Search

Stratospheric water vapor affects the Earth's radiative balance and stratospheric chemistry, yet its future changes are uncertain and not fully understood. The influence of deep convection on stratospheric water vapor remains subject to debate. This letter presents a detailed process‐based model study of the impact of convective ice sublimation on stratospheric water vapor in response to CO2 forced climate change. The influence of convective injection is found to be limited by the vertical profile of temperature and saturation vapor pressure in the tropical tropopause layer, not by the frequency of occurrence. Lagrangian trajectory analysis shows the relative contributions to stratospheric water vapor from sublimation and large‐scale transport are approximately unchanged when CO2 is increased. The results indicate the role of convective ice injection for stratospheric water vapor in a warmer climate remains constrained by large‐scale temperatures.

Substantial increases in the atmospheric concentration of well‐mixed greenhouse gases (notably CO2), such as those projected to occur by the end of the 21st century under large radiative forcing scenarios, have long been known to cause an acceleration of the Brewer‐Dobson circulation (BDC) in climate models. More recently, however, several single‐model studies have proposed that ozone‐depleting substances might also be important drivers of BDC trends. As these studies were conducted with different forcings over different periods, it is difficult to combine them to obtain a robust quantitative picture of the relative importance of ozone‐depleting substances as drivers of BDC trends. To this end, we here analyze—over identical past and future periods—the output from 20 similarly forced models, gathered from two recent chemistry‐climate modeling intercomparison projects. Our multimodel analysis reveals that ozone‐depleting substances are responsible for more than half of the modeled BDC trends in the two decades 1980–2000. We also find that, as a consequence of the Montreal Protocol, decreasing concentrations of ozone‐depleting substances in coming decades will strongly decelerate the BDC until the year 2080, reducing the age‐of‐air trends by more than half, and will thus substantially mitigate the impact of increasing CO2. As ozone‐depleting substances impact BDC trends, primarily, via the depletion/recovery of stratospheric ozone over the South Pole, they impart seasonal and hemispheric asymmetries to the trends which may offer opportunities for detection in coming decades.

We have derived values of the ultraviolet index (UVI) at solar noon using the Tropospheric Ultraviolet Model (TUV) driven by ozone, temperature and aerosol fields from climate simulations of the first phase of the Chemistry-Climate Model Initiative (CCMI-1). Since clouds remain one of the largest uncertainties in climate projections, we simulated only the clear-sky UVI. We compared the modelled UVI climatologies against present-day climatological values of UVI derived from both satellite data (the OMI-Aura OMUVBd product) and ground-based measurements (from the NDACC network). Depending on the region, relative differences between the UVI obtained from CCMI/TUV calculations and the ground-based measurements ranged between −5.9 % and 10.6 %. We then calculated the UVI evolution throughout the 21st century for the four Representative Concentration Pathways (RCPs 2.6, 4.5, 6.0 and 8.5). Compared to 1960s values, we found an average increase in the UVI in 2100 (of 2 %–4 %) in the tropical belt (30∘ N–30∘ S). For the mid-latitudes, we observed a 1.8 % to 3.4 % increase in the Southern Hemisphere for RCPs 2.6, 4.5 and 6.0 and found a 2.3 % decrease in RCP 8.5. Higher increases in UVI are projected in the Northern Hemisphere except for RCP 8.5. At high latitudes, ozone recovery is well identified and induces a complete return of mean UVI levels to 1960 values for RCP 8.5 in the Southern Hemisphere. In the Northern Hemisphere, UVI levels in 2100 are higher by 0.5 % to 5.5 % for RCPs 2.6, 4.5 and 6.0 and they are lower by 7.9 % for RCP 8.5. We analysed the impacts of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) on UVI from 1960 by comparing CCMI sensitivity simulations (1960–2100) with fixed GHGs or ODSs at their respective 1960 levels. As expected with ODS fixed at their 1960 levels, there is no large decrease in ozone levels and consequently no sudden increase in UVI levels. With fixed GHG, we observed a delayed return of ozone to 1960 values, with a corresponding pattern of change observed on UVI, and looking at the UVI difference between 2090s values and 1960s values, we found an 8 % increase in the tropical belt during the summer of each hemisphere. Finally we show that, while in the Southern Hemisphere the UVI is mainly driven by total ozone column, in the Northern Hemisphere both total ozone column and aerosol optical depth drive UVI levels, with aerosol optical depth having twice as much influence on the UVI as total ozone column does. ISSN:1680-7375 ISSN:1680-7367

