18 research outputs found
A novel quasi-Lagrangian perspective on the potential vorticity dynamics of blocked weather regime life cycles in the North Atlantic-European region
No full textIn den mittleren Breiten kommt es gelegentlich zu einer Strömungskonfiguration, bei welcher eine quasistationäre antizyklonale Zirkulationsanomalie (oftmals als „Block" bezeichnet) eine Umkehrung der großräumigen westlichen Strömung hervorruft. Diese Situation wird im Englischen als „Blocking" bezeichnet und kann in angrenzenden Regionen zu Extremwetter führen. Die korrekte Darstellung von Blocking stellt eine große Herausforderung in aktuellen numerischen Wettervorhersagemodellen dar. Ein Grund dafür liegt im mangelnden dynamischen Verständnis von Blocking. In der Vergangenheit wurden zahlreiche Theorien zur Dynamik von Blocking entwickelt, von denen jede einen bestimmten Aspekt der Dynamik betrachtet. Bis heute konnten die verschiedenen feuchtdynamischen und trockendynamischen Theorien noch nicht miteinander verbunden werden und lieferten sogar widersprüchliche Ergebnisse. Noch immer fehlt eine konsistente Sicht auf die relative Rolle trockener und feuchter Dynamik in den
Lebenszyklen von Blocking.
Diese Arbeit zielt darauf ab, die Dynamik von Blocking zu erfassen und insbesondere die relativen Beiträge trockener und feuchter Prozesse zu entflechten. Dazu wird eine neuartige quasi-Lagrangsche Methode auf Basis der potenziellen Vortizität (PV) entwickelt. Da Vorhersagefehler in Verbindung mit Blocking vor allem in Europa vorkommen, liegt der Fokus auf Blocking über dem Nordatlantik und über Europa. Anhand der hochmodernen ERA5-Reanalyse für den Zeitraum 1979–2021 werden negative PV Anomalien in der oberen Troposphäre (PVAs−) verfolgt, die mit Blocking in Verbindung stehen. Mithilfe stückweiser PV-Tendenzen werden die relativen Beiträge trockener und feuchter Dynamik zur Amplitudenentwicklung von PVAs− quantifiziert. Blocking wird in dieser Arbeit aus Sicht von Wetterregimen betrachtet, die großräumige, anhaltende und wiederkehrende Zustände der außertropischen Zirkulation darstellen. Eine einzigartige Definition von Wetterregimen ermöglicht die Untersuchung der Lebenszyklen von vier verschiedenen „blockierten“ Regimen: Blocking über Europa (EuBL), über Skandinavien
(ScBL), über dem Atlantik (AR) und über Grönland (GL).
Ein schwerwiegender Vorhersagefehler, der mit dem Lebenszyklus von Blocking im März 2016 über Europa zusammenhängt, war mit einer Unterschätzung feuchter Prozesse über dem östlichen Nordatlantik verbunden. Die neue quasi-Lagrangsche Methode zeigt, dass die mit dem Block verknüpfte PVA− sich nicht lokal über Europa entwickelte, sondern weit entfernt von der Region vor der Ostküste der Vereinigten Staaten zum ersten Mal identifiziert wurde und nach Europa propagierte. Während der Überquerung des Nordatlantiks durchlief die PVA− mehrere Episoden abrupter Verstärkung, hauptsächlich durch feuchte Prozesse im Zusammenhang mit der Aktivität von sogenannten ’Warm Conveyor Belts’ (WCB). Diese Erkenntnis bestätigt eine frühere Hypothese von Grams et al. (2018), dass die WCB-Aktivität stromaufwärts des beginnenden Blocks entscheidend für den Aufbau von Blocking im März 2016 war. Eulersche Diagnosen würden die trocken-dynamische Propagation der PVA− betonen und somit den erheblichen feuchten Beitrag in der Ferne der blockierten Region übersehen. Durch die Fokussierung auf die physikalischen Prozesse, die für den Beginn von Blocking relevant sind, ermöglicht die neuartige quasi-Lagrangsche Methode eine Entflechtung der trockenen und feuchten Beiträge.
