  Radiative cooling exploits the imbalance between the thermal emission from
the radiative cooling surface and the downward atmospheric emission. Since the
atmospheric emission power is polar angle-dependent, a mirror structure can be
used to increase this imbalance and to amplify the net cooling power. The
degree of amplification is determined by various parameters such as the sky
emissivity, the geometry of the mirror structure and the degree of thermal
insulation. A parametric study of the aperture mirror-enhanced radiative
cooling is presented using a model atmosphere, characterized by an average sky
window emissivity and the ambient temperature. A counterintuitive finding is
obtained, namely that the aperture mirror structure is more effective in the
tropics than in the desert, both in terms of the cooling power and the
temperature reduction. The power enhancement obtainable from a relatively
simple mirror structure can be significant. For example, in the tropics, the
cooling power can be enhanced by more than 40%. The aperture mirror structure
holds potential to be a practical augmentation to improve the stagnant
temperature and the response time of radiative cooling devices.
