The 3D-Var Data Assimilation Experiments on a Dense Fog Event over the Central Plain of China

Nonhydrostatic mesoscale WRF and its 3D-Var system are used to study a dense fog event occurring in 1314 January 2006. Three di erent observation data sets including GTS (Global Telecommunication System), AMDAR (Aircraft Meteorological Data Relay) data, and 9210 data are assimilated into the initial analysis elds in experiments. Experiments with three di erent assimilation time intervals (1, 3, and 6 h) are also carried out. Three experiments with di erent data sets have all modi ed the temperature and humidity eld of initial elds, and therefore show an obvious positive e ect on fog simulation. Further study indicates that the humidity and stability of boundary layer are improved obviously in assimilation experiments, although di erent data sets make di erent contribution to the analysis elds. The multi-time assimilation cycle experiments show that the analysis increment in experiment with 1-h interval is more realistic than that with 3- and 6-h intervals.