Interactions between the Madden-Julian oscillation and mesoscale to global scale phenomena

2019 Summer.Includes bibliographical references.The Madden-Julian Oscillation (MJO) influences and interacts with atmospheric phenomena across the globe, from the tropics to the poles. In this two-part study, the interactions of the MJO with other phenomena across a broad range of scales are considered, including mesoscale convective structures within the tropics and global teleconnection patterns. While the two studies are distinct in the scales of the interactions they discuss, each highlights an aspect of the importance of interactions between the MJO and variability across a broad range of scales within the climate system. The study of such cross-scale interactions is important for understanding our climate system, as these interactions can transfer energy between phenomena of starkly different spatial and temporal scales. Part one of the study uses a cloud-resolving model, the Regional Atmospheric Modeling System, to consider the relationship between mesoscale convective structures within the Indo-Pacific region and the regional, intraseasonal anomalies associated with the MJO. The simulation captures the entirety of a canonical boreal summertime MJO event, spanning 45 days in July and August of 2016, during which the convective anomaly associated with the MJO propagated over the Maritime Continent. The convective cloud structures, or cells, within the simulation were tracked and logged according to their location relative to the regional convective anomaly of the MJO. Using both spectral analysis and phase compositing, it was found that a progressive relationship exists between the boreal summertime MJO and mesoscale deep convective structures within the Indo-Pacific region, specifically within the convectively enhanced region of the MJO, as follows: increased cell longevity in the initial phases of the MJO, followed by increased cell number in the intermediate phases, progressing into increased cell expanse in the terminal phases. This progressive relationship is connected back to the low-frequency atmospheric response to the MJO. It is suggested that the bulk thermodynamic and kinematic anomalies of the MJO are closely related to the convective cell expanse and longevity, although the number of convective cells appears to be tied to another source of variability not identified within this study. These findings emphasize that while the MJO is commonly defined as an intraseasonal-scale convective anomaly, it is also intrinsically tied to the mesoscale variability of the convective systems that constitute its existence. The second part of the study quantifies the prevalence of the MJO within the overall climate system, along with the dependence of its teleconnections on variability in another tropical phenomena on a larger scale than itself. It is well known that the MJO exhibits pronounced seasonality in its tropical and global signature, and recent research has suggested that its tropical structure also depends on the state of the Quasi-Biennial Oscillation (QBO). We therefore first quantify the relationship between 300-mb geopotential anomalies and the MJO across the globe, then test the dependence of the relationship on both the meteorological season and the QBO phase using a derivative of cross-spectral analysis, magnitude-squared coherence Coh2. It is found that the global upper-tropospheric signature of the MJO exhibits pronounced seasonality, but also that the QBO significantly modulates the upper-tropospheric tropical and extratropical anomalies associated with the MJO. Globally, variability in upper tropospheric geopotential linked to the MJO is maximized during the boreal summertime and wintertime of easterly QBO phases, which is consistent with previous research that has shown easterly QBO phases to enhance the persistence of tropical convection associated with the MJO. Additional features are identified, such as the global maximum in upper-tropospheric variability associated with the MJO occurring during boreal summertime, rather than boreal wintertime. Overall, the MJO explains seven to thirteen percent of intraseasonal atmospheric variability in 300-mb geopotential, depending on season and QBO phase. These results highlight the importance of considering the phase of the QBO in analyses related to either global or local impacts of the MJO, along with the importance of cross-scale relationships, such as those between the MJO and QBO, in governing the coupling between the MJO and teleconnections across the globe. This thesis considers the relationship between the MJO and processes that operate on both longer and shorter timescales than itself, including tropical convection and the Quasi-Biennial Oscillation. In doing so, this work highlights the importance of considering relationships between the MJO and atmospheric phenomena on different spatial and temporal scales and with origins distinct from the MJO itself. While theories exist describing the MJO as its own distinct entity, this research corroborates the idea that it is at its core fundamentally linked to the rest of the climate system, both modulating and being modulated by a broad range of atmospheric processes

Indicator patterns of forced change learned by an artificial neural network

Many problems in climate science require the identification of signals obscured by both the "noise" of internal climate variability and differences across models. Following previous work, we train an artificial neural network (ANN) to identify the year of input maps of temperature and precipitation from forced climate model simulations. This prediction task requires the ANN to learn forced patterns of change amidst a background of climate noise and model differences. We then apply a neural network visualization technique (layerwise relevance propagation) to visualize the spatial patterns that lead the ANN to successfully predict the year. These spatial patterns thus serve as "reliable indicators" of the forced change. The architecture of the ANN is chosen such that these indicators vary in time, thus capturing the evolving nature of regional signals of change. Results are compared to those of more standard approaches like signal-to-noise ratios and multi-linear regression in order to gain intuition about the reliable indicators identified by the ANN. We then apply an additional visualization tool (backward optimization) to highlight where disagreements in simulated and observed patterns of change are most important for the prediction of the year. This work demonstrates that ANNs and their visualization tools make a powerful pair for extracting climate patterns of forced change.Comment: The first version of this manuscript has been submitted to the Journal of Advances in Modeling Earth Systems (JAMES), 202

Assessing factors associated with changes in the numbers of birds visiting gardens in winter : are predators partly to blame?

