Synoptic Charts of the Radial 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.

综合图表是对整个太阳在卡林顿坐标系下的映射。综合图表是通过合并多日收集的太阳观测数据构建而成。磁场综合图表则是利用HMI全盘磁图的中经线数据来制作。
综合图表由HMI 720秒视向磁图在27天太阳自转周期内收集而成。20张磁图近中经线数据共同构成了最终地图上的每一个点。
HMI 720秒视向磁图首先通过除以盘中心角度的余弦值转换为“径向场磁图”，即为此目的，我们假设HMI测量的是纯径向磁场的视向分量。然后，单个“径向”磁图被重新映射并插值到非常高的分辨率的卡林顿坐标网格上。对于每一个卡林顿经度，最接近该经度中经线经过（CMP）时间点的20张磁图的数据被平均。通过使用固定数量的贡献磁图，整个地图上噪声的变化被最小化。通常所有数据都取自约2度范围内的CMP。HMI综合图表的有效时间宽度约为三小时，即约在90分钟内获得20张720秒的磁图。最终的HMI综合图表大小为3600 x 1440，这意味着其分辨率低于单张HMI磁图的盘中心分辨率。对高分辨率重新映射的数据应用二维高斯函数以降低空间分辨率，从而生成3600*1440的综合图表。高斯函数的宽度为3像素。噪声的上限为2.3 Mx cm²。