Interdecadal Climate Variability Research Articles

Inter-decadal climate variability induces differential ice response along Pacific-facing West Antarctica

West Antarctica has experienced dramatic ice losses contributing to global sea-level rise in recent decades, particularly from Pine Island and Thwaites glaciers. Although these ice losses manifest an ongoing Marine Ice Sheet Instability, projections of their future rate are confounded by limited observations along West Antarctica’s coastal perimeter with respect to how the pace of retreat can be modulated by variations in climate forcing. Here, we derive a comprehensive, 12-year record of glacier retreat around West Antarctica’s Pacific-facing margin and compare this dataset to contemporaneous estimates of ice flow, mass loss, the state of the Southern Ocean and the atmosphere. Between 2003 and 2015, rates of glacier retreat and acceleration were extensive along the Bellingshausen Sea coastline, but slowed along the Amundsen Sea. We attribute this to an interdecadal suppression of westerly winds in the Amundsen Sea, which reduced warm water inflow to the Amundsen Sea Embayment. Our results provide direct observations that the pace, magnitude and extent of ice destabilization around West Antarctica vary by location, with the Amundsen Sea response most sensitive to interdecadal atmosphere-ocean variability. Thus, model projections accounting for regionally resolved ice-ocean-atmosphere interactions will be important for predicting accurately the short-term evolution of the Antarctic Ice Sheet.

Internal Ocean Dynamics Contribution to North Atlantic Interdecadal Variability Strengthened by Ocean–Atmosphere Thermal Coupling

Abstract Identifying the primary drivers of North Atlantic interdecadal climate variability is crucial for improving climatic prediction over the coming decades. Here the effect of thermal coupling on the leading energy sources of the interdecadal variability of the ocean–atmosphere system is examined by means of a stochastically forced idealized coupled model. The effect of coupling is quantified from a comparison of the buoyancy variance budget of coupled and uncoupled model configurations. The simplicity of the model allows us to contrast the effect of coupling between a supercritical regime where the deterministic ocean dynamics drive the variability and a damped regime where noise forcing is central to its existence. The results show that changes in surface buoyancy fluxes act as a sink of temperature variance in the supercritical regime, and only become a source in the strongly damped regime. By contrast, internal ocean dynamics associated with the interaction of transient buoyancy fluxes with mean buoyancy gradients always act as a source of interdecadal variability. In addition to the reduced thermal damping effect in coupled integrations, thermal coupling with the atmosphere is shown to significantly increase the role of internal ocean dynamics in the variability, particularly in the regime where interdecadal modes are damped. Only for oceanic background states in the strongly damped regime do changes in surface buoyancy fluxes play a leading role in the upper-ocean variability. A stochastically forced coupled box model is proposed that captures the basic effect of thermal coupling on atmospheric and oceanic energy sources of variability. Significance Statement The purpose of this study is to better understand the impact of ocean–atmosphere thermal coupling on the leading energy sources of Atlantic interdecadal variability. Increasing our understanding of the physical mechanisms driving climate variability at interdecadal time scales is important to improve climate prediction. We show that the effect of ocean–atmosphere thermal coupling, as measured by the atmospheric feedback on sea surface temperature anomalies, is to substantially increase the role of internal ocean dynamics in the low-frequency variability of the upper-ocean heat content and sea surface temperature. Atmospheric stochastic forcing only becomes the primary driver of the oceanic temperature variability in the large dissipative limit, when internal ocean modes are strongly damped.

Large-scale climate variability footprint in water levels of alluvial aquifers across Iran

