Summer Precipitation Variability Research Articles

Impact of Spring Snow Cover Anomaly Over the Russian Far East on the Early Summer Precipitation Variability in Northeast China

AbstractThe summer precipitation in Northeast China (NEC) exerts vital effects on the local crop yield and food security of our country, however, the prediction skill of it is still limited as yet. This study investigated the impact of snow cover anomaly over the Russian Far East during spring (March–April) on the succeeding early summer (May–June) precipitation variability in NEC as well as the underlying physical mechanisms during the years 1961–2020 based on diagnostic analyses and model simulation. The results showed that, on the interannual timescale, the decreased (increased) spring snow cover over the Russian Far East is conducive to the increased (decreased) NEC early summer precipitation. Further analyses indicated that the negative anomaly of spring snow cover can persist into early summer, which then enhances the diabatic heating and thereby warms the overlying atmosphere via the snow‐albedo effect. The warming atmosphere favors the intensified Okhotsk High and an associated prominent anticyclonic circulation over northeast Asia. The anomalous southeast winds on the southwest flank of the anticyclone could bring abundant water vapor to the NEC, induce moisture convergence and ascending motion, and eventually contribute to the above‐than‐normal precipitation. These physical processes operate in the opposite manner in the case of the positive anomaly of spring snow cover. Our findings are beneficial to further improve the understanding and prediction ability of the summer precipitation variability over NEC.

The upper tropospheric-lower stratospheric ozone drives summer precipitation and wildfire changes in West Siberia

Siberian wildfires are pivotal in determining the carbon cycle and climate dynamics, exerting a profound impact on the ecosystems of the entire Arctic region. Over the past few decades, variations in summer precipitation in West Siberia have significantly influenced wildfire activity. This study analyzed precipitation trends in West Siberia from 1982 to 2021 using observations and transient simulations, uncovering a strong correlation between precipitation variability and ozone concentrations in the upper troposphere-lower stratosphere (UTLS). Heightened UTLS ozone levels warm the upper atmosphere over West Siberia during summer. This warming modifies the regional polar jet stream, intensifying its southern branch and weakening the northern one, leading to a southward shift in the jet stream. Consequently, cyclonic circulation anomalies emerge in the upper troposphere, characterized by a barotropic structure with unusual upward movements around 60°N. This upward motion triggers corresponding anomalies in zonal winds in the lower troposphere, fostering a low-pressure system at the surface. This atmospheric shift results in an influx of warm, moist air from the south and cold, dry air from the north into Siberia, enhancing cloud formation and precipitation. Notably, our analysis suggests that the rise in summer precipitation in West Siberia between 1993 and 2010 is linked to increased UTLS ozone concentrations during this period. Conversely, the decline in UTLS ozone since 2010 may increase the risk of wildfires by suppressing precipitation. Our findings underscore the pivotal role of stratospheric chemistry in shaping the regional climate and wildfire behavior.

The contribution of Arabian Sea warming to decreasing summer precipitation in the northern Greater Mekong Subregion

The Greater Mekong Subregion (GMS) is one of the world's most important agricultural regions. Over recent decades, the declining trend in precipitation has caused more frequent droughts over the northern plateau of the GMS, and this has led to a significant reduction in agricultural productivity. These drought events can also affect agriculture within the middle and lower parts of the Mekong River basin. To reveal the main causes of the decline in precipitation, this study investigates interdecadal variations in summer precipitation over the northern GMS during 1979–2022. Results indicate that summer conditions over the northern GMS entered a relatively dry period after the late 1990s. The interdecadal decrease in summer precipitation is closely associated with the warming of the northern Arabian Sea (AS), which induces a cyclonic anomaly that enhances local precipitation and associated diabatic heating. The anomalous diabatic heating induces a downstream Rossby wave train that intensifies the circumglobal teleconnection (CGT) pattern and causes the South Asian high (SAH) to extend farther southeastwards. The southeastward-displaced SAH induces easterly anomalies over the northern Bay of Bengal (BOB) that weaken the Indian summer monsoon (ISM) southwesterly flows and reduce moisture transport from the northern BOB to the northern GMS. The southeastward displacement of the SAH also causes anomalous descent over the northern GMS. Both conditions result in reduced precipitation over the northern GMS. Numerical experiments substantiate the proposed modulating role of AS warming in the interdecadal decrease in summer precipitation over the northern GMS.

