Abstract
Southern China (SC) is often subjected to the impacts of extreme heat-wave (EHW) events with hot days covering large areas and lasting extended periods in the boreal summer. The present study explores new objective identification methods of the EHW events and reveals the controlling factors of different spatial-temporal variations in shaping the EHW events over SC from 2000 to 2017 with in-situ observations and latest reanalysis. A compound index of the EHW (with impact area, duration, and magnitude) was defined to quantify the overall intensity of the EHW events in SC. It was found that synoptic variability and 10–30-day intra-seasonal variability (ISV) induce the onsets of the EHW events, while 30–90-day ISV shapes the durations. An innovative daily compound index was introduced to track the outbreak of the EHW events. The occurrences of the EHW in SC are coincident with the arrivals of intra-seasonal signals (e.g., the anomalies of outgoing long-wave radiation (OLR) and 500 hPa geopotential height) propagating from the east and south. About 12 days before the onset of the EHW in SC, the 10–30-day positive anomalies of 500 hPa geopotential height and OLR appear near the equatorial western Pacific, which then propagate northwestward to initiate the EHW in SC. At the same time, the 30–90-day suppressed phase propagates northeastward from the Indian Ocean to the SC to sustain the EHW events. On the interannual time scale, it was found that the EHW events in SC occurred in those years with robust warming of the western North Pacific in early summer (May and June) and warming of the equatorial eastern Pacific in the preceding winter (December, January, and February). An interannual sea surface temperature anomalous (SSTA) index, which adds together the SSTA over the above two regions, serves as a very useful seasonal predictor for the EHW occurrences in SC at least one-month ahead.
Highlights
A recent World Meteorological Organization report [1] has clearly shown that, in association with global warming, the occurrences of extreme meteorological events have increased steadily in past decades
The outgoing longwave radiation (OLR) daily mean data used in the study were acquired from the National Oceanic and Atmospheric Administration (NOAA), with a resolution of 2.5◦ × 2.5◦
When there are more than 10 adjacent stations whose daily maximum air temperature exceeds its own threshold of 90th percentile and lasts for more than 7 days, this event is defined as a heat-wave event in Southern China (SC)
Summary
A recent World Meteorological Organization report [1] has clearly shown that, in association with global warming, the occurrences of extreme meteorological events have increased steadily in past decades. 2003 summer, a severe heat-wave occurred over a large area from the south of the Yangtze River to the middle of Southern China (SC), which caused tremendous stresses on the local transportation, water, electricity and other urban operational lifelines as well as societal and economic activities [2] For such a heat-wave event, the days with maximum air temperature exceeding 38 ◦ C are 5–20-days more than the climatology. On subseasonal-to-seasonal time scales, Chen et al [5] pointed out that the daily air temperature and circulation anomalies over the SC exhibit fluctuations with a period of about 10 days, largely resulting from the influence of quasi-biweekly oscillation, which originates from the tropical western.
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