Spring Land Temperature in Tibetan Plateau and Global-Scale Summer Precipitation: Initialization and Improved Prediction

Abstract

Subseasonal-to-seasonal (S2S) precipitation prediction in boreal spring and summer months, which contains a significant number of high-signal events, is scientifically challenging and prediction skill has remained poor for years. Tibetan Plateau (TP) spring observed surface temperatures show a lag correlation with summer precipitation in several remote regions, but current global land-atmosphere coupled models are unable to represent this behavior due to significant errors in producing observed TP surface temperatures. To address these issues, the Global Energy and Water Exchanges (GEWEX) program launched the “Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal-to-Seasonal Prediction” (LS4P) initiative as a community effort to test the impact of land temperature in high mountain regions on S2S prediction by climate models: more than 40 institutions worldwide are participating in this project. After using an innovative new land state initialization approach based on observed surface 2-meter temperature over the TP in the LS4P experiment, results from a multi-model ensemble provide evidence for a causal relationship in the observed association between the Plateau spring land temperature and summer precipitation over several regions across the world through teleconnections. The influence is underscored by an out-of-phase oscillation between the TP and Rocky Mountain surface temperatures. This study reveals for the first time that high mountain land temperature could be a substantial source of S2S precipitation predictability, and its effect is probably as large as ocean surface temperature over global “hot spot” regions identified here; the ensemble means in some “hot spots” produce more than 40% of the observed anomalies. This LS4P approach should stimulate more follow-on explorations.

Near-global Summer Circulation Response to the Spring Surface Temperature Anomaly in Tibetan Plateau ---- The GEWEX/LS4P Phase I experiment

“…For these regions, the TP LST/SUBT anomaly is the first order source of the S2S variability, comparable with the influence of SST. Among these connections, a strong linkage between the spring TP LST/SUBT and the summer precipitation over the west of North America was found, and a Tibetan Plateau-Rocky Mountain Circumglobal (TRC) wave train from the TP through northeast Asia and Bering Strait to the west of North America had been identified for the first time based on the reanalysis data and suggested to be responsible for the formation of most of the hotspots (Xue et al, 2022;. Although the teleconnections caused by the heating due to oceanic temperature anomalies, such as those between ENSO and the Asian monsoons, have been extensively investigated (e.g., Wang et al 2000;Li et al 2007;Li et al 2017), the remote effects of mountain heating on global atmospheric circulations have not been fully studied.…”

Atmospheric response to wintertime Tibetan Plateau cold bias in climate models

“…Considering the importance of the Central Asia orography for the climate of the Asia / Pacific sector, it is not surprising to find examples in literature where orographic surface and near-surface conditions (contributing to the tropospheric heat sources or sinks, Yanai et al, 1992) have an impact on the atmospheric conditions downstream. Indeed, evidence is found on the relevance of spring and summer temperatures over Asian orography for the successive atmospheric conditions far downstream (see Wu et al (2015) for a review and Xue et al (2021Xue et al ( , 2022 for recent work on the impact of spring TP land initialisation in subseasonal-to-seasonal predictions). In the extended winter season (October-March) the presence of anomalous snow cover changes the tropospheric energy budget through an increase of the surface albedo, enhancing the reflection of shortwave radiation and the cooling of the land surface and the atmosphere (Yeh et al, 1983).…”

Improved Subseasonal-to-Seasonal Precipitation Prediction of Climate Models with Nudging Approach for Better Initialization of Tibetan Plateau-Rocky Mountain Circumglobal Wave Train and Land Surface Conditions

“…The Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction (LS4P) project of the Global Energy and Water Exchanges (GEWEX) program aims to study the impact of springtime land surface temperature (LST)/subsurface temperature (SUBT) anomalies over high mountain areas on summertime precipitation prediction locally and remotely, and to improve process understanding of the driving mechanism (Xue et al, 2021(Xue et al, , 2022. During LS4P Phase I, twentyone climate models participated in simulating the precipitation response in June 2003 to LST/SUBT anomalies over the Tibetan Plateau (TP) in May 2003.…”