scholarly journals Rossby Waves in Astrophysics

2021 ◽  
Vol 217 (1) ◽  
Author(s):  
T. V. Zaqarashvili ◽  
M. Albekioni ◽  
J. L. Ballester ◽  
Y. Bekki ◽  
L. Biancofiore ◽  
...  
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
Magnetic Activity ◽  
Future Research ◽  
Rotating Stars ◽  
Spatial And Temporal Scales ◽  
Physical Role ◽  
Astrophysical Objects ◽  
Exoplanetary Atmospheres ◽  
Rapidly Rotating Stars

AbstractRossby waves are a pervasive feature of the large-scale motions of the Earth’s atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined.

Analysis of magnetic activity of the rapidly rotating stars He 373 and AP 225

2017 ◽  
Vol 61 (6) ◽  
pp. 521-532 ◽  
Author(s):  
A. I. Kolbin ◽  
V. V. Tsymbal
Keyword(s):  
Magnetic Activity ◽  
Rotating Stars ◽  
Rapidly Rotating Stars

scholarly journals Doppler Images of Spotted Late-Type Stars

1988 ◽  
Vol 132 ◽  
pp. 253-272 ◽  
Author(s):  
Steven S. Vogt
Keyword(s):  
Magnetic Activity ◽  
Doppler Imaging ◽  
Type Star ◽  
Quality Data ◽  
High Signal ◽  
Rotating Stars ◽  
Late Type ◽  
Dynamo Action ◽  
Type Boundary ◽  
Rapidly Rotating Stars

Doppler imaging is a technique for deriving resolved images of rapidly rotating stars from a detailed analysis of very high signal-to-noise high resolution spectral line profiles. An improved version of this technique is presented, which now uses principles of maximum entropy image reconstruction to invert the line profile information. The effects that noise, finite resolution, and uncertainties in the assumed stellar physics have on the resultant images were explored through various test simulations. The technique is found to be efficient, accurate, and robust at deriving images of certain classes of stars from realistic quality data. Doppler images are presented of two spotted late-type stars, the RS CVn-type star HR 1099, and the FK Com-type star HD 199178. Both stars show surprisingly similar spot distributions. In each case, there is a single large cool spot straddling the pole, and a number of small cool spots at low latitudes. We expect that the small low latitude spots on each star will migrate poleward to join the polar spot, and suspect that the observed long-lived polar spots are the result of the poleward migration and merging of many active region complexes. If true, the poleward migration of starspots suggests that magnetic activity on very rapidly rotating stars is qualitatively different than that seen on our Sun. We suggest that the observed rotational trigger velocity for the appearance of large spots on late-type stars marks the transition from solar-type boundary layer dynamos to distributed dynamos, which occur only in more rapidly rotating stars. The sizes, locations, and migrations of the spots, however, may be more a result of the convective flow patterns than of any dynamo action, since the spots are quite long-lived.

scholarly journals Effect of Instability-Generated Clumping on Wind Compressed Disk Inhibition

2000 ◽  
Vol 175 ◽  
pp. 621-625
Author(s):  
S. P. Owocki ◽  
D. H. Cohen
Keyword(s):  
Stellar Wind ◽  
Large Scale ◽  
Small Scale ◽  
Be Stars ◽  
Rotating Stars ◽  
Disk Formation ◽  
Line Force ◽  
Force Components ◽  
Hydrodynamical Simulations ◽  
Rapidly Rotating Stars

AbstractIn rapidly rotating stars with a purely radially driven stellar wind, conservation of wind angular momentum can lead to formation of an equatorial Wind Compressed Disk (WCD). However, for a line-driven stellar wind, recent 2D hydrodynamical simulations based on a localized, Sobolev treatment of the line-force indicate that nonradial components of the line-force can effectively inhibit formation of such a WCD. This presentation will describe current efforts to extend such 2D simulations to a nonlocal, smooth-source-function treatment of the line-force that can incorporate the intrinsically strong instability of line-driving to formation of small-scale, clumped structure. Key questions are how such small-scale clumped structure affects the nonradial line-force components that arise from large-scale velocity-gradient asymmetries, and in particular whether such nonradial forces can still inhibit WCD formation in a clumped flow. The results have important implications for the viability of the WCD mechanism as a paradigm for disk formation in Be stars.

