Cirrus clouds play an important role in the radiation budget of the Earth. Despite recent progress in their observation, the radiative impact of ultra-thin cirrus clouds (UTC) in the tropopause region and in the lowermost stratosphere remains poorly constrained. Sensitivity model simulations with different ice parameters provide an uncertainty range for the radiative effect of UTCs. There is a need for better observed UTCs to enable the simulation of their potentially large effect on climate.

We examined 11 winters of lidar measurements of polar stratospheric clouds (PSCs), performed in Kiruna, northern Sweden. We discriminated cases with and without mountain lee waves present. We found that under mountain-lee-wave conditions PSCs are on average at higher altitudes and are more likely to contain ice. Without such waves present, most PSCs consist of nitric acid.

Convection in the Asian monsoon provides an important pathway for the transport of boundary layer and tropospheric air, and potentially pollution and chemically active species, into the stratosphere. We analyzed the distribution of the fastest and deepest convection with geostationary satellite detections for the months of May through October of 2017. We find significant differences in the geographic and monthly distributions of cross-tropopause convection across the Asian monsoon region.

We estimate plume heights for the April 2021 La Soufrière daytime eruptions using GOES-17 near-limb side views and GOES-16–MODIS stereo views. These geometric heights are then compared with brightness-temperature-based radiometric height estimates to characterize the biases of the latter. We also show that the side view method can be applied to infrared imagery and thus nighttime eruptions, albeit with larger uncertainty.

Ice clouds in the stratosphere (SICs) greatly affect the water vapor balance and radiation budget in the upper troposphere and lower stratosphere (UTLS). We quantified the global SICs and analyzed their relationships with tropopause temperature, double tropopauses, UTLS clouds, gravity waves, and stratospheric aerosols. The correlations between SICs and all abovementioned processes indicate that the occurrence of and variability in SICs are spatiotemporally dependent on different processes.