On the relationship between static stability and anvil clouds

Abstract. The climate feedback mechanism of the anvil amount is still uncertain but is a key component in understanding the Earth’s climate sensitivity. The environmental cloud-controlling factors are helpful to reveal the underlying processes of the anvil climate responses and constrain the climate model projections. The 3-km-layer stability below the lapse-rate tropopause is defined as the upper-tropospheric stability (UTS) and usually used to analyze the environmental stability control on the anvil clouds. However, the UTS might underestimate the stability control on the anvil. Here, a novel estimated anvil-top stability (EAS) based on the minimum stability in the upper troposphere is proposed as a stronger anvil-controlling factor than the UTS. By the radiosondes and cloud observations at the tropical Manus ground-based site, the results show that the EAS can better stratify the ice cloud incidence from 0.16 to 0.91 with a negative linear relationship, while the UTS only controls the ice cloud incidence from 0.4 to 0.78 and their relationship is nonlinear. The EAS can also be derived from the pressure-level reanalysis data, but due to the relatively coarse vertical resolution of the reanalysis the EAS would not be perfectly reproduced from the reanalysis. In comparison, the reanalysis-based EAS has a correlation of 0.51 with the radiosonde-measured EAS but it is still a stronger anvil-controlling factor than both the reanalysis-based and radiosonde-measured UTS.

At the global scale, the relationships of the anvil clouds with the reanalysis-based EAS and UTS are examined by the satellite passive and active sensors, respectively. As observed by the passive radiometer imagers on board the geostationary satellites, the distribution of the high cloud coverage (HCC) above 300 hPa has the correlation of -0.6 with the EAS but the correlation with the UTS is only -0.01. Daily HCC variations are strongly correlated with EAS with the mean correlation of -0.52 in the HCC domains, while the UTS underestimates the stability controls on the HCC (the mean correlation is -0.33). By the combined active sensors of the radar and lidar on board the polar-orbit satellites, the results show that the ice cloud fraction profiles in tropics, subtropics and midlatitude are all linearly stratified by the EAS, while the large ice cloud fraction could happen in both the small and large UTS and the relationship of the ice cloud fraction with the UTS is nonlinear. With the strong linear correlation to the anvil, the EAS can be used as a good predictor to understand the anvil climate feedback processes.