Oceanic Atmospheric Circulation Patterns Research Articles

Decadal-scale variability and warming affect spring timing and forest growth across the western Great Lakes region.

The Great Lakes region of North America has warmed by 1-2 °C on average since pre-industrial times, with the most pronounced changes observable during winter and spring. Interannual variability in temperatures remains high, however, due to the influence of ocean-atmosphere circulation patterns that modulate the warming trend across years. Variations in spring temperatures determine growing season length and plant phenology, with implications for whole ecosystem function. Studying how both internal climate variability and the "secular" warming trend interact to produce trends in temperature is necessary to estimate potential ecological responses to future warming scenarios. This study examines how external anthropogenic forcing and decadal-scale variability influence spring temperatures across the western Great Lakes region and estimates the sensitivity of regional forests to temperature using long-term growth records from tree-rings and satellite data. Using a modeling approach designed to test for regime shifts in dynamic time series, this work shows that mid-continent spring climatology was strongly influenced by the 1976/1977 phase change in North Pacific atmospheric circulation, and that regional forests show a strengthening response to spring temperatures during the last half-century.

Spatio-temporal Variation Characteristics of Extreme Climate Events and Their Teleconnections to Large-scale Ocean-atmospheric Circulation Patterns in Huaihe River Basin, China During 1959–2019

Spatio-temporal Variation Characteristics of Extreme Climate Events and Their Teleconnections to Large-scale Ocean-atmospheric Circulation Patterns in Huaihe River Basin, China During 1959–2019

Historical and Projected Variations of Precipitation and Temperature and Their Extremes in Relation to Climatic Indices over the Gandaki River Basin, Central Himalaya

Changes in precipitation and temperature, especially in the Himalayan region, will have repercussions for socio-economic conditions in the future. Thus, this study aimed to understand the climatic trend and changes in one of the Himalayan River basins, i.e., Gandaki River Basin (GRB), Nepal. In particular, we analysed the historical (1985–2014) and projected (2015–2100) precipitation and temperature trend and their extremes using observation and 13 bias-corrected Coupled Model Intercomparison Project phase 6 (CMIP6) datasets. Additionally, the relationship between extreme precipitation/temperature indices and ocean-atmospheric circulation patterns were also analysed. The results showed an increasing trend of precipitation amount and temperature at annual and seasonal scales with the highest upward trend for precipitation in monsoon season and temperature in winter season. Among nine precipitation indices analysed, the wet extremes are projected to increase in all Shared Socioeconomic Pathways (SSP) scenarios; with the highest increment of high-intensity related extremes (R10 mm and R20 mm). In contrast, dry spells will decline in the distant-future (2075–2100) as compared to near (2015–2044) and mid-future (2045–2074). Further, increment in temperature trend resulted in a decrease in cold related temperature extremes and an increase in warm related extremes. Furthermore, it was observed that the changes in precipitation and temperature extremes over GRB were influenced by large-scale ocean-atmospheric circulation patterns. The Atlantic Multidecadal Oscillation (AMO), Sea Surface Temperature (SST) and Southern Oscillation Index (SOI) were found to have a major role in driving precipitation extremes while AMO, SST and Pacific Decadal Oscillation (PDO) have strong influence on temperature extremes. The results of this study will be useful for better understanding the implications of historical and future changes in precipitation and temperature and their extremes over the GRB.

Recent variations in the seasonality difference between precipitation and potential evapotranspiration in China

AbstractThe seasonality difference between precipitation (P) and potential evapotranspiration (E0) has a significant imprint on ecohydrological processes, but little attention has been given to this difference in China. A climate seasonality and asynchrony index (SAI), considering the amplitude and phase difference (PD) between P and E0, was thus applied to investigate the variation in seasonality difference between P and E0 across China from 1960 to 2017. The main results showed that the mean amplitudes of seasonal P (δP) were larger than that of E0 (δE0). Except for in east and central south China, the peak values of E0 had a time lag of 23 days behind those of P. The annual SAI in China showed a significantly downward trend (p < 0.05), suggesting a reduction in the difference in seasonal P and E0 in China. The attribution results showed that the variation in SAI was mainly controlled by δP changes across China with a relative contribution of 60.5%, followed by δE0 (35.9%) and PD (3.6%). Wavelet analysis showed that the annual SAI had a significant relationship with ocean–atmosphere circulation patterns at a scale of 1–6 years (p < 0.05). As an attempt to investigate the difference in seasonal P and E0 in China, the findings of this study can provide a reference for climate seasonality variations and support for the quantification of its effects on the ecohydrological environment.