The ability to predict the future variability of groundwater resources in time and space is of critical importance in society’s adaptation to climate variability and change. Periodic control of large-scale ocean-atmospheric circulations on groundwater levels serves as a potentially effective source for relatively long-term forecasting. In this study, as a first national-scale assessment, we use the continuous wavelet transform, global power spectrum, and wavelet coherence analyses to quantify the linkage between the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and El Niño Southern Oscillation (ENSO) and the representative groundwater levels of the 24 principal aquifers, scattered across 14 different climate zones of Iran. Aquifer storage variations are found to be partially derived from annual to interdecadal climate variability and not solely a function of pumping variability. Moreover, teleconnections are observed to be both frequency and time-specific. The significant coherence patterns between the climate indices and groundwater levels are concentrated at five frequency bands of the annual (~ 1 year), short-interannual (2–4 years), medium-interannual (4–6 years), decadal (8–12 years), and interdecadal (14–18 years), consistent with the dominant oscillations of climate indices. AMO’s strong linkage to groundwater variability is found to be at interdecadal and annual modes of groundwater levels while PDO’s highest imprint is concentrated in interannual, decadal, and interdecadal periodicities. Unlike ENSO for which the highest modulating influence is found to be across the decadal and interannual modes, the NAO’s footprint in aquifers is marked at annual and interdecadal frequency bands. Findings further show that the groundwater variability is driven primarily by a combination of multiple large-scale atmospheric circulations rather than a single atmospheric circulation index. The decadal and interdecadal oscillation modes are the dominant modes in Iranian aquifers. Findings also mark the unsaturated zone contribution in damping and lagging of the climate variability modes, particularly for the higher-frequency indices of ENSO and NAO so that groundwater variability is more correlated with those climate circulations that have lower frequency such as PDO and AMO. Finally, the data length is found to have a significant effect on the teleconnections if the time series are not contemporaneous and for each particular series, only one value of coherence/correlation is computed instead of separate computations for different frequency bands and different time spans.

Interdecadal climate variability identified in aeolian deposits in southern Santa Catarina, Brazil

Changes have occurred to the patterns of surface morphology in coastal aeolian deposits in a chrono-correlated way in different geographical areas at different time scales. These changes can be recognized and associated with meso and large-scale climatic events, thus establishing a teleconnection. In the present study, surface and subsurface data, combined with Optically Stimulated Luminescence (OSL) dating, allowed us to establish the evolutionary chronology and the environmental context of aeolian features that cover a stretch of the Holocene coastal barrier in the southern coast of Santa Catarina, Brazil. According to geophysical and geochronological data and geomorphological indicators, the section shows regressive coastal line behavior (progradational pattern). The sedimentary cover of this Holocene coastal barrier, so far dominated by active dunes, began to change after the 1930s. The subsequent decades were marked by a significant increase in vegetation, fixing the precipitation crests of the transgressive sand sheets (TSS). This increase in vegetation cover over the last century results from climatic variability associated with the Pacific Decadal Oscillation.

Synchronized interdecadal variations behind regime shifts in the Pacific Decadal Oscillation

Interdecadal climate variability over the North Pacific is investigated using a reconstructed 298-year-long annual Pacific Decadal Oscillation Index during 1700–1997. Here, we show that its interdecadal component can be decomposed into the bi-decadal (~ 20 years), the tri-decadal (~ 30 years), and the multi-decadal variations (~ 60 years) through bandpass filtering. The phase reversals of the bi-decadal and the tri-decadal variations were synchronized throughout the data, while the synchronization of the bi-decadal and the multi-decadal variations was maintained during 1780–1880 and 1920–1997. Monte Carlo simulation reveals that this synchronous temporal structure is statistically significant and could not occur from random processes. We further demonstrate that these three phase-locked variations play an important role in the regime shifts in the North Pacific, both during the data period (1700–1997) and thereafter. The bi-decadal variation, which is self-sustained through the North Pacific mid-latitude air–sea interaction, is also found to be possibly linked to the lunar nodal cycle. Moreover, the tri-decadal and the multi-decadal variations, whose periods are approximately 1.5 and 3 times longer than that of the bi-decadal variation, may be linked to the bi-decadal variation through nonlinear process. This simple relationship could largely contribute to understanding and predicting the interdecadal climate variability.

Weakening Atlantic overturning circulation causes South Atlantic salinity pile-up

The Atlantic Meridional Overturning Circulation (AMOC) is an active component of the Earth’s climate system1 and its response to global warming is of critical importance to society. Climate models have shown an AMOC slowdown under anthropogenic warming since the industrial revolution2–4, but this slowdown has been difficult to detect in the short observational record5–10 because of substantial interdecadal climate variability. This has led to the indirect detection of the slowdown from longer-term fingerprints11–14 such as the subpolar North Atlantic ‘warming hole’11. However, these fingerprints, which exhibit some uncertainties15, are all local indicators of AMOC slowdown around the subpolar North Atlantic. Here we show observational and modelling evidence of a remote indicator of AMOC slowdown outside the North Atlantic. Under global warming, the weakening AMOC reduces the salinity divergence and then leads to a ‘salinity pile-up’ remotely in the South Atlantic. This evidence is consistent with the AMOC slowdown under anthropogenic warming and, furthermore, suggests that this weakening has likely occurred all the way into the South Atlantic. The slowdown in the Atlantic Meridional Overturning Circulation (AMOC) is remotely detected in an increasing South Atlantic salinity trend. This salinity pile-up is caused by reduced divergence of surface salinity transport under a weakened AMOC.

