Interdecadal Oscillation Research Articles

Runoff change controlled by combined effects of multiple environmental factors in a headwater catchment with cold and arid climate in northwest China

The limited runoff in cold and arid regions is sensitive to environmental changes, and it is thus urgent to explore the change and controlling factors of runoff under the background of global warming and intensified human activities. However, previous studies have rarely considered the combined effects of multiple controlling factors at varying scales over time. With the headwater region of the Manas River in northwest China as the study area, we investigated the change in runoff for the period of 1954–2016 and its relationship with regional environmental factors (e.g. precipitation PCP, temperature TMP, potential evapotranspiration ET0, snow cover extent SCE, land use, and normalized difference vegetation index NDVI) and/or global atmospheric circulation (e.g. North Atlantic Oscillation NAO, Arctic Oscillation AO, Pacific Interdecadal Oscillation PDO, and El Nino Southern Oscillation ENSO). In particular, the combined effects of multiple environmental factors were determined at different scales by the multiple wavelet coherence. The annual runoff significantly increased at a rate of 0.508 × 108 m3/decade, and the climate tended to be warmer and wetter. Among the regional and global environmental factors, NDVI and ENSO were the single factor mostly correlated with runoff, while NDVI-TMP and ENSO-PDO were the combined factors with the stronger relations on runoff, respectively. The regional environmental factors had larger impacts on runoff than the global environmental factors, and the natural factors outperformed human activities in controlling runoff. The accelerated melting of snow/glacier induced by the increasing temperature dominated runoff change, and the increasing water inputs from wetter climate may play a second role in runoff. The runoff characteristics in cold and arid regions seem to be different from those regions with little snow/glacier, which should be paid more attention. The employed multiple wavelet coherence is helpful in determining the processes dominating runoff change.

Distinguishing Variability Regimes of Hawaiian Summer Rainfall: Quasi‐Biennial and Interdecadal Oscillations

AbstractSummer precipitation in Hawai'i accounts for 40% of the annual total and provides important water sources. However, our knowledge about its variability remains limited. Here we show that statewide Hawai'i summer rainfall (HSR) variability exhibits two distinct regimes: quasi‐biennial (QB, ~2 years) and interdecadal (~30–40 years). The QB variation is linked to alternating occurrences of the Western North Pacific (WNP) cyclone and anticyclone in successive years, which is modulated by the intrinsic El Niño–Southern Oscillation biennial variability and involves a positive feedback between atmospheric Rossby waves and underlying sea surface temperature (SST) anomalies. The interdecadal variation of HSR is largely modulated by the Pacific Decadal Oscillation through affecting upstream low‐level humidity that affects topographic rainfall. HSR shows weak long‐term drying trend during 1920–2019. This first description of the major physical drivers of summer rainfall variability provides key information for seasonal rainfall prediction in Hawai'i.

Interannual and decadal covariabilities in East Asian and Western North Pacific summer rainfall for 1979\u20132016

Understanding the variabilities of East Asian summer rainfall (EASR) and Western North Pacific summer rainfall (WNPSR) is essential because they play a key role to control the energy and water supply. Monsoon index is generally defined by seasonal mean, but it is not appropriate for considering various timescale characteristics. Because it includes the influence of not only the interannual but also longer timescales. Thus, the several timescale variances in the indices and background fields should be isolated as each variability to focus on their own features. Here, the present study defines the EASR and WNPSR indices to explore potential factors that may trigger the enhanced rainfall for the period 1979–2016. Interannual variation is shown to be dominant in both indices, while decadal variation is more significant in WNPSR than EASR. Each index is decomposed to obtain a signal on interannual and decadal timescales with 1–7 and 8–15 years. The interannual components in both indices perform opposite each other in atmospheric and oceanic fields and have a negative relationship with high covariance. Both location of subtropical jet and thermal condition over the Indian Ocean contribute to interannual EASR and WNPSR as factors. In contrast, related fields upon both decadal indices represent distinguished patterns. The EASR is modulated by Pacific sea surface temperature anomalies (SSTA) and interdecadal oscillation patterns in the decadal timescale. However, the WNPSR is controlled by the tri-polar SSTA over the North Atlantic. Consequently, the decadal and interannual variabilities show differing mechanisms to adjust rainfall during monsoon events.

