5:15 PM - 6:30 PM
[AOS19-P01] Long-term variability of summertime convective activity over the tropical northwestern Pacific and its influence on large-scale atmospheric circulation
Keywords:PJ pattern, South China Sea
It is known that convective activity over the tropical northwestern Pacific during boreal summer affects atmospheric circulation around East Asia. Nitta (1987) showed that convective activity around the Philippine Sea influences the pressure field around Japan, and this teleconnection pattern is called the Pacific-Japan (PJ) pattern. On the other hand, there are few studies on the impact of convective activity in the South China Sea on the large-scale atmospheric circulation. In this study, we focused on the convective activity in the South China Sea, in order to obtain new insights into the fluctuations of atmospheric circulation around Japan.
The main data used in this study are NOAA Interpolated OLR, ERA5 850 hPa geopotential height, and AMeDAS surface air temperature. We used monthly mean values of 1979–2018. The years which OLR averaged over the South China Sea (110°E-120°E, 7.5°N-22.5°N) exceeds plus one standard deviation were classified as South China Sea weak convection years, and minus one standard deviation were classified as strong convection years for the composite analysis. The PJ index was calculated based on Wakabayashi and Kawamura (2004).
First, we examined the spatial distribution and variability of OLR around tropical northwestern Pacific. Results indicate that both the convective activity and the amplitude of the variability around the South China Sea in July tend to be getting strong in recent years. Therefore, we focused on July. A correlation coefficient between the PJ index and OLR in the South China Sea was 0.44, which does not necessarily indicate a well agreement. Next, we conducted a composite analysis of OLR. As a result, it was found that the center of activity for the South China Sea OLR was located locally over the South China Sea, and significant signal is not extracted over the Philippine Sea. The composite map for 850 hPa height between the strong and weak convective years indicates a north-south dipole structure appears, showing a westward shift/movement of atmospheric circulation pattern compared to the PJ pattern. The South China Sea OLR variability affects a wide area of Japan, including southwest Japan, thought the PJ pattern influences surface air temperature mainly over eastern Japan. These suggest that convective activity in the South China Sea may have a different impact from the PJ pattern.
In the presentation, we also introduce results of the LBM experiment that simulated convective activity in the South China Sea and discuss convective activity in the South China Sea under the future climate of CMIP6 outputs.
The main data used in this study are NOAA Interpolated OLR, ERA5 850 hPa geopotential height, and AMeDAS surface air temperature. We used monthly mean values of 1979–2018. The years which OLR averaged over the South China Sea (110°E-120°E, 7.5°N-22.5°N) exceeds plus one standard deviation were classified as South China Sea weak convection years, and minus one standard deviation were classified as strong convection years for the composite analysis. The PJ index was calculated based on Wakabayashi and Kawamura (2004).
First, we examined the spatial distribution and variability of OLR around tropical northwestern Pacific. Results indicate that both the convective activity and the amplitude of the variability around the South China Sea in July tend to be getting strong in recent years. Therefore, we focused on July. A correlation coefficient between the PJ index and OLR in the South China Sea was 0.44, which does not necessarily indicate a well agreement. Next, we conducted a composite analysis of OLR. As a result, it was found that the center of activity for the South China Sea OLR was located locally over the South China Sea, and significant signal is not extracted over the Philippine Sea. The composite map for 850 hPa height between the strong and weak convective years indicates a north-south dipole structure appears, showing a westward shift/movement of atmospheric circulation pattern compared to the PJ pattern. The South China Sea OLR variability affects a wide area of Japan, including southwest Japan, thought the PJ pattern influences surface air temperature mainly over eastern Japan. These suggest that convective activity in the South China Sea may have a different impact from the PJ pattern.
In the presentation, we also introduce results of the LBM experiment that simulated convective activity in the South China Sea and discuss convective activity in the South China Sea under the future climate of CMIP6 outputs.