Hydrological cycle changes under global warming and their effects on multiscale climate variability.

Despite a globally uniform increase in the concentrations of emitted greenhouse gases, radiatively forced surface warming can have significant spatial variations. These define warming patterns that depend on preexisting climate states and through atmospheric and oceanic dynamics can drive changes of the hydrological cycle with global-scale feedbacks. Our study reviews research progress on the hydrological cycle changes and their effects on multiscale climate variability. Overall, interannual variability is expected to become stronger in the Pacific and Indian Oceans and weaker in the Atlantic. Global monsoon rainfall is projected to increase and the wet season to lengthen despite a slowdown of atmospheric circulation. Strong variations among monsoon regions are likely to emerge, depending on surface conditions such as orography and land-sea contrast. Interdecadal climate variability is expected to modulate the globally averaged surface temperature change with pronounced anomalies in the polar and equatorial regions, leading to prolonged periods of enhanced or reduced warming. It is emphasized that advanced global observations, regional simulations, and process-level investigations are essential for improvements in understanding, predicting, and projecting the modes of climate variability, monsoon sensitivity, and energetic fluctuations in a warming climate.

Tropical cyclones and multiscale climate variability: The active western North Pacific Typhoon season of 2018

The 2018 typhoon season in the western North Pacific (WNP) was highly active, with 26 named tropical cyclones (TCs) from June to November, which exceeded the climatological mean (22) and was the second busiest season over the past twenty years. More TCs formed in the eastern region of the WNP and the northern region of the South China Sea (SCS). More TCs took the northeast quadrant in the WNP, recurving from northwestward to northward and causing heavy damages in mainland China (69.73 billion yuan) in 2018. Multiscale climate variability is conducive to an active season via an enhanced monsoon trough and a weakened subtropical high in the WNP. The large-scale backgrounds in 2018 showed a favorable environment for TCs established by a developing central Pacific (CP) El Nino and positive Pacific meridional mode (PMM) episode on interannual timescales. The tropical central Pacific (TCP) SST forcing exhibits primary control on TCs in the WNP and large-scale circulations, which are insensitive to the PMM. During CP El Nino years, anomalous convection associated with the TCP warming leads to significantly increased anomalous cyclonic circulation in the WNP because of a Gill-type Rossby wave response. As a result, the weakened subtropical high and enhanced monsoon trough shift eastward and northward, which favor TC genesis and development. Although such increased TC activity in 2018 might be slightly suppressed by interdecadal climate variability, it was mostly attributed to the favorable interannual background. In addition, high-frequency climate signals, such as intraseasonal oscillations (ISOs) and synoptic-scale disturbances (SSDs), interacted with the enhanced monsoon trough and strongly modulated regional TC genesis and development in 2018.

Local Regions Associated With Interdecadal Global Temperature Variability in the Last Millennium Reanalysis and CMIP5 Models

AbstractDespite the importance of interdecadal climate variability, we have a limited understanding of which geographic regions are associated with global temperature variability at these timescales. The instrumental record tends to be too short to develop sample statistics to study interdecadal climate variability, and Coupled Model Intercomparison Project, Phase 5 (CMIP5) climate models tend to disagree about which locations most strongly influence global mean interdecadal temperature variability. Here we use a new paleoclimate data assimilation product, the Last Millennium Reanalysis (LMR), to examine where local variability is associated with global mean temperature variability at interdecadal timescales. The LMR framework uses an ensemble Kalman filter data assimilation approach to combine the latest paleoclimate data and state‐of‐the‐art model data to generate annually resolved field reconstructions of surface temperature, which allow us to explore the timing and dynamics of preinstrumental climate variability in new ways. The LMR consistently shows that the middle‐ to high‐latitude north Pacific and the high‐latitude North Atlantic tend to lead global temperature variability on interdecadal timescales. These findings have important implications for understanding the dynamics of low‐frequency climate variability in the preindustrial era.

Understanding Sea Level Change in the South Pacific During the Late 20th Century and Early 21st Century

AbstractA spatially nonuniform sea level rise was observed in the South Pacific with high trends of up to 8 mm/year in the southwest subtropical Pacific and much lower values in the eastern ocean during the 1993 to 2015 altimetry data period. Negative trends were observed further south. In recent decades, these trends have been interpreted as a spin‐up of subtropical gyre circulation. Here an analysis of altimetry data and data from the Coupled Model Intercomparison Project Phase 5 is presented, which attempts to separate natural climate variability from sea level changes. In order to quantify the impact of natural variability, a multiple linear regression was performed between sea level and dominant climate indices in the region, with the latter representing interannual to interdecadal climate variability. Our results indicate that the observed pattern cannot completely be explained by the climate modes but that a large residual trend remains.

