A new article by R. Plougonven and F. Zhang in Reviews of Geophysics presents current knowledge and understanding on gravity waves near jets and fronts. It has been known for several decades that jets and fronts are significant sources of internal gravity waves in the atmosphere, which contribute to local mixing and impact tropospheric convection, amongst other things. The mechanisms responsible for the emission of these waves remains uncertain, in part because of the complexity of the environment in which they appear. This paper presents a review of gravity waves near jets and fronts from observations, theory, and modelling, and also discusses challenges for progress in the coming years. The full abstract can be found here.

In a new ACPD article, M. Rex and co-authors show the existence of a minimum in OH and tropospheric ozone column over the west Pacific, one of the main source regions for stratospheric air. This minimum amplifies the impact of surface emissions on the stratospheric composition, in particular emissions from biogenic halogenated species may have an impact on stratospheric ozone depletion, while increasing anthropogenic emissions of SO₂ from south east Asia and minor volcanic eruptions may affect the stratospheric aerosol budget. 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 SPARC Data Initiative, S. Tegtmeier and co-authors present some of the main findings from the comparison of ozone climatologies from satellite limb sounders in a new JGR article. The ozone climatologies cover altitudes from the upper troposphere to the lower mesosphere and are obtained from a host of instruments over the period 1978-2010 (LIMS, SAGE I, SAGE II, UARS-MLS, HALOE, POAM II, POAM III, SMR, OSIRIS, SAGE III, MIPAS, GOMOS, SCIAMACHY, ACE-FTS, ACE-MAESTRO, Aura-MLS, HIRDLS, and SMILES). The inter-comparisons focus on mean biases based on monthly and annual zonal mean fields, on inter-annual variability and on seasonal cycles. Their results indicate that uncertainty in terms of the mean state of ozone is lowest in the tropical middle stratosphere and in the mid-latitude lower and middle stratosphere, where the instrument spread is less than ±5%. Large differences between data sets exist in the tropical lower stratosphere and in the high latitudes, where instrument spread is ±30% and ±15%, respectively. The evaluations provide a very useful guidance tool for choice of reliable data sets for different applications. The full abstract can be found here.

Using the WACCM chemistry-climate model, L.A. Holt and co-authors investigate the effect of major sudden stratospheric warmings (SSWs) and elevated-stratopause events (ES) on the transport of NOx produced by energetic particle precipitation (EPP) during the Northern Hemisphere winter. The model simulations indicate large increases in NOx following SSW and ES events, which are attributed to an increase in the descending branch of the residual circulation (w*) following an event. Interestingly, the earlier and event occurs in winter, the more NOx descends into the stratosphere. The full abstract can be found here.

As part of the SPARC Data Initiative, M. Toohey and co-authors investigate the instrument biases relating to non-uniform sampling of the atmosphere in a new JGR article. Potential sampling bias in the stratospheric climatologies of ozone and water vapour are characterised using a chemistry-climate model. For ozone, monthly sampling bias exceeds 10% for many instruments in the high latitudes as well as in the upper troposphere/lower stratosphere (UTLS). Sampling biases for water vapour were generally smaller, but still important in the UTLS and the Southern Hemisphere high latitudes. Non-uniform temporal sampling was found to be the most important mechanism leading to both monthly and annual sampling bias. Similarly, non-uniform spatial sampling was found to be relevant, particularly for those climatologies that were otherwise free of biases due to non-uniform temporal sampling. The full abstract can be found here.

A new JGR article by M. J. Alexander and A. W. Grimsdell focuses on the orographic gravity waves generated by flow over the topography of small islands in the southern oceans. They use AIRS observations to examine the frequency of occurrence of these waves above 14 islands at ∼40km altitude. They show that these waves occur most frequently from May to September, but not every day. Seasonal variations are observed at different islands and appear to be closely related to latitude and prevailing wind patterns. Further examination indicates that stratospheric winds have a first-order limiting effect of these island mountain waves. The full abstract can be found here.

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.

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.