Seasonal persistence of soil moisture anomalies related to freeze\u2013thaw over the Tibetan Plateau and prediction signal of summer precipitation in eastern China

Kai Yang,Chenghai Wang

doi:10.1007/s00382-019-04867-1

Abstract

Soil moisture can be an effective climate prediction signal due to its long memory. This study investigated seasonal persistence of soil moisture anomalies from the preceding autumn to spring dominated by the soil freeze–thaw (FT) process over the Tibetan Plateau (TP), and their relationship with summer precipitation in eastern China. Results demonstrated that soil moisture anomalies from the preceding autumn can persist until spring by water storage effect of the soil FT process. Soil moisture in the TP during the preceding autumn and winter had similar climatic effects as spring soil moisture. Positive soil moisture anomalies in the eastern TP during the spring led to less summer precipitation in south China and the Yellow River basin, and more summer precipitation in the Yangtze River basin and northeast China. A possible mechanism for this was that wetter soil moisture anomalies from the preceding autumn were stored in the soil by soil freezing, and were released with soil thawing in the spring, inducing surface diabatic heating anomalies over the TP. These anomalies then persisted into summer and enhanced the TP’s thermal forcing to the subtropical westerlies and affected stationary Rossby wave train propagation in middle latitudes, particularly on the northwest and northeast sides of the TP. This study suggests that most of spring soil moisture anomalies signal contains the preceding two seasons’ soil moisture anomalies information; therefore, summer precipitation predicting signals can be obtained from soil moisture anomalies from the preceding autumn, which could lengthen the seasonal climate prediction period.

Highlights

Seasonal climate prediction is a challenging issue, in which finding a robust signal connected with precipitation or temperature variability on seasonal scale is crucial
We investigate the relationship between soil moisture anomalies over the Tibetan Plateau (TP) in seasons before spring and subsequent summer precipitation in eastern China (EC) and explore possible physical mechanisms by which soil moisture anomalies persisting from preceding seasons affect summer precipitation in EC
When preceding winter [December–January–February (PDJF) (SE_PDJF) and preceding autumn [September–October–November (PSON) (SE_PSON) soil moisture were increased in the eastern part of the TP, simulated summer precipitation anomaly patterns (Fig. 5c, d) were similar to the SE_MAM simulations

Summary

Introduction

Seasonal climate prediction is a challenging issue, in which finding a robust signal connected with precipitation or temperature variability on seasonal scale is crucial. Summer precipitation over EC is closely related to spring soil moisture anomalies on the Tibetan Plateau (TP; Chow et al 2008; Wang et al 2009; Li and Wang 2016) These studies have suggested that soil moisture during the spring could be a signal for summer climate prediction (e.g., Koster et al 2003; Ma et al 2000; Guo et al 2007). We investigate the relationship between soil moisture anomalies over the TP in seasons before spring (autumn and winter in the previous year) and subsequent summer precipitation in EC and explore possible physical mechanisms by which soil moisture anomalies persisting from preceding seasons affect summer precipitation in EC Elucidating these aspects would benefit seasonal climate prediction and deepen understanding of FT’s role in land–atmosphere interactions.

Data and methodology

Experiment design

Results

Discussion and conclusions