Intrinsic and environmental drivers of growth in an Alaskan rockfish: an otolith biochronology approach

Otolith growth-increment chronologies provide an approach for evaluating the impacts of both high-frequency (e.g., interannual) and low-frequency (e.g., interdecadal) climate variability on fish growth. A growth-increment biochronology spanning six decades, spanning several warm and cold climate regime periods, was developed for a commercially important species of rockfish, Sebastes polyspinis, in the Gulf of Alaska. To confirm that all increments were correctly identified and placed in time, we borrowed the technique of crossdating from the tree-ring science of dendrochronology, which ensured high data quality. We then used a mixed effects model to partition variance in otolith growth-increment width among intrinsic (e.g., age-related) and extrinsic (e.g., climate-related) factors. This biochronology was contrasted with one recently developed for S. alutus, a closely-related species which exhibited a significant change in growth following the late 1970s North Pacific climate regime shift. Both species generally showed positive relationships between warm climate conditions and growth, though S. polyspinis experienced a relatively smaller step-increase in growth following the regime shift. The new S. polyspinis otolith biochronology represents a long-term record of growth that extends well before biological specimens were first collected in the Gulf of Alaska, providing a potential tool for fisheries managers to evaluate the effects of climate variability on growth and biological reference points.

Possible relationship between Pacific interdecadal climate variability and the periodic 18.6-year tidal oscillation in the ocean

Possible relationship between Pacific interdecadal climate variability and the periodic 18.6-year tidal oscillation in the ocean

Phenological cues intrinsic in indigenous knowledge systems for forecasting seasonal climate in the Delta State of Nigeria.

Shifts in the timing of phenological events in plants and animals are cited as one of the most robust bioindicators of climate change. Much effort has thus been placed on the collection of phenological datasets, the quantification of the rates of phenological shifts and the association of these shifts with recorded meteorological data. These outputs are of value both in tracking the severity of climate change and in facilitating more robust management approaches in forestry and agriculture to changing climatic conditions. However, such an approach requires meteorological and phenological records spanning multiple decades. For communities in the Delta State of Nigeria, small-scale farming communities do not have access to meteorological records, and the dissemination of government issued daily to seasonal forecasts has only taken place in recent years. Their ability to survive inter-annual to inter-decadal climatic variability and longer-term climatic change has thus relied on well-entrenched indigenous knowledge systems (IKS). An analysis of the environmental cues that are used to infer the timing and amount of rainfall by farmers from three communities in the Delta State reveals a reliance on phenological events, including the croaking of frogs, the appearance of red millipedes and the emergence of fresh rubber tree and cassava leaves. These represent the first recorded awareness of phenology within the Delta State of Nigeria, and a potentially valuable source of phenological data. However, the reliance of these indicators is of concern given the rapid phenological shifts occurring in response to climate change.

Estimating modes of inter-decadal variability and predictability in coupled climate models

A methodology is described that allows a separation of inter-decadal variability into components associated with intra-decadal noise and potentially predictable slow decadal processes. The method is applied to a 1200 year simulation of internal variability of sea surface temperature in a coupled atmosphere-ocean model using parameters and radiative forcing associated with the year 2000. The analysis shows large predictability in the extratropical regions. The two leading modes associated with intra-decadal variability are shown to be related to interannual variability in the El Nino--Southern Oscillation and the Atlantic Multi-decadal Oscillation. The leading four slow modes are shown to be related to slow decadal variability in the Pacific Decadal Oscillation, the Atlantic Multi-decadal Oscillation and the Arctic Oscillation. References C. S. Frederiksen, X. Zheng and S. Grainger. Simulated modes of inter-decadal predictability in sea surface temperature. Clim. Dyn. , 46 :2231–2245, 2016. doi:10.1007/s00382-015-2699-6 . J. Lou, X. Zheng, C. S. Frederiksen, H. Liu, S. Grainger and K. Ying. Simulated decadal modes of the NH atmospheric circulation arising from intra-decadal variability, external forcing and slow-decadal climate processes. Clim. Dyn. , 48 :2635–2652, 2016. doi:10.1007/s00382-016-3229-x Z. Liu. Dynamics of interdecadal climate variability: a historical perspective. J. Clim. , 25 :143–162, 2012. doi:10.1175/2011JCLI3980.1 H. von Storch and F. W. Zwiers. Statistical Analysis in Climate Research . Cambridge University Press, 484pp, 2001.

