33 research outputs found
Fluctuations in the Alpha-Effect and Grand Solar Minima
Parameters of a special kind of \alpha-effect known in dynamo theory as the
Babcock-Leighton mechanism are estimated using the data of sunspot catalogs.
The estimates evidence the presence of the Babcock-Leighton \alpha-effect on
the Sun. Fluctuations of the \alpha-effect are also estimated. The fluctuation
amplitude appreciably exceeds the mean value, and the characteristic time for
the fluctuations is comparable to the period of the solar rotation.
Fluctuations with the parameters found are included in a numerical model for
the solar dynamo. Computations show irregular changes in the amplitudes of the
magnetic cycles on time scales of centuries and millennia. The calculated
statistical characteristics of the grand solar minima and maxima agree with the
data on solar activity over the Holocene.Comment: To appear in Astronomy Reports, 20 pages, 9 figure
Current status of the temperature and humidity regime of the troposphere in the Siberian sector in different circulation periods
The paper studies the long-term dynamics of air temperature and relative humidity anomaly indices in the surface layer and at different levels of the troposphere in Siberia and neighboring regions (European and Far Eastern sectors). As the main cause of the observed variations in climatic parameters we considered circulation factors, which were taken into account using the typification of macrocirculation processes proposed by B.L. Dzerdzeevsky. Seasonal differences were revealed in the distribution of anomaly indices and the area occupied by anomalies of different signs of annual and monthly mean temperature and relative air humidity, which are most pronounced during circulation periods of increased duration of meridional northern processes in the Siberian sector and in the Northern Hemisphere as a whole. The highest rates of change in the temperature regime in the Siberian sector over recent decades have been observed at the level of the isobaric surface AT–700 hPa (3 km), which affects the advective-dynamic factors of surface cyclo- and frontogenesis, as well as the processes of cloud formation and precipitation. In general, an increase in the heat content of the lower and middle troposphere and a decrease in the relative moisture content near the tropopause can be accompanied by an increase in the amount of the potential energy and convective instability energy reserves and can lead to an increase in climate risks in the Siberian sector
Does the Babcock--Leighton Mechanism Operate on the Sun?
The contribution of the Babcock-Leighton mechanism to the generation of the
Sun's poloidal magnetic field is estimated from sunspot data for three solar
cycles. Comparison of the derived quantities with the A-index of the
large-scale magnetic field suggests a positive answer to the question posed in
the title of this paper.Comment: 5 pages, 2 figures, to apper in Astronomy Letter
Solar dynamo model with nonlocal alpha-effect
The first results of the solar dynamo model that allows for the diamagnetic
effect of inhomogeneous turbulence and the nonlocal alpha-effect due to the
rise of magnetic loops are discussed. The nonlocal alpha-effect is not subject
to the catastrophic quenching related to the conservation of magnetic helicity.
Given the diamagnetic pumping, the magnetic fields are concentrated near the
base of the convection zone, although the distributed-type model covers the
entire thickness of the convection zone. The magnetic cycle period, the
equatorial symmetry of the field, its meridional drift, and the
polar-to-toroidal field ratio obtained in the model are in agreement with
observations. There is also some disagreement with observations pointing the
ways of improving the model.Comment: To appear in Astronomy Letters, 10 pages, 5 figure
Differential rotation of main-sequence dwarfs and its dynamo-efficiency
A new version of a numerical model of stellar differential rotation based on
mean-field hydrodynamics is presented and tested by computing the differential
rotation of the Sun. The model is then applied to four individual stars
including two moderate and two fast rotators to reproduce their observed
differential rotation quite closely. A series of models for rapidly rotating
( day) stars of different masses and compositions is generated.
The effective temperature is found convenient to parameterize the differential
rotation: variations with metallicity, that are quite pronounced when the
differential rotation is considered as a function of the stellar mass, almost
disappear in the dependence of differential rotation on temperature. The
differential rotation increases steadily with surface temperature to exceed the
largest differential rotation observed to date for the hottest F-stars we
considered. This strong differential rotation is, however, found not to be
efficient for dynamos when the efficiency is estimated with the standard
-parameter of dynamo models. On the contrary, the small differential
rotation of M-stars is the most dynamo-efficient. The meridional flow near the
bottom of the convection zone is not small compared to the flow at the top in
all our computations. The flow is distributed over the entire convection zone
in slow rotators but retreats to the convection zone boundaries with increasing
rotation rate, to consist of two near-boundary jets in rapid rotators. The
implications of the change of the flow structure for stellar dynamos are
briefly discussed.Comment: 9 pages, 11 figures, submitted to MNRA