Abstract. The AMMA (African Monsoon Multidisciplinary Analysis) program is dedicated to providing a better understanding of the West African monsoon and its influence on the physical, chemical and biological environment regionally and globally, as well as relating variability of this monsoon system to issues of health, water resources, food security and demography for West African nations. Within this framework, an intensive field campaign took place during the summer of 2006 to better document specific processes and weather systems at various key stages of this monsoon season. This campaign was embedded within a longer observation period that documented the annual cycle of surface and atmospheric conditions between 2005 and 2007. The present paper provides a large and regional scale overview of the 2006 summer monsoon season, that includes consideration of of the convective activity, mean atmospheric circuCorrespondence to: S. Janicot (serge.janicot@locean-ipsl.upmc.fr) lation and synoptic/intraseasonal weather systems, oceanic and land surface conditions, continental hydrology, dust concentration and ozone distribution. The 2006 African summer monsoon was a near-normal rainy season except for a large-scale rainfall excess north of 15 • N. This monsoon season was also characterized by a 10-day delayed onset compared to climatology, with convection becoming developed only after 10 July. This onset delay impacted the continental hydrology, soil moisture and vegetation dynamics as well as dust emission. More details of some less-well-known atmospheric features in the African monsoon at intraseasonal and synoptic scales are provided in order to promote future research in these areas.

Abstract. During the second part of the TROCCINOX campaign that took place in Brazil in early 2005, chemical species were measured on-board the high-altitude research aircraft Geophysica (ozone, water vapor, NO, NO y , CH 4 and CO) in the altitude range up to 20 km (or up to 450 K potential temperature), i.e. spanning the entire TTL region roughly extending between 350 and 420 K.Here, analysis of transport across the TTL is performed using a new version of the Chemical Lagrangian Model of the Stratosphere (CLaMS). In this new version, the stratospheric model has been extended to the earth surface. Above the tropopause, the isentropic and cross-isentropic advection in CLaMS is driven by meteorological analysis winds and heating/cooling rates derived from a radiation calculation. Below the tropopause, the model smoothly transforms from the isentropic to the hybrid-pressure coordinate and, in this way, takes into account the effect of large-scale convective transport as implemented in the vertical wind of the meteorological analysis. As in previous CLaMS simulations, the irreversible transport, i.e. mixing, is controlled by the local horizontal strain and vertical shear rates.Stratospheric and tropospheric signatures in the TTL can be seen both in the observations and in the model. The composition of air above ≈350 K is mainly controlled by mixing on a time scale of weeks or even months. Based on CLaMS transport studies where mixing can be completely switched off, we deduce that vertical mixing, mainly driven by the vertical shear in the tropical flanks of the subtropical jets and, Correspondence to: P. Konopka (p.konopka@fz-juelich.de) to some extent, in the the outflow regions of the large-scale convection, offers an explanation for the upward transport of trace species from the main convective outflow at around 350 K up to the tropical tropopause around 380 K.

