Negative Pacific Decadal Oscillation Research Articles

A Nonlinear Full-Field Conceptual Model for ENSO Diversity

Abstract As the strongest year-to-year fluctuation of the global climate system, El Niño–Southern Oscillation (ENSO) exhibits spatial–temporal diversity, which challenges the classical ENSO theories that mainly focus on the canonical eastern Pacific (EP) type. Besides, the complicated interplay between the interannual anomaly fields and the decadally varying mean state is another difficulty in current ENSO theory. To better account for these issues, the nonlinear two-region recharge paradigm model is extended to a three-region full-field conceptual model to capture the physics in the western Pacific (WP), central Pacific (CP), and EP regions. The results show that the extended conceptual model displays a rich dynamical behavior as parameters setting the efficiencies of upwelling and zonal advection are varied. The model can not only generate El Niño bursting behavior but also simulate the statistical asymmetries between the two types of El Niños and the warm and cold phases of ENSO. Finally, since both the anomaly fields and mean states are simulated by the model, it provides a simple tool to investigate their interactions. The strengthening of the upwelling efficiency, which can be seen as an analogy to a cooling thermocline associated with the oceanic tunnel to the midlatitudes, will increase the zonal gradient of the mean state temperature between the WP and EP, i.e., resembling a negative Pacific decadal oscillation (PDO) pattern along the equatorial Pacific. The influence of the zonal advection efficiency is quite the opposite, i.e., its strengthening will reduce the zonal gradient of the mean state temperature along the equatorial Pacific.

Pacific Decadal Oscillation Modulates the Impacts of Bering Sea Ice Loss on North American Temperature

AbstractThe cold surges have frequently attacked North America (NA) in recent decades, which has been tied to the diminished sea‐ice over the Bering Sea. However, we find that the contribution of sea‐ice loss to NA winter coldness is state‐dependent on the Pacific Decadal Oscillation (PDO) phase. Using observations and CAM6 model simulations, we find that the phase regulates the atmospheric response to Bering ice loss. During the negative PDO phase (PDO−), there is an apparent eastward‐propagating wave train, accompanied by a strengthened Alaskan ridge and NA cold high, resulting in a robust cold over Central NA. Meanwhile, enhanced upward‐propagating planetary waves weaken the stratospheric polar vortex over the Pacific‐NA regions. During the positive phase (PDO+), the NA temperature response to Bering ice loss is quite weak or even warm. We speculate that more NA cold extremes will appear as the PDO− continues and less as the PDO− shifts to PDO+.

Thermal fronts in coastal waters regulate phytoplankton blooms via acting as barriers: A case study from western Guangdong, China

Oceanic fronts play an important role in regulating the distributions of phytoplankton and are subject to climate change. However, the relationship between climate change, oceanic fronts, and coastal phytoplankton blooms requires clarification. Using long-term satellite data, the seasonal, interannual, and decadal variations of the thermal fronts were examined, along with their effects on the distribution of phytoplankton in western Guangdong. Thermal fronts between the cold western Guangdong coastal current waters and the warm South China Sea (SCS) waters were found along the coast of western Guangdong during winter due to northeast winter monsoon. At decadal timescales, an increase (decrease) in frontal activities occurred during the negative (positive) Pacific Decadal Oscillation (PDO) phase. This pattern suggests that the positive (negative) PDO activity decreases (increases) sea level anomaly (SLA) and sea surface temperature in the SCS, thereby weakens (enhances) frontal activities along the coast. Accordingly, extensions and positive anomalies (> 1.5 mg/m3) in chlorophyll-a (Chl a) were observed during the positive PDO phase, whereas Chl a was concentrated in the nearshore areas during the negative PDO phase. These processes are primarily related to the barrier effects of enhanced thermal fronts and positive SLA on offshore materials transport during the negative PDO period. This study highlights the need to incorporate PDO activity into phytoplankton production in coastal oceans.

