The year-long unprecedented European heat and drought of 1540 – a worst case

The heat waves of 2003 in Western Europe and 2010 in Russia, commonly labelled as rare climatic anomalies outside of previous experience, are often taken as harbingers of more frequent extremes in the global warming-influenced future. However, a recent reconstruction of spring–summer temperatures for WE resulted in the likelihood of significantly higher temperatures in 1540. In order to check the plausibility of this result we investigated the severity of the 1540 drought by putting forward the argument of the known soil desiccation-temperature feedback. Based on more than 300 first-hand documentary weather report sources originating from an area of 2 to 3 million km², we show that Europe was affected by an unprecedented 11-month-long Megadrought. The estimated number of precipitation days and precipitation amount for Central and Western Europe in 1540 is significantly lower than the 100-year minima of the instrumental measurement period for spring, summer and autumn. This result is supported by independent documentary evidence about extremely low river flows and Europe-wide wild-, forest- and settlement fires. We found that an event of this severity cannot be simulated by state-of-the-art climate models.     

Fabrics and sequences of submarine carbonate cements in Holocene Bermuda cup reefs

A variety of precipitative synsedimentary CaCO₃ cements lines or fills cavities and surrounds sediment particles within Recent algal cup reefs which dot the rim of the Bermuda platform. These include aragonite needle, spherulitic, and lath cements as well as calcite micrite, palisade, scale, and blocky cements, listed according to respective relative abundances. No distribution pattern of cements is apparent; various combinations of three or four cements are found in almost every sample or thin section. From the occurrence of various cements, factors determining composition and fabric are deduced:

1. Morphology, composition, and coating of the substrate.
2. Direct or indirect influence of organisms such as algae, pelecypods, or crustaceans.
3. Micro-environment, specifically size and permeability, rate of sea-water circulation through the micro-environment, substrates and organisms within the microenvironment.

Various sequences of two or three precipitative cements result from changes in microenvironment; the only cause of such change recognized is the entrance of endolithic algae into partly cemented cavities. This study provides some insight into the origin of submarine cements and a basis for comparative interpretation of cements in fossil marine environments, especially fossil reefs.     

Unexpected waves: Intermediate depth simulations and comparison with observations

In an earlier study, we defined an “unexpected wave” as, for example, a wave twice as high as any of the preceding 30 waves. Here we extend earlier deep water simulations to allow for the greater crest enhancement in water of finite depth and find that the predicted frequency of unexpected waves increases significantly. We also analyze data obtained by wave buoys off the east and west coasts of Canada. In both deep and intermediate depth water, the occurrence of unexpected waves is in reasonable accord with our simulations, supporting our assumption of random superposition of waves though with local crest enhancement by the non-resonant second harmonic.     

V. Morphotektonik und Neogenbuchten in Ost-Bulgarien

Ohne ZusammenfassungAuf der Hauptversammlung der Geologischen Vereinigung in Frankfurt am 5. I. 30 vorgetragen.     

Sliding-no sliding zone effect and age determination of ice cores

At present the age of ice from ice cores taken at depths where the seasonal isotope fluctuations no longer are measurable is estimated from the Dansgaard-Johnsen-Nye analysis of the longitudinal thinning of ice sheets. A significant error occurs in such an age estimate if ice cores are taken from a hole drilled through ice that has flowed from a region of the ice sheet where ice slides over its bed to a region where it cannot slide over its bed. The Camp Century drill hole is in ice which may have had such a flow history. In the zone where sliding ceases to take place, the horizontal ice velocity decreases in magnitude in the lower part of the ice sheet while it increases in the upper part. The average ice velocity remains unchanged in value. As a consequence the upper part of the ice sheet is stretched and the lower part is compressed as ice moves through the sliding-no sliding transition zone. The upper part is stretched to a strain of the order of $\text{1}\text{2}$ and the lower part is compressed to a strain that is of the order of $\text{?}\text{1}\text{2}$. The age of ice from the Dansgaard-Johnsen-Nye analysis is underestimated; the error in the age is of the order of h/a, where h is the ice thickness and a is the accumulation rate. (Larger errors occur if the theory of Johnsen et al. is used to determine the age of the ice.) An error in age of a similar magnitude exists if ice flows from a region in which sliding does not take place into a region in which it does. The Byrd Station drill hole is in ice which probably has such a flow history. In this situation the age of the ice is overestimated. If the annual isotope fluctuations are detectable the sliding-no sliding zone effect will make it appear that a sudden change in the accumulation rate occurred at the time the ice at the upper surface of the ice sheet passed over this zone.     

A three-dimensional study of mesoscale model response to radiative forcing

An infrared radiation parameterization has been applied to a detailed three-dimensional mesoscale model in order to determine whether radiative forcing significantly affects mesoscale atmospheric processes. By taking into account water vapor, liquid water, and carbon dioxide absorption, the scheme differentiates between cloud and clear air regions. The parametric model is presented, along with an overview of the associated mesoscale model.Comparisons between a control run in which only a uniform cooling rate of l K day^–1 is specified, and runs with the infrared scheme are made for 12-hr simulations. The major feature of the radiative forcing is seen to be strong cloud-top cooling. This leads to enhanced destabilization of the upper cloud layer, which in turn results in faster growth of clouds (and which extend to higher levels) than in the control experiment. The deeper clouds force a more vigorous secondary circulation, in which thermodynamic feedbacks between clouds and their environment are substantially stronger than in the case with only a constant cooling rate. This confirms findings made in previous studies undertaken in small-scale numerical models. The discussion also focuses upon a simulation in which the cloud-top infrared cooling has been smoothed out over neighboring vertical levels, in order to represent a cloud-top height distribution crudely. The results indicate that although the absolute values of cloud-top cooling are reduced with respect to the unfiltered case, the fact that cooling extends even higher than previously predicted leads to the formation of thicker, more vigorous clouds. These clouds interact more intensely with their environment than in the unfiltered situation, thereby considerably modifying the mesoscale atmosphere.