Indian Ocean Sea Surface Temperature Research Articles

Regional tree-ring oxygen isotope deduced summer monsoon drought variability for Kumaun-Gharwal Himalaya

The precipitation in the Kumaun-Gharwal (Uttarakhand) Himalaya (KGH) is predominantly regulated by the Indian summer monsoon (ISM) and has been declining over the last century. However, because of limited historical data, it is difficult to place this recent decreasing trend in the context of pre-anthropogenic influences and understand a fuller range of hydroclimate scenarios for the region. Thus, we developed a 508-year regional tree-ring stable oxygen isotope (δ18OTR) record for multiple coniferous taxa (Abies spectabilis, Cedrus deodara and Picea smithiana) for the KGH, which spanned 1508–2015 CE. The δ18OTR record explained 35.8% of instrumental June–August Palmer Drought Severity Index (JJAPDSI) variance modelled from a nearby meteorological station. The JJAPDSI reconstruction shows regional coherency with both instrumental and proxy-based independent hydroclimatic records providing confidence that it is a reliable proxy to assess the long term hydroclimatic variability of the region. We identified decreasing strength of JJAPDSI reconstruction in KGH during recent decades indicating intensified drought. This is in the context of pre-anthropogenic influences and understand a fuller range of hydroclimate scenarios for the region. The δ18OTR also has coherency with Pacific and Indian Ocean sea surface temperature variability illustrating the broader teleconnections that influence the regional hydroclimate.

Effect of SST in the Northwest Indian Ocean on Synoptic Eddies over the South China Sea-Philippine Sea in June

Synoptic eddies (with a period of two to eight days) are active in the South China Sea-Philippine Sea (SCS-PS) and control weather variations. In addition, the intensity and frequency of synoptic eddies may change along with variations in sea surface temperatures (SST). This paper presented the influence of SST in the northwest Indian Ocean on synoptic eddies in the lower troposphere over the SCS-PS in June. Our statistical analysis showed a significant negative correlation between the SST in the northwest Indian Ocean and the synoptic scale eddy kinetic energy (EKE) in the SCS-PS. By analyzing the EKE budget of synoptic eddies, we found that the variation in the synoptic scale EKE over the SCS-PS is mainly due to the change in the monthly zonal wind gradient, which affects the barotropic energy conversion between the monthly mean flow and the synoptic eddies. Additionally, the northwest Indian Ocean SST modulates the monthly flow over the SCS-PS by alternating the strength of the Walker circulation in the west Pacific and Indian Ocean. Finally, the influence of SST in the northwest Indian Ocean on EKE in the SCS-PS was reproduced using the simplified atmospheric general circulation model, SPEEDY.

Combined Effect of the Tropical Indian Ocean and Tropical North Atlantic Sea Surface Temperature Anomaly on the Tibetan Plateau Precipitation Anomaly in Late Summer

Abstract Precipitation variability over the Tibetan Plateau (TP) depends largely on the atmospheric circulation pattern associated with remote oceanic forcing, while the contribution of sea surface temperature anomalies (SSTAs) in different ocean basins, especially the tropical North Atlantic (TNA), remains unclear. By using multisource data and atmospheric general circulation model, this study reveals the individual and combined effects of the Indian Ocean basin mode (IOBM) and TNA SSTA on the interannual variability of TP precipitation in late summer (August). During the positive phase of the IOBM, warm SSTAs in the Indian Ocean induce an anomalous anticyclone over the Bay of Bengal (BOBAC) via the Kelvin wave–induced Ekman divergence and a resulting positive precipitation anomaly over the southeastern TP. Simultaneously, an eastward-extending Kelvin wave triggered by the positive TNA SSTA overlaps with that caused by the IOBM, further strengthening the BOBAC. In addition, the Kelvin wave triggered by the TNA SSTA induces anomalous easterlies over the tropical Indo-Pacific, which contribute to the warm Indian Ocean SSTA and thus amplify the IOBM affecting TP precipitation. Moreover, the positive TNA SSTA generates a westward-extending Walker circulation anomaly that is responsible for the suppressed convection over the central Pacific, which in turn triggers a Rossby wave response and further strengthens the BOBAC. As a result, the positive precipitation anomaly over the southeastern TP is strengthened significantly. Particularly, considering the 2–3-month lead time of the IOBM and TNA SSTA, the tropical SSTA can be used as a predictor for the TP precipitation anomaly.