Aerosol and Solar Irradiance Effects on Decadal Climate Variability and Predictability

The expanding interest in decadal climate variability, predictability, and prediction highlights the importance of understanding the sources and mechanisms of decadal and interdecadal climate fluctuations. The purpose of this paper is to provide a critical review of our current understanding of externally forced decadal climate variability. In particular, proposed mechanisms determining decadal climate responses to variations in solar activity, stratospheric volcanic aerosols, and natural as well as anthropogenic tropospheric aerosols are discussed, both separately and in a unified framework. The review suggests that the excitation of internal modes of interdecadal climate variability, particularly centered in the Pacific and North Atlantic sectors, remains a paradigm to characterize externally forced decadal climate variability and to interpret the associated dynamics. Significant recent advancements are the improved understanding of the critical dependency of volcanically forced decadal climate variability on the relative phase of ongoing internal variability and on additional external perturbations, and the recognition that associated uncertainty may represent a serious obstacle to identifying the climatic consequences even of very strong eruptions. Particularly relevant is also the recent development of hypotheses about potential mechanisms (reemergence and synchronization) underlying solar forced decadal climate variability. Finally, outstanding issues and, hence, major opportunities for progress regarding externally forced decadal climate variability are discussed. Uncertain characterization of forcing and climate histories, imperfect implementation of complex forcings in climate models, limited understanding of the internal component of interdecadal climate variability, and poor quality of its simulation are some of the enduring critical obstacles on which to progress. It is suggested that much further understanding can be gained through identification and investigation of relevant periods of forced decadal climate variability during the preindustrial past millennium. Another upcoming opportunity for progress is the analysis of focused experiments with coupled ocean–atmosphere general circulation models within the umbrella of the next phase of the coupled model intercomparison project.

Future rainfall variability in Indonesia under different ENSO and IOD composites based on decadal predictions of CMIP5 datasets

El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are amongst important climate drivers that play a significant role in driving rainfall variability in Indonesia, especially on inter-annual timescales. The phenomena are suggested to have an association with interdecadal climate variability through the modulation of their oscillations. This study aims to analyse the characteristics of future rainfall variability in Indonesia during different condition of ENSO and IOD events based on decadal predictions of near-term climate change CMIP5 GCM data outputs up to year 2035. Monthly data of global rainfall data with 5x5 km grid resolutions of CHIRPS dataset is used in this study to represent historical rainfall variability as well to serve as a reference for future rainfall predictions. The current and future rainfall and sea surface temperature data have been bias corrected before performing the analysis. Given the comparison between rainfall composites during El-Nino and positive IOD events, the study showed that the future rainfall conditions in Indonesia will become drier than the historical condition resulted from the same composite approach. In general, this study showed the Indonesian rainfall variability in the future is expected to respond differently to a different combination of ENSO and IOD conditions.

Wet and cold climate conditions recorded by coral geochemical proxies during the beginning of the first millennium CE in the northern South China Sea

The past two millennia include some distinct climate intervals, such as the Medieval Warm Period (MWP) and the Little Ice Age (LIA), which were caused by natural forcing factors, as well as the Current Warm Period (CWP) that has been linked to anthropogenic factors. Therefore, this period has been of great interest to climate change researchers. However, most studies are based on terrestrial proxy records, historical documentary data, and simulation results, and the ocean and the tropical record are very limited. The Eastern Han, Three Kingdoms, and Western Jin periods (25–316 CE) cover the beginning first millennium CE in China, and were characterized by a cold climate and frequent wars and regime changes. This study used paired Sr/Ca and δ18O series recovered from a fossil coral to reconstruct the sea surface water conditions during the late Eastern Han to Western Jin periods (167–309 CE) at Wenchang, eastern Hainan Island in the northern South China Sea (SCS), to investigate climate change at this time. The long-term sea surface temperature (SST) during the study interval was 25.1°C, which is about 1.5°C lower than that of the CWP (26.6°C). Compared with the average value of 0.40‰ during the CWP, the long-term average seawater δ18O (−0.06‰) was more negative. These results indicate that the climate conditions during the study period were cold and wet and comparable with those of the LIA. This colder climate may have been associated with the weaker summer solar irradiance. The wet conditions were caused by the reduced northward shift of the intertropical convergence zone/monsoon rainbelt associated with the retreat of the East Asian summer monsoon. Interannual and interdecadal climate variability may also have contributed to the variations in SST and seawater δ18O recorded over the study period.

