This happens at both sunrise and sunset each day and adds over 4 extra minutes of daylight to each day. As a result, daylight is a little longer than the night period on the date of the Equinox by about 4 minutes. When the sun or moon are within a few degrees of the horizon, they can also lose their circular shape and appear flattened because of atmospheric refraction. In this piece I want to focus on refractive phenomena seen in the lower atmosphere under conditions of varying temperature with height which produce mirages. Temperature decreases with height.
Temperature increases with height.
Inferior mirages occur under strong lapse rate conditions, and superior mirages under inversion conditions. At times there may be several layers with distinct temperature gradients including inversion layers below or between layers with lapse conditions. We will delve more deeply into the variations possible with mirages in separate articles on this website. For the remainder of this piece, we will focus on describing the general conditions that form the inferior and superior mirages. In the lower layers of the atmosphere where most mirages are seen, the air refractivity is only weakly dependent upon changes in air pressure but strongly on temperature gradient changes.