The historical ozone trends simulated with the SOCOLv4 and their comparison with observations and reanalyses

There is evidence that the ozone layer has begun to recover owing to the ban on the production of halogenated ozone-depleting substances (hODS) accomplished by the Montreal Protocol and its amendments and adjustments (MPA). However, recent studies, while reporting an increase in tropospheric ozone from the anthropogenic NOx and CH4 and confirming the ozone recovery in the upper stratosphere from the effects of hODS, also indicate a continuing decline in the lower tropical and mid-latitudinal stratospheric ozone. While these are indications derived from observations, they are not reproduced by current global chemistry–climate models (CCMs), which show positive or near-zero trends for ozone in the lower stratosphere. This makes it difficult to robustly establish ozone evolution and has sparked debate about the ability of contemporary CCMs to simulate future ozone trends. We applied the new Earth system model (ESM) SOCOLv4 (SOlar Climate Ozone Links, version 4) to calculate long-term ozone trends between 1985–2018 and compare them with trends derived from the BAyeSian Integrated and Consolidated (BASIC) ozone composite and MERRA-2, ERA-5, and MSRv2 reanalyses. We designed the model experiment with a six-member ensemble to account for the uncertainty of the natural variability. The trend analysis is performed separately for the ozone depletion (1985–1997) and ozone recovery (1998–2018) phases of the ozone evolution. Within the 1998–2018 period, SOCOLv4 shows statistically significant positive ozone trends in the mesosphere, upper and middle stratosphere, and a steady increase in the tropospheric ozone. The SOCOLv4 results also suggest slightly negative trends in the extra-polar lower stratosphere, yet they barely agree with the BASIC ozone composite in terms of magnitude and statistical significance. However, in some realizations of the SOCOLv4 experiment, the pattern of ozone trends in the lower stratosphere resembles much of what is observed, suggesting that SOCOLv4 may be able to reproduce the observed trends in this region. Thus, the model results reveal marginally significant negative ozone changes in parts of the low-latitude lower stratosphere, which agrees in general with the negative tendencies extracted from the satellite data composite. Despite the slightly smaller significance and magnitude of the simulated ensemble mean, we confirm that modern CCMs such as SOCOLv4 are generally capable of simulating the observed ozone changes, justifying their use to project the future evolution of the ozone layer.</p

The influence of future changes in springtime Arctic ozone on stratospheric and surface climate

Stratospheric ozone is expected to recover by the mid-century due to the success of the Montreal Protocol in regulating the emission of ozone-depleting substances (ODSs). In the Arctic, ozone abundances are projected to surpass historical levels due to the combined effect of decreasing ODSs and elevated greenhouse gases (GHGs). While long-term changes in stratospheric ozone have been shown to be a major driver of future surface climate in the Southern Hemisphere during summertime, the dynamical and climatic impacts of elevated ozone levels in the Arctic have not been investigated. In this study, we use two chemistry climate models (the SOlar Climate Ozone Links – Max Planck Ocean Model (SOCOL-MPIOM) and the Community Earth System Model – Whole Atmosphere Community Climate Model (CESM-WACCM)) to assess the climatic impacts of future changes in Arctic ozone on stratospheric dynamics and surface climate in the Northern Hemisphere (NH) during the 21st century. Under the high-emission scenario (RCP8.5) examined in this work, Arctic ozone returns to pre-industrial levels by the middle of the century. Thereby, the increase in Arctic ozone in this scenario warms the lower Arctic stratosphere; reduces the strength of the polar vortex, advancing its breakdown; and weakens the Brewer–Dobson circulation. The ozone-induced changes in springtime generally oppose the effects of GHGs on the polar vortex. In the troposphere, future changes in Arctic ozone induce a negative phase of the Arctic Oscillation, pushing the jet equatorward over the North Atlantic. These impacts of future ozone changes on NH surface climate are smaller than the effects of GHGs, but they are remarkably robust among the two models employed in this study, canceling out a portion of the GHG effects (up to 20 % over the Arctic). In the stratosphere, Arctic ozone changes cancel out a much larger fraction of the GHG-induced signal (up to 50 %–100 %), resulting in no overall change in the projected springtime stratospheric northern annular mode and a reduction in the GHG-induced delay of vortex breakdown of around 15 d. Taken together, our results indicate that future changes in Arctic ozone actively shape the projected changes in the stratospheric circulation and their coupling to the troposphere, thereby playing an important and previously unrecognized role as a driver of the large-scale atmospheric circulation response to climate change.</p

Using modal decompositions to explain the sudden expansion of the mixing layer in the wake of a groyne in a shallow flow