The Contrast Precipitation Patterns in Yangtze River Valley Between the Two La Niña Decaying Summers in 2021 and 2022

AbstractAlthough the summers of 2021 and 2022 are both in the two successive La Niña decaying stages and under the same climate background of negative Pacific Decadal Oscillation (PDO) phase and global warming trend, they exhibit significantly different and even opposite precipitation patterns in the Yangtze River Valley (YRV) as well as in the Indian monsoon region (IMR). In contrast to the abundant precipitation and lower temperature in the YRV in summer 2021, in summer 2022 the YRV experiences severe drought and extremely high temperatures, which is also accompanied by Mega‐floods in the IMR. This study identifies the joint influence of sea surface temperature anomalies (SSTAs) in Niño4 and Barents Sea (BS) regions as the underlying cause for the contrast YRV precipitation anomalies in the summers of 2021 and 2022. Specifically, the cold SSTAs in both Niño4 and BS regions in summer 2021 favor stronger and southward shifted western North Pacific subtropical high (WNPSH), leading to more precipitation in the YRV, which is however generally reversed but more intense in summer 2022 because of the synergistic effect of cold Niño4 and warm BS SSTAs. Moreover, the induced extreme precipitation in the IMR in summer 2022, which is absent in summer 2021 due to the offsetting effect of cold SSTAs in both Niño4 and BS regions, in turn further strengthens the anomalous atmospheric circulations via its released large diabatic heating and serves as a relay pathway for the dramatic drought and heat wave in the YRV.

Decadal Modulation of the Relationship Between Tropical Southern Atlantic SST and Subsequent ENSO by Pacific Decadal Oscillation

AbstractThis study identifies the relationship between tropical southern Atlantic (TSA) sea surface temperature anomaly (SSTA) and the El Niño‐Southern Oscillation (ENSO) and focuses on how the Pacific Decadal Oscillation (PDO) modulates this relationship. Results suggest a significant but non‐stationary interannual TSA‐ENSO relationship which undergoes a significant decadal shift. A strong TSA‐ENSO relationship is observed during the positive PDO phase, while this relationship is weak during the negative PDO phase. Two processes, involving the anomalous Pacific Walker circulation (PWC) and the intensity of air‐sea interactions over the Pacific, are proposed for this decadal shift. During the positive PDO phase, the weak and variable PWC and strong air‐sea interaction facilitate the development of SSTA in the tropical Pacific triggered by TSA SSTA, resulting in a strong TSA‐ENSO relationship and vice versa. These findings emphasize the important role of the modulation of PDO on the TSA‐ENSO relationship.

Prevalent atmospheric and oceanic signals of the unprecedented heatwaves over the Yangtze River Valley in July–August 2022

Unprecedented heatwaves attacked the Yangtze River valley (YRV) in July–August of 2022. The heatwave-favorable circulation pattern for the YRV is identified by using a self-organizing map. Result shows that the dominant daily circulation pattern driving heatwaves in the YRV is the East Asian anticyclonic pattern (EAAP), characterized by an anomalous deep anticyclone over the East Asian mid-latitudes. Remarkably, the unprecedented frequent occurrence of EAAP in 2022 contributes about 84.6% of the temperature anomalies in the 35 YRV hot days, which is the key dynamical factor for the heatwave in 2022. Physical mechanisms for the occurrence of EAAP are revealed on interannual and interdecadal time scales. On interannual time scale, the dipole sea surface temperature (SST) anomalies over the North Atlantic, characterized by warm and cold SST anomalies in the midlatitudes and subtropics, respectively, exert an important influence on the EAAP days. This dipole SST pattern is unprecedentedly strong in 2022. It facilitates the EAAP through the maintenance of the coupled British–Okhotsk Corridor pattern and the Silk Road pattern in the mid-latitudes. Additionally, the persistent cold SST anomalies in tropical Indian ocean and the central-eastern Pacific from the preceding spring to summer contribute to cooling of the tropical troposphere and induce easterly anomalies in the East Asian subtropics, thereby further promoting the occurrence of EAAP. On interdecadal time scale, the negative Pacific Decadal Oscillation may establish favorable circulation conditions for the occurrence of the EAAP through modulating the interdecadal Silk Road pattern. These findings improve our understanding of the physical mechanisms for driving extreme heatwaves in the YRV and have an implication for enhancing regional heatwave prediction.