The Coordinated Influence of Indian Ocean Sea Surface Temperature and Arctic Sea Ice on Anomalous Northeast China Cold Vortex Activities with Different Paths during Late Summer

The Coordinated Influence of Indian Ocean Sea Surface Temperature and Arctic Sea Ice on Anomalous Northeast China Cold Vortex Activities with Different Paths during Late Summer

Slowdown in Landfalling Tropical Cyclone Motion in South China

AbstractChina is one of the countries suffering the most tropical cyclone (TC) disasters, while changes in translation speed of TCs landfalling in China remain unclear. Here we found that the translation speed of landfalling TCs in south China during the boreal summer has significantly decreased by 0.3 m s−1decade−1 during 1979–2019, which is largely driven by a decadal deceleration in steering flow in the late 1990s. The slowdown in steering flow is found to be a balance of the opposite effects of the negative phase of the Pacific Decadal Oscillation and sea surface temperature (SST) warming in the Indian Ocean since the late 1990s. Given the recent Indian Ocean SST warming has been viewed as a footprint of external forcing, the results suggest that the effects of external forcing and natural variability on TC translation speed can offset each other.

Variations of Summer Extreme and Total Precipitation over Southeast Asia and Associated Atmospheric and Oceanic Features

Abstract Southeast Asia lies at the heart of heavy precipitation on Earth, and a large amount of latent heat released here provides substantial energy for the global atmospheric circulation. Utilizing gauge-based daily precipitation and the self-organizing map technique, the summertime extreme and total precipitation over Southeast Asia during 1979–2019 are classified into three and five distinct patterns, respectively. The three extreme precipitation clusters are characterized by southern dry and northern wet (C1_extreme), overall wet (C2_extreme), and northern dry and southern wet (C3_extreme) structures. The frequencies of these patterns exhibit increasing trends during the analysis, although they are not statistically significant for C1_extreme. The C1_extreme pattern is accompanied by an anomalous cyclone over the South China Sea in response to negative Indian Ocean sea surface temperature anomalies (SSTAs). The C2_extreme and C3_extreme clusters are characterized by a westward extension of the western Pacific subtropical high, regulated by cool SSTAs over the tropical central-eastern Pacific that are induced by the tropical North Atlantic warming and the tropical Pacific and Atlantic SSTAs, respectively. For total precipitation, the first and second clusters show overall dry distributions, which are mainly composed of nonextreme precipitation. The spatial patterns and atmospheric and oceanic features associated with the other three clusters of total precipitation bear large resemblances to those of C1_extreme, C2_extreme, and C3_extreme, respectively, but their trends exhibit smaller similarities. Comparing the differences between extreme and total precipitation over Southeast Asia could improve our understanding of their regional variabilities and relationships, and potentially their global impacts. Significance Statement We explore the atmospheric and oceanic processes associated with extreme precipitation, and compare them with those for total precipitation over Southeast Asia. The three key modes of summertime extreme precipitation over Southeast Asia are characterized by southern drought and northern flood, overall flood, and northern drought and southern flood structures. Each pattern is closely linked to tropical sea surface temperature anomalies, but in different regions. Total precipitation can be classified into five distinct patterns. The first two modes are largely determined by nonextreme precipitation, while the other three bear large resemblances to the three extreme precipitation modes. These findings provide guidance on what is the key factor in driving each extreme precipitation mode over Southeast Asia, allowing better prediction.