Phytoplankton Responses to Climate‐Induced Warming and Interdecadal Oscillation in North‐Western Australia

AbstractGrowing evidence has suggested that ocean warming could cause a decline in marine phytoplankton productivity. However, studies in tropical waters have discovered that evolutionary adaptation of local species to warming and positive response to increasing rainfall could avoid the sharp decline in productivity. Here, the decadal trends of phytoplankton biomass, reconstructed using the biomarkers of brassicasterol (diatoms) and dinosterol (dinoflagellates), showed a 1.5–3 times increase since the 1950s along a large section of the Kimberley coast, north‐western Australia. Principal component analysis found that 56% of the phytoplankton variance was linked with climate change‐induced increases in sea surface temperature and rainfall associated with increased tropical cyclones, which can enhance nutrient supply favoring phytoplankton growth and production; 20.4% of the phytoplankton variance tended to be related to the Interdecadal Pacific Oscillation through a mechanism of ocean‐coast interaction. We empirically predict that the negative impact of rising temperatures on phytoplankton in north‐western Australia could be buffered by the increasing tropical cyclones and the coming warm phase of Interdecadal Pacific Oscillation.

Absence of internal multidecadal and interdecadal oscillations in climate model simulations

For several decades the existence of interdecadal and multidecadal internal climate oscillations has been asserted by numerous studies based on analyses of historical observations, paleoclimatic data and climate model simulations. Here we use a combination of observational data and state-of-the-art forced and control climate model simulations to demonstrate the absence of consistent evidence for decadal or longer-term internal oscillatory signals that are distinguishable from climatic noise. Only variability in the interannual range associated with the El Niño/Southern Oscillation is found to be distinguishable from the noise background. A distinct (40–50 year timescale) spectral peak that appears in global surface temperature observations appears to reflect the response of the climate system to both anthropogenic and natural forcing rather than any intrinsic internal oscillation. These findings have implications both for the validity of previous studies attributing certain long-term climate trends to internal low-frequency climate cycles and for the prospect of decadal climate predictability.

The combined effect of climate oscillations in producing extremes: the 2020 drought in southern Brazil

ABSTRACT The 2020 drought in southern Brazil, which culminated in late summer and early autumn (February-March-April), displayed one of the most deficient rainfall totals in such trimester. This period of the year has already been dominated by negative rainfall deviations since the end of the 1990s. This recent drought represents, therefore, a significant worsening in an already unfavorable situation of water availability. Such long-term behavior is due to the combination of opposite phases of two interdecadal oscillations in the sea surface temperature: the positive phase of the Atlantic Multidecadal Oscillation and the negative phase of the Pacific Interdecadal Oscillation. This combination produces variation in the atmospheric basic state that favors less rainfall in southern Brazil at this time of the year and more frequent occurrence of droughts. For an extreme event to occur, it is usually necessary that, in addition to interdecadal oscillations, an interannual oscillation event occurs that also favors drought, such as the events of Central El Niño in 2020 and La Niña in 2009 and 2012, years of droughts in southern Brazil during the same phase combination of the two interdecadal oscillations. Anthropic climate changes can intensify the frequency and intensity of these extreme events.

Wavelet analysis of precipitation extremes over India and teleconnections to climate indices

Precipitation patterns and extremes are significantly influenced by various climatic factors and large-scale atmospheric circulation patterns. This study uses wavelet coherence analysis to detect significant interannual and interdecadal oscillations in monthly precipitation extremes across India and their teleconnections to three prominent climate indices, namely, Nino 3.4, Pacific Decadal Oscillation, and Indian Ocean Dipole (IOD). Further, partial wavelet coherence analysis is used to estimate the standalone relationship between the climate indices and precipitation after removing the effect of interdependency. The wavelet analysis of monthly precipitation extremes at 30 different locations across India reveals that (a) interannual (2–8 years) and interdecadal (8–32 years) oscillations are statistically significant, and (b) the oscillations vary in both time and space. The results from the partial wavelet coherence analysis reveal that Nino 3.4 and IOD are the significant drivers of Indian precipitation at interannual and interdecadal scales. Intriguingly, the study also confirms that the strength of influence of large-scale atmospheric circulation patterns on Indian precipitation extremes varies with spatial physiography of the region.

