The nonlinear solar dynamo and differential rotation: A Taylor number puzzle?     

A. Brandenburg  D. Moss  G. Rüdiger  I. Tuominen 《Solar physics》1990,128(1):243-251

We consider dynamically consistent mean-field dynamos in a spherical shell of incompressible fluid. The generation of magnetic field and differential rotation is parameterized by the - and -effects, respectively. Extending previous investigations, we include now the cases of moderate and rapid rotation in the sense that the inverse Rossby number can approach or exceed unity: This can lead to disk-shaped -contours, which are in better accordance with recent results of helioseismology than cylindrical -contours. On the other hand, in order to obtain -dynamo cycles the Taylor number has to be so large, that eventually cylindrical -contours become unavoidable (cf. Taylor-Proudman theorem). We discuss the different possibilities in a state diagram, where the inverse Rossby number and the relative correlation length are taken as the elementary parameters for mean-field dynamos.  相似文献   

Rainfall thresholds for landsliding in the Himalayas of Nepal   总被引：5，自引：0，他引：5  

Emmanuel J. Gabet  Douglas W. Burbank  Jaakko K. Putkonen  Beth A. Pratt-Sitaula  Tank Ojha 《Geomorphology》2004,63(3-4):131-143

Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure.  相似文献   

Gravity change and land uplift in Fennoscandia 1966–1984     

Martin Ekman  Jaakko Mäkinen  Age Midtsundstad  Ole Remmer 《Journal of Geodesy》1987,61(1):60-64

An analysis is made of the results from all repeated gravity measurements of the Fennoscandian land uplift gravity line 63°. The line is, thereby, divided into two separate parts: one part west of the land uplift maximum, and the other part east of the land uplift maximum. A statistically significant change of gravity is found both for the western part and the eastern one. Both parts give a relation between gravity change and land uplift of about ?0.22μgal/mm.  相似文献   

Eighteen years of observations on the Fennoscandian land uplift gravity lines     

Jaakko Mkinen 《Journal of Geodynamics》1987,8(2-4)

In order to investigate the variation in gravity caused by the Fennoscandian land uplift, the Nordic countries have established 4 profiles with near-zero gravity differences along the latitudes 65°, 63°, 61° and 56° N. High-precision gravity measurements have been repeatedly made on these lines since 1975, 1966, 1976 and 1977, respectively. The observations have recently been published in one volume.  相似文献   

Driving Galactic Turbulence by Supernova Explosions     

Korpi  Maarit J.  Brandenburg  A.  Tuominen  I. 《Studia Geophysica et Geodaetica》1998,42(3):410-418

We investigate the general properties of supernova driven interstellar turbulence using local three-dimensional MHD simulations under Galactic conditions. Our model includes the effects of large-scale shear due to Galactic differential rotation, density stratification, compressibility, magnetic fields, heating via supernova explosions and parameterized radiative cooling of the interstellar medium. In addition to investigating isolated supernova explosions we allow for multiple supernovae distributed randomly in the Galactic disc and exponentially in the vertical direction. Single supernova explosions drive a strong shock, the lifetime of which is approximately 2 Myr in our model. This stage is found to be characterized by a kinetic energy spectrum in the diffuse gas with spectral index consistent with k = –2. Large-scale shear and Coriolis force act on the supernova remnant producing some vorticity inside it, but this process was found to be very weak. In the case of multiple supernova explosions, older remnants have an important role causing density fluctuations in the interstellar medium. In this clumpy medium, the propagation velocity of the shock fronts changes due to the changing density, and vorticity is generated. In the absence of these supernova interactions the kinetic energy spectrum shows a relatively wide shock spectrum with spectral index k = –2, but when the supernova interactions become dominant the classical k = –5/3 spectrum is observed.  相似文献   

Secular variation of hemispheric phase differences in the solar cycle     

N.V. Zolotova  D.I. Ponyavin  R. Arlt  I. Tuominen 《Astronomische Nachrichten》2010,331(8):765-771

  相似文献   

Does the Sun have a face?     

I. Tuominen  J. Pelt  J. Brooke  M. Korpi 《Astronomische Nachrichten》2007,328(10):1020-1022

We analyse the Greenwich sunspot data with methods using kinematic frames, which allow to detect and filter off any systematic motion, such as differential rotation, of the longitudinal activity traces. The aim is to check the recent claim of the existence of century-scale persistent solar active longitudes exhibiting antisolar differential rotation. As a result, we find no evidence for such features. Nevertheless, as is well known, the sunspot distribution is highly clustered in longitude (activity nests); the simple cell-counting statistics allows us to estimate the coherence time of these features, giving roughly10 Carrington rotations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Slow regolith degradation without creep determined by cosmogenic nuclide measurements in Arena Valley, Antarctica     

Jaakko Putkonen  Greg Balco  Daniel Morgan 《Quaternary Research》2008,69(2):242-249

Estimates of regolith degradation in the McMurdo Dry Valleys of Antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces. On the other hand, the existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are younger than the age of surface deposits inferred from stratigraphic relations. This suggests some combination of surface erosion or past ice cover, both of which would reduce the apparent exposure age. This paper quantifies the regolith degradation and/or past ice cover by measuring ¹⁰Be and ²⁶Al from a landslide deposit that contains 11.3 Ma volcanic ash. The surface sample yields an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice, and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit (2 m Ma⁻¹) is taken into account. Soil creep, which is a common degradational process in a wide variety of environments, is non-existent at this field site, which likely reflects the persistent lack of bio- and cryoturbation.  相似文献   

The permanent tide in GPS positioning     

Markku Poutanen  Martin Vermeer  Jaakko Mäkinen 《Journal of Geodesy》1996,70(8):499-504

The treatment of the permanent tidal deformation of the Earth in GPS computation has been an almost unmentioned topic in the GPS literature. However, the ever increasing accuracy and the need to combine the GPS based coordinates with other methods requires a consistent way to handle the tides. Our survey shows that both the ITRF-xx coordinates and the GPS based coordinates are nowadays reduced to a non-tidal crust, conventionally defined using physically meaningless parameters. We propose to use instead the zero-crust concept which corresponds to concepts already accepted in the resolution of IAG in 1983 for gravimetric works.  相似文献   

On the mean zonal and meridional circulations and the flux of moisture in the northern hemisphere during the summer season   总被引：6，自引：0，他引：6  

Lauri A. Vuorela  Ilkka Tuominen 《Pure and Applied Geophysics》1964,57(1):167-180

Summary The mean zonal and meridional wind components of the northern hemisphere at different pressure levels for the summer season June–August have been determined and the mean meridional mass circulation has been computed as a function of latitude. From the mass circulation the meridional flux of moisture is computed for the latitudinal belt 0°–45° N. Using the horizontal divergence of this flux the average difference between precipitation and evapotranspiration from the earth's surface is evaluated.  相似文献