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1 Primary & Middle School Mathematics1–9 年级在线 2 High School Mathematics10–12 年级在线 3 University Mathematics — Year 1本科一年级在线 4 University Mathematics — Year 2本科二年级在线 5 University Mathematics — Year 3本科三年级在线

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1 School Chemistry — Grades 1 to 121–12 年级在线 2 University Chemistry — Year 1本科一年级在线 3 University Chemistry — Year 2本科二年级在线 4 University Chemistry — Year 3本科三年级在线

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1 Markets I: The Ecosystem and Exchange-Traded Markets市场在线 2 Markets II: Rates, FX and Credit市场在线 3 Markets III: Commodities, Energy and Crypto市场在线 4 Quantitative Methods方法在线 5 Derivatives and Volatility衍生品在线 6 Rates, Credit, XVA and Risk利率、信用与风险在线 7 Research Craft: Predictors, Backtests, Measurement, Portfolios研究在线 8 Strategies I: Equities and Futures策略在线 9 Strategies II: Volatility, Relative Value, Macro and the Bank Desks策略在线 10 Microstructure and Execution交易执行在线 11 Market Making and High-Frequency Trading做市在线 12 Machine Learning for Markets机器学习在线 13 Low-Latency Software技术在线 14 Networks, Hardware and Trading Infrastructure技术在线 15 Research, Data and Risk Platforms技术在线 16 The Desk and the Firm公司运营在线 17 The Industry: Firms, Roles and Careers职业发展在线 18 Interviews I: Maths, Probability and Speed职业发展在线 19 Interviews II: Markets, Trading Games and the Final Round职业发展在线 20 Interviews III: Code职业发展在线

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Earth and Space Sciences · 术语表

什么是 International Geomagnetic Reference Field？

Definition 4.4 University Earth and Space Sciences — Year 3 · 第 4 章 — Geomagnetism and Palaeomagnetism

The International Geomagnetic Reference Field (IGRF) is the internationally agreed model of the main field: the potential, on and above the surface,

V(r,\theta,\varphi) = a\sum_{n=1}^{N}\Bigl(\frac ar\Bigr)^{n+1}\sum_{m=0}^{n} \bigl(g_n^m\cos m\varphi + h_n^m\sin m\varphi\bigr)P_n^m(\cos\theta),

with $a = 6371.2\,\mathrm{km}$ , $\mathbf B = -\nabla V$ , and Gauss coefficients $g_n^m$ , $h_n^m$ (in $\mathrm{nT}$ ) given every five years since 1900, together with their rate of change over the next five years.

The main field in 2025 from the fourteenth IGRF, at the surface of the sphere of radius 6371.2\, km. (a) Inclination in degrees; the thick line, I = 0, is the dip equator. (b) Total intensity in nT; the cross marks the weakest field, about 22\,100\, nT, over the South Atlantic, against about 66\,600\, nT at the strongest, south of Australia. — The main field in 2025 from the fourteenth IGRF, at the surface of the sphere of radius $6371.2\,\mathrm{km}$ . (a) Inclination in degrees; the thick line, $I = 0$ , is the dip equator. (b) Total intensity in $\mathrm{nT}$ ; the cross marks the weakest field, about $22\,100\,\mathrm{nT}$ , over the South Atlantic, against about $66\,600\,\mathrm{nT}$ at the strongest, south of Australia.

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