Die systematische Auswertung der Dynamik von Blocking zeigt in dieser Arbeit zum ersten Mal, dass sich PVAs− entfernt von der Region entwickeln und in die blockierte Region hineinwandern. Es wurden zwei Pfade identifiziert, über die PVAs− aus dem Westen (stromaufwärtiger Pfad) und aus dem Osten (retrograder Pfad) in die blockierte Region propagieren. Die PVAs− werden in den Tagen vor dem Blocking überwiegend durch Feuchtprozesse verstärkt. Allerdings unterscheidet sich der Zeitpunkt, sodass retrograd-wandernde PVAs− die maximale Verstärkung früher erfahren als stromaufwärts propagierende PVAs−. Infolgedessen erfolgt die westwärts gerichtete Propagation von PVAs− nicht rein barotrop, sondern ist das Resultat des Zusammenspiels mit feuchten Prozessen, welche die PVA− an der westlichen Flanke verstärken und sie somit nach Westen verschieben. Die Pfade der PVAs− und die jeweilige zugrundeliegende Dynamik waren zuvor nicht bekannt und liefern einen neuen Blickwinkel auf Blocking. Rund um die maximale Ausprägung des Regimes enthüllt die quasi-Lagrangsche Methode einen Zusammenhang zwischen dem Lebenszyklus des Regimes und dem Lebenszyklus der PVA−. Feuchtprozesse dominieren die Verstärkung und Aufrechterhaltung der PVA− vor dem Regime-Maximum, während quasi-barotrope Dynamik maßgeblich zum Abbau nach dem Regime-Maximum beiträgt. Der Zerfall des Regime-Lebenszyklus geht mit einer starken Abschwächung der PVA−-Amplitude einher und vor allem mit der Propagation von PVAs− aus der Region heraus. Erneut enthüllt die Methode zwei Pfade von PVAs− nach Westen und Osten, was zeigt, dass einige PVAs− zu nachfolgenden blockierten Regimen beitragen. Generell sind die Unterschiede in der Dynamik zwischen den blockierten Regimen geringer im Vergleich zu den Unterschieden zwischen den PVA− Pfaden. Dabei sticht Blocking über Grönland im Vergleich zu den anderen Regimen beim Aufbau von Blocking heraus. Erstens dominiert der retrograde
Pfad von PVAs− für GL, was nicht der Fall ist für EuBL, ScBL und AR. Und zweitens spielen feuchte Prozesse für PVAs− bei GL unabhängig vom Pfad eine ähnliche Rolle, während sie für stromaufwärts propagierende PVAs− von EuBL, ScBL und AR einen deutlich höheren Beitrag leisten. Diese Variation resultiert aus der Position des Blocks relativ zur typischen Zugbahn von Tiefdruckgebieten und zeigt die Empfindlichkeit der Dynamik von Blocking gegenüber dem genauen Ort von Blocking.
