Atmosphere–ocean–aerosol–chemistry–climate model SOCOLv4.0: description and evaluation

This paper features the new atmosphere–ocean–aerosol–chemistry–climate model, SOlar Climate Ozone Links (SOCOL) v4.0, and its validation. The new model was built by interactively coupling the Max Planck Institute Earth System Model version 1.2 (MPI-ESM1.2) (T63, L47) with the chemistry (99 species) and size-resolving (40 bins) sulfate aerosol microphysics modules from the aerosol–chemistry–climate model, SOCOL-AERv2. We evaluate its performance against reanalysis products and observations of atmospheric circulation, temperature, and trace gas distribution, with a focus on stratospheric processes. We show that SOCOLv4.0 captures the low- and midlatitude stratospheric ozone well in terms of the climatological state, variability and evolution. The model provides an accurate representation of climate change, showing a global surface warming trend consistent with observations as well as realistic cooling in the stratosphere caused by greenhouse gas emissions, although, as in previous model versions, a too-fast residual circulation and exaggerated mixing in the surf zone are still present. The stratospheric sulfur budget for moderate volcanic activity is well represented by the model, albeit with slightly underestimated aerosol lifetime after major eruptions. The presence of the interactive ocean and a successful representation of recent climate and ozone layer trends make SOCOLv4.0 ideal for studies devoted to future ozone evolution and effects of greenhouse gases and ozone-destroying substances, as well as the evaluation of potential solar geoengineering measures through sulfur injections. Potential further model improvements could be to increase the vertical resolution, which is expected to allow better meridional transport in the stratosphere, as well as to update the photolysis calculation module and budget of mesospheric odd nitrogen. In summary, this paper demonstrates that SOCOLv4.0 is well suited for applications related to the stratospheric ozone and sulfate aerosol evolution, including its participation in ongoing and future model intercomparison projects.

Simulating glacial dust changes in the Southern Hemisphere using ECHAM6.3-HAM2.3

Mineral dust aerosol constitutes an important component of the Earth’s climate system, not only on short timescales due to direct and indirect influences on the radiation budget, but also on long timescales by acting as a fertilizer for the biosphere and thus affecting the global carbon cycle. For a quantitative assessment of its impact on the global climate, state-of-the-art atmospheric and aerosol models can be utilized. In this study, we use the ECHAM6.3-HAM2.3 model to perform global simulations of the mineral dust cycle for present-day (PD), pre-industrial (PI) and Last Glacial Maximum (LGM) climate conditions. The intercomparison with marine sediment and ice core data as well as other modeling studies shows that the obtained annual dust emissions of 1221, 923 and 5159 Tg for PD, PI and LGM, respectively, generally agree well with previous findings. Our analyses focussing on the Southern Hemisphere suggest that over 90 % of the mineral dust deposited over Antarctica are of Australian or South American origin during both PI and LGM. However, contrary to previous studies, we find that Australia contributes a higher proportion during the LGM, which is mainly caused by changes in the precipitation patterns. Obtained increased particle radii during the LGM can be traced back to increased sulphate condensation on the particle surfaces as a consequence of longer particle lifetimes. The meridional transport of mineral dust from its source regions to the South Pole takes place at different altitudes, depending on the grain size of the dust particles. We find a trend of generally lower transport heights during the LGM compared to PI as a consequence of reduced convection due to colder surfaces, indicating a vertically less extensive Polar Cell.

On the Estimation of Deep Atlantic Ventilation from Fossil Radiocarbon Records. I. Modern Reference Estimates