The sudden expansion of the mixing layer created in the wake of a single groyne is investigated using Particle Image Velocimetry (PIV). In the region of the sudden expansion a patch of high Reynolds shear stresses are observed. Using low-order representations, created from a Dynamic Mode Decomposition and a search criteria based on a Proper Orthogonal Decomposition, the spatio-temporal mechanism of the sudden expansion is investigated. The present study demonstrates the sudden expansion is created by the periodic merging of eddies. These eddies originate from the upstream separation and the tip of the groyne and merge with recirculating eddies created, downstream of the groyne, at the interface of the mixing layer and the lateral wall

Dynamic drag modeling of submerged aquatic vegetation canopy flows

Vegetation has a profound effect on flow and sediment transport processes in natural rivers, by increasing both skin friction and form drag. The increase in drag introduces a drag discontinuity between the in-canopy flow and the flow above, which leads to the development of an inflection point in the velocity profile, resembling a free shear layer. Therefore, drag acts as the primary driver for the entire canopy system. Most current numerical hydraulic models which incorporate vegetation rely either on simple, static plant forms, or canopy-scaled drag terms. However, it is suggested that these are insufficient as vegetation canopies represent complex, dynamic, porous blockages within the flow, which are subject to spatially and temporally dynamic drag forces. Here we present a dynamic drag methodology within a CFD framework. Preliminary results for a benchmark cylinder case highlight the accuracy of the method, and suggest its applicability to more complex cases

Drivers of the tropospheric ozone budget throughout the 21st century under the medium-high climate scenario RCP 6.0

Because tropospheric ozone is both a greenhouse gas and harmful air pollutant, it is important to understand how anthropogenic activities may influence its abundance and distribution through the 21st century. Here, we present model simulations performed with the chemistry–climate model SOCOL, in which spatially disaggregated chemistry and transport tracers have been implemented in order to better understand the distribution and projected changes in tropospheric ozone. We examine the influences of ozone precursor emissions (nitrogen oxides (NOx /, carbon monoxide (CO) and volatile organic compounds (VOCs)), climate change (including methane effects) and stratospheric ozone recovery on the tropospheric ozone budget, in a simulation following the climate scenario Representative Concentration Pathway (RCP) 6.0 (a medium-high, and reasonably realistic climate scenario). Changes in ozone precursor emissions have the largest effect, leading to a global-mean increase in tropospheric ozone which maximizes in the early 21st century at 23% compared to 1960. The increase is most pronounced at northern midlatitudes, due to regional emission patterns: between 1990 and 2060, northern midlatitude tropospheric ozone remains at constantly large abundances: 31% larger than in 1960. Over this 70-year period, attempts to reduce emissions in Europe and North America do not have an effect on zonally averaged northern midlatitude ozone because of increasing emissions from Asia, together with the long lifetime of ozone in the troposphere. A simulation with fixed anthropogenic ozone precursor emissions of NOx , CO and non-methane VOCs at 1960 conditions shows a 6% increase in global-mean tropospheric ozone by the end of the 21st century, with an 11% increase at northern midlatitudes. This increase maximizes in the 2080s and is mostly caused by methane, which maximizes in the 2080s following RCP 6.0, and plays an important role in controlling ozone directly, and indirectly through its influence on other VOCs and CO. Enhanced flux of ozone from the stratosphere to the troposphere as well as climate change-induced enhancements in lightning NOx emissions also increase the tropospheric ozone burden, although their impacts are relatively small. Overall, the results show that under this climate scenario, ozone in the future is governed largely by changes in methane and NOx ; methane induces an increase in tropospheric ozone that is approximately one-third of that caused by NOx . Climate impacts on ozone through changes in tropospheric temperature, humidity and lightning NOx remain secondary compared with emission strategies relating to anthropogenic emissions of NOx , such as fossil fuel burning. Therefore, emission policies globally have a critical role to play in determining tropospheric ozone evolution through the 21st century

