Transition properties of potassium atom

We report here oscillator strengths, transition rates, branching ratios and lifetimes due to allowed transitions in potassium (K) atom. We evaluate electric dipole (E1) amplitudes using an all order relativistic many-body perturbation method. The obtained results are compared with previously available experimental and theoretical studies. Using the E1 matrix elements mentioned above and estimated from the lifetimes of the 4P states, we determine precise values of static and dynamic polarizabilities for the first five low-lying states in the considered atom. The static polarizabilities of the ground and 4P states in the present work are more precise than the available measurements in these states. Only the present work employs relativistic theory to evaluate polarizabilities in the 3D states for which no experimental results are known to compare with. We also reexamine "magic wavelengths" for the $4P_{1/2} \rightarrow 4S$ and $4P_{3/2} \rightarrow 4S$ transitions due to the linearly polarized light which are useful to perform state-insensitive trapping of K atoms.Comment: 12 pages, 2 figure

Estimation of osmotic potential and free amino acids in some mangroves of the Sundarbans, India

Osmotic potential (OP) of root and leaf was measured in 19 species of mangroves collected from the Sundarbans, India. Leaf OP was estimated in 11 taxa from among them, grown in fresh water and compared with that deriving from taxa grown in saline water. Free amino acids were estimated from leaves of 16 mangrove species of the Sundarbans. The osmotic potential in leaves collected from their natural habitat was more negative than that from those grown in fresh water conditions. Seedlings grown without salt provided less negative leaf OPthan those treated with 0.1 mol dm–3 NaCl. The more negative OP was found in more saline soil, which might be related to adaptation to facilitate water uptake from a highly saline and frequently waterlogged anaerobic substratum. Aspartic acid, alanine, proline, tryptophan, tyrosine and phenylalanine are the major free amino acids detected in the leaves. Leucine was recorded only in Avicennia spp., where phenylalanine content was negligible. Proline content was estimated in seven species. The positive linear trend obtained between leaf OP and proline content points to its role as an osmoticum in mangrove leaves. Cysteine, aspartic acid, alanine and phenylalanine were determined in seedlings, while proline could be estimated only in X. mekongensis. Cysteine and proline content in seedling leaves were gradually reduced with increasing soil salinity. Lack of cysteine in mature leaves and its decrease in more saline soil probably indicates salinity as a photorespiration restricting factor. A more or less inverse relationship was found between proline and alanine content both in seedlings and mature plants

Solar activity forecast with a dynamo model

Although systematic measurements of the solar polar magnetic field exist only from mid 1970s, other proxies can be used to infer the polar field at earlier times. The observational data indicate a strong correlation between the polar field at a sunspot minimum and the strength of the next cycle, although the strength of the cycle is not correlated well with the polar field produced at its end. This suggests that the Babcock Leighton mechanism of poloidal field generation from decaying sunspots involves randomness, whereas the other aspects of the dynamo process must be reasonably ordered and deterministic. Only if the magnetic diffusivity within the convection zone is assumed to be high, we can explain the correlation between the polar field at a minimum and the next cycle. We give several independent arguments that the diffusivity must be of this order. In a dynamo model with diffusivity like this, the poloidal field generated at the mid latitudes is advected toward the poles by the meridional circulation and simultaneously diffuses towards the tachocline, where the toroidal field for the next cycle is produced. To model actual solar cycles with a dynamo model having such high diffusivity, we have to feed the observational data of the poloidal field at the minimum into the theoretical model. We develop a method of doing this in a systematic way. Our model predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of solar activity is also calculated with our model and compared with observational data.Comment: 17 pages, 18 figures, submitted to MNRA

