Youbing Peng

Response of Summer Precipitation over Eastern China to Large Volcanic Eruptions

Studies of the effects of large volcanic eruptions on regional climate so far have focused mostly on temperature responses. Previous studies using proxy data suggested that coherent droughts over eastern China are associated with explosive low-latitude volcanic eruptions. Here, the authors present an investigation of the responses of summer precipitation over eastern China to large volcanic eruptions through analyzing a 1000-yr global climate model simulation driven by natural and anthropogenic forcing. Superposed epoch analyses of 18 cases of large volcanic eruption indicate that summer precipitation over eastern China significantly decreases in the eruption year and the year after. Model simulation suggests that this reduction of summer precipitation over eastern China can be attributed to a weakening of summer monsoon and a decrease of moisture vapor over tropical oceans caused by large volcanic eruptions.

The climate variability in northern Levant over the past 20,000 years

The Levant constitutes an important region for assessing linkages between climate and societal changes throughout the course of human history. However, large uncertainties remain in our understanding of the regions hydroclimate variability under varying boundary conditions. Here we present a new high-resolution, precisely dated speleothem oxygen-carbon isotope and Sr/Ca records, spanning the last 20 ka from Jeita Cave, northern Levant. Our record reveals a higher (lower) precipitation-evaporation (P-E) balance during the Last Glacial Maximum and Bolling interstadial (Heinrich stadial 1). The early-middle Holocene is characterized by a trend toward higher P-E state, culminating between similar to 7 and 6 ka. The middle-late Holocene is characterized by two millennial-length drier periods during 5.3-4.2 and 2.8-1.4 ka. On submillennial time scale, the northern Levant climate variability is dominated by 500 year periodicity. Comparisons with the regional proxy records suggest persistent out-of-phase climate variability between the northern and southern Levant on a wide range of timescales.

Climate variations of Central Asia on orbital to millennial timescales

The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia’s hydroclimate variability from Tonnel’naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel’naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.

Simulation of the Interdecadal Pacific Oscillation and its impacts on the climate over eastern China during the last millennium

The Interdecadal Pacific Oscillation (IPO) and its impacts on precipitation over eastern China during the last millennium are investigated through analyzing two 1000 year global climate model simulations. Results show that the model does not simulate a prolonged period of negative IPO before A.D. 1300 suggested by the proxy reconstruction, although it does simulate centennial periods of negative and positive IPO. The simulated IPO exhibits several low-frequency oscillations, including 10–23, 30–33, 35–70, and 85–110 years. However, it remains an open question whether simulated IPO oscillations longer than bidecadal mode can be or not be considered as essentially internal modes of variability. The simulations indicate that precipitation over eastern China is associated with the IPO. When the strongest IPO signal of 53–77 year oscillation occurs, the summer precipitation goes of opposite sign over North China (NC) and the middle and lower Yangtze River Vally (MLYRV), i.e., dipole mode such as the “flood-in-south and drought-in-north” pattern that occurs during the positive IPO episodes and vice versa. While coherent mode is dominant when the relatively weak IPO signal occurs, and warm phases of the IPO coincide with coherent drought and vice versa. The association between 53–77 year oscillation of the IPO and precipitation in NC is more marked than that in the MLYRV. Our results suggest that the internal variability of climate system like the IPO may play an important role in precipitation over eastern China, at least on the 53–77 year oscillation.

Simulated Interannual Teleconnection Between the Summer North Atlantic Oscillation and Summer Precipitation in Eastern China During the Last Millennium

The interannual teleconnections between the summer North Atlantic Oscillation and summer precipitation in eastern China over the last millennium are investigated in a 1,000-year simulation by the global climate model Community Climate System Model version 2.0.1. The model was able to roughly produce the general features of the teleconnection influences in eastern China, with negative (positive) precipitation anomalies north of 30°N and positive (negative) precipitation anomalies south of 30°N, associated with the positive (negative) phase of the North Atlantic Oscillation. The composite analysis reveals that the influence of the North Atlantic Oscillation on precipitation in summer in eastern China is chiefly via the “North Atlantic-Eurasian teleconnection pattern,” which extends from the subtropical North Atlantic to East Asia. Plain Language Summary The impacts of the North Atlantic Oscillation on the climate in eastern China have been highlighted over the last decade. Recently, the observed impacts of the North Atlantic Oscillation on precipitation in eastern China in summer, chiefly via the “North Atlantic-Eurasian teleconnection pattern,” have been noted. This pattern propagates along a high-latitude pathway and is different from the midlatitude circumglobal teleconnection pattern. Here this teleconnection pattern is investigated in a millennium context using a 1,000-year simulation of the Community Climate System Model version 2.0.1. The model results reveal that the simulated NAO-related teleconnection pattern during the summer season is very similar to the observed pattern. Along its path through Eurasia, a positive NAO index causes anomalously high sea level pressures and 500-hPa geopotential heights over Mongolia-north China that correspond to the anomalous anticyclone in the 850-hPa wind anomalies and hence cause reduced precipitation in north China. The opposite occurs during negative summer NAO phases. The model’s teleconnection patterns of the summer NAO capture the reconstructed and observed patterns of the summer precipitation changes in eastern China and provide further evidence for the climate model-based implications for predictions and future projections of seasonal precipitation in eastern China.

Past Millennium Contrasting Hydroclimate Patterns Between Monsoonal Northern China and Arid Central Asia: a Modeling Study

Widely distributed proxy records show that there were out-of-phase behaviors of moisture change between arid central Asia (ACA) and monsoonal northern China during the Little Ice Age (LIA) and Medieval Climate Anomaly (MCA). We examined spatial pattern differences between the MCA and LIA to identify contrasting patterns of summer precipitation variability, and to diagnose explanatory mechanisms through the analysis of a 1000-year global climate model simulation driven by natural and anthropogenic forcing. The results show that the model was able to roughly produce the general features of MCA-LIA hydroclimatic spatial differences between monsoonal northern China and ACA, with a relatively wet MCA found in monsoonal northern China and a relatively dry MCA found in ACA. A further analysis of associated circulations shows that increased summer precipitation in monsoonal northern China was caused by the strengthening of summer monsoon, while the decline in summer precipitation in ACA was caused by an anomalous northward displacement of the subtropical westerly jet stream. Our analyses suggest that both effective solar forcing and El-Niño Southern Oscillation (ENSO) may produce these contrasting patterns of precipitation between monsoonal northern China and ACA. Due to a change in the probability of ENSO phases at the centennial time scale found in our experiments may be attributed to solar irradiances, higher effective solar irradiances during the MCA relative to those of the LIA may have been the ultimate forcing mechanism for the simulated precipitation differences between the MCA and LIA.