The solar atmosphere undergoes several changes during the solar cycle. Those changes can be identified by observing several solar features and their respective dynamics, which can be observed in many different wavelengths, and by analyzing the variations in the total solar irradiance. The latter is characterized by an increase in the total solar irradiance during the solar maximum and a decrease in the decay phase. In this talk, we will present the intensity variations of the Mg II h&k lines emission peak, observed by IRIS, under quiet sun conditions close to the disk center over the decaying phase of the solar cycle. The observed variations will then be interpreted and put in the context of the solar atmospheric physical conditions.