The time series of 20th century Siberian warm season (May to October) precipitation (SWP) shows variations over decadal timescales, including a wetting trend since the 1970s. Here, it is shown that ...the Atlantic multidecadal variability (AMV) can be implicated as a remote driver of the decadal-scale variations in SWP. Observational analysis identifies a significant in-phase relationship between the AMV and SWP, and the SWP decadal variability can be largely explained by the AMV. The physical mechanism for this relationship is investigated using both observations and numerical simulations. The results suggest that North Atlantic sea surface temperature (SST) warming associated with the positive AMV phase can excite an eastward propagating wave train response across the entire Eurasian continent, which includes an east-west dipole structure over Siberia. The dipole then leads to anomalous southerly winds bringing moisture northward to Siberia; the precipitation increases correspondingly. The mechanism is further supported by linear barotropic modeling and Rossby wave ray tracing analysis.
In this study, the authors demonstrate that the two types of El Niño–Southern Oscillation (ENSO) have asymmetric features with respect to the impact of their positive and negative phases on boreal ...summer rainfall over the Yangtze River Valley (YRV) and South China (SC). The relationship between rainfall over the YRV and the warm pool (WP) La Niña is positive and significant, whereas the relationship with the WP El Niño is not. In the case of the cold tongue (CT) ENSO, its positive phase has a positive influence, while there is no significant relationship with the negative phase. In contrast, rainfall over SC has a significant positive relationship with WP El Niño, but a nonsignificant relationship with WP La Niña. The positive phase of the CT ENSO has a significant negative influence on SC rainfall, while the negative phase has a nonsignificant impact. An asymmetric atmospheric response to the asymmetric sea surface temperature anomalies (SSTAs) was also observed in the lower troposphere. The location of the center of the anomalous circulations over the study region differs during the opposite phases of the two types of ENSO. This asymmetric response is likely to be linked to the different spatial patterns of the two types of El Niño and La Niña. Atmospheric general circulation models confirm the authors’ analysis of the observed data. Numerical simulations show that the asymmetric response of the lower atmosphere is drivenmainly by differing SSTA patterns in the equatorial Pacific Ocean.
Abstract
To quantify the predictability limit of a chaotic system, the authors recently developed a method using the nonlinear local Lyapunov exponent (NLLE). The NLLE method provides a measure of ...local predictability limit of chaotic systems and is intended to supplement existing predictability methods. To apply the NLLE in studies of actual atmospheric predictability, an algorithm based on local dynamical analogs is devised to enable the estimation of the NLLE and its derivatives using experimental or observational data. Two examples are given to illustrate the effectiveness of the algorithm, involving the Lorenz63 three-variable model and the Lorenz96 forty-variable model; they reveal that the algorithm is applicable in estimating the NLLE of a chaotic system from its experimental time series. On this basis, the NLLE method is used to investigate temporal–spatial distributions of predictability limits of the daily geopotential height and wind fields. The limit of atmospheric predictability varies widely with region, altitude, and season. The predictability limits of the daily geopotential height and wind fields are generally less than 3 weeks in the troposphere, whereas they are approximately 1 month in the lower stratosphere, revealing a potential predictability source for forecasting weather from the stratosphere. Further work is required to examine broader applications of the NLLE method in predictability studies of the atmosphere, ocean, and other systems.
Deep Atlantic Multidecadal Variability Yang, Jiajun; Li, Jianping; An, Qirong
Geophysical research letters,
16 January 2024, Volume:
51, Issue:
1
Journal Article
Peer reviewed
Open access
Investigating deep‐sea temperature variability is essential for understanding deep‐sea variability and its profound impacts on climate. The first mode in the Atlantic is referred to as Deep Atlantic ...Multidecadal Variability (DAMV), characterized by a north‐south dipole pattern in the mid‐high latitudes with a quasi‐period of 20–50 years. The DAMV and Atlantic Multidecadal Variability, despite a statistical discrepancy, may be different responses to ocean heat transport (OHT) driven by the Atlantic Meridional Overturning Circulation (AMOC) at distinct depths separately. The relationship between the DAMV and the AMOC is established, indicating the AMOC is likely to transport surface heat downwards by deep convection and contribute to such dipole pattern in the deep Atlantic. Furthermore, meridional OHT proves the AMOC can explain the DAMV variation as a dynamic driver. These results reinforce the importance of deep‐sea studies concerning the Atlantic climate system.
