Haze aloft

(Section 2.5.3.2)

Haze aloft is composed of extremely small particles that scatter light. The scattering increases with concentration of the particles. Layers of haze aloft may be encountered by aircraft up to about 5 km (16 500 ft).

Below the haze. Viewed from below, haze aloft appears as a veil with a dark blue or blackish tint. An airborne observer entering such a haze layer from below experiences a gradual reduction in visibility.

Within haze aloft. It is often difficult to determine whether the aircraft is in haze alone or in clouds embedded within haze. Flying upward out of a layer of haze, a rapid improvement in horizontal visibility is usually observed.

Above the haze. Viewed from above, haze aloft tends to hide the landscape. Scattered light is especially strong in the direction of the Sun. In this direction, ground features are impossible to distinguish, except perhaps when the landscape includes very bright areas such as water surfaces. In the direction away from the Sun, visibility towards the ground is better.

The upper limit of haze aloft forms a horizon. Flying immediately above haze and looking down obliquely, it is almost impossible to distinguish any clouds that may be embedded within it, unless the tops of these clouds emerge above the haze layer. As with many stratiform clouds, the upper limit of the haze coincides with the base of a stable air layer (often a temperature inversion).