Paleofire, Vegetation, and Climate Reconstructions of the Middle to Late Holocene From Lacustrine Sediments of the Toushe Basin, Taiwan

<p>We identified four climatic stages between 6.2 and 1.3 cal kyr before present (BP) based on pollen and charcoal concentrations by high‐resolution Accelerated mass spectrometer (AMS) <sup>14</sup> C‐dated sediment profile from Taiwan's Toushe Basin. From 6.2 to 4.6 cal kyr BP, the region was warm‐wet with infrequent wildfires and dominant subtropical evergreen broad‐leaved forests. The climate was cooler‐drier from 4.6 to 3.0 cal kyr BP, with a decline in forest and increased fire frequency. From 3.0 to 2.1 cal kyr BP,climate further cooled and dried, with the development of alpine meadows and higher fire frequency. The region became warmer and wetter from 2.1 to 1.3 cal kyr BP, accompanied by forest recovery. Climatic changes were linked to changes in East Asia Summer Monsoon intensity,which is mainly controlled by solar radiation. Wildfires were likely controlled by precipitation variability that is influenced by East Asia Summer Monsoon and El Niño–Southern Oscillation. Toushe Basin experienced drought conditions and frequent wildfires during the El Niño years.</p>

Monsoonal Influences on Offshore Rapid Intensification of Landfalling Typhoons in a Sheared Environment over the South China Sea

Tropical cyclones (TCs) formed in the western North Pacific and South China Sea can undergo rapid intensification (RI) shortly before making landfall in China. Forecasting such offshore RI is a great challenge in operations. In this study the offshore RI events in a sheared environment are examined for TCs that made landfall in China during 1979–2017. It is found that there were only three offshore RI events in a sheared environment, all of which occurred to the south of Hainan Island within the monsoon trough in early to mid-July, coinciding with the termination of the mei-yu season. The specific geographic location and timing of the occurrence of the offshore RI in the sheared environment is associated with the adjustment of the East Asia summer monsoon system when the mei-yu season terminates in the Yangtze River valley. In addition to the adjustment favorable for TC intensification by enhancing the TC–trough interaction in the upper troposphere, this study suggests that two environmental factors also contribute to the offshore RI over the South China Sea in a sheared environment. One is the intrusion of dry air associated with the western North Pacific subtropical high (WNPSH) and the other is the penetration of the water vapor flux associated with the monsoon surge. The adjustment of the East Asia summer monsoon system allows the water vapor flux of the monsoon surge to penetrate the TC circulation and prevents the dry air of the WNPSH from intruding into the TC circulation.

The Influences of Tropical Volcanic Eruptions with Different Magnitudes on Persistent Droughts over Eastern China

In this study, the influences on persistent droughts over Eastern China from tropical volcanic eruptions with three categories of magnitudes, i.e., 25 Tg, 50 Tg, and 100 Tg, were investigated through three groups of volcanic sensitivity experiments based on the Community Earth System Model (CESM). The results showed that, the 25 Tg tropical volcanic eruptions are too weak to significantly influence the regional precipitation changes over Eastern China, while the 50 Tg tropical volcanic eruptions can strongly intensify droughts and prolong the drought conditions for about five years. Both the extension and intensification of the drought conditions induced by 100 Tg tropical volcanic eruption are the largest among the three sensitivity experiments. These drought conditions are mainly caused by the weakened East Asia Summer Monsoon (EASM), and their extension and intensification depend on the strength of the volcanic eruptions. The intensities of weakened EASMs after volcanic eruptions are associated with the distinct ocean–land thermal contrast after eruptions. The ocean–land thermal contrast is the largest after the 100 Tg tropical volcanic eruptions, while it is much weaker after the 25 Tg volcanic eruptions. The durations of drought extensions are determined by the recovery rates of the West Pacific Subtropical High (WPSH), which are associated with the magnitudes of the volcanic eruptions.

Lagged variation of moisture conditions in central Asia compared with monsoonal Asia during the last four interglacials

Previous research has indicated that variations in moisture conditions in arid central Asia (ACA) were out-of-phase with those of monsoonal Asia during the Holocene. In order to investigate this phenomenon, we compared the pattern of moisture variations in ACA and the region dominated by the East Asia summer monsoon (EASM) during the last four interglacials. The results indicate that moisture variations in ACA lagged those in the EASM region by ~ 6 kyr during MIS 5, by −3 kyr during MIS 7, by 3 kyr during MIS 9, and by 7 kyr during MIS 11. We suggest that this lagged pattern in three out of four interglacials was the result of a zonal climatic teleconnection, westerly wind intensity, and evaporation upstream. Overall, our results shed new light on the climatic variability of central Asia and its origins during the Holocene.