On the Southern Hemisphere stratospheric response to ENSO and its impacts on tropospheric circulation

As the leading mode of Pacific variability, the El Niño-Southern Oscillation (ENSO) causes vast and wide-spread climatic impacts, including in the stratosphere. Following discovery of a stratospheric pathway of ENSO to the Northern Hemisphere surface, here we aim to investigate if there is a substantial Southern Hemisphere (SH) stratospheric pathway in relation to austral winter ENSO events. Large stratospheric anomalies connected to ENSO occur on average at high SH latitudes as early as August, peaking at around 10 hPa. An overall colder austral spring Antarctic stratosphere is generally associated with the warm phase of the ENSO cycle, and vice versa. This behavior is robust among reanalysis and six separate model ensembles encompassing two different model frameworks. A stratospheric pathway is identified by separating ENSO events that exhibit a stratospheric anomaly from those that don’t and comparing to stratospheric extremes that occur during neutral-ENSO years. The tropospheric eddy-driven jet response to the stratospheric ENSO pathway is the most robust in the spring following a La Niña, but extends into summer, and is more zonally-symmetric compared to the tropospheric ENSO teleconnection. The magnitude of the stratospheric pathway is weaker compared to the tropospheric pathway and therefore when it is present, has a secondary role. For context, the magnitude is approximately half that of the eddy-driven jet modulation due to austral spring ozone depletion in the model simulations. This work establishes that the stratospheric circulation acts as an intermediary in coupling ENSO variability to variations in the austral spring and summer tropospheric circulation.

The leading mode and factors for coherent variations among the sub-systems of tropical Asian summer monsoon onset

Previous studies on the Asian summer monsoon (ASM) onset mainly focused on each monsoon sub-system. Mainly based on the monthly mean rainfall and low-level winds in May, this study investigated the dominant onset mode from the perspective of the entire tropical ASM region, which reveals the coherent features among the regional-scale onsets. The results of multivariate empirical orthogonal function (MV-EOF) analysis indicate that the MV-EOF1 presents reduced rainfall and anomalous low-level easterly winds at 850 hPa over the tropical ASM region in May during its positive phase. The corresponding principal component (PC1) is highly correlated with the local monsoon onset dates over Arabian Sea, Bay of Bengal, Indo-China Peninsula, and South China Sea, where the mean monsoon onsets occur in May. The only exception is India subcontinent, where the mean monsoon onsets occur in June. The results indicate that the leading mode captures the synchronized variation of monsoon onset over most of Asian monsoon sub-systems, which exhibits remarkably interannual and interdecadal changes. The factors that modulate the coherent variation of the tropical ASM onset are further examined. The simultaneously delayed ASM onset tends to occur during the easterly phase of the 30- to 80-day oscillation, the decaying phase of El Niño, and the positive phase of Pacific Decadal Oscillation (PDO). The 30- to 80-day oscillation serves as a background condition for the synchronized delayed or advanced ASM onset. El Niño-related sea surface temperature anomalies modulate the tropical ASM onset mode by modulating the tropical Walker Circulation and inducing an atmospheric Rossby wave response. The PDO affects the tropical ASM onset mode mainly via the equatorial Rossby wave response and the extratropical Rossby wave train.

On the Dynamical Mechanism of the Southern Annular Mode, Including Seasonality: Inter-Annual Variability: and Trends

