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Springtime stratospheric final warming (SFW) variability has been suggested to be linked to the tropospheric circulation, particularly over the North Atlantic sector. These findings, however, are based on reanalysis data that cover a rather short period of time (1979 to present). The present work aims to improve the understanding of drivers, trends and surface impact of dynamical variability of boreal SFWs using chemistry‐climate models. We use multidecadal integrations of the fully coupled chemistry‐climate models Community Earth System Model version 1 (Whole Atmosphere Community Climate Model) and ECHAM/Modular Earth Submodel System Atmospheric Chemistry‐O. Four sensitivity experiments are analyzed to assess the impact of external factors; namely, the quasi‐biennial oscillation, sea surface temperature (SST) variability, and anthropogenic emissions. SFWs are classified into two types with respect to their vertical development; that is, events which occur first in the midstratosphere (10‐hPa first SFWs) or first in the upper stratosphere (1‐hPa first SFWs). Our results confirm previous reanalysis results regarding the differences in the time evolution of stratospheric conditions and near‐surface circulation between 10 and 1‐hPa first SFWs. Additionally, a tripolar SST pattern is, for the first time, identified over the North Atlantic in spring months related to the SFW variability. Our analysis of the influence of remote modulators on SFWs revealed that the occurrence of major warmings in the previous winter favors the occurrence of 10‐hPa first SFWs later on. We further found that quasi‐biennial oscillation and SST variability significantly affect the ratio between 1‐hPa first and 10‐hPa first SFWs. Finally, our results suggest that ozone recovery may impact the timing of the occurrence of 1‐hPa first SFWs. Key Points: Northern Hemisphere stratospheric final warmings variability and dynamics are studied in multidecadal chemistry‐climate experimentsStratospheric final warmings characteristics in spring are influenced by the polar vortex variability in preceding winterQuasi‐biennial oscillation, sea surface temperature, and ozone depleting substances influence stratospheric final warming variability [ABSTRACT FROM AUTHOR]

The surface response to the 11 year solar cycle is assessed in ensemble simulations of the twentieth century climate performed in the framework of the fifth phase of the Coupled Model Inter-Comparison Project (CMIP5). A lead/lag multiple linear regression analysis identifies a multi-model mean (MMM) global mean surface warming of about 0.07K, lagging the solar cycle by 1-2 years on average. The anomalous warming penetrates to approximately the first 80-100m depth in the ocean. Solar signals in the troposphere show a similar time lag of 1-2 years and the strongest MMM warming is simulated in the Tropics above 300 hPa. At the surface, the MMM response in a subset of models that show statistically significant global mean warming (CMIP5-SIG95) is characterized by an anomalous warming in the west equatorial Pacific Ocean and the Arctic, at 1-2 years after solar maximum. The Arctic warming is twice as strong as the global mean response and appears in the winter months only. The surface warming in the equatorial Pacific Ocean is related to dynamical/thermodynamical processes. Different increase rates of global mean precipitation and atmospheric water vapour in response to a warmer surface lead to a weakerWalker circulation and anomalous westerly winds over the equatorial Pacific in the years following the solar maximum. Owing to atmosphere--ocean coupling, the anomalous westerly winds cool the subsurface and warm the surface in the western equatorial Pacific by ~0.14 K. The CMIP5-SIG95 MMM surface warming in the equatorial Pacific and Arctic is weak but qualitatively similar compared with solar signals in the HadCRUT4 dataset. [ABSTRACT FROM AUTHOR]

A multiple linear regression statistical method is applied to model data taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5) to estimate the 11-year solar cycle responses of stratospheric ozone, temperature, and zonal wind during the 1979-2005 period. The analysis is limited to the six CMIP-5 models which resolve the stratosphere (high-top models) and which include interactive ozone chemistry. All simulations assumed a conservative 11-year solar spectral irradiance (SSI) variation based on the Naval Research Laboratory model. These model responses are then compared to corresponding observational estimates derived from two independent satellite ozone profile datasets and from ERA-Interim reanalysis meteorological data. The models exhibit a range of 11-year responses with three models (CESM1-WACCM, MIROC-ESM-CHEM and MRI-ESM1) yielding substantial solar-induced ozone changes in the upper stratosphere which compare favourably with available observations. The remaining three models do not, apparently because of differences in the details of their radiation and photolysis rate codes. During winter in both hemispheres, the three models with stronger upper-stratospheric ozone responses produce relatively strong latitudinal gradients of ozone and temperature in the upper stratosphere which are associated with accelerations of the polar night jet under solar maximum conditions. This behaviour is similar to that found in the satellite ozone and ERA-Interim data, except that the latitudinal gradients tend to occur at somewhat higher latitudes in the models. The sharp ozone gradients are dynamical in origin and assist in radiatively enhancing the temperature gradients, leading to a stronger zonal wind response. These results suggest that simulation of a realistic solar-induced variation of upper-stratospheric ozone, temperature and zonal wind in winter is possible for at least some coupled climate models even if a conservative SSI variation is adopted. [ABSTRACT FROM AUTHOR]