Impact of Summer North Atlantic Sea Surface Temperature Tripole on Precipitation over Mid–High-Latitude Eurasia

Abstract Eurasia is a sensitive and high-risk region for global climate changes, where climate anomalies significantly influence natural ecosystems, human health, and economic development. The North Atlantic tripole (NAT) sea surface temperature anomaly is crucial to interannual precipitation variations in Eurasia. Several studies have focused on the link between the NAT and climate anomalies in winter and spring. However, the mechanism by which the summer NAT impacts climate anomalies in Eurasia remains unclear. This study examines how the NAT impacts interannual variations of summer precipitation in mid–high-latitude Eurasia. Precipitation variations are associated with the atmospheric teleconnection triggered by the NAT. When the NAT is in its positive phase, the anomalous atmospheric diabatic heating over the North Atlantic excites an equivalent-barotropic Rossby wave train response that propagates eastward toward Eurasia, resulting in atmospheric circulation anomalies over the region. The combined effects of atmospheric circulation, radiative forcing, and water vapor transport anomalies lead to decreased precipitation across northern Europe and central Eurasia, with higher precipitation anomalies over northeast Asia. Finally, numerical experiments verify that the summer NAT excites atmospheric teleconnections that propagate downstream, affecting precipitation anomalies in mid–high-latitude Eurasia. This study provides a scientific basis for predicting Eurasian summer precipitation and strengthening disaster management strategies.

Diurnal Variation in Summer Precipitation and the Characteristics of Precipitation Events in the Western Tarim Basin, China

The Tarim Basin in the western part of Northwest China (NWC) is the largest inland basin in the world and one of the most arid regions in the middle latitudes. In recent years, heavy precipitation events have occurred frequently in this region, especially in the western Tarim Basin (WTB), due to the climate change. Based on the hourly precipitation data from 2010 to 2022, the diurnal variation in summer precipitation and the characteristics of precipitation events with different durations in WTB have been analyzed. The results mainly show that (1) the diurnal variations in the precipitation amount (PA), precipitation frequency (PF) and precipitation intensity (PI) mainly present a unimodal pattern, but the times of maximum value do not coincide. The peak value of PA and PF appears between 01:00 and 03:00 BJT (Beijing Time), while the valley value appears around 18:00 BJT, yet the peak value of PI appears between 20:00 and 23:00 BJT with no obvious valley value. (2) There are some differences in the diurnal variation characteristics of precipitation among different summer months and different regions. (3) During the past decade, the precipitation structure in WTB has been continuously adjusted, and short-duration- and long-duration-precipitation-dominant periods appear alternately. On the whole, short-duration precipitation has been more frequent in summer, accounting for 70% of the total precipitation events and 40% of the total accumulated precipitation amount. These results can help us to better understand the refined physical characteristics of precipitation events and enhance our understanding of the local climate in the WTB under the background of climate change.

Contribution of internal variability to the Mongolian Plateau summer precipitation trends in MPI-ESM large-ensemble model

Summer precipitation over the Mongolian Plateau (MP) has experienced a consistent decline in recent decades. While the influence of atmospheric wave train on this reduction in precipitation has been recognized in prior studies, this study delves deeper into the physical mechanisms and quantifies the contributions of the internal atmosphere and oceanic variations to the diminishing precipitation utilizing a comprehensive 100-member ensemble simulations from the Max Planck Institute Earth System Model (MPI-ESM). Results show that the ensemble-mean precipitation in MP exhibits a positive trend and cannot explain the observed results. The precipitation trends vary significantly among individual ensemble members, highlighting the pivotal role of internal variability. The leading EOF mode of precipitation trends among ensemble members exhibits uniform variations. Further investigations reveal that the internal summer precipitation in MP is affected by the internal atmospheric circulation, the remote influence of the North Atlantic Dipole sea surface temperature (SST) anomalies, and Pacific Decadal Oscillation-like SST patterns. An eastward-propagating Rossby wave originating from the North Atlantic dipole SST anomalies provides the anomalous large-scale circulation that influences summer precipitation. The PDO contributes to reinforcing the anticyclonic anomaly over the MP. Additionally, the uncertainty of precipitation trends in MPI-ESM can be reduced by 13% through removing the internal atmospheric wave train-related precipitation variation, while oceanic factors only contribute about 7% uncertainty of precipitation variations. Our insights enhance the understanding of the physical drivers behind summer precipitation variability in the MP and effectively quantify the uncertainties stemming from internal variability.

