As a postdoctoral researcher at University of Washington, I have focused my
attention on the long-term trend of Southern Hemisphere (SH) circulation and the recent significant
changes of the Antarctic cryosphere. Published results regarding recent changes of SH climate have
mostly focused on the trend in austral summer, which has been widely believed to be anthropogenic in origin.
Climate variability in the SH and the Antarctica in other seasons has received much less attention. To make
progress, my coauthors and I used observational data and a climate model to understand the cause of the warming
trend in West Antarctica<6> and the Antarctic Peninsula<7> in recent decades during the non-summer seasons, as well as
the accelerated melting rate of Pine Island Glacier since 1980s<8>,<9>. We found that the low frequency SST variability
in the central tropical Pacific play a key role in warming the Pacific sector of Antarctica through generating a Rossby wave train.
A further look at the Southern Annular Mode (SAM), the leading mode of SH circulation variability,
indicates an important impact of the tropical forcing on the SAM on both interannual and long term variability<10>. Thus,
we suggest that the SAM should be redefined as a combination of an extratropical circulation response to the external tropical
forcing and an intrinsic mode of the high-latitude basic state. We also suggest that besides the anthropogenic forcing, the
tropical SST variability also exerts a significant impact on the recent trend of SH circulation.
The second project has been to understand the multi-decadal and centennial variability of the stable isotope
ratios of water (?D and ?18O) recorded in the Antarctic ice-core data<11>,<12>. I used an isotope-enabled global climate model to
reproduce ?D and ?18O in Antarctica. The experiment with observed tropical SSTs as the boundary condition can accurately simulate
the observed ?18O over West Antarctica in the last 100 years, supporting our early work that the tropical SST variability is
essential to drive low-frequency climate variability in West Antarctica.
Using the same model, my coauthors and I have performed and analyzed experiments to illuminate the impact of
precessional forcing and glacial forcing on the climate and the isotopic composition of precipitation. We have also initiated a
series of experiments to illuminate the impact of the evolution of the continental geometry and orography of Southern Asia on the
regional and global climate and the isotopic composition of precipitation. These experiments feature realistic and idealized
scenarios covering the past 50 million years, and are designed to isolate the impacts of evolving orography and continental geometry.
We are collaborating with several geology groups around the country and this is an exciting extension of my research approach to
more general problems in Earth System Science.
My current research also includes an ongoing project to understand the significant warming and sea-ice reduction
in the Arctic in recent decades, especially after 1990s. We mainly examine this problem with a special emphasis on the connection
between the circulation change in the Arctic and the remote SST forcing. We have made some progress and the result will be reported
soon<13>.