<p>This thesis considers the dynamics of the leading mode of extratropical atmospheric variability, the so-called annular modes, with a focus on the Southern Hemisphere (SH). Various aspects of the annular modes are addressed, from the underlying mechanism, to variability at progressively longer time-scales; ranging from the seasonality; to inter-annual variability; to the observed and predicted trends. The underlying mechanism of the annular modes is approached in the context of the recent theory that eddy-driven jets may be self-maintaining. We show that the leading mode of variability is associated with changes in the eddy source latitude, and that the latitude of the eddy source region is organised by the mean flow. This is consistent with the idea that the annular modes should be thought of as the meridional wandering of a self-maintaining jet, and that a positive baroclinic feedback prolongs these vacillations. Further, the degree to which the eddy-driven flow is self-maintaining determines the time-scale of the leading mode in a simplified general circulation model (GCM). Preliminary results indicate that the same dynamics are important in the real atmosphere. Secondly the seasonality of the southern annular mode (SAM) is investigated. As with previous studies, during summer the SAM is found to be largely zonally symmetric, whereas during winter it exhibits increased zonal wave number 2-3 variability. This is consistent with seasonal variations in the mean-state, and it is argued that the seasonal cycle of near-surface temperature over the Australian continent plays an important role, making the eddy driven jet, and hence the SAM, more zonally symmetric during summer than winter. During winter, the SAM exhibits little variability over the South Pacific and southeast of Australia. Dynamical reasons for this behaviour are discussed. This seasonality is discussed in the context of New Zealand climate, where it is shown that the variability in rainfall and temperature data are impacted by the large-scale seasonality of the SAM. Thirdly the zonally symmetric response of the SH to the El Nino Southern Oscillation (ENSO) is examined. Such a response is only observed in the mid-latitudes during austral summer and autumn, the same period when the climatological mean flow and storm-track is most zonally symmetric. During all seasons the ENSO stationary wave, or Pacific South American mode affects the baroclinicity at 850 hPa in the South Pacific region, so that during La Nina (El Nino) events the baroclinicity is increased (reduced). During summer La Nina events the anomalous transient eddy activity is increased over the entire meridional extent of the storm-track in the South Pacific region, whereas down-stream, over the Atlantic and Indian Oceans, the storm track moves poleward. It is suggested that during La Nina events, more vigorous eddy activity in the South Pacific leads to a poleward shift of the storm-track immediately down-stream, in the East Pacific. During summer and autumn the location of the storm-track in the Pacific region may be communicated around the hemisphere because there is a single climatological storm track, and so eddies can propagate from the Pacific region to the Atlantic region. There is some evidence of these dynamics in that the anomalous eddy activity associated with La Nina events begins in the South Pacific region and subsequently propagates zonally. Finally the cause of the poleward shift of the mid-latitude eddy-driven jet streams under global warming is considered. GCMs indicate that the recent poleward shift of the eddy-driven jet streams will continue throughout the 21st Century. Here it is shown that the shift is associated with an increase in the eddy length-scale. The cause of the increase in eddy length-scale is discussed. Larger eddies are shown to propagate preferentially poleward, and it is argued that this may induce a corresponding shift in the mean flow that they maintain. The mechanism is investigated using a simplified GCM.</p>

On the Dynamical Mechanism of the Southern Annular Mode, Including Seasonality: Inter-Annual Variability: and Trends

<p>This thesis considers the dynamics of the leading mode of extratropical atmospheric variability, the so-called annular modes, with a focus on the Southern Hemisphere (SH). Various aspects of the annular modes are addressed, from the underlying mechanism, to variability at progressively longer time-scales; ranging from the seasonality; to inter-annual variability; to the observed and predicted trends. The underlying mechanism of the annular modes is approached in the context of the recent theory that eddy-driven jets may be self-maintaining. We show that the leading mode of variability is associated with changes in the eddy source latitude, and that the latitude of the eddy source region is organised by the mean flow. This is consistent with the idea that the annular modes should be thought of as the meridional wandering of a self-maintaining jet, and that a positive baroclinic feedback prolongs these vacillations. Further, the degree to which the eddy-driven flow is self-maintaining determines the time-scale of the leading mode in a simplified general circulation model (GCM). Preliminary results indicate that the same dynamics are important in the real atmosphere. Secondly the seasonality of the southern annular mode (SAM) is investigated. As with previous studies, during summer the SAM is found to be largely zonally symmetric, whereas during winter it exhibits increased zonal wave number 2-3 variability. This is consistent with seasonal variations in the mean-state, and it is argued that the seasonal cycle of near-surface temperature over the Australian continent plays an important role, making the eddy driven jet, and hence the SAM, more zonally symmetric during summer than winter. During winter, the SAM exhibits little variability over the South Pacific and southeast of Australia. Dynamical reasons for this behaviour are discussed. This seasonality is discussed in the context of New Zealand climate, where it is shown that the variability in rainfall and temperature data are impacted by the large-scale seasonality of the SAM. Thirdly the zonally symmetric response of the SH to the El Nino Southern Oscillation (ENSO) is examined. Such a response is only observed in the mid-latitudes during austral summer and autumn, the same period when the climatological mean flow and storm-track is most zonally symmetric. During all seasons the ENSO stationary wave, or Pacific South American mode affects the baroclinicity at 850 hPa in the South Pacific region, so that during La Nina (El Nino) events the baroclinicity is increased (reduced). During summer La Nina events the anomalous transient eddy activity is increased over the entire meridional extent of the storm-track in the South Pacific region, whereas down-stream, over the Atlantic and Indian Oceans, the storm track moves poleward. It is suggested that during La Nina events, more vigorous eddy activity in the South Pacific leads to a poleward shift of the storm-track immediately down-stream, in the East Pacific. During summer and autumn the location of the storm-track in the Pacific region may be communicated around the hemisphere because there is a single climatological storm track, and so eddies can propagate from the Pacific region to the Atlantic region. There is some evidence of these dynamics in that the anomalous eddy activity associated with La Nina events begins in the South Pacific region and subsequently propagates zonally. Finally the cause of the poleward shift of the mid-latitude eddy-driven jet streams under global warming is considered. GCMs indicate that the recent poleward shift of the eddy-driven jet streams will continue throughout the 21st Century. Here it is shown that the shift is associated with an increase in the eddy length-scale. The cause of the increase in eddy length-scale is discussed. Larger eddies are shown to propagate preferentially poleward, and it is argued that this may induce a corresponding shift in the mean flow that they maintain. The mechanism is investigated using a simplified GCM.</p>

