Understanding the changes in the ocean-atmosphere interactions in the western tropical Pacific and its impact

Abstract

ABSTRACT

Understanding the changes in the ocean-atmosphere interactions in the western tropical Pacific and its impact

Hyun-Su Jo Dept. of Marine Sciences and Convergent Technology Graduate School of Hanyang University

This study examined the physical processes to understand the changes in the ocean-atmosphere interactions in the western tropical Pacific [130-150˚E, 0-15˚N] across the late-1990s during the boreal spring (March-April-May) and its impact in terms of oceanic and atmospheric teleconnections by analyzing the observational dataset as well as simple model experiments. For the entire analyzed period (1980-2015), it is found that the relationship between sea surface temperature (SST) and precipitation shows a positive correlation in the western tropical Pacific during the boreal spring. That is, anomalous warm SST leads to low-level moisture convergence and it can induce more precipitation accompanied with deep convective cloud (DCC) as well as vertical motion in the western tropical Pacific. Subsequently, an enhanced DCC acts dampen the anomalous warm SST by reflecting an incoming solar radiation, which is indicative of a negative cloud-radiation feedback. In particular, it was found that the low-level moisture convergence, which is mainly due to SST gradients in the central tropical Pacific and eastern Indian Ocean, is able to sustain the DCC in the western tropical Pacific through large-scale atmospheric circulations. However, it was found that a positive correlation of SST-precipitation became statistically insignificant after the late-1990s. In addition, the mean SST in the western tropical Pacific became warmer and the amount of mean precipitation also were increased before and after the late-1990s. After 1999, the anomalous warm SST leads more precipitation along with low-level moisture convergence as well as the enhanced DCC in the western tropical Pacific, which is similar to before 1999. However, the low-level convergence played more active role to lead more precipitation, which was closely associated with SST gradients in the central tropical Pacific and the eastern Indian Ocean. This led to quickly dampen the anomalous warm SST through a negative cloud-radiative feedback, which is in contrast to before 1999. That is, an enhanced negative cloud-radiation feedback as well as strong low-level convergence acted to weaken a positive correlation of SST-precipitation in the western tropical Pacific, which might be associated with a climate shift in the western tropical Pacific across the-1990s. Further study examined the changes in the oceanic and atmospheric teleconnections across the late 1990s in the Pacific basin by analyzing the observations and simple model experiments. It was found that the changes in the ocean-atmosphere interactions in the western tropical Pacific across the late-1990s led to the changes of correlation in the tropical forcing and the East Asian precipitation through atmospheric teleconnections. In addition, the mechanism which was responsible for the western North Pacific climate shift as well as the changes in the relationship in the SST variability between the tropical Pacific and the North Pacific across the late-1990s was also suggested in terms of oceanic and atmospheric teleconnections.