We use 20 years of continuous magnetic field measurements from the Ørsted, CHAMP and Swarm satellite missions, supplemented by calibrated platform magnetometer data from the CryoSat-2 satellite, to study time variations of the Earth’s core field at satellite altitude and at the core–mantle boundary (CMB). From the satellite data we derive composite time series of the core field secular variation (SV) with 4-month cadence, at 300 globally distributed Geomagnetic Virtual Observatories (GVO). A previous gap in the GVO series between 2010 and 2014 is successfully filled using CryoSat-2, and sub-decadal variations are identified during this period. Tests showed that similar sub-decadal SV patterns were obtained from the CryoSat-2 data regardless of whether IGRF-13 or CHAOS-6x9 was used in their calibration. Cryosat-2 radial field SV series at non-polar latitudes have a mean standard deviation level compared to smoothing spline fits of 3.5 nT/yr compared to 1.8 nT/yr for CHAMP and 0.9 nT/yr for Swarm. GVO radial SV series display regional fluctuations with 5–10 years duration and amplitudes reaching 20 nT/yr, most notably at low latitudes over Indonesia (2014), over South America and the South Atlantic (2007, 2011 and 2014), and over the central Pacific (2017). Applying the Subtractive Optimally Localized Averages (SOLA) method, we also map the radial SV at the CMB as a collection of locally averaged SV estimates. We demonstrate that using 2-year windows of CryoSat-2 data, it is possible to reliably estimate the SV and its time derivative, the secular acceleration (SA), at the CMB, with a spatial resolution, corresponding to spherical harmonic degree 10. Along the CMB geographic equator, we find strong SA features with amplitude \(\pm 2.5\mu \mathrm{T}/\mathrm{yr}^2\) under Indonesia from 2011–2014, under central America from 2015 to 2019, and sequences of SA with alternating sign under the Atlantic during 2004–2019. We find that platform magnetometer data from CryoSat-2 make a valuable contribution to the emerging picture of sub-decadal core field variations. Using 1-year windows of data from the Swarm satellites, we show that it is possible to study SA changes at low latitudes on timescales down to 1 year, with spatial resolution corresponding to spherical harmonic degree 10. We find strong positive and negative SA features appearing side-by-side in the Pacific in 2017, and thereafter drift westward.

我们使用来自Ørsted，CHAMP和Swarm的20年连续​​磁场测量卫星任务，再加上来自CryoSat-2卫星的经校准的平台磁力计数据，以研究地球核心场在卫星高度和核心-地幔边界（CMB）的时间变化。根据卫星数据，我们在300个全球分布的地磁虚拟天文台（GVO）上得出了具有4个月节奏的核心场长期变化（SV）的复合时间序列。使用CryoSat-2成功填补了2010年至2014年GVO系列中的先前空白，并在此期间确定了年代际变化。测试表明，无论在校准中使用IGRF-13还是CHAOS-6x9，都可以从CryoSat-2数据获得类似的年代际SV模式。与平滑样条拟合为3相比，非极性纬度上的Cryosat-2径向场SV系列的平均标准偏差水平。蜂拥而至。GVO径向SV系列显示了持续5-10年且幅度达到20 nT / yr的区域波动，最显着的是印度尼西亚（2014年），南美和南大西洋（2007年，2011年和2014年）以及整个低纬度地区。中太平洋（2017）。应用减法最优局部平均值（SOLA）方法，我们还将CMB处的径向SV映射为局部平均SV估计值的集合。我们证明了使用CryoSat-2数据的2年窗口可以可靠地估计SV及其时间导数在CMB处的长期加速度（SA），其空间分辨率对应于球谐度10。沿着CMB地理赤道，我们发现振幅为\（\ pm 2.5 \ mu \ mathrm {T} / \ mathrm {yr} ^ 2 \）的强大SA特征2011-2014年在印度尼西亚，2015-2019年在中美洲和2004-2019年在大西洋下具有交替符号的SA序列。我们发现，来自CryoSat-2的平台磁力计数据为近十年年代核心磁场变化的新图像做出了宝贵的贡献。使用来自Swarm卫星的1年数据窗口，我们显示了有可能在低纬度的低至1年的时间尺度上研究SA的变化，并且其空间分辨率对应于球谐度10。我们发现有很强的正负SA特征并排出现在2017年的太平洋地区，此后向西漂移。