Palaeo-environmental evolution of Central Asia during the Cenozoic: new insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)

Abstract. The Valley of Lakes basin (Mongolia) contains a unique continental sedimentary archive, suitable for constraining the influence of tectonics and climate change on the aridification of Central Asia in the Cenozoic. We identify the sedimentary provenance, the (post)depositional environment and the palaeo-climate based on sedimentological, petrographical, mineralogical, and (isotope) geochemical signatures recorded in authigenic and detrital silicates as well as soil carbonates in a sedimentary succession spanning from ∼34 to 21 Ma. The depositional setting was characterized by an ephemeral braided river system draining prograding alluvial fans, with episodes of lake, playa or open-steppe sedimentation. Metamorphics from the northern adjacent Neoarchean to late Proterozoic hinterlands provided a continuous influx of silicate detritus to the basin, as indicated by K–Ar ages of detrital muscovite (∼798–728 Ma) and discrimination function analysis. The authigenic clay fraction is dominated by illite–smectite and “hairy” illite (K–Ar ages of ∼34–25 Ma), which formed during coupled petrogenesis and precipitation from hydrothermal fluids originating from major basalt flow events (∼32–29 and ∼29–25 Ma). Changes in hydroclimate are recorded in δ18O and δ13C profiles of soil carbonates and in silicate mineral weathering patterns, indicating that comparatively humid to semi-arid conditions prevailed in the late(st) Eocene, changing into arid conditions in the Oligocene and back to humid to semi-arid conditions in the early Miocene. Aridification steps are indicated at ∼34–33, ∼31, ∼28 and ∼23 Ma and coincide with some episodes of high-latitude ice-sheet expansion inferred from marine deep-sea sedimentary records. This suggests that long-term variations in the ocean–atmosphere circulation patterns due to pCO2 fall, reconfiguration of ocean gateways and ice-sheet expansion in Antarctica could have impacted the hydroclimate and weathering regime in the basin. We conclude that the aridification in Central Asia was triggered by reduced moisture influx by westerly winds driven by Cenozoic climate forcing and the exhumation of the Tian Shan and Altai Mountains and modulated by global climate events.

Recent changes in climate seasonality in the inland river basin of Northwestern China

Representing regional available water and energy conditions, variations in precipitation (P) and potential evapotranspiration (E0) have received much attention in current studies on climate change. However, the changes in their mismatch, i.e. climate seasonality, have rarely been investigated. Considering the seasonal amplitudes of P and E0 (δP and δE0, respectively), as well as their phase difference, a climate seasonality and asynchrony index (SAI) was used to analyze the seasonal distribution of the available water–energy and their mismatch in the inland river basin of Northwestern China (IRB-NWC) during 1960–2017. We found that the annual δP, δE0, and SAI all decreased during the past few decades, indicating that the mismatch between the seasonal available water and energy in IRB-NWC has improved. Attribution analysis conducted by the elasticity method indicated that the changes in δP controlled the variations in SAI throughout the area, with a relative contribution of 43.7%. Furthermore, wavelet analysis indicated that large-scale ocean-atmosphere circulation patterns (including EI Niño Southern Oscillation, Indian Ocean Dipole, Pacific Decadal Oscillation and East Asian Summer Monsoon) were significantly linked with SAI on 2–6 years scale. Our findings may provide valuable information regarding the trends and causes of climate seasonality and aid in predicting and mitigating the effects of potential future climate changes in the dry region.