Dynamic controls of the interannual and interdecadal variations of the freezing level height over the Tibetan Plateau

The variation of freezing level height (FLH) is significantly indicated the cryosphere change under global warming. In this study, the FLH during boreal summer in the TP regions is investigated, with the leading mode of a mono-sign pattern both on interannual and interdecadal timescales. The interannual variation of the summer FLH is dominantly coupled with the summer Arctic Oscillation (AO). When the AO is in positive phase, positive geopotential height anomalies are prolonged in the mid-latitude and negative anomalies are present over the Arctic regions. Meanwhile, the westerly shifts northward and strengthened, preventing the cold air propagating southward. These conditions are beneficial for the surface and free-air temperature increasing and thus enhance the FLH over the TP. On the interdecadal timescale, the Pacific Decadal Oscillation (PDO) has mainly contributed to the variation of summer FLH. In the negative PDO phase, the warming sea surface temperature anomalies appear in the North Pacific, which could drive wave trains propagating eastward and induce high pressure around the northern TP. With the anomalous anticyclone from TP to western North Pacific, the southeasterly wind is prevalent in the TP. Consequently, the northern TP becomes warming remarkably and leads to the rising of FLH. This study provides an insight perspective for understanding the changes of FLH over the TP, which also suggests the influence on the cryosphere processes at multi-timescale variations.

Multidecadal variability of dust activity in Gobi desert and its connection with the pacific decadal oscillation

The multidecadal changes of dust column mass density (DCMD) in Gobi desert (GD) in spring are investigated based on the Modern-Era Retrospective analysis for Research and Applications version 2 dataset. In addition, the possible effects of the atmospheric circulation and sea surface temperature (SST) forcing on the multidecadal changes are analyzed. Results show that the dust aerosol over GD experienced a decadal change in 1999 with about 30% higher dust loading during 2000–2013 in comparison to that during 1987–1999. Further analysis indicates that the decadal change of dust aerosol over GD is attributed to the more strengthened northwesterly wind anomaly extending from lower to middle troposphere and the anticyclonic anomaly in middle troposphere over GD during the latter epoch, which is favorable to the increase of local dust activities. Furthermore, the decadal change of DCMD in GD is associated with the switch of Pacific Decadal Oscillation (PDO) phase. From 2000 to 2013, the PDO was in the negative phase, which induced to a positive potential height anomaly and northwesterly wind anomalies in the middle troposphere over GD. The dry and cold air brought by the anomalous northwesterly wind associated with the negative PDO phase reduces the relative humidity in the lower troposphere further amplify the effect of strengthened wind speed, being favorable for the increase of local dust loading and the resultant increase of DCMD there.