Outstanding Issues in Solar Dynamo Theory

The magnetic activity of the Sun, as manifested in the sunspot cycle, originates deep within its convection zone through a dynamo mechanism which involves non-trivial interactions between the plasma and magnetic field in the solar interior. Recent advances in magnetohydrodynamic dynamo theory have led us closer towards a better understanding of the physics of the solar magnetic cycle. In conjunction, helioseismic observations of large-scale flows in the solar interior has now made it possible to constrain some of the parameters used in models of the solar cycle. In the first part of this review, I briefly describe this current state of understanding of the solar cycle. In the second part, I highlight some of the outstanding issues in solar dynamo theory related to the the nature of the dynamo $\alpha$-effect, magnetic buoyancy and the origin of Maunder-like minima in activity. I also discuss how poor constraints on key physical processes such as turbulent diffusion, meridional circulation and turbulent flux pumping confuse the relative roles of these vis-a-vis magnetic flux transport. I argue that unless some of these issues are addressed, no model of the solar cycle can claim to be ``the standard model'', nor can any predictions from such models be trusted; in other words, we are still not there yet.Comment: To appear in "Magnetic Coupling between the Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten, Astrophysics and Space Science Proceedings, Springer-Verlag, Heidelberg, Berlin, 200

The Waldmeier Effect in Sunspot Cycles

We discuss two aspects of the Waldmeier Effect, namely (1) the rise times of sunspot cycles are anti-correlated to their strengths (WE1) and (2) the rates of rise of the cycles are correlated to their strengths (WE2). From analysis of four different data sets we conclude that both WE1 and WE2 exist in all the data sets. We study these effects theoretically by introducing suitable stochastic fluctuations in our regular solar dynamo model.Comment: Magnetic Coupling between the Interior and Atmosphere of the Sun; Astrophysics and Space Science Proceeding

Magnetic Non-Potentiality of Solar Active Regions and Peak X-Ray Flux of the Associated Flares

Predicting the severity of the solar eruptive phenomena like flares and Coronal Mass Ejections (CMEs) remains a great challenge despite concerted efforts for several decades. The advent of high quality vector magnetograms obtained from Hinode (SOT/SP) has increased the possibility of meeting this challenge. In particular, the Spatially Averaged Signed Shear Angle (SASSA) seems to be an unique parameter to quantify the non-potentiality of the active regions. We demonstrate the usefulness of SASSA for predicting the flare severity. For this purpose we present case studies of the evolution of magnetic non-potentiality using 115 vector magnetograms of four active regions namely ARs NOAA 10930, 10960, 10961 and 10963 during December 08-15, 2006, June 03-10, 2007, June 28-July 5, 2007 and July 10-17, 2007 respectively. The NOAA ARs 10930 and 10960 were very active and produced X and M class flares respectively, along with many smaller X-ray flares. On the other hand, the NOAA ARs 10961 and 10963 were relatively less active and produced only very small (mostly A and B-class) flares. For this study we have used a large number of high resolution vector magnetograms obtained from Hinode (SOT/SP). The analysis shows that the peak X-ray flux of the most intense solar flare emanating from the active regions depends on the magnitude of the SASSA at the time of the flare. This finding of the existence of a lower limit of SASSA for a given class of X-ray flare will be very useful for space weather forecasting. We have also studied another non-potentiality parameter called mean weighted shear angle (MWSA) of the vector magnetograms along with SASSA. We find that the MWSA does not show such distinction as the SASSA for upper limits of GOES X-Ray flux of solar flares, however both the quantities show similar trends during the evolution of all active regions studied.Comment: 25 pages, 5 figures, accepted for publication in the Astrophysical Journa

Relation of leaf micromorphology with photosynthesis and water efflux in some Indian mangroves

Stomatal size and frequency, cuticle thickness and the amount of mesophyll tissues were measured in leaves of 14 mangrove species belonging to seven families of the Sundarbans vegetation. The rate of assimilation and water efflux were estimated in vitro. In this tropical estuary high salinity prevails in soil and water, hence the dominating mangrove vegetation develops some morpho-anatomical adaptations to cope with such adverse ecology. Some architectural parameters of leaves have a significant relation with carbon assimilation and water-use characteristics. In all the studied taxa, photosynthesis is positively correlated to stomatal frequency and the amount of mesophyll tissue, while an inverse relation exists with stomatal size. Similarly, transpiration and stomatal conductance directly correlate to the abundance of stomata, but reciprocate to their size. Cuticle thickness is inversely related to transpiration, but hardly any relation was noticed with the rate of photosynthesis and stomatal conductance. The amount of mesophyll tissue has a direct relation with carbon assimilation, while its effect upon transpiration and stomatal conductance seems to be insignificant