Inter-Annual Variability of Winter Precipitation Over Nepal Coupled With Ocean-Atmospheric Patterns During 1987–2015

Nepal is a mountainous country located on the southern slope of the central Himalayas, where ~3% of the total annual rainfall occurs in the winter season. The inter-annual variability and shift in the winter precipitation are of great importance in space and time, however, has not been investigated in Nepal. This study sought to investigate the inter-annual variability of winter precipitation (DJF), below- and above-average winter precipitation anomalies over Nepal and their controlling factors associated with ocean-atmospheric circulation patterns during the historical period of 1987–2015. Here, we used Asian Precipitation-Highly Resolved Observational Data Integration towards Evaluation of Water Resources (APHRODITE), Climate Prediction Center (CPC) database of National Centres for Environmental Prediction (NCEP) and Japan Marine Science and Technology Centre (JAMSTEC) data from different sources to study the Empirical Orthogonal Function (EOF), Wavelet, Composite, and Correlation analysis, respectively. The results show that the leading EOF mode captures 62.1% of the total variance of precipitation exhibiting a single mode of variability. As determined by wavelet analysis, the winter precipitation of Nepal shows 2 to 2.6 year’s power spectrum for 29 years (1987–2015). The time series of winter precipitation anomalies revealed the years 1996, 1998, 2000, 2005, 2007, and 2008 as precipitation deficit years which is supported by the composite analysis showing negative precipitation anomalies with positive outgoing longwave radiation (OLR) and vertical velocity. These phenomena are converse for wet events during 1988, 1995, 1997, 2002, 2012, and 2014. The wet years exhibit moisture convergence with strong south-westerly wind anomalies originated from the Arabian Sea. The dry events reveal moisture divergence with weaker north-westerly wind anomalies. The temperature gradient over Tibetan Plateau is linked with a shift in precipitation regime over Nepal. The further finding indicates that preceding summer monsoon (JJAS) and post-monsoon (ON) warming over the Indo-Pacific Ocean influences the following year's winter precipitation over Nepal. The observed changes in the dry and wet years during winter are useful for disaster preparedness and the planning and monitoring of water resources and agriculture.

Hydrological Drought Forecasting Incorporating Climatic and Human-Induced Indices

Abstract Many drought forecasting methods have been proposed, but only a few have considered the changing environment. The main purpose of this study is to improve the accuracy of drought forecasting models under changing environments by considering the influence of large-scale climate patterns and human activities on hydrological drought. To select the most significant large-scale climatic index that influences drought events in the Luanhe River basin, Spearman’s rho correlation test was applied to detect the relationship between large-scale oceanic–atmospheric circulation patterns and the standardized runoff index (SRI). We also proposed a human activity index (HI) to represent the effect of human activities on hydrological drought. Based on a multivariate normal distribution, we included the above indices in a probabilistic forecasting model, which forecasted the probabilities of transition from the current to a future SRI value. Using the Liying hydrological station as an example, the impacts of a controlled large-scale climatic index (Niño-3.4) and the HI on the transition probabilities were illustrated, and the results showed that the turning point of the Niño-3.4 effect on the transition probabilities occurred within the range from 25.91 to 26.90. Finally, a scoring method was applied to compare the forecasting model performances. The results showed that the inclusion of the large-scale climatic index and HI improved the forecasting accuracy.

Spatiotemporal variations in extreme precipitation and their potential driving factors in non-monsoon regions of China during 1961–2017

Extreme precipitation events affect the ecological environment and are also important for the sustainable development of regional socioeconomics. Although there are some local studies on extreme precipitation events in which the temporal and spatial variation characteristics of extreme precipitation events in non-monsoon regions (NMRs) are systematically assessed, detailed study on the driving mechanisms of variation are becoming increasingly important. In this study, nine extreme precipitation indices were used to analyze the characteristics of extreme precipitation event spatiotemporal variations in NMRs in China during 1961–2017. The results show that except for the consecutive dry days, which shows a significant decreasing trend (P < 0.01) of −2.33 days/decade, all other indices showed obvious increasing trends, especially the indices of wet day precipitation (PRCPTOT), highest 5 day precipitation (RX5day) and light rain days (R5 mm), with significantly increasing trends (P < 0.01) of 6.80 mm/decade, 0.73 mm/decade and 0.45 days/decade, respectively. In addition, a correlation analysis between altitude, longitude, latitude and extreme precipitation shows that stations at an altitude of more than 3500 m have significant correlations with both extreme precipitation and longitude in NMRs (P < 0.05). In addition, results also indicated that there are significant relationships between extreme precipitation events in NMRs and large-scale ocean-atmosphere circulation patterns (P < 0.05). The rapid increase in extreme precipitation indices over the past 20 years is closely related to the Atlantic Multidecadal Oscillation shift to a warm phase, while the Pacific Decadal Oscillation, El Niño–Southern Oscillation and Summer Monsoon Index show significant correlation with the extreme indices only in certain seasons (P < 0.05).

