Solar Impact on Climate: Modeling the Coupling Between the Middle and the Lower Atmosphere

Solar variability influences the earth's atmosphere on different time scales. In particular, the impact of the 11-year solar cycle is of interest as it provides the major contribution to natural climate variability. Observations show clear 11-year variations in meteorological variables such as temperature or geopotential height from the upper atmosphere down to the troposphere and the earth's surface. In this paper the mechanisms will be discussed which are assumed to be responsible for the downward transfer of the solar signal within the atmosphere. These involve radiative, dynamical and chemical processes which have been studied in detail in model simulations and will be presented here

Baltic Gender Data Management Plan : Version 1

Provides a summary of the Data Management Plan (DMP) addressing FAIR (findable, accessible, interoperable, re-usable) data, allocation of resources, data security and ethical aspect

Understanding and forecasting polar stratospheric variability with statistical models

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

Comparison of Earth rotation excitation in data-constrained and unconstrained atmosphere models

Changes in Earth rotation are strongly related to fluctuations in the angular momentum of the atmosphere, and therefore contain integral information about the atmospheric state. Here we investigate the extent to which observed Earth rotation parameters can be used to evaluate and potentially constrain atmospheric models. This is done by comparing the atmospheric excitation function, computed geophysically from reanalysis data and climate model simulations constrained only by boundary forcings, to the excitation functions inferred from geodetic monitoring data. Model differences are assessed for subseasonal variations, the annual and semiannual cycles, interannual variations, and decadal-scale variations. Observed length-of-day anomalies on the subseasonal timescale are simulated well by the simulations that are constrained by meteorological data only, whereas the annual cycle in length-of-day is simulated well by all models. Interannual length-of-day variations are captured fairly well as long as a model has realistic, time-varying SST boundary conditions and QBO forcing. Observations of polar motion are most clearly relatable to atmospheric dynamics on subseasonal to annual timescales, though angular momentum budget closure is difficult to achieve even for data-constrained atmospheric simulations. Closure of the angular momentum budget on decadal timescales is difficult and strongly dependent on estimates of angular momentum fluctuations due to core-mantle interactions in the solid Earth. Key Points: Earth rotation parameters contain global information about atmospheric dynamics; Length-of-day observations can constrain modeled winds in tropical regions; Polar motion observations can constrain modeled mass movements in midlatitude

Baltic Gender Data Management Plan : Version 2

Provides a summary of the Data Management Plan (DMP) addressing FAIR (findable, accessible, interoperable, re-usable) data, allocation of resources, data security and ethical aspect

Quantifying contributions to the recent temperature variability in the tropical tropopause layer

The recently observed variability in the tropical tropopause layer (TTL), which features a warming of 0.9 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) and the dependence on the vertical resolution in the model. The results show that, in the TTL from 2001 through 2011, 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; stronger QBO westerlies result in a 0.2 K decade-1 warming; increasing aerosols in the lower stratosphere lead to a 0.2 K decade-1 warming; a prolonged solar minimum contributes about 0.2 K decade-1 to a cooling; and increased GHGs have no significant influence. Considering all the factors mentioned above, we compute a net 0.5 K decade-1 warming, which is less than the observed 0.9 K decade-1 warming over the past decade in the TTL. Two simulations with different vertical resolution show that, with higher vertical resolution, an extra 0.8 K decade-1 warming can be simulated through the last decade compared with results from the "standard" low vertical resolution simulation. Model results indicate that the recent warming in the TTL is partly caused by stratospheric aerosols and mainly due to internal variability, i.e. the QBO and tropical SSTs. The vertical resolution can also strongly influence the TTL temperature response in addition to variability in the QBO and SSTs

