C. McLandress and co-authors describe a simple procedure for removing unphysical temporal discontinuities in ERA-interim temperatures form 5-1hPa, which have arisen due to changes in the satellite radiance data used in the assimilation process. Adjustments to global mean temperatures are derived that can be applied to chemistry-climate models nudged to the ERA-interim reanalysis. Simulations using the CMAM model indicate that the inclusion of these adjustments produces a temperature time series without large jumps in the upper stratosphere. The full abstract can be found here.

S. P. Alexander and co-authors quantify the proportion of polar stratospheric clouds (PSCs) due to orographic wave forcing in a recent JGR article. Looking at data from four winter seasons for both the Antarctic and Arctic they show that in the regions downstream of mountain ranges more than 75% of water ice PSCs and around 50% of a high number density liquid nitric acid trihydrate mixture class result from orographic wave activity. In the synoptically warmer Arctic 12% of all PSCs are attributed to orographic wave forcing, while for the Antarctic this proportion is much lower (5%). The full abstract can be found here.

As part of the RECONCILE campaign, microphysical modelling of the 2009/2010 Arctic winter campaigns was carried out by I. Engel and co-authors in a new ACPD article. They show that including newly developed NAT (Nitric Acid Trihydrate) and ice nucleation parameterisations as well as small-scale temperature fluctuations are vital to reproducing the observed signals of redistribution of water vapour in the Arctic stratosphere under the extremely cold conditions of the 2009/2010 winter. The full abstract can be found here.

In a recent ACP article, S.S. Dhomse and co authors use a chemical transport model (CTM) to show that the stratospheric and lower mesospheric ozone changes during solar cycle 23 (1996-2008) can be reproduced using several different solar spectral flux datasets (SORCE, SSI, SATIRE-S). Model results agree well with both MLS and SABER observations regardless of the solar flux data set used, suggesting that the UV variations detected by SORCE are not necessary to reproduce observed stratospheric ozone changes from 2001-2010 in a CTM. The full abstract can be found here.

A new ACPD article by H. Zhang and co-authors investigates the effects of recovering stratospheric ozone on tropospheric chemistry and air quality using the global chemistry-transport model GEOS-Chem. They find that surface ozone photolysis rates decrease significantly while ozone lifetime in the troposphere increases by up to 7% and the tropospheric ozone burden increases slightly (0.78%). Perturbations of tropospheric and surface ozone show large seasonal and spatial variations, with increases of up to 5% for some regions. The full abstract can be found here.

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.