M. Brittnacher

Earthward flow bursts, auroral streamers, and small expansions

Earthward flow bursts associated with small auroral expansions, including pseudobreakups, and auroral streamers are studied by using Geotail plasma and magnetic field data and Polar ultraviolet imager data. These flow bursts are accompanied by dipolarization and decrease in the plasma pressure, which are consistent with the characteristics of so-called bubbles, and have a timescale of 2.5 min on average. Based on a statistical study of the flow bursts, it is shown that the location of the flows are centered about 0.4 hour magnetic local time east of the center of auroral expansion and are localized with a width of 3 – 5 RE. This relationship supports the idea that a dawn-to-dusk polarization electric field is created in the bubble to enhance the flows. The flow bursts associated with the small expansions, which are mainly observed in the region earthward of 15 RE, show more distinct signatures of compression at the front side of the flow, which possibly leads to the stopping of these flows. Flow bursts related to auroral streamers, which are observed mainly tailward of 15 RE, take place during relatively thick plasma sheet configurations, and are accompanied by stronger flow shear.

PGAT: a multistrain analysis resource for microbial genomes

Motivation: The Prokaryotic-genome Analysis Tool (PGAT) is a web-based database application for comparing gene content and sequence across multiple microbial genomes facilitating the discovery of genetic differences that may explain observed phenotypes. PGAT supports database queries to identify genes that are present or absent in user-selected genomes, comparison of sequence polymorphisms in sets of orthologous genes, multigenome display of regions surrounding a query gene, comparison of the distribution of genes in metabolic pathways and manual community annotation. Availability and Implementation:The PGAT website may be accessed at http://nwrce.org/pgat. Contact: mbrittna@uw.edu

Polar Spacecraft Based Comparisons of Intense Electric Fields and Poynting Flux Near and Within the Plasma Sheet-Tail Lobe Boundary to UVI Images: An Energy Source for the Aurora

In this paper, we present measurements from two passes of the Polar spacecraft of intense electric and magnetic field structures associated with Alfven waves at and within the outer boundary of the plasma sheet at geocentric distances of 4-6 R(sub E), near local midnight. The electric field variations have maximum values exceeding 100 mV/m and are typically polarized approximately normal to the plasma sheet boundary. The electric field structures investigated vary over timescales (in the spacecraft frame.) ranging front 1 to 30 s. They are associated with strong magnetic field fluctuations with amplitudes of 10-40 nT which lie predominantly ill the plane of the plasma sheet and are perpendicular to the local magnetic field. The Poynting flux associated with the perturbation fields measured at these altitudes is about 1-2 ergs per square centimeters per second and is directed along the average magnetic field direction toward the ionosphere. If the measured Poynting flux is mapped to ionospheric altitudes along converging magnetic field lines. the resulting energy flux ranges up to 100 ergs per centimeter squared per second. These strongly enhanced Poynting fluxes appear to occur in layers which are observed when the spacecraft is magnetically conjugate (to within a 1 degree mapping accuracy) to intense auroral structures as detected by the Polar UV Imager (UVI). The electron energy flux (averaged over a spatial resolution of 0.5 degrees) deposited in the ionosphere due to auroral electron beams as estimated from the intensity in the UVI Lyman-Birge-Hopfield-long filters is 15-30 ergs per centimeter squared per second. Thus there is evidence that these electric field structures provide sufficient Poynting flux to power the acceleration of auroral electrons (as well as the energization of upflowing ions and Joule heating of the ionosphere). During some events the phasing and ratio of the transverse electric and magnetic field variations are consistent with earthward propagation of Alfven surface waves with phase velocities of 4000-10000 kilometers per second. During other events the phase shifts between electric and magnetic fields suggest interference between upward and downward propagating Alfven waves. The E/B ratios are about an order of magnitude larger than typical values of C/SIGMA(sub p), where SIGMA(sub p), is the height integrated Pedersen conductivity. The contribution to the total energy flux at these altitudes from Poynting flux associated with Alfven waves is comparable to or larger than the contribution from the particle energy flux and 1-2 orders of magnitude larger than that estimated from the large-scale steady state convection electric field and field-aligned current system.