International audience; In the context of a changing climate, the acceleration of the Brewer-Dobson circulation [Butchart 2014] leadsto a decrease of the ozone total column in the tropics. This decrease affects directly surface ultraviolet radiation,which are already very high in this area. Following the work of (Bais et al., 2011), (Butchart, 2014)and (Hegglin & Shepherd, 2009) on the future evolution of surface irradiance derived from Chemistry ClimateModels (CCM) projections, we projected here surface irradiance from 2010 to 2100 with focus on the tropics.We used the latest chemistry climate projection exercise ; Chemistry Climate Model Initiative (CCMI) coupledwith a radiative transfer model (TUV (Madronich, 1993)) to calculate the evolution of surface Ultravioletradiation throughout the 21st century. Ultraviolet Index (UVi) has been specifically considered (McKenzie,Matthews, & Johnston, 1991).At first, simulation from RefC2 Chemistry Climate Model Initiative have been coupled with a radiativetransfer model, in order to obtained modeled UV index (UVi-M). UVi-M is then compared against availablesatellite ultraviolet radiation observations (OMI OMUVbd product) between 2005 and 2016. Statistical differenceand variance have been analysed versus different parameters: geographical location, model or ensembleof model outputs used in the radiative transfer calculation.

There is no known atmospheric phenomenon with a longer horizon of predictability than the quasibiennial oscillation (QBO) of tropical stratospheric circulation. With a mean period of about 28 months, the QBO phase can routinely be predicted at least a year in advance. This predictability arises from internal atmospheric dynamics, rather than from external forcings with long timescales, and it offers the tantalizing prospect of improved predictions for any phenomena influenced by the QBO. Observed QBO teleconnections include an apparent QBO influence on the stratospheric winter polar vortices in both hemispheres, the Madden-Julian Oscillation (MJO), and the North-Atlantic Oscillation (NAO). Yet the degree to which such teleconnections are real, robust, and sufficiently strong to provide useful predictive skill remains an important topic of research. Utilizing and understanding these linkages will require atmospheric models that adequately represent both the QBO and the mechanisms by which it influences other aspects of the general circulation, such as tropical deep convection. The 2016 QBO workshop in Oxford aimed to explore these themes, and to build on the outcomes of the first QBO workshop, held in March 2015 in Victoria, BC, Canada (as reported in SPARC Newsletter No. 45). This earlier workshop was the kick-off meeting of the SPARC QBOi (QBO Initiative) activity, and its key outcome was to plan a series of coordinated Atmosphere General Circulation Model (AGCM) experiments (the “phase-one” QBOi experiments). These experiments provide a multi-model dataset that can be used to investigate the aforementioned themes. While the focus of the Victoria meeting was primarily on the QBO itself, the Oxford workshop has broadened the scope of the QBOi activity to encompass QBO impacts. Its primary outcome is a planned set of core papers analysing the phaseone QBOi experiments

We present an overview of state-of-the-artchemistry–climate and chemistry transport models that areused within phase 1 of the Chemistry–Climate Model Initia-tive (CCMI-1). The CCMI aims to conduct a detailed evalua-tion of participating models using process-oriented diagnos-tics derived from observations in order to gain confidence inthe models’ projections of the stratospheric ozone layer, tro-pospheric composition, air quality, where applicable globalclimate change, and the interactions between them. Interpre-tation of these diagnostics requires detailed knowledge of theradiative, chemical, dynamical, and physical processes incor-porated in the models. Also an understanding of the degree towhich CCMI-1 recommendations for simulations have beenfollowed is necessary to understand model responses to an-thropogenic and natural forcing and also to explain inter-model differences. This becomes even more important giventhe ongoing development and the ever-growing complexityof these models. This paper also provides an overview ofthe available CCMI-1 simulations with the aim of informingCCMI data users., Geoscientific Model Development, 10 (2), ISSN:1991-9603, ISSN:1991-959X

The surface response to 11 year solar cycle variations is investigated by analyzing the long-term mean sea level pressure and sea surface temperature observations for the period 1870-2010. The analysis reveals a statistically significant 11 year solar signal over Europe, and the North Atlantic provided that the data are lagged by a few years. The delayed signal resembles the positive phase of the North Atlantic Oscillation (NAO) following a solar maximum. The corresponding sea surface temperature response is consistent with this. A similar analysis is performed on long-term climate simulations from a coupled ocean-atmosphere version of the Hadley Centre model that has an extended upper lid so that influences of solar variability via the stratosphere are well resolved. The model reproduces the positive NAO signal over the Atlantic/European sector, but the lag of the surface response is not well reproduced. Possible mechanisms for the lagged nature of the observed response are discussed. Key Points 11-year solar signal detected over N. Atlantic/Europe Signal is evident if data are lagged by ~3 years HadGEM climate model simulates signal but not the lag ©2013. The Authors.

