Planetary-Wave modulation of mesospheric and lower thermosphere nitric oxide structure and transport during major Sudden Stratospheric Warmings

Abstract. Nitric oxide (NO) produced by energetic particle precipitation in the polar mesosphere and lower thermosphere can descend into the winter stratosphere, where it contributes to catalytic ozone loss and links solar forcing to middle-atmosphere composition and dynamics. Previous studies have shown pronounced longitudinal structure in NO transport during individual sudden stratospheric warmings (SSWs), but it remains unclear whether this organization is a recurring feature of Arctic SSWs. Here, we use ACE-FTS NO observations, SABER temperature and geopotential height measurements, MERRA-2 meteorological fields, and specified-dynamics WACCM-X simulations to examine 11 major Arctic SSWs during 2006–2024. Composite analyses show coherent NO structures near 90 km organized by planetary-wave (PW) phase, with enhanced NO preferentially located in PW troughs and reduced NO in PW ridges. This phase dependence extends through much of the 70–100 km region. Profile-derived effective NO transport rates indicate consistently stronger downward transport in PW troughs than in ridges for split events, whereas displaced-vortex SSWs show smaller and more variable ridge–trough differences. WACCM-X qualitatively reproduces the observed behavior but generally underestimates the ridge–trough contrast for split events. These results show that PW organization of mesospheric NO is a recurring feature within the analyzed event sample and provide a framework for evaluating whole-atmosphere models beyond zonal-mean diagnostics.