Growth phenotypes of Pseudomonas aeruginosa lasR mutants adapted to the airways of cystic fibrosis patients

The opportunistic pathogen Pseudomonas aeruginosa undergoes genetic change during chronic airway infection of cystic fibrosis (CF) patients. One common change is a mutation inactivating lasR, which encodes a transcriptional regulator that responds to a homoserine lactone signal to activate expression of acute virulence factors. Colonies of lasR mutants visibly accumulated the iridescent intercellular signal 4‐hydroxy‐2‐heptylquinoline. Using this colony phenotype, we identified P. aeruginosa lasR mutants that emerged in the airway of a CF patient early during chronic infection, and during growth in the laboratory on a rich medium. The lasR loss‐of‐function mutations in these strains conferred a growth advantage with particular carbon and nitrogen sources, including amino acids, in part due to increased expression of the catabolic pathway regulator CbrB. This growth phenotype could contribute to selection of lasR mutants both on rich medium and within the CF airway, supporting a key role for bacterial metabolic adaptation during chronic infection. Inactivation of lasR also resulted in increased β‐lactamase activity that increased tolerance to ceftazidime, a widely used β‐lactam antibiotic. Loss of LasR function may represent a marker of an early stage in chronic infection of the CF airway with clinical implications for antibiotic resistance and disease progression.

A comprehensive transposon mutant library of Francisella novicida, a bioweapon surrogate

Francisella tularensis, the causative agent of tularemia, is one of the most infectious bacterial pathogens known and is a category A select agent. We created a sequence-defined, near-saturation transposon mutant library of F. tularensis novicida, a subspecies that causes a tularemia-like disease in rodents. The library consists of 16,508 unique insertions, an average of >9 insertions per gene, which is a coverage nearly twice that of the greatest previously achieved for any bacterial species. Insertions were recovered in 84% (1,490) of the predicted genes. To achieve high coverage, it was necessary to construct transposons carrying an endogenous Francisella promoter to drive expression of antibiotic resistance. An analysis of genes lacking (or with few) insertions identified nearly 400 candidate essential genes, most of which are likely to be required for growth on rich medium and which represent potential therapeutic targets. To facilitate genome-scale screening using the mutant collection, we assembled a sublibrary made up of two purified mutants per gene. The library provides a resource for virtually complete identification of genes involved in virulence and other nonessential processes.

Magnetotail flow bursts: Association to global magnetospheric circulation, relationship to ionospheric activity and direct evidence for localization

A series of bursty bulk flow events (BBFs) were observed by GEOTAIL and WIND in the geomagnetotail. IMP8 at the solar wind showed significant energy coupling into the magnetosphere, while the UVI instrument on POLAR evidenced significant energy transfer to the ionosphere during two substorms. There was good correlation between BBFs and ionospheric activity observed by UVI even when ground magnetic signatures were absent, suggesting that low ionospheric conductivity at the active sector may be responsible for this observation. During the second substorm no significant flux transport was evidenced past WIND in stark contrast to GEOTAIL and despite the small intersatellite separation ((3.54, 2.88, −0.06) RE). Throughout the intervals studied there were significant differences in the individual flow bursts at the two satellites, even during longitudinally extended ionospheric activations. We conclude that the half-scale-size of transport-bearing flow bursts is less than 3 RE.

Comparison of Francisella tularensis genomes reveals evolutionary events associated with the emergence of human pathogenic strains

BackgroundFrancisella tularensis subspecies tularensis and holarctica are pathogenic to humans, whereas the two other subspecies, novicida and mediasiatica, rarely cause disease. To uncover the factors that allow subspecies tularensis and holarctica to be pathogenic to humans, we compared their genome sequences with the genome sequence of Francisella tularensis subspecies novicida U112, which is nonpathogenic to humans.ResultsComparison of the genomes of human pathogenic Francisella strains with the genome of U112 identifies genes specific to the human pathogenic strains and reveals pseudogenes that previously were unidentified. In addition, this analysis provides a coarse chronology of the evolutionary events that took place during the emergence of the human pathogenic strains. Genomic rearrangements at the level of insertion sequences (IS elements), point mutations, and small indels took place in the human pathogenic strains during and after differentiation from the nonpathogenic strain, resulting in gene inactivation.ConclusionThe chronology of events suggests a substantial role for genetic drift in the formation of pseudogenes in Francisella genomes. Mutations that occurred early in the evolution, however, might have been fixed in the population either because of evolutionary bottlenecks or because they were pathoadaptive (beneficial in the context of infection). Because the structure of Francisella genomes is similar to that of the genomes of other emerging or highly pathogenic bacteria, this evolutionary scenario may be shared by pathogens from other species.