Examining prevalence and correlates of smoking opioids in British Columbia: opioids are more often smoked than injected

Background British Columbia (BC) is in the midst of an opioid overdose crisis. Since 2017, smoking illicit drugs has been the leading mode of drug administration causing overdose death. Yet, little is known about people who smoke opioids, and factors underlying choice of mode of administration. The study objectives are to identify the prevalence and correlates associated with smoking opioids. Methods The Harm Reduction Client Survey is a monitoring tool used by the BC Centre for Disease Control since 2012. This survey is disseminated to harm reduction sites across BC to understand drug use trends and drug-related harms. We examined data from the survey administered October–December 2019 and performed descriptive, univariate, and multivariate analyses to better understand factors associated with smoking opioids. Results A total of 369 people who used opioids in the past 3 days were included, of whom 251 (68.0%) reported smoking opioids. A total of 109 (29.5%) respondents experienced an overdose in the past 6 months; of these 79 (72.5%) smoked opioids. Factors significantly associated with smoking opioids were: living in a small community (AOR =2.41, CI =1.27–4.58), being a woman (AOR = 1.84, CI = 1.03–3.30), age under 30 (AOR = 5.41, CI = 2.19–13.40) or 30–39 (AOR = 2.77, CI = 1.33–5.78) compared to age ≥ 50, using drugs alone (AOR = 2.98, CI = 1.30–6.83), and owning a take-home naloxone kit (AOR = 2.01, CI = 1.08–3.72). Reported use of methamphetamines within the past 3 days was strongly associated with smoking opioids (AOR = 6.48, CI = 3.51–11.96). Conclusions Our findings highlight important correlates associated with smoking opioids, particularly the recent use of methamphetamines. These findings identify actions to better respond to the overdose crisis, such as targeted harm reduction approaches, educating on safer smoking, advocating for consumption sites where people can smoke drugs, and providing a regulated supply of opioids that can be smoked.

Moisture and the Persistence of Annular Modes

Annular modes are the leading mode of variability in extratropical atmospheres, and a key source of predictability at mid-latitudes. Previous studies of annular modes have primarily used dry atmospheric models, so that moisture’s role in annular mode dynamics is still unclear. In this study, a moist two-layer quasi-geostrophic channel model is used to study the effects of moisture on annular mode persistence. Using a channel model allows moisture’s direct effects to be studied, rather than changes in persistence due to geometric effects associated with shifts in jet latitude on the sphere. Simulations are performed in which the strength of latent heat release is varied, to investigate how annular mode persistence responds as precipitation becomes a leading term in the thermodynamic budget. At short lags (<20 model days ≈ 4 Earth days), moisture increases annular mode persistence, reflecting weaker eddy activity that is less effective at disrupting zonal-mean wind anomalies. Comparisons to dry simulations with weaker mean flows demonstrate that moisture is particularly effective at damping high frequency eddies, further enhancing short lag persistence. At long lags (>20 model days), moisture weakly increases persistence, though it decreases the amplitudes of low frequency annular mode anomalies. In the most realistic simulation, the greater short-lag persistence increases the e-folding time of the zonal index by 21 model days (≈4 Earth days). Moisture also causes a transition to propagating variability, though this does not seem to affect the leading mode’s persistence.

On the Use of Self-Organizing Maps in Detecting Teleconnections. Part I: Spatial Aspects

Self-organizing maps (SOMs) represent a popular classification tool, output of which has been used to link typical synoptic-scale circulation patterns to large-scale teleconnections, or modes of low-frequency circulation variability. However, recently there have been attempts to interpret SOM output directly as a continuum of teleconnections. In the present paper, we provide a theoretical study dealing with how predefined idealized modes of variability project onto SOM arrays. Three orthogonal modes are defined and their various linear combinations used to generate datasets of known structure. Multiple variants of SOMs that differ in their initialization are generated for SOMs of various shapes and sizes. The results show that how a mode projects on a SOM array is sensitive not only to data structure, but also to various SOM parameters. The leading mode of variability projects rather strongly on SOMs if its explained variance is markedly higher than that of the second-order mode; the remaining modes project considerably more weakly, and all modes tend to blend when their explained variance is close to each other, which leads to underrepresentation of some phases of modes and/or combinations of modes among the SOM patterns. Furthermore, non-linear features appear in SOM arrays even if the underlying modes of variability are strictly linear. The findings point to limitations in the applicability of SOMs in the research of teleconnections.