The 11 year solar-cycle component of climate variability is assessed in historical simulations of models taken from the Coupled Model Intercomparison Project, phase 5 (CMIP-5). Multiple linear regression is applied to estimate the zonal temperature, wind and annular mode responses to a typical solar cycle, with a focus on both the stratosphere and the stratospheric influence on the surface over the period ~1850-2005. The analysis is performed on all CMIP-5 models but focuses on the 13 CMIP-5 models that resolve the stratosphere (high-top models) and compares the simulated solar cycle signature with reanalysis data. The 11 year solar cycle component of climate variability is found to be weaker in terms of magnitude and latitudinal gradient around the stratopause in the models than in the reanalysis. The peak in temperature in the lower equatorial stratosphere (~70 hPa) reported in some studies is found in the models to depend on the length of the analysis period, with the last 30 years yielding the strongest response. A modification of the Polar Jet Oscillation (PJO) in response to the 11 year solar cycle is not robust across all models, but is more apparent in models with high spectral resolution in the short-wave region. The PJO evolution is slower in these models, leading to a stronger response during February, whereas observations indicate it to be weaker. In early winter, the magnitude of the modelled response is more consistent with observations when only data from 1979-2005 are considered. The observed North Pacific high-pressure surface response during the solar maximum is only simulated in some models, for which there are no distinguishing model characteristics. The lagged North Atlantic surface response is reproduced in both high- and low-top models, but is more prevalent in the former. In both cases, the magnitude of the response is generally lower than in observations. [ABSTRACT FROM AUTHOR]

The recently observed variability in the tropical tropopause layer, which features an unexpected warming of 1.1 K over the past decade (2001-2011), is investigated with a number of sensitivity experiments from simulations with NCAR's CESM-WACCM chemistry climate model. The experiments have been designed to specifically quantify the contributions from natural as well as anthropogenic factors, such as solar variability (Solar), sea surface temperatures (SSTs), the Quasi-Biennial Oscillation (QBO), stratospheric aerosols (Aerosol), greenhouse gases (GHGs), as well as the dependence on the vertical resolution in the model. The results show that, in the TTL: a cooling in tropical SSTs leads to a weakening of tropical upwelling around the tropical tropopause and hence relative downwelling and adiabatic warming of 0.3 K decade-1; an increased QBO amplitude results in a 0.3 K decade-1 warming; increasing aerosols in the lower stratosphere lead to a 0.4 K decade-1 warming; a prolonged solar minimum and increased GHGs contribute about 0.2 and 0.1 K decade-1 to a cooling, respectively. Two simulations with different vertical resolution show that the vertical resolution can strongly influence the response of the TTL temperature to changes such as SSTs. With higher vertical resolution, an extra 0.6 K decade-1 warming can be simulated through the last decade, compared with results from the "standard" low vertical resolution simulation. Considering all the factors mentioned above, we compute a net 1.3 K decade-1 warming, which is in very good agreement with the observed 1.1 K decade-1 warming over the past decade in the TTL. The model results indicate that the recent warming in the TTL is mainly due to internal variability, i.e. the QBO and tropical SSTs. [ABSTRACT FROM AUTHOR]

The lack of long and reliable time series of solar spectral irradiance (SSI) measurements makes an accurate quantification of solar contributions to recent climate change difficult. Whereas earlier SSI observations and models provided a qualitatively consistent picture of the SSI variability, recent measurements by the SORCE (SOlar Radiation and Climate Experiment) satellite suggest a significantly stronger variability in the ultraviolet (UV) spectral range and changes in the visible and near-infrared (NIR) bands in anti-phase with the solar cycle. A number of recent chemistry-climate model (CCM) simulations have shown that this might have significant implications on the Earth's atmosphere. Motivated by these results, we summarize here our current knowledge of SSI variability and its impact on Earth's climate. We present a detailed overview of existing SSI measurements and provide thorough comparison of models available to date. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. We investigate these direct and indirect effects using several stateof- the art CCM simulations forced with measured and modelled SSI changes. A unique asset of this study is the use of a common comprehensive approach for an issue that is usually addressed separately by different communities. We show that the SORCE measurements are difficult to reconcile with earlier observations and with SSI models. Of the five SSI models discussed here, specifically NRLSSI (Naval Research Laboratory Solar Spectral Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar Radiation Physical Modelling), and OAR (Osservatorio Astronomico di Roma), only one shows a behaviour of the UV and visible irradiance qualitatively resembling that of the recent SORCE measurements. However, the integral of the SSI computed with this model over the entire spectral range does not reproduce the measured cyclical changes of the total solar irradiance, which is an essential requisite for realistic evaluations of solar effects on the Earth's climate in CCMs. We show that within the range provided by the recent SSI observations and semi-empirical models discussed here, the NRLSSI model and SORCE observations represent the lower and upper limits in the magnitude of the SSI solar cycle variation. The results of the CCM simulations, forced with the SSI solar cycle variations estimated from the NRLSSI model and from SORCE measurements, show that the direct solar response in the stratosphere is larger for the SORCE than for the NRLSSI data. Correspondingly, larger UV forcing also leads to a larger surface response. Finally, we discuss the reliability of the available data and we propose additional coordinated work, first to build composite SSI data sets out of scattered observations and to refine current SSI models, and second, to run coordinated CCM experiments. [ABSTRACT FROM AUTHOR]

