Evolution of the Magnetic Field Distribution of Solar Active Regions

Magnetic flux emergence through the solar photosphere in the form of an active region (AR) and the subsequent evolution of this flux are crucial processes in the solar cycle for their role in converting toroidal magnetic field to poloidal magnetic field. Although the temporal evolution of ARs is relatively well understood, the processes involved continue to be the subject of investigation. To better characterise how ARs emerge and disperse, the distribution of the vertical component of the photospheric magnetic field (flux density) of a series of ARs has been studied. A kernel density estimation plot of the magnetic field distribution was created on a log-log scale for each AR at each time step. The central portion of the distribution was found to be approximately linear and its slope was used to characterise the evolution of the magnetic field. The slopes were seen to evolve with time, becoming less steep as the fragmented emerging flux coalesces. The slopes reached a maximum value of -1.5 just before the time of maximum flux before becoming steeper during the decay phase towards the quiet Sun value of -3. This behaviour differs significantly from a classical diffusion model, which produces a slope of -1, suggesting that simple classical diffusion is not responsible for the observed changes in field distribution. Other processes must play a significant role in flux dispersion, one of which may be magnetic flux reprocessing by (super)granular convective cells. Moreover, comparisons of the observed distributions to those produced by data from simulations of AR emergence with and without convection suggest that convective processes also play an important role in magnetic flux emergence

Insight into the Cellular Alterations Required for Establishing Opportunistic Pseudomonas aeruginosa Infections

The Gram-negative, opportunistic pathogen Pseudomonas aeruginosa (Pa) is responsible for causing disease of high morbidity and mortality in individuals who are immunocompromised, suffer from damaged epithelial barriers, and who have cystic fibrosis. However, the underlying host cell compromise that allows the establishment of Pa infections remains unknown and is of importance to the development of novel strategies that interrupt Pa infections. The type III secretion system (T3S) allows the direct translocation of bacterial effectors into the host cell cytosol, and in this study was used first, to identify host cell properties involved in the initiation of Pa infections, and then second, to dissect the Pa infectious process. Using the T3S effector ExoS to monitor T3S translocation and the initiation of Pa infections in HT-29 epithelial cells, we identified a relationship between leading edge focal complex adhesion properties involved in cell migration and sensitivity to Pa-T3S. Highly migratory T24 epithelial cells were used to further explore the role of host cell migration in Pa infections, using manipulations of ExoS GTPase activating (GAP) and ADP-ribosyltransferase (ADPRT) activities to manipulate T3S. These studies allowed dissection of the Pa infectious process, and found that Pa expressing wild type ExoS preferentially bound to the leading edge of T24 cells, where ExoS GAP activity interfered with Pa internalization, and ExoS ADPRT activity interrupted actin-plasma membrane associations required for T3S translocation. Interestingly, both toxic events limited the Pa infectious process. Further studies of MTC, MTLn3, and MDCK epithelial cells identified a reciprocal relationship between Rac1 and Rho activation at the leading edge and Pa internalization and T3S translocation efficiency. Together, the studies in this dissertation highlight the role of actin-plasma membrane associations and Rho-GTPases in directing T3S translocation and the Pa infectious process, and the ability of Pa to hijack these factors during cell migration. Our studies in turn are consistent with cell migration properties induced in response to tissue damage being the cellular compromise that leads to the initiation of Pa infections, and that effectors such as ExoS are able to interrupt these same properties to limit the infectious process and maintain the opportunistic nature of Pa infections

Flux cancellation and the evolution of the eruptive filament of 2011 June 7

We investigate whether flux cancellation is responsible for the formation of a very massive filament resulting in the spectacular 2011 June 7 eruption. We analyse and quantify the amount of flux cancellation that occurs in NOAA AR 11226 and its two neighbouring ARs (11227 & 11233) using line-of-sight magnetograms from the Heliospheric Magnetic Imager. During a 3.6-day period building up to the filament eruption, 1.7 x 10^21 Mx, 21% of AR 11226's maximum magnetic flux, was cancelled along the polarity inversion line (PIL) where the filament formed. If the flux cancellation continued at the same rate up until the eruption then up to 2.8 x 10^21 Mx (34% of the AR flux) may have been built into the magnetic configuration that contains the filament plasma. The large flux cancellation rate is due to an unusual motion of the positive polarity sunspot, which splits, with the largest section moving rapidly towards the PIL. This motion compresses the negative polarity and leads to the formation of an orphan penumbra where one end of the filament is rooted. Dense plasma threads above the orphan penumbra build into the filament, extending its length, and presumably injecting material into it. We conclude that the exceptionally strong flux cancellation in AR 11226 played a significant role in the formation of its unusually massive filament. In addition, the presence and coherent evolution of bald patches in the vector magnetic field along the PIL suggests that the magnetic field configuration supporting the filament material is that of a flux rope.Comment: 18 pages, 7 figures. Submitted to ApJ in December 2015, accepted in June 201

