Abstract. Variations in Northern Hemisphere ice volume over the past 3 million years have been described in numerous studies and well documented. These studies depict the mid-Pleistocene transition from 40 kyr oscillations of global ice to predominantly 100 kyr oscillations around 1 million years ago. It is generally accepted to attribute the 40 kyr period to astronomical forcing and to attribute the transition to the 100 kyr mode to a phenomenon caused by a slow trend, which around the mid-Pleistocene enabled the manifestation of nonlinear processes. However, both the physical nature of this nonlinearity and its interpretation in terms of dynamical systems theory are debated. Here, we show that ice-sheet physics coupled with a linear climate temperature feedback conceal enough dynamics to satisfactorily explain the system response over the full Pleistocene. There is no need, a priori, to call for a nonlinear response of the carbon cycle. Without astronomical forcing, the obtained dynamical system evolves to equilibrium. When it is astronomically forced, depending on the values of the parameters involved, the system is capable of producing different modes of nonlinearity and consequently different periods of rhythmicity. The crucial factor that defines a specific mode of system response is the relative intensity of glaciation (negative) and climate temperature (positive) feedbacks. To measure this factor, we introduce a dimensionless variability number, V. When positive feedback is weak (V∼0), the system exhibits fluctuations with dominating periods of about 40 kyr which is in fact a combination of a doubled precession period and (to smaller extent) obliquity period. When positive feedback increases (V∼0.75), the system evolves with a roughly 100 kyr period due to a doubled obliquity period. If positive feedback increases further (V∼0.95), the system produces fluctuations of about 400 kyr. When the V number is gradually increased from its low early Pleistocene values to its late Pleistocene value of V∼0.75, the system reproduces the mid-Pleistocene transition from mostly 40 kyr fluctuations to a 100 kyr period rhythmicity. Since the V number is a combination of multiple parameters, it implies that multiple scenarios are possible to account for the mid-Pleistocene transition. Thus, our theory is capable of explaining all major features of the Pleistocene climate, such as the mostly 40 kyr fluctuations of the early Pleistocene, a transition from an early Pleistocene type of nonlinear regime to a late Pleistocene type of nonlinear regime, and the 100 kyr fluctuations of the late Pleistocene. When the dynamical climate system is expanded to include Antarctic glaciation, it becomes apparent that climate temperature positive feedback (or its absence) plays a crucial role in the Southern Hemisphere as well. While the Northern Hemisphere insolation impact is amplified by the outside-of-glacier climate and eventually affects Antarctic surface and basal temperatures, the Antarctic ice-sheet area of glaciation is limited by the area of the Antarctic continent, and therefore it cannot engage in strong positive climate feedback. This may serve as a plausible explanation for the synchronous response of the Northern and Southern Hemisphere to Northern Hemisphere insolation variations. Given that the V number is dimensionless, we consider that this model could be used as a framework to investigate other physics that may possibly be involved in producing ice ages. In such a case, the equation currently representing climate temperature would describe some other climate component of interest, and as long as this component is capable of producing an appropriate V number, it may perhaps be considered a feasible candidate.
Abstract. The long-term evolution of scaling (fractal) characteristics of the ULF geomagnetic fields in the seismoactive region of the Guam Island is studied in relation to the strong (Ms = 8.0) nearby earthquake of 8 August 1993. The selected period covers 10 months before and 10 months after the earthquake. The FFT procedure, Burlaga-Klein approach and Higuchi method, have been applied to calculate the scaling exponents and fractal dimensions of the ULF time series. It is found that the spectrum of ULF emissions exhibits, on average, a power law behaviour S(f ) ∝ f −β , which is a fingerprint of the typical fractal (self-affine) time series. The spectrum slope β fluctuates quasi-periodically during the course of time in a range of β = 2.5−0.7, which corresponds to the fractional Brownian motion with both persistent and antipersistent behaviour. An tendency is also found for the spectrum slope to decrease gradually when approaching the earthquake date. Such a tendency manifests itself at all local times, showing a gradual evolution of the structure of the ULF noise to a typical flicker noise structure in proximity to the large earthquake event. We suggest considering such a peculiarity as an earthquake precursory signature. One more effect related to the earthquake is revealed: the longest quasiperiod, which is 27 days, disappeared from the variations of the ULF emission spectrum slope during the earthquake, and it reappeared three months after the event. Physical interpretation of the peculiarities revealed has been done on the basis of the SOC (self-organized criticality) concept.
