63 research outputs found
Heliospheric Evolution of Magnetic Clouds
Interplanetary evolution of eleven magnetic clouds (MCs) recorded by at least
two radially aligned spacecraft is studied. The in situ magnetic field
measurements are fitted to a cylindrically symmetric Gold-Hoyle force-free
uniform-twist flux-rope configuration. The analysis reveals that in a
statistical sense the expansion of studied MCs is compatible with self-similar
behavior. However, individual events expose a large scatter of expansion rates,
ranging from very weak to very strong expansion. Individually, only four events
show an expansion rate compatible with the isotropic self-similar expansion.
The results indicate that the expansion has to be much stronger when MCs are
still close to the Sun than in the studied 0.47 - 4.8 AU distance range. The
evolution of the magnetic field strength shows a large deviation from the
behavior expected for the case of an isotropic self-similar expansion. In the
statistical sense, as well as in most of the individual events, the inferred
magnetic field decreases much slower than expected. Only three events show a
behavior compatible with a self-similar expansion. There is also a discrepancy
between the magnetic field decrease and the increase of the MC size, indicating
that magnetic reconnection and geometrical deformations play a significant role
in the MC evolution. About half of the events show a decay of the electric
current as expected for the self-similar expansion. Statistically, the inferred
axial magnetic flux is broadly consistent with it remaining constant. However,
events characterized by large magnetic flux show a clear tendency of decreasing
flux.Comment: 64 pages, 10 figure
A statistical study of long-term evolution of coronal hole properties as observed by SDO
The study of the evolution of coronal holes (CHs) is especially important in
the context of high-speed solar wind streams (HSS) emanating from them. Stream
interaction regions may deliver large amount of energy into the Earths system,
cause geomagnetic storms, and shape interplanetary space. By statistically
analysing 16 long-living CHs observed by the SDO, we focus on coronal,
morphological and underlying photospheric magnetic field characteristics as
well as investigate the evolution of the associated HSSs. We use CATCH to
extract and analyse CHs using observations taken by AIA and HMI. We derive
changes in the CH properties and correlate them to the CH evolution. Further we
analyse the properties of the HSS signatures near 1au from OMNI data by
manually extracting the peak bulk velocity of the solar wind plasma. We find
that the area evolution of CHs mostly shows a rough trend of growing to a
maximum followed by a decay. No correlation of the area evolution to the
evolution of the signed magnetic flux and signed magnetic flux density enclosed
in the projected CH area was found. From this we conclude that the magnetic
flux within the extracted CH boundaries is not the main cause for its area
evolution. We derive CH area change rates (growth and decay) of 14.2 +/- 15.0 *
10^8 km^2/day showing a reasonable anti-correlation (cc =-0.48) to the solar
activity, approximated by the sunspot number. The change rates of the signed
mean magnetic flux density (27.3 +/- 32.2 mG/day) and the signed magnetic flux
(30.3 +/- 31.5 * 10^18 Mx/day) were also found to be dependent on solar
activity (cc =0.50 and cc =0.69 respectively) rather than on the individual CH
evolutions. Further we find that the CH area-to-HSS peak velocity relation is
valid for each CH over its evolution but revealing significant variations in
the slopes of the regression lines.Comment: Accepted at A&
Quantifying errors in 3D CME parameters derived from synthetic data using white-light reconstruction techniques
Current efforts in space weather forecasting of CMEs have been focused on predicting their arrival time and magnetic structure. To make these predictions, methods have been developed to derive the true CME speed, size, position, and mass, among others. Difficulties in determining the input parameters for CME forecasting models arise from the lack of direct measurements of the coronal magnetic fields and uncertainties in estimating the CME 3D geometric and kinematic parameters after eruption. White-light coronagraph images are usually employed by a variety of CME reconstruction techniques that assume more or less complex geometries. This is the first study from our International Space Science Institute (ISSI) team “Understanding Our Capabilities in Observing and Modeling Coronal Mass Ejections”, in which we explore how subjectivity affects the 3D CME parameters that are obtained from the Graduated Cylindrical Shell (GCS) reconstruction technique, which is widely used in CME research. To be able to quantify such uncertainties, the “true” values that are being fitted should be known, which are impossible to derive from observational data. We have designed two different synthetic scenarios where the “true” geometric parameters are known in order to quantify such uncertainties for the first time. We explore this by using two sets of synthetic data: 1) Using the ray-tracing option from the GCS model software itself, and 2) Using 3D magnetohydrodynamic (MHD) simulation data from the Magnetohydrodynamic Algorithm outside a Sphere code. Our experiment includes different viewing configurations using single and multiple viewpoints. CME reconstructions using a single viewpoint had the largest errors and error ranges overall for both synthetic GCS and simulated MHD white-light data. As the number of viewpoints increased from one to two, the errors