Radiocarbon dates of fossil carbonates sampled from sediment cores and the seafloor have been used to infer that deep ocean ventilation during the last ice age was different from today. In this first of paired papers, the time-averaged abyssal circulation in the modern Atlantic is estimated by combining a hydrographic climatology, observational estimates of volume transports, Argo float velocities at 1000 m, radiocarbon data, and geostrophic dynamics. Different estimates of modern circulation, obtained from different prior assumptions about the abyssal flow and different errors in the geostrophic balance, are produced for use in a robust interpretation of fossil records in terms of deviations from the present-day flow, which is undertaken in the second paper.For all estimates, the meridional transport integrated zonally and averaged over a hemisphere, 〈Vk〉, is southward between 1000-4000 m in both hemispheres, northward between 4000-5000 m in the South Atlantic, and insignificant between 4000-5000 m in the North Atlantic. Estimates of 〈Vk〉 obtained from two distinct prior circulations - one based on a level of no motion at 4000 m and one based on Argo oat velocities at 1000 m - become statistically indistinguishable when Δ14C data are considered. The transport time scale, defined as τk = /〈Vk〉, where is the volume of the kth layer, is estimated to about a century between 1000-3000 m in both the South and North Atlantic, 124±9 yr (203±23 yr) between 3000-4000 m in the South (North) Atlantic, and 269±115 yr between 4000-5000 m in the South Atlantic.

Interhemispheric transport of metallic ions within ionospheric sporadic <i>E</i> layers by the lower thermospheric meridional circulation

Long-lived metallic ions in the Earth's atmosphere (ionosphere) have been investigated for many decades. Although the seasonal variation in ionospheric “sporadic E” layers was first observed in the 1960s, the mechanism driving the variation remains a long-standing mystery. Here, we report a study of ionospheric irregularities using scintillation data from COSMIC satellites and identify a large-scale horizontal transport of long-lived metallic ions, combining the simulations of the Whole Atmosphere Community Climate Model with the chemistry of metals and ground-based observations from two meridional chains of stations from 1975–2016. We find that the lower thermospheric meridional circulation influences the meridional transport and seasonal variations of metallic ions within sporadic E layers. The winter-to-summer meridional velocity of ions is estimated to vary between −1.08 and 7.45 m/s at altitudes of 107–118 km between 10–60∘ N. Our results not only provide strong support for the lower thermospheric meridional circulation predicted by a whole atmosphere chemistry–climate model, but also emphasize the influences of this winter-to-summer circulation on the large-scale interhemispheric transport of composition in the thermosphere–ionosphere.

Atmosphere-Ocean-Aerosol-Chemistry-Climate Model SOCOLv4.0: description and evaluation

This paper features the new Atmosphere-Ocean-Aerosol-Chemistry-Climate Model SOCOLv4.0 and its validation. The new model was built by interactively coupling the MPI-ESM1.2 Earth System Model (T63, L47) with the chemistry (99 species) and size-resolving (40 bins) sulfate aerosol microphysics modules from the Aerosol-Chemistry-Climate Model SOCOL-AERv2. We evaluate its performance against reanalysis products and observations of atmospheric circulation, temperature, and trace gases distribution, with a focus on stratospheric processes. We show that SOCOLv4.0 captures the low- and mid-latitude stratospheric ozone well in terms of the climatological state, variability and evolution. The model provides an accurate representation of climate change, showing a global surface warming trend consistent with observations as well as realistic cooling in the stratosphere caused by greenhouse gas emissions, although, as in previous model versions, a too fast residual circulation and exaggerated mixing in the surf zone are still present. The stratospheric sulfur budget for moderate volcanic activity is well represented by the model, albeit with slightly underestimated aerosol lifetime after major eruptions. The presence of the interactive ocean and a successful representation of recent climate and ozone layer trends make SOCOLv4.0 ideal for studies devoted to future ozone evolution and effects of greenhouse gases and ozone-destroying substances, as well as the evaluation of potential solar geoengineering measures through sulfur injections. Potential further model improvements could be to increase the vertical resolution, which is expected to allow better meridional transport in the stratosphere, as well as to update the photolysis calculation module and budget of mesospheric odd nitrogen. In summary, this paper demonstrates that SOCOLv4.0 is well suited for applications related to the stratospheric ozone and sulfate aerosol evolution, including its participation in ongoing and future model intercomparison projects.