Assessment of hot weather seasonal temperatures over India using Monsoon Mission Coupled Forecasting System hindcasts

AbstractThe present study evaluates the skill of seasonal forecasts of temperatures over India during April to June using the Monsoon Mission Coupled Forecasting System (MMCFS) model hindcasts, which are initialized with February initial conditions. Model hindcast data of 1981–2017 period have been used for the analysis. The India Meteorological Department (IMD) gridded temperature dataset has been used for model verifications. The MMCFS model captures the annual cycle of temperatures reasonably well, but with a higher mean and smaller variability compared to observations. The model hindcasts show a significant skill for seasonal forecasts of temperatures over most of northwest and central India. Empirical Orthogonal Function (EOF) analysis suggests that the model captures temporal and spatial characteristics of different modes of maximum temperatures but with less accuracy. The model teleconnections of maximum temperatures with Indian Ocean sea surface temperatures (SSTs) and El Niño–Southern Oscillation (ENSO) are weakly represented. The model is also found capable of predicting the spatial distribution of heat wave characteristics such as heat wave frequency (HWF) and heat wave duration (HWD) reasonably well. The present study suggests that the MMCFS Model can be used to generate a useful outlook of hot weather seasonal temperatures and heat waves over India.

More profound impact of CP ENSO on Australian spring rainfall in recent decades

Most of Australia was in severe drought from 2018 to early 2020. Here we link this drought to the Pacific and Indian Ocean sea surface temperature (SST) modes associated with Central Pacific (CP) El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Over the last 20 years, the occurrence frequency of CP El Niño has increased. This study extends the previous understanding of eastern Pacific (EP) El Niño-Australian rainfall teleconnections, exhibiting that CP El Niño can bring much broader and stronger rainfall deficiencies than EP El Niño during austral spring (September–November) over the northern Australia (NAU), central inland Australia and eastern Australia (EAU). The correlations between SST fields and rainfall in three Cluster regions divided by clustering analysis also confirm this, with rainfall variability in most of Australia except southern Australia (SAU) most significantly driven by CP ENSO. Also, we demonstrate that the CP El Niño affects rainfall in extratropical EAU via the Pacific-South American (PSA) pattern. While the influence of EP El Niño is only confined in tropical NAU because its PSA pattern sits far too east to convey its variability. With the development of ENSO diversity since 2000, the footprint of El Niño on Australian rainfall has become more complex.

What caused the interdecadal shift in the El Niño–Southern Oscillation (ENSO) impact on dust mass concentration over northwestern South Asia?

Abstract. Changes in large-scale circulation, especially El Niño–Southern Oscillation (ENSO), have significant impacts on dust activities over the dust source and downwind regions. However, these impacts present an interdecadal pattern, and it remains less clear which factors lead to the interdecadal variability of the ENSO impact on dust activities over northwestern South Asia, although previous studies have discussed the response of interannual dust activities over northwestern South Asia to the ENSO circle. Based on the linear regression model and MERRA-2 atmospheric aerosol reanalysis data, this study investigated the interdecadal variability of the ENSO impact on dust activities as well as the associated possible atmospheric drivers under two different warming phases over northwestern South Asia. Results indicated that the relationship between ENSO and dust column mass density (DUCMASS) experienced an obvious shift from the accelerated global warming period (1982–1996) to the warming hiatus period (2000–2014). The change in Atlantic and Indian Ocean sea surface temperature anomaly (SSTA) patterns weakened the impact of ENSO on dust activities over northwestern South Asia during 1982–1996, while the change in Pacific Decadal Oscillation (PDO) strengthened ENSO's effect when it was in phase with ENSO. Both the Atlantic and Indian Ocean SSTA patterns were modulated by the duration of ENSO events (i.e., continuing and emerging ENSO). This study provides new insights into numerical simulation involving the influence of atmospheric teleconnections on the variability of dust activities and their influence mechanisms.