Insgesamt versöhnt diese Arbeit zum ersten Mal unterschiedliche Perspektiven und Theorien zu Blocking in der Region über dem Nordatlantik und Europa und liefert eine neuartige quasi-Lagrangsche PV-Methode mit Potenzial für zukünftige Arbeiten zur Dynamik von Blocking
Insidious Trauma in the Consciousnesses of the Zanzibari Arabs: A Reading of Selected Works of Abdulrazak Gurnah
No full textThis paper examines insidious trauma by closely studying Abdulrazak Gurnah’s novels. It explores the complexity of migration within East Africa and to Britain by the Zanzibari Arabs represented in the novels, and glosses over their reasons for not going back to Oman in Arabia. The study purposively selected two of Gurnah’s novels that provide narratives with insights into insidious trauma. From the study findings, it is concluded that Gurnah’s fiction uses reverse chronology as a strategy that could lend insight into how the author reorganizes the Zanzibari Arabs’ history to confront the insidious trauma manifested in the form of social and political oppression. The study demonstrates how characters strive to define their identity and sense of belonging amidst their struggles with the painful past and highly discriminative present realities. It is demonstrated that, though not always blatant or violent, the effects of insidious trauma threaten the basic well-being of the person who suffers it
Towards a holistic understanding of blocked regime dynamics through a combination of complementary diagnostic perspectives
No full textLife cycle dynamics of Greenland blocking from a potential vorticity perspective
No full textBlocking over Greenland stands out in comparison to blocking in other regions, as it favors accelerated Green-
land Ice Sheet melting and has substantial impacts on surface weather in adjacent regions, particularly in Europe and
North America. Climate models notoriously underestimate the frequency of blocking over Greenland in historical pe-
riods, but the reasons for this are not entirely clear, as we are still lacking a full dynamical understanding of Greenland
blocking from formation through maintenance to decay. This study investigates the dynamics of blocking life cycles over
Greenland based on ERA5 reanalysis data from 1979–2021. A year-round weather regime definition allows us to identify
Greenland blocking as consistent life cycles with an objective onset, maximum, and decay stage. By applying a new quasi-
Lagrangian potential vorticity (PV) perspective, following the negative, upper-tropospheric PV anomalies (PVAs−) as-
sociated with the block, we examine and quantify the contribution from different physical processes, including dry and
moist dynamics, to the evolution of the PVA− amplitude. We find that PVAs− linked to blocking do not form lo-
cally over Greenland but propagate into the region along two distinct pathways (termed “upstream” and “retrogres-
sion”) during the days before the onset. The development of PVAs− differs more between the pathways than between
seasons. Moist processes play a key role in the amplification of PVAs− before the onset and are linked to midlati-
tude warm conveyor belts. Interestingly, we find moist processes supporting the westward propagation of retrograding
PVAs− from Europe, too, previously thought to be a process dominated by dry-barotropic Rossby wave propagation. Af-
ter onset, moist processes remain the main contribution to PVA− amplification and maintenance. However, moist pro-
cesses weaken markedly after the maximum stage, and dry processes, i.e., barotropic, nonlinear wave dynamics, domi-
nate the decay of the PVAs− accompanied by a general decrease in blocking area. Our results corroborate the impor-
tance of moist processes in the formation and maintenance of Greenland blocking and suggest that a correct represen-
tation of moist processes might help reduce forecast errors linked to blocking in numerical weather prediction models
and blocking biases in climate models
A weather system perspective on winter–spring rainfall variability in southeastern Australia during El Niño
No full textThe El Niño phase of the El Niño Southern Oscillation (ENSO) is typically associated with below-average cool-season rainfall in southeastern Australia (SEA). However, there is also large case-to-case variability on monthly time-scales. Despite recent progress in understanding the links between remote climate drivers and this variability, the underlying dynamical processes are not fully understood. This reanalysis-based study aims to advance the dynamical understanding by quantifying the contribution of midlatitude weather systems to monthly precipitation anomalies over SEA during the austral winter–spring season. A k-means clustering reveals four rainfall anomaly patterns with above-average rainfall (Cluster 1), below-average rainfall (Cluster 2), above-average rainfall along the East Coast (Cluster 3) and along the South Coast (Cluster 4). Cluster 2 occurs most frequently during El Niño, which highlights the general suppression of SEA rainfall