Understanding the Dry-to-Wet Transition of Summer Precipitation over the Three-Rivers Headwater Region: Atmospheric Circulation Mechanisms

Summer precipitation has changed over the Three-Rivers Headwater (TRH) region, which may have an impact on droughts and floods in Asia. This study examines the notable interdecadal variation from dry to wet conditions in summer (June to August) precipitation over the TRH region during the period of 1979–2020. The changes could have been influenced by atmospheric circulations. This study aims to improve our understanding of the interdecadal variation in summer precipitation over the TRH region. Our findings reveal that a zonally oriented teleconnection wave train is generated across the Eurasian mid-to-high latitudes, originating from the North Atlantic and propagating to northern East Asia along the westerly jet. This results in a weakened and northward-shifted westerly jet. Additionally, anticyclonic circulation anomalies over the northern Tibetan Plateau contribute to easterly water-vapor transport anomalies in the region, reducing water-vapor export at the eastern boundary. Concurrently, an anomalous cyclone over the Arabian Sea and an anomalous anticyclone over the Bay of Bengal enhance the influx of oceanic water vapor into the TRH region. The enhanced Walker circulation further augments the equatorial easterly, which in turn strengthens the anomalous anticyclone over the Bay of Bengal. Consequently, these atmospheric changes contribute to the increased summer precipitation over the TRH region, elucidating the mechanisms behind the observed dry-to-wet transition.

Variations of summer precipitation in Tarim Basin and their linkages with the westerly, Asian monsoons and extratropical circulation

Variations of summer precipitation in Tarim Basin and their linkages with the westerly, Asian monsoons and extratropical circulation

Interdecadal variability of summer precipitation in the Three River Source Region: Influences of SST and zonal shifts of the East Asian subtropical westerly jet

Summer precipitation in the Three Rivers Source Region (TRSR) of China is vital for the headwaters of the Yellow, Yangtze, and Lancang rivers and exhibits significant interdecadal variability. This study investigates the influence of the East Asian westerly jet (EAWJ) on TRSR rainfall. A strong correlation is found between TRSR summer precipitation and the Jet Zonal Position Index (JZPI) of the EAWJ from 1961 to 2019 (R = 0.619, p < 0.01). During periods when a positive JZPI indicates a westward shift in the EAWJ, enhanced water vapor anomalies, warmer air, and low-level convergence anomalies contribute to increased TRSR summer precipitation. Using empirical orthogonal function and regression analyses, this research identifies the influence of large-scale circulation anomalies associated with the Atlantic–Eurasian teleconnection (AEA) from the North Atlantic (NA). The interdecadal variability between the NA and central tropical Pacific (CTP) significantly affects TRSR precipitation. This influence is mediated through the AEA via a Rossby wave train extending eastward along the EAWJ, and another south of 45°N. Moreover, the NA–CTP Opposite Phase Index (OPI), which quantifies the difference between the summer mean sea surface temperatures of the NA and the CTP, is identified as a critical factor in modulating the strength of this teleconnection and influencing the zonal position of the EAWJ.摘要本研究探讨了年代际东亚西风急流的纬向移动对黄河, 长江和澜沧江源头—三江源区夏季降水的影响. 研究发现, 在1961–2019年间, 三江源区夏季降水量与急流纬向位置指数 (JZPI) 在年代际尺度上存在强正相关 (R=0.619, p<0.01) . 当JZPI呈正值, 也就是东亚西风急流向西移动时, 增强的水汽, 温暖的气流和低层辐合异常有助于三江源区夏季降水增加. 北大西洋与中太平洋之间的年代际变化对三江源区的降水有着显著的影响, 主要以北大西洋–欧亚遥相关 (AEA) 方式, 通过沿东亚西风急流向东延伸的罗斯贝波列, 以及45°N以南的另一波列来影响三江源区的降水. 进一步分析发现, 北大西洋与中太平洋反向相位指数 (OPI) 作为一个关键因素, 可量化北大西洋与中太平洋之间夏季平均海表温度的差异, 调控该遥相关的强度并影响急流的纬向位置.

