Are Peak Summer Sultry Heat Wave Days over the Yangtze–Huaihe River Basin Predictable?

Abstract

The Yangtze–Huaihe River basin (YHRB) is the core region of sultry heat wave occurrence over China during peak summer [July and August (JA)]. The extremely hot and muggy weather is locally controlled by a descending high pressure anomaly connected to the western Pacific subtropical high. During 1961–2015, the heat wave days (HWDs) in JA over the YHRB exhibit large year-to-year and decadal variations. Prediction of the total number of HWDs in JA is of great societal and scientific importance. The summer HWDs are preceded by a zonal dipole SST tendency pattern in the tropical Pacific and a meridional tripole SST anomaly pattern over the North Atlantic. The former signifies a rapid transition from a decaying central Pacific El Niño in early spring to a developing eastern Pacific La Niña in summer, which enhances the western Pacific subtropical high and increases pressure over the YHRB by altering the Walker circulation. The North Atlantic tripole SST anomalies persist from the preceding winter to JA and excite a circumglobal teleconnection pattern placing a high pressure anomaly over the YHRB. To predict the JA HWDs, a 1-month lead prediction model is established with the above two predictors. The forward-rolling hindcast achieves a significant correlation skill of 0.66 for 1981–2015, and the independent forecast skill made for 1996–2015 reaches 0.73. These results indicate the source of predictability of summer HWDs and provide an estimate for the potential predictability, suggesting about 55% of the total variance may be potentially predictable. This study also reveals greater possibilities for dynamical models to improve their prediction skills.

Two Types of Heat Wave in Korea Associated With Atmospheric Circulation Pattern

“…Meanwhile, previous studies on heat waves in eastern China, which is close to Korea, highlighted the role of North Atlantic Oscillation (NAO) in affecting heat waves through Rossby wave train that consists of successive high‐ and low‐pressure anomalies from North Atlantic Ocean to Eurasian continent (Gao et al, ; Sun, ). Moreover, Lee et al () recently reported that the high‐pressure cores of midlatitude zonal wave number 5 pattern coincide with regions of frequent occurrence of heat wave.…”

Roles of the Tropical/Extratropical Intraseasonal Oscillations on Generating the Heat Wave Over Yangtze River Valley: A Numerical Study

“…Yangtze River valley (YRV) is the core region for the occurrence of HW in China (Gao, Yang, et al, ). Many previous studies have widely addressed how HW events in this region are generated from the perspective of the anomalous large‐scale features of atmospheric circulation (e.g., Freychet et al, ) and anomalous boundary characteristics in observational diagnostics (Hu et al, ; Gao, Wang, et al, ).…”

Predictability of the mid‐summer surface air temperature over the Yangtze River valley in the National Centers for Environmental Prediction Climate Forecast System

“…In the tropical Pacific, the anomalous warm SST is located in the central and eastern equatorial Pacific in early spring (Figure 9a), and evolves into the anomalous cold SST in mid‐summer (Figure 9b), which continues to enhance from summer to the following early winter (Figure 9c). This finding suggests that the decaying El Niño in early spring and the developing La Niña in summer promote positive SAT anomalies over the YRV through the enhancement and long‐term maintenance of the WPSH (Du et al ., 2009; Wu et al ., 2009; Xie et al ., 2009; Wang et al ., 2013; Gao et al ., 2018). On the other hand, SST anomalies in the North Atlantic present a meridional “warm‐cold‐warm” pattern similar to the North Atlantic tripole in early spring (Figure 9a).…”