So, the evolution of temperature can be numerically simulated
by using this last equation during the day or modified for night use
(by setting Sn ¼ 0) and by setting T ¼ Ta during the earliest hours
before sunrise. For this study the irradiance flux from the sun
reaching the Earth's surface (I) is considered as constant along the
day despite changes induced by atmospheric conditions, and this
constant I value is estimated from average data of the daily total
irradiance G00 on a level surface, available from local solar maps.