Validation of SCIAMACHY limb NO<sub>2</sub> profiles using solar occultation measurements

Abstract

The increasing amounts of reactive nitrogen in the stratosphere necessitates accurate global measurements of stratospheric nitrogen dioxide (NO₂). Over the past decade, the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument on ENVISAT (European Environmental Satellite) has been providing global coverage of stratospheric NO₂ every 6 days, which is otherwise difficult to achieve with other systems (e.g. balloon measurements, solar occultation). In this study, the vertical distributions of NO₂ retrieved from limb measurements of the scattered solar light from the SCIAMACHY instrument are validated using NO₂ products from three different satellite instruments (SAGE II, HALOE and ACE-FTS). The retrieval approach, as well as the sensitivity of the SCIAMACHY NO₂ limb data product are discussed, and the photochemical corrections needed to make this validation feasible, as well as the chosen collocation criteria are described. For each instrument, a time period of two years is analyzed with several hundreds of collocation pairs for each year and instrument. The agreement between SCIAMACHY and each instrument is found to be better than 10 % between 22–24 km and 40 km. Additionally, NO₂ amounts in three different latitude regions are validated individually, with considerably better agreements in high and middle latitudes compared to tropics. Differences with SAGE II and ACE-FTS below 20 km are consistent with those expected from the diurnal effect

Proposed standardized definitions for vertical resolution and uncertainty in the NDACC lidar ozone and temperature algorithms – Part 2: Ozone DIAL uncertainty budget

“…The term "a priori" here does not mean that the ozone DIAL retrieval uses a variational/optimal estimation method (it does not), but simply means that the information comes from ancillary (i.e., non-lidar) measurements or models, and is input as "truth" in the ozone DIAL processing chain. The input quantities in this case can be of different nature, namely mixing ratio or number density (e.g., Ahmad et al, 2007;Bauer et al, 2012;Bracher et al, 2005;Brohede et al, 2007;Brühl et al, 2013;Cao et al, 2006;He et al, 2014;McLinden et al, 2014). In order to ensure self-consistency in our measurement model, input quantities independent of air number density should be chosen.…”

Proposed standardized definitions for vertical resolution and uncertainty in the NDACC lidar ozone and temperature algorithms – Part 3: Temperature uncertainty budget

“…(12) comprise the sum of ancillary ozone and NO 2 number densities taken at all altitudes from the ground to the altitude considered z(k). Depending on the data source, these ancillary profiles may be mixing ratio or number density (Ahmad et al, 2007;Bauer et al, 2012;Bracher et al, 2005;Brohede et al, 2007). Assuming that all values within the same ancillary profile are fully correlated, uncertainty components owing to the ancillary ozone and NO 2 profiles can be propagated to temperature similarly to the uncertainty component owing to air number density (i.e., Eq.…”

Modeling the inorganic bromine partitioning in the tropical tropopause layer over the eastern and western Pacific Ocean

“…Their O 3 scaling technique allowed retrieval of NO 2 concentrations of 15 ± 15 ppt in the TTL, with a range of 70-170 ppt in the mid-latitude lower stratosphere associated with older stratospheric air intrusions. However, previous studies have shown large associated uncertainties in NO 2 measurements based on remote sensing instruments, which also depends on the individual observation geometries and instrument operation times (e.g., 30 % of total relative error of NO 2 measurements below 25 km; Weidner et al, 2005 and 50 % error for satellite measurements from SAGE II bellow 25 km; Bauer et al, 2012).…”