It is important to understand the dynamical processes that cause heat waves at regional scales. This study examined the physical mechanism that was responsible for a heat wave in South Korea in August 2016. Unlike previous August heat waves over the Korean Peninsula, the intensity of the geopotential height over the Kamchatka Peninsula in August 2016 was the strongest since 1979, which acted as an atmospheric blocking in the downstream region of the Korean Peninsula. Therefore, the anomalous high geopotential height in Mongolia, where the surface temperature was quite high, was observed persistently in August 2016. This anomalous high in Mongolia induced northerly winds with warm temperatures onto the Korean Peninsula, which contributed to a heat wave in August 2016. We further showed that the anomalous high geopotential height over the Kamchatka Peninsula in August 2016 was triggered by strong convection in the western-to-central subtropical Pacific through atmospheric teleconnections, which was quite different from a typical heat wave over the Korean Peninsula, in which convective forcing around the South China Sea is strong. This implies that convective forcing in the subtropical Pacific should also be monitored to predict heat wave events in East Asia, including South Korea. On the other hand, the zonal wave train associated with the circumglobal teleconnection pattern is also associated with the anomalous high geopotential height around Mongolia and the Kamchatka Peninsula, which may have contributed to the heat wave in August 2016.
This study analyzes differences in the mechanisms leading to anomalously high‐temperature weather events, such as heat waves and tropical nights, in Korea. We identify pure heat wave and pure tropical night events during the period from 1979 to 2016. Based on composite analyses for each case, we identify different mechanisms leading to pure heat waves and pure tropical nights. The structures including low‐level atmospheric circulations, specific humidity, wind, and the atmospheric stability are quite different between pure heat waves and pure tropical nights. Pure heat waves occur under barotropic‐like atmospheric conditions, with a stable low layer and dry air due to anomalous easterly winds over the Korean Peninsula. In contrast, pure tropical nights occur under baroclinic‐like atmospheric conditions, with warm, humid air advected by southwesterly winds. These results indicate that above‐normal levels of incoming shortwave radiation combined with adiabatic warming contribute to pure heat waves, whereas pure tropical nights are associated with above‐normal longwave radiation and/or warm advection over the Korean Peninsula. This implies that different physical factors must be considered for accurate, regional‐scale predictions of heat waves and tropical night events.
The authors investigated the inter-basin interactions between the Pacific and Atlantic Oceans depending on the phase relationship of Pacific decadal oscillation (PDO)/Atlantic multi-decadal oscillation (AMO) based on observations and idealized model experiments. When the AMO and the PDO are in-phase (i.e., +PDO/+AMO or −PDO/-AMO), the Pacific Ocean regulates the SST anomalies in the equatorial Atlantic Ocean with altering a Walker circulation. During this period, there is a negative SST-precipitation relationship in the equatorial Atlantic Ocean where the atmosphere forces the ocean. In contrast, when they are out-of-phase (i.e., either +PDO/-AMO or −PDO/+AMO), the Atlantic Ocean influences the equatorial Pacific Ocean by modifying Walker circulation, resulting in a westward shift of a center of convective forcing in the equatorial Pacific Ocean compared to that during an inphase relationship of PDO/AMO. During this period, a positive SST-precipitation relationship is dominant in the equatorial Atlantic Ocean where the ocean forces the atmosphere. To verify this result, we conducted pacemaker experiments using the Nanjing University of Information Science and Technology Earth System Model version 3 (NESM3). Model results supported our findings obtained from the observations. We infer that the characteristics of the Pacific-Atlantic inter-basin interactions depend on whether the PDO and AMO phases are either in-phase or out of phase.
Here we analysed the long‐term change in extreme hot days (EHDs) in East Asia during boreal summer (June–July–August) since 1979, where EHDs was defined as days exceeding or equalling the 90th percentile threshold of the climatological (1991–2020) daily Tmax and Tmin. EHDs frequency occurrence in East Asia during summer showed not only an increasing trend but also a distinct regime shift increase since the late 1990s. Based on this regime shift, we divided these years into two periods, P1 (1979–1998) and P2 (1999–2021), and found that different physical processes operated for each period's EHDs variability. P2's EHDs was related to the stationary wave originating from both the North Atlantic Ocean and the Indo‐Pacific warm pool, but these influences did not appear in P1. To investigate whether the observed regime shift increase was caused by natural variability or greenhouse gas concentration increases, we conducted a CO2 quadrupling experiment as well as a present‐day experiment with a fixed CO2 concentration using the Community Earth System Model with 28 ensemble members. We demonstrated that the regime shift increase of East Asian EHDs occurrences was due to increasing greenhouse gas concentrations. We further discussed the influence of Arctic sea ice reduction due to global warming on EHDs occurrences in East Asia.
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