Variability of Summer Apparent Temperature in China

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ABSTRACT The apparent temperature (APT) has significant impacts on human health; however, its variability across China, in particular, based on in situ observations, remains unclear. Based on daily meteorological station observation datasets, this study analysed the variability and spatial distribution of summer APT in China during 1960–2019, which is a compound variable combining surface air temperature (SAT), relative humidity, and wind speed. The contribution of SAT, relative humidity, and wind speed to the variation of APT is examined. It is shown that the variation of SAT plays a determining role in the variation of APT, whereas it displays strong regional differences from the impacts of relative humidity and wind speed. The leading mode of APT displays a mono‐sign pattern throughout China, explaining 31.6% of the variance, which is significantly related to the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). The combination of the negative phase of PDO and the positive phase of AMO is associated with higher APT in China, whereas the negative AMO and positive PDO phases tend to accompany with lower APT. Results show that the combination of the opposite phases of AMO and PDO is associated with anomalous teleconnections and surface conditions. Anomalous cyclonic circulation is observed over China during the PDO–AMO+ phase, and abnormal thermal low pressure exists in the lower troposphere. Meanwhile, the soil moisture and cloud cover decreased, allowing more solar radiation to reach the ground. This causes an increase in SAT and water vapour convergence, resulting in an increase in the humidity and leading to an increase in APT. An opposite situation is found in the associated circulation pattern and surface conditions during the PDO + AMO‐phase, contributing to decreased APT. The above results provide scientific insights into the long‐term variability of summer APT in China, highlighting the modulation of natural variability in impacting the variation of summer APT over China.

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