Identification of the non-stationarity of extreme precipitation events and correlations with large-scale ocean-atmospheric circulation patterns: A case study in the Wei River Basin, China

The investigation of extreme precipitation events in terms of variation characteristics, stationarity, and their underlying causes is of great significance to better understand the regional response of the precipitation variability to global climate change. In this study, the Wei River Basin (WRB), a typical eco-environmentally vulnerable region of the Loess Plateau in China was selected as the study region. A set of precipitation indices was adopted to study the changing patterns of precipitation extremes and the stationarity of extreme precipitation events. Furthermore, the correlations between the Pacific Decadal Oscillation (PDO)/El Niño-Southern Oscillation (ENSO) events and precipitation extremes were explored using the cross wavelet technique. The results indicate that: (1) extreme precipitation events in the WRB are characterized by a significant decrease of consecutive wet days (CWD) at the 95% confidence level; (2) compared with annual precipitation, daily precipitation extremes are much more sensitive to changing environments, and the assumption of stationarity of extreme precipitation in the WRB is invalid, especially in the upstream, thereby introducing large uncertainty to the design and management of water conservancy engineering; (3) both PDO and ENSO events have a strong influence on precipitation extremes in the WRB. These findings highlight the importance of examining the validity of the stationarity assumption in extreme hydrological frequency analysis, which has great implications for the prediction of extreme hydrological events.

Uncovering global climate fields causing local precipitation extremes

ABSTRACTEarlier studies have focused on establishing the hydroclimatic teleconnection between hydrological extremes and a single or a few preselected coupled oceanic–atmospheric circulation patterns (OACP). In this study, we hypothesise that local (continental-scale) hydrological extremes are, in general, influenced by a concurrent effect of different climate variables from several regions across the globe. The suite of these variables is termed the global climate pattern (GCP) behind the target hydrological event. To explore our hypothesis, we considered monthly Indian rainfall, which is a complex, continental-scale hydrological phenomenon. Extreme events are identified through the standardized precipitation anomaly index (SPAI), used as an indicator of dry and wet events. The global fields of different climate variables—sea surface temperature (SST), surface pressure (SP), air temperature (AT), wind speed (WS) and total precipitable water (TPW)—are explored for possible revelatory patterns. In all, 15 different variables, each designated by a climate anomaly from a distinct zone on the globe, are found to form a potential global climate signal pool, which can be designated as the GCP for Indian rainfall. The combined information extracted from this GCP is proven to be highly efficient in predicting dry and wet events in Indian rainfall.EDITOR Z. W. Kundzewicz; ASSOCIATE EDITOR G. Di Baldassarre

Analysis of spatio‐temporal changes in annual and seasonal precipitation variability in South America‐Chile and related ocean–atmosphere circulation patterns

ABSTRACTEstablishing relationships between coupled ocean–atmospheric patterns and precipitation accumulation is important to describe and predict spatio‐temporal variability on annual or seasonal scales, and also to evaluate how this variability is influenced by global warming. The objective of this study was to examine the leading modes of interannual and seasonal (summer, autumn, winter, and spring) precipitation variability in South America‐Chile, and their significant relationship to seasonally aggregated gridded data and climatic indices. Applying exhaustive data quality control measures to data from 238 rain gauges with different lengths of records between 1893 and 2013, a new data set was created with the objective of obtaining reliable records for further analysis. A comprehensive analysis through empirical orthogonal functions (EOF) allowed for determination of the leading modes of annual and seasonal precipitation and their main spatial patterns for the whole country. The percentage of explained variance in the relationship between seasonally aggregated indices and the leading modes of precipitation confirmed that most of the interannual and winter precipitation variability in Chile is linked to the seasonal aggregation of El Nino Southern Oscillation (ENSO). The leading modes of summer, autumn, and spring precipitation were mostly linked to seasonal aggregations of the Madden and Julian Oscillation (MJO), and the Antarctic Oscillation (AAO).

