Radiative contributions of different cloud types to regional energy budget over the SACOL site

Different cloud types have distinct radiative effects on the energy budget of the earth–atmosphere system. To better understand
the cloud radiative impacts, it is necessary to distinguish the effects of different cloud types, which can be achieved through
the cloud radar data that can provide cloud profiles for both day-to-day and diurnal variations. In this study, we use 6-year
high-temporal resolution data from the Ka-Band Zenith Radar (KAZR) at the Semi-Arid Climate and Environment Observa-
tory of Lanzhou University (SACOL) site to analyze the physical properties and radiative effects of main cloud types. The
three types of clouds that occur most frequently at the SACOL site are single-layer ice clouds, single-layer water clouds, and
double-layer clouds with the annual occurrence frequencies being 29.1%, 3.4%, and 8.3%, respectively. By using the Fu–Liou
radiative transfer model simulation, it is found that the distinct diurnal variations of both the occurrence frequency and their
macro- and micro-physical properties significantly affect the cloud-radiation. On annual mean, the single-layer ice clouds
have a positive radiative forcing of 7.4 W/m 2 to heat the system, which is a result of reflecting 12.9 W/m 2 shortwave (SW)
radiation and retaining 20.3 W/m 2 longwave (LW) radiation; while the single-layer water clouds and double-layer clouds
have much stronger SW cooling effect than LW warming effect, causing a net negative forcing of 8.5 W/m 2 . Although all
these clouds have an overall small cooling effect of 1.1 W/m 2 on the annual radiative energy budget, the significant differ-
ences of the diurnal and seasonal distributions for different type clouds can lead to distinct radiative forcing. Especially the
LW warming effect induced by the exclusive ice clouds in the cold season may have an important contribution to the rapid
winter warming over the semi-arid regions.