Particle production in the lowermost stratosphere by convective lifting of the tropopause

Abstract

Abstract. Aircraft measurements of aerosol particles and trace gases were performed in the upper free troposphere and lower stratosphere during the Stratosphere and Troposphere Experiment by Aircraft Measurements (STREAM-96) campaign from Shannon airport, Ireland. During one measurement flight, ultrafine particle number densities up to 10 4 cm -3 (STP) were observed in the lowermost stratosphere. Concurrent with these very high number densities of ultrafine particles, high accumulation mode particle number densities were observed over the same geographical location in the free troposphere, which were attributed to convective transport in the troposphere. The observations suggest that adiabatic cooling of the stratospheric air, as a result of the convective transport in the troposphere that lifted the tropopause and the air in the lowermost stratosphere, was responsible for triggering the formation of new particles.However, also aircraft emissions could have contributed to the enhancement in ultrafine particles. level of the anvil outflow. They explain particle formation in these regions by the high relative humidity and the low preexisting particle number concentration in the air detraining from the cloud. Both conditions are favorable for new particle formation. Similar observations were made by Hegg et al. [1990] near the tops of marine stratiform clouds. They, however, also showed one case where the enhanced Aitken particle layer was separated from the cloud, which they explained by advection of continental air. In this study we present observations of high number densities of ultrafine particles in the lowermost stratosphere, which are proposed to be associated with convective activity in the troposphere. ExperimentDuring the Stratosphere and Troposphere Experiment by Aircraft Measurements (STREAM-96) campaign, six flights were conducted in the free troposphere and lower stratosphere from Shannon airport, Ireland. Instruments for in situ measurements of aerosols and trace gases were installed on a Cessna Citation II twinjet aircraft, operated by the Technical University of Delft, Netherlands. This study focuses on the particle measurements performed on May 22, 1996, over the Atlantic Ocean close to the west coast of Ireland, since this was the only flight where indications for new particle formation were observed in the lower stratosphere. A selection of the measured trace gases is used for the interpretation of the data, namely, ozone, carbon dioxide, and water vapor. On this day a vertical "stack flight," composed of five isobaric flight legs in the free troposphere and lower stratosphere, was carried out between 1400 and 1800 UTC. The flight pattern is shown in Figure 1. The flight section that we focus on covered a region of 6 km in altitude (between 6.5 and 12.5 km altitude), 2 ø in latitude (•220 km) and 1.5 ø in longitude (• 135 km). Horizontal flight tracks were flown at 428, 315, 262, 216, and 178 hPa, respectively.The flight was performed about 6 to 10 hours after the passage of a cold front, whi...

The Extratropical Upper Troposphere and Lower Stratosphere

“…While deep pyrocumulus are infrequent, observations have shown episodic injection of tropospheric species and biomass burning products into the Ex‐UTLS above the tropopause [ Waibel et al , 1999; Fromm and Servranckx , 2003]. The effect of convective uplifting near the tropopause may also lead to in situ particle formation in the lower stratosphere [ de Reus et al , 1999]. However, it is not clear these processes are important climatologically or for maintaining the Ex‐UTLS.…”

The effects of airmass history on new particle formation in the free troposphere: case studies

“…Recent aircraft studies showed new particle formation (NPF) in the free troposphere and lower stratosphere (de Reus et al, 1998(de Reus et al, , 1999Nyeki et al, 1999;Twohy et al, 2002;Lee et al, 2003;Young et al, 2007) with high frequencies (up to 86-100%) (Young et al, 2007) and strong magnitudes (up to 45 000 cm −3 ) (Twohy et al, 2002). Hermann et al (2003) have provided so far the most comprehensive statistical analysis of NPF in the Northern Hemisphere tropopause region from three-year aircraft measurements; elevated particle number concentrations of 1500-8000 cm −3 were frequently observed in a wide range of latitudes (5 • N-50 • N).…”

Columnar modelling of nucleation burst evolution in the convective boundary layer – first results from a feasibility study Part I: Modelling approach

“…The influence of atmospheric waves, such as Kelvin-Helmholtz instabilities, on NPF was investigated by Bigg (1997), Nyeki et al (1999) and Nilsson et al (2000a). The effects of synoptic weather, planetary boundary layer (PBL) evolution, e.g., adiabatic cooling, turbulence, entrainment and convection, respectively, on aerosol formation were analysed: -In the MBL by Russell et al (1998), Coe et al (2000), Pirjola et al (2000) and O'Dowd et al (2002); -In the CBL by Nilsson et al (2000b), Aalto et al (2001), Buzorius et al (2001), Nilsson et al (2001a,b), Boy and Kulmala (2002), Buzorius et al (2003), Stratmann et al (2003), Uhrner et al (2003), Boy et al (2004) and Siebert et al (2004); -In the free troposphere (FT) and UT by Schröder and Ström (1997), Clarke et al (1999), de Reus et al (1999, Hermann et al (2003) and Khosrawi and Konopka (2003).…”