Remote Effects of Tibetan Plateau Spring Land Temperature on Global and Regional Summer Precipitation ---- The GEWEX/ LS4P Phase I Highlight

Dr. Kuo-Nan Liou has made pioneering contributions to atmospheric physics and his works in atmospheric radiation have been followed by numerous research in the fields. He is also a great educator in training a large number of students and young scientists through his rigorously scientific training and encouragement in pursuing new innovative ideas in the scientific research. When the research on land-atmosphere interaction just started to emerge during the early 1980s, he had instructed me to pursue this field and eventually led to a paper in the Journal of Climate in 1990, which was the first research at that time using a vegetation model to study the effect of land use and land cover change on the Sahel climate, which now became a field with numerous researches. Dr. Liou had a far-reaching vision that had gone through his entire research career and was one of the earliest explorers in the field of land-atmosphere interaction study when it was just at its infant stage.

Since then, the land-atmosphere interaction studies have made great progress. In recent years, in addition to the land surface processes’ local and regional effects, studies have revealed that the land surface processes have had remote effects on precipitation and atmospheric circulation at global scale. This presentation reports the results from the GEWEX/LS4P (Impact of initialized land temperature and snowpack on sub-seasonal to seasonal prediction) Initiative, which aims to improve the subseasonal to seasonal prediction (S2S) over different regions through initialization of large-scale land surface temperature (LST)/subsurface temperature (SUBT) over high elevation regions in climate models. The LS4P Phase I (LS4P-I) experiment focused on the Tibetan Plateau (TP) LST/SUBT contribution for subseasonal-to-seasonal (S2S) predictability. The summer 2003, when there was a severe drought/flood over the southern/northern part of the Yangtze River basin, respectively, has been selected as the focus case. The cause of the 2003 drought has never been identified. More than forty institutions worldwide have participated in this effort, many of which are the major climate/weather centers.

With the newly developed LS4P initialization method for TP land temperature, the observed surface temperature anomaly over the TP has been partially produced by the LS4P-I model ensemble mean, and 8 hotspot regions in the world were identified where June precipitation is significantly associated with anomalies of May TP land temperature. Consideration of the TP LST/SUBT effect has produced about 25%-50% of observed precipitation anomalies in most hotspot regions. A TP- RM (Rocky Mountains) Circumglobal (TRC) wave train has also been identified. The multiple models have shown more consistency in the hotspot regions along the TRC wave train. This study suggests that the TP LST/SUBT effect is a first-order source of S2S precipitation predictability, comparable in magnitude to that of the sea surface temperature effect.