Plain Language Summary
The deep sea is an indispensable component of the Earth's climate system, owing to its substantial heat capacity. Despite challenges posed by the reliability of ocean data sets deeper than 2,000 m, exploration of the deep sea is of immense social and scientific significance. This study identifies the dominant mode of deep Atlantic potential temperature at a depth of approximately 3,000 m, known as Deep Atlantic Multidecadal Variability (DAMV). The DAMV exhibits a dipole pattern in the mid‐high latitudes, cooling (warming) in the North Atlantic and warming (cooling) in the South Atlantic during its positive (negative) phase. The DAMV is a multidecadal variability with a meaningful quasi‐period of 20–50 years, similar to the Atlantic Multidecadal Variability (AMV). However, statistical methods indicate that the DAMV and the AMV are distinct climate variabilities, closely connected by the AMOC. By lead‐lag correlation and ocean heat transport analysis, deep convection of the AMOC might facilitate the surface heat downward transport over approximately a decade. As a result, it is highly likely that the DAMV pattern can be attributed to the AMOC.
Key Points
Deep Atlantic Multidecadal Variability (DAMV) displays a mid‐high latitudes north‐south dipole pattern with a quasi‐period of 20–50 years
The meridional ocean heat transport, driven by the Atlantic Meridional Overturning Circulation (AMOC), can explain the DAMV variation
The AMOC transports surface heat downwards over more than a decade and contributes to the DAMV pattern in the deep Atlantic
In this study, an interhemispheric teleconnection pattern across the critical latitude from southern Africa through South Asia to the North Pacific was revealed in boreal winter monthly averaged ...250-hPa streamfunction fields obtained from both the 40-yr ECMWF Re-Analysis (ERA-40) and the NCEP–NCAR reanalysis data from 1957/58 to 2001/02. Classical Rossby wave theory for zonally varying flow in which the effects of the basic-state meridional wind are ignored predicts that stationary Rossby waves cannot propagate across easterlies. To elucidate the underlying mechanisms responsible for this interhemispheric teleconnection, the theoretical basis for stationary wave propagation across the critical latitude is considered, taking into account meridional ambient flow. The theoretical results suggest that the southerly flow over East Africa, the western Indian Ocean, and South Asia creates a path for the northward propagation of stationary waves across the critical latitude. Stationary wavenumber and group velocity analysis, ray tracing, and simple model experiments applied to nearly realistic boreal winter mean flows confirm that disturbances excited in southern Africa and the western Indian Ocean can propagate across the critical latitude to South Asia through the southerly duct and then continue downstream along the North African–Asian subtropical jet.
Nanomaterials have received much attention during the past decade because of their excellent optical, electronic, and catalytic properties. Nanomaterials possess high chemical reactivity, also high ...surface energy. Thus, provide a stable immobilization platform for biomolecules, while preserving their reactivity. Due to the conductive and catalytic properties, nanomaterials can also enhance the sensitivity of molecularly imprinted electrochemical sensors by amplifying the electrode surface, increasing the electron transfer, and catalyzing the electrochemical reactions. Molecularly imprinted polymers that contain specific molecular recognition sites can be designed for a particular target analyte. Incorporating nanomaterials into molecularly imprinted polymers is important because nanomaterials can improve the response signal, increase the sensitivity, and decrease the detection limit of the sensors. This study describes the classification of nanomaterials in molecularly imprinted polymers, their analytical properties, and their applications in the electrochemical sensors. The progress of the research on nanomaterials in molecularly imprinted polymers and the application of nanomaterials in molecularly imprinted polymers is also reviewed.
The behavior of the El Niño–Southern Oscillation (ENSO) has undergone significant changes since the year 2000. Meanwhile, a notable westward shift and strengthening in the atmosphere‐to‐ocean ...Bjerknes feedback were observed. We find that this shift can be primarily attributed to a weakened relationship between the zonal gradient of precipitation anomaly and that of sea surface temperature (SST) anomaly since 2000.This weakened relationship is a comprehensive manifestation of reduced El Niño‐related precipitation anomalies in the central‐eastern tropical Pacific and increased anomalies in the western tropical Pacific. These changes are connected to the mean state change in the tropical Pacific after 2000, where the cooler background SSTs in the central‐eastern tropical Pacific suppress upward motion, and the warmer background SSTs in the western tropical Pacific promote upward motion in the overlying atmosphere. Our findings offer a potential explanation for the westward shift and strengthening in the atmosphere‐to‐ocean Bjerknes feedback since 2000.
Plain Language Summary
The El Niño–Southern Oscillation (ENSO) is a climate phenomenon that plays a major role in global weather and climate systems. The development of ENSO is mainly attributed to a positive feedback known as the Bjerknes feedback, which represents the atmospheric response to the oceanic forcing and vice versa. It is noted that ENSO has behaved differently since the year 2000. Concurrently, a pronounced westward movement and strengthening in the atmosphere‐to‐ocean Bjerknes feedback have also been observed. Analyses show that changes in the Bjerknes positive feedback are largely due to a weakened relationship between anomalous rainfall patterns and sea surface temperatures (SSTs). This implies that during El Niño events, there is less rainfall in the central and eastern parts of the tropical Pacific, and more rainfall in the western tropical Pacific. These changes are linked to a cooling of background SSTs in the central‐eastern tropical Pacific, which reduces the upward air movement and rainfall in that region, and a warming of background SSTs in the western Pacific, which promotes the upward air movement and rainfall.