Precipitation-induced abrupt decrease of Siberian wildfire in summer 2022 under continued warming

Wildfires in Northeast (NE) Siberia have become more frequent owing to the warming climate, exerting a profound impact on the global carbon cycle. While an increase in global temperature is recognized as a primary driver of unprecedented wildfires, the role of precipitation during wildfire season is relatively unexplored. Here, we present evidence that an increase in summer precipitation led to a sudden decrease in NE Siberian wildfires, especially in 2022, notwithstanding the persistent warming trend in the northern high latitudes. The interannual variability of summer precipitation, linked to the large-scale atmospheric circulation, known as the Scandinavia (SCAND) pattern, significantly impacts the regulation of wildfires. Climate models project enhanced variability in summer precipitation, potentially amplifying year-to-year fluctuations in wildfire occurrences. The interplay between the temperature and precipitation patterns in NE Siberia under ongoing warming may increase the occurrence of extreme wildfires, leading to a substantial release of carbon and further contributing to climate warming.

Arctic summer precipitation variability and its association with Indian summer monsoon anomalies

In recent years, there has been an increased focus on changes in Arctic precipitation，however, dominant characteristics of Arctic summer precipitation variability and their relationship to atmospheric circulation anomalies in the mid-low latitudes remain debatable. Spatially, the leading mode of Arctic summer precipitation variability is positive in most regions of the Arctic, corresponding to a cold anomaly in the middle and lower troposphere of the Arctic. As the temperature gradient between the Arctic and high latitudes increases, the zonal westerlies over the Arctic enhanced and lead to increased local baroclinicity and moisture convergence over the Arctic. This creats favorable conditions for increased summer precipitation. Additionally, it is found that there is a robust correlation between the first mode of Arctic summer precipitation and the Indian summer monsoon. Specifically, the positive Arctic summer precipitation anomaly is accompanied by a systematic northward shift of the zonal westerlies in the mid-latitude. The northward shift of the Asian westerly jet stream is associated with the intensified tropical easterly jet in the upper-troposphere and low-stratosphere, resulting in the strengthening of the monsoon circulation over the Indian Peninsula and then facilitating the precipitation anomaly over India. Numerical experiments reproduce the major features of the observed Arctic-Indian summer monsoon association, implying that Arctic summer precipitation variability is dynamically linked to tropical atmospheric circulation anomalies.

Role of the Indian Ocean basin mode in driving the interdecadal variations of summer precipitation over the East Asian monsoon boundary zone

Abstract. Based on long-term observational and reanalysis datasets from 1901 through 2014, this study investigates the characteristics and physical causes of the interdecadal variations in the summer precipitation over the East Asian monsoon boundary zone (EAMBZ), which is a peculiar domain defined from the perspective of the interplay between climatic systems (i.e., mid-latitude westerly and East Asian summer monsoon). Observational evidence reveals that, similarly to previous studies, the EAMBZ precipitation featured prominent interdecadal fluctuations, e.g., with dry summers during the periods preceding 1927, 1939–1945, 1968–1982, and 1998–2010 and wet summers during the periods of 1928–1938, 1946–1967, and 2011 onwards. Further analyses identify that, amongst the major interdecadal oceanic forcings (e.g., Atlantic multidecadal oscillation and Pacific decadal oscillation), the Indian Ocean basin mode (IOBM) is a significant oceanic forcing responsible for the interdecadal variations of the EAMBZ precipitation, playing an independent and critical modulation role. When the cold phase of the IOBM occurs, an anomalous cyclonic circulation is excited around the northeast corner of the tropical Indian Ocean, which further induces a north-low–south-high meridional seesaw pattern over the Northeast China–subtropical western Pacific (SWP) sector. Such seesaw pattern is conducive to the enhanced EAMBZ precipitation by linking favorable environments for the transportation of water vapor from the SWP and the convergence over the EAMBZ at interdecadal timescales. For this reason, a physical–empirical model for the EAMBZ precipitation is developed in terms of the IOBM cooling. Despite the fact that the extreme summer EAMBZ precipitation cannot be captured by this model, it can still well capture its interdecadal fluctuations and reflect their steady relationship. The key physical pathway connecting the IOBM cooling with the interdecadal variations of the summer EAMBZ precipitation is supported by the numerical results based on the large ensemble experiment and the Indian Ocean pacemaker experiment. Our findings may provide new insights into the understanding of the causes of the interdecadal variations in the summer EAMBZ precipitation, which may favor the long-term policy decision-making for the local hydrometeorological planning.

