A formation mechanism of magnetic elements in regions of mixed polarity     

Gadun  A.S.  Solanki  S.K.  Sheminova  V.A.  Ploner  S.R.O. 《Solar physics》2001,203(1):1-7

We present 2-D, fully compressible radiation-MHD simulations of the solar photospheric and subphotospheric layers that run for 2 hours of solar time starting from a magnetic configuration with mixed polarities. In the atmospheric layers the simulation reveals a correlation between field strength and inclination, with a nearly vertical strong-field magnetic component and a more horizontal weak-field component, in agreement with the observations. Our simulation also shows that magnetic flux is converted from one of these states to the other. In particular, magnetic flux sheets can also be formed when a new downflow lane starts due to granule fragmentation. The dynamics of the granulation and field-line reconnection are found to play a role in the initial stages of a magnetic element's formation. The simulation predicts that during or shortly after their formation magnetic elements could be associated with oppositely polarized flux at a small spatial scale.  相似文献   

In-flight geometric calibration of different cameras of IRS-P6 using a physical sensor model   总被引：2，自引：1，他引：1  

P. V. Radhadevi    S. S. Solanki 《The Photogrammetric Record》2008,23(121):69-89

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Comments on the publication by M. Deb,D. M. Banerjee and A. K. Bhattacharya     

M. K. Pandya  S. L. Solanki 《Mineralium Deposita》1980,15(3):397-399

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Solar Irradiance Variations: From Current Measurements to Long-Term Estimates     

Sami K. Solanki  Natalie A. Krivova 《Solar physics》2004,224(1-2):197-208

Variations of solar total and spectral irradiance are prime solar quantities purported to have an influence on the Earth’s climate. Quantitative estimates of irradiance over as long a time as possible are needed to judge their effectiveness in forcing the climate. In order to do this reliably, first the measured record must be reproduced and a feeling for the physics underlying the irradiance variations must be developed. With the help of this knowledge combined with the available proxy data, reconstructions of irradiance in the past, generally since the Maunder minimum, are attempted. Here a brief introduction to some of the irradiance reconstruction work aiming at irradiance on time scales of days to the solar cycle is given, followed by a brief and incomplete overview of the longer-term reconstructions.  相似文献   

Automated co-registration of images from multiple bands of Liss-4 camera     

P.V. Radhadevi  S.S. Solanki  M.V. Jyothi  V. Nagasubramanian  Geeta Varadan 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):17-26

Three multi-spectral bands of the Liss-4 camera of IRS-P6 satellite are physically separated in the focal plane in the along-track direction. The time separation of 2.1 s between the acquisition of first and last bands causes scan lines acquired by different bands to lie along different lines on the ground which are not parallel. Therefore, the raw images of multi-spectral bands need to be registered prior to any simple application like data visualization. This paper describes a method for co-registration of multiple bands of Liss-4 camera through photogrammetric means using the collinearity equations. A trajectory fit using the given ephemeris and attitude data, followed by direct georeferencing is being employed in this model. It is also augmented with a public domain DEM for the terrain dependent input to the model. Finer offsets after the application of this parametric technique are addressed by matching a small subsection of the bands (100×100 pixels) using an image-based method. Resampling is done by going back to original raw data when creating the product after refining image coordinates with the offsets. Two types of aligned products are defined in this paper and their operational flow is described. Datasets covering different types of terrain and also viewed with different geometries are studied with extensive number of points. The band-to-band registration (BBR) accuracies are reported. The algorithm described in this paper for co-registration of Liss-4 bands is an integral part of the software package Value Added Products generation System (VAPS) for operational generation of IRS-P6 data products.  相似文献   

Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold     

P. Petit  B. Dintrans  S. K. Solanki  J.-F. Donati  M. Aurière  F. Lignières  J. Morin  F. Paletou  J. Ramirez  C. Catala  R. Fares 《Monthly notices of the Royal Astronomical Society》2008,388(1):80-88

