Deep convective injection of boundary layer air into the lowermost stratosphere at midlatitudes

Abstract

Abstract.On 22 August 2001 a measurement flight was performed with the German research aircraft FALCON from Sardinia to Crete as part of the Mediterranean Oxidant Study (MINOS). Cruising at 8.2 km, the aircraft was forced to climb to 11.2 km over the southern tip of Italy to stay clear of the anvil of a large cumulonimbus tower. During ascent into the lowermost stratosphere in-situ measurements onboard the FALCON indicated several sharp increases in the concentrations of tropospheric trace gases, e.g. CO, acetone, methanol, benzene and acetonitrile, above the anvil. During one particular event deep in the stratosphere, at O 3 concentrations exceeding 200 ppv, CO increased from about 60 to 90 ppv, while the concentration of acetone and methanol increased by more than a factor of 2 (0.7 to 1.8 ppv for acetone; 0.4 to 1.4 ppv for methanol). Enhancements for the short lived species benzene are even higher, increasing from 20 pptv in the stratosphere to approx. 130 pptv. The concentrations during the event were higher than background concentrations in the upper troposphere, indicating that polluted boundary layer air was directly mixed into the lowermost stratosphere.

Influence of corona discharge on the ozone budget in the tropical free troposphere: a case study of deep convection during GABRIEL

“…This leads to ozone mixing ratios of only a few ppbv in the marine boundary layer (Johnson et al, 1990). In continental regions the O 3 mixing ratio typically varies between about 15 and 30 ppbv (Fortuin and Kelder, 1998;Folkins et al, 2002). At higher altitudes there is a local maximum in the profile around 6-7 km due to reduced ozone destruction compared to the boundary layer.…”

“…During convective transport, air from different layers throughout the whole troposphere can be mixed into the updraft region and lifted to the upper troposphere (UT), a process called entrainment, which can contribute a fraction of more than 50 % to the total mass flux (Dickerson et al, 1987;Fischer et al, 2003). Additionally, detrainment is possible, which means that the outflow of air from the updraft region can be transported outside the cloud into the troposphere below the cloud top (Lawrence and Rasch, 2005).…”

“…In continental areas the local minimum at around 11 km is not always present (Folkins et al, 2002). In the continental boundary layer ozone precursors from local emissions by vegetation and anthropogenic pollution can have high concentrations.…”

“…Following Fischer et al (2003) the mixing ratio of an inert trace gas in the outflow of the Cb cloud can be described with the following equation:…”

“…A 1-D model, with the ozone mixing ratio in the convective outflow treated as a free parameter, reproduces this profile reasonably well. In this model vertical advection, including downward transport from the stratosphere, convective transport and photochemical production of ozone are considered (Folkins et al, 2002). This generic ozone profile indicates a local minimum in the remote boundary layer caused by local ozone destruction under warm, moist and low NO x conditions (Lelieveld and Crutzen, 1994).…”