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Saline lakes contributions to the carbon cycle is crucial to the Qinghai‐Tibetan Plateau (QTP) carbon budget. Here, based on the 8‐year direct measurement of CO2 flux over the Qinghai Lake (QHL) and 83 collected CO2 flux data estimated by pCO2 sampling from 45 lakes over the QTP, we identified the interannual variations of CO2 flux and its response to the extreme climate events. Results showed: (a) the QHL CO2 absorption weakened in the spring, autumn and winter and turn to CO2 emissions in the summer during 2013–2020; (b) with higher Ts and less precipitation, coupling of positive Pacific Decadal Oscillation (PDO) and El Niño enhanced the summer CO2 emissions; and (c) the PDO and ENSO had obvious superposition effect on the decrease of CO2 absorption in autumn. Our results show the potential mechanism of lake CO2 flux responses to extreme climate and further defines the significance of the QTP carbon budget and cycling. Plain Language Summary The CO2 flux at the water‐air interface is especially important since it directly affects the accurate evaluation of the global carbon budget. However, lacking of long‐term continuous observation data left an undeniable gap on the interannual variations of CO2 flux and its respond to extreme climate events (the El Niño‐Southern Oscillation and Pacific Decadal Oscillation: ENSO and PDO) in saline lakes, although they are globally significant. Here, based on the 8‐year direct measurement of CO2 flux by eddy covariance system over the QHL and 83 collected CO2 flux data estimated by pCO2 sampling from 45 lakes over the QTP. This study found a weakening of CO2 absorption in the spring, autumn and winter, and an enhancing of CO2 emissions in the summer in QHL during 2013–2020, and first reported a notable transformation of carbon sink to source of saline lakes for responding to the extreme climate events. Moreover, the enhancing of CO2 emissions may be stronger in saline lakes than that in fresh lakes over QTP. The results firstly show the potential mechanism of lake CO2 flux responses to extreme climate and further defines the significance of the QTP carbon budget and cycling. Key Points The QHL CO2 absorption weakened in spring, autumn and winter, and even turn to CO2 emissions in summer during 2013–2020 In‐phase PDO and El Niño events enhanced the summer CO2 emissions in saline lake over QTP Rising in Ts and decreasing in precipitation dominated the CO2 variations

The interannual variation of intraseasonal (10–30-day) oscillation (ISO) intensity for the eastward- and westward- propagating types over the mid-high latitudes in austral summer is studied. It indicates that during strong ISO years, the wave train has a larger amplitude and wider zonal influencing range. The wave train propagates eastward in both strong and weak eastward-propagating ISO years, while it propagates westward only in strong westward-propagating ISO years. One possible explanation for the larger magnitude of the wave train in strong ISO years is that the ISO perturbation acquires more energy from the mean flow through the barotropic kinetic energy and potential energy conversion. Based on the diagnostic results of the geopotential height trend, the maximum contributor to the eastward propagation is the same during strong and weak ISO years, as well as for the westward propagation. However, the relative contribution of the relative vorticity’s meridional advection in weak years is smaller than that in strong years, which may be the reason why there is no significant westward propagation in weak ISO years. Due to the difference in amplitude and influencing range of the wave train during strong and weak ISO years, the two ISO types have different effects on the surface air temperate over land areas at the Southern Hemisphere. The interannual variation of the eastward-propagating ISO intensity appears to be linked to the El Niño-Southern Oscillation and Southern Annular Mode, while the westward-propagating ISO appears unrelated to them.

