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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 | Year: 2015

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)

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 | Year: 2012

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.

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 | Year: 2010

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).

Done J.M.,NCAR Earth System Laboratory | Holland G.J.,NCAR Earth System Laboratory | Bruyere C.L.,NCAR Earth System Laboratory | Bruyere C.L.,North West University South Africa | And 2 more authors.
Climatic Change | Year: 2015

Although the societal impact of a weather event increases with the rarity of the event, our current ability to assess extreme events and their impacts is limited by not only rarity but also by current model fidelity and a lack of understanding and capacity to model the underlying physical processes. This challenge is driving fresh approaches to assess high-impact weather and climate. Recent lessons learned in modeling high-impact weather and climate are presented using the case of tropical cyclones as an illustrative example. Through examples using the Nested Regional Climate Model to dynamically downscale large-scale climate data the need to treat bias in the driving data is illustrated. Domain size, location, and resolution are also shown to be critical and should be adequate to: include relevant regional climate physical processes; resolve key impact parameters; and accurately simulate the response to changes in external forcing. The notion of sufficient model resolution is introduced together with the added value in combining dynamical and statistical assessments to fill out the parent distribution of high-impact parameters. © 2013, The Author(s).

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 | Year: 2013

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.

Fasullo J.,NCAR Earth System Laboratory
Nature Geoscience | Year: 2013

Understanding the processes that govern the complex spatial structure of rainfall is crucial. Idealized numerical simulations reveal the strong influence that ocean heat transport exerts on this structure. © 2013 Macmillan Publishers Limited. All rights reserved.

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 | Year: 2013

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.

De Arellano J.V.-G.,Wageningen University | Patton E.G.,NCAR Earth System Laboratory | Karl T.,NCAR Earth System Laboratory | Van Den Dries K.,Wageningen University | And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

We investigate diurnal variability of isoprene and related chemical species in the Amazonian region. The dynamics and chemistry of an atmospheric boundary layer are studied with a large-eddy simulation code and a mixed-layer model which are guided by observations available for the same area. The main features of isoprene and related species are reproduced well, but their evolution raises questions regarding the physical and chemical processes responsible for the observed diurnal behaviors. To address these questions, we systematically examine the role of (1) the exchange of chemical species between the free troposphere and the atmospheric boundary layer (entrainment), (2) surface isoprene and nitric oxide emissions, and (3) new chemical pathways to recycle the hydroxyl radical. The entrainment flux of isoprene is shown to be equally important as surface isoprene emissions in determining the isoprene temporal evolution. Varying the relationship between the initial isoprene mixing ratio in the boundary layer and that in the overlying free troposphere in the early morning results in an 50% increase/decrease in isoprene mixing ratio or more within the atmospheric boundary layer at noon. Entrainment of free tropospheric nitrogen oxides creates changes of similar magnitude to the boundary layer isoprene mixing ratio. These effects of entrainment and surface emissions on isoprene are found for two different chemical regimes. The introduction of an OH recycling pathway in the chemical mechanism increases midday OH. Our findings show that atmospheric dynamics and chemistry are equally important for interpreting the diurnal observation of reactants and for including in regional-scale modeling efforts where turbulence is parameterized. Copyright 2011 by the American Geophysical Union.

Powers J.G.,U.S. National Center for Atmospheric Research | Powers J.G.,NCAR Earth System Laboratory | Manning K.W.,U.S. National Center for Atmospheric Research | Bromwich D.H.,Ohio State University | And 2 more authors.
Bulletin of the American Meteorological Society | Year: 2012

AMPS has now been serving Antarctic scientific and logistical needs for over a decade. This mesoscale NWP system currently centers on a real-time implementation of the WRF model optimized for Antarctica. While AMPS was developed with the priority mission of supporting NSF forecasting, over the years it has expanded to a spectrum of applications. These include research, field campaigns, and emergencies. The original goals of the AMPS effort, all now accomplished, were as follows: to provide tailored, real-time model guidance for the USAP Antarctic forecasters; to improve model physics for Antarctic applications; to perform model verification; and to stimulate collaboration among forecasters, modelers, and researchers. The AMPS webpage freely provides products reflecting user input. The development of model polar modifications (e.g., Bromwich et al. 2009) has improved WRF for the worldwide user community. AMPS verification is performed periodically and has been done both via long-term review and case study (see, e.g., Bromwich et al. 2003, 2005; Powers 2007; Nigro et al. 2011b). The creation of the annual Antarctic Meteorological Observation, Modeling, and Forecasting Workshop has yielded a forum for fostering collaborations in Antarctic science and operations. AMPS has also been a context for operational meteorologists to work with the scientific community, fostering the collaboration of research and operations. Last, AMPS's support of Antarctic emergencies (e.g., medevac assistance) and special needs (e.g., research vessels and site planning) has been an unanticipated contribution. AMPS's ability to respond to immediate and changing requests has contributed to the effort exceeding the original goals. © 2012 American Meteorological Society.

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