Tropospheric QBO-ENSO interactions and differences between Atlantic and Pacific

This study investigates the interaction of the Quasi-Biennial Oscillation (QBO) and the El Niño-Southern Oscillation (ENSO) in the troposphere separately for the North Pacific and North Atlantic region. Three 145-year model simulations with NCAR’s Community Earth Sytem Model (CESM-WACCM) are analyzed where only natural and no anthropogenic forcings are considered. These long simulations allow us to obtain statistically reliable results from an exceptional large number of cases for each combination of the QBO (westerly and easterly) and ENSO phases (El Niño and La Niña). Two different analysis methods were applied to investigate where nonlinearity might play a role in QBO-ENSO interactions. The analyses reveal that the stratospheric equatorial QBO anomalies extend down to the troposphere over the North Pacific during Northern hemisphere winter only during La Niña and not during El Niño events. The Aleutian low is deepened during QBO westerly (QBOW) as compared to QBO easterly (QBOE) conditions, and the North Pacific subtropical jet is shifted northward during La Niña. In the North Atlantic, the interaction of QBOW with La Niña conditions (QBOE with El Niño) results in a positive (negative) North Atlantic Oscillation (NAO) pattern. For both regions, nonlinear interactions between the QBO and ENSO might play a role. The results provide potential to enhance the skill of tropospheric seasonal predictions in the North Atlantic and North Pacific region

Der Einfluss des 11-jährigen Sonnenfleckenzyklus und der QBO auf die Atmosphäre - eine Modellstudie = The Influence of the 11-Year Solar Cycle and the QBO on the Atmosphere - a model study

Diese Arbeit zeigt den Einfluss von 11-jährig variierenden solaren UV-Strahlungsänderungen auf die Atmosphäre anhand von Studien mit einem dreidimensionalen Modell der Mittleren Atmosphäre (Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM)). Erstmals kann der Mechanismus für die Übertragung des Sonnensignales von der oberen Stratosphäre bis in die Troposphäre, wie er bisher verstanden und aus Beobachtungen abgeleitet wurde, mit einem Modell nachvollzogen werden. Im FUB-CMAM wurde zuerst die kurzwellige Strahlungsparametrisierung verfeinert, um die stark wellenlängenabhängigen solaren UV-Strahlungsänderungen mit dem 11-jährigen Sonnenfleckenzyklus genauer vorgeben zu können. Die Ergebnisse der Simulationen mit dieser erweiterten Modellversion wurden im Rahmen eines internationalen Modellvergleich-Projektes GRIPS mit den Ergebnissen von vier anderen Klimamodellen verglichen und die Defizite dieser Simulationen untereinander und im Vergleich zu Beobachtungen analysiert. Unter Berücksichtigung dieser Ergebnisse wurden weitere Experimente mit dem FUB-CMAM durchgeführt, in denen systematisch die äquatoriale Windklimatologie verbessert wurde. Die Anpassung der äquatorialen Modellwinde an beobachtete Winde über die gesamte Stratosphäre mit einer quasi zweijährigen Windschwingung (Quasi-Biennial Oscillation) in der unteren und einer halbjährigen Schwingung (Semi-Annual Oscillation) in der oberen Stratosphäre stellte einen entscheidenden Schritt für die erste realistische Repräsentation des beobachteten stratosphärischen Sonnensignales im nordhemisphärischen Winter in einem Modell dar. Die Ergebnisse zeigen, dass das direkte Sonnensignal aus der oberen Stratosphäre über dynamische Wechselwirkungsmechanismen verstärkt und bis in die Troposphäre hinein übertragen wird. Neben einer Erwärmung der mittleren Atmosphäre im Sonnenfleckenmaximum ergeben sich auch Änderungen von Zirkulationsmustern in der Troposphäre. Das Modell ist nicht nur in der Lage das Sonnensignal, sondern auch die beobachtete Wechselwirkung mit den tropischen Windschwingungen in den hohen Breiten zu reproduzieren: Wie in der Realität treten im Modell große Stratosphärenerwärmungen in der Westphase der QBO unter Sonnenfleckenmaximum-Bedingungen auf. Das Verständnis für den Einfluss der Sonnenvariabilität auf das Klima ist für eine genauere Bestimmung der natürlichen Variabilität der Atmosphäre von außerordentlicher Bedeutung. Damit können der anthropogen bedingte Anteil der globalen Erwärmung besser abgeschätzt und künftige Klimaentwicklungen genauer vorhergesagt werden. Die Arbeit zeigt unter anderem, dass die indirekten Zirkulationsänderungen aufgrund von direkten UV-Strahlungsänderungen in der Stratosphäre nicht zu vernachlässigende Größenordnungen erreichen und daher bei zukünftigen Klimaabschätzungen ergänzend zu den anthropogenen Faktoren berücksichtigt werden sollten