Abstract
Abstract. An aircraft measurement campaign involving the Russian high-altitude aircraft M55 Geophysica and the German DLR Falcon was conducted in Darwin, Australia in November and December 2005 as part of the European integrated project SCOUT-O3. The overall objectives of the campaign were to study the transport of trace gases through the tropical tropopause layer (TTL), mechanisms of dehydration close to the tropopause, and the role of deep convection in these processes. In this paper a detailed roadmap of the campaign is presented, including rationales for each flight, and an analysis of the local and large-scale meteorological context in which they were embedded. The campaign took place during the pre-monsoon season which is characterized by a pronounced diurnal evolution of deep convection including a mesoscale system over the Tiwi Islands north of Darwin known as "Hector". This allowed studying in detail the role of deep convection in structuring the tropical tropopause region, in situ sampling convective overshoots above storm anvils, and probing the structure of anvils and cirrus clouds by Lidar and a suite of in situ instruments onboard the two aircraft. The large-scale flow during the first half of the campaign was such that local flights, away from convection, sampled air masses downstream of the "cold trap" region over Indonesia. Abundant cirrus clouds enabled the study of active dehydration, in particular during two TTL survey flights. The campaign period also encompassed a Rossby wave breaking event transporting stratospheric air to the tropical middle troposphere and an equatorial Kelvin wave modulating tropopause temperatures and hence the conditions for dehydration.
Highlights
SCOUT-O3 is a European integrated project aiming at a better understanding of the link between stratospheric chemistry and, in particular, stratospheric ozone and climate change
A tropical aircraft measurement campaign was conducted in the framework of the European integrated project SCOUTO3 at Darwin, Australia in November/December 2005
The campaign aimed at studying the mechanisms of transport through the tropical tropopause layer (TTL) and into the stratosphere, and the role of deep convection versus large-scale transport, details of cirrus formation and dehydration, and the fate of very short lived substances
Summary
SCOUT-O3 is a European integrated project aiming at a better understanding of the link between stratospheric chemistry and, in particular, stratospheric ozone and climate change. Similar conclusions were drawn by Bonazzola and Haynes (2004) and Fueglistaler et al (2004, 2005) by means of trajectory calculations based on large-scale wind fields They modeled freeze-drying in each air parcel undergoing TST by assuming its water partial pressure to relax to the equilibrium vapor pressure over ice at the lowest temperature encountered. Complemented with an excellent ground infrastructure with a polarimetric radar, regular radiosondes, and the Atmospheric Radiation Monitoring (ARM) site, Darwin may be considered a “natural laboratory” for studies of tropical deep convection It further hosts a regional forecasting center of the Australian Bureau of Meteorology (BoM) which generously supported the campaign by addressing specific questions during their regular briefings and providing access to real-time radar data and other analysis tools.
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