During periods of high solar activity, the Earth receives ≈0.1% higher total solar irradiance (TSI) than during low activity periods. Variations of the solar spectral irradiance (SSI) however, can be larger, with relative changes of 1 to 20% observed in the ultraviolet (UV) band, and in excess of 100% in the soft X-ray range. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. Lack of long and reliable time series of SSI measurements makes the accurate quantification of solar contributions to recent climate change difficult. In particular, the most recent SSI measurements show a larger variability in the UV spectral range and anomalous changes in the visible and near-infrared (NIR) bands with respect to those from earlier observations and from models. A number of recent studies based on chemistry-climate model (CCM) simulations discuss the effects and implications of these new SSI measurements on the Earth's atmosphere, which may depart from current expectations. This paper summarises our current knowledge of SSI variability and its impact on Earth's climate. An interdisciplinary analysis of the topic is given. New comparisons and discussions are presented on the SSI measurements and models available to date, and on the response of the Earth's atmosphere and climate to SSI changes in CCM simulations. In particular, the solar induced differences in atmospheric radiative heating, temperature, ozone, mean zonal winds, and surface signals are investigated in recent simulations using atmospheric models forced with the current lower and upper boundaries of SSI solar cycle estimated variations from the NRLSSI model data and from SORCE/SIM measurements, respectively. Additionally, the reliability of available data is discussed and additional coordinated CCM experiments are proposed. [ABSTRACT FROM AUTHOR]

The variability of the north-polar stratospheric vortex is a prominent aspect of the middle atmosphere. This work investigates a wide class of statistical models with respect to their ability to model geopotential and temperature anomalies, representing variability in the polar stratosphere. Four partly nonstationary, nonlinear models are assessed: linear discriminant analysis (LDA); a cluster method based on finite elements (FEM-VARX); a neural network, namely the multi-layer perceptron (MLP); and support vector regression (SVR). These methods model time series by incorporating all significant external factors simultaneously, including ENSO, QBO, the solar cycle, volcanoes, to then quantify their statistical importance. We show that variability in reanalysis data from 1980 to 2005 is successfully modeled. The period from 2005 to 2011 can be hindcasted to a certain extent, where MLP performs significantly better than the remaining models. However, variability remains that cannot be statistically hindcasted within the current framework, such as the unexpected major warming in January 2009. Finally, the statistical model with the best generalization performance is used to predict a winter 2011/12 with warm and weak vortex conditions. A vortex breakdown is predicted for late January, early February 2012. [ABSTRACT FROM AUTHOR]

The variability of the north-polar stratospheric vortex is a prominent aspect of the middle atmosphere. This work investigates a wide class of statistical models with respect to their ability to model geopotential and temperature anomalies, representing variability n the polar stratosphere. Four partly nonstationary, nonlinear models are assessed: inear discriminant analysis (LDA); a cluster method based on finite elements (FEM-VARX); a neural network, namely a multi-layer perceptron (MLP); and support vector regression (SVR). These methods model time series by incorporating all significant external factors simultaneously, including ENSO, QBO, the solar cycle, volcanoes, etc., to then quantify their statistical importance. We show that variability in reanalysis data from 1980 to 2005 is successfully modeled. FEM-VARX and MLP even satisfactorily forecast the period from 2005 to 2011. However, internal variability remains that cannot be statistically forecasted, such as the unexpected major warming in January 2009. Finally, the statistical model with the best generalization performance is used to predict a vortex breakdown in late January, early February 2012. [ABSTRACT FROM AUTHOR]

