236 research outputs found
Effect of Drought Stress on Epicuticular Wax Load in Peanut Genotypes
The changes in epicuticular wax load (EWL) and the leaf temperature in two peanut genotypes such as JL-24 (drought susceptible) and K-9 (drought tolerant) was studied under drought stress and its recovery. The drought stress was induced at different soil moisture level (100%, 60%, 40% and 20% FC) for 7 days and subsequent recovery for 7 days. In both JL-24 and K-9 genotypes, the EWL was found to be increase with the increase in the intensity of drought stress. However, the increase in EWL in K-9 genotype was found to be significantly higher than JL-24 genotype. Moreover, the leaf temperature was also found to be increased with the increase in the intensity of drought stress and the degree of increase in leaf temperature was more pronounced in JL-24 compared to K-9 genotype. Further, after the recovery of drought stress, the EWL and leaf temperature decreased consistently in both the genotypes. The results are discussed in terms of the differences in EWL and temperature of leaf in two genotypes studied under drought stres
Detection of spatially structured scattering polarization of Sr i 4607.3 Ã… with the Fast Solar Polarimeter
Context. Scattering polarization in the Sr I 4607.3 Ã… line observed with high resolution is an important diagnostic of the Sun's atmosphere and magnetism at small spatial scales. Investigating the scattering polarization altered by the Hanle effect is key to constraining the role of small-scale magnetic activity in solar atmospheric activity and energy balance. At present, spatially resolved observations of this diagnostic are rare and have not been reported as close to the disk center as for μ = 0.6. Aims. Our aim is to measure the scattering polarization in the Sr I line at μ = 0.6 and to identify the spatial fluctuations with a statistical approach. Methods. Using the Fast Solar Polarimeter (FSP) mounted on the TESOS filtergraph at the German Vacuum Tower Telescope (VTT) in Tenerife, Spain, we measured both the spatially resolved full Stokes parameters of the Sr I line at μ = 0.6 and the center-to-limb variation of the spatially averaged Stokes parameters. Results. We find that the center-to-limb variation of the scattering polarization in the Sr I line measured with FSP is consistent with previous measurements. A statistical analysis of Stokes Q/I (i.e., the linear polarization component parallel to the solar limb), sampled with 0.16″ pixel-1 in the line core of Sr I reveals that the signal strength is inversely correlated with the intensity in the continuum. We find stronger linear polarimetric signals corresponding to dark areas in the Stokes I continuum image (intergranular lanes). In contrast, independent measurements at μ = 0.3 show a positive correlation of Q/I with respect to the continuum intensity. We estimate that the subregion diameter responsible for the excess Q/I signal is on the order of 0.5″-1″. Conclusions. The presented observations and the statistical analysis of Q/I signals at μ = 0.6 complement reported scattering polarization observations as well as simulations. The FSP has proven to be a suitable instrument to measure spatially resolved scattering polarization signals. In the future, a systematic center-to-limb series of observations with subgranular spatial resolution and increased polarimetric sensitivity (<10-3) compared to that in the present study is needed in order to investigate the change in trend with μ that the comparison of our results with the literature suggests.Fil: Zeuner, F.. Universität Göttingen; Alemania. Institut für Sonnensystemforschung; AlemaniaFil: Feller, A.. Institut für Sonnensystemforschung; AlemaniaFil: Iglesias, Francisco Andres. Institut für Sonnensystemforschung; Alemania. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Mendoza; ArgentinaFil: Solanki, S.K.. Institut für Sonnensystemforschung; Alemania. Kyung Hee University; Corea del Su
Swirls in the solar corona
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 695075).Context. Vortex flows have been found in the photosphere, chromosphere, and low corona in observations and simulations. It has been suggested that vortices play an important role in channeling energy and plasma into the corona. However, the impact of vortex flows on the corona has not been studied directly in a realistic setup. Aims. We investigate the role vortices play for coronal heating using high-resolution simulations of coronal loops. The vortices are not artificially driven and they arise, instead, self-consistently from magnetoconvection. Methods. We performed 3D resistive (magnetohydrodynamic) MHD simulations with the MURaM code. Studying an isolated coronal loop in a Cartesian geometry allows us to resolve the structure of the loop interior. We conducted a statistical analysis to determine vortex properties as a function of height from the chromosphere into the corona. Results. We find that the energy injected into the loop is generated by internal coherent motions within strong magnetic elements. A significant part of the resulting Poynting flux is channeled through the chromosphere in vortex tubes forming a magnetic connection between the photosphere and corona. Vortices can form contiguous structures that reach up to coronal heights, but in the corona itself, the vortex tubes get deformed and eventually lose their identity with increasing height. Vortices show increased upward directed Poynting flux and heating rate in both the chromosphere and corona, but their effect becomes less pronounced with increasing height. Conclusions. While vortices play an important role for the energy transport and structuring in the chromosphere and low corona, their importance higher up in the atmosphere is less clear since the swirls are less distinguishable from their environment. Vortex tubes reaching the corona reveal a complex relationship with the coronal emission.Publisher PDFPeer reviewe
Towards a long-term record of solar total and spectral irradiance
The variation of total solar irradiance (TSI) has been measured since 1978
and that of the spectral irradiance for an even shorter amount of time.
