Stratospheric influence on the seasonal cycle of nitrous oxide in the troposphere as deduced from aircraft observations and model simulations

Abstract

[1] The atmospheric N 2 O variations between the Earth's surface and the lower stratosphere, simulated by an atmospheric general circulation model-based chemistry transport model (ACTM), are compared with aircraft and satellite observations. We validate the newly developed ACTM simulations of N 2 O for loss rate and transport in the stratosphere using satellite observations from the Aura Microwave Limb Sounder (Aura-MLS), with optimized surface fluxes for reproducing N 2 O trends observed at the surface stations. Observations in the upper troposphere/lower stratosphere (UT/LS) obtained by the Japan AirLines commercial flights commuting between Narita (36°N), Japan, and Sydney (34°S), Australia, have been used to study the role of stratospheretroposphere exchange (STE) on N 2 O variability near the tropopause. Low N 2 O concentration events in the UT region are shown to be captured statistically significantly by the ACTM simulation. This is attributed to successful reproduction of stratospheric air intrusion events and N 2 O vertical/horizontal gradients in the lower stratosphere. The meteorological fields and N 2 O concentrations reproduced in the ACTM are used to illustrate the mechanisms of STE and subsequent downward propagation of N 2 O-depleted stratospheric air in the troposphere. Aircraft observations of N 2 O vertical profile over Surgut (West Siberia, Russia; 61°N), Sendai-Fukuoka (Japan; 34°N-38°N), and Cape Grim (Tasmania, Australia; 41°S) have been used to estimate the relative contribution of surface fluxes, transport seasonality in the troposphere, and STE to N 2 O seasonal cycles at different altitude levels. Stratospheric N 2 O tracers are incorporated in the ACTM for quantitative estimation of the stratospheric influence on tropospheric N 2 O. The results suggest strong latitude dependency of the stratospheric contribution to the tropospheric N 2 O seasonal cycle. The periods of seasonal minimum in the upper troposphere, which are spring over Japan and summer over Surgut, are in good agreement between the ACTM and observation and indicate a different propagation path of the stratospheric signal between the two sites in the Northern Hemisphere. The stratospheric tracer simulations, when utilized with the observed seasonal cycle, also provide qualitative information on the seasonal variation in surface fluxes of N 2 O.Citation: Ishijima, K., et al. (2010), Stratospheric influence on the seasonal cycle of nitrous oxide in the troposphere as deduced from aircraft observations and model simulations,

Variations of tropospheric methane over Japan during 1988–2010

“…(3) The N 2 O concentration data lower by more than 2.7 ppb (3s at altitudes 4Á6 km over eastern Japan) than the long-term trends were defined as STEinfluenced samples (open circles in Figure A1 in Supplementary file). In general, the STE events are frequent above 7 km over Japan (Ishijima et al, 2010). It is noted that the N 2 O criterion in this study is less restrictive than that of 1.0 ppb in Assonov et al (2013), who also applied a similar method for analysing data taken by passenger aircraft.…”

“…Previous studies have reported details of the Tohoku University (TU) aircraft observations for CO 2 (Tanaka et al, 1987;Nakazawa et al, 1993b), N 2 O (Ishijima et al, 2001(Ishijima et al, , 2010 and O 2 /N 2 (Ishidoya et al, 2012). To collect air samples using aircraft, two programs have been conducted (Fig.…”

“…The MD-80 and MD-90 aircraft frequently encounter STE events or intersect the tropopause at their cruise altitudes over Japan particularly in JanuaryÁApril, in association with tropopause breaks, tropopause folds and seasonal descent of the tropopause (Ishijima et al, 2010 Volk et al, 1997) and relatively well mixed in the troposphere without any measurable loss mechanism (e.g. Prinn et al, 1990;Ishijima et al, 2010). As a result, the N 2 O concentration has a sharp gradient around the tropopause, allowing us to detect STE events by low N 2 O concentrations (Ishijima et al, 2010;Assonov et al, 2013).…”

“…Prinn et al, 1990;Ishijima et al, 2010). As a result, the N 2 O concentration has a sharp gradient around the tropopause, allowing us to detect STE events by low N 2 O concentrations (Ishijima et al, 2010;Assonov et al, 2013). Detection of STE-influenced samples was made as follows.…”

Vertical distributions of N<sub>2</sub>O isotopocules in the equatorial stratosphere

“…To examine the factors controlling the stratospheric distributions of N 2 O isotopocules, a numerical simulation was conducted using the Center for Climate System Research/National Institute for Environmental Studies/Frontier Research Center for Global Change atmospheric general circulation model with chemical reactions (CCSR/NIES/FRCGC ACTM) (Ishijima et al, 2010(Ishijima et al, , 2015. Because Ishijima et al (2015) have already given a detailed description of the N 2 O isotopocule model, we briefly explain it here.…”