during these events. However, the remaining three clusters with local above-average rainfall are found in ∼52% of all El Niño months. Changes of weather system frequency determine the respective rainfall anomaly pattern. Results indicate significantly more cut-off lows and warm conveyor belts (WCBs) over SEA in El Niño Cluster 1 and significantly fewer in El Niño Cluster 2. In El Niño Cluster 3, enhanced blocking south of Australia favours cut-off lows leading to increased rainfall along the East Coast. Positive rainfall anomalies along the South Coast in El Niño Cluster 4 are associated with frontal rainfall due to an equatorward shift of the midlatitude storm track. Most of the rainfall is produced by WCBs and cut-off lows but the contributions strongly vary between the clusters. In all clusters, rainfall anomalies result from changes in rainfall frequency more than in rainfall intensity. Backward trajectories of WCB and cut-off low rainfall highlight the importance of moist air masses from the Coral Sea and the northwest coast of Australia during wet months
The Linkage of Serial Cyclone Clustering in Western Europe and Weather Regimes in the North Atlantic‐European Region in Boreal Winter
No full textAbstract Extra‐tropical cyclones are an important source of weather variability in the mid‐latitudes. Multiple occurrences in a short period of time at a particular location are denominated serial cyclone clustering (SCC), and potentially lead to large societal impacts. We investigate the relationship between SCC affecting Western Europe and large‐scale weather regimes (WRs) in the North Atlantic‐European region in boreal winter. We find that SCC in low latitudes (45°N) is predominantly associated with the anticyclonic Greenland Blocking WR. In contrast, SCC in mid and high latitudes (55°N, 65°N) is mostly linked to different cyclonic WRs. Thereby, SCC occurs typically within a well‐established WR that builds up prior to SCC and decays after SCC. Thus, SCC events are closely associated with recurrent, quasi‐stationary and persistent large‐scale flow patterns (WRs). This mutual relationship reveals the potential of WRs in forecasting storm series and associated impacts on sub‐seasonal to seasonal time scales
Similarity and variability of blocked weather-regime dynamics in the Atlantic–European region
No full textWeather regimes govern an important part of the sub-seasonal variability of the mid-latitude circulation. Due to their role in weather extremes and atmospheric predictability, regimes that feature a blocking anticyclone are of particular interest. This study investigates the dynamics of these “blocked” regimes in the North Atlantic–European region from a year-round perspective. For a comprehensive diagnostic, wave activity concepts and a piecewise potential vorticity (PV) tendency framework are combined. The latter essentially quantifies the well-established PV perspective of mid-latitude dynamics. The four blocked regimes (namely Atlantic ridge, European blocking, Scandinavian blocking, and Greenland blocking) during the 1979–2021 period of ERA5 reanalysis are considered.
Wave activity characteristics exhibit distinct differences between blocked regimes. After regime onset, Greenland blocking is associated with a suppression of wave activity flux, whereas Atlantic ridge and European blocking are associated with a northward deflection of the flux without a clear net change. During onset, the envelope of Rossby wave activity retracts upstream for Greenland blocking, whereas the envelope extends downstream for Atlantic ridge and European blocking. Scandinavian blocking exhibits intermediate wave activity characteristics. From the perspective of piecewise PV tendencies projected onto the respective regime pattern, the dynamics that govern regime onset exhibit a large degree of similarity:
linear Rossby wave dynamics and nonlinear eddy PV fluxes dominate and are of approximately equal relative importance, whereas baroclinic coupling and divergent amplification make minor contributions. Most strikingly, all blocked regimes exhibit very similar (intra-regime) variability: a retrograde and an upstream pathway to regime onset. The retrograde pathway is dominated by nonlinear PV eddy fluxes, whereas the upstream pathway is dominated by linear Rossby wave dynamics. Importantly, there is a large degree of cancellation between the two pathways for some of the mechanisms before regime onset. The physical meaning of a regime-mean perspective before onset can thus be severely limited.
Implications of our results for understanding predictability of blocked regimes are discussed. Further discussed are the limitations of projected tendencies in capturing the importance of moist-baroclinic growth, which tends to occur in regions where the amplitude of the regime pattern, and thus the projection onto it, is small. Finally, it is stressed that this study investigates the variability of the governing dynamics without prior empirical stratification of data by season or by type of regime transition.
