Search

To date, the radiative impact of dust and the Sahar an air layer (SAL) on North Atlantic hurricane activity is not yet known. According to previous studies, dust stabilizes the atmosphere due to absorption of solar radiation but thus shifts convection to regions more conducive for hurricane genesis. Here we analyze differences in hurricane genesis and frequency from ensemble sensitivity simulations with radiatively active and inactive dust in the aerosol-climate model ECHAM6-HAM. We investigate dust burden and other hurricane-related variables and determine their influence on disturbances which develop into hurricanes (developing disturbances, DDs) and those which do not (nondeveloping disturbances, NDDs). Dust and the SAL are found to potentially have both inhibiting and supporting influences on background conditions for hurricane genesis. A slight southward shift of DDs is determined when dust is active as well as a significant warming of the SAL, which leads to a strengthening of the vertical circulation associated with the SAL. The dust burden of DDs is smaller in active dust simulations compared to DDs in simulations with inactive dust, while NDDs contain more dust in active dust simulations. However, no significant influence of radiatively active dust on other variables in DDs and NDDs is found. Furthermore, no substantial change in the DD and NDD frequency due to the radiative effects of dust can be detected.

Nitrous oxide (N2O), which decomposes in the stratosphere to form nitrogen oxides (NOx), is currently the dominant anthropogenic ozone-depleting substance emitted. Ozone depletion potentials (ODPs) of specific compounds, commonly evaluated for present-day conditions, were developed for long-lived halocarbons and are used by policymakers to inform decision-making around protection of the ozone layer. However, the effect of N2O on ozone will evolve in the future due to changes in stratospheric dynamics and chemistry induced by rising levels of greenhouse gases. Despite the fact that NOx-induced ozone loss slows with increasing concentrations of CO2 and CH4, we show that ODPN2O for year 2100 varies under different scenarios and is mostly larger than ODPN2O for year 2000. This occurs because the traditional ODP approach is tied to ozone depletion induced by CFC-11, which is also sensitive to CO2 and CH4. We therefore suggest that a single ODP for N2O is of limited use.

In this paper, we investigate why current state-of-the-art chemistry-climate models underestimate the tropospheric ozone increase from the 1950s to the 1990s by approximately 50%. The accuracy of these models is vital, not only for understanding and predicting air quality globally, but also since they are used to quantify the contribution of ozone in the troposphere and lower stratosphere to climate change, where its greenhouse effect is largest. We briefly describe available northern mid-latitude ozone measurements, which include representative and reliable data from European sites that extend back to the 1950s. We use the SOCOLv3 (Solar Climate Ozone Links version 3) global chemistry-climate model to investigate the individual terms of the tropospheric ozone budget. These include: inflow from the stratosphere, dry deposition, and chemical formation and destruction. For 1960 to 2000 SOCOLv3 indicates a tropospheric ozone increase at 850 hPa over the Swiss Alps (Arosa) of 17 ppb, or around 30%. This increase is smaller than that seen in the surface ozone measurements but similar to other chemistry-climate models, including those with more complex NMVOC (Non Methane Volatile Organic Compound) schemes than SOCOLv3’s. It is likely that the underestimated increase in tropospheric ozone could be explained by issues in the underlying emissions inventories used in the model simulations, with ozone precursor emissions, particularly NOx (NO + NO2), from the 1960s being too large., Atmosphere, 8 (9), ISSN:2073-4433

Recently, it was shown that of the ozone-depleting substances currently emitted, N2O emissions (the primary source of stratospheric NOx) dominate, and are likely to do so throughout the 21st century. To investigate the links between N2O and NOx concentrations, and the effects of NOx on ozone in a changing climate, the evolution of stratospheric ozone from 1960 to 2100 was simulated using the NIWA-SOCOL chemistry-climate model. The yield of NOx from N2O is reduced due to stratospheric cooling and a strengthening of the Brewer-Dobson circulation. After accounting for the reduced NOx yield, additional weakening of the primary NOx cycle is attributed to reduced availability of atomic oxygen, due to a) stratospheric cooling decreasing the atomic oxygen/ozone ratio, and b) enhanced rates of chlorine-catalyzed ozone loss cycles around 2000 and enhanced rates of HOx-induced ozone depletion. Our results suggest that the effects of N2O on ozone depend on both the radiative and chemical environment of the upper stratosphere, specifically CO2-induced cooling of the stratosphere and elevated CH4 emissions which enhance HOx-induced ozone loss and remove the availability of atomic oxygen to participate in NOx ozone loss cycles.

[1] Biofuels are becoming increasingly popular sources of renewable energy as economic pressures and environmental consequences encourage the use of alternatives to fossil fuels. However, growing crops destined for use as biofuels incurs large N2O emissions associated with the use of nitrogen-based fertilizers. Besides being a greenhouse gas, N2O is also the primary source of stratospheric NOx (NO + NO2) which leads to stratospheric ozone depletion. In this paper, the potential effects on the ozone layer of a large-scale shift away from fossil fuel use to biofuels consumption over the 21st century are examined. Under such a scenario, global-mean column ozone decreases by 2.6 DU between 2010 and 2100 in contrast to a 0.7 DU decrease under a control simulation (the IPCC SRES B1 scenario for greenhouse gases) and a 9.1 DU increase under the more commonly used SRES A1B scenario. Two factors cause the decrease in ozone in the biofuels simulation: 1) large N2O emissions lead to faster rates of the ozone-depleting NOx cycles and; 2) reduced CO2 emissions (due to less fossil fuel burning) lead to relatively less stratospheric cooling over the 21st century, which decreases ozone abundances. Reducing CO2 emissions while neglecting to reduce N2O emissions could therefore be damaging to the ozone layer.

International audience; • Current-era GCMs overestimate sea spray concentrations relative to measurements in the Ross Sea • Better constraints for sea spray flux were found by tuning wind-speed based parameterizations to these observations • Variations in sea surface temperature did not explain further variability within the temperature range studied

The Southern Hemisphere (SH) zonal-mean circulation change in response to Antarctic ozone depletion is re-visited by examining a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models reasonably well reproduce Antarctic ozone depletion in the late 20th century. The related SH-summer circulation changes, such as a poleward intensification of westerly jet and a poleward expansion of the Hadley cell, are also well captured. All experiments exhibit quantitatively the same multi-model mean trend, irrespective of whether the ocean is coupled or prescribed. Results are also quantitatively similar to those derived from the Coupled Model Intercomparison Project phase 5 (CMIP5) high-top model simulations in which the stratospheric ozone is mostly prescribed with monthly- and zonally-averaged values. These results suggest that the ozone-hole-induced SH-summer circulation changes are robust across the models irrespective of the specific chemistry-atmosphere-ocean coupling. ISSN:1748-9326 ISSN:1748-9318