Science Update: Contributions to 20th Century Total Column Ozone Change From Halocarbons, Tropospheric Ozone Precursors, and Climate Change

M. C. Reader and co-authors present a modeling study of zone changes from pre-industrial times in a recent GRL article. The influence of changes in climate, ozone-depleting substances, N2O, and tropospheric ozone precursors was estimated using equilibrium simulations. From the pre-industrial to the present, it was found that a significant contributor to total column ozone can be attributed to the increase in lower-stratospheric ozone resulting from the increase in tropospheric ozone precursors. The full abstract can be found here.

Science Update: Improved seasonal forecasting using ozone hole variability?

S.-W. Son and co-authors show that the ozone hole has not only affected long-term climate change, but also interannual variability of the southern hemisphere (SH) surface climate. In their new GRL article, they show that a significant negative correlation is observed between September ozone concentration and the October Southern Annular Mode index, resulting in systematic variations in precipitation and surface air temperature throughout the SH. This time-lagged relationship is independent of those associated with ENSO and the Indian Ocean Dipole Mode, suggesting that SH seasonal forecasts could be improved through including Antarctic stratospheric variability. The full abstract can be found here.

Science Update: Comparison between SMILES and Ozonesonde profile measurements

In a new JGR article, K. Imai and co-authors compare ozone profiles measured by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) with those from ozonesondes. Comparing profiles between the 16-30km range, they found generally good agreement (within 5-7% for 18-30km at mid- and high latitudes). At low latitudes the SMILES observations showed higher ozone values (6-15% larger between 20-26km). Exploring several possible issues that may induce bias, they found that a biases from the ozonesonde pressure sensors were likely to be within a few percent. In contrast, they found that the ozonesonde response time could account for a negative bias of the ascending ozonesonde measurement of up to 7% at 20km in equatorial latitudes. Applying a bias correction for this factor improved the agreement between ozonesondes and SMILES. The full abstract can be found here.

Science Update: Detecting the solar signal in the tropical stratosphere

In a recent ACPD article, G. Chiodo and co-authors use the WACCM chemistry-climate model to perform transient simulations looking at the solar cycle in the tropics. They investigate the relative role of volcanic eruptions, ENSO, and the QBO signals in the tropical stratosphere temperatures and ozone commonly attributed to the 11-year solar cycle. Simulations from 1960-2004 were carried out and a multiple regression technique used to diagnose the 11-year solar signal. Results show that most of the solar-induced lower stratospheric temperature and ozone increase diagnosed in the simulation including all forcing factors is due to the two major volcanic eruptions during the period studied (El Chichón and M. Pinatubo), which were concurrent with periods of high solar activity. Thus, the portion of decadal variability that can unambiguously be linked to the solar cycle may be smaller than previously thought. The full abstract can be found here.

EGU session announcement: Dynamical coupling between the stratosphere and the troposphere

Session conveners Thomas Reichler from the University of Utah, Bo Christiansen from the Danish Meteorological Institute, and Seak-Woo Son from the McGill University are inviting you to submit an abstract to session AS1.15 on the "Dynamical coupling between the stratosphere and the troposphere" at the EGU 2014. Deadline for abstracts is 16 Janaury 2014, and for financial support: 29 November 2013 CET. EGU 2014 will take place in Vienna, Austria, on 27 April-2 May 2014.

Science Update: A tropical west Pacific OH minimum and implications for stratospheric composition

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.

Science Update: Review: Gravity waves from atmospheric jets and fronts

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.

Science Update: A simple procedure for removing temporal discontinuities in ERA-interim upper stratospheric temperatures

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.

Science Update: Effect of seasonal cycle of orographic wave occurrence above small Southern Hemisphere islands on general circulation

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.

Science Update: Characterizing sampling biases in the trace gas climatologies of the SPARC Data Initiative

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.