Coupling between middle and upper atmospheric NO: Constraints from HALOE observations

Observations of NO, NO 2 , and CH 4 from the HALOE instrument on the UARS satellite are used to investigate the transport of thermospheric NO into the middle atmosphere. By comparing the variation of NO and NO 2 with simultaneous measurements of a long lived stratospheric tracer like CH 4 , regions of enhanced odd nitrogen can be quantified. Our results indicate substantial enhancement of NO in the high latitude winter mesosphere extending from thermospheric altitudes down to about 55–60 km. We also see evidence of substantial equator ward mixing of mesospheric NO. Occasional enhancements of NOx are seen extending down into the upper stratosphere in winter; however, they do not appear to persist. Observations by HALOE at latitudes up to 75–80 degrees in early spring show no evidence for enhanced NOx. This suggests that the effect of thermospheric NO on high latitude upper stratospheric O 3 may be less than previously thought.