Synoptic Charts of the Line-of-Sight Component of the Photospheric Magnetic Field

Synoptic charts are maps of the entire Sun produced in Carrington coordinates. Synoptic maps are constructed by merging together solar observations taken over many days. Magnetic-field synoptic charts are produced using central meridian data from HMI full-disk magnetograms.

Synoptic maps are constructed from HMI 720s line-of-sight Magnetograms collected over a 27-day solar rotation. Near-central-meridian data from 20 magnetograms contribute to each point in the final map.

HMI 720s line-of-sight magnetograms are first converted to 'radial field magnetograms' by dividing by the cosine of the angle from disk center, i.e. for this purpose we assume that HMI measures the line-of-sight component of a purely radial magnetic field. Individual 'radial' magnetograms are then remapped and interpolated onto a very high-resolution Carrington coordinate grid. For each Carrington longitude the values from the 20 magnetograms obtained closest in time to the central meridian passage (CMP) of that longitude are averaged. By using a constant number of contributing magnetograms, the variation of the noise over the entire map is minimized. Generally all data are taken within about 2 degrees of CMP. The effective temporal width of the HMI synoptic map contribution is about three hours, i.e. 20 720-s magnetograms are obtained within about 90 minutes of central meridian passage. The final HMI synoptic maps have a size of 3600 x 1440, which means the resolution is lower than the disk-center resolution of a single HMI magnetogram. A two-dimensional Gaussian function is applied to high-resolution remapped data to reduce the spatial resolution before generating the 3600*1440 synoptic maps. The width of the Gaussian is 3 pixels. The upper limit of the noise is 2.3 Mx cm2.

综合图是整个太阳在卡林顿坐标系中的映射图。综合图通过合并多日观测到的太阳观测数据而构建。利用HMI全圆盘磁图的中心子午线数据，生成磁场综合图。综合图由HMI 720秒视线磁图组成，这些磁图是在27天的太阳旋转周期内收集的。来自20个磁图的近中心子午线数据共同构成了最终图中的每一个点。首先，将HMI 720秒视线磁图转换为“径向场磁图”，即通过除以从盘中心的角度余弦值实现，即为此目的，我们假设HMI测量的是纯径向磁场的视线分量。然后，将单个“径向”磁图重新映射并插值到非常高的分辨率卡林顿坐标系网格上。对于每个卡林顿经度，取最接近该经度中心子午线通过（CMP）时间的20个磁图的数据进行平均。通过使用固定数量的贡献磁图，整个图上噪声的变化被最小化。通常，所有数据都在大约2度范围内采集。HMI综合图的贡献有效时间宽度约为三小时，即大约在中央子午线通过90分钟内获得20个720秒磁图。最终的HMI综合图大小为3600 x 1440，这意味着其分辨率低于单个HMI磁图的盘中心分辨率。在生成3600*1440的综合图之前，对高分辨率重映射数据应用二维高斯函数以降低空间分辨率。高斯函数的宽度为3像素。噪声的上限为2.3 Mx cm2。