Global Atmospheric Responses to Observed Tibetan Plateau Snow Anomalies in Winter and Spring

Impacts of winter/spring snow anomalies over the Tibetan Plateau (TP) on the Asian summer monsoon have been extensively studied. Instead, our recent studies have investigated global atmospheric responses to satellite-derived TP snow anomalies in winter and spring using multiple ensemble transient integrations of the CAM4 and CLM4.0 models. In various forcing experiments, model boundary conditions are based on climatological sea ice extent and sea surface temperature, and satellite observations of snow cover extent (SCE) and snow water equivalent (SWE) over the TP, and with model derived SCE and SWE elsewhere.

In our 2017 study, model boundary snow conditions are based on satellite observations of SCE and SWE over the Tibetan Plateau (TP) and Mongolia from October to March in 1997/98 (heavy TP and light Mongolia snow) and 1984/85 (light TP and heavy Mongolia snow). The ensemble-mean difference between simulations with these heavy and light snow states identifies local, distant, concurrent, and delayed climatic responses. The simulated atmospheric responses to a dipole of high TP and low Mongolia SCE persisting from October to March include a winter positive Pacific-North America (PNA)-like response, which demonstrates that large positive snow cover anomalies over the TP in autumn and winter can cause a significant hemispheric PNA-like response in winter, as suggested in our 2011 observational study.

In our 2019 study, model ensemble simulations are forced by satellite-derived observed March to May TP SCE and SWE in heavy or light TP snow years. Six March-May spring periods are chosen, specifically, 1981, 1983 and 1998 with persistent heavy SCE and SWE over the TP, and 1984, 1985 and 1992 with persistent light SCE and SWE over the TP. Simulations show that heavy spring TP snow causes significant tropospheric cooling from the TP into the North Pacific, and induces a negative North Pacific Oscillation (NPO)/West Pacific (WP)-like teleconnection response throughout the troposphere and stratosphere in spring. Atmospheric responses also include significantly increased Pacific trade winds, a strengthened Intertropical Convergence Zone over the equatorial Pacific Ocean, and an enhanced local Hadley circulation, indicating a near-global impact of the TP snow anomaly.

These results indicate the significant role of TP snow anomalies in global climate variability, and highlight the need for dynamical prediction systems to correctly represent and forecast the evolution of TP snow variability for improving their skill at predicting the surface climate.

References:

• Wu, Q., H. Hu and L. Zhang, 2011: Observed influences of autumn-early winter Eurasian snow cover anomalies on the hemispheric PNA-like variability in winter. Journal of Climate, 24, 2017-2023.
• Liu, S., Q. Wu*, X. Ren, Y. Yao, S. R. Schroeder and H. Hu, 2017: Modeled Northern Hemisphere autumn and winter climate responses to realistic Tibet Plateau and Mongolia snow anomalies. Journal of Climate, 30, 9435-9454.
• Liu, S., Q. Wu*, S. R. Schroeder, Y. Yao, Y. Zhang, T. Wu, and L. Wang, 2019: Global Atmospheric Responses to Observed Tibetan Plateau Snow Anomalies. Revised manuscript submitted to Journal of Climate.