Differences in the QBO response to stratospheric aerosol modification depending on injection strategy and species

A known adverse side effect of stratospheric aerosol modification (SAM) is the modification of the quasi-biennial oscillation (QBO), which is caused by the stratospheric heating associated with an artificial aerosol layer. Multiple studies found the QBO to slow down or even completely vanish for point-like injections of SO2 at the equator. The cause for this was found to be a modification of the thermal wind balance and a stronger tropical upwelling. For other injection strategies, different responses of the QBO have been observed. It has not yet been presented a theory which is able to explain those differences in a comprehensive manner, which is further complicated by the fact that the simulated QBO response is highly sensitive to the used model even under identical boundary conditions. Therefore, within this study we investigate the response of the QBO to SAM for three different injection strategies (point-like injection at the equator, point-like injection at 30° N and 30° S simultaneously, and areal injection into a 60° wide belt along the equator). Our simulations confirm that the QBO response significantly depends on the injection location. Based on the thermal wind balance, we demonstrate that this dependency is explained by differences in the meridional structure of the aerosol-induced stratospheric warming, i.e. the location and meridional extension of the maximum warming. Additionally, we also tested two different injection species (SO2 and H2SO4). The QBO response is qualitatively similar for both investigated injection species. Comparing the results to corresponding results of a second model, we further demonstrate the generality of our theory as well as the importance of an interactive treatment of stratospheric ozone for the simulated QBO response

Upper tropospheric ice sensitivity to sulfate geoengineering

Aside from the direct surface cooling that sulfate geoengineering (SG) would produce, investigations of the possible side effects of this method are still ongoing, such as the exploration of the effect that SG may have on upper tropospheric cirrus cloudiness. The goal of the present study is to better understand the SG thermodynamical effects on the freezing mechanisms leading to ice particle formation. This is undertaken by comparing SG model simulations against a Representative Concentration Pathway 4.5 (RCP4.5) reference case. In the first case, the aerosol-driven surface cooling is included and coupled to the stratospheric warming resulting from the aerosol absorption of terrestrial and solar near-infrared radiation. In a second SG perturbed case, the surface temperatures are kept unchanged with respect to the reference RCP4.5 case. When combined, surface cooling and lower stratospheric warming tend to stabilize the atmosphere, which decreases the turbulence and updraft velocities (−10&thinsp;% in our modeling study). The net effect is an induced cirrus thinning, which may then produce a significant indirect negative radiative forcing (RF). This RF would go in the same direction as the direct effect of solar radiation scattering by aerosols, and would consequently influence the amount of sulfur needed to counteract the positive RF due to greenhouse gases. In our study, given an 8&thinsp;Tg-SO2&thinsp;yr−1 equatorial injection into the lower stratosphere, an all-sky net tropopause RF of −1.46&thinsp;W&thinsp;m−2 is calculated, of which −0.3&thinsp;W&thinsp;m−2 (20&thinsp;%) is from the indirect effect on cirrus thinning (6&thinsp;% reduction in ice optical depth). When surface cooling is ignored, the ice optical depth reduction is lowered to 3&thinsp;%, with an all-sky net tropopause RF of −1.4&thinsp;W&thinsp;m−2, of which −0.14&thinsp;W&thinsp;m−2 (10&thinsp;%) is from cirrus thinning. Relative to the clear-sky net tropopause RF due to SG aerosols (−2.1&thinsp;W&thinsp;m−2), the cumulative effect of the background clouds and cirrus thinning accounts for +0.6&thinsp;W&thinsp;m−2, due to the partial compensation of large positive shortwave (+1.6&thinsp;W&thinsp;m−2) and negative longwave adjustments (−1.0&thinsp;W&thinsp;m−2). When surface cooling is ignored, the net cloud adjustment becomes +0.8&thinsp;W&thinsp;m−2, with the shortwave contribution (+1.5&thinsp;W&thinsp;m−2) almost twice as much as that of the longwave (−0.7&thinsp;W&thinsp;m−2). This highlights the importance of including all of the dynamical feedbacks of SG aerosols.</p

Sulfate geoengineering impact on methane transport and lifetime: results from the Geoengineering Model Intercomparison Project (GeoMIP)

