Cloud temperature gradient and inversion distribution in Xi’an, China, based on long-sequence radiosonde data

Abstract

Clouds are a critical component of the Earth–atmosphere system, exerting strong influence on climate change and the global water cycle. Temperature is a fundamental parameter governing cloud development and evolution, and its vertical gradient directly shapes the vertical structure of clouds, thereby modulating key cloud physical processes. However, cloud temperature observations remain limited, and previous studies have primarily focused on single-layer clouds (SLC) or a single inversion layer. In this study, ten years of radiosonde data (2014–2023) in Xi’an were used to investigate the occurrence frequency and vertical temperature structure of SLC, double-layer clouds (DLC), and multi-layer clouds (MLC). The results show that the occurrence frequency of SLC tends to decrease over time, while the frequency of DLC and MLC increases year by year in Xi’an. Cloud top heights (CTH) exhibit significant seasonal variations. In SLC, temperature inversions (TI) occur more frequently in the upper cloud during winter and spring and are generally stronger at cloud tops than at cloud bases, with the probability of strong cloud-top TI exceeding that at the cloud base by more than a factor of two. While SLC is dominated by single-layer radiative cooling, TI in DLC and MLC exhibits complex interlayer radiative coupling mechanisms. In DLC and MLC, upper clouds tend to show shallow inversion depths under strong TI, whereas weak TI is associated with deeper inversions. Lower clouds, in contrast, exhibit nearly twice the probability of strong cloud-top TI compared with upper clouds. This pronounced enhancement suggests that radiative forcing from upper clouds plays a key intermediary role in strengthening TI in lower clouds. When temperature gradients are small, however, this enhancement is reduced and inversion development in lower clouds may be suppressed. Overall, these findings clarify the vertical coupling between cloud layers and TI, providing refined insights and valuable observational evidence for future studies on cloud–radiation interactions and cloud physical processes.