Abstract
This study uses photochemical calculations along kinematic trajectories in conjunction with Limb Infrared Monitor of the Stratosphere (LIMS) observations to examine the changes in HNO3 and NO2 near 30 hPa in the region of the Aleutian High (AH) during the minor warming event of January 1979. An earlier analysis of Version 5 (V5) LIMS data indicated increases in HNO3 without a corresponding decrease in NO2 in that region and a quasi-wave 2 signature in the zonal distribution of HNO3, unlike the wave 1 signal in ozone and other tracers. Version 6 (V6) LIMS also shows an increase of HNO3 in that region, but NO2 is smaller than from V5. The focus here is to convey that V6 HNO3 and NO2 are of good quality, as shown by a re-examination of their mutual changes in the AH region. Photochemical model calculations initialized with LIMS V6 data show increases of about 2 ppbv in HNO3 over 10 days along trajectories terminating in the AH region on 28 January. Those increases are mainly a result of the nighttime heterogeneous conversion of N2O5 on background stratospheric sulfuric acid aerosols. Changes in the composition of the air parcels depend on the extent of exposure to sunlight and, hence, on the dynamically controlled history of the trajectories. Trajectories that begin in low latitudes and traverse to across the North Pole in a short time lead to the low HNO3 in the region separating the anticyclone from the polar vortex, both of which contain higher HNO3. These findings help to explain the observed seasonal evolution and areal extent of both species. V6 HNO3 and NO2 are suitable, within their errors, for the validation of stratospheric chemistry-climate models.
Highlights
Introduction and objectivesThe Limb Infrared Monitor of the Stratosphere (LIMS) experiment operated on Nimbus 7 from 25 October 1978 through 28 May 1979
We show the results of sample trajectories that behave similar to those of the ensemble and discuss the transformations occurring in the composition of the air parcels over their 10-day transit
Both the Version 6 (V6) HNO3 and NO2 are of good quality, at least to within their respective error estimates and away from very cold regions of the vortex and their polar stratospheric clouds (PSCs) remnants
Summary
The Limb Infrared Monitor of the Stratosphere (LIMS) experiment operated on Nimbus 7 from 25 October 1978 through 28 May 1979. The present study reconsiders that anomaly but using the V6 data set and a trajectory model that includes the chemistry of reactive nitrogen (NOy), or the sum of NO, NO2, 2N2O5, NO3, HNO3, HO2NO2, and ClONO2 In their analysis of the V5 data, R93 noted finding high values of HNO3 in both the polar vortex and the AH and lower values around the periphery of both circulation systems, resulting in a quasi-wave 2 signature in the HNO3 distribution. 7 time series of variations of PV and of V6 HNO3, H2O, and NO2 on the 550 K potential temperature surface across most of the Northern Hemisphere for the entire 7.25 months of LIMS data In this way, the variations for January are set in the context of the longer-term seasonal changes for those species.
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