Cirrus clouds have been observed over the Himalayan region between 10 km and the tropopause at 17–18 km. Data from backscattersonde, hygrometers, and particle cloud spectrometers have been compared to assess their consistency. Empirical relationships between optical parameters accessible with remote sensing lidars and cloud microphysical parameters (such as ice water content, particle number and surface area density, and particle aspherical fraction) have been established.

The T-matrix theory was used to compute the backscatter and depolarization of mixed-phase PSC, assuming that particles are solid (NAT or possibly ice) above a threshold radius R and liquid (STS) below, and a single shape is common to all solid particles. We used a dataset of coincident lidar and balloon-borne backscattersonde and OPC measurements. The agreement between modelled and measured backscatter is reasonable and allows us to constrain the parameters R and AR.

We study Mie theory on aspherical scatterers, computing on coincident measurements of PSC by lidar and Particle Counters, the backscatter and depolarization of mixed phase PSC. WParticles are assumed solid if larger than R; for these, Mie results are reduced by C < 1 and only a common fraction X < 1 of the backscattering is polarized. We retrieve R, C and X. The match of model and measurement is good for backscattering, poor for depolarization. The hypothesis on X may be not fulfilled.

A lidar was used in Palau from February–March 2016. Clouds were observed peaking at 3 km below the high cold-point tropopause (CPT). Their occurrence was linked with cold anomalies, while in warm cases, cirrus clouds were restricted to 5 km below the CPT. Thin subvisible cirrus (SVC) near the CPT had distinctive characteristics. They were linked to wave-induced cold anomalies. Back trajectories are mostly compatible with convective outflow, while some distinctive SVC may originate in situ.

A total of 5 years of polar stratospheric cloud (PSC) observations by ground-based lidar at Concordia station (Antarctica) are presented. These data have been recorded in coincidence with the overpasses of the CALIOP lidar on the CALIPSO satellite. First we demonstrate that both lidars observe essentially the same thing, in terms of detection and composition of the PSCs. Then we use both datasets to study seasonal and interannual variations in the formation temperature of NAT mixtures.