Global energy deposition during the January 1997 magnetic cloud event

The passage of an interplanetary magnetic cloud at Earth on January 10–11, 1997, induced significant geomagnetic disturbances, with a maximum AE in excess of 2000 nT and a minimum Dst of about −85 nT. We use a comprehensive set of data collected from space-borne instruments and from ground-based facilities to estimate the energy deposition associated with the three major magnetospheric sinks during the event. It is found that averaged over the 2-day period, the total magnetospheric energy deposition rate is about 400 GW, with 190 GW going into Joule heating rate, 120 GW into ring current injection, and 90 GW into auroral precipitation. By comparison, the average solar wind electromagnetic energy transfer rate as represented by the e parameter is estimated to be 460 GW, and the average available solar wind kinetic power USW is about 11,000 GW. A good linear correlation is found between the AE index and various ionospheric parameters such as the cross-polar-cap potential drop, hemisphere-integrated Joule heating rate, and hemisphere-integrated auroral precipitation. In the northern hemisphere where the data coverage is extensive, the proportionality factor is 0.06 kV/nT between the potential drop and AE, 0.25 GW/nT between Joule heating rate and AE, and 0.13 GW/nT between auroral precipitation and AE. However, different studies have resulted in different proportionality factors. One should therefore be cautious when using empirical formulas to estimate the ionospheric energy deposition. There is an evident saturation of the cross-polar-cap potential drop for large AE (>1000 nT), but further studies are needed to confirm this.

Multiple-spacecraft observation of a narrow transient plasma jet in the Earth's plasma sheet

We use observations from five magnetospheric spacecraft in a fortuitous constellation to show that narrow transient plasma flow jets of considerable length formed in the tail can intrude into the inner magnetosphere and provide considerable contribution to the total plasma transport. A specific auroral structure, the auroral streamer, accompanied the development of this narrow plasma jet. These observations support the ‘boiling’ plasma sheet model consisting of localized underpopulated plasma tubes (bubbles) moving Earthward at high speeds as a realistic way to resolve the ‘convection crisis’ and to close the global magnetospheric circulation pattern.

Convection and auroral response to a southward turning of the IMF: Polar UVI, CUTLASS, and IMAGE signatures of transient magnetic flux transfer at the magnetopause

We present the first spacecraft-borne imager observations of the auroral manifestation of transient magnetic flux transfer at the magnetopause. During an interval of interplanetary magnetic field Bz ≈ −10 nT, By ≈ 10 nT, and solar wind dynamic pressure and velocity Psw ≈ 5 nPa and vsw ≈ 650 km s−1, Polar Ultraviolet Imager (UVI) images show a sequence of events, each of which begins as a bifurcation of the main auroral oval in the 14 to 16 magnetic local time (MLT) sector which subsequently progresses antisunward (eastward) at 2 km s−1 toward the 19 MLT sector. The poleward portion of the bifurcation is interpreted as a poleward-moving auroral form (PMAF) as has previously been observed by ground-based optical instrumentation and identified as the auroral signature of flux transfer events. Ground-based measurements of the associated plasma drift, made with the Cooperative U.K. Twin Located Auroral Sounding System (CUTLASS) Finland HF radar, show poleward (1 km s−1) and westward (1 km s−1) convection flow, consistent with the By tension force, as well as poleward-moving regions of backscatter. International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers within the radar field of view observe poleward-progressing, 10 min period, X component magnetic deflections, which are consistent with the effect of Hall currents associated with the plasma flow. The combined radar and optical observations suggest that the PMAFs can be 3500 km or 7 hours of MLT in length. The antisunward motion of the bifurcation of the auroral oval is interpreted as an expansion of the reconnection X line along the flank of the magnetopause.