Iodine chemistry in the chemistry-climate model SOCOL-AERv2-I

In this paper, we present a new version of the chemistry-climate model SOCOL-AERv2 supplemented by an iodine chemistry module. We perform three 20-year ensemble experiments to assess the validity of the modeled iodine and to quantify the effects of iodine on ozone. The iodine distributions obtained with SOCOL-AERv2-I agree well with AMAX-DOAS observations and with CAM-chem model simulations. For the present-day atmosphere, the model suggests that the iodine-induced chemistry leads to a 3ĝ€¯%-4ĝ€¯% reduction in the ozone column, which is greatest at high latitudes. The model indicates the strongest influence of iodine in the lower stratosphere with 30ĝ€¯ppbv less ozone at low latitudes and up to 100ĝ€¯ppbv less at high latitudes. In the troposphere, the account of the iodine chemistry reduces the tropospheric ozone concentration by 5ĝ€¯%-10ĝ€¯% depending on geographical location. In the lower troposphere, 75ĝ€¯% of the modeled ozone reduction originates from inorganic sources of iodine, 25ĝ€¯% from organic sources of iodine. At 50ĝ€¯hPa, the results show that the impacts of iodine from both sources are comparable. Finally, we determine the sensitivity of ozone to iodine by applying a 2-fold increase in iodine emissions, as it might be representative for iodine by the end of this century. This reduces the ozone column globally by an additional 1.5ĝ€¯%-2.5ĝ€¯%. Our results demonstrate the sensitivity of atmospheric ozone to iodine chemistry for present and future conditions, but uncertainties remain high due to the paucity of observational data of iodine species.Fil: Karagodin Doyennel, Arseniy. The Institute for Atmospheric and Climate Science; Suiza. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; SuizaFil: Rozanov, Eugene. The Institute for Atmospheric and Climate Science; Suiza. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; Suiza. Saint Petersburg State University; RusiaFil: Sukhodolov, Timofei. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; Suiza. Saint Petersburg State University; Rusia. University of Natural Resources and Life Sciences; AustriaFil: Egorova, Tatiana. Physikalisch-Meteorologisches Observatorium Davos/World Radiation Center; SuizaFil: Saiz López, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Cuevas, Carlos A.. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Fernandez, Rafael Pedro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentina. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Sherwen, Tomás. University of York; Reino UnidoFil: Volkamer, Rainer. The Institute for Atmospheric and Climate Science ; Suiza. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados Unidos. Paul Scherrer Institute; SuizaFil: Koenig, Theodore K.. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Giroud, Tanguy. The Institute for Atmospheric and Climate Science; SuizaFil: Peter, Thomas. The Institute for Atmospheric and Climate Science; Suiz

Экспериментальная проверка адекватности математической модели возвратно-поступательного электрического генератора с электромагнитным возбуждением

The article presents a mathematical simulation of the electromagnetically excited generator of reciprocating type, which resulted in an equivalent circuit diagram, a magnetic circuit design of the generator and some expressions describing the electromagnetic processes in the electromagnetically excited generator of reciprocating type. The nonlinear mathematical model of the electromagnetically excited generator of reciprocating type has been developed. In order of the experimental verification of the adequacy of the mathematical model of the reciprocating electric generator, as well as of the validity of the assumptions made, a breadboard sample of the reciprocating electric generator has been made consisting of a fixed part in the form of two U-shaped magnetic cores and a moving part representing an H-shaped magnetic cores. There is focused operating winding on both the U-shaped magnetic cores. The N-shaped magnetic core is coiled with excitation winding which is connected to a DC power source. In a breadboard sample of the reciprocating electric generator a drive motor of 100 W with an amplitude of reciprocating oscillations of the moving part equal to 16 mm, and a frequency of oscillations adjustable in the range from 5 to 50 Hz is used in order to simulate a free-piston engine. The main characteristics of the generator (viz., idle speed and external characteristics) have been experimentally obtained. Comparison of experimental and calculated results demonstrated their discrepancy of no more than 4 %; therefore, the nonlinear mathematical model reflects the characteristics of the generator of longitudinal type with a high degree of adequacy.В статье представлено математическое моделирование генератора возвратнопоступательного типа с электромагнитным возбуждением, в результате которого получены эквивалентная электрическая схема, схема магнитной цепи генератора и выражения, описывающие электромагнитные процессы в генераторе возвратно-поступательного типа с электромагнитным возбуждением. Разработана нелинейная математическая модель генератора возвратно-поступательного типа с электромагнитным возбуждением. Для экспериментальной проверки адекватности математической модели возвратно-поступательного электрического генератора, а также правомерности принятых допущений был изготовлен макетный образец возвратно-поступательного электрического генератора, состоящий из неподвижной части в виде двух П-образных магнитопроводов и подвижной части, представляющей собой Н-образный магнитопровод. На обоих П-образных магнитопроводах устанавливается сосредоточенная рабочая обмотка. На Н-образный магнитопровод намотана обмотка возбуждения и подключена к источнику постоянного тока. В макетном образце возвратно-поступательного электрического генератора для имитации свободнопоршневого двигателя применяется приводной электродвигатель мощностью 100 Вт с амплитудой возвратно-поступательных колебаний подвижной части, равной 16 мм, и частотой колебаний, регулируемой в диапазоне от 5 до 50 Гц. Экспериментально получены основные характеристики генератора (характеристика холостого хода и внешняя характеристика). Сравнение экспериментальных и расчетных результатов показывает их расхождение не более чем на 4 %, следовательно, нелинейная математическая модель отражает характеристики генератора продольного типа с высокой степенью адекватности