scholarly journals Magnetic field evolution in solar-type stars

2019 ◽  
Vol 15 (S354) ◽  
pp. 169-180
Author(s):  
Axel Brandenburg
Keyword(s):  
Magnetic Field ◽  
Linear Polarization ◽  
Large Scale ◽  
Rossby Number ◽  
Rotating Stars ◽  
Field Evolution ◽  
Solar Type ◽  
Activity Cycles ◽  
Rapidly Rotating Stars ◽  
The Magnetic Field

AbstractWe discuss selected aspects regarding the magnetic field evolution of solar-type stars. Most of the stars with activity cycles are in the range where the normalized chromospheric Calcium emission increases linearly with the inverse Rossby number. For Rossby numbers below about a quarter of the solar value, the activity saturates and no cycles have been found. For Rossby numbers above the solar value, again no activity cycles have been found, but now the activity goes up again for a major fraction of the stars. Rapidly rotating stars show nonaxisymmetric large-scale magnetic fields, but there is disagreement between models and observations regarding the actual value of the Rossby number where this happens. We also discuss the prospects of detecting the sign of magnetic helicity using various linear polarization techniques both at the stellar surface using the parity-odd contribution to linear polarization and above the surface using Faraday rotation.

scholarly journals Rossby waves and polar spots in rapidly rotating stars: implications for stellar wind evolution

2011 ◽  
Vol 532 ◽  
pp. A139 ◽  
Author(s):  
T. V. Zaqarashvili ◽  
R. Oliver ◽  
J. L. Ballester ◽  
M. Carbonell ◽  
M. L. Khodachenko ◽  
...  
Keyword(s):  
Stellar Wind ◽  
Rossby Waves ◽  
Rotating Stars ◽  
Rapidly Rotating Stars

Analysis of interaction between parameterized orographic gravity wave drag and resolved dynamics in CMAM.

2021 ◽  
Author(s):  
Petr Šácha ◽  
Aleš Kuchař ◽  
Christoph Jacobi ◽  
Petr Pišoft ◽  
Roland Eichinger ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Rossby Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Dynamical Analysis ◽  
Future Research ◽  
Stratospheric Polar Vortex

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics herein. In current generation chemistry-climate models (CCMs), GWs are usually smaller than the model resolution and the majority of their spectrum therefore must be parameterized. From observations, we know that GWs are intermittent and asymmetrically distributed around the globe, which holds to some extent also for the parameterized GW drag (GWD) (in particular for orographic GWD (oGWD)). The GW parameterizations in CCMs are usually tuned to mitigate biases in the zonal mean climatology of particular quantities, but the complex interaction of parameterized GWs with the large- scale circulation and resolved waves in the models remains to date poorly understood.</p> <p>This presentation will combine observational evidence, idealized modeling and dynamical analysis of a CCM output to study both the short-term and long-term model response to the oGWD. Our results demonstrate that the oGW-resolved dynamics interaction is a complex two-way process, with the most prominent oGWD impact being the alteration of propagation of planetary-scale Rossby waves on a time-scale of a few days. The conclusions give a novel perspective on the importance of oGWD for the stratospheric polar vortex and atmospheric transport studies outlining potential foci of future research.</p> </div> </div> </div>

scholarly journals On the connections between solar and stellar dynamo models

2016 ◽  
Vol 12 (S328) ◽  
pp. 12-21
Author(s):  
Laurène Jouve ◽  
Rohit Kumar
Keyword(s):  
Large Scale ◽  
Mean Field ◽  
Active Regions ◽  
Rotating Stars ◽  
Flux Transport ◽  
Dynamo Mechanism ◽  
Solar Type ◽  
Rapidly Rotating Stars ◽  
Observational Techniques

AbstractWe here discuss the various dynamo models which have been designed to explain the generation and evolution of large-scale magnetic fields in stars. We focus on the models that have been applied to the Sun and can be tested for other solar-type stars now that modern observational techniques provide us with detailed stellar magnetic field observations. Mean-field flux-transport dynamo models have been developed for decades to explain the solar cycle and applications to more rapidly-rotating stars are discussed. Tremendous recent progress has been made on 3D global convective dynamo models. They do not however for now produce regular flux emergence that could be responsible for surface active regions and questions about the role of these active regions in the dynamo mechanism are still difficult to address with such models. We finally discuss 3D kinematic dynamo models which could constitute a promising combined approach, in which data assimilation could be applied.