The empirical description of the shape of the sunspot cycle is one of the oldest problems of solar physics. Here we show that an accurate two-parameter fit is achievable where the parameters are correlated (r = 0.88) for 23 solar cycles. The correlation between the parameters of our fit provides the possibility of a one-parameter fit if the times of the minima are known a priori. A one-parameter fit can also be derived from truncated dynamo models, but the goodness of the fit is not better than as achieved for the empirical fit. We suggest that the goodness of a one-parameter fit can serve as a criterion to compare different dynamo models. A one-parameter fit provides the possibility to forecast the shape of the coming cycle via a forecast of one parameter which changes synchronously with the secular variation. A previous estimation of the coming decadal average sunspot number is converted into the forecast of the shape of the 24th cycle with a maximum of 118 ± 26 W. The accuracy is limited mostly by the uncertainties of the predicted secular variation and the uncertainty of the time of the minimum.
In this work a new information resource located at http://www.gao.spb.ru/database/esai and hereinafter referred to as ESAI ("Extended time series of Solar Activity Indices") is presented. ESAI includes observational, synthetic and simulated sets to study solar magnetic field variations and their influence on the Earth. ESAI extends the ordinary lengths of some traditional indices, parameterizing time variations of physically different characteristics of solar activity. In particular, long-term sets of the following indices are presented: sunspot areas, the Wolf numbers, polar faculae numbers, sunspot mean latitudes and north-south asymmetry of hemispheres for different components of activity. Some methods for making correct conclusions from incomplete data and some criteria to estimate the reliability of the obtained information are discussed.
Abstract. Variations of NorthernHemisphere ice volume over the past 3 million years have been described in numerous studies and well documented. These studies depict the mid-Pleistocene transition from 40-ky oscillations of global ice to predominantly 100-ky oscillations around 1 million years ago. It is generally accepted to attribute the 10 40-ky period to astronomical forcing, and to attribute the transition to the 100-ky mode to a phenomenon caused by a slow trend which, around the mid-Pleistocene, enabled the manifestation of non-linear processes. However, both the physical nature of this non-linearity, and its interpretation in terms of dynamical systems theory, are debated. Here, we show that ice sheet physics, coupled with a linear ocean feedback, conceal enough dynamics to satisfactorily explain the system response over the full Pleistocene. There is no need, a priori, to call for a non-linear 15 response of the carbon cycle. Without astronomical forcing, the obtained dynamical system evolves to equilibrium. When it is astronomically forced, then, depending on the values of parameters involved, the system is capable of producing different modes of non-linearity and consequently -different periods of rhythmicity. The crucial factor that defines a specific mode of system response is the relative intensity of glaciation and ocean feedbacks. To measure this factor, we introduce a dimensionless variability number V. When ocean positive feedback is weak 20 (V~0), the system exhibits fluctuations with dominating periods of about 40 ky which is in fact a combination of doubled precession period and (to smaller extent) obliquity period. When ocean positive feedback increases (V~0.75), the system evolves with a roughly 100-ky period due to doubled obliquity period. If ocean positive feedback increases further (V~0.95), the system produces fluctuations of about 400 ky. When V-number is gradually increased from its low early Pleistocene values to its late Pleistocene value of V~0.75, the system reproduces mid- 25Pleistocene transition from mostly 40-ky fluctuations to 100-ky-period rhythmicity. Since V-number is a combination of multiple parameters, it implies that multiple scenarios are possible to account for the midPleistocene transition. Thus, our theory is capable to explain all major features of the Pleistocene climate such as mostly 40-ky fluctuations of the early Pleistocene, a transition from an early Pleistocene type of non-linear regime to a late Pleistocene type of non-linear regime, and 100-ky fluctuations of the late Pleistocene.
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