Abstract. Sulfate geoengineering (SG), made by sustained injection of SO2 in the tropical lower stratosphere, may impact the CH4 abundance through several photochemical mechanisms affecting tropospheric OH and hence the methane lifetime. (a) The reflection of incoming solar radiation increases the planetary albedo and cools the surface, with a tropospheric H2O decrease. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D). (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-to-upper troposphere, thus reducing the amount of NOx and O3 production. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rate perturbation is highly latitude dependent, producing a stronger meridional component of the Brewer–Dobson circulation. The net effect on tropospheric OH due to the enhanced stratosphere–troposphere exchange may be positive or negative depending on the net result of different superimposed species perturbations (CH4, NOy, O3, SO4) in the extratropical upper troposphere and lower stratosphere (UTLS). In addition, the atmospheric stabilization resulting from the tropospheric cooling and lower stratospheric warming favors an additional decrease of the UTLS extratropical CH4 by lowering the horizontal eddy mixing. Two climate–chemistry coupled models are used to explore the above radiative, chemical and dynamical mechanisms affecting CH4 transport and lifetime (ULAQ-CCM and GEOSCCM). The CH4 lifetime may become significantly longer (by approximately 16 %) with a sustained injection of 8 Tg-SO2 yr−1 starting in the year 2020, which implies an increase of tropospheric CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH4 changes (+0.10 W m−2 in the 2040–2049 decade and +0.15 W m−2 in the 2060–2069 decade)

Dependency of the impacts of geoengineering on the stratospheric sulfur injection strategy - Part 1: Intercomparison of modal and sectional aerosol modules

Injecting sulfur dioxide into the stratosphere with the intent to create an artificial reflective aerosol layer is one of the most studied options for solar radiation management. Previous modelling studies have shown that stratospheric sulfur injections have the potential to compensate for the greenhouse-gas-induced warming at the global scale. However, there is significant diversity in the modelled radiative forcing from stratospheric aerosols depending on the model and on which strategy is used to inject sulfur into the stratosphere. Until now, it has not been clear how the evolution of the aerosols and their resulting radiative forcing depends on the aerosol microphysical scheme used - that is, if aerosols are represented by a modal or sectional distribution. Here, we have studied different spatio-temporal injection strategies with different injection magnitudes using the aerosolclimate model ECHAM-HAMMOZ with two aerosol microphysical modules: the sectional module SALSA (Sectional Aerosol module for Large Scale Applications) and the modal module M7. We found significant differences in the model responses depending on the aerosol microphysical module used. In a case where SO2 was injected continuously in the equatorial stratosphere, simulations with SALSA produced an 88 %-154% higher all-sky net radiative forcing than simulations with M7 for injection rates from 1 to 100 Tg(S) yr(-1). These large differences are identified to be caused by two main factors. First, the competition between nucleation and condensation: while injected sulfur tends to produce new particles at the expense of gaseous sulfuric acid condensing on pre-existing particles in the SALSA module, most of the gaseous sulfuric acid partitions to particles via condensation at the expense of new particle formation in the M7 module. Thus, the effective radii of stratospheric aerosols were 10 %-52% larger in M7 than in SALSA, depending on the injection rate and strategy. Second, the treatment of the modal size distribution in M7 limits the growth of the accumulation mode which results in a local minimum in the aerosol number size distribution between the accumulation and coarse modes. This local minimum is in the size range where the scattering of solar radiation is most efficient. We also found that different spatial-temporal injection strategies have a significant impact on the magnitude and zonal distribution of radiative forcing. Based on simulations with various injection rates using SALSA, the most efficient studied injection strategy produced a 33 %-42% radiative forcing compared with the least efficient strategy, whereas simulations with M7 showed an even larger difference of 48 %-116 %. Differences in zonal mean radiative forcing were even larger than that. We also show that a consequent stratospheric heating and its impact on the quasi-biennial oscillation depend on both the injection strategy and the aerosol microphysical model. Overall, these results highlight the crucial impact of aerosol microphysics on the physical properties of stratospheric aerosol which, in turn, causes significant uncertainties in estimating the climate impacts of stratospheric sulfur injections

