In this paper, trends of the widely used stability indices (SIs) and environmental parameters (EPs) were examined by using the 30-year routine rawinsonde data observed in three upper air observatories (Osan, Gwangju and Pohang) over South Korea. To take into account of the contribution of water vapor to a parcel density, we applied the virtual temperature correction in calculating the SIs and EPs. The trends of SIs and EPs indicated significant increases of temperature and moisture contents, especially at the low-to-mid troposphere during the last 10 years. The warming trend in the lower troposphere shows about 3 times greater than that of the global average (+0.10-+0.20 o C/10 years), whereas the cooling trend of lower stratosphere demonstrates a similar trend with the global average (−0.33-−0.60 o C/10 years). The vertical stability is clearly reduced due to the unsymmetrical change of atmospheric elements. The unstabilizing trend with the increased moisture contents gradually changed the atmospheric environment in South Korea into the conditions favorable for the occurrence of severe weather or intensifications of such events. These trends are consistent with the recent observations, which showed clear increase in the intensity and frequency of heavy rainfalls.
Seasonal and diurnal variations of commonly used stability indices (SIs) and environmental parameters (EPs) over East Asia were examined by using eight years (2000~2007) 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.
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