From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun's, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars.
We reconstruct the large-scale magnetic geometry of the targets as a low-order  (ℓ < 10)  spherical harmonic expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (i) The magnetic energy of the large-scale field increases with rotation rate. The increase in chromospheric emission with the mean magnetic field is flatter than observed in the Sun. Since the chromospheric flux is also sensitive to magnetic elements smaller than those contributing to the polarimetric signal, this observation suggests that a larger fraction of the surface magnetic energy is stored in large scales as rotation increases. (ii) Whereas the magnetic field is mostly poloidal for low rotation rates, more rapid rotators host a large-scale toroidal component in their surface field. From our observations, we infer that a rotation period lower than ≈12 d is necessary for the toroidal magnetic energy to dominate over the poloidal component.  相似文献   

Applications of generalized additive model (GAM) to satellite-derived variables and fishery data for prediction of fishery resources distributions in the Arabian Sea   总被引：2，自引：0，他引：2  

H. U. Solanki  Dhyey Bhatpuria  Prakash Chauhan 《国际地球制图》2017,32(1):30-43

This study aims to illustrate how remotely sensed oceanic variables and fishing operations data can be used to predict suitable habitat of fishery resources in Geographic Information System. We used sea surface height anomaly (SSHa), sea surface temperature (SST), chlorophyll concentration (CC), photosynthetically active radiation (PAR) and fishing depth as predictor variables. Fishery data of Indian squid (Loligo spp.) and catfish (Tachysurus spp.) for study period (1998–2004) were segregated randomly to create training and validation. Catch was normalized into Catch per unit Effort (kg h^?1). Generalized additive modelling was performed on training data and then tested on validation data. Suitable ranges of SST, CC, SSHa and PAR for different species distributions were derived and integrated to predict their spatial distributions. Results indicated good match between predicted and actual catch. Monthly probability maps of predicted habitat areas coincide with high catch of the particular month for the study period.  相似文献   

The Wave-Front Correction System for the Sunrise Balloon-Borne Solar Observatory     

T. Berkefeld  W. Schmidt  D. Soltau  A. Bell  H. P. Doerr  B. Feger  R. Friedlein  K. Gerber  F. Heidecke  T. Kentischer  O. v.?d. L??he  M. Sigwarth  E. W?lde  P. Barthol  W. Deutsch  A. Gandorfer  D. Germerott  B. Grauf  R. Meller  A. ??lvarez-Herrero  M. Kn?lker  V. Mart??nez Pillet  S. K. Solanki  A. M. Title 《Solar physics》2011,268(1):103-123

This paper describes the wave-front correction system developed for the Sunrise balloon telescope, and it provides information about its in-flight performance. For the correction of low-order aberrations, a Correlating Wave-Front Sensor (CWS) was used. It consisted of a six-element Shack??C?Hartmann wave-front sensor (WFS), a fast tip-tilt mirror for the compensation of image motion, and an active telescope secondary mirror for focus correction. The CWS delivered a stabilized image with a precision of 0.04?arcsec (rms), whenever the coarse pointing was better than ???45?arcsec peak-to-peak. The automatic focus adjustment maintained a focus stability of 0.01?waves in the focal plane of the CWS. During the 5.5?day flight, good image quality and stability were achieved during 33?hours, containing 45?sequences, which lasted between 10 and 45?min.  相似文献   

Evolution of the Fine Structure of Magnetic Fields in the Quiet Sun: Observations from Sunrise/IMaX and Extrapolations     

T. Wiegelmann  S. K. Solanki  J. M. Borrero  H. Peter  P. Barthol  A. Gandorfer  V. Martínez Pillet  W. Schmidt  M. Knölker 《Solar physics》2013,283(2):253-272

Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sun’s atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun.  相似文献   

Properties of flux tubes and the relation with solar irradiance variability     

M. Fligge  S. K. Solanki 《Journal of Astrophysics and Astronomy》2000,21(3-4):275-282

At the solar surface the magnetic field is bundled into discrete elements of concentrated flux, often referred to as magnetic flux tubes, which cover only a small fraction of the solar surface. Flux tubes span a whole spectrum of sizes, ranging from sunspots to features well below the best currently obtainable spatial resolution. Whereas sunspots have been well studied, our knowledge of the true brightness of small-scale magnetic features is hampered by the insufficient spatial resolution of the observations. A better understanding of the thermal and magnetic properties of these small-scale features, however, is crucial for an understanding of (climate-relevant) long-term solar irradiance variations.  相似文献