It is demonstrated, however, that our dynamics-centered approach does not merely reflect variability that is associated with these factors. The main modes of dynamical variability revealed herein and the large similarity of the blocked regimes in exhibiting this variability are thus significant results.</p
Expression of the Fusogenic Protein Syncytin in Macrophages
No full textabstract: Cell fusion is a process that occurs in normal cells as well as in pathological cells. This process does not occur spontaneously, fusogens are required to mediate the process. Syncytin is one of the proteins that was determined to have fusogenic properties. Syncytin is a newly discovered transmembrane protein that is generally expressed in mammalian placenta and it is known for its role in cell fusion during placentation. The recent studies in Ugarova’s laboratory suggest syncytin is expressed in macrophages, thus it may be involved in macrophage cells fusion. This paper provides a literature review of syncytin protein; it also contains an experimental study conducted to determine syncytin expression on both RNA and protein level. The study was conducted on RNA and protein isolated from macrophages isolated from mouse peritoneum. Agarose gel electrophoresis and Western blot analysis were used to determine syncytin expression on RNA and protein level respectively. Using these methods, syncytin expression was determined at different time points during macrophage fusion. The results show that syncytin is not expressed in freshly isolated macrophages, but its expression is initiated during macrophage adhesion in the presence of IL-4
Genetically Encoded Copper(I) Reporters with Improved Response for Use in Imaging
No full textCopper represents one of the most important biological metal ions due to its role as a catalytic cofactor in a multitude of proteins. However, an excess of copper is highly toxic. Thus, copper is heavily regulated, and copper homeostasis is controlled by many metalloregulatory proteins in various organisms. Here we report a genetically encoded copper(I) probe capable of monitoring copper fluctuations inside living cells. We insert the copper regulatory protein Ace1 into a yellow fluorescent protein, which selectively binds copper(I) and generates improved copper(I) probes.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000315618900047&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Chemistry, MultidisciplinarySCI(E)EIPubMed16ARTICLE83144-314913
Perceptions of college and career readiness among rural high school seniors
No full textRural students are the least likely to enroll in college immediately following high school graduation (National Student Clearinghouse Research Center, 2016; Smith, Beaulieu, & Seraphine, 1995). From 2000 to 2015, the gap in bachelor’s degree attainment between rural and urban populations grew to 14 percentage points (U. S. Department of Agriculture, 2017). Rural students that do access higher education enroll in public institutions at higher rates than their urban and suburban counterparts with many of them relying on community colleges as a pathway to the baccalaureate (Byun, Meece, & Agger, 2017; Hu, 2003). College readiness has been identified as a leading cause of inequality in college access (Arnold, Lu, & Armstrong, 2012).
This dissertation study explored the influence of a rural community context on perceptions of college and career readiness among graduating high school seniors. A phenomenological approach that incorporated a case study design was conducted and bound to one rural, public PK-12 Midwestern school district. This study identified the district’s community college as an asset toward the development of college and career readiness for students with varying aspirations. Furthermore, this study revealed the ways in which the community college established familiarity with students and was perceived as consistent with rural students’ values and interests. These findings suggest that community colleges can be critical assets toward filling gaps in opportunity that exist in rural contexts for the development of college and career readiness. Implications for theory and research include disrupting deficit frameworks of rural students and community colleges. Within the realm of policy and practice, equitable funding and the establishment of purposeful partnerships are identified as critical to supporting economic and educational opportunities for rural students.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-05-01The student, Marci Rockey, accepted the attached license on 2019-04-09 at 10:58.The student, Marci Rockey, submitted this Dissertation for approval on 2019-04-09 at 11:09.This Dissertation was approved for publication on 2019-04-10 at 10:26.DSpace SAF Submission Ingestion Package generated from Vireo submission #13533 on 2019-08-22 at 15:05:38Made available in DSpace on 2019-08-23T20:35:47Z (GMT). No. of bitstreams: 3
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