Mimicking the oxygen evolution center Making a synthetic analog of plant photosynthesis is a key goal for exploiting solar energy and replacing fossil fuels. Zhang et al. synthesized a manganese-calcium cluster that looks and acts like the oxygen evolution center in photosystem II (see the Perspective by Sun). The mimic structurally resembles the biological complex, with the notable exception of bridging protein ligands and water-binding sites on a dangling Mn atom. Functionally, however, the cluster's metal center readily undergoes four redox transitions, which contribute to splitting water into oxygen. This and other synthetic mimics will pave the way for developing more efficient catalysts for artificial photosynthesis. Science , this issue p. 690 ; see also p. 635

Abstract:One of the most repeatable phenomena seen in the atmosphere, the quasi-biennial oscillation (QBO) between prevailing eastward and westward wind-jets in the equatorial stratosphere (~16-50 km altitude), was unexpectedly disrupted in February 2016. An unprecedented westward jet formed within the eastward phase in the lower stratosphere and cannot be accounted for by the standard QBO paradigm based on vertical momentum transport. Instead the primary cause was waves transporting momentum from the Northern Hemisphere. Seasonal forecasts did not predict the disruption but analogous QBO disruptions are seen very occasionally in some climate simulations. A return to more typical QBO behavior within the next year is forecast, though the possibility of more frequent occurrences of similar disruptions is projected for a warming climate. One Sentence Summary:In 2016 the usual quasi-periodic equatorial oscillation in the stratosphere between eastward and westward winds unexpectedly breaks down around 25 km altitude. Main Text:Aside from those variations governed by the changing seasons or diurnal cycle, the quasibiennial oscillation (QBO) is arguably the most repeatable mode of natural variability seen anywhere in the atmosphere. It was first discovered in the late 1950s (1, 2) and features alternating eastward and westward wind-jets descending through the equatorial stratosphere, at roughly 1 km per month (3), from ~50 km (~1 hPa) down to ~16km (~100 hPa), with the quasibiennial periodicity being most evident in the ~20-40 km layer. Since the 1950s the period of the oscillation has varied between 22 to 36 months. The oscillation is nearly zonally uniform and so is seen in both local observations and in longitudinally averaged data with roughly the same amplitude, at least for monthly means, and is confined to equatorial latitudes (4, 5). On the other hand its influence is felt throughout the atmosphere. For example, the fate of ash and sulfur from large volcanic eruptions in the tropics is affected by the QBO (6) and there are known surface weather and climate impacts resulting from the QBO's extra-tropical teleconnections (7-9); such

A modified Tiedtke cumulus parameterization (CP) scheme has been implemented into the Advanced Research Weather Research and Forecasting model (ARW-WRF) to improve the representation of marine boundary layer (MBL) clouds over the southeast Pacific (SEP). A full month simulation for October 2006 was performed by using the National Centers for Environmental Prediction (NCEP) final analysis (FNL) as both the initial and lateral boundary conditions and the observed sea surface temperature (SST). The model simulation was compared with satellite observations and with results from an intense ship-based campaign of balloon soundings during 16-20 October 2006 at 208S, 858W.The model with the modified Tiedtke scheme successfully captured the main features of the MBL structure and low clouds over the SEP, including the geographical distribution of MBL clouds, the cloud regime transition, and the vertical structure of the MBL. The model simulation was repeated with the various CP schemes currently provided as standard options in ARW-WRF. The simulations with other CP schemes failed to reproduce the geographical distribution of cloud fraction and the observed cloud regime transition, and displayed an MBL too shallow compared to observations. The improved simulation with the modified Tiedtke scheme can be attributed to a more active parameterized shallow convection with the modified Tiedtke scheme than with the other CP schemes tested, which played a critical role in lifting the inversion base and the low cloud layer. Results from additional sensitivity experiments employing different planetary boundary layer (PBL) parameterization schemes demonstrated that the basic feature of the MBL structure and low clouds over the SEP were not particularly sensitive to the choice of the PBL scheme.