Spatial organization of convection is found to play an important role in modulating tropical radiation budget by altering the distribution of moisture and structural characteristics and radiative properties of tropical clouds. It is still unclear how large-scale convective aggregation interacts with the distribution of moisture, clouds and the related atmospheric cloud radiative effects, and large-scale circulation, and how it potentially affects cloud feedback to surface warming. Here, we first compare six convective aggregation metrics to investigate how well these metrics represent convective aggregation associated with the observed mesoscale convection systems (MCS). Only three convective aggregation metrics (convective organization potential, area fraction of precipitating MCS, and precipitation fraction of MCS) are found to increase with the area of MCS and are suited for studying the observed convective aggregation of MCS. We then use multiple independent satellite and reanalysis datasets to explore the relationship between convective aggregation and the atmospheric cloud radiative heating (ACRE) in the tropics. Our results show that the ACRE makes a substantial contribution to the development of MCS-related convective aggregation. The effect of convective aggregation on the observed variations of subtropical low clouds is disentangled from several local clouds controlling factors including sea surface temperature, lower tropospheric stability, free tropospheric and boundary layer mixing, and subsidence rate. Our preliminary results indicate that convective aggregation of MCS is responsible for an increase of subtropical low clouds in the southeastern Pacific, although the significance of such a relationship is uncertain. Results from climate model simulations in terms of these relationships will also be presented and discussed.