Short.Term Reactivity & Power Control: Reactor Regulating System (RRS)

For CANDU reactors, the control of the long-term reactivity and of the power is carried out by on-power refuelling, while the control of the short-term reactivity and of power is done by the RRS. The RRS is part of the overall plant-control system that maintains the reactor power at a specified level, or, when required, manoeuvres the reactor power between specified setpoints. The reactor power setpoint can be entered by the operator (in the reactor-leading mode) or it can be calculated automatically by the Steam Generator (SG) pressure-control program (in the turbine-leading mode). The RRS consists of the following main components:

Paleoceanography of the northwestern Pacific across the Early–Middle Pleistocene boundary (Marine Isotope Stages 20–18)

The fluctuating position of the boundary between the Kuroshio (warm) and Oyashio (cold) currents in the mid-latitude western North Pacific affects both heat transport and air–ocean interactions and has significant consequences for the East Asian climate. We reconstruct the paleoceanography of Marine Isotope Stages (MIS) 20–18, MIS 19 being one of the closest astronomical analogues to the present interglacial, through multiple proxies including microfossil assemblage data, planktonic foraminiferal isotopes (δ18O and δ13C), and foraminiferal Mg/Ca-based temperature records, from the Chiba composite section (CbCS) exposed on the Boso Peninsula, east-central Japan. Principal component analysis (PCA) is used to capture dominant patterns of the temporal variation in these marine records, and shows that the relative abundances of calcareous nannofossil and radiolarian taxa are consistent with the water mass types inferred from geochemical proxies. The leading mode (36.3% of total variance) mirrors variation in the terrestrial East Asian winter monsoon (EAWM), reflecting seasonal trends dominated by the winter monsoon system. In the CbCS, this mode is interpreted as reflecting the interplay between the warm Kuroshio and cold Oyashio waters, which is likely related to the latitudinal shift of the subtropical–subarctic gyre boundary in the North Pacific. The second mode (15.4% of total variance) is closely related to subsurface conditions. The leading mode indicates that MIS 19b and 19a are represented by millennial-scale stadial/interstadial oscillations. Northerly positions for the gyre boundary during late MIS 19c, the interstadials of MIS 19a, and early MIS 18 are inferred from the leading mode, which is consistent with a weak EAWM and consequent mild winter climate in East Asia. Nonetheless, the northerly positions for the gyre boundary during late MIS 19c and early MIS 19a were not associated with subsurface warming presumably due to the suppressed gyre circulation itself caused by the weak Aleutian Low. Intermittent southerly positions for the gyre boundary are inferred for the stadials of MIS 19b and 19a. Regional sea surface temperature (SST) comparisons in the western North Pacific reveal that the moderate SSTs during MIS 19a through early MIS 18 were restricted to the mid- to high latitudes, influenced by the weak EAWM. Comparison between MIS 20–18 and MIS 2–1 suggests that glacial MIS 20 and 18 had significantly milder winters than MIS 2, likely related to the relatively weak EAWM.

The Southern Annular Mode in CMIP6 simulations

&lt;p&gt;Stratospheric ozone depletion, along with increases in long-lived greenhouse gases, is well known to cause a strengthening of the Southern Annular Mode (SAM), the leading mode of variability in the Southern Hemisphere.&amp;#160; I here analyze simulations contributed to CMIP6 for signatures of these two leading drivers of climate change. For the period 1957-2014, seasonally large disagreements are found between four observational references; CMIP6-derived trends are in agreement with two out of four commonly used references. Using a regression analysis applied to model simulations with and without interactive ozone chemistry, a strengthening of the SAM in summer is attributed nearly completely to ozone depletion because a further strengthening influence due to long-lived greenhouse gases is almost fully counterbalanced by a weakening influence due to stratospheric ozone increases associated with these greenhouse gas increases. Ignoring such ozone feedbacks (an approach commonly used with no-chemistry climate models) would yield comparable contributions from these two influences, an incorrect result. In winter, trends are smaller but an influence of greenhouse gas-mediated ozone feedbacks is also identified. The regression analysis furthermore yields significant differences in the attribution of SAM changes to the two influences between models with and without interactive ozone chemistry, with ozone depletion and GHG increases playing seasonally a stronger and weaker, respectively, role in the chemistry models versus the no-chemistry ones. The results suggest that adequately representing stratospheric ozone feedbacks in climate models is critical for a correct attribution of trends in the SAM.&lt;/p&gt;