decreased by approximately 4° in latitude, 22° in longitude, 14° in tilt, and 10° in half-angle. Our results quantitatively show the critical need for at least two viewpoints to be able to reduce the uncertainty in deriving CME parameters. We did not find a significant decrease in errors when going from two to three viewpoints for our specific hypothetical three spacecraft scenario using synthetic GCS white-light data. As we expected, considering all configurations and numbers of viewpoints, the mean absolute errors in the measured CME parameters are generally significantly higher in the case of the simulated MHD white-light data compared to those from the synthetic white-light images generated by the GCS model. We found the following CME parameter error bars as a starting point for quantifying the minimum error in CME parameters from white-light reconstructions: Δθ (latitude)=6°-3°+2°, Δϕ (longitude)=11°-6°+18°, Δγ (tilt)=25°-7°+8°, Δα(half-angle)=10°-6°+12°, Δh (height)=0.6-0.4+1.2 R⊙, and Δκ (ratio)=0.1-0.02+0.03.Fil: Verbeke, Christine. Royal Observatory Of Belgium (rob);Fil: Mays, M. Leila. NASA Goddard Space Flight Center. Heliophysics Science Division; Estados UnidosFil: Kay, Christina. NASA Goddard Space Flight Center. Heliophysics Science Division; Estados Unidos. The Catholic University of America; Estados UnidosFil: Riley, Pete. Predictive Science Inc.; Estados UnidosFil: Palmerio, Erika. Predictive Science Inc.; Estados UnidosFil: Dumbović, Mateja. University of Zagreb; CroaciaFil: Mierla, Marilena. Institute of Geodynamics of the Romanian Academy; Rumania. Royal Observatory of Belgium; BélgicaFil: Scolini, Camilla. University of New Hampshire; Estados Unidos. University Corporation for Atmospheric Research; Estados UnidosFil: Temmer, Manuela. University of Graz; AustriaFil: Paouris, Evangelos. George Mason University; Estados Unidos. University Johns Hopkins; Estados UnidosFil: Balmaceda, Laura Antonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; Argentina. George Mason University; Estados Unidos. NASA Goddard Space Flight Center; Estados UnidosFil: Cremades Fernandez, Maria Hebe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad de Mendoza; ArgentinaFil: Hinterreiter, Jürgen. University of Graz; Austri
The Tug1 locus is essential for male fertility
Background: Several long noncoding RNAs (lncRNAs) have been shown to function as central components of molecular machines that play fundamental roles in biology. While the number of annotated lncRNAs in mammalian genomes has greatly expanded, their functions remain largely uncharacterized. This is compounded by the fact that identifying lncRNA loci that have robust and reproducible phenotypes when mutated has been a challenge. Results: We previously generated a cohort of 20 lncRNA loci knockout mice. Here, we extend our initial study and provide a more detailed analysis of the highly conserved lncRNA locus, Taurine Upregulated Gene 1 (Tug1). We report that Tug1 knockout male mice are sterile with complete penetrance due to a low sperm count and abnormal sperm morphology. Having identified a lncRNA loci with a robust phenotype, we wanted to determine which, if any, potential elements contained in the Tug1 genomic region (DNA, RNA, protein, or the act of transcription) have activity. Using engineered mouse models and cell-based assays, we provide evidence that the Tug1 locus harbors three distinct regulatory activities - two noncoding and one coding: (i) a cis DNA repressor that regulates many neighboring genes, (ii) a lncRNA that can regulate genes by a trans-based function, and finally (iii) Tug1 encodes an evolutionary conserved peptide that when overexpressed impacts mitochondrial membrane potential. Conclusions: Our results reveal an essential role for the Tug1 locus in male fertility and uncover three distinct regulatory activities in the Tug1 locus, thus highlighting the complexity present at lncRNA loci
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Using "ghost front" to predict the arrival time and speed of CMEs at Venus and Earth
Using in-situ measurements and remote-sensing observations, we study two Coronal Mass Ejections
(CMEs) that left the Sun on 13-14 June 2012 and impacted both Venus and Earth while the planets
were in close radial alignment. The two CMEs generate multiple fronts in STEREO/HI images,
which can also be observed in ‘J-map’ as bifurcated features. We present the ‘ghost front’ model to
combine remote observations from STEREO/SECCHI and in-situ observations from the Wind and
VEX spacecraft, and to derive the kinematics and propagation directions of the CMEs. By fitting the
observations of multiple fronts to a kinematically evolving flux rope (KEFR) model and assuming the
CMEs undergo deceleration through frictional drag with a steady-state solar wind, we confirm that
the outer and inner fronts of the CMEs as detected in HI images are consistent with peaks in Thomson
scattered light returned from the flank and nose of a single front for each CME. An interaction takes
place between the CME-1 and CME-2 that can be observed in the HI-1 field of view before CME-1
encounters Venus. The multi-point in-situ observations of the shock-CME interaction event serve as
further evidence of the interaction between CMEs. The arrival times calculated from the ghost-front
model are within 2.5 hours of those observed at VEX and Wind. Our analysis indicates that ghost
fronts could provide information about the longitudinally-extended shape of the CME in the field of
view of HI-1, which can be used to improve the forecast of ICME arrival time at Earth
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