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.

M. Schoeberl and co-authors use forward trajectory modelling to investigate the processes influencing upper tropospheric/lower stratospheric (UTLS) water vapour anomalies. Examining the pathways taken by parcels from the base of the tropical tropopause layer (TTL) upwards, they find that the belt of TTL parcel origins is much wider than the final dehydration zone near the top of the TTL. In the lower stratosphere, the driest air parcels originate from the Tropical West Pacific where they dehydrate in the cold upper troposphere as they move upwards, while the wettest air parcels originate from the edge of this region as well as in the American and Asian monsoon regions in summer. The full abstract can be found here.

Over the last two decades of the 20^th century the southern hemisphere stratospheric stationary wave amplitude increased in late spring and early summer. Using the results from several chemistry-climate models, L. Wang and co-authors separate the effects of anthropogenic forcing from ozone-depleting substances (ODSs) and greenhouse gases (GHGs) on these changes. The increase in amplitude is reproduced in simulations with changing ODSs, a response related to changes in the strength and timing of the breakdown of the polar vortex. GHGs have little impact on the simulated stationary wave amplitude, but are projected to induce an eastward shift of the waves, which is linked to the strengthening of the subtropical jet. The full abstract can be found here.

A recent JGR article by A. Kunz and co-authors uses thirty years of balloon-borne measurements to investigate the water vapour trend in the tropopause region over Boulder, Colorado, USA. They apply two new concepts: trends are presented on a thermal tropopause (TP) relative coordinate system and sonde profiles are selected according to TP height. Although this should reduce the dynamically induced water vapour variability at the TP, their results suggest there is still significant uncertainty in trends at altitudes -2 to +4km around the TP. This uncertainty in turn has an influence on the uncertainty and interpretation of water vapour radiative effects at the TP, which are locally estimated for the 30-year period to be of uncertain sign. Their results also do not indicate any detectable decrease in water vapour at the beginning of 2001. However, on the lower stratospheric isentropes, the water vapour change for this period is stronger for extra-tropical than for tropical air mass types, suggesting a possible link to changing dynamics above the jet stream. The full abstract can be found here.

W. Yuan and co-authors investigate the influence of the El Niño/Southern Oscillation (ENSO) on the quasi-biennial oscillation (QBO) modulation of cold-point tropopause (CPT) temperatures. Using almost five decades of radiosonde data from eleven near-equatorial stations, they show that the ENSO influence on the QBO is quite zonally symmetric. The data indicate that the QBO has larger amplitude and longer period during La Niña conditions than during El Niño. Their results also indicate that the warmer CPT temperatures during QBO westerly shear conditions and colder temperatures during QBO easterly shear conditions, are larger during La Niña than during El Niño. This strengthens earlier findings that the greatest dehydration of air entering the stratosphere from the troposphere occurs during the winter under La Niña and easterly QBO conditions. The full abstract can be found here.