Understanding the inter‐decadal variability of autumn precipitation over North Central China using model simulations

AbstractA recent study has shown a robust relationship between the Pacific Decadal Oscillation (PDO) and inter‐decadal variations in autumn precipitation over North Central China (NCC). However, the physical processes underlying these inter‐decadal precipitation variations are not fully understood. Here we analyse multi‐member ensembles of atmospheric reanalysis and model simulations to examine the atmospheric and precipitation responses to sea surface temperature (SST) forcing. Despite the large inter‐member spread resulting from atmospheric internal variability, the model simulations forced by the observed SSTs show an important role of mid‐latitude atmospheric circulation in influencing the inter‐decadal precipitation variations over NCC. We also analyse the sensitivity experiments using three atmospheric models forced by the Inter‐decadal Pacific Oscillation (IPO)/PDO‐like SST fields. The results suggest that the SST anomalies associated with a negative IPO phase can induce anomalous positive pressure anomalies over the East Asia‐Japan‐North Pacific region, which weakens the East Asian trough (EAT) and produces southerly advection of warm and moist air into NCC, leading to increased precipitation there. This study provides a depiction of how the IPO/PDO‐associated SSTs induce inter‐decadal oscillations in mid‐latitude atmospheric circulations, which in turn cause inter‐decadal precipitation variations over NCC.

The variability of South Korean temperature associated with climate indicators

Examining the physical mechanisms through which large-scale climate indicators, e.g., El Nino–Southern Oscillation and Indian Ocean Dipole, affect hydroclimatic variables in the tropics and extratropics is a forefront scientific challenge. We examined climatic teleconnections between large-scale climate indices and temperature variability over South Korea. To do this, we calculated not only leading patterns of observed monthly mean and extreme temperature through an empirical orthogonal teleconnection (EOT) decomposition technique but also statistical correlations on a monthly basis using cross-correlation and lag regression analyses for the leading modes and global atmospheric circulation dataset. As a result, the spatial pattern of the leading EOT modes for mean (extreme high) temperature represents an eastern (southern) coastal mode for boreal summer and a northern (middle) inland mode in boreal winter, while extreme low EOTs exhibit a northern inland mode in summer and a western coastal mode in winter. The temporal evolution of the leading EOT modes exhibits a mostly increasing trend and an interdecadal oscillation. The leading EOT modes of mean temperature explain more variance than those of extreme temperature during warm and cold seasons. The findings from this study illustrate that tropical ENSO forcing has a coherent association with August and December temperature patterns, while the Indian Ocean Dipole is identified as a driver for temperature variability during fall season. The monsoon circulation over the western North Pacific also exhibits a significant negative correlation with the December temperature EOTs. The leading EOTs for October temperature exhibit the positive correlation with the tropical cyclone variability, while the leading EOTs for mean and extreme high temperature exhibit significant negative correlations with the snow depth over northeastern Eurasia in November. The leading patterns of the August and December mean temperature time series are predictable at up to 5-month lead time from the tropical Pacific sea surface temperatures (SSTs), while a predictable response from Indian Ocean SSTs was detected at up to 4-month lead time.

Northeast Atlantic Storm Activity and Its Uncertainty from the Late Nineteenth to the Twenty-First Century

AbstractGeostrophic wind speeds calculated from mean sea level pressure readings are used to derive time series of northeast Atlantic storminess. The technique of geostrophic wind speed triangles provides relatively homogeneous long-term storm activity data and is thus suited for statistical analyses. This study makes use of historical air pressure data available from the International Surface Pressure Databank (ISPD) complemented with data from the Danish and Norwegian Meteorological Institutes. For the first time, the time series of northeast Atlantic storminess is extended until the most recent year available, that is, 2016. A multidecadal increasing trend in storm activity starting in the mid-1960s and lasting until the 1990s, whose high storminess levels are comparable to those found in the late nineteenth century, initiated debate over whether this would already be a sign of climate change. This study confirms that long-term storminess levels have returned to average values in recent years and that the multidecadal increase is part of an extended interdecadal oscillation. In addition, new storm activity uncertainty estimates were developed and novel insights into the connection with the North Atlantic Oscillation (NAO) are provided.

