Monsoon System Research Articles

Mid-Holocene pine forest expansion caused by the weakening of the East Asian winter monsoon and linked to climate change in the North Atlantic region

The East Asian winter monsoon (EAWM) system is one of the most active components of the global winter atmospheric circulation, and it has a major impact on the Eurasian climate in winter. However, relatively few proxy indicators are available to reconstruct the past evolution of the EAWM. Based on the physiology and modern distribution of the temperate forest and boreal forest in Northeast Asia, we found that the northern boundary of temperate pine forest is sensitive to winter temperature and thus it can be used as a proxy for EAWM intensity. A Holocene pollen record from Lake Woniupaozi in Northeast China shows that an expansion of temperate pine forest since ∼6.0 ka cal BP was linked to a weakening of the EAWM. This pattern is consistent with other paleoclimatic records from Northeast Asia and elsewhere, including the North Atlantic region, Middle East, Arabian Sea, and the Tibetan Plateau/Southwest China, which suggests a major climatic transition in the mid-Holocene. The mechanism responsible for this teleconnection may have been the continuous melting of the Laurentide ice which lowered the SST in the North Atlantic and maintained the North Atlantic Oscillation (NAO) in a positive winter phase. This influence was subsequently transmitted from the North Atlantic region to Eurasia via the winter southern Eurasian (SEA) teleconnection.

Tracing isotope precipitation patterns across Mexico

Mexico encompasses a large spectrum of landscapes with topographic, geographic, and climatic factors interacting in a complex ecohydrological setting. For decades, isotope hydrogeological tools have been applied in Mexico using short-term or seasonal local meteoric water lines as valid input functions. Yet, a systematic evaluation of meteoric isotope characteristics is still lacking. Here we report on the spatial and temporal isotope variations of 21 precipitation monitoring stations across Mexico. Our database includes 608 monthly samples collected from 2018 to 2021 over four regions (between 5 and 2,365 m asl): the Pacific coast, the Gulf of Mexico/Caribbean Sea region, and the Central and Northern plateaus. Precipitation δ18O seasonality from the dry (winter) to the wet season (summer) was characterized by a notable W-shaped variability. Monthly precipitation amounts and δ18O compositions exhibited poor to strong linear regressions (Adj. r2<0.01 to 0.75), with inverse (positive) relationships over the northern monsoon-affected region. Low d-excess (5.1 to 9.7‰) corresponded with greater terrestrial moisture contributions (20.5%) over the arid northern regions. Moisture inputs from the Gulf of Mexico/Caribbean Sea and the Pacific Ocean were associated with near-equilibrium or greater d-excess values (8.8 to 14.3‰), respectively. The best-fit linear models for δ18O (Adj. r2 = 0.85) and δ2H (Adj. r2 = 0.88) were determined for topographic and geographical predictors, resulting in an updated high-resolution precipitation isoscape (100 m2 grid) for Mexico. Orographic barriers (-2.10‰ in δ18O/km) coupled with the interaction of tropical cyclones and cold fronts, the evolution of the North American Monsoon system, and the passage of easterly trade winds play a remarkable role in controlling the spatial isotope rainfall variability. Our findings provide a robust baseline for ecohydrological, climatic, forensic, archeological, and paleoclimate studies in North America.

Long term trends and variabilities of rainfall of the global monsoon systems during boreal and austral summer seasons

Long term trends and variabilities of rainfall of the global monsoon systems during boreal and austral summer seasons

Geochemical records provide evidences for the evolution of the marine redox environment in the southwestern Sumatra waters over the past 35,000 years

