Seasonal and Diurnal Variations of Stability Indices and Environmental Parameters Using NCEP FNL Data over East Asia

Seasonal and diurnal variations of commonly used stability indices (SIs) and environmental parameters (EPs) over East Asia were examined by using eight years (2000 similar to 2007) 6-hr National Centers for Environmental Prediction (NCEP) final (FNL) global reanalysis data. The quality of the FNL data was also evaluated by using the routine rawinsonde data over South Korea. Most of the SIs and EPs shows significant seasonal variation (SV) and diurnal variation (DV), but their magnitudes are dependent on the geographic locations and seasons. In general, the SV and DV of SIs and EPs are greater over the inland area than that over the waters around the Korean peninsula, and the magnitude of DV is significantly larger during summer than during other seasons. The mid-to-upper atmosphere of the East Sea also exhibits relatively stable conditions during the summer due to the extended Okhotsk sea air mass. As a result, the SIs and EPs of the summer show a "C" shape with a minimum instability over the East Sea. The spatial distribution of the SIs and EPs also shows that the eastern and south-eastern region of China is the most favorable for deep convection during the summer. The DV of SIs and EPs are more significant in the inland area than on the coast with maximum (minimum) at 0600 UTC (1800 UTC). Although the spatial distribution of DV pattern is well suited to that of rawinsonde data, the time of the maximum and minimum instability over South Korea does not correspond to that of the rawinsonde data, which occurred at 1200 UTC and 0000 UTC (Eom et al., 2008). Compared to the rawinsonde data, the FNL data have a large RMSE in the temperature, wind, and mixing ratio especially at the lower troposphere. Therefore, the FNL data should be used with caution, especially for the perfect boundary condition experiments with various numerical simulation models.