Transport of Nitric Oxide Via Lagrangian Coherent Structures Into the Top of the Polar Vortex

Abstract

The energetic particle precipitation (EPP) indirect effect (IE) refers to the downward transport of reactive odd nitrogen (NOx = NO + NO2) produced by EPP (EPP‐NOx) from the polar winter mesosphere and lower thermosphere to the stratosphere where it can destroy ozone. Previous studies of the EPP IE examined NOx descent averaged over the polar region, but the work presented here considers longitudinal variations. We report that the January 2009 split Arctic vortex in the stratosphere left an imprint on the distribution of NO near the mesopause, and that the magnitude of EPP‐NOx descent in the upper mesosphere depends strongly on the planetary wave (PW) phase. We focus on an 11‐day case study in late January immediately following the 2009 sudden stratospheric warming during which regional‐scale Lagrangian coherent structures (LCSs) formed atop the strengthening mesospheric vortex. The LCSs emerged over the north Atlantic in the vicinity of the trough of a 10‐day westward traveling planetary wave. Over the next week, the LCSs acted to confine NO‐rich air to polar latitudes, effectively prolonging its lifetime as it descended into the top of the polar vortex. Both a whole atmosphere data assimilation model and satellite observations show that the PW trough remained coincident in space and time with the NO‐rich air as both migrated westward over the Canadian Arctic. Estimates of descent rates indicate five times stronger descent inside the PW trough compared to other longitudes. This case serves to set the stage for future climatological analysis of NO transport via LCSs.

Abrupt Change in the Lower Thermospheric Mean Meridional Circulation During Sudden Stratospheric Warmings and Its Impact on Trace Species

“…(2021) and Harvey et al. (2021). Outside of the periods of ES‐SSW events, the current version of SD‐WACCM‐X features westward winds while the radar observed weak westerlies, indicating that the GW‐induced westward drag in the model might be too strong or applied at an altitude range that is too low.…”

NRLMSIS 2.1: An Empirical Model of Nitric Oxide Incorporated Into MSIS

“…This effect is also evident, but not as clear, at northern high latitudes, as shown in Figure S6 in Supporting Information . This behavior of the data may be a reflection of downward transport of NO during intense geomagnetic storms (e.g., Harvey et al., 2021; Smith et al., 2011; and references therein). Alterations in the MSIS formula would be necessary to capture this effect, including a more tailored treatment of the geomagnetic activity time history and possibly coupling with the seasonal dependence.…”

“…of NO during intense geomagnetic storms (e.g., Harvey et al, 2021;Smith et al, 2011;and references therein). Alterations in the MSIS formula would be necessary to capture this effect, including a more tailored treatment of the geomagnetic activity time history and possibly coupling with the seasonal dependence.…”

Lower Thermospheric Material Transport via Lagrangian Coherent Structures

“…While zonally averaged quantities are useful to quantify differences in latitude and altitude, LCSs aggregate differences in flows that vary in latitude, longitude, and time by examining the effect on material transport. LCS analysis has been applied to investigate the transport of nitric oxide in the polar vortex (Harvey et al., 2021 ) at 90 km and ionosphere‐thermosphere interactions above 350 km (Wang et al., 2021 ), and points to a potentially new diagnostic method for analyzing lower thermospheric flow. However, the analysis shown here indicates that the effects of small‐scale waves on material transport may be significant and unconstrained by observations in the lower thermosphere.…”