Retraction Statement: Plio‐Pleistocene Indonesian Throughflow Variability Drove Eastern Indian Ocean Sea Surface Temperatures

Retraction: Smith, R. A., Castañeda, I. S., Groeneveld, J., De Vleeschouwer, D., Henderiks, J., Christensen, B. A., et al. (2020). Plio‐Pleistocene Indonesian Throughflow variability drove Eastern Indian Ocean sea surface temperatures. Paleoceanography and Paleoclimatology, 35, e2020PA003872. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020PA003872. The above article from Paleoceanography and Paleoclimatology, published online on 22 October 2020, has been retracted by agreement among the authors, the journal Editor‐in‐Chief, the American Geophysical Union, and Wiley Periodicals LLC. The retraction has been agreed because the authors identified a spreadsheet error in the calculation of the Long‐Chain Diol Index (LDI). Additionally, errors in the calculation of alkenone and GDGT concentrations were identified that change the values but not the overall trends. The authors note that because they mainly focused their interpretations on the TEX86‐derived sea‐surface temperature (SST) record, the overall conclusions of the manuscript remain unchanged. The authors intend to submit a new manuscript to reflect the corrected information.

The Interdecadal Change of the Relationship Between North Indian Ocean SST and Tropical North Atlantic SST

AbstractThe summertime North Indian Ocean (NIO) and tropical North Atlantic (TNA) sea surface temperature (SST) anomalies exert important impacts on atmospheric circulation and climate variation. Little attention is paid on the interdecadal change of NIO–TNA SST connection. This study reveals that the NIO–TNA SST relationship experiences an obvious interdecadal change around the early 2000s. The NIO and TNA SST correlation is positive and significant before the early 2000s, while this connection becomes weak and insignificant after that. This interdecadal change is closely associated with the changes in the El Niño‐Southern Oscillation (ENSO) intensity. During 1980–2001, strong ENSO forces a sustained SST warming in the southwest Indian Ocean, which further warms the summertime NIO via inducing antisymmetric circulation and reducing the upward surface latent heat flux. Meanwhile, strong ENSO forces a summertime TNA warming via arousing the Pacific North American (PNA) teleconnection. The PNA weakens the TNA trade winds, then reduces the upward surface heat flux and consequently warms the TNA. Thus, NIO and TNA SST connection is established via ENSO events during 1980–2001. In contrast, during 2002–2020, the summertime NIO SST anomaly is still related to ENSO. However, the connection between the TNA SST anomaly and ENSO is interrupted due to the weak ENSO intensity. Such weak ENSO yields a much weaker PNA teleconnection, which is inefficient to generate the TNA warming. Further analysis shows that the TNA warming during 2002–2020 is generated mainly by the negative North Atlantic Oscillation. Therefore, the connection between NIO and TNA SST anomalies collapses under the weak ENSO condition.

Effect of Interdecadal Variation in Southern Indian Ocean SST on the Relationship Between ENSO and Summer Precipitation in the Asian‐Pacific Monsoon Region

AbstractThe relationships between the El Niño‐Southern Oscillation (ENSO), Asian‐Pacific region summer precipitation and its corresponding atmospheric circulations exhibit interdecadal changes. From the early 1990s to the early 2000s, these relationships were significant. Therefore, we divided this time frame into three periods for analysis: 1979–1991 (P1), 1992–2005 (P2), and 2006–2019 (P3). The possible mechanism underlying these relationships is as follows: the southern Indian Ocean sea surface temperature (SST) over the east of Madagascar exhibits interdecadal variation. During P2, the SST was relatively cold, which induced an anomalously high mascarene high (MH). The strengthened MH enhanced the Somali jet and Indian monsoon westerlies, which intensified the strong center of the Indian Ocean Walker circulation. Therefore, owing to the strength and location changes of the Indian Walker circulation and the Walker circulation, the connection between the ENSO and the western Pacific vertical motions strengthened, resulting in the close relationship of the ENSO with the atmospheric circulation over the Asian‐Pacific region. Hence, ENSO can influence a north‐south tripole pattern of precipitation over the Asian‐Pacific monsoon region through local vertical activities and meridional Hadley circulation over western Pacific. Numerical experiments using an atmospheric general circulation model, with prescribed three times southern Indian Ocean SST anomalies of 1995–2005 relative to 1979–2019, also lend support to the southern Indian Ocean SST's contribution to modulating the relationship between ENSO and summer precipitation over the Asian‐Pacific monsoon region.