El Niño–Southern Oscillation related teleconnections over South America under distinct Atlantic Multidecadal Oscillation and Pacific Interdecadal Oscillation backgrounds: La Niña

The Pacific Interdecadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) influence in different ways the La Niña (LN) related teleconnections in South America. The low‐frequency backgrounds in the Atlantic and Pacific Oceans play an important role in modulating the LN‐related Walker and Hadley cells and the Rossby wavetrain pattern in the Southern Hemisphere. The illustration shows the LN‐related SST anomaly pattern during the austral summer for distinct low‐frequency backgrounds.This analysis investigates the concomitant influence of two dominant low‐frequency modes, the Pacific Interdecadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), on the La Niña (LN) related climate teleconnections over South America (SA). Four possible low‐frequency backgrounds are analysed: WAMO/WPDO, WAMO/CPDO, CAMO/WPDO and CAMO/CPDO, with the letters “W” and “C” referring, respectively, to the warm and cold phases of the AMO and PDO. The low‐frequency anomalous sea surface cooling (warming) in the tropical Pacific during the CPDO (WPDO) favours (impedes) the settling of the LN‐related negative SST anomalies in this oceanic sector. Thus, the LN‐related SST anomaly patterns in the tropical Pacific in the CPDO backgrounds are meridionally more extensive and stronger than those in the WPDO backgrounds. The highest and lowest percentages of the years that experienced LN events occurred during the WAMO/CPDO and CAMO/WPDO backgrounds, respectively. The northern node of the LN‐related wet–dry dipole between northern SA and southeastern SA (SESA) occurs in most seasons for all backgrounds. However, the southern node occurs in specific seasons: spring and summer for the WAMO/WPDO, winter and spring for the WAMO/CPDO, winter and summer for the CAMO/WPDO and spring for the CAMO/CPDO. Also, the LN effect on the South American monsoon with a wet–dry dipole between northern SA and eastern Brazil during summer is noted in most backgrounds, but with differences among them. We discuss here the differences in the precipitation anomaly patterns, Walker and Hadley cells and Rossby wavetrain patterns among the backgrounds. The low‐frequency Atlantic and Pacific backgrounds play an important role in defining the rainfall anomaly pattern associated with the LN. The results shown here have not been discussed before and might be useful mainly for climate monitoring purposes.

Interannual Variation of the Spring and Summer Precipitation over the Three River Source Region in China and the Associated Regimes

AbstractThis study analyzes the interannual and interdecadal variability of spring and summer precipitation over the Three River Source (TRS) region in China using four datasets. A general consistency is revealed among the four datasets with regard to the interannual and interdecadal variability of TRS precipitation during 1979–2015, demonstrating a confidence of the four datasets in representing the precipitation variability over the TRS region. The TRS spring and summer precipitation shows distinct interannual and interdecadal variability, with an overall increasing trend in the spring precipitation and an interdecadal oscillation in the summer precipitation. The regimes associated with the interannual variability of TRS spring and summer precipitation are further investigated. The interannual variability of TRS spring precipitation is essentially modulated by an anomalous easterly water vapor transport (WVT) branch associated with the leading mode of Eurasian spring circulation. El Niño–Southern Oscillation (ENSO) may affect the interannual variability of TRS spring precipitation by causing southerly WVT anomalies toward the TRS region. The interannual variability of TRS summer precipitation is essentially modulated by an anomalous southwesterly WVT branch over the TRS region, which is mainly associated with a Eurasian wave train connected with the summer North Atlantic Oscillation. A strong East Asian summer monsoon and an El Niño–decaying summer may also contribute to the southwesterly WVT anomalies over the TRS region.

Pacific Decadal and El Niño oscillations shape survival of a seabird.