The response of stratospheric ozone and dynamics to changes in atmospheric oxygen

&lt;p&gt;Photolysis of molecular oxygen (O&lt;sub&gt;2&lt;/sub&gt;) maintains the stratospheric ozone layer, protecting living organisms on Earth by absorbing harmful ultraviolet radiation. The atmospheric oxygen level has not always been constant, and has been held responsible for species extinctions via a thinning of the ozone layer in the past. On paleo-climate timescales, it ranged between 10 and 35% depending on the level of photosynthetic activity of plants and oceans. Previous estimates, however, showed highly uncertain ozone (O&lt;sub&gt;3&lt;/sub&gt;)&amp;#160;&lt;sub&gt;&lt;/sub&gt;responses to atmospheric O&lt;sub&gt;2&lt;/sub&gt; changes, including monotonic positive or negative correlations, or displaying a maximum in O&lt;sub&gt;3 &lt;/sub&gt;column around a certain oxygen level. Motivated by these discrepancies we reviewed how the ozone layer responds to atmospheric oxygen changes by means of a state-of-the-art chemistry-climate model (CCM). We used the CCM SOCOL-AERv2 to assess the ozone layer sensitivity to past and potential future concentrations of atmospheric oxygen varying from 5 to 40 %. Our findings are at odds with previous studies: we find that the current mixing ratio of O&lt;sub&gt;2&lt;/sub&gt;, 21 %, indeed maximizes the O&lt;sub&gt;3&lt;/sub&gt; layer thickness and, thus, represents an optimal state for life on Earth. In the model, any alteration in atmospheric oxygen would result globally in less total column ozone and, therefore, more UV reaching the troposphere. Total ozone column in low-latitude regions is less sensitive to the changes, because of the &amp;#8220;self-healing&amp;#8221; effect, i.e. more UV entering lower levels, where O&lt;sub&gt;2&lt;/sub&gt; photolyzes, can partly compensate the O&lt;sub&gt;3&lt;/sub&gt; lack higher up. Mid- and high-latitudes, however, are characterized by &amp;#177;20 DU ozone hemispheric redistributions even for small (&amp;#177;5 %) variations in O&lt;sub&gt;2&lt;/sub&gt; content. Additional regional patterns result from the hemispheric asymmetry of meridional transport pathways via the Brewer-Dobson circulation (BDC). We will discuss the different ozone responses resulting from changes in the BDC. These effects are further modulated by the influence of ozone on stratospheric temperatures and thus on the BDC. Lower O&lt;sub&gt;2 &lt;/sub&gt;cases result in a deceleration of the BDC. This renders the relation between ozone and molecular oxygen changes non-linear on both global and regional scales.&lt;/p&gt;

Overturning Variations in the Subpolar North Atlantic in an Ocean Reanalyses Ensemble

&lt;p&gt;The ocean&amp;#8217;s Atlantic Meridional Overturning Circulation (AMOC) has a significant influence on global climate through its meridional transport of heat and carbon. Deep water formation occurring in the subpolar North Atlantic is an essential component the AMOC. Understanding the nature and causes of its multidecadal variation at these high latitudes is critical to more accurately predict future changes. We analyse the subpolar overturning in an ensemble of eddy permitting &amp;#188; degree global ocean reanalyses, restrained by observations and historical forcings, over the period 1993-2018. This overturning transport is validated against the continuous measurements obtained along the Overturning in the Subpolar North Atlantic Program (OSNAP) mooring array since 2014. The ability of each reanalysis to capture the observed changes in the overturning will be determined, providing confidence in their ability to simulate changes prior to the availability of OSNAP, and exposing their limitations. We analyse the eastern and western sections of the OSNAP array to determine the relative importance of the overturning along these sections and the temporal variability on various timescales. This research complements a previous study investigating changes in the subtropical Atlantic overturning using the same reanalyses ensemble which was shown to provide a good approximation to observations.&lt;/p&gt;

The atmosphere circulation movements in the matching with space weather parameters variations