The marine redox environment (MRE) can affect marine productivity and nutrient cycling, as well as governs material and energy transport. However, its evolution process and driving mechanism in different historical periods revealed significant regional characteristics. Southwestern Sumatra waters, located at the Indo-Pacific Ocean convergence, are an ideal region for studying the evolution of MRE due to significant upwelling and variable productivity levels resulting from the seasonal monsoonal activity. In this study, based on the sediment core SO184–10043, systematic trace element geochemical analysis was conducted for reconstructing the MRE over the past 35,000 years using redox proxies, namely, Ni/Co, U/Th, and biogenic Barium (Babio). Ni/Co and U/Th varied in a range of 1–4 and 0.2–1, indicating general oxic conditions with matching productivity levels indicated by Babio (ranging from 300 × 10–6 to 580 × 10–6). A comparison with other reconstructed archives indicated that the MRE records of the sediment core in this study were in consistence in responding to the high-latitude climate records with strong semi-precession and millennial fluctuations. Suggestively, these fluctuations correspond to the natural summertime insolation, triggering the latitudinal motions of the Intertropical Convergence Zone (ITCZ), as well as leading to corresponding changes in the seasonal Indian monsoon system. Freshwater lids modulate the mixing effect by acting as barriers and influencing the upwelling development, thereby leading to strong oxic conditions in the MRE. Therefore, robust evidence on the millennial-scale variability in MRE driven by the ITCZ movement and regional monsoon changes in the tropical Indian Ocean is provided by the trace element archives employed in the present study, thereby providing novel insights into the evolution of MRE in response to global and local climate changes.

Different responses of precipitation patterns to the East Asian summer monsoon weakening: The 7.2 and 8.2 ka events

The 8.2 ka abrupt cooling event has been extensively studied, whereas the 7.2 ka event and their comparations rarely mentioned. Here, we present a high resolution (∼4 years) and precisely dated (±25 years) speleothem multi-proxy record from Zhangjia Cave (northern margin of Sichuan basin, China) spanning the 7.2 and 8.2 ka events within the transition of early to middle Holocene. The speleothem δ18O mainly reflects the dynamic facets of the East Asian summer monsoon (EASM) system, while its δ13C and trace elements ratios serve as an indicator of local hydrological conditions. Our results reveal intense dry conditions in southwest China during the 7.2 ka event, despite the 7.2 event was characterized by a relatively stronger monsoon compared to the 8.2 ka event. Furthermore, the hydrological conditions during the 7.2 ka event and the middle Holocene appear to exhibit “north flood and south drought” pattern when compared to different paleoclimate records in EASM domains, while it can be summarized as “spatially consistent drought” in the 8.2 ka event. These different hydrological conditions are a response to the weakening of the EASM, a phenomenon also observed in modern climatic observations and empirical simulations, which underpins our understanding that the speleothem δ18O variations are mainly dynamical manifestations of the EASM system, likely different with its thermodynamical appearances.

Constraining flow and sediment transport intermittency in the geological past

Quantitative investigations of ancient rivers usually provide insights into either instantaneous or mean flow conditions. There is a critical gap between these time scales of investigation, which reflects the intermittency of flow and sediment transport, and closing this gap is crucial to fully explore the dynamics and evolution of ancient fluvial landscapes. Here, we combined fluvial stratigraphic data sets, flow and sediment transport models, and paleoclimate general circulation model (GCM) results to develop new methods to estimate intermittency in the geological past, specifically flow intermittency factors (Iw) and sediment transport intermittency factors (Is), and we show how they can be used to explore past hydrograph shapes. We illustrated these methods using the Upper Cretaceous Last Chance Ferron Sandstone in Utah, western United States. For sand-transporting flow conditions in Last Chance Ferron rivers, we estimated Iw values of 0.54−0.90, which imply that channel-forming conditions were sustained for the majority of the year, consistent with perennial systems in which relatively large discharges were sustained. In contrast, for gravel-transporting flow conditions, Iw values of 0.28−0.38 suggest that the largest formative flows may have occupied Last Chance Ferron rivers for nearly a third of the year, which could be explained by a monsoonal system in which high-magnitude discharge events were sustained, or a subtropical system in which high-magnitude discharge events had short durations but high frequencies. Meanwhile, Is values of 0.075−0.15 suggest that annual sediment budgets could have been transported in as little as 10 days and up to 2 months, if channel-forming conditions were sustained, and these values highlight that small changes in the duration of channel-forming conditions could significantly impact sediment budgets. Our results are consistent with independent facies- and proxy-based insights into Last Chance Ferron rivers, which point to a perennially wet system characterized by a monsoonal or subtropical discharge regime. Further, our results highlight new opportunities to use paleoclimate GCMs to constrain intermittency factors in the geological past. Going forward, paleoclimate GCMs will be particularly useful where the rock record is incomplete or inaccessible, or where stratigraphic approaches are limited, and they will enable us to tackle pertinent research questions pertaining to past surface processes on both Earth and other planets.