Understanding and modeling population change is urgently needed to predict effects of climate change on biodiversity. High trophic-level organisms are influenced by fluctuations of prey quality and abundance, which themselves may depend on climate oscillations. Modeling effects of such fluctuations is challenging because prey populations may vary with multiple climate oscillations occurring at different time scales. The analysis of a 28-yr time series of capture-recapture data of a tropical seabird, the Nazca Booby (Sula granti), in the Galápagos, Ecuador, allowed us to test for demographic effects of two major ocean oscillations occurring at distinct time-scales: the inter-annual El Niño Southern Oscillation (ENSO) and inter-decadal oscillations. As expected for a tropical seabird, survival of fledgling birds was highly affected by extreme ENSO events; by contrast, neither recruitment nor breeding participation were affected by either ENSO or decadal oscillations. More interesting, adult survival, a demographic trait that canalizes response to environmental variations, was unaffected by inter-annual ENSO oscillations yet was shaped by the Pacific Decadal Oscillation and small pelagic fish regime. Adult survival decreased during oceanic conditions associated with higher breeding success, an association probably mediated in this species by costs of reproduction that reduce survival when breeding attempts end later. To our knowledge, this is the first study suggesting that survival of a vertebrate can be vulnerable to a natural multidecadal oscillation.

Global climate teleconnection with rainfall erosivity in South Korea

Rainfall Erosivity Index (REI) defined as the product of rainfall kinetic energy and rainfall intensity is a well-known hydrologic indicator of the potential risk of soil erosion. Global and regional scale climatic teleconnections with REI variability over South Korea are examined. We calculate leading patterns of observed monthly REIs using the Empirical Orthogonal Teleconnection (EOT) and Function (EOF) decomposition techniques. Also we used monthly statistical analyses using cross-correlation and lag regression for the leading modes and global atmospheric circulation measurement in the Pacific and Indian Ocean. As a result, the northern inland mode is applicable during summer season and the southern coastal mode applies to fall-winter season. The temporal evolution of REI exhibits mostly increasing and depends on interdecadal oscillation patterns. The leading EOT modes explain more variance in REI than the EOF modes during warm and cold seasons. The findings from this study illustrate that the tropical ENSO forcing has the coherent association with fall and winter REI patterns, and the Indian Ocean dipole is identified as a driver for REI variability in November. The monsoon circulations over western North Pacific also exhibit significant negative correlation with the December modes. The September leading modes also show a positive correlation with the tropical cyclone activity. Leading patterns in September and November have predictability up to five month lead time from the tropical Pacific Sea Surface Temperatures (SSTs). In addition, predictability from the Pacific SSTs for above normal extreme value of REI is greater than that for below normal value in winter. In conclusion, South Korea experiences climatic teleconnection between the large scale climate indices and mid-latitude hydrologic variables.

Intercomparison of the Extended Reconstructed Sea Surface Temperature v4 and v3b Datasets

Version 4 (v4) of the Extended Reconstructed Sea Surface Temperature (ERSST) dataset is compared with its precedent, the widely used version 3b (v3b). The essential upgrades applied to v4 lead to remarkable differences in the characteristics of the sea surface temperature (SST) anomaly (SSTa) in both the temporal and spatial domains. First, the largest discrepancy of the global mean SSTa values around the 1940s is due to ship-observation corrections made to reconcile observations from buckets and engine intake thermometers. Second, differences in global and regional mean SSTa values between v4 and v3b exhibit a downward trend (around −0.032°C per decade) before the 1940s, an upward trend (around 0.014°C per decade) during the period of 1950–2015, interdecadal oscillation with one peak around the 1980s, and two troughs during the 1960s and 2000s, respectively. This does not derive from treatments of the polar or the other data-void regions, since the difference of the SSTa does not share the common features. Third, the spatial pattern of the ENSO-related variability of v4 exhibits a wider but weaker cold tongue in the tropical region of the Pacific Ocean compared with that of v3b, which could be attributed to differences in gap-filling assumptions since the latter features satellite observations whereas the former features in situ ones. This intercomparison confirms that the structural uncertainty arising from underlying assumptions on the treatment of diverse SST observations even in the same SST product family is the main source of significant SST differences in the temporal domain. Why this uncertainty introduces artificial decadal oscillations remains unknown.

