Since the mid-19th century, direct measurements of both intensity and directions of the Earth's magnetic field have been available, allowing an accurate determination of its spatio-temporal variations. Prior to this time, between ∼1600 and 1840, only direct directional measurements are available. Therefore, the construction of global field models over this period requires either a specific treatment of the axial dipole field component or the use of archeomagnetic intensity data. In this study, we use a regional approach based on the construction of an archeointensity variation curve in Central Asia. We analyze baked clay brick fragments sampled in Bukhara (Uzbekistan), dated between the end of the 16th century and the beginning of the 19th century. This city is of particular interest for archeomagnetism due to the well-preserved old buildings accurately dated by documentary archives. A series of archeointensity results is obtained using the Triaxe experimental protocol, which shows a decreasing trend in intensity from ∼1600 to ∼1750, with intensities during the 18th century lower than expected from global geomagnetic field models. These new data appear consistent with other Triaxe data previously obtained in western Europe and western Russia, when transferred to Bukhara using the field geometry of the gufm1 model. Together, these data are used to recalibrate the axial dipole moment evolution provided by this model. The resulting evolution appears non-linear, with a clear relative minimum in the magnitude of the axial dipole during the late 18th century. We illustrate the fact that at present this evolution can neither be satisfactorily confirmed nor refuted by other datasets available in western Eurasia (as well as at a wider spatial scale), mainly due to the significant dispersion of the data. Our interpretation relies on the accuracy of the field geometry of the gufm1 model, which appears less reliable prior to ∼1750. Nevertheless, the minimum proposed in the 18th century seems to be a true feature of axial dipole behavior.

自19世纪中叶以来，可以直接测量地球磁场的强度和方向，从而可以准确确定其时空变化。在此之前，大约在1600年到1840年之间，只有直接方向测量可用。因此，在此期间构建全局场模型需要对轴向偶极子场分量进行特定处理，或者需要使用地磁强度数据。在这项研究中，我们使用了基于中亚地区考古强度变化曲线构建的区域方法。我们分析了在16世纪末至19世纪初之间在布哈拉（乌兹别克斯坦）采样的烤制粘土砖碎片。由于记录档案馆准确保存了保存完好的旧建筑，因此这座城市对考古磁性特别感兴趣。使用Triaxe实验协议获得了一系列的古地强度结果，显示了从1600到1750的强度下降趋势，而18世纪的强度低于全球地磁场模型的预期。这些新数据看起来与以前在西欧和俄罗斯西部获得的其他Triaxe数据一致，这些数据是通过使用gufm1模型。这些数据一起用于重新校准此模型提供的轴向偶极矩演变。由此产生的演化是非线性的，在18世纪后期，轴向偶极子的幅度明显相对最小。我们说明了一个事实，目前，这一进展既不能令人满意地得到证实，也不能被欧亚大陆西部（以及更广泛的空间范围）的其他数据集所驳斥，这主要是由于数据的分散性。我们的解释依赖于gufm1模型的场几何精度，在1750年之前，可靠性似乎不太可靠。尽管如此，在18世纪提出的最小值似乎是轴向偶极子行为的真实特征。