Hydrocarbons in the upper troposphere and lower stratosphere observed from ACE‐FTS and comparisons with WACCM

Abstract

[1] Satellite measurements from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) are used to examine the global, seasonal variations of several hydrocarbons, including carbon monoxide (CO), ethane (C 2 H 6 ), acetylene (C 2 H 2 ), and hydrogen cyanide (HCN). We focus on quantifying large-scale seasonal behavior from the middle troposphere to the stratosphere, particularly in the tropics, and furthermore make detailed comparisons with the Whole Atmosphere Community Climate Model (WACCM) chemistry climate model (incorporating tropospheric photochemistry, time-varying hydrocarbon emissions, and meteorological fields nudged from reanalysis). Comparisons with Microwave Limb Sounder (MLS) measurements of CO are also included to understand sampling limitations of the ACE-FTS data and biases among observational data sets. Results show similar overall variability for CO, C 2 H 6, and C 2 H 2 , with a semiannual cycle in the tropical upper troposphere related to seasonallyvarying sources and deep tropical convection, plus a maximum during Northern Hemisphere summer tied to the Asian monsoon anticyclone. These species also reveal a strong annual cycle above the tropical tropopause, tied to annual variations in the upward branch of Brewer-Dobson circulation. HCN reveals substantial differences from the other species, due to a longer photochemical lifetime and a chemical sink associated with ocean surface contact, which produces a minimum in the tropical upper troposphere not observed in the other species. For HCN, transport to the stratosphere occurs primarily through the Asian summer monsoon anticyclone. Overall, the WACCM simulation is able to reproduce most of the large-scale features observed in the ACE-FTS data, suggesting a reasonable simulation of sources and large-scale transport. The model is too low in the Southern Hemisphere subtropics during Austral spring, which indicates underestimate of biomass burning emissions and/or insufficient vertical transport in the model.

Quantifying tracer transport in the tropical lower stratosphere using WACCM

“…Randel et al (2007) proposed that this behavior results primarily from vertical transport; seasonal variations in the Brewer-Dobson circulation acting on the strong background vertical gradient in ozone can account for the phase, amplitude and vertical structure of the ozone annual cycle. Similar effects occur for other tracers with strong vertical gradients across the tropopause, including carbon monoxide (CO) or tropospheric hydrocarbons such as ethane (C 2 H 6 ) (Park et al, 2013). On the other hand, complementary modeling analyses using a Lagrangian transport framework suggest that the large annual cycle in ozone mainly results from horizontal in-mixing, in particular due to transport associated with the Asian summer monsoon anticyclone (Konopka et al, 2009(Konopka et al, , 2010.…”

Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS

“…In contrast to MIPAS observations, in this region the ACE-FTS distribution is dominated by measurements from January, when the plume is already considerably weaker than in December. HCN climatologies derived from ACE-FTS measurements have already been published by Lupu et al (2009), Randel et al (2010 and Park et al (2013). As a more quantitative intercomparison, Fig.…”

“…However, they expected an irregular cycle for a longer time series, because Indonesian biomass burning is strongly influenced by El Niño events. Park et al (2013), who analysed a longer time series of tropical HCN from ACE-FTS, found tape recorder cycles of 1 and 2 years. Thus the question of whether there is a periodicity in the HCN tape recorder signal is still open, and the long time series of MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) data is well suited for providing insight into this problem.…”

“…Spaceborne observations of global HCN have been performed by the Fourier transform spectrometer of the Atmospheric Chemistry Experiment (ACE-FTS) on SCISAT Boone et al, 2005;Rinsland et al, 2005) and, generally restricted to the middle atmosphere, by the Microwave Limb Sounder (MLS) on the Aura satellite (Pumphrey et al, 2006). Climatologies of the HCN distribution derived from ACE-FTS measurements have been presented by Lupu et al (2009), Randel et al (2010) and Park et al (2013).…”

Five years of CO, HCN, C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, CH<sub>3</sub>OH, HCOOH and H<sub>2</sub>CO total columns measured in the Canadian high Arctic

“…As shown previously, the ACE-FTS measures VMR profiles of CO (Clerbaux et al, 2008), hydrocarbons, such as HCN, C 2 H 6 , C 2 H 2 (Park et al, 2013) and HCOOH (González Abad et al, 2009) in the upper troposphere and lower stratosphere. In addition to these species, CH 3 OH and H 2 CO have been measured by the ACE-FTS globally (Dufour et al, , 2009) and in biomass burning plumes over northern high latitudes Tereszchuk et al, 2011Tereszchuk et al, , 2013 and in the Southern Hemisphere .…”