(b) and (c) What do the red and green arrows in the geomagnetic field model mean?

In the geomagnetic field model of Li Yongxiang and Liu Xinyu (2020), the black arrow in figure (a) indicates the direction of the magnetic induction line, while the green and red arrows in figures (b) and (c) indicate the magnitude and direction of the geomagnetic field. In these images, the color of the arrow represents the positive and negative polarity of the magnetic field, while the size of the arrow represents the strength of the magnetic field.

The red arrow usually indicates the positive (or outward) magnetic field direction, while the green arrow usually indicates the negative (or inward) magnetic field direction. In the representation of non-dipole field and geocentric axial dipole field, these two colors of arrows are helpful to describe the complex distribution and change of magnetic field.