Magnetorotational instability driven dynamos at low magnetic Prandtl numbers

7 pages, 7 figures, submitted to MNRAS. Version with higher resolution figures is available at http://www.helsinki.fi/~kapyla/publ.htmlNumerical simulations of the magnetorotational instability (MRI) with zero initial net flux in a non-stratified isothermal cubic domain are used to demonstrate the importance of magnetic boundary conditions. In fully periodic systems the level of turbulence generated by the MRI strongly decreases as the magnetic Prandtl number (Pm), which is the ratio of kinematic viscosity and magnetic diffusion, is decreased. No MRI or dynamo action below Pm=1 is found, agreeing with earlier investigations. Using vertical field conditions, which allow magnetic helicity fluxes out of the system, the MRI is found to be excited in the range 0.1Peer reviewe

Open and closed boundaries in large-scale convective dynamos

9 pages, 7 figures, submitted to Astron. AstrophysEarlier work has suggested that large-scale dynamos can reach and maintain equipartition field strengths on a dynamical time scale only if magnetic helicity of the fluctuating field can be shed from the domain through open boundaries. To test this scenario in convection-driven dynamos by comparing results for open and closed boundary conditions. Three-dimensional numerical simulations of turbulent compressible convection with shear and rotation are used to study the effects of boundary conditions on the excitation and saturation level of large-scale dynamos. Open (vertical field) and closed (perfect conductor) boundary conditions are used for the magnetic field. The contours of shear are vertical, crossing the outer surface, and are thus ideally suited for driving a shear-induced magnetic helicity flux. We find that for given shear and rotation rate, the growth rate of the magnetic field is larger if open boundary conditions are used. The growth rate first increases for small magnetic Reynolds number, Rm, but then levels off at an approximately constant value for intermediate values of Rm. For large enough Rm, a small-scale dynamo is excited and the growth rate in this regime increases proportional to Rm^(1/2). In the nonlinear regime, the saturation level of the energy of the mean magnetic field is independent of Rm when open boundaries are used. In the case of perfect conductor boundaries, the saturation level first increases as a function of Rm, but then decreases proportional to Rm^(-1) for Rm > 30, indicative of catastrophic quenching. These results suggest that the shear-induced magnetic helicity flux is efficient in alleviating catastrophic quenching when open boundaries are used. The horizontally averaged mean field is still weakly decreasing as a function of Rm even for open boundaries.Peer reviewe

Coronal ejections from convective spherical shell dynamos

Volume: 286 Host publication title: Comparative Magnetic Minima: Characterizing quiet times in the Sun and StarsNon peer reviewe

Ejections of Magnetic Structures Above a Spherical Wedge Driven by a Convective Dynamo with Differential Rotation

Peer reviewe

Multiperiodicity, modulations and flip-flops in variable star light curves II. Analysis of II Peg photometry during 1979-2010

According to earlier Doppler images of the magnetically active primary giant component of the RS CVn binary II Peg, the surface of the star was dominated by one single active longitude that was clearly drifting in the rotational frame of the binary system during 1994-2002; later imaging for 2004-2010, however, showed decreased and chaotic spot activity, with no signs of the drift pattern. Here we set out to investigate from a more extensive photometric dataset whether such a drift is a persistent phenomenon, in which case it could be due to either an azimuthal dynamo wave or an indication of the binary system orbital synchronization still being incomplete. We analyse the datasets using the Carrier Fit method (hereafter CF), especially suitable for analyzing time series in which a fast clocking frequency (such as the rotation of the star) is modulated with a slower process (such as the stellar activity cycle). We combine all collected photometric data into one single data set, and analyze it with the CF method. As a result, we confirm the earlier results of the spot activity having been dominated by one primary spotted region almost through the entire data set, and the existence of a persistent, nearly linear drift. Disruptions of the linear trend and complicated phase behavior are also seen, but the period analysis reveals a rather stable periodicity with P(spot)=6.71054d plus/minus 0.00005d. After the linear trend is removed from the data, we identify several abrupt phase jumps, three of which are analyzed in more detail with the CF method. These phase jumps closely resemble what is called flip-flop event, but the new spot configurations do not, in most cases, persist for longer than a few months.Comment: 9 pages, 7 figures, submitted to Astronomy and Astrophysic

Multiperiodicity, modulations and flip-flops in variable star light curves II. Analysis of II Pegasus photometry during 1979–2010

Aims. According to previously published Doppler images of the magnetically active primary giant component of the RS CVn binary II Peg, the surface of the star was dominated by one single active longitude that was clearly drifting in the rotational frame of the binary system during 1994-2002; later imaging for 2004–2010, however, showed decreased and chaotic spot activity, with no signs of the drift pattern. Here we set out to investigate from a more extensive photometric dataset whether this drift is a persistent phenomenon, in which case it could be caused either by an azimuthal dynamo wave or be an indication that the binary system’s orbital synchronization is still incomplete. On a differentially rotating stellar surface, spot structures preferentially on a certain latitude band could also cause such a drift, the disruption of which could arise from the change of the preferred spot latitude. Methods. We analyzed the datasets using the carrier fit (CF) method, which is especially suitable for analyzing time series in which a fast clocking frequency (such as the rotation of the star) is modulated with a slower process (such as the stellar activity cycle). Results. We combined all collected photometric data into one single data set and analyzed it with the CF method. We confirm the previously published results that the spot activity has been dominated by one primary spotted region almost through the entire data set and also confirm a persistent, nearly linear drift. Disruptions of the linear trend and complicated phase behavior are also seen, but the period analysis reveals a rather stable periodicity with Pspot = 671054 ± 000005. After removing the linear trend from the data, we identified several abrupt phase jumps, three of which are analyzed in more detail with the CF method. These phase jumps closely resemble what is called a flip-flop event, but the new spot configurations do not persist for longer than a few months in most cases. Conclusions. There is some evidence that the regular drift without phase jumps is related to the high state, while the complex phase behavior and disrupted drift pattern are related to the low state of magnetic activity. The most natural explanation of the drift is weak anti-solar (pole rotating faster than the equator) differential rotation with a coefficient k ≈ 0.002 combined with the preferred latitude of the spot structure