The rise and emergence of untwisted toroidal flux ropes on the sun

Magnetic flux ropes (MFRs) rising buoyantly through the Sun's convection zone are thought to be subject to viscous forces preventing them from rising coherently. Numerous studies have suggested that MFRs require a minimum twist in order to remain coherent during their rise. Furthermore, even MFRs that get to the photosphere may be unable to successfully emerge into the corona unless they are at least moderately twisted, since the magnetic pressure gradient needs to overcome the weight of the photospheric plasma. To date, however, no lower limit has been placed on the critical minimum twist required for an MFR to rise coherently through the convection zone or emerge through the photosphere. In this paper, we simulate an untwisted toroidal MFR that is able to rise from the convection zone and emerge through the photosphere as an active region that resembles those observed on the Sun. We show that untwisted MFRs can remain coherent during their rise and then pile up near the photosphere, triggering undular instability, allowing the MFR to emerge through the photosphere. We propose that the toroidal geometry of our MFR is critical for its coherent rise. Upon emergence, a pair of lobes rises into the corona. The two lobes then interact and reconnect, resulting in a localized high speed jet. The resulting photospheric magnetogram displays the characteristic salt-and-pepper structure often seen in observations. Our major result is that MFRs need not be twisted to rise coherently through the convection zone and emerge through the photosphere. © 2021. The American Astronomical Society. All rights reserved

Temperature-dependence of the clear-sky feedback in radiative-convective equilibrium

Abstract We quantify the temperature-dependence of the clear-sky climate sensitivity in a one-dimensional radiative-convective equilibrium model. The atmosphere is adjusted to fixed surface temperatures between 280 and 330 K while preserving other boundary conditions in particular the relative humidity and the CO2 concentration. We show that an out-of-bounds usage of the radiation scheme rapid radiative transfer model for GCMs (RRTMG) can lead to an erroneous decrease of the feedback parameter and an associated ?bump? in climate sensitivity as found in other modeling studies. Using a line-by-line radiative transfer model, we find no evidence for a strengthening of the longwave radiative feedback for surface temperatures between 305 and 320 K. However, the line-by-line simulations also show a slight decrease in climate sensitivity when surface temperatures exceed 310 K. This decrease is caused by water-vapor masking the radiative forcing at the flanks of the CO2 absorption band, which reduces the total radiative forcing by about 18%

Primary chronic cold agglutinin disease: An update on pathogenesis, clinical features and therapy

Chronic cold agglutinin disease (CAD) is a subgroup of autoimmune hemolytic anemia. Primary CAD has traditionally been defined by the absence of any underlying or associated disease. The results of therapy with corticosteroids, alkylating agents and interferon-a have been poor. Cold reactive immunoglobulins against erythrocyte surface antigens are essential to pathogenesis of CAD. These cold agglutinins are monoclonal, usually IgMκ auto antibodies with heavy chain variable regions encoded by the VH4-34 gene segment. By flowcytometric and immunohistochemical assessments, a monoclonal CD20+κ+B-lymphocyte population has been demonstrated in the bone marrow of 90% of the patients, and lymphoplasmacytic lymphoma is a frequent finding. Novel attempts at treatment for primary CAD have mostly been directed against the clonal B-lymphocytes. Phase 2 studies have shown that therapy with the chimeric anti-CD20 antibody rituximab produced partial response rates of more than 50% and occasional complete responses. Median response duration, however, was only 11 months. In this review, we discuss the clinical and pathogenetic features of primary CAD, emphasizing the more recent data on its close association with clonal lymphoproliferative bone marrow disorders and implications for therapy. We also review the management and outline some perspectives on new therapy modalities

Observations and Modelling of the Pre-flare Period of the 29 March 2014 X1 Flare

On 29 March 2014, NOAA Active Region (AR) 12017 produced an X1 flare that was simultaneously observed by an unprecedented number of observatories. We have investigated the pre-flare period of this flare from 14:00 UT until 19:00 UT using joint observations made by the Interface Region Imaging Spectrometer (IRIS) and the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Spectral lines providing coverage of the solar atmosphere from the chromosphere to the corona were analysed to investigate pre-flare activity within the AR. The results of the investigation have revealed evidence of strongly blue-shifted plasma flows, with velocities up to 200kms−1, being observed 40 minutes prior to flaring. These flows are located along the filament present in the active region and are both spatially discrete and transient. In order to constrain the possible explanations for this activity, we undertake non-potential magnetic field modelling of the active region. This modelling indicates the existence of a weakly twisted flux rope along the polarity inversion line in the region where a filament and the strong pre-flare flows are observed. We then discuss how these observations relate to the current models of flare triggering. We conclude that the most likely drivers of the observed activity are internal reconnection in the flux rope, early onset of the flare reconnection, or tether-cutting reconnection along the filament

Observations and modelling of the pre-flare period of the 29 March 2014 X1 flare

MMW and SD acknowledge STFC for support via their PhD Studentships. DML is an Early-Career Fellow, funded by the Leverhulme Trust.On the 29 March 2014 NOAA active region (AR) 12017 produced an X1 flare which was simultaneously observed by an unprecedented number of observatories. We have investigated the pre-flare period of this flare from 14:00 UT until 19:00 UT using joint observations made by the Interface Region Imaging Spectrometer (IRIS) and the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS). Spectral lines providing coverage of the solar atmosphere from chromosphere to the corona were analysed to investigate pre-flare activity within the AR. The results of the investigation have revealed evidence of strongly blue-shifted plasma flows, with velocities up to 200 km-1, being observed 40 minutes prior to flaring. These flows are located along the filament present in the active region and are both spatially discrete and transient. In order to constrain the possible explanations for this activity, we undertake non-potential magnetic field modelling of the active region. This modelling indicates the existence of a weakly twisted flux rope along the polarity inversion line in the region where a filament and the strong pre-flare flows are observed. We then discuss how these observations relate to the current models of flare triggering. We conclude that the most likely drivers of the observed activity are internal reconnection in the flux rope, early onset of the flare reconnection, or tether cutting reconnection along the filament.Publisher PDFPeer reviewe