Characteristics of the East Asian Summer Monsoon Using GK2A Satellite Data

In East Asia, where concentrated summer precipitation often leads to climate disasters, understanding the factors that cause such extreme rainfall is crucial for effective forecasting and preparedness. The western North Pacific subtropical high (WNPSH) is a key driver of summer precipitation variability, and therefore, its monitoring is critical to predicting the wet or dry periods during the East Asian summer monsoon. Using the Geo-KOMPSAT 2A (GK2A) satellite cloud amount data and ERA5 reanalysis data during the years 2020–2023, this study identified three leading empirical orthogonal function (EOF) modes and investigated the associated WNPSH variability at synoptic and subseasonal scales. The analysis includes a linear regression of meteorological fields onto the principal component (PC) time series. All three modes play a role in the spatiotemporal variability of the WNPSH, exhibiting lead–lag relationships. In particular, the second mode is responsible for its northwestward shift and intensification. As the WNPSH moves northwestward, the position of the monsoon rain band also shifts, and its intensity is modulated mainly by the moisture transport along the WNPSH boundary. Our results highlight the potential of high-resolution, real-time data from the GK2A satellite to elucidate WNPSH variability and its impact on the East Asian summer monsoon. By addressing the variability of the WNSPH using GK2A data, we pave the way for the development of a real-time monitoring framework with GK2A, which will improve our predictability and readiness for extreme weather events in East Asia.

Spatiotemporal variability at seasonal and interannual scales of terrestrial water variation over Tibetan Plateau from geodetic observations

ABSTRACT In the context of ongoing global climate warming, researchers have observed an intricate relationship between the variability of Terrestrial Water Storage (TWS) on the Tibetan Plateau (TP) and climate anomalies. In this study, we utilize a combination of Global Navigation Satellite System (GNSS), Gravity Recovery and Climate Experiment (GRACE), and precipitation data to investigate the response of TWS on the TP to extreme climate changes, with a focus on seasonal and interannual variations. Our findings reveal that the first Common Mode Component (1st CMC) extracted from GNSS coordinate time series exhibits strong interannual fluctuations. Additionally, both GNSS and GRACE-inferred TWS demonstrate noticeable anomalous changes during the 2015/2016 period. The estimated periods of the 1st CMC of GNSS and GRACE-inferred TWS are approximately 5 and 7 years, respectively. Both reach a minimum during the extreme climate event in 2015/2016. Furthermore, we investigate the spatial variation of summer precipitation before and after the extreme drought event on the TP. It reveals that the inflection point of TWS occurs approximately 1 year prior to the drought event, suggesting a consistent spatial propagation process between precipitation and TWS. This indicates that the changes of TWS during this drought event were primarily influenced by precipitation. Finally, we evaluate the response of 12 sub-basins on the TP to the drought event that occurred in 2015/2016. The regions experiencing significant abnormal fluctuations in TWS are mainly located in inner and northeastern plateau. These regions show rapid upward changes in the TWS and demonstrate a strong spatial consistency with summer precipitation.

Precursory signals of summer precipitation over southern Central Asia: Combined effect of April soil moisture and sea surface temperature

AbstractThis study investigates the interannual variability of summer precipitation over Central Asia and explores its precursory signals through soil moisture (SM) and sea surface temperature (SST) anomalies. The results reveal that southern Central Asia (SCA) is a crucial SM‐precipitation coupling region where summer precipitation is significantly linked to the preceding April SM in the Turan Plain, between the Caspian Sea and the Tibetan Plateau. The preceding Turan Plain SM (TPSM) anomaly can reflect the ensuing summer SM anomalies in the SCA region due to the persistence of SM. The higher TPSM can stimulate anomalous convective ascent and associated negative geopotential height anomalies over the SCA region, which is favourable for more SCA precipitation (SCAP) during summer. Additionally, Indian and Pacific Ocean SST (IPOS) anomalies can regulate the summer SCAP through ocean and land relay effects. The preceding April can reflect the subsequent summer SST anomalies across the northern Indian Ocean and South China Sea, which trigger a Matsuno‐Gill response and induce anomalous water vapour transport into the SCA region, providing favourable moisture conditions for more SCAP during summer. Apart from such an ocean relay effect, the preceding IPOS can modulate the April TPSM first and then affect the summer SCAP through the land relay effect caused by persistent SM anomalies from April to summer. The combined effect of the preceding TPSM and IPOS on the summer SCAP is more pronounced than the respective effect of either TPSM or IPOS. Incorporating the TPSM signal as a supplementary precursor can enhance the predictive skill of summer SCAP. These findings may provide valuable insights into the reasons and prediction of the variability of summer SCAP.

