Marion Müller

Large NAT particle formation by mother clouds: Analysis of SOLVE/THESEO‐2000 observations

[1] During the SOLVE/THESEO-2000 Arctic stratospheric campaign in the winter 1999/2000 widespread occurrences of very large HNO3-containing particles, probably composed of nitric acid trihydrate (NAT), were observed in situ by instruments on board the ER-2 stratospheric research aircraft. These large NAT particles were found with low number densities (n 10 4 cm 3 ) in vast regions, in air generally supersaturated with respect to NAT. Within the same campaign other instruments have performed airborne and ground-based measurements of polar stratospheric clouds (PSCs), often showing the existence of type 1a and type 1a-enh clouds. Such PSCs often occur on the mesoscale with particle number densities n ^ 10 2 cm 3 and are also mostlikelycomposedofNAT.Weuseforwardtrajectoriesfor thepathofNATparticles, whichareadvectedbywindsbased on ECMWF analyses and sediment due to gravity, to show that high number density NAT PSCs (mother clouds) could give rise to low number density NAT particle populations several daysdownstream. INDEXTERMS:0305Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere—constituent transport and chemistry (3334)

Non‐uniform PSC occurrence within the Arctic Polar Vortex

A multi-year dataset of lidar measurements of polar stratospheric clouds (PSCs) from two sites in the Arctic (Sodankyla, 67°N, 27°E, and Ny-Alesund, 79°N, 12°E) has been analyzed with respect to the existence temperature of different PSC types. Due to the location of the measurement sites relative to the polar vortex, their observations are most of the time representative of vortex edge and vortex center conditions, respectively. The comparison of the aerosol lidar measurements with local and trajectory temperatures reveals that PSC occurrence is favored at the edge of the Arctic polar vortex. One possibility discussed here is a differential distribution of water vapor that could be responsible for the non-uniform threshold temperatures and thus differential PSC occurrence within the polar vortex.