The Circumhorizontal Arc, popularly known as a fire rainbow, is an atmospheric optical phenomenon that manifests as a band of spectral colors in cirrus clouds. It occurs when sunlight strikes hexagonal ice crystals suspended in the atmosphere at mid-altitudes, typically during the summer months. Its digital representation requires a precise understanding of light refraction and crystal orientation, a technical challenge we can address with modern 3D tools.
Physical Simulation in Unreal Engine 5 and Blender Cycles 🌈
To recreate this effect in Unreal Engine 5, we must configure the Sky Atmosphere system with a low solar angle (between 57 and 68 degrees above the horizon) and a high density of ice particles in the cirrus layer. The key is adjusting the Aerosol Density parameter and Mie scattering to simulate refraction in horizontally oriented crystals. In Blender, the process involves modeling a cloud volume with a volumetric scattering shader and a spectral gradient that follows Snell's law. Ice crystals are represented as particles with a refractive index of 1.31, illuminated by a directional sun. The phenomenon's altitude (between 6 and 12 km) and seasonality (summer in mid-latitudes) are critical parameters to avoid visual artifacts.
Technical Reflection on Scientific Accuracy 🔬
The main technical difficulty lies in the lack of a render engine that calculates refraction in individual crystals in real time. In UE5, the atmosphere simplifies the process using precalculated tables, which limits spectral fidelity. Blender Cycles offers greater physical control, but at the cost of high render times. For a rigorous scientific visualization project, I recommend Blender for the reference simulation and UE5 for interactive demonstrations, always maintaining the exact solar altitude and crystal orientation as fundamental variables.
How light dispersion and refraction in ice crystals can be recreated to simulate the circumhorizontal arc in Unreal Engine 5 using procedural materials and high-fidelity visual shaders
(PS: if your manta ray animation doesn't excite, you can always add some documentary music from channel 2)