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.

A recent JGR article by J. Hsu and co-authors uses the NCAR Community Atmosphere Model to evaluate the sensitivity of stratospheric dynamics to the uncertainty in ozone production related to uncertainty in O2 cross-sections in the Hertzberg Continuum. Reducing the O2 cross-sections by 30% is found to increase ozone abundances in the lower stratosphere, which as a result warms between 60°S -60°N (2K maximum at the equator) and lowers the tropopause height by 100-200m between 30°S -30°N. The study points to the important role of ozone in the lower tropical stratosphere in determining the physical characteristics of the tropical tropopause layer. The full abstract can be found here.

The effects of imposed stratospheric cooling on the maximum intensity of tropical cyclones

Using a cloud-resolving model, H. Ramsay presents results that elucidate the effect of stratospheric cooling and sea surface warming on the potential intensity (PI) of tropical cyclones in a recent article in the Journal of Climate. With fixed sea surface temperatures, cooling near and above the tropopause (~90hPa) is shown to increase PI at a rate of 1m/s per degree cooling. With fixed stratospheric temperatures, sea surface warming increases the PI by approximately twice as much, as a rate of about 2m/s per degree warming. These results have significant implications in terms of global tropical cyclone PI trends in response to climate change. Tropical sea surface temperatures have warmed by about 0.15K/decade since the 1970s, while the stratosphere has cooled anywhere from 0.3K/decade to over 1K/decade, depending on the data set used. Therefore, global PI trends in recent decades appear to have been driven more by stratospheric cooling than by surface warming. Find the full abstract here.

Drivers of hemispheric differences in return dates of mid-latitude stratospheric ozone

In a new ACP paper, H. Garny and co-authors investigate the main factors driving the hemispherical asymmetry in ozone return dates. They find that the hemispherical return date differences, which range between 0-30 years across the CCM projections analysed, are affected by both the sensitivity of ozone to Cly (ozone trends have a larger effect on return dates when sensitivity is lower) and the difference in ozone trends between hemispheres. An attribution analysis performed with two CCMs shows that chemically-induced changes in ozone are the major driver of the earlier return of ozone to 1980 levels in northern mid-latitudes. The causes for chemically-induced asymmetric ozone trends relevant for the total column ozone return date differences are found to be (i) stronger increases in ozone production due to enhanced NOx concentrations in the Northern Hemisphere lowermost stratosphere and troposphere, (ii) stronger decreases in the destruction rates of ozone by the NOx cycle in the Northern Hemisphere lower stratosphere linked to effects of dynamics and temperature on NOx concentrations, and (iii) an increasing efficiency of heterogeneous ozone destruction by Cly in the Southern Hemisphere mid-latitudes as a result of decreasing lower stratospheric temperatures. The full abstract can be found here.

A.T. Brown and co-authors use measurements from the ACE-FTS satellite instrument to calculate the stratospheric lifetimes of CFC-12, CCl4, CH4, CH3Cl and N2O in a recent ACP article. The lifetimes are calculated using the slope of the tracer–tracer correlation of these species with CFC-11 (assuming a lifetime of 45 years) at the tropopause. The correlation slopes are corrected for changing atmospheric concentrations based on the age-of-air and CFC-11 measurements from samples taken aboard the Geophysica aircraft – along with the effective linear trend of the volume mixing ratio (VMR) from tropical ground based AGAGE (Advanced Global Atmospheric Gases Experiment) sites. Calculated lifetimes are: 113 +(−) 26(18) years [CFC-12], 35 +(−) 11(7) years [CCl4], 69 +(−) 65(23) years [CH3Cl], 123 +(−) 53(28) years [N2O], and 195 +(−) 75(42) years [CH4]. The errors on these values are the weighted 1σ non-systematic errors. For CH3Cl & CH4 this represents the first calculation of the stratospheric lifetime using data from a space-based instrument. The full abstract can be found here.

Impact of a potential 21st century “grand solar minimum” on surface temperatures and stratospheric ozone

A new GRL article by J. Anet and co-authors investigates the effects of recently proposed 21^st century Dalton-minimum-like decline of solar activity on the climate and ozone layer. Using the IPCC RCP 4.5 scenario and the SOCOL3-MPIOM coupled ocean-atmosphere model, they find that a future grand solar minimum reduces mean global surface warming by 0.2-0.3K and that the decrease in solar UV radiation leads to a significant delay in the recovery of stratospheric ozone by up to 10 years and longer. The full abstract can be found here.

M. Abalos and co-authors investigate recent contrasting results regarding the seasonality of ozone about the tropical tropopause in a new ACPD article. In the literature, different methods (Lagrangian versus Eulerian, and isentropic versus pressure vertical coordinates) yield different results in terms of ozone transport, and the results must be carefully compared in equivalent terms to avoid misinterpretation. By examining the Lagrangian calculations in the Eulerian formulation, they show that the results are in fact consistent with each other and with a common understanding of the ozone transport processes near and above the tropical tropopause. The analysis of the Transformed Eulerian Mean ozone budget indicates that the annual tropical upwelling cycle is the main forcing of ozone seasonality at altitudes with large vertical gradients in the tropical lower stratosphere. Using a Lagrangian framework, it is found that a large fraction (~50%) of the ozone molecules ascending through the tropical lower stratosphere is of extra-tropical origin and has been in-mixed from mid-latitudes. The full abstract can be found here.

A recent JGR article by M. Holzer and L. Polvani uses the MATCH transport model to quantify the flux of idealized trace gases across the thermal tropopause as a function of their chemical lifetime. Emissions of the trace species are idealized as time dependent with either a generic anthropogenic pattern or a uniform ocean source. Globally averaged fluxes into the stratosphere normalized by surface emissions are dependent on the tropospheric chemistry, which is idealized as decay with a constant lifetime (τc). For τc=8 days and τc~140 days the fluxes are 1% and 30%, respectively. Interestingly, the flux patterns computed with MATCH are insensitive toτc~ and reveal preferred pathways into the stratosphere – divergent circulation feeding isentropic cross-tropopause transport and isentropic transport to high latitudes. Find the full abstract here.

A recent GRL article by S.M. Kang and co-authors explores the impacts of stratospheric ozone depletion on daily precipitation extremes during the austral summer. The two models used both suggest that ozone losses since the late 1970’s have resulted in an increase in frequency and intensity of heavy rainfall events over the southern mid-latitudes. This hemispheric response pattern projects strongly onto a previously identified pattern of seasonal mean precipitation response, both of which are shown to be likely of dynamic rather than thermodynamic origin. The full abstract can be found here.

Browse the table of contents and find supplementary material and online-first publication now online: SPARC newsletter No. 41.