Compositions of hydrogen and oxygen isotopes of precipitation in Xiamen, southeast China coast: Seasonal variations, synoptic processes, and typhoons impact

AbstractIn this study, the δ2H and δ18O values of 162 precipitation samples (including 33 typhoon‐related samples), collected in Xiamen, southeast China coast, during June 2018 to August 2019, were investigated and analysed. The findings indicate an obvious seasonal variation in the δ2H and δ18O, primarily influenced by the East Asia Monsoon system with notable impact from typhoon occurrences during summer months. The synoptic time‐series variation of δ2H and δ18O exhibits greater complexity: three distinct types of isotopic variations were observed, indicating a clear influence from re‐evaporation processes and continuing equilibrium fractionation during condensation. The variation patterns of δ2H and δ18O were dominated by the local meteorological parameters that govern the re‐evaporation, whereas the overall isotopic composition of precipitation was primarily regulated by the moisture sources. The unique atmospheric structure and dynamic processes of typhoons led to a three‐stage variation of δ2H and δ18O in precipitation as the distance between the typhoon's centre and the study area changed. The consistent configuration of typhoon structure prompts analogous staged changes in different typhoon‐related precipitation. The trajectory of moisture source for typhoon‐related precipitation demonstrates a clear spiral structure (excluding typhoon Yutu), revealing notable impacts from typhoon events.

North African humid periods over the past 800,000 years

The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the intensity of the African monsoon system. However, most climate models cannot reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we utilise a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800 kyr which have good agreement with NAHPs identified in proxy data. Our results show that precession determines NAHP pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacial periods, enhanced ice-albedo driven cooling suppresses NAHP amplitude at precession minima, when humid conditions would otherwise be expected. This highlights the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.

Heat band, rain band and heat low migration: process-based evaluation of some CMIP6 GCMs over West Africa

Climate model evaluation presents a crucial pathway into the investigation of the simulation of future climate. It presents the only lens through which the future states of the climate of the planet can be explored. In this study, reference datasets including reanalysis products have been used to demonstrate the climatological annual migration of the West African Monsoon System (WAMS) in three components, namely, the West African Heat Low (WAHL), the West African Heat Band (WAHB) and the West African Rain Band (WARB). We have used 8 Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to assess how the models represent the climatological annual migration of these three features over the same domain for the same period. The results show close linkages between the WAHL, WAHB and the WARB as signature components of the WAMS in their climatological annual dynamics. All three features migrate from the south (with the minimum intensities) in January to the north (with the maximum intensities) in August over the region. The GCMs represent the climatological annual dynamics of all three features to some extent. However, in most of the models analysed the WAHL is too weak, and the WAHB and WARB are located too far south. Insights from this study can be beneficial for investigations of the future state of the WAMS. Also, development of models for the region should target the improved simulation of these features, specifically the intensity of the WAHL, and the locations of the WAHB and WARB.

Paleofire dynamics in response to climate change during late Miocene derived from microcharcoal records in the Weihe Basin