Key Points
Westward shift and strengthening of the atmosphere‐to‐ocean Bjerknes feedback in the tropical Pacific have been observed since 2000
A weakened precipitation‐to‐sea surface temperature (SST) response drives the changes in the atmosphere‐to‐ocean Bjerknes feedback
Changes in precipitation‐to‐SST response are linked to the interdecadal shift in the tropical Pacific background state
China is located in a large monsoon domain; variations in meteorological fields associated with the Asian summer monsoon can influence transport, deposition, and chemical reactions of aerosols over ...eastern China. We apply a global three‐dimensional Goddard Earth Observing System (GEOS) chemical transport model (GEOS‐Chem) driven by NASA/GEOS‐4 assimilated meteorological data to quantify the impacts of the East Asian summer monsoon on seasonal and interannual variations of aerosols over eastern China. During the summer monsoon season, four channels of strong cross‐equatorial flows located within 40°E–135°E are found to bring clean air to China from the Southern Hemisphere. These channels have the effect of diluting aerosol concentrations in eastern China. In the meantime, rain belts associated with the summer monsoon move from southeastern to northern China during June–August, leading to a large wet deposition of aerosols. As a result, aerosol concentrations over eastern China are the lowest in summer. Sensitivity studies with no seasonal variations in emissions indicate that the Asian summer monsoon can reduce surface layer PM2.5 (particles with a diameter of 2.5 μm or less) aerosol concentration averaged over eastern China (110°E–120°E, 20°N–45°N) by about 50–70%, as the concentration in July is compared to that in January. We also compare simulated PM2.5 concentrations in the weak monsoon year of 1998 with those in the strong monsoon year of 2002, assuming same emissions in simulations for these 2 years. Accounting for sulfate, nitrate, ammonium, black carbon, organic carbon, as well as submicron mineral dust and sea salt, surface layer PM2.5 concentration averaged over June–August and over eastern China is 7.06 μg m−3 (or 44.3%) higher in the weak monsoon year 1998 than in the strong monsoon year 2002, and the column burden of PM2.5 is 25.1 mg m−2 (or 73.1%) higher in 1998 than in 2002. As a result, over eastern China, the difference in summer aerosol optical depth between 1998 and 2002 is estimated to be about 0.7. These results have important implications for understanding air quality and climatic effects of aerosols in eastern China.
Significant interhemispheric teleconnections are identified that span the tropical easterlies in the boreal summer 300-hPa streamfunction, such as the North Africa-Antarctic (NAA) and the North ...Pacific-South America (NPSA) patterns. These patterns are not supported by traditional wave theory, since stationary waves in a basic state without meridional wind would be trapped in the easterlies. To describe the interhemispheric responses more realistically, two-dimensional spherical Rossby wave theory in a horizontally nonuniform basic state is considered. Conditions sufficient for the existence of one propagating wave are obtained, and the meridional group velocity of the wave is shown to have the same direction as the meridional basic wind at the traditional critical latitude. It is concluded that stationary waves with a specific wavelength can propagate across the easterlies from south (north) to north (south) via southerly (northerly) flows. Hence, energy transport by stationary waves on a horizontally nonuniform basic state may produce interhemispheric responses that could pass through the tropical easterly belt. The wave theory and a barotropic model are then applied to idealized and climatological flows. Model results agree well with the theory. In boreal winter and summer, cross-equatorial flows steer stationary waves propagating from one hemisphere to the other across the tropical easterlies, especially over the Australian-Asian monsoon region. It seems that the large-scale monsoonal background flows play a critical role in the interhemispheric teleconnection. Additionally, the wave ray trajectory and model results suggest that the NAA pattern may result from Rossby wave energy dispersion.
•Information spillover between WTI returns and investor sentiment indices is studied.•Sentiment by trader type is highly correlated with WTI returns.•Speculator sentiment makes the largest ...contribution to WTI returns variation over the full sample period.•Hedger sentiment plays the leading role in information transmission when oil price is low.
This paper examines information spillover between WTI returns and investor sentiment indices measured by various trader positions using a connectedness approach. Our findings show that sentiment by trader type is highly correlated with WTI returns. Among the different sentiment types, speculator sentiment makes the largest contribution to WTI returns variation over the full sample period. The dynamic results show that the influence of investor sentiment increases significantly when oil prices are in a downward movement in which hedger sentiment plays the leading role in information transmission.
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