N₂O and NO_y observations in the 1999/2000 Arctic polar vortex: Implications for transport processes in a CTM

Abstract

[1] We compare the evolution of simulated NO y and N 2 O with observations made during the 1999/2000 NASA Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment/Third European Stratospheric Experiment on Ozone-2000 to understand the different effects of transport on these two species and evaluate model transport processes in the Arctic lower stratosphere during mid to late winter. The simulations were made with the Goddard Space Flight Center chemistry and transport model, driven by meteorological analyses from the Goddard Data Assimilation Office. In January, model NO y and N 2 O distributions agree well with observations, provided a substantial loss of NO y due to polar stratospheric cloud sedimentation is included in the model simulation. In late winter, model NO y is $2-3 times larger than observed, despite the continued reasonable agreement of N 2 O. Anomalously large vertical transport of NO y due to overly vigorous descent in the CTM is primarily responsible for the large late winter NO y mixing ratios. However, the rapid descent is not apparent in the evolution of modeled N 2 O and presumably other similar species due to compensating horizontal transport of N 2 O across the vortex edge, which results in the reasonable agreement between modeled and measured N 2 O at ER-2 altitudes throughout the winter. The need to properly represent the seasonal evolution of NO y when studying lower stratospheric polar wintertime photochemistry places strong constraints on the meteorological data used to drive global chemistry and transport models.

Sensitivity of Global Modeling Initiative model predictions of Antarctic ozone recovery to input meteorological fields

“…Residual circulations inferred from analyzed meteorological data are typically too vigorous, producing young stratospheric air. [ Considine et al , 2003; Schoeberl et al , 2003; Weaver et al , 1993].…”

Understanding the Changes of Stratospheric Water Vapor in Coupled Chemistry–Climate Model Simulations

“…In this study, the model was run at a resolution of 2°latitude by 2.5°longitude with 55 layers up to 80 km. The gasphase stratospheric chemistry used in the model runs is from Douglass and Kawa (1999), with the representation of polar stratospheric clouds and their heterogeneous chemical impacts taken from Considine et al (2003), as described in Stolarski et al (2006).…”

The impact of model grid zooming on tracer transport in the 1999/2000 Arctic polar vortex

“…However, this comparison does not separate horizontal and vertical model transport, so that both may have contributed to the discrepancies. A way to separate horizontal and vertical transport was described by Considine et al (2003). They isolated the vertical model transport by eliminating tracer concentration gradients along the isentropic model levels.…”

“…In this study, we increased the horizontal resolution of TM5 up to 1 • ×1 • for a relatively large area (northward of 30 • N). Nevertheless, the discrepancies remain, which may be an indication that the accuracy of the mass fluxes as provided by ECMWF is insufficient (Considine et al, 2003;Plumb et al, 2002). Recent studies indicate that errors in the stratospheric circulation in assimilated meteo fields exist that may play a crucial role here, e.g.…”

“…It was suggested that this was related to the underlying meteorological data, since doubling their original horizontal resolution of 2.8 • ×2.8 • did not make a difference. Another study of N 2 O and NOy transport during this winter showed that increasing the vertical resolution did not improve the comparison of model results with observations either (Considine et al, 2003).…”