共查询到20条相似文献，搜索用时 15 毫秒
1.
E. P. Popova 《Astronomy Reports》2009,53(9):863-868
We examine the effects of solar meridional circulation on the propagation of dynamo waves depending on the type of matter motion in a Parker approximation. The meridional circulation can lengthen the solar-activity cycle, with the dynamo-wave behavior depending on the latitude variations in the velocity of the moving material. The results obtained can qualitatively explain the Maunder minimum. 相似文献
2.
E. P. Popova 《Astronomy Reports》2012,56(10):784-789
A dynamic system for the Parker dynamo including meridional circulation that is applicable to astrophysical objects is constructed. The meridional circulation is able to control the regimes for the generation of magnetic fields. If the meridional flows are weak, regimes with steady oscillations, dynamo bursts, fluctuations, and chaotic components are possible. When the meridional circulation is strengthened, the range of dynamo numbers required for fluctuations and dynamo bursts is reduced, and gradually vanishes; at the same time, the range required for oscillations is increased and raised to higher dynamo numbers. The latitude-time distributions of the toroidal and poloidal magnetic fields for steady oscillations are presented. 相似文献
3.
The effects of meridional circulation on the solar dynamo wave are investigated in the Parker approximation using WKB techniques. The meridional circulation can substantially prolong the activity cycle; however, in the framework of the approximation considered, it cannot reverse the direction of propagation of the dynamo wave. If the circulation speed is too high, the solution is concentrated near the pole and can no longer be described in the Parker approximation. 相似文献
4.
Excitations of two oppositely directed waves of stellar activity generated by two dynamo-active layers located in a single stellar hemisphere are examined using simple dynamo models. The domains of model parameters corresponding to various types and directions of the activity waves are found. It is shown that oppositely directed waves of activity are generated if the dynamo numbers have the same order of magnitude, ~105?106, but opposite signs. How frequently this case can be observed among real stars remains open to question. The report of oppositely directed waves of stellar activity in the literature is especially valuable in this connection. 相似文献
5.
Latitude-time (butterfly) diagrams of the large-scale solar magnetic field differ appreciably from the butterfly diagrams
for sunspots. Tilted features corresponding to waves propagating from the middle latitudes to the equator are virtually absent
from the diagrams for the large-scale magnetic field. The latitude-time diagram of the 22-year solar cycle based on data for
the large-scale surface field appears as a checkerboard pattern rather than a traveling wave. Solutions describing similar
behavior for the poloidal magnetic field are found for Parker’s solar-dynamo equations. These solutions agree with observations
especially well if meridional circulation is added to the two sources generating the magnetic-field in this dynamo-differential
rotation and mirror-asymmetric convection. 相似文献
6.
L. L. Kitchatinov 《Astronomy Reports》2006,50(6):512-516
Global meridional flows in stars transport angular momentum, thus giving rise to nonuniform rotation. The pattern of differential rotation associated with slow meridional circulation depends on the direction of this circulation. A flow directed from the poles to the equator at the surface and from the equator to the poles in deep layers results in relatively fast rotation of the equatorial zone. If the circulation is directed oppositely, the angular velocity increases from the equator to the poles. Relatively fast rotation at the poles may also result from fast circulation, irrespective of its direction. A simple illustrative explanation is given here to these results. Analytical estimates are supported by numerical calculations. The time variations in the meridional flow observed on the Sun should contribute to torsional oscillations. 相似文献
7.
A possible mechanism for the formation of near-polar magnetic spots on some stars with convective envelopes is proposed. The mechanism is based on the idea that the maximum of the dynamo waves that are excited in thin convective shells by the dynamo mechanism is shifted appreciably from the maximum of the magnetic-field sources in the direction of motion of the dynamo wave. If there is no region of super-rotation near the equator for some reason (as a consequence of disruption due to tidal interaction with a companion in a binary system, for example) and the wave of stellar activity propagates toward the poles rather than toward the equator, this maximum will be in the near-polar regions. 相似文献
8.