Upper tropospheric ice sensitivity to sulfate geoengineering

Abstract. Aside from the direct surface cooling that sulfate geoengineering (SG) would produce, investigations of the possible side effects of this method are still ongoing, such as the exploration of the effect that SG may have on upper tropospheric cirrus cloudiness. The goal of the present study is to better understand the SG thermodynamical effects on the freezing mechanisms leading to ice particle formation. This is undertaken by comparing SG model simulations against a Representative Concentration Pathway 4.5 (RCP4.5) reference case. In the first case, the aerosol-driven surface cooling is included and coupled to the stratospheric warming resulting from the aerosol absorption of terrestrial and solar near-infrared radiation. In a second SG perturbed case, the surface temperatures are kept unchanged with respect to the reference RCP4.5 case. When combined, surface cooling and lower stratospheric warming tend to stabilize the atmosphere, which decreases the turbulence and updraft velocities (−10 % in our modeling study). The net effect is an induced cirrus thinning, which may then produce a significant indirect negative radiative forcing (RF). This RF would go in the same direction as the direct effect of solar radiation scattering by aerosols, and would consequently influence the amount of sulfur needed to counteract the positive RF due to greenhouse gases. In our study, given an 8 Tg-SO2 yr−1 equatorial injection into the lower stratosphere, an all-sky net tropopause RF of −1.46 W m−2 is calculated, of which −0.3 W m−2 (20 %) is from the indirect effect on cirrus thinning (6 % reduction in ice optical depth). When surface cooling is ignored, the ice optical depth reduction is lowered to 3 %, with an all-sky net tropopause RF of −1.4 W m−2, of which −0.14 W m−2 (10 %) is from cirrus thinning. Relative to the clear-sky net tropopause RF due to SG aerosols (−2.1 W m−2), the cumulative effect of the background clouds and cirrus thinning accounts for +0.6 W m−2, due to the partial compensation of large positive shortwave (+1.6 W m−2) and negative longwave adjustments (−1.0 W m−2). When surface cooling is ignored, the net cloud adjustment becomes +0.8 W m−2, with the shortwave contribution (+1.5 W m−2) almost twice as much as that of the longwave (−0.7 W m−2). This highlights the importance of including all of the dynamical feedbacks of SG aerosols

Postharvest quality of 'Emerald' blueberry cultivated in a subtropical region

O objetivo deste trabalho foi avaliar os aspectos qualitativos, na colheita e na pós-colheita, de mirtilos 'Emerald' cultivados em região de clima subtropical, sem frio hibernal, no Brasil. Os frutos foram colhidos no município de Piracicaba, no estado de São Paulo, em dois picos de colheita, em agosto e outubro, e avaliados quanto aos seus atributos qualitativos na colheita e aos seus atributos físicos, químicos e bioquímicos na pós-colheita. Os frutos foram mantidos em condições de temperatura ambiente, a 22°C e 70% de umidade relativa, e analisados no dia da colheita e a cada três dias até o décimo-segundo dia de armazenamento. Os mirtilos colhidos em agosto foram maiores e mais arredondados, e os colhidos em outubro apresentaram coloração azul mais intensa e maiores concentrações de compostos fenólicos, pH e sólidos solúveis, além de maior relação sólidos solúveis totais e acidez titulável. Durante o armazenamento, observou-se aumento no conteúdo de antocianinas, quercetinas e compostos fenólicos totais, bem como na atividade antioxidante, além de redução na acidez e na firmeza dos frutos. Independentemente do mês de colheita, os mirtilos cultivados em região subtropical no Brasil apresentam boa durabilidade pós-colheita por até 12 dias em temperatura ambiente, com níveis satisfatórios de qualidade dos frutos.The objective of this work was to evaluate the qualitative attributes, at harvest and postharvest, of 'Emerald' blueberries grown in a subtropical climate region, without winter chilling, in Brazil. Fruit were harvested in the municipality of Piracicaba, in the state of São Paulo, in two harvest peaks, in August and October, and evaluated for their qualitative attributes at harvest and for their physical, chemical, and biochemical attributes at postharvest. The fruit were maintained at ambient conditions, at 22°C and 70% relative humidity, and evaluated on the day of harvest and every three days until the twelfth day of storage. The blueberries harvested in August were larger and rounder, and those harvested in October had a more intense blue coloration and higher concentrations of phenolic compounds, pH, and soluble solids, in addition to a higher total soluble solids and titratable acidity ratio. During storage, an increase was observed in the contents of anthocyanins, quercetins, and total phenolic compounds, as well as in antioxidant activity, besides a decrease in fruit acidity and firmness. Regardless of the harvest month, blueberries grown in a subtropical region of Brazil have a good postharvest shelf life up to 12 days at ambient temperature, with satisfactory fruit quality levels