Seasonal flows of international British Columbia-Alaska rivers: The nonlinear influence of ocean-atmosphere circulation patterns

The northern portion of the Pacific coastal temperate rainforest (PCTR) is one of the least anthropogenically modified regions on earth and remains in many respects a frontier area to science. Rivers crossing the northern PCTR, which is also an international boundary region between British Columbia, Canada and Alaska, USA, deliver large freshwater and biogeochemical fluxes to the Gulf of Alaska and establish linkages between coastal and continental ecosystems. We evaluate interannual flow variability in three transboundary PCTR watersheds in response to El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Arctic Oscillation (AO), and North Pacific Gyre Oscillation (NPGO). Historical hydroclimatic datasets from both Canada and the USA are analyzed using an up-to-date methodological suite accommodating both seasonally transient and highly nonlinear teleconnections. We find that streamflow teleconnections occur over particular seasonal windows reflecting the intersection of specific atmospheric and terrestrial hydrologic processes. The strongest signal is a snowmelt-driven flow timing shift resulting from ENSO- and PDO-associated temperature anomalies. Autumn rainfall runoff is also modulated by these climate modes, and a glacier-mediated teleconnection contributes to a late-summer ENSO-flow association. Teleconnections between AO and freshet flows reflect corresponding temperature and precipitation anomalies. A coherent NPGO signal is not clearly evident in streamflow. Linear and monotonically nonlinear teleconnections were widely identified, with less evidence for the parabolic effects that can play an important role elsewhere. The streamflow teleconnections did not vary greatly between hydrometric stations, presumably reflecting broad similarities in watershed characteristics. These results establish a regional foundation for both transboundary water management and studies of long-term hydroclimatic and environmental change.

Palaeoclimate and palaeoceanographic conditions in the westernmost Mediterranean over the last millennium: an integrated organic and inorganic approach

Previous studies have revealed the excellence of the westernmost Mediterranean records for reconstructing climate conditions over the last two millennia. In particular, inorganic and organic proxies have revealed a coherent signal of climate and oceanographic responses during this time. Here we compare and integrate both proxy records for reconstructing climate and oceanographic conditions with focus on the last millennium. The higher temperatures indicated by lipid-based proxies during the Medieval Climate Anomaly (MCA) are coincident with drier conditions indicated by inorganic proxies. In contrast, lower temperatures and humid conditions are indicated during the Little Ice Age (LIA). The industrial period was characterized by increasing humidity in comparison with the previous LIA. However, a progressive aridification occurred since the second half of the twentieth century, coexisting with a warming trend and higher contribution of C3 grasses. Proxy records are also interpreted to show Atlantic water inflow at AD 1450 and 1950 and an intensification of the upwelling conditions coinciding with a prolonged positive North Atlantic Oscillation (NAO) phase in the intervals AD 1000–1450 and 1960–1990. Large-scale oceanic–atmospheric circulation patterns (the NAO and the Atlantic meridional circulation) and solar irradiance variations seem to have played the major key role during the last millennium, together with anthropogenic contributions in the more recent record.