Can Coastal Upwelling Trigger a Climate Mode? A Study on Intraseasonal‐Scale Coastal Upwelling Off Java and the Indian Ocean Dipole

AbstractCoastal upwelling along the southern coast of Java brings cold and nutrient‐rich subsurface water to the surface. We explored whether the upwelling could trigger the onset of the Indian Ocean Dipole (IOD) by supplying cold water to the southeastern tropical Indian Ocean. We used satellite‐based daily chlorophyll‐a concentration (Chl‐a) data during 2003–2020 as a proxy of the coastal upwelling. We focused on first Chl‐a bloom that occurred in April‐June, the onset phase of the positive IOD (pIOD). We found that the timing and strength of the upwelling signals were significantly correlated with the subsequent IOD peaks. We diagnosed processes associated with the upwelling affecting sea surface temperature (SST) in the southeastern Indian Ocean. Results indicate that after the cold‐water upwelling south of Java, westward surface temperature advection plays a role in anomalously cooling the SST in the southeastern Indian Ocean and setting a favorable condition for the subsequent pIOD development.

Analysis of Influencing Factors of SST in Tropical West Indian Ocean Based on COBE Satellite Data

The time-frequency domain analysis of the sea surface temperature (SST) in the tropical western Indian Ocean was conducted using wavelet analysis, cross wavelet transform (XWT), the Mann–Kendall (MK) test, and other methods based on COBE-SST data for the last 50 years (1974–2020). From the perspective of time-frequency combination, examining the data of precipitation, sea surface heat flux, total cloud cover, and long-wave radiation, helped contribute to exploring the periodic changes of SST. Moreover, the Western Hemisphere Warm Pool (WHWP) was selected to analyze the role of SST from 1974 to 2020. Present results have demonstrated that the SST in the western Indian Ocean was in a stage of rising, particularly in 1998. According to the fast Fourier transform of the filtered SST time series, the tropical western Indian Ocean SST has a short period of 3–6 years, a medium period of about 10 years, and a long period of 40 years. The SST in the tropical western Indian Ocean has a resonance period of 2–6 years with precipitation, a resonance period of 2–6 years with sea surface heat flux, a resonance period of 4–5 years with total cloud cover, and a resonance period of 2–5 years with long-wave radiation. Importantly, SST was negatively associated with precipitation, total cloud cover, and long-wave radiation, and positively for sea surface heat flux before 1997. Seasonal migration activities are significantly correlated with the WHWP and the tropical western Indian Ocean SST. The spatial lattice point correlation coefficient is generally from 0.6 to 0.9, and the inter-annual serial correlation value is more than 0.89. Furthermore, the two exist with a resonance period of 2–5 years.

Exceptionally prolonged extreme heat waves over South China in early summer 2020: The role of warming in the tropical Indian Ocean

South China experienced a series of unprecedented extreme heat wave (EHW) events in early summer (June–July) 2020, which broke the historical record for the frequency of EHW events since 1979. Observational analyses showed that the prolonged EHW events were primarily induced by an anomalous tropospheric circulation over South China with a barotropic structure. This was attributed to the exceptional westward displacement of the western Pacific subtropical high (WPSH) and the eastward-extended upper-level South Asia high (SAH). In addition, the value of the SAH–WPSH index, which describes the relative displacement of the SAH and WPSH, also broke the historical record. Further analysis revealed that the EHW events in South China were closely associated with warming of the tropical Indian Ocean (TIO) sea surface temperature (SST), which affected both the SAH and WPSH via atmospheric teleconnections. Sensitivity and pacemaker experiments using an atmosphere-only and a coupled global climate model, respectively, suggested that the anomalous warming of the SST in the TIO directly caused the significant southeastward displacement of the intensified SAH as a result of diabatic heating in the troposphere. This heating also led to a westward-displaced WPSH via an induced mid- to lower tropospheric Kelvin wave and the associated Ekman divergence. In summary, warming in the TIO sustained exceptional shifts in both the SAH and WPSH, which favored the formation of a stationary anomalous high over South China that ultimately contributed to the record-breaking EHW events in early summer 2020.