BTS was part‐funded by EPSRC/NERC grant EP/10009171/1.The factors governing the recent declines observed in many songbirds have received much research interest, in particular whether increases of avian predators have had a negative effect on any of their prey species. In addition, further discussion has centered on whether or not the choice of model formulation has an effect on model inference. The study goal was to evaluate changes in the number of 10 songbird species in relation to a suite of environmental covariates, testing for any evidence in support of a predator effect using multiple model formulations to check for consistency in the results. We compare two different approaches to the analysis of long‐term garden bird monitoring data. The first approach models change in the prey species between 1970 and 2005 as a function of environmental covariates, including the abundance of an avian predator, while the second uses a change–change approach. Significant negative relationships were found between Eurasian Sparrowhawk Accipiter nisus and three of the 10 species analyzed, namely house Sparrow Passer domesticus, starling Sturnus vulgaris, and blue tit Cyanistes caeruleus. The results were consistent under both modeling approaches. It is not clear if this is a direct negative impact on the overall populations of these species or a behavioral response of the prey species to avoid feeding stations frequented by Sparrowhawks (which may in turn have population consequences, by reducing available resources). The species showing evidence of negative effects of Sparrowhawks were three of the four species most at risk to Sparrowhawk predation according to their prevalence in the predator's diet. The associations could be causal in nature, although in practical terms the reduction in the rate of change in numbers visiting gardens accredited to Sparrowhawks is relatively small, and so unlikely to be the main driver of observed population declines.Publisher PDFPeer reviewe

Rapid laminated clastic alluviation associated with increased Little Ice Age flooding co-driven by climate variability and historic land-use in the middle Severn catchment, UK

The analysis of exceptionally well-preserved visible clastic laminations in deep alluvial sediments at Kempsey, Worcestershire (UK), allows a new high-resolution analysis of late-Holocene flood-history in the largest UK catchment, as well as local human response. At the sample site over 4.5 m of sandy-silt overbank-alluvium accumulated on the floodplain and optically stimulated luminescence (OSL) dating of the upper 2.25 m demonstrates accretion from the late 14th century CE onwards. Sub-centimetre to centimetre resolution multi-proxy sediment analysis (loss on ignition, magnetic susceptibility, particle size, ITRAX and portable XRF) demonstrate clear variations in depositional history over the last millennium due to channel stability. Between c. 1380 and 1550 CE overbank sedimentation was driven by lower energy flood events, with negligible effect from climatic conditions during the Spörer Minimum (1460–1550 CE). After c. 1550 CE the magnitude of flooding events increased and by c. 1610 CE, the start of the visible sub-centimetre laminations, the accumulation rate regularly exceeded 3 mm year−1, which increased to 4.5 mm year−1 between c. 1690 and 1710 CE, and 3 and 3.5 mm year−1 between c. 1790 and 1840 CE before alluviation was altered by an embankment. The greatest extent of coarse overbank deposition and increased accumulation rate occur concurrently with periods of climatic instability associated with the Maunder (1645–1715 CE) and Dalton (1790–1820 CE) Minima, the periods of largest historical floods and during the intensification of arable cultivation across the middle Severn catchment. This data correlates well with other sites in the catchment suggesting that these are basin-wide forcing-responses. We also present evidence that this catchment-wide hydro-geomorphological history had local effects in shifting the geographical focus of an important settlement away from its historic floodplain edge location – which can be viewed as an adaptation to the flood risk

Uncertainty about rater variance and small dimension effects impact reliability in supervisor ratings

We modeled the effects commonly described as defining the measurement structure of supervisor performance ratings. In doing so, we contribute to different theoretical perspectives, including components of the multifactor and mediated models of performance ratings. Across two reanalyzed samples (Sample 1, N ratees = 392, N raters = 244; Sample 2, N ratees = 342, N raters = 397), we found a structure primarily reflective of general (>27% of variance explained) and rater-related (>49%) effects, with relatively small performance dimension effects (between 1% and 11%). We drew on findings from the assessment center literature to approximate the proportion of rater variance that might theoretically contribute to reliability in performance ratings. We found that even moderate contributions of rater-related variance to reliability resulted in a sizable impact on reliability estimates, drawing them closer to accepted criteria

Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV

The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT≥20 GeV and pseudorapidities {pipe}η{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≤pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≤{pipe}η{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. © 2013 CERN for the benefit of the ATLAS collaboration

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final version published in European Physical Journal

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

Observation of associated near-side and away-side long-range correlations in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector

Two-particle correlations in relative azimuthal angle (Δϕ) and pseudorapidity (Δη) are measured in √sNN=5.02  TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1  μb-1 of data as a function of transverse momentum (pT) and the transverse energy (ΣETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Δη|<5) “near-side” (Δϕ∼0) correlation that grows rapidly with increasing ΣETPb. A long-range “away-side” (Δϕ∼π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣETPb, is found to match the near-side correlation in magnitude, shape (in Δη and Δϕ) and ΣETPb dependence. The resultant Δϕ correlation is approximately symmetric about π/2, and is consistent with a dominant cos⁡2Δϕ modulation for all ΣETPb ranges and particle pT