کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
6428403 1634745 2015 7 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
A power spectrum for the geomagnetic dipole moment
ترجمه فارسی عنوان
یک طیف قدرت برای لحظه ای دو قطبی زمین شناسی
کلمات کلیدی
جودینامو، طیف ژئومغناطیس، مدل تصادفی
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
چکیده انگلیسی


- Stochastic model is used derive a power spectrum for the geomagnetic field.
- Spectrum has the form f−n, where n=0,2,4,… takes even integer values.
- Observed transition in paleomagnetic spectrum provides evidence for high electrical conductivity.

We use stochastic models for fluctuations in the dipole moment to derive a geomagnetic power spectrum. The theoretical spectrum is represented as a function of frequency f in the general form Af−n with smooth transitions between changes in the exponent n. A flat spectrum (n=0) at low frequencies changes to n=2 at intermediate frequencies. We attribute the transition frequency to the decay time of dipole fluctuations. Accounting for correlated noise in the stochastic model introduces another transition from n=2 to 4, where the transition frequency is set by the correlation time of the noise. Numerical geodynamo models suggest that the correlation time is less than the convective overturn time and may be related to the lifetime of helical eddies. Applying these results to paleomagnetic estimates of the power spectrum yields a correlation time of 100 to 200 yrs. Evidence for a transition between n=0 and n=2 in paleomagnetic power spectra is interpreted as a constraint on the electrical conductivity of the core. Additional correlation times in the noise model are expected to produce a transition to n=6, possibly associated with diffusion of the dipole field through a magnetic boundary layer at the top of the core.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 411, 1 February 2015, Pages 20-26
نویسندگان
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