Semi-empirical models are now available that reproduce over 80% of the measured
irradiance variations. An extension of these models into the more distant past
is needed in order to serve as input to climate simulations. Here we review our
most recent efforts to model solar total and spectral irradiance on time scales
from days to centuries and even longer. Solar spectral irradiance has been
reconstructed since 1947. Reconstruction of solar total irradiance goes back to
1610 and suggests a value of about 1-1.5 Wm for the increase in the
cycle-averaged TSI since the end of the Maunder minimum, which is significantly
lower than previously assumed but agrees with other modern models. First steps
have also been made towards reconstructions of solar total and spectral
irradiance on time scales of millennia
Aldo-keto reductase-1 (AKR1) protect cellular enzymes from salt stress by detoxifying reactive cytotoxic compounds
Cytotoxic compounds like reactive carbonyl compounds such as methylglyoxal (MG), melandialdehyde (MDA), besides the ROS accumulate significantly at higher levels under salinity stress conditions and affect lipids and proteins that inhibit plant growth and productivity. The detoxification of these cytotoxic compounds by overexpression of NADPH-dependent Aldo-ketoreductase (AKR1) enzyme enhances the salinity stress tolerance in tobacco. The PsAKR1 overexpression plants showed higher survival and chlorophyll content and reduced MDA, H2O2, and MG levels under NaCl stress. The transgenic plants showed reduced levels of Na+ levels in both root and shoot due to reduced reactive carbonyl compounds (RCCs) and showed enhanced membrane stability resulted in higher root growth and biomass. The increased levels of antioxidant glutathione and enhanced activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) suggest AKR1 could protect these enzymes from the RCC induced protein carbonylation by detoxification process. The transgenics also showed higher activity of delta 1-pyrroline-5- carboxylate synthase (P5CS) enzyme resulted in increasedproline levels to maintain osmotic homeostasis. The results demonstrates that the AKR1 protects proteins or enzymes that are involved in scavenging of cytotoxic compounds by detoxifying RCCs generated under salinity stress. © 2017 Elsevier Masson SA
Gossamer roadmap technology reference study for a solar polar mission
A technology reference study for a solar polar mission is presented. The study uses novel analytical methods to quantify the mission design space including the required sail performance to achieve a given solar polar observation angle within a given timeframe and thus to derive mass allocations for the remaining spacecraft sub-systems, that is excluding the solar sail sub-system. A parametric, bottom-up, system mass budget analysis is then used to establish the required sail technology to deliver a range of science payloads, and to establish where such payloads can be delivered to within a given timeframe. It is found that a solar polar mission requires a solar sail of side-length 100 – 125 m to deliver a ‘sufficient value’ minimum science payload, and that a 2. 5μm sail film substrate is typically required, however the design is much less sensitive to the boom specific mass
Width of Sunspot Generating Zone and Reconstruction of Butterfly Diagram
Based on the extended Greenwich-NOAA/USAF catalogue of sunspot groups it is
demonstrated that the parameters describing the latitudinal width of the
sunspot generating zone (SGZ) are closely related to the current level of solar
activity, and the growth of the activity leads to the expansion of SGZ. The
ratio of the sunspot number to the width of SGZ shows saturation at a certain
level of the sunspot number, and above this level the increase of the activity
takes place mostly due to the expansion of SGZ. It is shown that the mean
latitudes of sunspots can be reconstructed from the amplitudes of solar
activity. Using the obtained relations and the group sunspot numbers by Hoyt
and Schatten (1998), the latitude distribution of sunspot groups ("the Maunder
butterfly diagram") for the 18th and the first half of the 19th centuries is
reconstructed and compared with historical sunspot observations.Comment: 16 pages, 11 figures; accepted by Solar Physics; the final
publication will be available at www.springerlink.co
Stokes Diagnostis of 2D MHD-simulated Solar Magnetogranulation
We study the properties of solar magnetic fields on scales less than the
spatial resolution of solar telescopes. A synthetic infrared
spectropolarimetric diagnostics based on a 2D MHD simulation of
magnetoconvection is used for this. We analyze two time sequences of snapshots
that likely represent two regions of the network fields with their immediate
surrounding on the solar surface with the unsigned magnetic flux density of 300
and 140 G. In the first region we find from probability density functions of
the magnetic field strength that the most probable field strength at logtau_5=0
is equal to 250 G. Weak fields (B < 500 G) occupy about 70% of the surface,
while stronger fields (B 1000 G) occupy only 9.7% of the surface. The magnetic
flux is -28 G and its imbalance is -0.04. In the second region, these
parameters are correspondingly equal to 150 G, 93.3 %, 0.3 %, -40 G, and -0.10.