GEFSv12 High- and Low-Skill Day-10 Tornado Forecasts

Abstract On average, modern numerical weather prediction forecasts for daily tornado frequency exhibit no skill beyond day 10. However, in this extended-range lead window, there are particular model cycles that have exceptionally high forecast skill for tornadoes because of their ability to correctly simulate the future synoptic pattern. Here, model initial conditions that produced a more skillful forecast for tornadoes over the United States were exploited while also highlighting potential causes for low-skill cycles within the Global Ensemble Forecasting System, version 12 (GEFSv12). There were 88 high-skill and 91 low-skill forecasts in which the verifying day-10 synoptic pattern for tornado conditions revealed a western U.S. thermal trough and an eastern U.S. thermal ridge, a favorable configuration for tornadic storm occurrence. Initial conditions for high skill forecasts tended to exhibit warmer sea surface temperatures throughout the tropical Pacific Ocean and Gulf of Mexico, an active Madden–Julian oscillation, and significant modulation of Earth-relative atmospheric angular momentum. Low-skill forecasts were often initialized during La Niña and negative Pacific decadal oscillation conditions. Significant atmospheric blocking over eastern Russia—in which the GEFSv12 overforecast the duration and characteristics of the downstream flow—was a common physical process associated with low-skill forecasts. This work helps to increase our understanding of the common causes of high- or low-skill extended-range tornado forecasts and could serve as a helpful tool for operational forecasters. Significance Statement This research provides a framework for the anticipation of a more (or less) skillful 10-day tornado forecast in an operational numerical weather prediction system. High-skill forecasts were associated with substantial tropical convection and warm sea surface temperature throughout the Pacific Ocean and Gulf of Mexico, whereas the underlying cause of low-skill forecasts were typically associated with a blocking anticyclone over eastern Russia. These findings are important because they permit increased or decreased confidence in a long-range forecast of tornado occurrence based on a dynamical prediction system.

The Pacific Decadal Oscillation modulated marine heatwaves in the Northeast Pacific during past decades

The Pacific Decadal Oscillation has been suggested to play an important role in driving marine heatwaves in the Northeast Pacific during recent decades. Here we combine observations and climate model simulations to show that marine heatwaves became longer, stronger and more frequent off the Northeast Pacific coast under a positive Pacific Decadal Oscillation scenario, unlike what is found during a negative Pacific Decadal Oscillation scenario. This primarily results from the different mean-state sea surface temperatures between the two Pacific Decadal Oscillation phases. Compared to the cool (negative) phase of the Pacific Decadal Oscillation, warmer coastal sea surface temperatures occur during the positive Pacific Decadal Oscillation phase due to reduced coastal cold upwelling and increased net downward surface heat flux. Model results show that, relative to the background anthropogenic global warming, the positive Pacific Decadal Oscillation in the period 2013–2022 prolongs marine heatwaves duration by up to 43% and acts to increase marine heatwaves annual frequency by up to 32% off the Northeast Pacific coast.

Southern California winter precipitation variability reflected in 100-year ocean salinity record

Rainfall in southern California is highly variable, with some fluctuations explainable by climate patterns. Resulting runoff and heightened streamflow from rain events introduces freshwater plumes into the coastal ocean. Here we use a 105-year daily sea surface salinity record collected at Scripps Pier in La Jolla, California to show that El Niño Southern Oscillation and Pacific Decadal Oscillation both have signatures in coastal sea surface salinity. Averaging the freshest quantile of sea surface salinity over each year’s winter season provides a useful metric for connecting the coastal ocean to interannual winter rainfall variability, through the influence of freshwater plumes originating, at closest, 7.5 km north of Scripps Pier. This salinity metric has a clear relationship with dominant climate phases: negative Pacific Decadal Oscillation and La Niña conditions correspond consistently with lack of salinity anomaly/ dry winters. Fresh salinity anomalies (i.e., wet winters) occur during positive phase Pacific Decadal Oscillation and El Niño winters, although not consistently. This analysis emphasizes the strong influence that precipitation and consequent streamflow has on the coastal ocean, even in a region of overall low freshwater input, and provides an ocean-based metric for assessing decadal rainfall variability.