Magnetic geometry and activity of cool stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 341-342
Author(s):  
Sudeshna Boro Saikia ◽  
Theresa Lüftinger ◽  
Manuel Guedel
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Central Star ◽  
Doppler Imaging ◽  
Rotating Stars ◽  
Surface Magnetic Field ◽  
Chromospheric Activity ◽  
Field Geometry ◽  
Atmospheric Loss ◽  
Rapidly Rotating Stars

AbstractStellar magnetic field manifestations such as stellar winds and EUV radiation are the key drivers of planetary atmospheric loss and escape. To understand how the central star influences habitability, it is very important to perform detailed investigation of the star’s magnetic field. We investigate the surface magnetic field geometry and chromospheric activity of 51 sun-like stars. The magnetic geometry is reconstructed using Zeeman Doppler imaging. Chromospheric activity is measured using the Ca II H& K lines. We confirm that the Sun’s large-scale geometry is dominantly poloidal, which is also true for slowly rotating stars. Contrary to the Sun, rapidly rotating stars can have a strong toroidal field and a weak poloidal field. This separation in field geometry appears at Ro=1. Our results show that detailed investigation of stellar magnetic field is important to understand its influence on planetary habitability.

scholarly journals Destruction of Be star disk by large scale magnetic fields

2016 ◽  
Vol 12 (S329) ◽  
pp. 453-453
Author(s):  
Asif ud-Doula ◽  
Stanley Owocki ◽  
Nathaniel (Dylan) Kee ◽  
Michael Vanyo
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Circumstellar Disks ◽  
Be Stars ◽  
Rotating Stars ◽  
Apparent Lack ◽  
B Stars ◽  
Large Scale Magnetic Field ◽  
Be Star ◽  
Rapidly Rotating Stars

AbstractClassical Be stars are rapidly rotating stars with circumstellar disks that come and go on time scale of years. Recent observational data strongly suggests that these stars lack the 10% incidence of global magnetic fields observed in other main-sequence B stars. Such an apparent lack of magnetic fields may indicate that Be disks are fundamentally incompatible with a significant large scale magnetic field. In this work, using numerical magnetohydrodynamics (MHD) simulations, we show that a dipole field of only 100G can lead to the quick disruption of a Be disk. Such a limit is in line with the observational upper limits for these objects.

Change of Attitude, Technology and Practice: Identifying the Change for Increased Value Creation with Customer Co-creation

2017 ◽  
Vol 5 (1) ◽  
pp. 70-82
Author(s):  
Soumi Paul ◽  
Paola Peretti ◽  
Saroj Kumar Datta
Keyword(s):  
Social Media ◽  
New Product Development ◽  
Value Creation ◽  
Large Scale ◽  
Customer Orientation ◽  
Customer Relationships ◽  
Future Research ◽  
Management Competencies ◽  
Business Decisions ◽  
Prime Concern

Building customer relationships and customer equity is the prime concern in today’s business decisions. The emergence of internet, especially social media like Facebook and Twitter, changed traditional marketing thought to a great extent. The importance of customer orientation is reflected in the axiom, “The customer is the king”. A good number of organizations are engaging customers in their new product development activities via social media platforms. Co-creation, a new perspective in which customers are active co-creators of the products they buy and use, is currently challenging the traditional paradigm. The concept of co-creation involving the customer’s knowledge, creativity and judgment to generate value is considered not only an upcoming trend that introduces new products or services but also fitting their need and increasing value for money. Knowledge and innovation are inseparable. Knowledge management competencies and capacities are essential to any organization that aspires to be distinguished and innovative. The present work is an attempt to identify the change in value creation procedure along with one area of business, where co-creation can return significant dividends. It is on extending the brand or brand category through brand extension or line extension. This article, through an in depth literature review analysis, identifies the changes in every perspective of this paradigm shift and it presents a conceptual model of company-customer-brand-based co-creation activity via social media. The main objective is offering an agenda for future research of this emerging trend and ensuring the way to move from theory to practice. The paper acts as a proposal; it allows the organization to go for this change in a large scale and obtain early feedback on the idea presented. 

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