An interdecadal decrease in extreme heat days in August over Northeast China around the early 1990s

Northeast China(NEC)witnessed an interdecadal increase in summer extreme heat days(EHDs)around the mid-1990s.The current study reveals that this interdecadal increase only occurs in June and July,while August features a unique interdecadal decrease in EHDs around the early 1990s.Plausible reasons for the interdecadal decrease in EHDs in August are further investigated.Results show that the interdecadal decrease in EHDs in August is due to the deceased variability of daily maximum temperature(Tmax).Overall,the variation of the Tmax over NEC in August is modulated by the Eurasian teleconnection pattern,Silk Road pattern,and East AsiaPacific pattern.However,the influence of the Silk Road pattern dramatically weakens after the early 1990s because the meridional wind variability along the westerly jet significantly decreases.The weakened influence of the Silk Road pattern contributes to the decreased Tmax variability over NEC.Meanwhile,the convection over the western North Pacific,which accompanies the East Asia-Pacific pattern,presents a significant decrease in variance after the early 1990s,further decreasing the Tmax variability over NEC.

Causes of the Extreme Hot Midsummer in Central and South China during 2017:Role of the Western Tropical Pacific Warming

This study investigates why an extreme hot midsummer occurred in Central and South China(CSC) during 2017. It is shown that the western North Pacific subtropical high(WNPSH) was abnormally intensified and westward-extending,resulting in anomalous high pressure and consequent extreme heat over CSC. The abnormal WNPSH was favored by the warming of the western tropical Pacific(WTP), which was unrelated to ENSO and manifested its own individual effect.The WTP warming enhanced the convection in-situ and led to anomalous high pressure over CSC via a local meridional circulation. The influence of the WTP was confirmed by CAM4 model experiments. A comparison between the 2017 midsummer and 2010 midsummer(with a stronger WNPSH but weaker extreme heat) indicated that the influence of the WNPSH on extreme heat can be modulated by the associated precipitation in the northwestern flank.The role of the WTP was verified by regression analyses on the interannual variation of the WTP sea surface temperature anomaly(SSTA). On the other hand, the WTP has undergone prominent warming during the past few decades, resulting from decadal to long-term changes and favoring extreme warm conditions. Through a mechanism similar to the interannual variation, the decadal to long-term changes have reinforced the influence of WTP warming on the temperature over CSC,contributing to the more frequent hot midsummers recently. It is estimated that more than 50% of the temperature anomaly over CSC in the 2017 midsummer was due to the WTP warming, and 40% was related to the decadal to long-term changes of the WTP SSTA.

Heat waves in summer 2022 and increasing concern regarding heat waves in general

The year 2022 featured an unprecedented hot summer that has attracted worldwide attention.Abnormal warming spread over most of the Eurasian continent and North America(Fig.1),with Europe and China especially suffering from extraordinarily long-lasting extreme heat events.In addition,severe droughts,which are a common accompaniment to heat waves,attacked Europe and the Yangtze River basin in China.Droughts in Sichuan Province,which is in the upstream region of the Yangtze River basin and is proud of its water resources and hydro power,led to power shortages and adverse effects on the lives and productivity of local people.Extremely high temperatures and severe drought induced massive wildfires in Europe,North America,and Asia,including Chongqing(Fig.2),a neighboring municipality of Sichuan Province.

Effects of Tropical Cyclone Activity on the Boundary Moisture Budget over the Eastern China Monsoon Region

In summer, water vapor over the eastern China monsoon region （ECMR） comes mainly from low latitudes and is modu- lated by tropical cyclone （TC） activity in East Asia （EA）. This study examines the variability of water vapor transport over the ECMR, especially of the moisture inflow via the southern and eastern boundaries. The results of composite and correlation analyses, using data from 1979 to 2010, reveal significant differences in moisture budgets along the boundaries between TC days and non-TC days. Almost 80% of the water vapor transport via the eastern boundary occurs during TC days, while at the southern boundary most inflow occurs on non-TC days. The ratio of the total water vapor transport between TC and non-TC days is about 4：6. In addition, the E1 Nifio-Southem Oscillation （ENSO） exhibits a remarkable influence on moisture trans- port over EA and the contributions of moisture inflow on TC days increase （reduce） in E1 Nifio （La Nifia） years. Moreover, different types of TCs, based on their tracks, have different effects on the moisture budgets along the southern and eastern boundaries. When TCs enter EA （but not the ECMR）, they favor the moisture inflow via the eastern boundary and hinder the moisture inflow via the southern boundary. After TCs enter the ECMR, the inhibition of moisture inflow via the southern boundary will be weakened, and more water vapor can be brought into the ECMR. For some recurring TCs with an increase in TC activity in the midlatitudes, the influence is uncertain in different cases. The results herein suggest that TC activity is an important factor that influences the boundary moisture budgets in the ECMR.