Simultaneous Evolution of Gyre and Atlantic Meridional Overturning Circulation Anomalies as an Eigenmode of the North Atlantic System

The authors identify an interdecadal oscillatory mode of the North Atlantic atmosphere–ocean system in a general circulation model (GFDL CM2.1) via a linear inverse model (LIM). The oscillation mechanism is mostly embedded in the subpolar gyre: anomalous advection generates density anomalies in the eastern subpolar gyre, which propagate along the mean gyre circulation and reach the subpolar gyre center around 10 years later, when associated anomalous advection of the opposite sign starts the other half cycle. As density anomalies reach the Labrador Sea deep convection region, Atlantic meridional overturning circulation (AMOC) anomalies are also induced. Both the gyre and AMOC anomalies then propagate equatorward slowly, following the advection of density anomalies. The oscillation is further demonstrated to be more likely an ocean-only mode while excited by the atmospheric forcing; in particular, it can be approximated as a linearly driven damped oscillator that is partly excited by the North Atlantic Oscillation (NAO). The slowly evolving interdecadal oscillation significantly improves and prolongs the LIM’s prediction skill of sea surface temperature (SST) evolution.

Dryness and wetness variations for the past 1000 years in Guanzhong Plain

In this study, spatial-temporal statistical technologies were utilized to interpolate a dryness and wetness grade dataset, which was reconstructed from previous Chinese historical documents, but with significant data gaps in the past 1000 years, and a complete grade dataset of dryness and wetness was developed for Guanzhong Plain including seven sites at Linfen, Changzhi, Xi’an, Fengxiang, Luoyang, Nanyang and Hanzhong. The probit model was used to interpolate the missing values at the spatial scale depending on the highest variance explanation between neighbouring stations, and the Markov chain model was used to interpolate the temporal series depending on the known features of the dataset from 1470 to 2010. On the basis of this dataset, long-term variation features and extreme drought and flood events in the Guanzhong Plain were identified. By means of wavelet analysis and ensemble empirical mode decomposition methods, the main cycles of interannual-interdecadal-centennial scales of dryness and wetness variations were detected and the relationships between periodicity and driving forces were analyzed. Results indicated that the dry-wet change of the Guanzhong Plain has had three stages in the past 1000 years, that is, the climate changed from wet to dry in 960–1150, then from dry to wet in 1151–1800, and again from wet to dry after 1801. On the half-centennial time scale, five wet periods in 960–1000, 1151–1200, 1251–1300, 1351–1400 and 1651–1900, and five dry periods in 1001–1150, 1201–1250, 1301–1350, 1401–1650 and after 1901 were identified. Extreme drought and flood events occurred with high frequency in the 17th and 19th–20th centuries, about once every two years. Extreme drought events lasting 5 years occurred in 1070–1089, 1212–1216, 1327–1331, 1431–1445, 1481–1491, 1634–1641, 1688–1692, 1714–1722, 1875–1878, 1925–1931 and 1993–1997. Extreme flood events lasting 5 years occurred in 981–985, 1647–1653, 1658–1664, 1676–1680, 1725–1730, 1848–1854 and 1882–1889. The dry-wet changes of the Guanzhong Plain has an inter-annual oscillation with a 3–7-year scale, inter-decadal oscillations with quasi-10-year, quasi-30-year and quasi-70-year scales and a centennial oscillation with a quasi-100-year scale. The climate of Guanzhong Plain tends to be drier than in a normal year in the year of the occurrence of the El Nino or the following year. On the quasi-70-year scale, the correlation of the Pacific Decadal Oscillations and the dry-wet change shows a positive (negative) relationship before (after) 1435, which suggested that the relationship between them is not stable in the long term. In addition, the solar maximum corresponds to the dry climate. It is worth noting that due to the lack of long climate series, both reconstruction and model simulation approaches are used to study climate change during historical times. The reconstructed dryness and wetness variations for the past 1000 years in Guanzhong Plain may still lack certainty, and in the future, further analyses and comparisons between the reconstructions and simulations need to be conducted, in order to diagnose the dynamic mechanisms of the climate features in Guanzhong Plain.

