• Atmosphere
• /
• v.34 no.4
• /
• pp.349-358
• /
• 2024

The accurate prediction of Changma (Korean summer monsoon) onset and withdrawal dates is crucial for various sectors including agriculture, water resource management, and disaster prevention. This study applies 25 ensemble members from the operational Korean Integrated Model (KIM) to the Korea Meteorological Administration (KMA) Changma Index (CMI) to diagnose the forecast skill for the onset and withdrawal dates of the 2021 Changma, which marked as the third shortest period on record. The CMI, consisting of 200 hPa geopotential height and zonal wind variables around the Korean Peninsula, was used to compare reanalysis data and KIM's ensemble forecast data. While the CMI from individual ensemble members showed significant variability in predicting the Changma onset and withdrawal dates, the ensemble mean CMI accurately predicted the Changma onset date 12 days in advance with a one-day error margin, and also accurately predicted the Changma withdrawal date 9 days in advance. Detailed analysis of the variables constituting the CMI in KIM's ensemble forecast data indicated that variations in the 200 hPa geopotential height were particularly influential in determining the Changma onset and withdrawal dates. These results demonstrate that the ensemble mean forecast of KIM is more effective than individual ensemble member forecasts for predicting Changma onset and withdrawal dates, highlights the utility of KIM's ensemble forecast data and the effectiveness of using upper atmospheric variables (specifically 200 hPa geopotential height) for these predictions.

• Atmosphere
• /
• v.21 no.1
• /
• pp.109-121
• /
• 2011

This study revisits the definition of Changma, which is the major rainy season in Korea and corresponds to a regional component of the East Asian summer monsoon system. In spite of several decades of researches on Changma, questions still remain on many aspects of Changma that include its proper definition, determination of its onset and retreat, and relevant large-scale dynamical and thermodynamical features. Therefore, this study clarifies the definition of Changma (which is a starting point for the study of interannual and interdecadal variability) using a basic concept of air mass and front by calculating equivalent potential temperature (${\theta}_e$) that considers air temperature and humidity simultaneously. A negative peak in the meridional gradient of this quantity signifies the approximate location of Changma front. This front has previously been recognized as the boundary between the tropical North Pacific air mass and cold Okhotsk sea air mass. However, this study identifies three more important air masses affecting Changma: the tropical monsoon air mass related to the intertropical convergence zone over Southeast Asia and South China Sea, the tropical continental air mass over North China, and intermittently polar continental air mass. The variations of these five air masses lead to complicated evolution of Changma and modulate intensity, onset and withdrawal dates, and duration of Changma on the interannual time scale. Importantly, use of ${\theta}_e$, 500-hPa geopotential height and 200 hPa zonal wind fields for determining Changma onset and withdrawal dates results in a significant increase (up to~57%) in the hindcast skill compared to a previous study.