Objective: In this study we aimed to assess the image quality and degree of vascular enhancement using low-concentration contrast media (LCCM) (300 mg I ml-1) and high-concentration contrast media (HCCM) (370 mg I ml-1) on 64-slice multidetector row CT (MDCI) abdominal CT angiography (CTA). In addition, we aimed to study the feasibility of using HCCM with a reduced total iodine dose. Methods: CTA of the abdomen on a 64-slice MDCT was performed on 15 anaesthetised pigs. Study pigs were divided into three groups of five each based on the iodine concentration and dose received: Group A (LCCM; 300 mg I ml-1), Group B (HCCM; 370 mg I ml-1) and Group C HCCM with 20% less iodine dose. The total iodine injected was kept constant (600 mg kg-1) in Groups A and B. Qualitative and quantitative analyses were performed to study and compare each group for image quality, visibility of the branch order of the superior mesenteric artery (SMA), artefacts, degree of enhancement in the aorta and main stem arteries and uniformity of enhancement in the aorta. Groups were compared using the analysis of variance test. Results: The image quality of 64-slice MDCT angiography was excellent with a mean score of 4.63 and confident visualisation of the third to fifth order branches of the SMA in all groups. Group B demonstrated superior vascular enhancement, as compared with Groups A and C (p≤0.05). Uniform aortic enhancement was achieved with the use of LCCM and HCCM with 20% less iodine dose. Conclusion: 64-slice MDCT angiography of the abdomen was of excellent quality. HCCM improves contrast enhancement and overall CTA image quality and allows the iodine dose to be, reduced. [ABSTRACT FROM AUTHOR]

We introduce the improved Freie Universität Berlin (FUB) high-resolution radiation scheme FUBRad and compare it to the 4-band standard ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. A reduction of the spectral resolution to 6 bands for solar irradiance and ozone absorption cross sections leads to a degradation (reduction) of the solar SW heating rate signal by about 20%. The simulated temperature response agrees qualitatively well with observations in the summer upper stratosphere and mesosphere where irradiance variations dominate the signal. Comparison of the total short-wave heating rates under solar minimum conditions shows good agreement between FUBRad, FB and libRadtran up to the middle mesosphere (60-70 km) indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account. The FUBRad scheme has been implemented as a subsubmodel of the Modular Earth Submodel System (MESSy). [ABSTRACT FROM AUTHOR]

It is shown that a high-resolution short-wave (SW) heating rate parameterization is necessary to simulate solar cycle variations in atmospheric models. The improved Freie Universität Berlin (FUB) high-resolution radiation scheme (FUBRad) is introduced and compared to the 4-band ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle and a temperature response that is in good agreement with observations. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. Comparison of the total short-wave heating rates under moderate solar conditions shows good agreement between FUBRad, FB and libRadtran up to 80km indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account. The FUBRad scheme has been implemented as a sub-submodel of the Modular Earth Submodel System (MESSy). [ABSTRACT FROM AUTHOR]

Because of its chemical and radiative properties, atmospheric ozone constitutes a key element of the Earth’s climate system. Absorption of sunlight by ozone in the ultraviolet wavelength range is responsible for stratospheric heating, and determines the temperature structure of the middle atmosphere. Changes in middle atmospheric ozone concentrations result in an altered radiative input to the troposphere and to the Earth’s surface, with implications on the energy balance and the chemical composition of the lower atmosphere. Although a wide range of ground- and satellite-based measurements of its integrated content and of its vertical distribution have been performed since several decades, a number of uncertainties still remain as to the response of middle atmospheric ozone to changes in solar irradiance over decadal time scales. This paper presents an overview of achieved findings, including a discussion of commonly applied data analysis methods and of their implication for the obtained results. We suggest that because it does not imply least-squares fitting of prescribed periodic or proxy data functions into the considered times series, time-domain analysis provides a more reliable method than multiple regression analysis for extracting decadal-scale signals from observational ozone datasets. Applied to decadal ground-based observations, time-domain analysis indicates an average middle atmospheric ozone increase of the order of 2% from solar minimum to solar maximum, which is in reasonable agreement with model results. [ABSTRACT FROM AUTHOR]

The understanding of natural and anthropogenic climatic change is an important issue in recent studies. The influence of the Sun (11-year solar cycle) as a natural variability factor on the atmosphere is discussed. Statistical studies with observational data (NCEP/NCAR re-analyses) covering four solar cycles show high correlations between the 11-year solar signal and meteorological parameters, e.g., the geopotential heights and temperatures, in the lower stratosphere and troposphere. Studies with general circulation models (GCM) have discussed the possibility of an indirect dynamical response to direct changes in solar irradiance and ozone in the stratosphere. A physical mechanism explaining the solar influence on the atmosphere is still missing. Part of the mechanism understood so far and ideas from model and observational studies are presented. [ABSTRACT FROM AUTHOR]

Proves that a large class of equilibria of branching particle systems obey a one-zero law on the sigma-algebra of remote events, or spatial tail fields, provided only that the mean nth generation offspring numbers of single particles are uniformly bounded. Examples and formulation of the result; Proof of the theorem.

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Copyright of Klinische Wochenschrift is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)