Science Update: Chemical composition observations of stratospheric aerosol particles

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.

Science Update: New merged vertically resolved ozone observations: SAGE-II and OSIRIS

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.

Science Update: Indirect effects of the ozone hole: cloud-radiative anomalies in response to the poleward jet shift

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.

Science Update: Chemical composition and severe ozone loss during the 2010/2011 Arctic winter

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.

Science Update: Contrasting effects of El Niño variants on stratospheric water vapour

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.

Science Update: Balloon measurements of Antarctic ozone variability inside the Polar Vortex

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.

Science Update: Improved annular mode variability using a very high resolution AGCM

E. Palipane and co-authors, in a recent GRL paper, use the ECMWF IFS global AGCM run at 16km resolution to assess the benefit of resolving sub-synoptic to mesoscale processes on annular mode (AM) variability. The model run at this resolution was found to be more skilful, particularly in terms of the variance of AMs, the intrinsic e-folding time scales of the AMs, as well as the downward influence from the stratosphere to the troposphere in the AMs. The full abstract can be found here.

Science update: ACE-FTS satellite observations of PAN in the UTLS

K.A. Tereszchuk and co-authors present a new PAN (peroxyacetyl nitrate) data product from the ACE-FTS satellite in a recent ACP paper. The estimated detection limit is 5pptv while the total systematic error contribution to the retrieval is approximately 16%. Comparison between the ACE-FTS product and measurements from the MIPAS instrument demonstrate good agreement, differing by no more than 70pptv. The data are used to produce zonal mean distributions of seasonal averages from 5-20km, with a strong seasonality being observed in the UTLS. Find the full abstract here.

Science Update: Comparison of three vertically-resolved ozone data sets

A recent ACP paper by B. Hassler and co-authors compares three vertically-resolved ozone data sets, the data set of Randel and Wu (2007), Cionni et al., (2011) and Bodeker et al., (2013). All three data sets represent multiple-linear regression fits to vertically resolved ozone observations and cover at least the period from 1979-2005. They find that the main differences among the data sets result from the underlying regression models used, which use different observations and include different basis functions. Climatologies, trends and calculated stratospheric ozone radiative forcing are compared between the three data sets as well. Find the full abstract here.

Science Update: Stratospheric ozone depletion a key driver of precipitation trends

A recent paper in Climate Dynamics by Paula L.M. Gonzalez and co-authors focuses on understanding the regional precipitation trends in South Eastern South America (SESA). Using 6 different climate models they show that the impact of ozone depletion on SESA precipitation has been as large as, or possibly even larger than, the impact of increasing greenhouse gas concentrations over the period 1960-1999. Find the full abstract here.