ALBERT

Description: Petroleum systems located at passive continental margins received increasing attention in the last decade mainly because of deep- and ultra‐deep-water hydrocarbon exploration and production. The high risks associated with these settings originate mainly from the poor understanding of inherent geodynamic processes. The new priority program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution), established by the German Science Foundation in 2009 for a total duration of 6 years, addresses a number of open questions related to continental breakup and post‐breakup evolution of passive continental margins. 27 sub‐projects take advantage of the exceptional conditions of the South Atlantic as a prime “Geo‐archive.” The regional focus is set on the conjugate margins located east of Brazil and Argentina on one side and west of Angola, Namibia and South Africa on the other (Figure 1) as well as on the Walvis Ridge and the present‐day hotspot of Tristan da Cunha. The economic relevance of the program is demonstrated by support from several petroleum companies, but the main goal is research on fundamental processes behind the evolution of passive continental margins.

Description: Volcanic eruptions play a significant role on the global climate of the Earth system and have led to significant ozone loss in mid-latitudes observed after the El Chichon and Mt. Pinatubo eruptions. It is thus important to include the effect of such volcanic eruptions in the climate model simulations of the past if one wants to accurately reconstruct past ozone abundances. We present here analysis of a series of chemistry climate model runs of the 20th century (REF_B1) in the frame of the SPARC Chemistry-Climate Model Validation Activity (CCMVal). Our analysis shows that CCMVal-2 REF-B1 runs show a considerable spread in their simulated response to volcanic eruptions as seen in examination of modeled temperature and ozone. The fact that many fundamentally different methods have been employed to parameterize the direct effect of volcanic aerosols on the radiative transfer of the stratosphere helps explain, at least in part, the wide range of post-eruption temperature anomalies seen in the different models. Total column ozone changes after eruptions are well correlated with changes in lower stratospheric ClO. It thus appears that while most models use a common aerosol SAD data set to drive anomalous post-eruption chemistry, the models display differing degrees of sensitivity to those aerosols, which is likely due to biases in model temperatures and background chemical fields. By examining the models response to volcanic eruptions, we are thus able to qualitatively identify some model deficiencies, as well as test the robustness and consistency of the volcanic parametrization schemes used.

Description: Sudden stratospheric warmings are prominent examples of dynamical wave-mean flow interactions in the Arctic polar stratosphere during Northern Hemisphere winter. They are characterised by a strong increase in temperature and a rapid change of zonal wind in the middle stratosphere on time scales of a few days. Since their discovery in Berlin in 1952 they are well observed but their frequency of occurrence and their prediction remains a difficult task. Observations show a significant dependence of the warming events on various forcings, such as 11-year solar cycle variations, the Quasi-Biennial Oscillation, the El Nino-Southern Oscillation as well as the Northern Annular Mode or the North Atlantic Oscillation. The relatively short length of existing stratospheric observations of about 50 years makes it difficult to statistically isolate the influence of these factors on the frequency of stratospheric warmings. Additionally, non-linear interactions between the forcing factors occur that are difficult to extract with linear time series analysis. In this work we present results from non-linear, multi-dimensional time series analysis. The non-linear contributions of various forcing factors to the occurence of sudden stratospheric warmings are subject of investigation. In particular, the behaviour of temperature and wind data in the polar stratosphere obtained from observation as well as chemistry climate model simulations are studied to obtain a better understanding of frequency and intensity of sudden stratospheric warming events.

Description: We present a set of six 20 year experiments made with a state-of-the-art chemistry-climate model that incorporates the atmosphere from the surface to the lower thermosphere. The response of the middle atmosphere to the 11 year solar cycle, its impact on the troposphere, and especially the role of an externally prescribed stratospheric quasi-biennial oscillation (QBO) is investigated with NCAR's Whole Atmosphere Community Climate Model (WACCM3). The model experiments use either fixed solar cycle inputs or fixed solar cycle together with prescribed QBO phase. The annual mean solar response in temperature and ozone in the upper stratosphere is in qualitative agreement with other modeling and observational studies and does not depend on the presence of the imposed QBO. However, the solar response in the middle to lower stratosphere differs significantly for the two QBO phases. During solar maxima a weaker Brewer-Dobson circulation with relative downwelling, warming, and enhanced ozone occurs in the tropical lower stratosphere during QBO east conditions, while a stronger circulation, cooling, and decreased ozone exists during QBO west conditions. The net ozone increase during QBO east is the combined result of production and advection, whereas during QBO west the effects cancel each other and result in little net ozone changes. Especially during Southern Hemisphere late winter to early spring, the solar response at polar latitudes switches sign between the two QBO phases and qualitatively confirms observations and other recent model studies. During a poleward downward modulation of the polar night jet and a corresponding modulation of the Brewer-Dobson circulation in time, solar signals are detected all the way down to the extratropical troposphere. Possible limitations of the model experiments with respect to the fixed solar cycle conditions or the prescribed QBO phases, as well as the constant sea surface temperatures, are discussed.

Description: Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions, and the mechanisms determining the response of the Earth's climate system. We provide a summary of our current understanding in each of these three areas. Observations and mechanisms for the Sun's variability are described, including solar irradiance variations on both decadal and centennial time scales and their relation to galactic cosmic rays. Corresponding observations of variations of the Earth's climate on associated time scales are described, including variations in ozone, temperatures, winds, clouds, precipitation, and regional modes of variability such as the monsoons and the North Atlantic Oscillation. A discussion of the available solar and climate proxies is provided. Mechanisms proposed to explain these climate observations are described, including the effects of variations in solar irradiance and of charged particles. Finally, the contributions of solar variations to recent observations of global climate change are discussed.

Description: Variation of the global angular momentum of the atmosphere (AAM) results from fluctuations in the massdistribution and large-scale wind patterns of the atmosphere. It has moreoever been known for some time that global-scale natural modes of variability (such as ENSO) have clear footprints in the AAM history. Due to exchange of angular momentum between the atmosphere and the solid earth, fluctuations in AAM are reflected in observations of the Earth Rotation Parameters(ERPs). ERPs therefore provide an observational constraint for global climate models, via the simulated AAM. We are planning to assimilate ERPs into the chemistry-climate model ECHAM5/MESSy, to not only improve the agreement with observations but also to better diagnose model deficiencies. As a step toward developing such an assimilation system, we present a comparison between modeled AAM, and the AAM implied by ERP observations. We also illustrate and discuss the problem of extracting information about individual components of a model state from observations of a global integral quantity. This is done via data assimilation experiments in a highly simplified (Lorenz) dynamical system.