| publications-1431 |
PEER REVIEWED ARTICLE |
2015 |
P. I. Orvos , V. Homonnai , A. Várai , Z. Bozóki , I. M. Jánosi |
Global trend analysis of the MODIS drought severity index |
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10.5194/gi-4-189-2015 |
Data Management & Analytics |
Natural Water Bodies |
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Abstract. Recently, Mu et al. (2013) compiled an open access database of a remotely sensed global drought severity index (DSI) based on MODIS (Moderate Resolution Imaging Spectroradiometer) satellite measurements covering a continuous period of 12 years. The highest spatial resolution is 0.05° × 0.05° in the geographic band between 60° S and 80° N latitudes (more than 4.9 million locations over land). Here we present a global trend analysis of these satellite-based DSI time series in order to identify geographic locations where either positive or negative trends are statistically significant. Our main result is that 17.34 % of land areas exhibit significant trends of drying or wetting, and these sites constitute geographically connected regions. Since a DSI value conveys local characterization at a given site, we argue that usual field significance tests cannot provide more information about the observations than the presented analysis. The relatively short period of 12 years hinders linking the trends to global climate change; however, we think that the observations might be related to slow (decadal) modes of natural climate variability or anthropogenic impacts. |
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| publications-1432 |
PEER REVIEWED ARTICLE |
2014 |
Froila M. Palmeiro , Natalia Calvo , Rolando R. Garcia |
Future Changes in the Brewer–Dobson Circulation under Different Greenhouse Gas Concentrations in WACCM4 |
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10.1175/jas-d-13-0289.1 |
Data Management & Analytics |
Precipitation & Ecological Systems |
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Abstract The climatology and future changes of the Brewer–Dobson circulation (BDC) in three climate change scenarios are studied using the latest version of the Whole Atmosphere Community Climate Model (WACCM4), which is fully coupled to an ocean model. The results show an acceleration in both the shallow and deep branches of circulation in response to increasing greenhouse gases (GHGs) together with an upward displacement of the tropical upwelling in the deep branch near the stratopause. The downward control principle reveals that different waves are involved in forcing the acceleration of the upper and lower branches. Climatological-mean tropical upwelling in both the lower and upper stratosphere is dominated by explicitly resolved, planetary-scale waves. Trends in the tropical upwelling in the lower stratosphere are mainly attributed to explicitly resolved, planetary-scale waves. However, in the upper stratosphere, despite the fact that resolved waves control the forcing of the climatological upwelling, their contribution to the long-term trend diminishes with increasing GHGs, while the role of gravity waves associated with fronts increases and becomes dominant in the model scenario with the largest GHG increases. The intensification and upward displacement of the subtropical tropospheric jets due to climate change leads to filtering of the westerly part of the frontal gravity wave spectrum, leaving the easterly components to reach the upper stratosphere and force the changes in the circulation there. |
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| publications-1433 |
PEER REVIEWED ARTICLE |
2015 |
Palmeiro, F.M., D. Barriopedro,R. García-Herrera, and N. Calvo |
Comparing Sudden Stratospheric Warming Definitions in Reanalysis Data |
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10.1175/jcli-d-15-0004.1 |
Simulation & Modeling |
Precipitation & Ecological Systems |
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Abstract Sudden stratospheric warmings (SSWs) are characterized by a pronounced increase of the stratospheric polar temperature during the winter season. Different definitions have been used in the literature to diagnose the occurrence of SSWs, yielding discrepancies in the detected events. The aim of this paper is to compare the SSW climatologies obtained by different methods using reanalysis data. The occurrences of Northern Hemisphere SSWs during the extended-winter season and the 1958–2014 period have been identified for a suite of eight representative definitions and three different reanalyses. Overall, and despite the differences in the number and exact dates of occurrence of SSWs, the main climatological signatures of SSWs are not sensitive to the considered reanalysis. The mean frequency of SSWs is 6.7 events decade−1, but it ranges from 4 to 10 events, depending on the method. The seasonal cycle of events is statistically indistinguishable across definitions, with a common peak in January. However, the multidecadal variability is method dependent, with only two definitions displaying minimum frequencies in the 1990s. An analysis of the mean signatures of SSWs in the stratosphere revealed negligible differences among methods compared to the large case-to-case variability within a given definition. The stronger and more coherent tropospheric signals before and after SSWs are associated with major events, which are detected by most methods. The tropospheric signals of minor SSWs are less robust, representing the largest source of discrepancy across definitions. Therefore, to obtain robust results, future studies on stratosphere–troposphere coupling should aim to minimize the detection of minor warmings. |
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| publications-1434 |
PEER REVIEWED ARTICLE |
2015 |
F. Ploeger , M. Abalos , T. Birner , P. Konopka , B. Legras , R. Müller , M. Riese |