Possible Linkage Between Tropical Indian Ocean SST Anomalies and the Date of First and Last Tropical Cyclones Landfalling in the Chinese Mainland

Bases on the NCEP / NCAR reanalysis products, HadISST dataset, and data of tropical cyclone (TC)landfalling in the Chinese mainland during 1960-2019, the possible impacts of Indian Ocean Dipole (IOD) mode andIndian Ocean basin (IOB) mode on the last-TC-landfall date (LLD) and first-TC-landfall date (FLD), respectively, areinvestigated in this study. The LLD is in significantly negative correlation with autumn IOD on the interannual time-scale and their association is independent of El Niño-Southern Oscillation (ENSO). The LLD tends to be earlier when theIOD is positive while becomes later when the IOD is negative. An anomalous lower-level anticyclone is located aroundthe Philippines during October-November, resulting from the change of Walker circulation over the tropical Indo-westPacific Ocean forced by sea surface temperature (SST) anomalies related to a positive IOD event. The Philippinesanticyclone anomaly suppresses TCs formation there and prevents TCs from landfalling in the Chinese mainland due tothe anomalous westerly steering flows over southeast China during October-November, agreeing well with the earlierLLD. However, the robust connection between spring IOB and FLD depends on ENSO episodes in preceding winter.There is an anticyclonic anomaly around the Philippines caused by the tropical SST anomalies through modulating theWalker circulation during May-June when the IOB is warming in the El Niño decaying phase. Correspondingly, the TCsgenesis is less frequent near the Philippines and the mid-level steering flows associated with the expanded westernPacific subtropical high are disadvantageous for TCs moving towards southeast China and making landfall during May-June, in accordance with the later FLD. By contrast, cooling IOB condition in spring of a La Niña decaying year andnegative IOD cases during autumn could produce a completely reversed atmospheric circulation response, leading to anearlier FLD and a later LLD over the Chinese mainland, respectively.

Prediction and mechanistic analysis of May precipitation in North China based on April Indian Ocean SST and the Northwest Pacific Dipole

North China May precipitation (NCMP) accounts for a relatively small percentage of annual total precipitation in North China, but its climate variability is large and it has an important impact on the regional climate and agricultural production in North China. Based on observed and reanalysis data from 1979 to 2021, a significant relationship between NCMP and both the April Indian Ocean sea surface temperature (IOSST) and Northwest Pacific Dipole (NWPD) was found, indicating that there may be a link between them. This link, and the possible physical mechanisms by which the IOSST and NWPD in April affect NCMP anomalies, are discussed. Results show that positive (negative) IOSST and NWPD anomalies in April can enhance (weaken) the water vapor transport from the Indian Ocean and Northwest Pacific to North China by influencing the related atmospheric circulation, and thus enhance (weaken) the May precipitation in North China. Accordingly, an NCMP prediction model based on April IOSST and NWPD is established. The model can predict the annual NCMP anomalies effectively, indicating it has the potential to be applied in operational climate prediction.摘要尽管华北区域五月降水 (NCMP) 占华北区域年总降水量的比率较少, 但是其气候变率较大, 对华北区域气候和农业生产等具有重要影响. 基于观测和再分析资料, 发现NCMP与前期四月的印度洋海温 (IOSST) 和西北太平洋偶极子 (NWPD) 具有显著关系, NCMP可能受到IOSST和NWPD的协同影响. 进一步分析表明, 前期四月暖 (冷) 的IOSST和正 (负) 位相的NWPD能够分别通过调节印度洋和西北太平洋区域的局地环流增强 (减弱) 从印度洋和西北太平洋向华北区域输送的水汽, 进而增强 (减弱) NCMP. 最后基于四月IOSST和NWPD构建了NCMP异常的预测模型, 后报检验显示该模型对NCMP异常具有较好的预测能力.

