Variations in the geomagnetic dipole moment during the Holocene and the past 50 kyr     

Mads Faurschou Knudsen  Peter Riisager  Fabio Donadini  Ian Snowball  Raimund Muscheler  Kimmo Korhonen  Lauri J. Pesonen 《Earth and Planetary Science Letters》2008,272(1-2):319-329

All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMAGIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50  kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides (¹⁰Be and ¹⁴C). This comparison generally lends support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding  40  kyr, and that  4 · 10²²  Am² appears to represent a critical threshold below which geomagnetic excursions and reversals occur.  相似文献   

Constraints on majoron models, neutrino masses and baryogenesis     

James M. Cline  Kimmo Kainulainen  Keith A. Olive 《Astroparticle Physics》1993,1(4):387-398

We derive strong constraints on the Yukawa couplings and the vacuum expectation value in the singlet majoron model. The presence of a small gravitationally induced mass for the majoron can be used to set a constraint on its vacuum expectation value. If the singlet symmetry breaking scale is larger than the electroweak symmetry breaking scale, lepton number violating interactions in equilibrium with electroweak sphaleron interactions would destroy any prior baryon asymmetry. If the baryon asymmetry is not generated at the electroweak scale or later, strong bounds on the Yukawa couplings h 10⁻⁷ and VEVs v_s < v_EW are derived. We also carefully rederive baryogenesis bounds on neutrino masses, finding that in general they apply not to the masses themselves, but only to related parameters, and they are numerically somewhat less stringent than has previously been claimed.  相似文献   

Retention of mercury in sediments of the Baltic Sea near Oulu,Finland     

Kimmo Tolonen  Erkki Alasaarela  Anita Liehu 《Journal of Paleolimnology》1988,1(2):133-140

Several cores were compared to elucidate the grade of mercury retention in sediments of the Baltic Sea near Oulu, Finland. The known history of the mercury discharge to waste water from a chlor-alkali plant, the primary pollution source, was compared to that in the sedimentary record. One core was dated by lead-210 and varve counts. During the past thirty years, the rate of sedimentation was up to 10 mm per year corresponding to a dry matter accumulation rate of about 3 kg m^–2a^–1. Under these conditions, most of the mercury reaching the sediment was retained. Correspondingly, the mercury levels in fish were considerably lower, with a delay of some five years.The present mercury content of the upper layers is some 1/4 or 1/5 that of the late 1970's, but it is still some twentyfold compared to levels at the beginning of the century. The extent to which the present mercury level in the sediment represents the various phases of industrial emission remains unsolved due to the origin of mercury in this sea area from several other sources and due to difficulties in exact core correlations from different years.  相似文献   

Why we study the geological record for evidence of the solar oscillation about the galactic midplane     

John J. Matese  Patrick G. Whitman  Kimmo A. Innanen  Mauri J. Valtonen 《Earth, Moon, and Planets》1995,71(3):7-12

The Solar System oscillates about the plane defined by the disk of matter in our Galaxy. This oscillatory motion gives rise to a substantial modulation in the tidally induced flux of Oort cloud comets. An observational determination of the quasi-periodicity of this motion carries with it significant information about the population, distributions, dynamics and origins of short-period and long-period comets. An additional incentive for emphasizing such a study is the information about dark disk matter that a period can yield. If dark disk matter is completely negligible, the amplitude of the solar motion will be sufficiently large that the peak-to-trough flux ratio will be 2.5 and the plane-crossing period will exceed 40 Myr. Dark disk matter comparable in mass to bright disk matter and distributed in any manner is inconsistent with K-dwarf distributions and can be rejected as a working hypothesis. But if a modest fraction of the disk matter is dark and distributed like the interstellar medium, as is consistent with limits deduced from K-giant and K-dwarf velocity distributions, the peak-to-trough flux ratio can increase to a factor of 4 even though the solar z amplitude is decreased. In that case the period can be as little as 30 Myr and the implied Oort population is smaller by a factor of 3. We should carefully reconsider the geological record as a potential discriminator of these options.  相似文献   

Origins of Early Mesozoic granitoids and their enclaves from West Kunlun,NW China: implications for evolving magmatism related to closure of the Paleo-Tethys ocean     

Chao Wang  Liang Liu  Fawna Korhonen  Wen-Qiang Yang  Yu-Ting Cao  Shi-Ping He  Xiao-Hui Zhu  Wen-Tian Liang 《International Journal of Earth Sciences》2016,105(3):941-964

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Geometric test field calibration of digital photogrammetric sensors   总被引：1，自引：0，他引：1  

Eija Honkavaara  Eero Ahokas  Juha Hyypp  Juha Jaakkola  Harri Kaartinen  Risto Kuittinen  Lauri Markelin  Kimmo Nurminen 《ISPRS Journal of Photogrammetry and Remote Sensing》2006,60(6):387