The Weihe Basin, situated in the central part of Shaanxi Province between the Qinling and Weibei Mountains, falls under the influence of the Asian monsoon system. The basin's thick and continuous Cenozoic sedimentary layers offer a valuable repository for investigating environmental changes within a typical monsoon climate. Based on previous chronological research, our study delved into the microcharcoal concentration (MCC) of the samples extracted from Bahe Formation. This analysis aimed to reconstruct the paleo-fire and drought history during the late Miocene, shedding light on the region's evolutionary trajectory. Our findings unveil five distinct peaks in the microcharcoal record, occurring at approximately 9.9–9.7 million years ago (Ma), ∼9.5 Ma, ∼8.1 Ma, ∼7.6 Ma, and 7.4–7.2 Ma. These peaks signify high-frequency fire events, primarily taking place during periods of aridity. The combustion of broadleaved and coniferous trees was the predominant source of fuel for fires during 9.9–9.7 Ma, ∼9.5 Ma and ∼8.1 Ma, with elevated temperatures acting as the principal ignition catalyst. In contrast, the subsequent two fire events (∼7.6 Ma, and 7.4–7.2 Ma) coincided with drier climatic conditions, featuring xerophytic herbs s as the primary biomass. Drought emerged as the pivotal driving force behind these fire occurrences in this phase. The microcharcoal records of the Bahe Formation reveal a noteworthy pattern: the MCC during the latter two periods surpassed that of the initial three, indicating an escalated frequency of fires during dry intervals. This trend signifies a transition towards a dry and cold climate post ∼8.0 Ma. The expansion of grasslands and the occurrence of drought events since the late Miocene (∼8.0 Ma) can be attributed to the weakening of the Asian Monsoon. In summary, our investigation of microcharcoal concentration in the Bahe Formation provides valuable insights into the late Miocene paleo-fire and drought dynamics. By deciphering the interplay between vegetation, climate, and fire occurrences, our study contributes to a more comprehensive understanding of the environmental evolution within the Weihe Basin under the influence of the Asian monsoon system.

Observed Air–Sea Turbulent Heat Flux Anomalies during the Onset of the South China Sea Summer Monsoon in 2021

Abstract This study presents observational findings of air–sea turbulent heat flux anomalies during the onset of the South China Sea summer monsoon (SCSSM) in 2021 and explains the mechanism for high-resolution heat flux variations. Turbulent heat flux discrepancies are not uniform throughout the basin but indicate a significant regional disparity in the South China Sea (SCS), which also experiences evident year-to-year variability. Based on buoy- and cruise-based air–sea measurements, high-temporal-resolution (less than hourly) anomalies in the latent heat flux during the SCSSM burst are unexpectedly determined by sea–air humidity differences instead of wind effects under near-neutral and mixed marine atmospheric boundary layer (MABL) stability conditions. However, latent heat anomalies are mainly induced by wind speed under changing MABL conditions. The sensible heat flux is much weaker, with its anomalies dominated by sea–air temperature differences regardless of the boundary layer condition. The observational results are used to examine the discrepancies in turbulent heat fluxes and associated air–sea variables in reanalysis products. The comparisons indicate that latent and sensible heat fluxes in the reanalysis are overestimated by approximately 55 and 3 W m−2, respectively. These overestimations are mainly induced by higher estimates of sea–air humidity/temperature differences. The relative humidity is underestimated by approximately 4.2% in the two high-resolution reanalysis products. The higher SST (near-surface specific humidity) and lower air temperature (specific air humidity) eventually lead to higher estimates of sea–air humidity/temperature differences (1.75 g kg−1/0.25°C), which are the dominant factors controlling the variations in the air–sea turbulent heat fluxes. Significance Statement Air–sea interactions are significant in predicting the onset of East Asian monsoon systems, including the SCSSM. During the SCSSM in 2021, four buoys and cruise observations are used to investigate anomalies in the latent and sensible heat fluxes. The physical mechanism of the variations in turbulent heat fluxes under different MABL stability conditions is explored in this study. The humidity and wind speed anomalies play roles under mixed boundary conditions in determining the high-resolution variations in latent heat fluxes. Based on these observational results, the heat fluxes and associated air–sea variables from reanalysis products are compared to identify the differences in the operational systems. These comparison results can help improve the reanalysis to obtain better monsoon predictions.

South American Monsoon Lifecycle Projected by Statistical Downscaling with CMIP6-GCMs

This study analyzed the main features (onset, demise, and length) of the South American Monsoon System (SAMS) projected in different time slices (2020–2039, 2040–2059, 2060–2079, and 2080–2099) and climate scenarios (SSP2–4.5 and SSP5–8.5). Eight global climate models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) that perform well in representing South America’s historical climate (1995–2014) were initially selected. Thus, the bias correction–statistical downscaling (BCSD) technique, using quantile delta mapping (QDM), was applied in each model to obtain higher-resolution projections than their original grid. The horizontal resolution adopted was 0.5° of latitude × longitude, the same as the Climate Prediction Center precipitation analysis used as a reference dataset in BCSD. The QDM technique improved the monsoon onset west of 60° W and the simulated demise and length in southwestern Amazonia. Raw and BCSD ensembles project an onset delay of approximately three pentads compared to the historical period over almost all regions and a demise delay of two pentads northward 20° S. Additionally, the BCSD ensemble projects a reduced length with statistical significance in most South Atlantic Convergence Zone regions and a delay of three pentads in the demise over the Brazilian Amazon from the second half of the 21st century.

