An ACP article by F. Jégou and co-authors investigates the emissions released into the stratosphere by the Sarychev volcano, on the Kuril Islands, northeast of Japan. The strongest sulphur dioxide emissions occurred from 15-16 April 2009 and an estimated 0.9Tg were injected into the UTLS. By the first week of July the aerosol plume had spread over much of the Arctic region, and was measured by several satellites (OSIRIS, CALIOP), at the surface (lidar), as well as by balloon-borne instruments during the STAC campaign. The OSIRIS stratospheric aerosol optical depth observations indicate an enhancement at 750nm of a factor of 6, with a value of 0.02 in late July compared to 0.0035 before the eruption. Model simulations of the eruption using the HadGEM2 and MIMOSA models agree well with the satellite, in situ, and ground-based observations. Aerosol concentrations returned to near-background levels by spring 2010. The full abstract can be found here.

F. Ploeger and co-authors compare MLS water vapour observations with simulations from the CLaMS model to investigate pathways of water vapour transport in the lower stratosphere during the boreal summer in a new JGR article. In the northern hemisphere (NH) mid- and high latitudes, a negative correlation is found between water vapour and ozone daily tendencies, indicative of frequent horizontal transport from the low latitudes. Analysis of the zonal mean tracer continuity equation shows that poleward of 50°N eddy mixing dominates the horizontal water vapour transport, while in the subtropics horizontal transport is largely due to the residual circulation. Model simulations with transport barriers confirm that most of the annual cycle in NH mid-latitude water vapour above 360K results from horizontal transport from low latitudes. The full abstract can be found here.

J. Liu and co-authors have produced a new ozone climatology utilising ozone soundings and trajectory techniques. The data cover the period 1965-2008, and are available as monthly means at a resolution of 5°x5° from the surface through to 26km. The dataset compares well with SAGE and OSIRIS seasonal and zonal means, with maximum differences of 20% found above 15km. Agreement is better in the northern hemisphere, where more ozone soundings are available, and in the mid- and high latitudes, where reanalysis winds are more accurate. The full abstract can be found here.

P. Baron and co-authors present stratospheric wind observations between 8-0.01hPa (~35-80km) from the SMILES instrument from October 2009 to April 2010. Good agreement between the ECMWF analysis and the observations is found, except for the zonal winds over the equator, where differences greater than 5m/s are found. The results demonstrate that the SMILES instrument and others like it have the potential to provide high quality observations of stratospheric winds. The full abstract can be found here.

D.M. Murphy and co-authors present results distinguishing various stratospheric aerosol particles and their components in a new article in the Quarterly Journal of the Royal Meteorological Society. Under background conditions, between major volcanic eruptions, they find that most stratospheric aerosol are either relatively pure sulphuric acid, sulphuric acid mixed with meteoritic material, or mixed organic-sulphate particles originating from the troposphere. Certain meteoritic elements are dissolved in the particles (e.g. iron and magnesium), while others are found as solid phase inclusions. These solid phases could have large but unknown implications in terms of the particles acting as freezing nuclei for polar stratospheric clouds. Find the full abstract here.

Using a new merged ozone data set, C.E. Sioris and co-authors investigate the trends and variability of ozone in the tropical lower stratosphere. The results presented in a recent ACPD article indicate a statistically significant negative trend at all altitudes from 18-25km over the period 1984-2012 in the merged SAGE-II/OSIRIS dataset. Trends reach up to -6.5% per decade at 18.5km, with underlying strong variations from ENSO, the QBO and tropopause height. The full abstract can be found here.

A recent GRL paper by K.M. Grise and co-authors looks at the effects of the poleward shift in southern hemisphere (SH) tropospheric circulation induced by the Antarctic ozone hole. Using climate model simulations in which only stratospheric ozone depletion is specified, they find that high and mid-level clouds follow the poleward shift of the SH mid-latitude jet, and that low-level clouds decrease over much of the Southern Ocean. The annual hemispheric mean radiation response to the cloud anomalies is estimated at approximately +0.25 W m-2, largely a response to the reduction of total cloud fraction in the SH mid-latitudes in austral summer. Find the full abstract here.

A new paper by R. Hommel and co-authors in ACPD focuses on the exceptionally high ozone loss that occurred during the 2010/2011 Arctic winter. Using both satellite and ground-based observations they examine the composition and transformations occurring in the Arctic polar vortex. A chemical transport model is also used to compare 2011 winter-spring conditions with previous years. The observations show that between ~16–20km ozone is depleted by more than 70%, in comparison with the only slightly more than 20% that occurred in below 20km previous winters. The large ozone loss was found to result from halogen-driven catalytic destruction cycles, activated by the large volume of polar stratospheric clouds generated during the 2010/2011 winter-spring period. Prior to the catalytic cycles being fully effective (mid-January 2011), ozone loss of up to 60% was already observed below ~19km, and is thought to result from meteorological changes resulting in this “mini-hole” event. Such events are expected to increase in frequency as anthropogenically-induced climate change evolves. The full abstract can be found here.

C.I. Garfinke and co-authors present new results in GRL regarding the contrasting impacts of different El Niño types on stratospheric water vapour. Making use of chemistry-climate model, they find that the seasonality and location of peak sea surface temperature (SST) warming impacts the amount of water vapour entering the stratosphere. El Niño events with maximum SST warming in the eastern Pacific in spring result in warming at the tropopause above the warm pool region, leading to more water vapour entering the stratosphere. In contrast, El Niño events with peak warming in the central Pacific in autumn and early winter result in non-uniform warming above the warm pool region and less water vapour entering the stratosphere. Differences in lower stratospheric water vapour between the two El Niño variants approach 0.3ppmv, while differences between spring and autumn responses are greater than 0.5ppmv. The full abstract can be found here.

A recent ACP article by M.C. Parrondo and co-authors looked at 13 years of ozone soundings taken at the Antarctic Belgrano II station. These observations, taken inside the polar vortex when chemical ozone depletion occurs, are particularly valuable during the winter period, when satellite and ground-based observations based on solar radiation are lacking. The decrease of total ozone in spring was found to strongly depend on meteorological conditions, with greatest depletion occurring during coldest years (up to 59%) and considerably less occurring in warmer years (22%). In addition, they found that about 11% of total ozone loss in the layer where maximum depletion occurs takes place before the sun returns and occurs rather as a result of transport of low latitude air masses into the region, indicative of mixing inside the vortex. Comparison with observations from the South Pole station suggest that ozone loss rates at Belgrano are up to 25% lower than at the South Pole. The full abstract can be found here.