15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatr...耕作 茂木
Qoosaku Moteki, Japan Agency for Marine Earth Science and Technology, Yokosuka city, Japan; and K. Yoneyama, M. Katsumata, K. Ando, and T. Hasegawa
The drastic thickening of the barrier layer in the marginal sea off the western coast of Sumatra during the passage of the Madden Julian Oscillation (MJO) observed during December 2015 is investigated. Before the MJO arrival, the halocline above 20 m depth was very strong and the barrier layer thickness was 5-10 m from based on R/V Mirai observations. During the MJO forcing of 13-16 December, the isothermal layer was drastically deepened from 20 m to 100 m. Meanwhile, the mixed layer deepening was lagged behind the isothermal layer deepening by 1 day, and the barrier layer underwent dramatic thickening to 60 m within 24 hours. An evaluation of the vertical salinity gradient tendency showed that the dramatic thickening of the barrier layer was due to the vertical oceanic mixing by the atmospheric MJO forcing and the vertical stretching by the oceanic downwelling coastal Kelvin wave intruding from the open ocean. One of the important factors in the drastic barrier layer thickening was concluded to be the atmospheric external forcing and the oceanic internal wave being in-phase. The downwelling oceanic Kelvin wave continuously lowered the thermocline from the middle of November to the end of December, and the salinity stratification in the vicinity of the thermocline was continuously mitigated by the vertical stretching. Under such conditions, the MJO forcing caused vertical mixing of the freshwater with the strong salinity stratification and temperature stratification near the surface. The combination of the two distinct processes caused the drastic thickening of the barrier layer, and the barrier layer thickness reached a maximum of 85 m 5 days after the MJO arrival.
The document discusses how the barrier layer off the western coast of Sumatra drastically deepened due to the passage of a Madden-Julian Oscillation (MJO) during the Pre-YMC period. The barrier layer thickness increased from 5m to 60m within one day and up to 85m over five days, which had never been observed before. This drastic deepening was caused by vertical mixing from the MJO forcing and downwelling of the thermocline by an oceanic Kelvin wave occurring in phase with the MJO. High-frequency observations are needed to better understand the ocean's response and role in rainfall formation during MJO events.
Kim, H. M., D. Kim, F. Vitart, V. E. Toma, J. S. Kug, and P. J. Webster, 2016:
MJO Propagation across the Maritime Continent in the ECMWF Ensemble Prediction System.
J. Climate, 29, 3973-3988.
A triggering factor of the eastward propagation of the Madden–Julian oscillation (MJO) is proposed from a case study of the first MJO generated in late October during CINDY2011. The proposed scenario is that the eastward propagation of the MJO is triggered by an extratropical cyclone in the Southern Hemisphere. The ridge and trough pair meridionally extending between 30°S~15°N accompanied by the extratropical cyclone was found to be completely synchronized with the eastward propagating MJO convection. The ascending areas of the cold front extending from the extratropical cyclone partially combined with those of the MJO and the large-scale ridge and trough below 500 hPa were formed across the midlatitudes in the Southern Hemisphere and the tropics. The convection center of the MJO shifted eastward as a result of the westerly winds in the tropics, expanding eastward by the zonal pressure gradient force between the ridge and trough.
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatr...耕作 茂木
Qoosaku Moteki, Japan Agency for Marine Earth Science and Technology, Yokosuka city, Japan; and K. Yoneyama, M. Katsumata, K. Ando, and T. Hasegawa
The drastic thickening of the barrier layer in the marginal sea off the western coast of Sumatra during the passage of the Madden Julian Oscillation (MJO) observed during December 2015 is investigated. Before the MJO arrival, the halocline above 20 m depth was very strong and the barrier layer thickness was 5-10 m from based on R/V Mirai observations. During the MJO forcing of 13-16 December, the isothermal layer was drastically deepened from 20 m to 100 m. Meanwhile, the mixed layer deepening was lagged behind the isothermal layer deepening by 1 day, and the barrier layer underwent dramatic thickening to 60 m within 24 hours. An evaluation of the vertical salinity gradient tendency showed that the dramatic thickening of the barrier layer was due to the vertical oceanic mixing by the atmospheric MJO forcing and the vertical stretching by the oceanic downwelling coastal Kelvin wave intruding from the open ocean. One of the important factors in the drastic barrier layer thickening was concluded to be the atmospheric external forcing and the oceanic internal wave being in-phase. The downwelling oceanic Kelvin wave continuously lowered the thermocline from the middle of November to the end of December, and the salinity stratification in the vicinity of the thermocline was continuously mitigated by the vertical stretching. Under such conditions, the MJO forcing caused vertical mixing of the freshwater with the strong salinity stratification and temperature stratification near the surface. The combination of the two distinct processes caused the drastic thickening of the barrier layer, and the barrier layer thickness reached a maximum of 85 m 5 days after the MJO arrival.
The document discusses how the barrier layer off the western coast of Sumatra drastically deepened due to the passage of a Madden-Julian Oscillation (MJO) during the Pre-YMC period. The barrier layer thickness increased from 5m to 60m within one day and up to 85m over five days, which had never been observed before. This drastic deepening was caused by vertical mixing from the MJO forcing and downwelling of the thermocline by an oceanic Kelvin wave occurring in phase with the MJO. High-frequency observations are needed to better understand the ocean's response and role in rainfall formation during MJO events.
Kim, H. M., D. Kim, F. Vitart, V. E. Toma, J. S. Kug, and P. J. Webster, 2016:
MJO Propagation across the Maritime Continent in the ECMWF Ensemble Prediction System.
J. Climate, 29, 3973-3988.
A triggering factor of the eastward propagation of the Madden–Julian oscillation (MJO) is proposed from a case study of the first MJO generated in late October during CINDY2011. The proposed scenario is that the eastward propagation of the MJO is triggered by an extratropical cyclone in the Southern Hemisphere. The ridge and trough pair meridionally extending between 30°S~15°N accompanied by the extratropical cyclone was found to be completely synchronized with the eastward propagating MJO convection. The ascending areas of the cold front extending from the extratropical cyclone partially combined with those of the MJO and the large-scale ridge and trough below 500 hPa were formed across the midlatitudes in the Southern Hemisphere and the tropics. The convection center of the MJO shifted eastward as a result of the westerly winds in the tropics, expanding eastward by the zonal pressure gradient force between the ridge and trough.