New insights into potential effects of solar activity on the oxygen isotope composition of modern speleothems: Observations from Jiguan Cave, central China II

The oxygen isotope compositions (δ18O) of stalagmites have been widely used to reconstruct summer monsoon variability, which is primarily controlled by the solar radiation on orbital to seasonal timescales. However, the relationship between solar activity and the monsoon system remains unclear. This study is based on a 13-year, from 2010 to 2022, monitoring campaign of the δ18O values of precipitation, cave drips and modern speleothems in Jiguan Cave, central China. By analyzing moisture circulation and the local meteoric water line (LMWL) under different ENSO (El Niño Southern Oscillation) events, it was found that on seasonal–interannual timescales, the precipitation δ18O values reflect the atmospheric moisture circulation. In addition, we used cross-wavelet transform analysis to investigate the periodic relationship between the sunspot number (SSN) and the Asian Summer Monsoon (ASM) since solar activity is one of the most important external influences on the ASM. The stalagmite δ18O data for our study areas reflect the solar activity-induced decadal-scale variations in the local precipitation. The key factors related to the δ18O value include the driving mechanism of the solar activity and ENSO-related sea surface temperature (SST) anomalies. We speculate that changes in solar activity cause anomalies in the tropical SST gradient, which affects central China's hydrological cycle by changing the variability of ENSO and the Indian Ocean Dipole (IOD) and ultimately causes the variations in stalagmites δ18O records.

Persistently Southward of the South Asian High During the Radiative Forcing Stabilization

AbstractThe South Asian high (SAH), a large‐scale anticyclone at 100 and 200 hPa on the Asian continent, is driven by South Asian summer monsoon rainfall and heating over the Tibetan Plateau. As one member of the Asian summer monsoon system, the changes of its location and intensity may cause other climate responses. Rainfall‐induced latent heating can affect the SAH change. Previous study revealed that rainfall responses in Indian Ocean are opposite in periods of increased and stabilizing radiative forcing (RF) due to the deep ocean warming over the Southern Ocean. SAH responses during RF increase and stabilization are studied with 13 models from the Extended Representative Concentration Pathway scenario 4.5 (ECP4.5) experiment. At 100 hPa, the SAH intensifies and moves equatorward in increased RF scenario; when RF stabilizing, SAH still shifts southward but with little change in intensity. At 200 hPa, the SAH changes little in both RF increase and stabilization. These opposite responses at different altitudes may be due to the maximum potential temperature at 150–200 hPa, leading to the opposite changes in vertical motion. Results of the linear baroclinic model indicate that (a) during RF increase, diabatic heating () contributes to SAH strengthening, both and the mean advection of stratification change (MASC) lead to SAH southward movement; (b) during RF stabilization, and MASC, contribute to the SAH equatorward displacement. Two components of , the latent heating and residual heating, are canceled out and lead to little change in SAH intensity.

Impacts of Oceanic Mesoscale Structures on Sea Surface Temperature in the Arabian Sea and Indian Summer Monsoon Revealed by Climate Model Simulations