Impacts of Tibetan Plateau sensible heat and El Niño–Southern Oscillation on precipitation over South China under the background of the PDO

This study aims to investigate the impacts of the spring sensible heat (SH) over the Tibetan Plateau (TP) and the El Niño–Southern Oscillation (ENSO) in the preceding wintertime on midsummer (July–August) precipitation over South China under the different Pacific decadal oscillation (PDO) phases. More specifically, eight classifications are adopted at the demarcation point around 1996 when the spring SH over the TP and the midsummer precipitation in South China occurred as well as the PDO phase transition, including positive and negative SHs and ENSOs under a positive PDO phase (1979–1996) and a negative PDO phase (1997–2019), respectively, based on the Niño-3 index and the spring SH calculated from 48 stations over the central and eastern parts of the TP. The results show that both the spring SH and the ENSO in preceding wintertime have a significant impact on the midsummer precipitation over South China; that is, when the two factors are in their respective positive (negative) phase, the midsummer precipitation in South China is generally less (more). Importantly, the phase change of background field PDO can significantly enhance the effect of the SH and the ENSO on summer precipitation over South China. Moreover, compared with the preceding wintertime ENSO, the spring SH over the TP contributes more to the midsummer precipitation in South China based on analyses of their independent and synergistic effects. The main mechanism responsible for the anomalous midsummer precipitation over South China are the combined effects of the South Asian high (SAH) and the western Pacific subtropical high (WPSH), which are controlled by the spring SH anomaly over the TP and the ENSO, respectively. Deep understanding of the dominant factors of the midsummer precipitation over South China will help understand the local climate change and reduce the losses caused by drought and flood disasters.

Increasing peak intensity of tropical cyclones passing through the Korean Peninsula

An increasing trend along with an abrupt increase in the peak intensity of tropical cyclones (TCs) passing through the Korean Peninsula (KP) are significantly detected from 1981 to 2020 and since 2003, respectively. Here we present observational evidence that such trend and shift are largely attributed with the increased passages of intense TCs in the KP during the mature boreal autumn (i.e., September–October, SO) and linked with the recent shift of the Pacific Decadal Oscillation (PDO) to its negative phase. A negative PDO during SO is related to environmental changes that are favorable for more intense TC passages in the KP including a weakened East Asian subtropical jet stream, weaker vertical wind shear, warmer subtropical sea surface temperature, and stronger low-level relative vorticity. Such findings are expected to provide new insights on understanding regional TC variability and ultimately, contribute to long range TC prediction initiatives in the KP region.

ENSO and PDO Effect on Stratospheric Dynamics in Isca Numerical Experiments

The deterministic forecast of the stratospheric polar vortex intensity (iSPV) is limited by 2 weeks, but it can be probabilistically predicted for a longer period due to low-frequency components of the climate system, such as large-scale sea surface temperature anomalies (SSTAs) (e.g., El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)). For a qualitative and quantitative assessment of the effect of the large-scale Pacific SSTAs on the iSPV anomalies formation, idealized model experiments were carried out using the Isca platform. There is no statistically significant response of the SPV dynamics to the SSTAs corresponding to PDO phases, but they noticeably correct the effect of ENSO modes when added to it. The effect of the El Niño (EN) and La Niña (LN) events with neutral PDO phases on the iSPV is asymmetric; in the “single” EN experiment the vortex is 40% weaker relative to the control values, and, in the “single” LN, the SPV is weakened by no more than 20%. When EN accompanied with the positive PDO phase, iSPV is reduced by 58%. When the negative PDO phase is added, the EN effect is significantly weakened. The LN effect is weakened by both positive and negative PDO phases.

Colder Eastern Equatorial Pacific and Stronger Walker Circulation in the Early 21st Century: Separating the Forced Response to Global Warming From Natural Variability

AbstractSince the early 1990s the Pacific Walker circulation shows a multi‐decadal strengthening, which contradicts future model projections. Whether this trend, evident in many climate indices especially before the 2015 El Niño, reflects the coupled ocean‐atmosphere response to global warming or the negative phase of the Pacific Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature trends during 1980–2020 are dominated by three signals: a spatially uniform warming trend, a negative PDO pattern, and a Northern Hemisphere‐Indo‐West Pacific warming pattern. The latter pattern, which closely resembles the transient ocean thermostat‐like response to global warming emerging in a subset of CMIP6 models, shows cooling in the central‐eastern equatorial Pacific but warming in the western Pacific and tropical Indian Ocean. Together with the PDO, this pattern drives the Walker circulation strengthening in the equatorial band. Historical simulations appear to underestimate this pattern, contributing to the models' inability to replicate the Walker cell strengthening.

