Intraseasonal variation in extreme precipitation in southern China during winter 2015/16, and its precursors

Abstract

Extremely heavy rainstorms occurred over southern China during the winter of 2015/16, with record-breaking rainfall in the cold season. These extraordinary rainfalls were featured by pronounced intraseasonal variation in terms of both meridional displacement and amount of heavy precipitation. The main rain belt meandered around the lower reaches of the Yangtze River during December 2015, and then penetrated southward to the Pearl River basin with a dramatic increase in rainfall amount during January 2016. The intraseasonal features of heavy rainfall cannot be well explained by the quasi-steady El Niño condition, but are possibly governed by the circulation modulations at different latitudes. The transition of anomalous height from low to high over the Urals brought strong cold air outbreaks and therefore southward displacement of the main rain belt. This transition together with increased southwesterly flows in front of the deepened India-Burma trough led to strong moisture convergence and thus torrential rains during January 2016. These circulation transitions might be related to certain changes in the preceding ocean conditions. A negative Arctic sea-ice anomaly to the west of 90°E persisted throughout the winter, while the previously excessive Arctic sea ice over east of 100°E vanished in November 2015. This conversion from dipole to monopole structure of sea-ice anomalies could favor the development of the Ural highs and enhancement of cold air intrusion from the expanded Siberian highs. Additionally, the deepened India-Burma trough and further intensified southwesterly flows might be related to the warming sea surface temperature over the tropical Indian Ocean.