1. Temperature Analysis
Comparison of Daily Maximum Temperature (Tmax) between ASOS and ERA5
This analysis compares daily maximum temperature (Tmax) from ASOS observations and ERA5 reanalysis data over the Korean Peninsula during the summer of 2024 (June–August). The same preprocessing procedure and datasets described in the Data & Method section were applied throughout.
The comparison between ASOS and ERA5 Tmax showed a strong overall correlation, indicating that both datasets reproduced similar temperature variations. However, the spread of the data increased as temperatures became higher.
Most data points were distributed below the 1:1 reference line (y=x), indicating that ERA5 generally underestimated actual observed temperatures. This bias became more pronounced in extreme high-temperature conditions above 33°C.
→ In summary, ERA5 reproduced general temperature variability reasonably well, but showed limitations in accurately simulating extremely severe heatwave conditions.
Fig. Comparison of Tmax Scatter Plot
The spatial analysis of station-based mean temperature differences revealed a clear contrast between coastal and inland regions.
Large differences between ASOS and ERA5 were observed in the southwestern coastal and island regions, including Jindo, Goheung, and Heuksando, where ERA5 tended to simulate lower temperatures than observations. This is interpreted as the result of strong grid-averaging effects in regions heavily influenced by the ocean.
In contrast, inland areas in the Chungcheong region, such as Seocheongju, Cheonan, and Sejong, showed relatively small differences between the two datasets. In some cases, ERA5 even produced slightly higher temperatures than observations.
→ ERA5 showed relatively stable temperature reproduction performance over flat inland regions, but exhibited limitations in complex coastal and island environments.
Fig. Spatial Distribution of Tmax Bias
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Regions with Minimum Bias
Seocheongju (-1.27°C), Cheonan (-0.87°C), and Sejong (-0.44°C) showed relatively small differences between ERA5 and observations. This suggests that ERA5 reproduces temperature variations more reliably over inland plain regions.
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Regions with Maximum Bias
Jindo (+3.72°C), Heuksando (+3.21°C), and Goheung (+3.15°C) showed significantly lower temperatures in ERA5 compared to observations. This is interpreted as the result of excessive ocean cooling effects caused by the higher ocean fraction within ERA5 grid cells.
Even when strong heatwaves occurred over land, ERA5 tended to suppress temperature increases due to the influence of nearby ocean areas.