March rainfall over southern China (SC) experiences a significant decrease of the intensity of interannual variation (IIV) around 1996/1997. During 1982–1996, the IIV of March rainfall over southern China (SCMR) are stronger than during 1997–2011, and the interannual variation of SCMR is closely related to sea surface temperature (SST) anomalies. The eastern Pacific El Niño (La Niña) would weaken (strengthen) the Walker circulation, accompanying convergence (divergence) anomalies over tropical eastern Pacific and divergence (convergence) anomalies over western Pacific in the lower level. The divergent wind anomalies blow from western Pacific (SC) to SC (western Pacific) and converge (diverge) over SC, which favors ascending (descending) motions over there. The water vapor convergence (divergence) anomalies and ascending (descending) motions over SC cause more (less) SCMR. Besides, positive (negative) tropical southeastern Indian Ocean SST anomalies are of benefit to the more (less) SCMR by affecting vertical circulation. However, the relation between SCMR and SST anomalies decreases after 1997. During 1997–2011, SCMR experiences the lower IIV period than before. The snow depth over the Eurasia continent has an important impact on the SCMR. The SCMR is negatively correlated with the snow depth from the Siberia to Northeast China, but positively correlated with the snow depth over the Tibetan Plateau (TP). The ground obtains more (less) heat flux with less (more) snow, accompanying positive (negative) outward long wave radiation anomalies and latent heat flux anomalies, which helps to maintain positive (negative) air temperature anomalies over the Siberia to Northeast China. Meanwhile, the ground over TP obtains less (more) heat flux with more (less) snow, favoring negative (positive) air temperature anomalies. The configuration of air temperature and geopotential height dipole anomalies conforms to static equilibrium over East Asia, and favors the cyclone-anticyclone (anticyclone-cyclone) dipole anomalies from the low latitudes to the mid-high latitudes in the upper level, which represents the southward (northward) subtropical upper-level westerly jet over TP, conducive to more (less) SCMR. The external forcings that have impacts on the interannual variation of SCMR experience an interdecadal change before and after 1996/1997.

The South Asian summer monsoon (SASM) is of considerable scientific and social importance to the densely populated South Asia. Existing literature signified that the interannual variation of the SASM can be reflected by multiple dynamical and radiative processes. However, quantifying their relative contributions remains inadequate, particular for the contribution of aerosol process. Here, the land-sea thermal contrast index (LSTCI) is employed to represent the large-scale thermal driving at the mid–upper troposphere associated with the SASM, which is defined as temperature difference between the southern Eurasia (SE) and the tropical Indian Ocean (TIO) at the mid–upper troposphere. Based on the coupled atmosphere-surface climate feedback-response analysis method, this study linearly decomposes the total temperature change associated with the LSTCI into several partial temperature changes associated with individual dynamical and radiative processes. Our result demonstrates that the LSTCI is mainly explained by the positive contributions of atmospheric dynamic (69%), water vapor (35%), and aerosol (11%) processes, which are partially offset by a negative contribution of cloud process (-18%). Surface dynamic process play a neglectable role in the LSTCI, because it exerts similar effects on the temperature anomalies over the SE and the TIO. Further analysis indicates that the total effect of aerosols is dominated by change in black carbon. As two important components, the temperature anomalies over the SE and the TIO separately account for about 55% and 45% to the LSTCI. Our finding provides a new insight onto quantitatively understanding the relevant processes involved in the SASM variation.

