New results from OSIRIS: upper-stratospheric temperature trends

Temperature trends in the upper stratosphere, particularly above ∼ 45 km, are difficult to quantify due to a lack of observational data with high vertical resolution in this region that span multiple decades. The recent v7.3 upper-stratospheric (35–60 km) temperature data product from the Optical Spectrograph and InfraRed Imager System (OSIRIS) includes over 22 years of observations that can be used to estimate temperature trends. The trends in OSIRIS temperatures over 2005–2021 are compared to those from two other satellite limb instruments: Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS). We find that the upper stratosphere cooled by ∼ 0.5 to 1 K per decade during this period. Results from the three instruments are generally in agreement. By merging the OSIRIS observations with those from channel 3 of the Stratospheric Sounding Unit (SSU), we find that the stratosphere cooled at a rate of approximately −0.6 K per decade between 1979 and 2021 near 45 km, in agreement with earlier results based on SSU and MLS. The similarity between OSIRIS temperature trends and those from other records improves confidence in observed upper-stratospheric temperature changes over the last several decades.

Figure 1: Temperature trends for 2005–2021. Trends are shown for (a) MLS, (b) SABER, and (c) OSIRIS. Hatching denotes statistically insignificant trends at the 2σ level. The bottom row, panels (d) to (h), shows vertical profiles comparing the same trends from the three instruments in 20° latitude bins. The shaded regions denote the 2σ uncertainty in the MLR.

OSIRIS temperature data products spans over 22 years

A new upper stratospheric (35–60 km) temperature data product has been produced using OSIRIS limb-scattered spectra that now spans over 22 years. Temperature is calculated by first estimating the Rayleigh scattering signal and then integrating hydrostatic balance combined with the ideal gas law. Uncertainties are estimated to be 1–5 K, with a vertical resolution of 3–4 km. Correlative comparisons with the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and the Microwave Limb Sounder on Aura (MLS) are consistent with these uncertainty estimates and generally have no regions of statistically significant drift. The temperature data product is publicly distributed as part of the recently released OSIRIS v7.3 data products. An example of the produced data is shown in Figure 1. The technique differs from previous techniques in that multiple scattering is included rigorously in the forward model, with a novel method to estimate the amount of upwelling radiation.

Figure 1: Tropical (20oS to 20oN) monthly zonal mean time series calculated from OSIRIS v7.3 temperature data product.

Chemistry Contribution to Stratospheric Ozone Depletion After the Unprecedented Water-Rich Hunga Tonga Eruption

Following the Hunga Tonga-Hunga Ha'apai (HTHH) eruption in January 2022, stratospheric ozone depletion was observed at Southern Hemisphere mid-latitudes and over Antarctica during the 2022 austral wintertime and springtime, respectively. The eruption injected sulfur dioxide and unprecedented amounts of water vapor into the stratosphere. This work examines the chemistry contribution of the volcanic materials to ozone depletion using chemistry-climate model simulations with nudged meteorology. Simulated 2022 ozone and nitrogen oxide (NOx = NO + NO2) anomalies show good agreement with satellite observations. We find that chemistry yields up to 4% ozone destruction at mid-latitudes near ∼70 hPa in August and up to 20% ozone destruction over Antarctica near ∼80 hPa in October. Most of the ozone depletion is attributed to internal variability and dynamical changes forced by the eruption. Both the modeling and observations show a significant NOx reduction associated with the HTHH aerosol plume, indicating enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol.

OSIRIS data helps to unravel complex behaviour of ozone layer recovery

After decades of depletion in the 20th century, near-global ozone now shows clear signs of recovery in the upper stratosphere.  In the tropical lower stratosphere, ozone is expected to decrease as a consequence of enhanced upwelling driven by increasing greenhouse gas concentrations, and this is consistent with observations. There is recent evidence, however, that mid-latitude ozone continues to decrease as well, contrary to model predictions. We use OSIRIS ozone profile measurements to show that these differences might be related to changes in atmospheric circulation.