We perform a comparison of temperature changes in the free atmosphere over the period 1961-2010 using a high-top (lid at 84 km) and low-top (lid at 40 km) version of the HadGEM2 atmosphere-ocean global climate model. Model simulations of historical climate change that include key anthropogenic and natural external forcings are compared with three different radiosonde data sets. We also apply a regression-based "optimal fingerprinting" method to determine whether model-predicted temperature-change signals in response to external forcing are identifiable in observations. This method employs simulations that isolate the signals associated with different sets of external forcings (well-mixed GHGs and natural external factors). In both high- and low-top models, we obtain positive detection of the signals arising from anthropogenic influences. We find statistically significant differences between the latitude-height temperature signals simulated by the high- and low-top models, particularly in the tropical lower stratosphere. The scaling factors associated with each of the separate forcings are more tightly constrained in the high-top over the low-top model, but otherwise are similar in nature. Finally, we show that in detecting the GHG fingerprint, it is the entire vertical temperature profile that is important, not simply the lower-most tropospheric levels. © 2013. American Geophysical Union. All Rights Reserved.

The structure of the Arctic stratospheric polar vortex in three chemistry-climate models (CCMs) taken from the CCMVal-2 intercomparison is examined using zonal mean and geometric-based methods. The geometric methods are employed by taking 2D moments of potential vorticity fields that are representative of the polar vortices in each of the models. This allows the vortex area, centroid location and ellipticity to be determined, as well as a measure of vortex filamentation. The first part of the study uses these diagnostics to examine how well the mean state, variability and extreme variability of the polar vortices are represented in CCMs compared to ERA-40 reanalysis data, and in particular for the UMUKCA-METO, NIWA-SOCOL and CCSR/NIES models. The second part of the study assesses how the vortices are predicted to change in terms of the frequency of sudden stratospheric warmings and their general structure over the period 1960-2100. In general, it is found that the vortices are climatologically too far poleward in the CCMs and produce too few large-scale filamentation events. Only a small increase is observed in the frequency of sudden stratospheric warming events from the mean of the CCMVal-2 models, but the distribution of extreme variability throughout the winter period is shown to change towards the end of the twentyfirst century. © 2012 Royal Meteorological Society and British Crown, the Met Office.

It has been suggested that the Sun may evolve into a period of lower activity over the 21st century. This study examines the potential climate impacts of the onset of an extreme “Maunder Minimum‐like” grand solar minimum using a comprehensive global climate model. Over the second half of the 21st century, the scenario assumes a decrease in total solar irradiance of 0.12% compared to a reference Representative Concentration Pathway 8.5 experiment. The decrease in solar irradiance cools the stratopause (∼1 hPa) in the annual and global mean by 1.2 K. The impact on global mean near‐surface temperature is small (∼−0.1 K), but larger changes in regional climate occur during the stratospheric dynamically active seasons. In Northern Hemisphere wintertime, there is a weakening of the stratospheric westerly jet by up to ∼3–4 m s−1, with the largest changes occurring in January–February. This is accompanied by a deepening of the Aleutian Low at the surface and an increase in blocking over Northern Europe and the North Pacific. There is also an equatorward shift in the Southern Hemisphere midlatitude eddy‐driven jet in austral spring. The occurrence of an amplified regional response during winter and spring suggests a contribution from a top‐down pathway for solar‐climate coupling; this is tested using an experiment in which ultraviolet (200–320 nm) radiation is decreased in isolation of other changes. The results show that a large decline in solar activity over the 21st century could have important impacts on the stratosphere and regional surface climate., Key Points A future decline in solar activity would not offset projected global warmingA future decline in solar activity could have larger regional effects in winterTop‐down mechanism contributes to Northern Hemisphere regional response

There was a numerical error in the abstract of Mitchell et al. (2012). In the fourth sentence of the abstract the number should be 7 events per decade, not 0.7. The full sentence should read, Analysis of the standard stratospheric zonal mean wind diagnostic shows no significan increase over the twenty-first century in the number of major sudden stratospheric warmings (SSWs) from its historical value of 7 events per decade, although the monthly distribution of SSWs does vary, with events becoming more evenly dispersed through thwinter.

