PP53D-08
A Millennial Simulation of Isotope-Enable GCM with a Special Focus on Antarctic Climate Variability in the Past 1,000 Years
Friday, 18 December 2015: 15:25
2012 (Moscone West)
Qinghua Ding, Polar Science Center, Seattle, WA, United States, Eric J. Steig, University of Washington, Earth and Space Sciences, Seattle, WA, United States and Martin Werner, awi, potsdam, Germany
Abstract:
Our knowledge of changes in Southern Hemisphere (SH) circulation during the last millennium is extremely limited in comparison to the Northern Hemisphere (NH) because of the low density of proxy records in the SH. This period provides a good opportunity for placing the recent and twentieth-century SH circulation change into a longer term context and examining the effect of both the anthropogenic and natural external forces on SH circulation. The instrumental data in the SH can provide only at most 100 years of climate information back to the early twentieth century. Thus, we have to rely on various paleoclimate proxy data to evaluate the model’s millennial simulation. Several scientific works have pointed out the existence of climate changes in Antarctica, Australia, New Zealand, and South America and their relationships to the Medieval Warm Period (MWP) and Little Ice Age (LIA). There is an advantage to directly comparing model-generated δ18O and observed δ18O in the ice core. However, the models used to produce the millennial simulations in the AR5 and most model comparison projects do not have the ability to produce water isotopes. So a direct comparison between ice-core data and the millennial simulations is impossible. To fill this gap, we take a new approach to generate an Antarctica-wide δ18O field associate with each millennial run. Using the 100 to 200 year climatology of SSTs and sea-ice conditions during three key periods—MWP (1000-1200), LIA (1500-1700), and PWP (1850-present)—generated by existing millennial run to force our isotope GCM model. To better include the meteorological information in our new experiment, corresponding atmospheric states (U, V and T) for each period could also be retrieved from these existing runs, and the atmospheric field of our isotope-enable GCM can be nudged onto this meteorological pattern. Through this method, we can roughly produce a virtual δ18O pattern in Antarctica for each millennial run, which allows us to directly compare it with ice-core data in Antarctica. Thus, a qualitative evaluation of millennial run is feasible for three key periods (WMP, LIA, PWP) by comparing the model simulations and δ18O of ice-core data in Antarctica.
