Recent Arctic ozone loss has been linked with climate change resulting from increasing greenhouse gases. In a recent GRL paper, H. Rieder and co-authors provide evidence to the contrary, by focusing on the volume of polar stratospheric clouds (PSCs), a simple proxy for polar ozone loss. Analysis of three reanalysis datasets and results from a stratosphere-resolving chemistry-climate model indicate no statistically significant trends in PSC volume, nor any change in their probability density functions, during the period 1979-2011. The full abstract can be found here.

Using both satellite observations and chemistry-climate models, C.I. Garfinkel and co-authors examine the zonal structure of tropical lower stratospheric temperature, water vapour, and ozone trends in a recent JGR article. Trends in both the tropical upper troposphere (warming) and lower stratosphere (cooling) have been strongest over the Indo-Pacific warm pool region and much weaker over the western and central Pacific. The model simulations suggest that the sea surface temperatures (SSTs) drive this zonal asymmetry with warming SSTs in the Indian Ocean and warm pool region having led to enhanced moist heating in the upper troposphere, and in turn to a Gill-like response that extends into the lower stratosphere. This has led to a zonal structure in ozone and water vapour trends and subsequently to less water vapour entering the stratosphere. Projected future SSTs drive a similar zonally-structure response in temperature and water vapour, which, for the lower stratosphere are similar in strength to that due directly to projected future CO2, ozone, and methane. The full abstract can be found here.

A recent GRL paper by M. McGillen and co-authors presents measurements of the CFC-11 (CFCl3) absorption spectrum over various wavelengths (184.95–230nm) and temperatures (216–296K). Uncertainty in the temperature dependence, particularly in the UV absorption spectrum, is a significant contributing factor of overall uncertainty in CFC-11’s global lifetime. They find that the spectrum temperature dependence is less than that currently in use and that this slightly reduces the CFC-11 lifetime calculated with a 2D model using a spectrum parameterization developed in this work. Find the full abstract here.

S. Oberländer and co-authors investigate the different processes affecting the Brewer Dobson Circulation in future using the EMAC chemistry-climate model in a new JGR article. Using several sensitivity simulations they isolate the effects of external forcings such as greenhouse gases, sea surface temperatures (SSTs) and ozone-depleting substances. They find that in boreal winter the tropical upward mass flux increases by about 1%/decade (2%/decade) in the upper (lower) stratosphere until the end of the 21^st century. The mean stratospheric age of air decreases by up to 60 and 30 days/decade, respectively. Changes in transient planetary and synoptic waves account for the strengthening of the BDC in the lower stratosphere, whereas upper stratospheric changes are due to improved propagation properties for gravity waves in future climate. The radiative impact of increasing GHG concentrations is detected only in the upper stratosphere, whereas the effect of increasing SSTs dominates the lower stratospheric signal. Changes in tropical SSTs influence not only the shallow but also the deep branch of the BDC as confirmed from both changes in residual circulation and mixing. Declining ODSs were found to slightly counteract the BDC increase in the Southern Hemisphere. The full abstract can be found here.

Some of the first results from the SPARC Data Initiative to be published, this new article by M.I. Hegglin and co-authors in JGR compares the water vapour climatologies from various satellite limb sounders for the period 1978-2010. Monthly zonal means from LIMS, SAGE II, UARS-MLS, HALOE, POAM III, SMR, SAGE III, MIPAS, SCIAMACHY, ACE-FTS, and Aura-MLS were calculated on a common latitude-pressure grid and then compared with the multi-instrument mean. Evaluations include comparisons of monthly or annual zonal mean cross-sections and seasonal cycles in the tropical and extra-tropical upper troposphere and stratosphere, comparisons of interannual variability, and the study of features such as the water vapour tape recorder. The instruments agree best in the mid-latitude and tropical middle and lower stratosphere, with a relative uncertainty of ±2–6% (as quantified by the standard deviation of the instruments’ multi-annual means). The uncertainty increases toward the polar regions (±10–15%), the mesosphere (±15%), and the upper troposphere/lower stratosphere below 100 hPa (±30–50%), where sampling issues add uncertainty due to large gradients and high natural variability in water vapour. The knowledge gained from these comparisons and regarding the quality of the individual data sets in different regions of the atmosphere will help to improve model-measurement comparisons (e.g., for diagnostics such as the tropical tape recorder or seasonal cycles), data merging activities, and studies of climate variability. The full abstract can be found here.

Using high-precision measurements of the isotopic ratios of N2, O2, and Ar, as well as the mole fraction of Ar, S. Ishidoya and co-authors show that gravitational separation occurs in the stratosphere below the turbopause. Observed vertical profiles agree well with those expected theoretically from molecular mass differences. Simulations with a 2D model of the middle atmosphere indicate that a relationship between gravitational separation and stratospheric age-of-air would be significantly affected if the Brewer Dobson Circulation was enhanced. Therefore they suggest that gravitational separation could serve as a new indicator of changes in stratospheric circulation. The full abstract can be found here.

At a press conference held today in Stockholm, Sweden, the Summary for Policymakers of the Working Group I contribution of AR5 on Climate Change 2013: The Physical Science Basis was presented by the Co-Chairs Dahe Qin and Thomas Stocker.

Find the presentation by Dahe Qin and Thomas Stocker, IPCC Working Group I Co-Chairs.

Find the Summary for Policy Makers and approved final draft of the Scientific-technical Report; of particular interest to the SPARC community are Chapter 2 on Observations: Atmosphere and Surface, and Chapter 7 on Clouds and Aerosols.

Find online registration and programme at http://royalsociety.org/events/2013/climatescience-next-steps/

Find full report at http://www.ncdc.noaa.gov/bams-state-of-the-climate/2012.php.

A new ACP article by N.A. Kramarova and co-authors presents a validation of ozone profiles from the Solar Backscatter Ultraviolet (SBUV and SBUV/2) instruments that were recently reprocessed using an updated (version 8.6) algorithm. The SBUV data record covers the period 1970-2011, with a 5 year gap in the 1970s. Validation with MLS (on board the UARS and Aura satellites) and SAGE-II satellite observations, as well as ground-based observations from microwave spectrometers, lidars, Umkehr instruments and balloon-borne ozonesondes. They find that in the stratosphere, between 25 and 1 hPa, the mean biases and standard deviations are mostly within 5% for monthly zonal mean ozone profiles. Above and below this layer the vertical resolution of the SBUV algorithm decreases. In order to account for the lower resolution in the troposphere/lower stratosphere, they combine several layers of data. The drift of the SBUV instruments is also estimated, as well as its potential effect on the long-term stability of the combined data record. The features of individual SBUV(/2) instruments are discussed and recommendations for creating a merged SBUV data set are provided. The full abstract can be found here.