Blocking and its response to climate change

Purpose of review: Atmospheric blocking events represent some of the most high-impact weather patterns in the mid-latitudes, yet they have often been a cause for concern in future climate projections. There has been low confidence in predicted future changes in blocking, despite relatively good agreement between climate models on a decline in blocking. This is due to the lack of a comprehensive theory of blocking and a pervasive underestimation of blocking occurrence by models. This paper reviews the state of knowledge regarding blocking under climate change, with the aim of providing an overview for those working in related fields. Recent Findings: Several avenues have been identified by which blocking can be improved in numerical models, though a fully reliable simulation remains elusive (at least, beyond a few days lead time). Models are therefore starting to provide some useful information on how blocking and its impacts may change in the future, although deeper understanding of the processes at play will be needed to increase confidence in model projections. There are still major uncertainties regarding the processes most important to the onset, maintenance and decay of blocking and advances in our understanding of atmospheric dynamics, for example in the role of diabatic processes, continue to inform the modelling and prediction efforts. Summary: The term ‘blocking’ covers a diverse array of synoptic patterns, and hence a bewildering range of indices has been developed to identify events. Results are hence not considered fully trustworthy until they have been found using several different methods. Examples of such robust results are the underestimation of blocking by models, and an overall decline in future occurrence, albeit with a complex regional and seasonal variation. In contrast, hemispheric trends in blocking over the recent historical period are not supported by different methods, and natural variability will likely dominate regional variations over the next few decades

Improvement of the runoff in the hydrological model ParFlow by a scale-consistent river parameterization

Improvement of the runoff in the hydrological model ParFlow by ascale-consistent river parameterizationVincent Häfliger (1), Stefan Kollet (2,3), Bernd Schlage (1), and Clemens Simmer (1)(1) Meteorologisches Institut, Bonn Universität, Bonn, Germany, (2) Forschungszentrum Jülich IBG-3, Jülich, Germany , (3)Centre for High-Performance Scientific Computing in Terrestrial Systems, Geoverbund ABC/JThe study focuses on the improvement of the surface-runoff parametrization in the hydrological ParFlow model.Currently, overland flow is calculated everywhere using the kinematic wave approximation (Manning-Stricklerequations). In the implementation, the code does not distinguish between a hillslope and a channel. Thus, rivers andstreams are simulated at the resolution of the computational grid (case A). One solution is to change parameters inthe model in order to better represent a true river routing (case B) : we decided to modify the Manning’s coefficientvalues. The first step was to determine which is the river width value in every surface grid cell of the model, byassuming that the width is linked to the mean annual discharge. In order to compare the flood wave propagationbetween case A and case B, a certain discharge in a virtual grid cell was applied ; the impact on the flow velocityin the two cases was analyzed. We assume a rectangular river channel cross section for which in steady state theManning’s equation is valid. Results show that the flow velocity is higher in case B than in case A, simply becausethe river width is smaller. Assuming this relation between river width and flow velocity, it is possible to calculatehow much scaling of the Manning’s coefficient is necessary in case A, in order to simulate the same flow velocitythan in case B which represents the truth. The conclusion is that it is possible to compensate the error of riverwidths (because of the coarse resolution of the model) by using scaled parameters allowing to improve the surfacemass balance, thanks to a better representation of the flood wave propagation in the river channels

Evidence for a fluctuation theorem in an atmospheric circulation model

An investigation of the distribution of finite time trajectory divergence is performed on an atmospheric global circulation model. The distribution of the largest local Lyapunov exponent shows a significant probability for negative values over time spans up to 10 days. This effect is present for resolutions up to wave numbers l = 42 (approximate to 250 km). The probability for a negative local largest Lyapunov exponent decreases over time, similarly to the predictions of the fluctuation theorem for entropy production. The model used is hydrostatic with variable numbers of vertical levels and different horizontal resolutions

Improved Characterisation of Fluxes Across Compartmental Interfaces of the Terrestrial System

Combining numerical models, which simulate water and energy fluxes in the subsurface-landsurface-atmosphere system in a physically consistent way, becomes increasingly important tounderstand and study processes at compartmental boundaries and interdependencies of statesacross these boundaries. Complete state evolutions generated by such models, when run athighest computationally possible resolutions while incorporating as many processes as attainable,may be regarded as a proxy of the real world, which can be used to test hypotheses onfunctioning of the coupled terrestrial system and may serve as source for virtual measurementsto develop data-assimilation methods. Such simulation systems, however, face severe problemscaused by the vastly different scales of the processes acting in the compartments of the terrestrialsystem. This study is motivated by the development of cross-compartmental data-assimilationmethods, which face the difficulty of data scarcity in the subsurface when applied to real data.With appropriate and realistic measurement operators, the virtual reality not only allows takingvirtual observations in any part of the terrestrial system at any density, thus overcomingdata-scarcity problems of real-world applications, but also provides full information about truestates and parameters aimed to be reconstructed from the measurements by data assimilation.We have used the Terrestrial Systems Modelling Platform TerrSysMP to set up the virtual catchmentfor a regional terrestrial system oriented at the Neckar catchment in southwest Germany.We find that the simulated catchment is in many aspects quite close to reality concerning, e.g.,atmospheric boundary-layer height, precipitation, and runoff. But also discrepancies becomeapparent both in the ability of such models to correctly simulate certain processes and the realismof the results of some observation operators like the SMOS and SMAP sensors. In asucceeding step, we will use this virtual reality to generate observations in all compartments ofthe system for coupled data assimilation. The data assimilation will have to rely on a coarsenedand simplified version of the model system because ensembles with up to 100 members mustbe generated in parallel

Genetically engineered V79 Chinese hamster cells for stable expression of human cytochrome P450IA2.

V79 Chinese hamster cells were genetically engineered for stable expression of human P450IA2. Full length cDNA, encoding human P450IA2, was inserted into an SV40 early promoter containing eukaryotic expression vector and cointroduced with the selection marker neomycin phosphotransferase (conferring resistance to the neomycin derivative G418) into V79 Chinese hamster cells. The recombinant expression vector was introduced into two different V79 sublines, one expressing an endogenous acetyltransferase (V79-NH), the other not (V79-MZ). The presence of human cytochrome CYP1A2 cDNA in the G418 resistant V79 cell clones was confirmed by Southern blotting. The transcription of the cDNA into mRNA was detected by Northern blotting and the translation into an authentic cytochrome P450IA protein was shown by Western blotting. The enzymatic activity in these cells was determined by the cytochrome P450IA2-dependent methoxy-, ethocy-, and pentoxyresooruffa dealkylation activity