We describe the HadGEM2 family of climate configurations of the Met Office Unified Model, MetUM. The concept of a model "family" comprises a range of specific model configurations incorporating different levels of complexity but with a common physical framework. The HadGEM2 family of configurations includes atmosphere and ocean components, with and without a vertical extension to include a well-resolved stratosphere, and an Earth-System (ES) component which includes dynamic vegetation, ocean biology and atmospheric chemistry. The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1, namely Northern Hemisphere continental temperature biases and tropical sea surface temperature biases and poor variability. Targeting these biases was crucial in order that the ES configuration could represent important biogeochemical climate feedbacks. Detailed descriptions and evaluations of particular HadGEM2 family members are included in a number of other publications, and the discussion here is limited to a summary of the overall performance using a set of model metrics which compare the way in which the various configurations simulate present-day climate and its variability.

Coupled chemistry‐climate model simulations covering the recent past and continuing throughout the 21st century have been completed with a range of different models. Common forcings are used for the halogen amounts and greenhouse gas concentrations, as expected under the Montreal Protocol (with amendments) and Intergovernmental Panel on Climate Change A1b Scenario. The simulations of the Antarctic ozone hole are compared using commonly used diagnostics: the minimum ozone, the maximum area of ozone below 220 DU, and the ozone mass deficit below 220 DU. Despite the fact that the processes responsible for ozone depletion are reasonably well understood, a wide range of results is obtained. Comparisons with observations indicate that one of the reasons for the model underprediction in ozone hole area is the tendency for models to underpredict, by up to 35%, the area of low temperatures responsible for polar stratospheric cloud formation. Models also typically have species gradients that are too weak at the edge of the polar vortex, suggesting that there is too much mixing of air across the vortex edge. Other models show a high bias in total column ozone which restricts the size of the ozone hole (defined by a 220 DU threshold). The results of those models which agree best with observations are examined in more detail. For several models the ozone hole does not disappear this century but a small ozone hole of up to three million square kilometers continues to occur in most springs even after 2070.

We have estimated changes in surface solar ultraviolet (UV) radiation under cloud free conditions in the 21st century based on simulations of 11 coupled Chemistry-Climate Models (CCMs). The total ozone columns and vertical profiles of ozone and temperature projected from CCMs were used as input to a radiative transfer model in order to calculate the corresponding erythemal irradiance levels. Time series of monthly erythemal irradiance received at the surface during local noon are presented for the period 1960 to 2100. Starting from the first decade of the 21st century, the surface erythemal irradiance decreases globally as a result of the projected stratospheric ozone recovery at rates that are larger in the first half of the 21st century and smaller towards its end. This decreasing tendency varies with latitude, being more pronounced over areas where stratospheric ozone.

We have estimated changes in surface solar ultraviolet (UV) radiation under cloud free conditions in the 21st century based on simulations of 11 coupled Chemistry-Climate Models (CCMs). The total ozone columns and vertical profiles of ozone and temperature projected from CCMs were used as input to a radiative transfer model in order to calculate the corresponding erythemal irradiance levels. Time series of monthly erythemal irradiance received at the surface during local noon are presented for the period 1960 to 2100. Starting from the first decade of the 21st century, the surface erythemal irradiance decreases globally as a result of the projected stratospheric ozone recovery at rates that are larger in the first half of the 21st century and smaller towards its end. This decreasing tendency varies with latitude, being more pronounced over areas where stratospheric ozone has been depleted the most after 1980. Between 2000 and 2100 surface erythemal irradiance is projected to decrease over midlatitudes by 5 to 15%, while at the southern high latitudes the decrease is twice as much. In this study we have not included effects from changes in cloudiness, surface reflectivity and tropospheric aerosol loading, which will likely be affected in the future due to climate change. Consequently, over some areas the actual changes in future UV radiation may be different depending on the evolution of these parameters., Atmospheric Chemistry and Physics, 9 (4), ISSN:1680-7375, ISSN:1680-7367

A Global 40-year simulation from 1980 to 2019 was performed with the FinROSE chemistry-transport model based on the use of coupled chemistry GCM-data. The main focus of our analysis is on climatological-scale processes in high latitudes. The resulting trend estimates for the past period (1980–1999) agree well with observation-based trend estimates. The results for the future period (2000–2019) suggest that the extent of seasonal ozone depletion over both northern and southern high-latitudes has likely reached its maximum. Furthermore, while climate change is expected to cool the stratosphere, this cooling is unlikely to accelerate significantly high latitude ozone depletion. However, the recovery of seasonal high latitude ozone losses will not take place during the next 15 years.