Stars similar to the Sun demonstrate super-flares, which are considerably more powerful than solar flares. It is believed that the magneticfield energies of these stars are much higher than that of the Sun. The present study attempts to explain such an anomalously high magnetic energy by resonance phenomena related to the stellar dynamo, which involve significant changes in the behavior of the solutions subject to certain external effects and satisfy certain parametric relationships. These resonance phenomena are studied using low-mode models for a dynamo occurring in two or one spherical shells. It is shown that resonance effects arising in these models can result in increases of the magnetic energies by one and a half orders of magnitude compared with nonresonance cases. It is also shown that resonance dynamo conditions can differ considerably from the simple resonance conditions used for oscillating systems. This can probably be explained by the fact that the excitation and propagation of magnetic waves in dynamo problems are closely connected with each other, so that the resonance equations remain nonlinear even when they are maximally simplified. 相似文献
9.
It is shown that a hypothetical relict magnetic field in the solar radiative-transport zone that penetrates into the convective
zone would affect the solar dynamo, resulting in radical changes in the butterfly diagrams. This would transform the traveling
waves of activity into standing waves. A comparison of our results with the well-known butterfly diagrams for the Sun gives
an upper limit of the order of some tens G for the value of relict magnetic field penetrating into the solar convective zone.
At the same time, it is not ruled out that such relict magnetic fields in other solar-type stars are strong enough to make
the activity waves become standing waves. 相似文献
10.
The statistical relationship between the summer monsoon rainfall over all India, northwest India and peninsular India, onset
dates of monsoon and the index of mid latitude, (35° to 70°N) meridional circulation at 500 hPa level over different sectors
and hemisphere based on 19 years (1971–1989) data, have been examined. The results indicate that (i) the summer monsoon rainfalls
over all India, northwest India and peninsular India show a significant inverse relationship with the strength of meridional
index during previous January over sector 45°W to 90°E. (ii) The summer monsoon rainfalls over all India and peninsular India
show a significant inverse relationship with the strength of meridional index during previous December over sector 90°E to
160°E, (iii) The summer monsoon rainfall over northwest India shows a significant direct relationship with the meridional
index during previous May over sector 160°E to 45°W.
Significant negative relationships are also observed between the meridional circulation indices of previous October (sector
3 and 4), previous December (sectors 1, 3 and 4), previous winter season (sector 3 and 4) and the onset dates of summer monsoon
over India. The meridional circulation index thus can have some possible use for long range forecasting of monsoon rainfall
over all India, northwest India and peninsular India, as well as the onset dates of monsoon. 相似文献
11.
John E. Kutzbach 《Quaternary Research》1976,6(4):471-480
The climate system consists of the atmosphere, the oceans, the cryosphere (land ice, snow, sea ice), the lithosphere, and the biomass. The behavior of the individual components of the system is governed by processes occurring over a broad range of time and space scales. The components are coupled by physical, biological, and chemical processes, and the coupled system seems capable of undergoing fluctuations on all time scales. In addition to these “internal” climatic processes, external processes (such as variability in the solar irradiance or human activities) must also be considered. Space and time scales of climatic variability are reviewed, with emphasis on the Holocene. Regional patterns of climatic variability may be associated with changes in the amplitude and longitudinal position of the long waves in the westerlies of midlatitudes, and with changes in the intensity and latitude of meridional circulation features such as the Hadley cell. Possible examples of this are mentioned. The variance spectrum of climatic time series is described and certain implications for climate modeling are suggested. 相似文献
12.
