scholarly journals How sensitive are modeled contemporary subsea permafrost thaw and thickness of the methane clathrates stability zone in Eurasian Arctic to assumptions on Pleistocene glacial cycles?

2016 ◽  
Author(s):  
Valentina V. Malakhova ◽  
Alexey V. Eliseev
Keyword(s):  
Time Scales ◽  
Thermal State ◽  
Initial Conditions ◽  
Single Point ◽  
Ice Core ◽  
Oceanic Water ◽  
Stability Zone ◽  
Glacial Cycles ◽  
The Impact ◽  
Subsea Permafrost

Abstract. Single-point simulations with a model for thermal state of subsea sediments driven by the forcing constructed from the ice core data show that the impact of initial conditions is lost after ~ 100 kyr. The time scales of temperature propagation in sediments and respective permafrost response are ~ 10–20 kyr which is longer than the present interglacial. The timings of shelf exposure during oceanic regressions and flooding during transgressions are important for representation of sediment thermal state and hydrates stability zone (HSZ). These timings should depend on the contemporary shelf depth (SD). During glacial cycles temperature at the top of sediments is a major driver of HSZ vertical boundaries change for SD of few tens of meters, while the pressure exerted by oceanic water becomes more important for larger SD. Thus, even the existence of HSZ and its disappearance might not be easily tied to oceanic transgressions and regressions.

scholarly journals The role of boundary and initial conditions for dynamical seasonal predictability

2003 ◽  
Vol 10 (3) ◽  
pp. 211-232 ◽  
Author(s):  
T. J. Reichler ◽  
J. O. Roads
Keyword(s):  
Boundary Conditions ◽  
Time Scales ◽  
General Circulation ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Circulation Model ◽  
Forecast Skill ◽  
Initial State ◽  
Tropical Forcing ◽  
The Impact

Abstract. The importance of initial state and boundary forcing for atmospheric predictability is explored on global to regional spatial scales and on daily to seasonal time scales. A general circulation model is used to conduct predictability experiments with different combinations of initial and boundary conditions. The experiments are verified under perfect model assumptions as well as against observational data. From initial conditions alone, there is significant instantaneous forecast skill out to 2 months. Different initial conditions show different predictability using the same kind of boundary forcing. Even on seasonal time scales, using observed atmospheric initial conditions leads to a substantial increase in overall skill, especially during periods with weak tropical forcing. The impact of boundary forcing on predictability is detectable after 10 days and leads to measurable instantaneous forecast skill at very long lead times. Over the Northern Hemisphere, it takes roughly 4 weeks for boundary conditions to reach the same effect on predictability as initial conditions. During events with strong tropical forcing, these time scales are somewhat shorter. Over the Southern Hemisphere, there is a strongly enhanced influence of initial conditions during summer. We conclude that the long term memory of initial conditions is important for seasonal forecasting.

Ensemble decadal predictions from analysed initial conditions

2007 ◽  
Vol 365 (1857) ◽  
pp. 2179-2191 ◽  
Author(s):  
Alberto Troccoli ◽  
T.N Palmer
Keyword(s):  
Time Scales ◽  
Initial Conditions ◽  
Coupled Model ◽  
Seasonal Prediction ◽  
Model Configuration ◽  
Global Cooling ◽  
The Impact ◽  
Climatic Signals ◽  
Different Levels ◽  
Initialization Procedure

Sensitivity experiments using a coupled model initialized from analysed atmospheric and oceanic observations are used to investigate the potential for interannual-to-decadal predictability. The potential for extending seasonal predictions to longer time scales is explored using the same coupled model configuration and initialization procedure as used for seasonal prediction. It is found that, despite model drift, climatic signals on interannual-to-decadal time scales appear to be detectable. Two climatic states have been chosen: one starting in 1965, i.e. ahead of a period of global cooling, and the other in 1994, ahead of a period of global warming. The impact of initial conditions and of the different levels of greenhouse gases are isolated in order to gain insights into the source of predictability.

