Improved Maritime Continent MJO Simulation in the KMA GloSea6 through Enhanced Thermodynamic Processes.
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| Title: | Improved Maritime Continent MJO Simulation in the KMA GloSea6 through Enhanced Thermodynamic Processes. |
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| Authors: | Kim, Gayoung1 (AUTHOR) gayoungkim.125@gmail.com, Shin, Sun-Hee1 (AUTHOR), Lee, Kang-Jin1 (AUTHOR) |
| Source: | Journal of Climate. Jan2026, Vol. 39 Issue 2, p571-589. 19p. |
| Subjects: | Madden-Julian oscillation, Thermodynamics, Long-range weather forecasting, Humidity, Climate change |
| Abstract: | Given the critical role of the Madden–Julian oscillation (MJO) in modulating global climate variability and subseasonal to seasonal predictability, this study evaluates its simulation in the Korea Meteorological Administration's Global Seasonal Forecast System, version 6 (GloSea6), and compares it with GloSea, version 5 (GloSea5), focusing on prediction skill and key physical processes over the Maritime Continent (MC). Both models exhibit systematic biases, including weaker amplitudes and a tendency for the MJO to stall over the MC. Nevertheless, GloSea6 shows enhanced propagation across the MC, consistent with improved thermodynamic processes. The eastward-to-westward spectral power ratio increases from 1.52 in GloSea5 to 1.93 in GloSea6, closer to the observed 2.79, reflecting a more realistic dominance of eastward propagation. Process-based diagnostics reveal region-dependent improvements: more pronounced over the MC but limited over the Indian Ocean. MC improvements are linked to better simulation of lower-level moisture convergence, equivalent potential temperature, and available potential energy, supported by reduced SST biases and a steeper meridional moisture gradient. These background state changes strengthen moistening processes that precondition convection and sustain eastward propagation over the MC. These findings highlight that GloSea6's advancements are process and region dependent, emphasizing the role of mean-state biases in shaping MJO prediction skill and providing guidance for targeted improvements in subseasonal to seasonal prediction systems. However, improvements in spatial pattern similarity did not always translate into propagation skill gains, particularly over the Indian Ocean (IO), underscoring the complexity of dynamical responses. Significance Statement: The Madden–Julian oscillation (MJO) is one of the most important sources of subseasonal to seasonal predictability, yet its simulation and prediction remain challenging, particularly across the Maritime Continent (MC). This study demonstrates that the new Korea Meteorological Administration (KMA) Global Seasonal Forecast System version 6 (GloSea6), prediction system offers clear improvements over its predecessor, GloSea version 5 (GloSea5), in representing MJO propagation. A notable advancement is the improved balance between eastward and westward spectral power, reflecting a more realistic dominance of eastward-propagating signals. Our process-based analysis shows that the improvements are especially pronounced over the MC, while skill over the Indian Ocean remains limited. The MC improvements arise from better representation of thermodynamic processes such as lower-level moisture convergence, equivalent potential temperature, and available potential energy. In addition, background state changes—including reduced SST biases and a steeper meridional moisture gradient—help strengthen moistening processes that precondition deep convection and sustain MJO propagation. These findings highlight that the benefits of GloSea6 are region and process dependent, offering valuable guidance for the continued development of S2S prediction systems and their application in climate services. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | Given the critical role of the Madden–Julian oscillation (MJO) in modulating global climate variability and subseasonal to seasonal predictability, this study evaluates its simulation in the Korea Meteorological Administration's Global Seasonal Forecast System, version 6 (GloSea6), and compares it with GloSea, version 5 (GloSea5), focusing on prediction skill and key physical processes over the Maritime Continent (MC). Both models exhibit systematic biases, including weaker amplitudes and a tendency for the MJO to stall over the MC. Nevertheless, GloSea6 shows enhanced propagation across the MC, consistent with improved thermodynamic processes. The eastward-to-westward spectral power ratio increases from 1.52 in GloSea5 to 1.93 in GloSea6, closer to the observed 2.79, reflecting a more realistic dominance of eastward propagation. Process-based diagnostics reveal region-dependent improvements: more pronounced over the MC but limited over the Indian Ocean. MC improvements are linked to better simulation of lower-level moisture convergence, equivalent potential temperature, and available potential energy, supported by reduced SST biases and a steeper meridional moisture gradient. These background state changes strengthen moistening processes that precondition convection and sustain eastward propagation over the MC. These findings highlight that GloSea6's advancements are process and region dependent, emphasizing the role of mean-state biases in shaping MJO prediction skill and providing guidance for targeted improvements in subseasonal to seasonal prediction systems. However, improvements in spatial pattern similarity did not always translate into propagation skill gains, particularly over the Indian Ocean (IO), underscoring the complexity of dynamical responses. Significance Statement: The Madden–Julian oscillation (MJO) is one of the most important sources of subseasonal to seasonal predictability, yet its simulation and prediction remain challenging, particularly across the Maritime Continent (MC). This study demonstrates that the new Korea Meteorological Administration (KMA) Global Seasonal Forecast System version 6 (GloSea6), prediction system offers clear improvements over its predecessor, GloSea version 5 (GloSea5), in representing MJO propagation. A notable advancement is the improved balance between eastward and westward spectral power, reflecting a more realistic dominance of eastward-propagating signals. Our process-based analysis shows that the improvements are especially pronounced over the MC, while skill over the Indian Ocean remains limited. The MC improvements arise from better representation of thermodynamic processes such as lower-level moisture convergence, equivalent potential temperature, and available potential energy. In addition, background state changes—including reduced SST biases and a steeper meridional moisture gradient—help strengthen moistening processes that precondition deep convection and sustain MJO propagation. These findings highlight that the benefits of GloSea6 are region and process dependent, offering valuable guidance for the continued development of S2S prediction systems and their application in climate services. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 08948755 |
| DOI: | 10.1175/JCLI-D-25-0201.1 |