M. M. Katsova L. L. Kitchatinov M. A. Livshits D. L. Moss D. D. Sokoloff I. G. Usoskin 《Astronomy Reports》2018,62(1):72-80
Recent data from the Kepler mission has revealed the occurrence of superflares in Sun-like stars which exceed by far any observed solar flares in released energy. Radionuclide data do not provide evidence for occurrence of superflares on the Sun over the past eleven millennia. Stellar data for a subgroup of superflaring Kepler stars are analysed in an attempt to find possible progenitors of their abnormal magnetic activity. A natural idea is that the dynamo mechanism in superflaring stars differs in some respect from that in the Sun. We search for a difference in the dynamo-related parameters between superflaring stars and the Sun to suggest a dynamo mechanism as close as possible to the conventional solar/stellar dynamo but capable of providing much higher magnetic energy. Dynamo based on joint action of differential rotation and mirror asymmetric motions can in principle result in excitation of two types of magnetic fields. First of all, it is well-known in solar physics dynamo waves. The point is that another magnetic configuration with initial growth and further stabilisation can also be excited. For comparable conditions, magnetic field of second configuration is much stronger than that of the first one just because dynamo does not spend its energy for periodic magnetic field inversions but uses it for magnetic field growth. We analysed available data from the Kepler mission concerning the superflaring stars in order to find tracers of anomalous magnetic activity. As suggested in a recent paper [1], we find that anti-solar differential rotation or anti-solar sign of the mirror-asymmetry of stellar convection can provide the desired strong magnetic field in dynamo models. We confirm this concept by numerical models of stellar dynamos with corresponding governing parameters. We conclude that the proposed mechanism can plausibly explain the superflaring events at least for some cool stars, including binaries, subgiants and, possibly, low-mass stars and young rapid rotators. 相似文献
13.
14.
Space spectral analysis of zonal (u) and meridional (v) components of wind and time spectral analysis of kinetic energy of zonal waves at 850 hPa during monsoon 1991 (1st June
1991 to 31st August 1991) for the global belt between equator and 40°N are investigated. Space spectral analysis shows that
long waves (wavenumbers 1 and 2) dominate the energetics of Region 1 (equator to 20°N) while over Region 2 (20°N to 40°N)
the kinetic energy of short waves (wavenumbers 3 to 10) is more than kinetic energy of long waves. It has been found that
kinetic energy of long waves is dominated by zonal component while both (zonal and meridional) the components of wind have
almost equal contribution in the kinetic energy of short waves.
Temporal variations of kinetic energy of wavenumber 2 over Region 1 and Region 2 are almost identical. The correlation matrix
of different time series shows that (i) wavenumber 2 over Regions 1 and 2 might have the same energy source and (ii) there
is a possibility of an exchange of kinetic energy between wavenumber 1 over Region 1 and short waves over Region 2. Wave to
wave interactions indicate that short waves over Region 2 are the common source of kinetic energy to wavenumber 2 over Regions
1 and 2 and wavenumber 1 over Region 1. Time spectral analysis of kinetic energy of zonal waves indicates that wavenumber
1 is dominated by 30–45 day and bi-weekly oscillations while short waves are dominated by weekly and bi-weekly oscillations.
The correlation matrix, wave to wave interaction and time spectral analysis together suggest that short period oscillations
of kinetic energy of wavenumber 1 might be one of the factors causing dominant weekly (5–9 day) and bi-weekly (10–18 day)
oscillations in the kinetic energy of short waves. 相似文献
15.
It is shown that the meridional drift of large-scale fields starts in the equatorial zone and continues over 15–16 yrs (16–17 according to another estimate), i.e., during three fourths of the 22-year cycle. There is an abrupt retardation of the drift at latitudes of 30°–50°, and a stagnation region where the drift rate does not exceed several meters per second arises. The drift becomes rapid again at higher latitudes. The stagnation region coincides with the area in which the radial gradient of the rotational velocity is close to zero in the convective zone. This drift is compared with helio-seismological data on the rotation in the convective zone. A model taking into account some elements of dynamo theory is proposed. 相似文献
16.
P. A. MAYEWSKI T. BRACEGIRDLE I. GOODWIN D. SCHNEIDER N. A. N. BERTLER S. BIRKEL A. CARLETON M. H. ENGLAND J‐H. KANG A. KHAN J. RUSSELL J. TURNER I. VELICOGNA 《第四纪科学杂志》2015,30(5):391-395
Climate model results suggest that future climate change in Antarctica will be accompanied by continued strengthening and poleward contraction of the Southern Ocean westerly wind belt. Paleoclimate records suggest past changes in the westerly winds can be abrupt and that healing of the Antarctic ozone hole could lead to poleward contraction of the westerlies and increased meridional atmospheric transport of warm air regionally into Antarctica. An abrupt shift to more meridional circulation could lead to notable changes in moisture availability for extra‐Antarctic regions, increased Antarctic ice sheet disintegration and more rapid sea‐level rise. 相似文献
17.