Abstract Climate models typically have a cold sea surface temperature (SST) bias for the Arabian Sea, which regulates the Indian monsoon system as a water vapor source. Since the SST for the Arabian Sea is critical for the Indian monsoon, a better understanding of the processes that affect the SST is required. In this study, the effects of mesoscale oceanic variability on simulations of the Arabian Sea SST and Indian summer monsoon precipitation were investigated based on a comparison of climate model experiments in which non-eddying and eddy-permitting ocean components are coupled. In the eddy-permitting model, warm water advection driven by mesoscale variability near the Gulf of Aden and the Gulf of Oman increases the SST in the western Arabian Sea. Lateral eddy heat transport enhances warm water outflows to the Arabian Sea and suppresses surface water cooling by coastal upwelling during the southwestern monsoon season. Furthermore, a sensitivity experiment shows the primary importance of resolving oceanic mesoscale eddies and the secondary importance of resolving the Persian Gulf and Red Sea for the Arabian Sea SST. Also, the summer monsoonal precipitation decreases (increases) over the southeastern Arabian Sea (western and northern India) in the eddy-permitting model due to enhancement of wind convergence in the lower troposphere. Atmospheric general circulation model experiments indicate that the precipitation difference is partly caused by SST changes over the western Arabian Sea. The findings imply that the ocean resolution of climate models is a key factor in efficiently simulating the Indian monsoon.

Hydro-climatic variability and consequent vegetation response during CE 1219–1942 from the Western Ghats, India

We present a pollen proxy record of hydro-climatic variability in the Somwarpet area of Karnataka State (Western Ghats), India, receiving monsoon rainfall from both the southwest summer monsoon (SWM; June to September: JJAS) and the northeast winter monsoon (NEM; October to December: OND). This record covers the last 723 years (CE 1219–1942) and is based on high-resolution lacustrine sediment pollen proxy data. The pollen evidence indicates that between 731 and 576 cal yr BP (CE [AD] 1219–1374), the landscape was dominated by mixed moist/semi-evergreen–dry tropical deciduous forests under a warm and moist climate, possibly indicating increased monsoon rainfall. This phase is globally correlated with the Medieval Climate Anomaly (MCA; CE 750–1200). Between 576 and 279 cal yr BP (CE 1374–1671), dense mixed moist/semi-evergreen–dry tropical deciduous forests came into existence and transformed the existing forests of the previous phase under a warm and more moist climate with further increase in monsoon rainfall. Finally, between 279 and 8 cal yr BP (CE 1671–1942), mixed moist/semi-evergreen–dry tropical deciduous forests again came into being, replacing the existing dense mixed forests of the previous phase under a warm and comparatively less moist climate with increased monsoon (may be NEM) rainfall, corresponds to the global Little Ice Age (LIA; CE 1550–1850). The hydro-climatic variability during CE 1219–1942 offers valuable insights into the impact of monsoonal variability and human activities on ecosystems in the Western Ghats (India), which are subject to dual monsoon systems (SWM and NEM).

Meridional Heat Transport in the DeepMIP Eocene Ensemble: Non‐CO2 and CO2 Effects

AbstractThe total meridional heat transport (MHT) is relatively stable across different climates. Nevertheless, the strength of individual processes contributing to the total transport are not stable. Here we investigate the MHT and its main components especially in the atmosphere, in five coupled climate model simulations from the Deep‐Time Model Intercomparison Project (DeepMIP). These simulations target the early Eocene climatic optimum, a geological time period with high CO2 concentrations, analog to the upper range of end‐of‐century CO2 projections. Preindustrial and early Eocene simulations, at a range of CO2 levels are used to quantify the MHT changes in response to both CO2 and non‐CO2 related forcings. We found that atmospheric poleward heat transport increases with CO2, while oceanic poleward heat transport decreases. The non‐CO2 boundary conditions cause more MHT toward the South Pole, mainly through an increase in the southward oceanic heat transport. The changes in paleogeography increase the heat transport via transient eddies at the northern mid‐latitudes in the Eocene. The Eocene Hadley cells do not transport more heat poleward, but due to the warmer atmosphere, especially the northern cell, circulate more heat in the tropics, than today. The monsoon systems' poleward latent heat transport increases with rising CO2 concentrations, but this change is counterweighted by the globally smaller Eocene monsoon area. Our results show that the changes in the monsoon systems' latent heat transport is a robust feature of CO2 warming, which is in line with the currently observed precipitation increase of present day monsoon systems.

