Articles | Volume 11, issue 6
Research article
21 Jun 2018
Research article |  | 21 Jun 2018

On the consistency of HNO3 and NO2 in the Aleutian High region from the Nimbus 7 LIMS Version 6 data set

Ellis Remsberg, Murali Natarajan, and V. Lynn Harvey

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.

Short summary
Version 6 of the Nimbus 7 LIMS stratospheric data set contains improved profiles of NO2. The variations of V6 HNO3 and NO2 at 31.6 hPa are reassessed for their consistency in the region of the Aleutian High (AH) from 14 to 28 January 1979. Photochemical model calculations initialized with the V6 data and including effects of heterogeneous reactions mimic the observed decreases of NO2 and increases in HNO3 over a period of 10 days along trajectories terminating in the AH region on 28 January.