One step in untangling the roles of natural variability and anthropogenic forcing on our climate system is understanding how the ocean varies on interannual to decadal time scales. My current research is focused on changes in the North Pacific Ocean that happen over several years to several decades.
In the North Pacific, the Kuroshio responds to the winds by transporting huge amounts of warm water northward in a manner analogous to the Gulf Stream in the North Atlantic. It turns out that the amount of water carried in the Kuroshio varies, on interannual to decadal time scales, coherently with the Pacific Decadal Oscillation (PDO, which is a measure of the state of sea-surface-temperature in the North Pacific). And the closer we look at the observations, the more intriguing the results are: sometimes the Kuroshio’s strength and the PDO vary in concert, but sometimes variation in the Kuroshio’s strength occurs only years after changes in the PDO. Why? And why is PDO correlated with the strength of the Kuroshio in the first place?
I am interested in the dynamics behind these correlations, so my work is two-pronged. The first step is characterizing variability in the North Pacific, especially in the East China Sea, using observations. Then the second step is diagnosing the underlying physics through data analysis and idealized models to isolate the essential physical processes. My research boils down to two questions: What is the North Pacific Ocean doing and why it is doing it?
One of the exciting things about physical oceanography is the wealth of observations that are available and the clever measurement techniques these employ. As part of a project I was involved in during my PhD research at the University of Rhode Island, 11 CPIES were deployed under the Kuroshio in the East China Sea. A CPIES is a package of electronics housed in a glass ball. This instrument can rest on the seafloor for a year or two (or, as battery technology improves, for 3 or 4 years). Every hour it pings and then listens for the echo of that ping reflecting off the sea surface. By measuring the time between a ping and its echo, the instruments allow us to deduce the temperature and salinity of the overlying water column. These are key measurements, because with them and the help of very sensitive pressure gages on the CPIES, we can calculated the transport – that is, we can calculate how much water is flowing in a current like the Kuroshio.
Other rich data sets are available to help answer the “what is the North Pacific doing”-question. Over the years, the ocean has been probed again and again by hydrocasts, each one helping to characterize the vertical distribution of salinity and temperature. In addition, remote data are collected by satellites, providing continual observations of the sea surface height and wind stress on the ocean.
Careful analysis of these data, combined with idealized models, will lead to a better understanding of the nature of North Pacific variability and a more complete picture of the global climate system.