Quantifying the effects of mixing and residual circulation on trends of stratospheric mean age of air |
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10.1002/2014gl062927 |
Simulation & Modeling |
Uncategorized |
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AbstractIt is an outstanding issue to what degree trends in stratospheric mean age of air reflect changes in the (slow) residual circulation and how they are affected by (fast) eddy mixing. We present a method to quantify the effects of mixing and residual circulation on mean age trends, based on simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by ERA‐Interim reanalysis and on the integrated tracer continuity equation. During 1990–2013, mean age decreases throughout most of the stratosphere, qualitatively consistent with results based on climate model simulations. During 2002–2012, age changes show a clear hemispheric asymmetry in agreement with satellite observations. We find that changes in the residual circulation transit time cannot explain the mean age trends, and including the integrated effect of mixing is crucial. Above about 550 K (about 22 km), trends in the mixing effect on mean age appear to be coupled to residual circulation changes. |
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| publications-1435 |
PEER REVIEWED ARTICLE |
2016 |
V. Poulain , S. Bekki , M. Marchand , M.P. Chipperfield , M. Khodri , F. Lefèvre , S. Dhomse , G.E. Bodeker , R. Toumi , M. De Maziere , J.-P. Pommer |
Evaluation of the inter-annual variability of stratospheric chemical composition in chemistry-climate models using ground-based multi species time series |
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10.1016/j.jastp.2016.03.010 |
Simulation & Modeling |
Precipitation & Ecological Systems |
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No abstract available |
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| publications-1436 |
PEER REVIEWED ARTICLE |
2016 |
T. Runde , M. Dameris , H. Garny , D. E. Kinnison |
Classification of stratospheric extreme events according to their downward propagation to the troposphere |
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10.1002/2016gl069569 |
Data Management & Analytics |
Uncategorized |
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AbstractThis study presents a classification of stratospheric extreme events during northern winter into events with or without a consistent downward propagation of anomalies to the troposphere. Anomalous strong and weak stratospheric polar vortex events are detected from daily time series of the polar cap averaged (60°–90°N) geopotential height anomaly. The method is applied to chemistry‐climate model data (E39CA and WACCM3.5) and reanalyses data (ERA40). The analyses show that in about 80% of all events no significant tropospheric response can be detected. The stratospheric perturbation of both weak and strong events with a significant tropospheric response persists significantly longer throughout the stratosphere compared to the events without a tropospheric response. The strength of the stratospheric perturbation determines the strength of the tropospheric response only to a small degree. Results are consistent across all three data sets. |
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| publications-1437 |
PEER REVIEWED ARTICLE |
2016 |
Timofei Sukhodolov , Eugene Rozanov , William T. Ball , Alkiviadis Bais , Kleareti Tourpali , Alexander I. Shapiro , Paul Telford , Sergey Smyshlyaev |
Evaluation of simulated photolysis rates and their response to solar irradiance variability |
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10.1002/2015jd024277 |
Simulation & Modeling |
Uncategorized |
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AbstractThe state of the stratospheric ozone layer and the temperature structure of the atmosphere are largely controlled by the solar spectral irradiance (SSI) through its influence on heating and photolysis rates. This study focuses on the uncertainties in the photolysis rate response to solar irradiance variability related to the choice of SSI data set and to the performance of the photolysis codes used in global chemistry‐climate models. To estimate the impact of SSI uncertainties, we compared several photolysis rates calculated with the radiative transfer model libRadtran, using SSI calculated with two models and observed during the Solar Radiation and Climate Experiment (SORCE) satellite mission. The importance of the calculated differences in the photolysis rate response for ozone and temperature changes has been estimated using 1‐D a radiative‐convective‐photochemical model. We demonstrate that the main photolysis reactions, responsible for the solar signal in the stratosphere, are highly sensitive to the spectral distribution of SSI variations. Accordingly, the ozone changes and related ozone‐temperature feedback are shown to depend substantially on the SSI data set being used, which highlights the necessity of obtaining accurate SSI variations. To evaluate the performance of photolysis codes, we compared the results of eight, widely used, photolysis codes against two reference schemes. We show that, in most cases, absolute values of the photolysis rates and their response to applied SSI changes agree within 30%. However, larger errors may appear in specific atmospheric regions because of differences, for instance, in the treatment of Rayleigh scattering, quantum yields, or absorption cross sections. |
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| publications-1438 |
PEER REVIEWED ARTICLE |
2015 |
Anita Várai , Viktória Homonnai , Imre M. Jánosi , Rolf Müller |
Early signatures of ozone trend reversal over the Antarctic |
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10.1002/2014ef000270 |
Data Management & Analytics |
Precipitation & Ecological Systems |