Numerical modeling of the thermal state of Earth after the Moon-forming impact event

2021 ◽  
Author(s):  
Laetitia Allibert ◽  
Nicole Güldemeister ◽  
Lukas Manske ◽  
Miki Nakajima ◽  
Kai Wünnemann
Keyword(s):  
Thermal State ◽  
Initial Conditions ◽  
Thermal Evolution ◽  
Three Dimensional ◽  
Impact Angle ◽  
Impact Event ◽  
The Moon ◽  
Magma Ocean ◽  
Self Gravity ◽  
The Impact

<p align="justify">Planetary collisions play an important role in the compositional and thermal evolution of planetary systems and such collisions are caracteristics of the final stage of planetary formation. The Moon-forming impact event is thought to (re)set the conditions for the subsequent thermochemical evolution of Earth and Moon. Large parts of proto-Earth are thought to melt as a consequence of the impact [e.g.1] and the extent of melting affects the evolution of the Earth’s interior and atmosphere. It is then critical to address the initial conditions of the proto-Earth and the volume and shape of a possible magma ocean after the impact. Previously, the Moon-forming giant impact was modeled with mesh-free so-called smoothed particle hydrodynamics (SPH [1, 2, 3]). In this study, we, in contrast, carried out numerical simulations of the Moon-forming impact event considering different impact scenarios with the three-dimensional (3D) iSALE code [4, 5], that tends to be more accurate in the description of thermodynamics and shock waves than SPH simulations. We also compare simulation results from our iSALE code with SPH models for benchmarking ([1]) because SPH uses self-gravity, whereas iSALE uses central gravity. We vary the impact angle (15° to 90°) and impact velocities (12 to 20 km/s). In order to quantify the volume of impact-induced melt, we use the so-called peak-shock pressure approach (‘Tracer method’) that has been used in several modeling studies [6,7] and is described in more detail by [8].</p> <p align="justify">The benchmark study shows a good agreement of the two different numerical approaches with respect to pressure evolution. However the production of a magma ocean show some differences that need to be further explored, with notably the effects of considering central gravity instead of self-gravity into iSALE 3D simulations.</p> <p align="justify"> </p> <p align="justify"><strong>Acknowledgments</strong>: We gratefully thank the iSALE developers, including Gareth Collins, Kai Wünnemann, Dirk Elbeshausen, Boris Ivanov and Jay Melosh and Thomas Davison for the development of the pysaleplot tool. We also thank the Deutsche Forschungsgemeinschaft (SFB-TRR 170, subproject C2 and C4) for funding.</p> <p align="justify"> </p> <p align="justify"><strong>References</strong>:[1] Nakajima M. and Stevenson D. J. (2015) EPSL, 427, 286-295. [2] Canup R. M. et al. (2013) ICARUS 222, 200-219. [3] Canup R, M. (2004) Science 338, 1052-1054. [4] Collins G. S. et al. (2004) Meteoritics & Planet. Sci., 39, 217-231. [5] Wünnemann K. (2006) ICARUS 180, 514-527. [6] Wünnemann K. et al. (2008) EPSL 269, 529-538. [7] Pierazzo et al. (1997) ICARUS 127, 408-423. [8] Manske L. et al. (2018) 49th LPSC, abstract# 2269.[11] Pierazzo and Melosh (1999) EPSL 165, 163-176</p>

scholarly journals Impact of Initial Conditions versus External Forcing in Decadal Climate Predictions: A Sensitivity Experiment*

2015 ◽  
Vol 28 (11) ◽  
pp. 4454-4470 ◽  
Author(s):  
Susanna Corti ◽  
Tim Palmer ◽  
Magdalena Balmaseda ◽  
Antje Weisheimer ◽  
Sybren Drijfhout ◽  
...  
Keyword(s):  
Time Scales ◽  
Prediction Models ◽  
Initial Conditions ◽  
Heat Content ◽  
Meridional Overturning Circulation ◽  
Northwestern Pacific ◽  
External Forcing ◽  
Sensitivity Experiment ◽  
External Forcings ◽  
The Impact