Most previous studies have investigated East Asian summer rainfall as one element. This study investigates the East Asian summer monsoon (EASM), Western North Pacific (WNP) tropical cyclones (TCs), and the concurrent rainfall occurring between May and September from 1983 to 2021. Three distinct types of rainfall are identified: monsoon-only rainfall, TC-only rainfall, and monsoon-TC joint rainfall (MS-TC rainfall), each exhibiting its own unique characteristics. Monsoon-only rainfall is characterized by positive anomalies along the East Asian subtropical front, while a decrease in TC activity leads to negative rainfall anomalies in the tropical WNP. TC-only rainfall, on the other hand, contributes to positive rainfall anomalies in the tropical WNP, as more TCs exhibit westward movement. In the case of MS-TC rainfall, positive precipitation anomalies are observed in the Philippines, the Korean Peninsula, and southern Japan. These anomalies can be attributed to an enhanced northward movement of TCs during such rainfall events. During strong monsoon-only (TC-only) rainfall years, the tropical western Pacific experiences anticyclonic (cyclonic) anomalies, along with a westward (eastward) shift of monsoon trough and WNP subtropical high (WNPSH). In strong MS-TC years, a localized cyclonic anomaly dominates the Philippine Basin, resulting in an eastward shift of the monsoon trough and WNPSH. Additionally, a significant increase (decrease) in vertical wind shear (VWS) is observed in the tropical WNP during strong monsoon-only (TC-only) years, while a moderate decrease is observed in strong MS-TC years. Distinct influential factors are associated with each rainfall type. Preceding positive sea surface temperature (SST) anomalies in the offshore China seas and WNP, in conjunction with the El Niño-Southern Oscillation (ENSO), play a primary role in driving interannual variations of monsoon-only rainfall. ENSO serves as the principal modulator of interannual variations in TC-only rainfall. Additionally, anomalous thermal conditions in the Maritime Continent (MC) act as major drivers for MS-TC rainfall. This study enhances our understanding of the underlying mechanisms and influential factors contributing to the diverse patterns of East Asian summer rainfall.

The impact of the positive and negative phase of the Indian Ocean dipole (IOD) on the Pacific blocking frequency (PBF) during boreal autumn is investigated based on the ERA5 daily reanalysis data from 1979 to 2021. It is found that the IOD index are characterized by an obvious interannual variation, and the most obvious dipole feature appears in boreal autumn, which is agree with previous studies. Strong 8 positive and 8 negative phases in boreal autumn are selected to further reveal the regulation of different IOD phases on PBF. The results show that the PBF exhibits negative (positive) anomaly in the North Pacific (East Siberia and Central Siberia) during the positive (negative) IOD phase. During the positive (negative) phase, the cold sea surface temperature anomaly (SSTA) in the tropical southeastern (western) Indian Ocean forces teleconnection wave trains, which are likely results of the northeastward propagation of Rossby wave energy. With such a wave train, a geopotential height anomaly of ‘north negative–south positive’ (‘north positive–south negative’) appears around the Bering Strait (Central Siberia) during the positive (negative) phase, which causes negative (positive) PBF anomalies, based on the ERA5 daily reanalysis data and ECHAM4.6 climate model output from 1979 to 2021.

In this study, based on the ECMWF 20-year (1997 ~ 2016) hindcasts, the subseasonal prediction of the weekly summer rainfall anomaly over the middle and lower reaches of the Yangtze River (YR) were studied. The skill at 2-week lead time exhibits prominent interannual variation, which is significantly correlated with the preceding winter ENSO. That is, rainfall anomaly can be better predicted in El Niño decaying summer than in La Niña decaying summer. Observation analyses show that in El Niño decaying summer the intraseasonal variation of YR summer rainfall is featured by strong low-frequency (> 30 days) intraseasonal oscillation (ISO) partly associated with the first boreal summer ISO mode (BSISO1) activity, in comparison with La Niña decaying summer. This is possibly because El Niño-induced mean state western North Pacific (WNP) anti-cyclone blocks the northward propagation of convection over the WNP, resulting in BSISO1 stagnation in phases 3–4. The phase stagnation could force stable atmospheric teleconnection, which is favorable to sufficient moisture transportation to the YR and persistent rainfall formation. Finally, prediction verification showed that more accurate prediction for the middle-low-level circulation contribute to the better prediction of rainfall anomaly in El Niño decaying summer than in La Niña decaying summer.