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AbstractWe report on a detailed time series analysis of long total column ozone (TO) records based on multi‐satellite observations of daily resolution. We concentrate on three geographic latitudes over and around the Antarctic area, specifically on three circles at 58.5°S, 59.5°S, and 79.5°S. Almost continuous observations are available at the two former latitudes; however, data are lacking during the polar winter periods at 79.5°S, because the measurement technique requires sunlight. The methodology is motivated by level‐crossing statistics, where subsets of the records above or below particular threshold levels are evaluated. Long‐term trend reversal at around the turn of the century is already detectable for low TO levels in the raw time series in the “ozone‐hole” region (79.5°S). In order to overcome the apparent non‐stationarities of the time series, we determined daily TO differences (ΔTO) belonging to the same geographic longitudes between the different latitudinal circles. The result is a stable, stationary behavior for small (absolute) ΔTO values in the period January–February–March without any significant detectable trends. The high absolute value ΔTO subsets (September–October–November) indicate a robust trend reversal in the middle of the 1990s. The observed trend reversal in the total column ozone time series is consistent with the temporal development of the stratospheric halogen loading. However, a close correspondence of ozone and halogen turnaround years is not expected because of the statistical uncertainties in the determination of the ozone turnaround, and the many factors contributing to ozone depletion processes. |
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| publications-1439 |
PEER REVIEWED ARTICLE |
2016 |
Davide Zanchettin1, Myriam Khodri2, Claudia Timmreck3, Matthew Toohey3,4, Anja Schmidt5, Edwin P. Gerber6, Gabriele Hegerl7, Alan Robock8, Francesco S |
The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): experimental design and forcing input data for CMIP6 |
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10.5194/gmd-9-2701-2016 |
Data Management & Analytics |
Precipitation & Ecological Systems |
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Abstract. The enhancement of the stratospheric aerosol layer by volcanic eruptions induces a complex set of responses causing global and regional climate effects on a broad range of timescales. Uncertainties exist regarding the climatic response to strong volcanic forcing identified in coupled climate simulations that contributed to the fifth phase of the Coupled Model Intercomparison Project (CMIP5). In order to better understand the sources of these model diversities, the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) has defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the CMIP6 protocol. VolMIP provides a common stratospheric aerosol data set for each experiment to minimize differences in the applied volcanic forcing. It defines a set of initial conditions to assess how internal climate variability contributes to determining the response. VolMIP will assess to what extent volcanically forced responses of the coupled ocean–atmosphere system are robustly simulated by state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in the treatment of physical processes. This paper illustrates the design of the idealized volcanic perturbation experiments in the VolMIP protocol and describes the common aerosol forcing input data sets to be used. |
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| publications-1440 |
PEER REVIEWED ARTICLE |
2017 |
Chaitri Roy , Suvarna Fadnavis , Rolf Müller , D. C. Ayantika , Felix Ploeger , Alexandru Rap |
Influence of enhanced Asian NO<sub><i>x</i></sub> emissions on ozone in the upper troposphere and lower stratosphere in chemistry&ndash;climate model simulations |
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10.5194/acp-17-1297-2017 |
Simulation & Modeling |
Uncategorized |
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Abstract. The Asian summer monsoon (ASM) anticyclone is the most pronounced circulation pattern in the upper troposphere and lower stratosphere (UTLS) during northern hemispheric summer. ASM convection plays an important role in efficient vertical transport from the surface to the upper-level anticyclone. In this paper we investigate the potential impact of enhanced anthropogenic nitrogen oxide (NOx) emissions on the distribution of ozone in the UTLS using the fully coupled aerosol–chemistry–climate model, ECHAM5-HAMMOZ. Ozone in the UTLS is influenced both by the convective uplift of ozone precursors and by the uplift of enhanced-NOx-induced tropospheric ozone anomalies. We performed anthropogenic NOx emission sensitivity experiments over India and China. In these simulations, covering the years 2000–2010, anthropogenic NOx emissions have been increased by 38 % over India and by 73 % over China with respect to the emission base year 2000. These emission increases are comparable to the observed linear trends of 3.8 % per year over India and 7.3 % per year over China during the period 2000 to 2010. Enhanced NOx emissions over India by 38 % and China by 73 % increase the ozone radiative forcing in the ASM anticyclone (15–40° N, 60–120° E) by 16.3 and 78.5 mW m−2 respectively. These elevated NOx emissions produce significant warming over the Tibetan Plateau and increase precipitation over India due to a strengthening of the monsoon Hadley circulation. However, increase in NOx emissions over India by 73 % (similar to the observed increase over China) results in large ozone production over the Indo-Gangetic Plain and Tibetan Plateau. The higher ozone concentrations, in turn, induce a reversed monsoon Hadley circulation and negative precipitation anomalies over India. The associated subsidence suppresses vertical transport of NOx and ozone into the ASM anticyclone. |
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