We estimate the distribution of line-of-sight velocities on the surface of log
tau_5=-1. The mean velocity is equal to 0.4 km/s in the first simulated region.
The averaged velocity in the granules is -1.2 km/s and in the intergranules is
2.5 km/s. In the second region, the corresponding values of the mean velocities
are equal to 0, -1.8, 1.5 km/s. In addition we analyze the asymmetry of
synthetic Stokes-V profiles of the Fe I 1564.8 nm line. The mean values of the
amplitude and area asymmetry do not exceed 1%. The spatially smoothed amplitude
asymmetry is increased to 10% while the area asymmetry is only slightly varied.Comment: 24 pages, 12 figure
Spectral Inversion of Multi-Line Full-Disk Observations of Quiet Sun Magnetic Fields
Spectral inversion codes are powerful tools to analyze spectropolarimetric
observations, and they provide important diagnostics of solar magnetic fields.
Inversion codes differ by numerical procedures, approximations of the
atmospheric model, and description of radiative transfer. Stokes Inversion
based on Response functions (SIR) is an implementation widely used by the solar
physics community. It allows to work with different atmospheric components,
where gradients of different physical parameters are possible, e.g., magnetic
field strength and velocities. The spectropolarimetric full-disk observations
were carried out with the Stokesmeter of the Solar Telescope for Operative
Predictions (STOP) at the Sayan Observatory on 3 February 2009, when neither an
active region nor any other extended flux concentration was present on the Sun.
In this study of quiet Sun magnetic fields, we apply the SIR code
simultaneously to 15 spectral lines. A tendency is found that weaker magnetic
field strengths occur closer to the limb. We explain this finding by the fact
that close to the limb, we are more sensitive to higher altitudes in an
expanding flux tube, where the field strength should be smaller since the
magnetic flux is conserved with height. Typically, the inversions deliver two
populations of magnetic elements: (1) high magnetic field strengths (1500-2000
G) and high temperatures (5500-6500 K) and (2) weak magnetic fields (50-150 G)
and low temperatures (5000-5300 K).Comment: 10 pages, 6 figures, accepted for Solar Physic
Locating current sheets in the solar corona
Current sheets are essential for energy dissipation in the solar corona, in
particular by enabling magnetic reconnection. Unfortunately, sufficiently thin
current sheets cannot be resolved observationally and the theory of their
formation is an unresolved issue as well. We consider two predictors of coronal
current concentrations, both based on geometrical or even topological
properties of a force free coronal magnetic field. First, there are
separatrices related to magnetic nulls. Through separatrices the magnetic
connectivity changes discontinuously. Coronal magnetic nulls are, however, very
rare. At second, inspired by the concept of generalized magnetic reconnection
without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the
magnetic connectivity changes continuously, though strongly. The strength of
the connectivity change can be quantified by measuring the squashing of the
flux tubes which connect the magnetically conjugated photospheres.
We verify the QSL and separatrix concepts by comparing the sites of magnetic
nulls and enhanced squashing with the location of current concentrations in the
corona. Due to the known difficulties of their direct observation we simulated
the coronal current sheets by numerically calculating the response of the
corona to energy input from the photosphere heating a simultaneously observed
EUV Bright Point. We did not find coronal current sheets not at the
separatrices but at several QSL locations. The reason is that although the
geometrical properties of force free extrapolated magnetic fields can indeed,
hint at possible current concentrations, a necessary condition for current
sheet formation is the local energy input into the corona
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