کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4741344 1641482 2016 16 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
A gaussian model for simulated geomagnetic field reversals
ترجمه فارسی عنوان
یک مدل گاوسی برای شبیهسازی میدانهای زمینشناسی
کلمات کلیدی
ژیودینامو، معکوس میدان، گشت و گذار در میدان، شبیه سازی عددی
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات فیزیک زمین (ژئو فیزیک)
چکیده انگلیسی


• Our simulations show that the dynamics of the axial dipole decides whether the dynamo reverses.
• Reversals happen when the mean axial dipole moment is low enough so that fluctuations can lead to reversals.
• Dipole moment larger than 60
• Reversals and excursion become likely once the dipole moment has dropped to 30
• The axial dipole moment tends to linger in a weak configuration around reversals and excursions.

Field reversals are the most spectacular events in the geomagnetic history but remain little understood. Here we explore the dipole behaviour in particularly long numerical dynamo simulations to reveal statistically significant conditions required for reversals and excursions to happen. We find that changes in the axial dipole moment behaviour are crucial while the equatorial dipole moment plays a negligible role. For small Rayleigh numbers, the axial dipole always remains strong and stable and obeys a clearly Gaussian probability distribution. Only when the Rayleigh number is increased sufficiently the axial dipole can reverse and its distribution becomes decisively non-Gaussian. Increased likelihoods around zero indicate a pronounced lingering in a new low dipole moment state. Reversals and excursions can only happen when axial dipole fluctuations are large enough to drive the system from the high dipole moment state assumed during stable polarity epochs into the low dipole moment state. Since it is just a matter of chance which polarity is amplified during dipole recovery, reversals and grand excursions, i.e. excursions during which the dipole assumes reverse polarity, are equally likely. While the overall reversal behaviour seems Earth-like, a closer comparison to palaeomagnetic findings suggests that the simulated events last too long and that grand excursions are too rare. For a particularly large Ekman number we find a second but less Earth-like type of reversals where the total field decays and recovers after a certain time.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Physics of the Earth and Planetary Interiors - Volume 259, October 2016, Pages 45–60
نویسندگان
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