Multi-scale impacts of the Pacific SST and PDO on the summer precipitation of North-Central China from 1870 to 2002

Climate variability has become a hot topic worldwide in recent years. Although large numbers of climate data series have been reconstructed based on hundreds to thousands, or even tens of thousands, of years, our understanding of this problem is still controversial. We use the precipitation index (PI) series to study the periodicity of the precipitation in northern China from 1870 to 2002 and explore the climate variability on a large timescale. The analysis shows that the precipitation has periods of 2.27–3.03, 7.14, 10.00, 11.11, 12.50, 14.29, 16.67, 20.00, and 25.00 a. Based on complete ensemble empirical mode decomposition (CEEMD), the Pacific sea surface temperature (SST) and Pacific interdecadal oscillation (PDO) are decomposed into different frequencies. The results show that the SST and PDO have interannual to interdecadal periodicity. To determine the impact of the Pacific SST and PDO on the PI, we make use of the cross wavelet power spectrum and wavelet coherency spectrum to analyze their period relation and reveal their periodic change characteristics; it is found that different bands of the Pacific SST, PDO, and PI have high power.

Wavelet analysis of precipitation extremes over Canadian ecoregions and teleconnections to large‐scale climate anomalies

AbstractTo detect significant interannual and interdecadal oscillations and their teleconnections to large‐scale climate anomalies such as El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO), monthly and seasonal maximum daily precipitation (MMDP and SMDP) from 131 stations across Canada were analyzed by using variants of wavelet analysis. Interannual (1–8 years) oscillations were found to be more significant than interdecadal (8–30 years) oscillations for all selected stations, and the oscillations are both spatial and time‐dependent. Similarly, the significant wavelet coherence and the phase difference between leading principal components of monthly precipitation extremes and climate indices were highly variable in time and in periodicity, and a single climate index explains less than 40% of the total variability. Partial wavelet coherence analysis shows that both ENSO and PDO modulated the interannual variability and PDO modulated the interdecadal variability, of MMDP over Canada. NAO is correlated with the western MMDP at interdecadal scale and the eastern MMDP at interannual scale. The composite analysis shows that precipitation extremes at about three fourths of the stations have been significantly influenced by ENSO and PDO patterns, while about one half of the stations by the NAO patterns. The magnitude of SMDP in extreme El Niño years, and extreme PDO event of positive phase, was mostly lower (higher) over the Canadian Prairies in summer and winter (spring and autumn) than in extreme La Niña years. Overall, the degree of influence of large‐scale climate patterns on Canadian precipitation extremes varies by season and by region.

Climatic variability of transport in the upper layer of the Antarctic Circumpolar Current from hydrological and satellite data

Based on the satellite altimetry dataset of sea level anomalies, the climatic hydrological database World Ocean Atlas-2009, ocean reanalysis ECMWF ORA-S3, and wind velocity components from NCEP/NCAR reanalysis, the interannual variability of Antarctic Circumpolar Current (ACC) transport in the ocean upper layer is investigated for the period 1959–2008, and estimations of correlative connections between ACC transport and wind velocity components are performed. It has been revealed that the maximum (by absolute value) linear trends of ACC transport over the last 50 years are observed in the date-line region, in the Western and Eastern Atlantic and the western part of the Indian Ocean. The greatest increase in wind velocity for this period for the zonal component is observed in Drake Passage, at Greenwich meridian, in the Indian Ocean near 90° E, and in the date-line region; for the meridional component, it is in the Western and Eastern Pacific, in Drake Passage, and to the south of Africa. It has been shown that the basic energy-carrying frequencies of interannual variability of ACC transport and wind velocity components, as well as their correlative connections, correspond to the periods of basic large-scale modes of atmospheric circulation: multidecadal and interdecadal oscillations, Antarctic Circumpolar Wave, Southern Annual Mode, and Southern Oscillation. A significant influence of the wind field on the interannual variability of ACC transport is observed in the Western Pacific (140° E–160° W) and Eastern Pacific; Drake Passage and Western Atlantic (90°–30° W); in the Eastern Atlantic and Western Indian Ocean (10°–70° E). It has been shown in the Pacific Ocean that the ACC transport responds to changes of the meridional wind more promptly than to changes of the zonal wind.