Hemispheric-wide climate response to regional COVID-19-related aerosol emission reductions: the prominent role of atmospheric circulation adjustments

Abstract. The national and global restrictions in response to the COVID-19 pandemic led to a sudden, albeit temporary, emission reduction of many greenhouse gases (GHGs) and anthropogenic aerosols, whose near-term climate impact were previously found to be negligible when focusing on global- and/or annual-mean scales. Our study aims to investigate the monthly scale coupled climate-and-circulation response to regional, COVID-19-related aerosol emission reductions, using the output from 10 Earth system models participating in the Covid model intercomparison project (CovidMIP). We focus on January–February and March–May 2020, which represent the seasons of largest emission changes in sulfate (SO2) and black carbon (BC). During January–February (JF), a marked decrease in aerosol emissions over eastern China, the main emission region, resulted in a lower aerosol burden, leading to an increase in surface downwelling radiation and ensuing surface warming. Regional sea-level pressure and circulation adjustments drive a precipitation increase over the Maritime Continent, embedded in a negative Pacific Decadal Oscillation (PDO)- and/or El Niño–Southern Oscillation (ENSO)-like response over the Pacific, in turn associated with a northwestward displacement and zonal shrinking of the Indo-Pacific Walker cell. Remote climate anomalies across the Northern Hemisphere, including a weakening of the Siberian High and Aleutian Low, as well as anomalous temperature patterns in the northern mid-latitudes, arise primarily as a result of stationary Rossby wave trains generated over East Asia. The anomalous climate pattern and driving dynamical mechanism reverse polarity between JF and MAM (March–May) 2020, which is shown to be consistent with an underlying shift of the dominant region of SO2 emission reduction from eastern China in JF to India in MAM. Our findings highlight the prominent role of large-scale dynamical adjustments in generating a hemispheric-wide aerosol climate imprint even on short timescales, which are largely consistent with longer-term (decadal) trends. Furthermore, our analysis shows the sensitivity of the climate response to the geographical location of the aerosol emission region, even after relatively small, but abrupt, emission changes. Scientific advances in understanding the climate impact of regional aerosol perturbations, especially the rapidly evolving emissions over China and India, are critically needed to reduce current uncertainties in near-future climate projections and to develop scientifically informed hazard mitigation and adaptation policies.

Stage-dependent influence of PDO on interdecadal summer precipitation anomalies in eastern China

Pacific decadal oscillation (PDO) has been regarded as one of the most important interdecadal factors to the interdecadal summer precipitation in eastern China, which, however, cannot keep a consistent pattern during the same positive or negative PDO phase. Because sea surface temperature (SST) anomalies vary along with PDO evolvement, the PDO impacts are investigated in terms of developing and decaying stages of its positive and negative phases, respectively. It is found that the SST cooling in mid-latitude North Pacific and SST warming in off-equator central-eastern Pacific are generally intensified from the developing stage to the decaying stage for positive PDO phase, and vice versa. Particularly, during the decaying stage of positive (negative) PDO phase, the enhanced SST warming (cooling) in northeastern tropical Pacific triggers a stronger (weaker) large-scale Walker circulation and suppresses (enhances) the convective activities in western tropical Pacific, which favors a meridional wave train like East Asia–Pacific (EAP) teleconnection over East Asia. Meanwhile, the westward extended SST cooling (warming) in mid-latitude North Pacific together with the SST warming (cooling) to its south significantly increases (decreases) the meridional SST gradient and low-level atmospheric baroclinicity, conductive to the strengthened (weakened) and southward (northward) shifted East Asian subtropical westerly jet as well as an equivalent barotropic “cold trough” in western North Pacific. Because of such tropical and extratropical dynamical processes, a meridional tripole pattern of precipitation anomalies occurs in eastern China which dominates the PDO impact in the same phase and distinctly different from the dipole pattern during the developing stage.