The Internal and ENSO-Forced Modes of the Indian Ocean Sea Surface Temperature

Abstract The internal and ENSO-forced modes of the Indian Ocean sea surface temperature (SST) are investigated using a high-resolution regional coupled model. Five different model simulations were performed by controlling atmospheric and oceanic boundary conditions (BCs), which are lateral walls of the model domain. In the internal run performed by prescribing the climatological mean oceanic and atmospheric BCs, the first and second empirical orthogonal functions (EOF1 and EOF2) of internal mode are similar to the observed Indian Ocean basin (IOB) and dipole (IOD) modes with relatively weak amplitudes, respectively. In the control run with observed BCs, those EOFs are much amplified with their power spectrums significantly changed, and their spatial patterns are modified, particularly for the EOF2. Three ENSO runs with combinations of ENSO-related and climatological mean BCs show that the modification of spatial pattern of EOFs is mainly due to ENSO forcing. Furthermore, ENSO forcing determines the major 4-yr period of IOB mainly through the atmosphere, whereas the major 3-yr period of IOD is determined by both ENSO atmosphere and ocean forcings. It is also found that IOB and IOD exhibit a significant seasonally dependent relationship in both internal and ENSO-forced simulations. Most importantly, by applying the empirical singular vector method to both observed and modeled data, it is found that the IOD–IOB relationship is associated with an unstable mode of Indian Ocean SST anomalies, evolving from boreal fall to the next spring. This unstable mode is intrinsic within the Indian Ocean but is substantially amplified by the ENSO.

Dynamical Seasonal Prediction of the Asian Summer Monsoon in the China Meteorological Administration Climate Prediction System Version 3

Based on the 20 years of ensemble hindcast data, we evaluated the performance of the new version climate prediction system developed by the China Meteorological Administration (CMA CPSv3) on the Asian summer monsoon (ASM) seasonal prediction in this study. Many major features of the ASM are well predicted by CPSv3, including the intensity and location of the heavy precipitation centers, large-scale monsoon circulations, monsoon onset, and the interannual variation of dynamical monsoon indices. The model captures realistically interannual variability of the summer western North Pacific subtropical high (WNPSH) and is highly skillful for the WNPSH index. Compared with its predecessor, the prediction skill of summer precipitation over Asia in CPSv3 is obviously improved, especially over eastern China. The improvement mainly benefits from skillful predictions of the tropical Pacific Ocean and tropical Indian Ocean sea surface temperatures and ocean–atmosphere coupling associated with them.

Local ocean–atmosphere interaction in Indian summer monsoon multi-decadal variability

The significant multi-decadal mode (MDM) of the Indian summer monsoon rainfall (ISMR) during the past two millennia provides a basis for decadal predictability of the ISMR and has a strong association with the North-Atlantic (NA) variability with the Atlantic Multi-decadal Oscillation (AMO) as a potential external driver. It is also known that the annual cycles and interannual variability of ISMR and sea surface temperatures (SST) over the tropical Indian Ocean (IO) are strongly coupled. However, the role of local air–sea interactions in maintaining or modifying the ISMR MDM remains unknown. A related puzzle we identify is that the IO SST has an increasing trend during two opposite phases of the ISMR MDM, namely during an increasing phase of ISMR (1901–1957) as well as a decreasing phase of ISMR (1958–2007). Here, using a twentieth-century reanalysis (20CR), we examine the role of air-sea interactions in maintaining two opposite phases of the ISMR MDM and unravel that the Bjerknes feedback is at the heart of maintaining the ISMR MDM but cannot explain the increasing trend of SST in the tropical IO during the opposite phases. Large-scale low-level vorticity influence on SST and net heat flux changes through circulation and cloudiness changes associated with the two phases of the ISMR MDM together contribute to the SST trends. The decreasing trend of low-level wind convergence during the period between 1958 and 2007 is a determining factor for the decreasing trend of ISMR in the backdrop of an increasing trend of atmospheric moisture content. Consistent with the lead of the AMO with respect to ISMR by about a decade, the AMO drives the transition from one phase of ISMR MDM to another by changing its phase first and setting up low-level equatorial zonal winds conducive for the transition.