Test field system calibration will be a fundamental part of the future photogrammetric production line. Accurate calibration and performance evaluations are necessary for fully assessing the stability and accuracy of digital sensing techniques. In this paper, a method of comprehensive geometric calibration in a test field has been developed and empirically tested using eight image blocks collected with three UltraCamD digital large format photogrammetric cameras. Permanent photogrammetric test fields form the basis of the method. Important components of the method are determination of system parameters, evaluation of systematic errors, and assessment of geometric accuracy. The results showed that UltraCamD images contained systematic deformations that could not be modeled with single lens additional parameter models. Good point determination accuracy was obtained despite the systematic errors; the typical accuracy was 2–3 μm in image space in the horizontal coordinates and 0.05–0.09‰ of the object distance in height. One of the cameras had significantly poorer performance. In the worst cases, the horizontal accuracy was 5 μm in image space and the height accuracy was 0.18‰ of the object distance. The analog cameras gave better results than the UltraCamD, but the development of appropriate mathematical models for UltraCamD as well as improvements in digital sensors may change the situation in the near future.  相似文献   

Hygroscopicity of pre-existing particle distribution and formation of cloud droplets: a model study     

P. Korhonen  M. Kulmala  H. -C. Hansson  I. B. Svenningsson  N. Rusko 《Atmospheric Research》1996,41(3-4)

The effects of the hygroscopicity of a pre-existing particle distribution and condensation of nitric acid on cloud droplet formation were studied by using an air parcel and multicomponent condensation model. The pre-existing particle distribution used is a bimodal distribution in which the particles are assumed to be internally mixed, i.e. they are composed partly from ammonium nitrate salt and partly from some insoluble substance. The mean diameters of the distributions and the mass fraction of soluble salt were varied in the simulations. Generally, the number of activated cloud droplets was found to be increased, when the initial mass fraction of salt (i.e. the initial amount of salt) was increased. However, the effects of increased initial amount of salt on the cloud droplet formation were not straightforward in all cases studied. The effects of the condensing hygroscopic substance, with initial nitric acid concentrations of 0.1, 1.0 and 10.0 ppbv on the activation of cloud droplets were also studied. The number of activated droplets increased when the initial concentration of nitric acid was increased.  相似文献   

On the stability of high inclination Trojans     

Seppo Mikkola  Kimmo Innanen 《Earth, Moon, and Planets》1995,71(3):195-198

Numerical integrations have been performed for orbits of Venus', Earth's and Mars' Trojan-asteroid test particles in a self consistent model of the solar system to study the stability of inclined Trojan orbits. In the case of Mars low inclination orbits tend to be unstable while the contrary seems to apply to Venus and Earth, although the stability of some very high inclination orbits may not be excluded on the basis of these computations.  相似文献   

GCM-based regional temperature and precipitation change estimates for Europe under four SRES scenarios applying a super-ensemble pattern-scaling method     

Kimmo Ruosteenoja  Heikki Tuomenvirta  Kirsti Jylhä 《Climatic change》2007,81(1):193-208

Seasonal GCM-based temperature and precipitation projections for the end of the 21st century are presented for five European regions; projections are compared with corresponding estimates given by the PRUDENCE RCMs. For most of the six global GCMs studied, only responses to the SRES A2 and B2 forcing scenarios are available. To formulate projections for the A1FI and B1 forcing scenarios, a super-ensemble pattern-scaling technique has been developed. This method uses linear regression to represent the relationship between the local GCM-simulated response and the global mean temperature change simulated by a simple climate model. The method has several advantages: e.g., the noise caused by internal variability is reduced, and the information provided by GCM runs performed with various forcing scenarios is utilized effectively. The super-ensemble method proved especially useful when only one A2 and one B2 simulation is available for an individual GCM. Next, 95% probability intervals were constructed for regional temperature and precipitation change, separately for the four forcing scenarios, by fitting a normal distribution to the set of projections calculated by the GCMs. For the high-end of the A1FI uncertainty interval, temperature increases close to 10°C could be expected in the southern European summer and northern European winter. Conversely, the low-end warming estimates for the B1 scenario are ~ 1°C. The uncertainty intervals of precipitation change are quite broad, but the mean estimate is one of a marked increase in the north in winter and a drastic reduction in the south in summer. In the RCM simulations driven by a single global model, the spread of the temperature and precipitation projections tends to be smaller than that in the GCM simulations, but it is possible to reduce this disparity by employing several driving models for all RCMs. In the present suite of simulations, the difference between the mean GCM and RCM projections is fairly small, regardless of the number or driving models applied.  相似文献   

Photospheric and chromospheric activity on EY Dra     

H. Korhonen  K. Brogaard  K. Holhjem  S. Ramstedt  J. Rantala  C.C. Thne  K. Vida 《Astronomische Nachrichten》2007,328(9):897-903

Magnetic activity in the photosphere and chromosphere of the M dwarf EY Dra is studied and possible correlations between the two are investigated using photometric observations in the V and R bands and optical and near infrared spectroscopy. The longitudinal spot configuration in the photosphere is obtained from the V band photometry, and the chromospheric structures are investigated using variations in the Hα line profile and observations of the Paschen β line. The shape of the V band light‐curve indicates two active regions on the stellar surface, about 0.4 in phase apart. The spectroscopic observations show enhanced Hα emission observed close to the phases of the photometrically detected starspots. This could indicate chromospheric plages associated with the photospheric starspots. Some indications of prominence structures are also seen. The chromospheric pressure is limited to log m_TR < –4 based on the non‐detection of emission in the Paschen β wavelength region. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献