The 30–60-day boreal summer intraseasonal oscillation (BSISO) is a dominant variability of the Asian summer monsoon (ASM), with its intensity being quantified by intraseasonal standard deviations based on OLR data. The spatial and interannual variations of the BSISO intensity are identified via empirical orthogonal function (EOF) analysis for the period 1981–2014. The first EOF mode (EOF1) shows a spatially coherent enhancement or suppression of BSISO activity over the entire ASM region, and the interannual variability of this mode is related to the sea surface temperature anomaly (SSTA) contrast between the central–eastern North Pacific (CNP) and tropical Indian Ocean. In contrast, the second mode (EOF2) exhibits a seesaw pattern between the southeastern equatorial Indian Ocean (EIO) and equatorial western Pacific (EWP), with the interannual fluctuation linked with developing ENSO events. During strong years of EOF1 mode, the enhanced low-level westerlies induced by the summer-mean SSTA contrast between the warmer CNP and cooler tropical Indian Ocean tend to form a wetter moisture background over the eastern EIO, which interacts with intraseasonal low-level convergent flows, leading to stronger equatorial eastward propagation. The intensified easterly shear favors stronger northward propagation over the South Asian and Eastern Asian/Western North Pacific sectors, respectively. Opposite situation is for weak years. For interannual variations of EOF2 mode, the seesaw patterns with enhanced BSISO activity over the southeastern EIO while weakened activity over the EWP mostly occur in the La Niña developing summers, but inverse patterns appear in the El Niño developing summers.

The present study contrasts interannual variations in the intensity of boreal summer 10–20-day and 30–60-day intraseasonal oscillations (ISOs) over the tropical western North Pacific and their factors. A pronounced difference is found in the relationship of the two ISOs to El Niño-Southern Oscillation. The 10–20-day ISO intensity is enhanced during El Niño developing summer, whereas the 30–60-day ISO intensity is enhanced during La Niña decaying summer. The above different relationship is interpreted as follows. The equatorial central and eastern Pacific SST anomalies modify vertical wind shear, lower-level moisture, and vertical motion in a southeast-northwest oriented band from the equatorial western Pacific to the tropical western North Pacific where the 10–20-day ISOs originate and propagate. These background field changes modulate the amplitude of 10–20-day ISOs. Preceding equatorial central and eastern Pacific SST anomalies induce SST anomalies in the North Indian Ocean in summer, which in turn modify vertical wind shear and vertical motion over the tropical western North Pacific. The modified background fields influence the amplitude of the 30–60-day ISOs when they reach the tropical western North Pacific from the equatorial region. A feedback of ISO intensity on local SST change is identified in the tropical western North Pacific likely due to a net effect of ISOs on surface heat flux anomalies. This feedback is more prominent from the 10–20-day than the 30–60-day ISO intensity change.

In this study, based on total column ozone observations from eight Antarctic stations, we evaluate the applicability of ERA5, C3S-MSR, MERRA-2, and JRA-55 reanalysis datasets and the NIWA-BS merged satellite dataset, in terms of interannual variation and long-term trend, using the correlation coefficient (R), root-mean-square error (RMSE), interannual variability skill score (IVS), and linear trend bias (TrBias). The results show that for interannual variation, C3S-MSR performs well at multiple stations, while JRA-55 performs poorly at most stations, especially Marambio, Rothera, and Faraday/Vernadsky, which are located at lower latitudes on the Antarctic Peninsula. Additionally, all datasets show significantly higher RMSE at Dumont D’Urville and Arrival Heights, which generally are located around the edge of the Antarctic stratospheric vortex where total column ozone values are more variable and on average larger than in the core of the vortex. The comprehensive ranking results show that C3S-MSR performs the best, followed by ERA5 and NIWA-BS, with MERRA-2 and JRA-55 ranking lower. For the long-term trend, each of the datasets has large bias values at Arrival Heights, and the absolute TrBias values of JRA-55 are larger at three stations on the Antarctic Peninsula. The overall averaged results show that C3S-MSR and NIWA-BS have the smallest absolute TrBias, and perform best in reflecting the Antarctic ozone trends, while ERA5 and JRA-55 significantly overestimate the Antarctic ozone recovery trend and perform poorly. Based on our analysis, the C3S-MSR dataset can be recommended to be prioritized when analyzing the interannual variations in Antarctic stratospheric ozone, and both the C3S-MSR reanalysis and NIWA-BS datasets should be prioritized for trend analysis.