Abstract:

The dominant sea surface temperature anomaly (SSTa) modes of decadal and interannual variations in summer precipitation over the eastern part of Northwest China (ENC) were here analyzed by power spectrum and composite analyses. The summer precipitation averaged at 155 stations over the ENC, the monthly SSTa, and circulation reanalysis data from 1961 to 2020 were used. The SSTa predictors before and after the timescale decomposition were obtained to establish precipitation prediction models by using linear regression. The results showed that the summer precipitation over the ENC has not only an decadal period of about 30 years but also a 3-year interannual cycle. The Pacific Decadal Oscillation (IPO) has played a leading role in decadal variations in summer precipitation. The positive phase of IPO in the precedent spring is conducive to more precipitation; meanwhile, it is in the background of less precipitation. The tropical Indian Ocean, the tropical western Pacific, and the North Atlantic provide interannual SSTa signals. The negative (positive) phase of tropical Indian Ocean SSTa, the positive (negative) phase of the Atlantic tripole SSTa, and the cold (warm) SSTa in the tropical western Pacific Ocean in the precedent spring, corresponding to the high (low) pressure anomalies over Lake Balkhash in mid- to high latitudes, with northward (southward) and weak (strong) characteristics in the subtropical High over the Western Pacific, favor less (more) summer precipitation over the ENC. Moreover, taking the decadal and interannual variations of SSTa into account can potentially contribute to improving forecasting of summer precipitation over the ENC, with the annual average Ps and Pc scores during the independent test samples based on the scale decomposition model being 6% and 7% higher than those in the original model, respectively.

Key words: time-scale decomposition, sea surface temperature mode, the eastern part of Northwest China, precipitation prediction