11:05 AM - 11:25 AM
[ACG40-07] Impact of RAMA Buoy Observations over the Tropical Indian Ocean in Boreal Winter in an Atmospheric Reanalysis
★Invited Papers
Keywords:EFSOI, ensemble data assimilation, moored buoy
The tropical Indian Ocean is a key region for active air-sea interactions, playing an important role in the occurrence and development of large-scale atmospheric disturbances, such as the Madden-Julian Oscillation (MJO). Accurate atmospheric and oceanic observations in this region are essential for improving weather forecasts and advancing climate change research. This study focuses on evaluating the impact of meteorological observations, particularly from the moored buoys located at 5°S 95°E, and 8°S 95°E, within the RAMA observational network in the Indian Ocean (referred to as the RAMA-95E buoys). For the evaluation, AFES (Atmospheric General Circulation Model for Earth Simulator) - LETKF (Local Ensemble Transform Kalman Filter) experimental ensemble reanalysis (ALERA) is used.
To evaluate the impact of the observations, we use the Ensemble Forecast Sensitivity to Observation Impact (EFSOI), which estimates the impact of individual observations on subsequent forecast errors. The analysis period spans from 2018 to 2021 during the boreal winter, focusing on how the meteorological observation data in the Indian Ocean affect forecasts. Specifically, we investigate the relationship between atmospheric disturbances associated with the eastward propagation of MJO and the EFSOI, examining whether the RAMA-95E buoy observations show high sensitivity in the MJO's active regions.
The analysis reveals that the EFSOI from the RAMA-95E buoys corresponds to variations in eddy kinetic energy (EKE) at 850 hPa. Notably, during periods of active MJO, regions of high beneficial EFSOI shift eastward in tandem with the MJO’s progression. Specifically, the observations from the RAMA-95E buoys showed a tendency to have a greater impact on the forecast during the MJO events in December 2018, January 2020, and February 2020. Moreover, when compared with other observation types, satellite observations exhibit higher sensitivity in the western Indian Ocean, whereas buoy observations show markedly enhanced sensitivity around the RAMA-95E buoy locations. This suggests that the RAMA-95E buoys effectively capture localized air-sea interactions with high accuracy. Further energy analysis of the EFSOI indicates that moist energy contributes the most to the estimated impact, highlighting the maximized influence of RAMA-95E buoy observations when moist atmospheric disturbances such as the MJO pass through the region.
Future challenges include examining summer data from the RAMA-95E buoys to assess the impact on the Indian Ocean Dipole (IOD). Additionally, conducting similar analyses using TRITON buoys in the western Pacific and considering regional and seasonal variations in the analysis will further expand the scope of the study. Finally, extending the analysis to long-term observation data will be crucial to assess the sustained impact of ocean buoy observations over time.
To evaluate the impact of the observations, we use the Ensemble Forecast Sensitivity to Observation Impact (EFSOI), which estimates the impact of individual observations on subsequent forecast errors. The analysis period spans from 2018 to 2021 during the boreal winter, focusing on how the meteorological observation data in the Indian Ocean affect forecasts. Specifically, we investigate the relationship between atmospheric disturbances associated with the eastward propagation of MJO and the EFSOI, examining whether the RAMA-95E buoy observations show high sensitivity in the MJO's active regions.
The analysis reveals that the EFSOI from the RAMA-95E buoys corresponds to variations in eddy kinetic energy (EKE) at 850 hPa. Notably, during periods of active MJO, regions of high beneficial EFSOI shift eastward in tandem with the MJO’s progression. Specifically, the observations from the RAMA-95E buoys showed a tendency to have a greater impact on the forecast during the MJO events in December 2018, January 2020, and February 2020. Moreover, when compared with other observation types, satellite observations exhibit higher sensitivity in the western Indian Ocean, whereas buoy observations show markedly enhanced sensitivity around the RAMA-95E buoy locations. This suggests that the RAMA-95E buoys effectively capture localized air-sea interactions with high accuracy. Further energy analysis of the EFSOI indicates that moist energy contributes the most to the estimated impact, highlighting the maximized influence of RAMA-95E buoy observations when moist atmospheric disturbances such as the MJO pass through the region.
Future challenges include examining summer data from the RAMA-95E buoys to assess the impact on the Indian Ocean Dipole (IOD). Additionally, conducting similar analyses using TRITON buoys in the western Pacific and considering regional and seasonal variations in the analysis will further expand the scope of the study. Finally, extending the analysis to long-term observation data will be crucial to assess the sustained impact of ocean buoy observations over time.