Beijing-Tianjin-Hebei region, China

In this study, the impacts of land use and land cover (LULC) change, four–dimensional data assimilation (FDDA), Topo-wind and urban canopy module (UCM) schemes on meteorology and air quality were investigated with the latest LULC data in Weather Research and Forecasting Model-Community Multiscale Air Quality (WRF-CMAQ) by scenarios analysis. Results showed that LULC change had significant effects on meteorological conditions and air quality at urban stations, which was attributed to the increasing surface roughness and impervious surface caused by the significant growth of urban land use. Considering the fraction of impervious surfaces and thermal and radiative processes related to urban geometry, UCM improved simulation of 2-m temperature (T2) and relative humidity (RH) in comparison to LULC change at urban stations. Topo-wind scheme slowed down surface wind speed domain-widely especially at valley stations in the nighttime. Based on the Final Operational Global Analysis data, the effects of FDDA varied with stations and layers. FDDA scheme had significant impacts on surface wind speed and aloft wind speed in the vertical range of 60–3500 m obviously. Meanwhile, the simulation results of O3 in FDDA scheme was better than other schemes. Moreover, the combination of LULC change, FDDA, Topo-wind and UCM schemes showed the best simulation performance of surface wind speed, pressure, SO2 and PM2.5 among scenarios, and the distributions of days under different pollution levels of O3 and PM2.5 were much closer to observed data than other scenarios, especially for stations with severe air pollution.

Preliminary Meteorological Results of a Four-Dimensional Data Assimilation Technique in Southern Italy

A four-dimensional data assimilation (FDDA) scheme based on a Newtonian relaxation (or “nudging”) was tested using observational asynoptic data collected at a coastal site in the Central Mediterranean peninsula of Calabria, southern Italy. The study is referred to an experimental campaign carried out in summer 2008. For this period a wind profiler, a sodar and two surface meteorological stations were considered. The collected measurements were used for the FDDA scheme, and the technique was incorporated into a tailored version of the Regional Atmospheric Modeling System (RAMS). All instruments are installed and operated routinely at the experimental field of the CRATI-ISAC/CNR located at 600 m from the Tyrrhenian coastline. Several simulations were performed, and the results show that the assimilation of wind and/or temperature data, both throughout the simulation time (continuous FDDA) and for a 12 h time window (forecasting configuration), produces improvements of the model performance. Considering a whole single day, improvements are substantial in the case of continuous FDDA while they are smaller in the case of forecasting configuration. Enhancements, during the first six hours of each run, are generally higher. The resulting meteorological fields are finalised as input into air quality and agro-meteorological models, for short-term predictions of renewable energy production forecast, and for atmospheric model initialization.

Linearizing iterative processes for four-dimensional data-assimilation schemes

Linearizing iterative processes for four-dimensional data-assimilation schemes

The Impact of Ocean Initial Conditions on ENSO Forecasting with a Coupled Model

Abstract A coupled atmosphere–ocean GCM (general circulation model) has been developed for climate predictions on seasonal to interannual timescales. The atmosphere model is a global spectral GCM T30L18 and the ocean model is global on a 1° grid. Initial conditions for the atmosphere were obtained from National Meteorological Center (now known as the National Centers for Environmental Prediction) analyses, while those for the ocean came from three ocean data assimilation (DA) systems. One system is a four-dimensional DA scheme that uses conventional SST observations and vertical temperature profiles inserted into the ocean model and is forced from winds from an operational analysis. The other two initialization schemes are based on the coupled model, both nudging the surface temperature toward observed SSTs and one nudging surface winds from an operational analysis. All three systems were run from 1979 to 1988, saving the state of the ocean every month, thus initial conditions may be obtained for any mont...