Summer Extreme Precipitation in Southern China from the Perspective of Moisture Static Energy

Abstract The extreme precipitation (EP) in the early and late rainy seasons in Southern China is investigated from the perspective of moist static energy (MSE). At the synoptic time scale, the EP is accompanied by the charge–discharge paradigm of the vertically integrated MSE (〈MSE〉); the positive 〈MSE〉 anomaly reaches the peak one day before EP and decreases quickly during the event. The charge–discharge paradigm of 〈MSE〉 is dominated by the horizontal and vertical advection, respectively. However, synoptic systems responsible for the 〈MSE〉 charge in the early and late rainy seasons are different due to the different horizontal distributions of climatological MSE in the lower troposphere caused by the northward migration of solar radiation and the monsoon system. At the interannual time scale, more EP in the early (late) rainy season is associated with the higher seasonal-mean 〈MSE〉 that can be caused by the anomalous anticyclone (cyclone) in the western North Pacific induced by the SST anomalies in the tropical Indian Ocean and central North Pacific (the tropical Pacific). The multimodel ensemble mean of CMIP6 models reproduces well the observed 〈MSE〉–EP relationship in both the historical and Shared Socioeconomic Pathway 5–8.5 (SSP5–8.5) runs. Moreover, the mean state of 〈MSE〉 increases in the SSP5–8.5 compared to historical runs along with more frequent occurrence of EP events. Hence, 〈MSE〉 can serve as a useful metric for studying EP in Southern China at various time scales.

Latest Neogene Paleoclimate Variation in Yunnan, Southwest China, Revealed by Fossil Leaf Physiognomy

AbstractYunnan Province, located in the southeastern margin of the Tibetan Plateau, can provide important information on how climate change was influenced by global cooling. However, its variation patterns in temperature and precipitation during the latest Neogene are not well‐understood. Based on the 357 specimens assigned to 31 morphotypes of plant fossils from the upper Pliocene Ciying Formation in Yiliang County, Yunnan Province, Southwest China, paleoclimate was estimated by Leaf Margin Analysis and Climate Leaf Analysis Multivariate Program. Compared to the present climate, the mean annual temperature and coldest month temperature have not changed significantly since the late Pliocene, whereas the warmest month temperature has decreased significantly. All precipitation‐related parameters have decreased, particularly winter precipitation. Combined with the climatic data of the same period in other areas of Yunnan, the western and eastern Yunnan has shown a similar pattern in temperature variation since the late Pliocene except for central Yunnan; whereas the variation in precipitation does not follow a common law except for a consistent decrease in winter precipitation. Our study reinforced the fact that under the background of global cooling and intensified monsoon systems, different areas of Yunnan exhibit different climatic responses to these changes because of their topographic heterogeneities.

Determination and assessment of GNSS-derived precipitable water vapor in Indonesia using Ina-CORS

This work is the first attempt to investigate the accuracy and reliability of the Ina-CORS (Indonesian Continuously Operating Reference Stations) for meteorological applications. We used the standard procedures to determine and assess the precipitable water vapor (PWV) obtained from the Global Navigation Satellite System (GNSS) measurements. The GNSS-derived zenith tropospheric delay (ZTD) was estimated using the GAMIT software, and it was then converted to PWV using surface pressure measurements and the water vapor weighted mean temperature. The results were compared against those derived from the fifth generation of the European Centre for Medium-Range Weather Forecasts (ECMWF ERA5) data.Comparisons against the ECMWF ERA5 data reveal the following findings. Values for the mean bias and root mean square deviation (RMSD) of the GNSS-derived ZTD over the period 2011–2020 are −6.6 mm and 14.1 mm, respectively, representing the total percentage error of about 0.4%. The total errors from the surface pressure measurements and the calculations of water vapor weighted mean temperature introduce errors to the PWV values with the magnitude less than 1 mm. The GNSS-derived PWV values over Indonesia are comparable with those derived from the ECMWF ERA5 data. The mean bias and RMSD of PWV values are −0.60 mm and 2.59 mm, respectively. In addition, spatio-temporal variations of the GNSS-derived PWV can capture the main atmospheric features that are consistent with the other results deduced from long-term rainfall data. One of the features is the annual and semiannual cycles of PWV that largely correspond to the annual migration of the Asian-Australian monsoon system. Based on these results, we can conclude that the Ina-CORS is capable enough for accurate monitoring of the Indonesian weather and climate variations.