Abstract. In-situ ice crystal size distribution measurements are presented within the tropical troposphere and lower stratosphere. The measurements were performed using a combination of a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP), which were installed on the Russian high altitude research aircraft M55 "Geophysica" during the SCOUT-O 3 campaign in Darwin, Australia. One of the objectives of the campaign was to characterise the Hector convective system, which appears on an almost daily basis during the pre-monsoon season over the Tiwi Islands, north of Darwin. In total 90 encounters with ice clouds, between 10 and 19 km altitude were selected from the dataset and were analysed. Six of these encounters were observed in the lower stratosphere, up to 1.4 km above the local tropopause. Concurrent lidar measurements on board "Geophysica" indicate that these ice clouds were a result of overshooting convection. Large ice crystals, with a maximum dimension up to 400 µm, were observed in the stratosphere. The stratospheric ice clouds included an ice water content ranging from 7.7×10 −5 to 8.5×10 −4 g m −3 and were observed at ambient relative humidities (with respect to ice) between 75 and 157%. Three modal lognormal size distributions were fitted to the average size distributions for different potential temperature intervals, showing that the Correspondence to: S. Borrmann (stephan.borrmann@mpic.de) shape of the size distribution of the stratospheric ice clouds are similar to those observed in the upper troposphere.In the tropical troposphere the effective radius of the ice cloud particles decreases from 100 µm at about 10 km altitude, to 3 µm at the tropopause, while the ice water content decreases from 0.04 to 10 −5 g m −3 . No clear trend in the number concentration was observed with altitude, due to the thin and inhomogeneous characteristics of the observed cirrus clouds.The ice water content calculated from the observed ice crystal size distribution is compared to the ice water content derived from two hygrometer instruments. This independent measurement of the ice water content agrees within the combined uncertainty of the instruments for ice water contents exceeding 3×10 −4 g m −3 .Stratospheric residence times, calculated based on gravitational settling, and evaporation rates show that the ice crystals observed in the stratosphere over the Hector storm system had a high potential of humidifying the stratosphere locally.

Abstract. Processes occurring in the tropical upper troposphere (UT), the Tropical Transition Layer (TTL), and the lower stratosphere (LS) are of importance for the global climate, for stratospheric dynamics and air chemistry, and for their influence on the global distribution of water vapour, trace gases and aerosols. In this contribution we present aerosol and trace gas (in-situ) measurements from the tropical UT/LS over Southern Brazil, Northern Australia, and West Africa. The instruments were operated on board of the Russian high altitude research aircraft M-55 "Geophysica" and the DLR Falcon-20 during the campaigns TROCCI-

In situ measurements of ice crystal size distributions in tropical upper troposphere/lower stratosphere (UT/LS) clouds were performed during the SCOUT-AMMA campaign over West Africa in August 2006. The cloud properties were measured with a Forward Scattering Spectrometer Probe (FSSP-100) and a Cloud Imaging Probe (CIP) operated aboard the Russian high altitude research aircraft M-55 Geophysica with the mission base in Ouagadougou, Burkina Faso. A total of 117 ice particle size distributions were obtained from the measurements in the vicinity of Mesoscale Convective Systems (MCS). Two to four modal lognormal size distributions were fitted to the average size distributions for different potential temperature bins. The measurements showed proportionately more large ice particles compared to former measurements above maritime regions. With the help of trace gas measurements of NO, NO_y, CO₂, CO, and O₃ and satellite images, clouds in young and aged MCS outflow were identified. These events were observed at altitudes of 11.0 km to 14.2 km corresponding to potential temperature levels of 346 K to 356 K. In a young outflow from a developing MCS ice crystal number concentrations of up to (8.3 ± 1.6) cm^&minus;3 and rimed ice particles with maximum dimensions exceeding 1.5 mm were found. A maximum ice water content of 0.05 g m^&minus;3 was observed and an effective radius of about 90 &mu;m. In contrast the aged outflow events were more diluted and showed a maximum number concentration of 0.03 cm^&minus;3, an ice water content of 2.3 &times; 10^&minus;4 g m^&minus;3, an effective radius of about 18 &mu;m, while the largest particles had a maximum dimension of 61 &mu;m. <br><br> Close to the tropopause subvisual cirrus were encountered four times at altitudes of 15 km to 16.4 km. The mean ice particle number concentration of these encounters was 0.01 cm^&minus;3 with maximum particle sizes of 130 &mu;m, and the mean ice water content was about 1.4 &times; 10^&minus;4 g m^&minus;3. All known in situ measurements of subvisual tropopause cirrus are compared and an exponential fit on the size distributions is established for modelling purposes. <br><br> A comparison of aerosol to ice crystal number concentrations, in order to obtain an estimate on how many ice particles may result from activation of the present aerosol, yielded low ratios for the subvisual cirrus cases of roughly one cloud particle per 30 000 aerosol particles, while for the MCS outflow cases this resulted in a high ratio of one cloud particle per 300 aerosol particles