Changes in atmospheric circulation patterns associated with high and low rainfall regimes in the Hawaiian Islands region on multiple time scales

We examine a suite of climate variables in the North Pacific associated with different temporal scales of dry and wet episodes in the Hawaiian Islands. The goal is to ascertain whether varying the length in the occurrence of such events from seasonal to multi-decadal results from different ocean–atmosphere circulation patterns over the North Pacific region. We find that as the dryness period lengthens, the spatial scale of the anomalies widens, but the characteristics of the anomalous circulation fields exhibit elements evident at each time scale. At the longest (multi-decadal) time scales during the wet season (November–April), the major anomalous circulation features associated with above (below) average rainfall in Hawai'i are a strengthening (weakening) of the North Pacific mid-latitude westerlies associated with a strengthened (weakened) Aleutian Low system, a slight weakening (strengthening) of the northeast trade winds, with anomalous northerly (southerly) component to the south of the Islands, together with diminished (enhanced) precipitation across most of the tropical North Pacific.During the summer dry season (May–October) a characteristic pattern that is evident at different time scales during drier than normal periods is a strengthening of the trade winds to the south of the Islands, with sinking motion extending from the latitude of Hawai'i eastward to Central America. Conversely, wet summers are associated with generally weaker trades to the south with a tendency for anomalous southwesterly component. We also consider possible changes in the relationship of Hawaiian rainfall to changes in the Pacific-Decadal Oscillation (PDO) but conclude that the record is too short to establish the significance of any changes in an overall negative correlation.

Grain size records reveal variability of the East Asian Winter Monsoon since the Middle Holocene in the Central Yellow Sea mud area, China

Three cores (ZY-1, ZY-2 and ZY-3) retrieved from the Central Yellow Sea mud (CYSM) were analyzed in sensitive grain size and AMS 14C dating to reconstruct the history of the East Asian Winter Monsoon (EAWM) since the Middle Holocene in the study area. The results show that these data provide a continuous history of the EAWM over the past 7.2 ka and that the EAWM can be divided into three periods: strong and highly fluctuating during 7.2–4.2 ka BP; moderate and relatively stable during 4.2–1.8 ka BP; and weakened during 1.8–0 ka BP. Compared with the East Asian Summer Monsoon (EASM) recorded in the previous studies, the evolutionary history of the EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the EASM. At the centennial scale, however, the EAWM intensified events correlate well with the EASM weakened events and the North Atlantic climatic variations (Bond events 0 to 5) within the dating error, most likely forced by the reduction of solar irradiance through changes in the oceanic-atmospheric circulation patterns.

Late Holocene forcing of the Asian winter and summer monsoon as evidenced by proxy records from the northern Qinghai–Tibetan Plateau

Little is known about decadal- to centennial-scale climate variability and its associated forcing mechanisms on the Qinghai–Tibetan Plateau. A decadal-resolution record of total organic carbon (TOC) and grainsize retrieved from a composite piston core from Kusai Lake, NW China, provides solid evidence for decadal- to centennial-scale Asian monsoon variability for the Northern Qinghai–Tibetan Plateau during the last 3770 yr. Intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance. A number of intensified Asian winter monsoon phases are potentially correlated with North Atlantic climatic variations including Bond events 0 to 2 and more recent subtle climate changes from the Medieval Warm Period to the Little Ice Age. Our findings indicate that Asian monsoon changes during the late Holocene are forced by changes in both solar output and oceanic–atmospheric circulation patterns. Our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid-latitude regions (the Northern Qinghai–Tibetan Plateau).

Trends and periodicities in the Canadian Drought Code and their relationships with atmospheric circulation for the southern Canadian boreal forest

Trends and periodicities in summer drought severity are investigated on a network of Canadian Drought Code (CDC) monthly average indices extending from central Quebec to western Manitoba and covering the instrumental period 1913–1998. The relationship and coherency between CDC indices and ocean–atmosphere circulation patterns are also examined. Trend analyses indicate that drought severity is unchanged in eastern and central Canada. Composite analyses indicate that for most of the corridor, severe drought seasons occur with a combination of positive 500-hPa geopotential height anomalies centered over the Gulf of Alaska and over the Baffin Bay. Additional severe drought seasons develop across the corridor in the presence of positive height anomalies located over or upstream of the affected regions. According to spectral analyses, the North Atlantic and the North Pacific circulation patterns modulate the drought variability at the decadal scale. Our results lead us to conclude that climate warming and the increases in the amount and frequency of precipitation in eastern Canada during the last century had no significant impact on summer drought severity. It is unlikely that linear climate change contributed to the change in the boreal forest dynamics observed over the past 150 years.