Diurnal Cycle and Seasonality of Cirrus Clouds Over the Amazon From a Seven‐Year Ground‐Based Lidar Record

Abstract Cirrus clouds strongly influence Earth's radiation balance, yet their optical properties and formation pathways add uncertainty to climate models. Satellites offer a global view of cirrus but have key limitations: passive sensors struggle to detect thin layers, and active instruments in polar orbits miss the diurnal cycle. Long‐term records of ground‐based lidar measurements can help fill this important observational gap. Here, we analyzed of lidar data gathered near Manaus, Brazil (July 2011–December 2017), to characterize the cirrus clouds over the Amazon rainforest. An automated routine set cloud boundaries, and multiple‐scattering‐corrected retrievals yielded cloud optical depth (COD) and the lidar ratio. Cirrus were found to occur with a frequency of 73.1%. Thin layers (‐0.30) are the most prevalent with a 48.4% relative frequency, followed by opaque (; 26.4%) and subvisual (; 25.2%). The mean base and top altitudes were and , and the lidar ratio averaged . Thinner clouds clustered near the tropopause, while higher tops tracked the tropopause variability. A clear diurnal cycle shows a noon minimum frequency of occurrence and a late‐afternoon maximum, strongest for opaque cirrus and consistent with convective‐anvil outflow. Optical properties such as COD, lidar ratio, and geometric properties follow a well‐defined daily rhythm. Seasonally, cirrus are more frequent in the wet season (81.8%) than in the dry (56.7%). Bases, tops, and thickness are likewise larger in the wet season, whereas lidar ratios peak in the dry season. This long‐term record benchmarks satellite retrievals, sharpens radiative impact calculations, and clarifies cirrus formation over tropical forests.