Annual velocities of the ablation zone of Panchi Nala Glacier, western Himalaya: Trends and controlling factors

Information on the glacier velocity is imperative to understand the glacier ice volume, supraglacial feature evolution and glacier-climate interaction. The present study investigates annual velocities of the ablation zone (∼4500–4800 m asl) of Panchi Nala Glacier, western Himalaya through feature tracking. For this, multi-temporal Landsat (TM and OLI) and Sentinel −2 MSI images, acquired between 2000 and 2021, were correlated using the Co-registration of Optically Sensed Images and Correlation (COSI-Corr) tool. Results reveal a mean velocity of the ablation zone to be 10.6 ± 5.6 m/y during 2000–2021, with the highest (13.8 ± 4.6 m/y) and lowest velocity (8.9 ± 2.8 m/y) observed in 2005 and 2015, respectively. There is no significant trend in the velocity, rather it is highly heterogeneous on the inter-annual scale. Further, the influence of several factors such as slope, debris cover, altitude, annual average temperature and precipitation on the glacier velocity was investigated. Results indicate that the inter-annual heterogeneity in velocity is inversely correlated with the variation of summer precipitation implying that an increase in summer precipitation decreases the glacier velocity. The spatio-temporal velocity variations are also linked with the presence of supraglacial ponds, ice cliffs and heterogeneous debris distribution over the glacier. Findings indicate that, though annual glacier velocities have not changed significantly, their magnitudes are consistently low which coupled with consistent debris increase (19.74%) and gentle slope (8.2° over ablation zone) can promote rapid growth of supraglacial ponds and ice cliffs.

Climatic implications in earlywood and latewood width indices of Chinese pine in north central China

Latewood width (LWW) indices of trees are considered a reliable proxy of summer precipitation in the Northern Hemisphere. However, the strong coupling and high correlation between earlywood width (EWW) and LWW indices often prevent registration of climate signals of the LWW index. In this study, 328-year-long earlywood width and latewood width chronologies were developed from Chinese pine at two sites in the Hasi Mountains, north central China. The climate responses of these chronologies were analyzed and the LWW index used to derive summer precipitation signals. Correlation analyses showed that LWW was particularly influenced by earlywood growth and recorded stronger climate signals of the previous year as EWW, rather than those of the current year with infrequent summer climate signals. However, after removing the effect of earlywood growth using a simple regression model, the adjusted LWW chronology (LWWadj) showed a strong relationship with July precipitation in dry years. This suggests that the LWWadj chronology has the potential to be used to investigate long-term variability in summer precipitation in drought-limited regions.

Interdecadal Change in the Covariability of the Tibetan Plateau and Indian Summer Precipitation and Associated Circulation Anomalies

This study investigates the interdecadal change in the covariability between the Tibetan Plateau (TP) east–west dipole precipitation and Indian precipitation during summer and primarily explores the modulation of atmospheric circulation anomalies on the covariability. The results reveal that the western TP precipitation (WTPP), eastern TP precipitation (ETPP), and northwestern Indian precipitation (NWIP) have covariability, with an in-phase variation between the WTPP and NWIP and an out-of-phase variation between the WTPP and ETPP. Moreover, this covariability was unclear during 1981–2004 and became significant during 2005–2019, showing a clear interdecadal change. During 2005–2019, a thick geopotential height anomaly, which tilted slightly northward, governed the TP, forming upper- and lower-level coupled circulation anomalies (i.e., anomalous upper-level westerlies over the TP and lower-level southeasterlies and northeasterlies around the southern flank of the TP). As such, the upper- and lower-tropospheric circulation anomalies synergistically modulate the summer WTPP, ETPP, and NWIP, causing the covariability of summer precipitation over the TP and India during 2005–2019. The upper- or lower-level circulation anomalies cannot independently result in significant precipitation covariability. During 1981–2004, the upper- and lower-level circulation anomalies were not strongly coupled, which caused precipitation non-covariability. The sea surface temperature anomalies (SSTAs) in the western North Pacific (WNP) and tropical Atlantic (TA) may synergistically modulate the upper- and lower-level coupled circulation anomalies, contributing to the covariability of the WTPP, ETPP, and NWIP during 2005–2019. The modulation of the WNP and TA SSTs on the coupled circulation anomalies was weaker during 1981–2004, which was therefore not conducive to this precipitation covariability. This study may provide valuable insights into the characteristics and mechanisms of spatiotemporal variation in summer precipitation over the TP and its adjacent regions, thus offering scientific support for local water resource management, ecological environment protection, and social and economic development.