M. M. Katsova L. L. Kitchatinov D. Moss K. Oláh D. D. Sokoloff 《Astronomy Reports》2018,62(8):513-519
The Kepler mission has identified huge flares on various stars, including some solar-type stars. These events are substantially more energetic than solar flares, and are referred to as superflares. Even a low probability of such a superflare occurring on the Sun would be a menace to modern society. A flare comparable in energy to that of superflares was observed on September 24 and 25, 1989 on the binary HK Lac. Unlike the Kepler stars, observations of differential rotation are available for HK Lac. This differential rotation appears to be anti-solar. In the case of anti-solar differential rotation, dynamo models can producemagnetic-activity waves with dipolare symmetry, as well as quasi-stationary magnetic configurations with quadrupolar symmetry. The magnetic energy of such stationary configurations is usually about two orders of magnitude higher than the energy associated with activity waves. We believe that this mechanism could provide sufficient energy to produce superflares on late-type stars. Some simple models in support of this idea are presented. 相似文献
18.
The stability analyses of the stream function at the upper atmosphere have been conducted using a global barotropic spectral
model with a view to examine the seasonal characteristics. The growing eigen modes are classified into three groups with periods
in the range of 3–8, 11–18 and 20–50 days. This study indicates that the growth and movement of all the three types of modes
are adequately sustained by the asymmetric basic flow. All the modes grow faster in summer than in winter. The meridional
shear of the basic flow is the most important source of growth of the perturbations. In the absence of the meridional wind
shear, the eigen modes grow slowly, in which case, the quasi-nonlinear triad interaction between the waves is identified to
contribute significantly to the growth of the modes. The robustness of the eigen modes is also examined in this study using
the barotropic model at different horizontal resolutions in the triangular truncation scheme. 相似文献
19.
Sourabh Bal Semjon Schimanke Thomas Spangehl Ulrich Cubasch 《Journal of Earth System Science》2017,126(2):19
Sudden stratospheric warming (SSW) events are identified to investigate their influence on the equatorial tropospheric climate. Composite analysis of warming events from Era-Interim (1979–2013) record a cooling of the tropical lower stratosphere with corresponding changes in the mean meridional stratospheric circulation. A cooling of the upper troposphere induces enhanced convective activity near the equatorial region of the Southern Hemisphere and suppressed convective activity in the off-equatorial Northern Hemisphere. After selecting vortex splits, the see-saw pattern of convective activity in the troposphere grows prominent and robust. 相似文献
20.
Catherine A. Jessen Sandrine Solignac Niels Nørgaard‐Pedersen Naja Mikkelsen Antoon Kuijpers Marit‐Solveig Seidenkrantz 《第四纪科学杂志》2011,26(3):286-296
Variability in the abundance of exotic (non‐native) pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation, but the difficulty of gaining sufficient total exotic pollen and the incomplete understanding of atmospheric pollen transport patterns has hindered its application. In light of recent advances in the study of pollen transport, we present an exotic pollen record from two fjord sediment cores taken from the west (Placentia Bay, Newfoundland) and east (Narsaq Sund, Greenland) Labrador Sea as a basis for studying variations in regional atmospheric circulation. The two cores cover the last ca. 5500 years and indicate a shift in dominant spring/summer air masses at ca. 2000 (southern Greenland) and 3000 cal a BP (Newfoundland) transporting reduced concentrations of pollen from southerly and south‐westerly vegetation zones. This may suggest a shift away from more dominantly zonal atmospheric circulation (a feature of positive North Atlantic Oscillation years) to more frequent meridional circulation. These results support sea ice/sea‐surface temperature proxy reconstructions from Newfoundland, investigated as part of the same project, which also suggest increased winter atmospheric circulation during the early part of the time period studied. In this region, more positive North Atlantic Oscillation years, and therefore more zonal atmospheric circulation, are associated with increased atmospheric circulation in both the winter and the summer seasons. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献