Modelling interdecadal climate variability and the role of the ocean

To estimate the anthropogenic contribution to climate signals in the recent past and future decades implies a certain degree of confidence in both understanding and simulating natural internal variability at interdecadal time scales. If we are to embark on the challenge of decadal prediction, we must be able to mechanistically attribute events to known processes and phenomena, and reproduce their features and statistics within our models. To date, models have succeeded in reproducing only partially spatial patterns, statistics and climatic impacts of interdecadal modes of variability. Reasons for the partial success and agreement among models are to be attributed to the short observational record, the different and complex flavours of coupling between the many subcomponents of the climate system, and the present inability to resolve all climate processes. At an even more fundamental level, this difficulty is aggravated by the limited understanding of the physical mechanisms involved. Here, we review the proposed mechanisms giving rise to interdecadal climate variability, we discuss the hypotheses explaining the main interdecadal modes of variability, and present an overview on the ability and level of agreement in their simulation by the latest generation of coupled climate models. To achieve any progress, the modeling community should focus on both improving the representation and parameterization of key ocean physical processes and obtaining a firmer grasp on the physical mechanisms generating the variability. Both goals can benefit from process studies, intercomparisons with perturbation experiments to study model's sensitivities, and the use of a hierarchy of climate models. WIREs Clim Change 2017, 8:e441. doi: 10.1002/wcc.441This article is categorized under: Climate Models and Modeling > Earth System Models

Evaluation of the interdecadal variability of sea surface temperature and sea level in the Pacific in CMIP3 and CMIP5 models

With significant impacts on the regional weather and climate, interdecadal climate variability is of great importance in understanding historical observations and predicting the climate in the near future. Using the currently available observation-based products, this study evaluates the ability of climate models participating in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5) to simulate the dominant interdecadal variability in the Pacific, i.e. the Interdecadal Pacific Oscillation (IPO). Our results indicate that compared with the CMIP3 models, the CMIP5 models exhibit slightly better performance in reproducing the observed interdecadal variability patterns of both sea surface temperature (SST) and sea level, and also exhibit smaller inter-model spread. Climate models tend to simulate more realistic interdecadal variability patterns for SST than for sea level. A prominent deficiency among CMIP3 and CMIP5 models lies in the northwestern tropical Pacific, where the observations show large sea level variations associated with the IPO, but the simulations are usually much weaker or even of the wrong sign. These biases can be generally associated with the inaccurate representation of wind forcing patterns at the corresponding latitudes (∼12°N). We further suggest that the air–sea coupling may play a role in the bias of interdecadal wind patterns in coupled climate models, and the representation of climatological mean states in climate models could influence the simulated interdecadal variability patterns. This study provides necessary skill information on climate models for further studying the Pacific interdecadal variability, as well as for better distinguishing the climate change signal from internal climate variability.

Impact of synoptic weather patterns and inter-decadal climate variability on air quality in the North China Plain during 1980–2013

Abstract Potential relationships between air quality, synoptic weather patterns, and the East Asian Monsoon (EAM) over the North China Plain (NCP) were examined during the time period of 1980–2013 using a weather typing technique and ground-based air pollution index (API) data from three cities: Beijing, Tianjin and Shijiazhuang. Using the Kirchhofer method, circulation patterns during the 34-yr study period were classified into 5 categories, which were further used to understand the quantitative relationship between weather and air quality in NCP. The highest API values were associated with a stagnant weather condition when wide-spread stable conditions controlled most part of NCP, while westerly and southerly wind flowed over the northern and eastern part of this region, resulting in both the regional transport and local build-up of air pollutants. Under the continuous control of this weather pattern, API values were found to increase at a rate of 8.5 per day on average. Based on the qualitative and quantitative analysis, a significant correlation was found between the strength of EAM and inter-annual variability of frequencies of the weather patterns. The strengthening of summer/winter monsoon could increase the frequency of occurrence of cyclone/anticyclone related weather patterns. Time series of climate-induced variability in API over the 34 years were reconstructed based on the quantitative relationship between API and predominant weather patterns during 2001–2010. Significant connections between EAM and reconstructed API were found on both the inter-annual and inter-decadal scales. In winter and summer, strengthening/weakening of EAM, which was generally associated with the change of the representative circulation patterns, could improve/worsen air quality in this region.