The modulation of Pacific Decadal Oscillation on ENSO-East Asian summer monsoon relationship over the past half-millennium.

Monsoon precipitation affects natural and social systems in East Asia, one of the most densely populated regions in the world. Monsoon precipitation variability is strongly influenced by El Niño-Southern Oscillation (ENSO) and may be related to the phase of the Pacific Decadal Oscillation (PDO). However, a collective understanding of the long-term PDO-ENSO-monsoon relationship remains limited because related studies are almost exclusively based on short instrumental records. Although paleoclimate proxies for PDO and ENSO are currently available, there is a lack of high-quality proxies for East Asian summer monsoon (EASM) precipitation. Moreover, the strengthening of the ENSO-EASM relationship since the 1970s has raised the question of anthropogenic impact. Reconstructing EASM precipitation is thus crucial to understanding its variability under natural and anthropogenic forcings. In this study, we addressed these challenges using tree ring oxygen isotopes of red cypress (Chamaecyparis formosensis Matsum), a long-lived endemic tree species in Taiwan. We developed an annual-resolved and well-validated EASM precipitation proxy from 1533 CE to 2011 which explained 49 % of the variance in instrumental precipitation. In comparison with multiple paleoclimate proxies, we revealed that PDO persistently modulated the ENSO-EASM relationship over the past half-millennium. The ENSO-EASM relationship was enhanced during the positive PDO phases and dynamically weakened during the negative PDO phases, notably in the early-17th, 18th, and early to mid-20th centuries. The strengthened relationship since the 1970s concurred with an unusually high PDO and ENSO and fell within its natural variability. Nevertheless, as the amplitude of the PDO is predicted to weaken under warming, the modulation effects may become less predictable.

Lagged effect of the Pacific Decadal Oscillation on decadal variation in global land precipitation

<p>The Pacific Decadal Oscillation (PDO), as the leading mode of sea surface temperature (SST) in the North Pacific, modulates the global temperature and precipitation. While previous studies have shown a negative relationship between the global precipitation and the PDO, the time-delayed feature of this relationship remains underexplored. Here we investigate the lagged effect of the decadal variations in the PDO on the global land precipitation using cross-correlation at multiple scales. We find that there is a delayed response of precipitation to the PDO, with the regional correlation peaking at a certain delay and gradually decreasing with increasing lag time. We note the asymmetric impacts of the positive and negative PDO phases on precipitation. Seasonal analysis reveals that the PDO is related to land precipitation during the subsequent season relative to the rest of the year, with the highest correlation occurring in the boreal winter. The delay in response is likely due to the constant SST forcing of the PDO to the atmospheric circulation. This study highlights the lag duration of the PDO�Cprecipitation relationship, potentially enriching our understanding of this relationship and enhancing climate predictions on decadal timescales.</p>

Modulation of ENSO teleconnections over North America by the Pacific decadal oscillation

In this study, we investigate whether the Pacific decadal oscillation (PDO) can enhance or diminish El Niño Southern Oscillation (ENSO) temperature and precipitation teleconnections over North America using five single model initial-condition large ensembles (SMILEs). The use of SMILEs facilitates a statistically robust comparison of ENSO events that occur during different phases of the PDO. We find that a positive PDO enhances winter and spring El Niño temperature and precipitation teleconnections and diminishes La Niña teleconnections. A negative PDO has the opposite effect. The modulation of ENSO by the PDO is mediated by differences in the location and strength of the Aleutian Low and Pacific Jet during ENSO events under different phases of the PDO. This modulation is a simple combination of the individual effects of the PDO and ENSO over North America. Finally, we show that ENSO and the PDO can be used to evaluate the likelihood of the occurrence of temperature and precipitation anomalies in different regions, but cannot be used as a deterministic predictor of these anomalies due to the large variability between individual events.