Robust variation trends in cloud vertical structure observed from three-decade radiosonde record at Lindenberg, Germany

Abstract

Clouds substantially affect Earth's energy budget by their interactions with short/long-wave radiation, and small changes in cloud vertical structure (CVS, i.e., the locations of cloud base and top, the thickness and number of cloud layers) can fluctuate the warming effects of anthropogenic forcing. However, the knowledge regarding how the CVS changes over time is still poor owing to a lack of reliable and available datasets. Here, the long-term temporal variations in four-times-daily radiosonde-derived CVS at Lindenberg, Germany, from 1992 to 2020 are analyzed. Robust increasing trends in cloud height/thickness and overlap frequency are found during this three-decade period. Observational results show that the interannual variabilities of the cloud-top height, cloud-base height, and cloud thickness are consistently increasing, with linear trends of 137.75 ± 6.65 m yr−1, 45.73 ± 6.22 m yr−1, and 29.52 ± 3.53 m yr−1, respectively. The occurrence of multi-layer cloud generally increases with a trend of 1.57 ± 0.06% yr−1, whereas the percentages of single-layer cloud and cloudless conditions decrease with trends of −0.44 ± 0.05% yr−1 and −1.12 ± 0.07% yr−1, respectively. Continuous surface warming increases thermal instability, which raises cloud height, particularly for single-layer clouds and the lower layer of multi-layer clouds. The upper-level cloud generates and maintains itself as the upper water vapor and vertical velocity enlarge, thus increasing the cloud top height, total cloud thickness, and cloud overlap frequency. These findings shed new light on the long-term changes in cloud properties caused by climate change.