Impact of Stratospheric Volcanic Aerosols on Age-of-Air and Transport of Long-Lived Species

The radiative perturbation associated to stratospheric aerosols from major explosive volcanic eruptions may induce significant changes in stratospheric dynamics. The aerosol heating rates warm up the lower stratosphere and cause a westerly wind anomaly, with additional tropical upwelling. Large scale transport of stratospheric trace species may be perturbed as a consequence of this intensified Brewer–Dobson circulation. The radiatively forced changes of the stratospheric circulation during the first two years after the eruption of Mt. Pinatubo (June 1991) may help explain the observed trend decline of long-lived greenhouse gases at surface stations (approximately −8 and −0.4 ppbv/year for CH4 and N2O, respectively). This decline is partly driven by the increased mid- to high-latitude downward flux at the tropopause and also by an increased isolation of the tropical pipe in the vertical layer near the tropopause, with reduced horizontal eddy mixing. Results from a climate-chemistry coupled model are shown for both long-lived trace species and the stratospheric age-of-air. The latter results to be younger by approximately 0.5 year at 30 hPa for 3–4 years after the June 1991 Pinatubo eruption, as a result of the volcanic aerosols radiative perturbation and is consistent with independent estimates based on long time series of in situ profile measurements of SF6 and CO2. Younger age of air is also calculated after Agung, El Chichon and Ruiz eruptions, as well as negative anomalies of the N2O growth rate at the extratropical tropopause layer. This type of analysis is made comparing the results of two ensembles of model simulations (1960–2005), one including stratospheric volcanic aerosols and their radiative interactions and a reference case where the volcanic aerosols do not interact with solar and planetary radiation

Stratospheric Aerosols from Major Volcanic Eruptions: A Composition-Climate Model Study of the Aerosol Cloud Dispersal and e-folding Time

Large explosive volcanic eruptions are capable of injecting considerable amounts of particles and sulfur gases above the tropopause, causing large increases in stratospheric aerosols. Five major volcanic eruptions after 1960 (i.e., Agung, St. Helens, El Chichon, Nevado del Ruiz and Pinatubo) have been considered in a numerical study conducted with a composition-climate coupled model including an aerosol microphysics code for aerosol formation and growth. Model results are compared between an ensemble of numerical simulations including volcanic aerosols and their radiative effects (VE) and a reference simulations ensemble (REF) with no radiative impact of the volcanic aerosols. Differences of VE-REF show enhanced diabatic heating rates; increased stratospheric temperatures and mean zonal westerly winds; increased planetary wave amplitude; and tropical upwelling. The impact on stratospheric upwelling is found to be larger when the volcanically perturbed stratospheric aerosol is confined to the tropics, as tends to be the case for eruptions which were followed by several months with easterly shear of the quasi-biennial oscillation (QBO), e.g., the Pinatubo case. Compared to an eruption followed by a period of westerly QBO, such easterly QBO eruptions are quite different, with meridional transport to mid- and high-latitudes occurring later, and at higher altitude, with a consequent decrease in cross-tropopause removal from the stratosphere, and therefore longer decay timescale. Comparing the model-calculated e-folding time of the volcanic aerosol mass during the first year after the eruptions, an increase is found from 8.1 and 10.3 months for El Chichon and Agung (QBO westerly shear), to 14.6 and 30.7 months for Pinatubo and Ruiz (QBO easterly shear). The corresponding e-folding time of the global-mean radiative flux changes goes from 9.1 and 8.0 months for El Chichon and Agung, to 28.7 and 24.5 months for Pinatubo and Ruiz