&lt;p&gt;The work presents some investigation results of the Space Weather state during the macrosynoptic processes movements in North Atlantic and Eurasia extratropical latitudes. The types of these processes, as it is known, were defined by A. F. Vangengeim as atmosphere circulation types: E-type (east transport in the troposphere which matches with stable anticyclone above the continent), W-type (west transport), and C-type (meridional transport).&lt;/p&gt;&lt;p&gt;The investigation time interval: 1.01.2007 &amp;#8211; 1.01.2014. That corresponds to: the Solar Activity (SA) 23 cycle fall branch, the SA minimum, the rise branch of the 24 SA cycle, the maximum of 24 SA cycle.&lt;/p&gt;&lt;p&gt;From the investigation we have found out the different periods of the circulation types conservation: &amp;#160;(5-7) days which corresponds to the Natural Synoptic Period (NSP) in Europe region &amp;#8211; in our study we have registered 95 NSP cases - it occurs 45% of all discovered periods); (7-10) days &amp;#8211; 27% (58 cases), and the Long Period (LP) which endured more than 10 days - 28% (59 cases).&lt;/p&gt;&lt;p&gt;Here we compare the space weather state at the beginnings of NSP and LP.&lt;/p&gt;&lt;p&gt;We have investigated the matching of LP-circulation with registered Long-live Pressure Systems (LPS) on different terrestrial latitude locations - Saint-Petersburg (59&lt;sup&gt;o&lt;/sup&gt;57&amp;#8216;N, 30&lt;sup&gt;o&lt;/sup&gt;19&amp;#8216;E) and Tambov (52&lt;sup&gt;o&lt;/sup&gt;43&amp;#8216;N, 41&lt;sup&gt;o&lt;/sup&gt;27&amp;#8216;E).&lt;/p&gt;&lt;p&gt;Space Weather&amp;#160;parameters were: global &amp;#160;variations of SA parameters; daily characteristics of the SA flare component in various bands of the electromagnetic spectrum; variations of Interplanetary Space characteristics in Earth vicinity; variations of daily statistics of Geomagnetic Field characteristics.&lt;/p&gt;&lt;p&gt;Results: (1) The modes of LP-circulation distributions are in the SA maximum and on the SA rise branch (37% and 36% of all LP cases respectively). (2) LP- E-type occurs 56% of all LP. (3) NSP- W-type occurs 48% of all NSP. (4) Most frequent LP- E- type placed on the SA rise branch (24% of all LP). (5) The opening and final moments of LP-circulations was not the same for those moments of LPS on different terrestrial latitude locations but 50% of Saint-Petersburg LPS and 81% of Tambov LPS were intersecting with the time intervals of LP-circulations. (6) All Saint-Petersburg anticyclonic LPS and 82% of them in Tambov area have registered with the E-type of atmosphere circulation. (7) The behaviour of the whole Space Weather parameters complex is specific for LP and differs from it for NSP of different circulation types. (8) The days of the maximal difference of abovementioned complexes were discovered in the folder epoch&amp;#8217;s interval &amp;#8211; that shows the good forecast perspective. (9) The concrete Space Weather parameters which difference the moments of LP-beginnings from NSP-beginnings are listed in the work.&lt;/p&gt;&lt;p&gt;Results may be useful for the understanding of the solar-terrestrial connections and can create the base for the forecast of atmosphere response to the space impact.&lt;/p&gt;

Direct inversion of circulation from tracer measurements – Part 2: Sensitivity studies and model recovery tests

The direct inversion of the 2D continuity equation allows for the inference of the effective meridional transport of trace gases in the middle stratosphere. This method exploits the information given by both the displacement of patterns in measured trace gas distributions and the approximate balance between sinks and horizontal as well as vertical advection. Model recovery tests show that with the current setup of the algorithm, this method reliably reproduces the circulation patterns in the entire analysis domain from 6 to 66 km altitude. Due to the regularization of the inversion, velocities above about 30 km are more likely under- than overestimated. This is explained by the fact that the measured trace gas distributions at higher altitudes generally contain less information and that the regularization of the inversion pushes results towards 0. Weaker regularization would in some cases allow a more accurate recovery of the velocity fields, but there is a price to pay in that the risk of convergence failure increases. No instance was found where the algorithm generated artificial patterns not present in the reference fields. Most information on effective velocities above 50 km is included in measurements of CH4, CO, H2O, and N2O, while CFC-11, HCFC-22, and CFC-12 constrain the inversion most efficiently in the middle stratosphere. H2O is a particularly important tracer in the upper troposphere or lower stratosphere. SF6 and CCl4 generally contain less information but still contribute to the reduction in the estimated uncertainties. With these tests, the reliability of the method has been established.