Abstract The impact of initial conditions relative to external forcings in decadal integrations from an ensemble of state-of-the-art prediction models has been assessed using specifically designed sensitivity experiments (SWAP experiments). They consist of two sets of 10-yr-long ensemble hindcasts for two initial dates in 1965 and 1995 using either the external forcings from the “correct” decades or swapping the forcings between the two decades. By comparing the two sets of integrations, the impact of external forcing versus initial conditions on the predictability over multiannual time scales was estimated as the function of lead time of the hindcast. It was found that over time scales longer than about 1 yr, the predictability of sea surface temperatures (SSTs) on a global scale arises mainly from the external forcing. However, the correct initialization has a longer impact on SST predictability over specific regions such as the North Atlantic, the northwestern Pacific, and the Southern Ocean. The impact of initialization is even longer and extends to wider regions when below-surface ocean variables are considered. For the western and eastern tropical Atlantic, the impact of initialization for the 700-m heat content (HTC700) extends to as much as 9 years for some of the models considered. In all models the impact of initial conditions on the predictability of the Atlantic meridional overturning circulation (AMOC) is dominant for the first 5 years.

scholarly journals On Kaufmann's theory of the impact of the pianoforte hammer

1920 ◽  
Vol 97 (682) ◽  
pp. 99-110 ◽  
Keyword(s):  
Initial Conditions ◽  
Practical Importance ◽  
Prima Facie ◽  
Point Of View ◽  
Infinite Length ◽  
Modes Of Vibration ◽  
Rigorous Treatment ◽  
The Subject ◽  
Set Up ◽  
The Impact

The theory of the vibrations of the pianoforte string put forward by Kaufmann in a well-known paper has figured prominently in recent discussions on the acoustics of this instrument. It proceeds on lines radically different from those adopted by Helmholtz in his classical treatment of the subject. While recognising that the elasticity of the pianoforte hammer is not a negligible factor, Kaufmann set out to simplify the mathematical analysis by ignoring its effect altogether, and treating the hammer as a particle possessing only inertia without spring. The motion of the string following the impact of the hammer is found from the initial conditions and from the functional solutions of the equation of wave-propagation on the string. On this basis he gave a rigorous treatment of two cases: (1) a particle impinging on a stretched string of infinite length, and (2) a particle impinging on the centre of a finite string, neither of which cases is of much interest from an acoustical point of view. The case of practical importance treated by him is that in which a particle impinges on the string near one end. For this case, he gave only an approximate theory from which the duration of contact, the motion of the point struck, and the form of the vibration-curves for various points of the string could be found. There can be no doubt of the importance of Kaufmann’s work, and it naturally becomes necessary to extend and revise his theory in various directions. In several respects, the theory awaits fuller development, especially as regards the harmonic analysis of the modes of vibration set up by impact, and the detailed discussion of the influence of the elasticity of the hammer and of varying velocities of impact. Apart from these points, the question arises whether the approximate method used by Kaufmann is sufficiently accurate for practical purposes, and whether it may be regarded as applicable when, as in the pianoforte, the point struck is distant one-eighth or one-ninth of the length of the string from one end. Kaufmann’s treatment is practically based on the assumption that the part of the string between the end and the point struck remains straight as long as the hammer and string remain in contact. Primâ facie , it is clear that this assumption would introduce error when the part of the string under reference is an appreciable fraction of the whole. For the effect of the impact would obviously be to excite the vibrations of this portion of the string, which continue so long as the hammer is in contact, and would also influence the mode of vibration of the string as a whole when the hammer loses contact. A mathematical theory which is not subject to this error, and which is applicable for any position of the striking point, thus seems called for.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

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