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Asrar G.R.,World Climate Research Program | Hurrell J.W.,NCAR Earth System Laboratory | Busalacchi A.J.,The Interdisciplinary Center
Bulletin of the American Meteorological Society

The World Meteorological Organization's (WMO) creation of a global framework for climate services (GFCS) (WMO 2011) demonstrated that the complexity of the information requested for a diverse set of economic sectors and geographic regions around the world was increasing. A better understanding of the behavior of Earth's climate and its interactions with other Earth system components was critical to predict its future evolution, reduce vulnerability to high impact weather and climate events, and sustain life. Progress on the scientific understanding required to skillfully predict future states of the climate system would require an increasingly holistic approach across scientific disciplines. The World Climate Research Program (WCRP) convened its entire research community in a major open science conference (OSC) to advance such challenges. Source

Hodzic A.,NCAR Earth System Laboratory | Jimenez J.L.,University of Colorado at Boulder | Prevot A.S.H.,Paul Scherrer Institute | Szidat S.,University of Bern | And 2 more authors.
Atmospheric Chemistry and Physics

A 3-D chemistry-transport model has been applied to the Mexico City metropolitan area to investigate the origin of elevated levels of non-fossil (NF) carbonaceous aerosols observed in this highly urbanized region. High time resolution measurements of the fine aerosol concentration and composition, and 12 or 24 h integrated 14C measurements of aerosol modern carbon have been performed in and near Mexico City during the March 2006 MILAGRO field experiment. The non-fossil carbon fraction (fNF), which is lower than the measured modern fraction (fM) due to the elevated 14C in the atmosphere caused by nuclear bomb testing, is estimated from the measured fM and the source-dependent information on modern carbon enrichment. The fNF contained in PM1 total carbon analyzed by a US team (fNFTC) ranged from 0.37 to 0.67 at the downtown location, and from 0.50 to 0.86 at the suburban site. Substantially lower values (i.e. 0.24-0.49) were found for PM10 filters downtown by an independent set of measurements (Swiss team), which are inconsistent with the modeled and known differences between the size ranges, suggesting higher than expected uncertainties in the measurement techniques of 14C. An increase in the non-fossil organic carbon (OC) fraction (fNF OC) by 0.10-0.15 was observed for both sets of filters during periods with enhanced wildfire activity in comparison to periods when fires were suppressed by rain, which is consistent with the wildfire impacts estimated with other methods. Model results show that the relatively high fraction of non-fossil carbon found in Mexico City seems to arise from the combination in about equal proportions of regional biogenic SOA, biomass burning POA and SOA, as well as non-fossil urban POA and SOA. Predicted spatial and temporal variations for fNFOC are similar to those in the measurements between the urban vs. suburban sites, and high-fire vs. low-fire periods. The absolute modeled values of fNFOC are consistent with the Swiss dataset but lower than the US dataset. Resolving the 14C measurement discrepancies is necessary for further progress in model evaluation. The model simulations that included secondary organic aerosol (SOA) formation from semi-volatile and intermediate volatility (S/IVOC) vapors showed improved closure for the total OA mass compared to simulations which only included SOA from VOCs, providing a more realistic basis to evaluate the f NF predictions. fNFOC urban sources of modern carbon are important in reducing or removing the difference in fNF between model and measurements, even though they are often neglected on the interpretation of 14C datasets. An underprediction of biomass burning POA by the model during some mornings also explains a part of the model-measurement differences. The fNF of urban POA and SOA precursors is an important parameter that needs to be better constrained by measurements. Performing faster (≤3 h) 14C measurements in future campaigns is critical to further progress in this area. To our knowledge this is the first time that radiocarbon measurements are used together with aerosol mass spectrometer (AMS) organic components to assess the performance of a regional model for organic aerosols. © 2010 Author(s). Source

Prein A.F.,NCAR Earth System Laboratory | Gobiet A.,Zentralanstalt fr Meteorologie und Geodynamik ZAMG | Truhetz H.,University of Graz | Keuler K.,TU Brandenburg | And 10 more authors.
Climate Dynamics

In the framework of the EURO-CORDEX initiative an ensemble of European-wide high-resolution regional climate simulations on a (Formula presented.) grid has been generated. This study investigates whether the fine-gridded regional climate models are found to add value to the simulated mean and extreme daily and sub-daily precipitation compared to their coarser-gridded (Formula presented.) counterparts. Therefore, pairs of fine- and coarse-gridded simulations of eight reanalysis-driven models are compared to fine-gridded observations in the Alps, Germany, Sweden, Norway, France, the Carpathians, and Spain. A clear result is that the (Formula presented.) simulations are found to better reproduce mean and extreme precipitation for almost all regions and seasons, even on the scale of the coarser-gridded simulations (50 km). This is primarily caused by the improved representation of orography in the (Formula presented.) simulations and therefore largest improvements can be found in regions with substantial orographic features. Improvements in reproducing precipitation in the summer season appear also due to the fact that in the fine-gridded simulations the larger scales of convection are captured by the resolved-scale dynamics. The (Formula presented.) simulations reduce biases in large areas of the investigated regions, have an improved representation of spatial precipitation patterns, and precipitation distributions are improved for daily and in particular for 3 hourly precipitation sums in Switzerland. When the evaluation is conducted on the fine (12.5 km) grid, the added value of the (Formula presented.) models becomes even more obvious. © 2015 The Author(s) Source

Done J.M.,University of Reading | Done J.M.,NCAR Earth System Laboratory | Craig G.C.,University of Reading | Craig G.C.,Ludwig Maximilians University of Munich | And 3 more authors.
Quarterly Journal of the Royal Meteorological Society

Successful quantitative precipitation forecasts under convectively unstable conditions depend on the ability of the model to capture the location, timing and intensity of convection. Ensemble forecasts of two mesoscale convective outbreaks over the UK are examined with a view to understanding the nature and extent of their predictability. In addition to a control forecast, twelve ensemble members are run for each case with the same boundary conditions but with perturbations added to the boundary layer. The intention is to introduce perturbations of appropriate magnitude and scale so that the large-scale behaviour of the simulations is not changed. In one case, convection is in statistical equilibrium with the large-scale flow. This places a constraint on the total precipitation, but the location and intensity of individual storms varied. In contrast, the other case was characterised by a large-scale capping inversion. As a result, the location of individual storms was fixed, but their intensities and the total precipitation varied strongly. The ensemble shows case-to-case variability in the nature of predictability of convection in a mesoscale model, and provides additional useful information for quantitative precipitation forecasting. © 2011 Royal Meteorological Society and British Crown Copyright, the Met Office. Source

Hurrell J.W.,NCAR Earth System Laboratory | Holland M.M.,NCAR Earth System Laboratory | Gent P.R.,NCAR Earth System Laboratory | Ghan S.,Pacific Northwest National Laboratory | And 19 more authors.
Bulletin of the American Meteorological Society

The National Center for Atmospheric Research (NCAR) has a proud history of strong collaboration with scientists from universities, national laboratories, and other research organizations to develop, document, improve, and support the scientific use of a comprehensive modeling system that is at the forefront of international efforts to understand and predict the behavior of Earth's climate. Several versions of the CCSM have been used in many hundreds of peer-reviewed studies to better understand climate variability and climate change. In addition, simulations performed with CCSM have made a significant contribution to both national and international assessments of climate, including those of the Intergovernmental Panel on Climate Change (IPCC) and the US Global Change Research Program (USGCRP). The CCSM thus provides the broader academic community with a core modeling system for multiple purposes. Source

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