Starspots due to large-scale vortices in rotating turbulent convection

We study the generation of large-scale vortices in rotating turbulent convection by means of Cartesian direct numerical simulations. We find that for sufficiently rapid rotation, cyclonic structures on a scale large in comparison to that of the convective eddies, emerge, provided that the fluid Reynolds number exceeds a critical value. For slower rotation, cool cyclonic vortices are preferred, whereas for rapid rotation, warm anti-cyclonic vortices are favored. In some runs in the intermediate regime both types of cyclones co-exist for thousands of convective turnover times. The temperature contrast between the vortices and the surrounding atmosphere is of the order of five per cent. We relate the simulation results to observations of rapidly rotating late-type stars that are known to exhibit large high-latitude spots from Doppler imaging. In many cases, cool spots are accompanied with spotted regions with temperatures higher than the average. In this paper, we investigate a scenario according to which the spots observed in the temperature maps could have a non-magnetic origin due to large-scale vortices in the convection zones of the stars.Comment: 8 pages, 8 figures, version published in ApJ. Version with higher resolution figures can be found at http://www.helsinki.fi/~kapyla/publ.htm

Kokemusasiantuntija- ja tukihenkilövalmennus lastensuojelun asiakasvanhemmille

Tämän tutkimuspainotteisen opinnäytetyön tarkoituksena oli kartoittaa Kasper –kasvatus- ja perheneuvonta ry:lle heidän yhteistyökumppaneidensa halukkuutta ja mahdollisuuksia lähteä kehittämään sijoitettujen lasten vanhemmille suunnattua kokemusasiantuntija- ja tukihenkilötoimintaa heidän omissa työyhteisöissään. Vanhempien ääni lastensuojeluun -osallisuushankkeen työntekijöiden on tarkoitus hyödyntää vastauksia suunnitellessaan alkavaa Soihtu-valmennusta. Opinnäytetyön teoriaosuus pohjautuu kodin ulkopuolelle sijoitettujen lasten vanhempien tuen tarpeen tukemiseen sekä kokemusasiantuntija- ja tukihenkilötoimintaan. Opinnäytetyömme on laadullinen tutkimus, jossa aineisto on kerätty haastattelumenetelmällä. Tiedonkeruutavaksi valitsimme teemahaastattelun. Haastattelut toteutettiin etäyhteyksin ja kaikki haastattelut nauhoitettiin aineiston litterointia varten. Aineiston analysoimme sisällönanalyysin avulla ja tuotimme analyysistä taulukoinnin. Haastatteluista kävi ilmi, että sijoitettujen lasten vanhempien kanssa tehtävään kokemusasiantuntija- ja tukihenkilötoimintaan suhtaudutaan pääosin myönteisesti. Haastateltavat olivat kauttaaltaan sitä mieltä, että nykyinen vertais- tai tukitoiminta sijoitettujen lasten vanhemmille on riittämätöntä ja tätä tulisi kehittää. Tärkeänä pidettiin tulevan valmennuksen onnistumista ja sitä myötä mahdollisesti luotavaa valtakunnallista mallia kokemusasiantuntija- ja tukihenkilötoiminnan järjestämiseen ja ylläpitämiseen. Myös kokemusasiantuntijoiden laajempi hyödyntäminen esimerkiksi palvelujen organisoimisessa ja rakenteisiin vaikuttamisessa nähtiin hyvänä vaihtoehtona tulevaisuudessa. Haastatteluissa nousseissa näkökulmissa korostui se, että kokemusasiantuntija- ja tukihenkilötoimintaa tahdotaan kehittää määrätietoisesti. Asiakkaat tulee ottaa mukaan toiminnan käyttöönottamiseen ja suunnitteluun heti alkuvaiheessa, jotta toiminta saadaan kehitettyä kaikkia hyödyttävälle tasolle. Avainsanat: Tukihenkilö, KokemusasiantuntijaThe aim of this research-focused thesis was to find out the willingness and opportunities for Kasper educational and family counselling association’s partners to start developing their experienced expert and support person activities for parents of placed children. The employees of the Parental voice for Child Protection project are expected to use the information when planning Soihtu-coaching that is starting soon. The theoretical part of the thesis is based on supporting the parents of children placed outside their home, experienced expert and support person work. The thesis is a qualitative study in which the material is collected by the interview method. We chose a thematic interview as the data collection method. The interviews were conducted remotely, and all interviews were recorded for spelling. We analysed the data using content analysis, from which we produced a tabulation. The interviews showed that the experience of working with experienced experts and support person parents is generally welcomed. General opinion of the interviewees was that the current peer or support activities for parents of placed children are insufficient and should be developed. The success of future coaching and the nationwide model that might be created with it for organizing and maintaining experienced expert and peer support activities were considered important. The wider use of experienced experts, for example in organizing services and influencing structures, was also seen to be more common in the future. From the perspectives of the interviewees, it was emphasized that there is a determined desire to develop the activities of experienced experts and support persons. Customers should be involved in the implementation and planning of operations at an early stage so that operations can be developed to a level that benefits everyone. Keywords: A support person, Experienced exper