The centennial-resolution loess δDwax record indicates summer precipitation variations in the marginal region of the East Asian monsoon during the last deglaciation

Precipitation isotopic composition variations that are directly recorded in geological samples play an important role in understanding past hydroclimatic changes. In arid regions, the hydrogen isotopes of leaf wax (δDwax) in loess sections can provide records of summer precipitation isotopes. However, previous studies have primarily focused on the orbital scale, and there was still a lack of clear understanding of variations in precipitation isotopes on shorter timescales and their implications for climate change. In this study, we report centennial-resolution loess δDwax records from the central Chinese Loess Plateau (CLP) from the last deglaciation to the early Holocene. We compared the loess optically stimulated luminescence chronology and U-Th ages conveyed by linking stalagmite δ18O and loess δDwax to validate the δDwax method as a potential tool for assessing loess chronology on the suborbital scale. Our findings also indicated that regional precipitation isotopes experienced a depletion of approximately 24‰ for δD and around 3.2‰ for δ18O during the last deglaciation. The overall precipitation isotope amplitude in the central CLP was similar to that of typical East Asian monsoon regions and lower than that of the Indian monsoon and westerly regions. However, the precipitation isotope oscillations on the millennial scale in the central CLP were significantly weaker than those in eastern to central China. The finding affirmed that although the summer precipitation in the CLP was primarily influenced by the East Asian monsoon system at the orbital scale, the northern boundary of the summer rain belt remained a distance away from the interior of the CLP during the last deglaciation. As a result, the short-term oscillations of atmospheric circulation were not strongly reflected in the precipitation isotopes of the central CLP. This result highlighted spatial and temporal differences in precipitation isotope variability between the dominant and marginal regions of the East Asian monsoon system.

Modulation of the intraseasonal variability in early summer precipitation in eastern China by the Quasi-Biennial Oscillation and the Madden–Julian Oscillation

Abstract. Using the reanalysis and multiple observations, the possible impact of the Madden–Julian Oscillation (MJO) on early summer (June–July) rainfall in eastern China and its modulation by the Quasi-Biennial Oscillation (QBO) are examined. The composite results show that the suppressed (enhanced) convection anomalies for MJO phases 8–1 (4–5) are more concentrated over the maritime continent and the western Pacific during easterly QBO (EQBO). As a consequence, more significant wet (dry) anomalies develop in South (eastern) China during MJO phases 8–1 (4–5) configured with easterly (westerly) QBO. The enhancement and expansion of the anomalous tropical convection band do not necessarily correspond to enhancement of the extratropical circulation response to MJO phases 8–1 (4–5) configured with westerly (easterly) QBO. The anomalous high (low) over the maritime continent and western Pacific associated with MJO phases 8–1 (4–5) is intensified (deepened) during easterly (westerly) QBO, leading to large southwesterly (northeasterly) anomalies in South China and the coasts, carrying abundant (sparse) moisture. Two anomalous meridional circulation cells are observed for MJO phases 8–1 in the East Asia sector, with downwelling anomalies around 5–20∘ N, upwelling anomalies around 20–30∘ N, and another downwelling branch northward of 30∘ N, which are enhanced during easterly QBO. The anomalous meridional circulation cells are reversed for MJO phases 4–5, which are stronger during westerly QBO with the anomalous downwelling and dry anomalies covering eastern China. The combined impact of MJO phases 8–1 and easterly QBO on the early summer rainfall is noticeable in 1996, 2016, and 2020. The enormous rainfall amount appeared along the Yangtze River in 1996, 2016, and 2020 due to the extended period of MJO phases 8–1 under the background of the easterly QBO.