Abstract. The combined UK/Denmark record of noctilucent cloud (NLC) observations over the period is analysed. This data set is based on visual observations by professional and voluntary observers, with around 40 observers each year contributing reports. Evidence is found for a significantly longer NLC season, a greater frequency of bright NLC, and a decreased sensitivity to 5-day planetary waves, from 1973-1982, compared to the rest of the time interval. This coincides with a period when the length of the summer season in the stratosphere was also longer (defined by zonal winds at 60 • N, 30 hPa). At NLC heights, lower mean temperatures, and/or higher water vapour and/or smaller planetary wave amplitudes could explain these results. The time series of number of NLC nights each year shows a quasi-decadal variation with good anti-correlation with the 10.7 cm solar flux, with a lag of 13-17 months. Using multi-parameter linear fitting, it is found that the solarcycle and the length of summer in the stratosphere together can explain ∼40% of the year-to-year variation in NLC numbers. However, no statistically confidant long-term trend in moderate or bright NLC is found. For NLC displays of moderate or greater intensity, the multi-parameter fit gives a trend of ∼0.08 nights (0.35%) per year with a statistical probability of 28% that it is zero, or as high as 0.16 nights (0.7%) per year. There is a significant increasing trend in the number of reports of faint or very faint NLC which is inconsistent with other observations and may be due changes in observing practices.

We focus on improvement of the retrieval of optical properties of cirrus clouds by combining two lidar methods. We retrieve the cloud's optical depth by using independently the molecular backscattering profile below and above the cloud [molecular integration (MI) method] and the backscattering profile inside the cloud with an a priori effective lidar ratio [particle integration (PI) method]. When the MI method is reliable, the combined MI-PI method allows us to retrieve the optimal effective lidar ratio. We compare these results with Raman lidar retrievals. We then use the derived optimal effective lidar ratio for retrieval with the PI method for situations in which the MI method cannot be applied.

The aim of this work is to document cirrus characteristics using ground‐based measurements. A climatology of sub‐tropical cirrus clouds is presented from the analysis of the Rayleigh‐Mie lidar data collected at the “Observatoire de Physique de l'Atmosphere de la Reunion” (OPAR) over the period 1996–2001. The lidar laser operates at 532 nm. This climatology is based on the analysis of upward laser beam over 533 nights corresponding to 1643 hours of lidar probing. In this sub‐tropical zone, two main seasons prevail for cirrus clouds occurrence: an austral winter, from May to October, and an austral summer, from November to April. As expected, cirrus are present more frequently during the austral summer, 13% of measurements, than during the austral winter, 1%. Subvisible cirrus clouds, characterised by an optical thickness below 0.03, compose a significant fraction, 65%, of the total cirrus observations.

A climatology of tropospheric ozone profiles associated with tropical convection in the southwestern part of the Indian Ocean and over South Africa is presented. Then case studies of stratospheric‐tropospheric exchange are documented using radiosoundings, ozone lidar, satellite and ECMWF global model data. In three distinct cases of varying tropical convection intensity (depression and cyclone Guillaume near Reunion in February 2002 and convection near Irene in November 2000), strong interaction between convection‐induced upper level circulation, jet front systems and Rossby Wave Breaking induces stratosphere to troposphere exchanges. Stratospheric filaments in the upper troposphere evident in the ECMWF analyses are in good agreement with ozone, humidity and temperature vertical profile observations. For the Guillaume case study near Reunion, filaments and subsidence occur in both cases (depression on 15 February and cyclone on 19 February 2002). On 15 February, a moderate enhancement of ozone in the free troposphere is observed and on 19 February, a 100 ppbv ozone peak is recorded. In the Irene case study, a large upper level depression coming from the stratosphere, fed by a filament wrapped around the convective area in the Mozambican channel, induces an ozone peak of larger magnitude (170 ppbv). Secondary ozone sources (jet front system in the Atlantic and biomass burning in South America) could further amplify this ozone enhancement. The radiosounding indicates a strong ozone enhancement in the upper troposphere, without a signature of pumping from the lower layers, in contrast to the Guillaume case.