Seminars - OSTI Modeling
STI had initiated a seminar series to facilitate communication among researchers and model developers. Slides were posted and were available for download before the presentation.
More accuracy with less precision - assessing information content for reliable weather and climate prediction
Tim Palmer, Royal Society Research Professor, University of Oxford presented September 25, 2017
Abstract:
The reasons for stochastic parametrisation are reviewed. From this, we conclude that conventional 64-bit floating-point representations in NWP and climate models are, for the most part, unnecessary and energetically profligate. It is argued that a new start is needed for the development of Earth-System Models, based on the primacy of information content.
The stratiform region of squall lines and its representation in convection-allowing numerical models
George H. Bryan, (NCAR ) presented June 14, 2017
Abstract:
The stratiform region of a squall line is the mesoscale area of relatively low radar reflectivity (20-40 dBZ) that often develops near the more-intense convective region (40-60 dBZ). Real-time numerical models that explicitly represent convection (with grid spacing of ~3 km) often fail to produce stratiform regions. This talk focuses on some microphysical and dynamical processes that can improve the structure of the stratiform region in such models. A key microphysical process is the inclusion of a fast-falling frozen hydrometeor (i.e., hail), which is primarily associated with the high-reflectivity convective region, but allows for the production of slower-falling snow aloft which ultimately forms the stratiform region. Turbulent mixing processes also play a key role, as revealed by high-resolution simulations (with grid spacing ~100 m) that show how air in stratiform regions has a history of mixing between mid-level and boundary-layer air. Identical simulations with relatively coarser resolution (grid spacing ~1 km) show practically no mixing and, consequently, inaccurate humidity profiles. In summary, stratiform regions are produced by a combination of microphysical and dynamical processes, and thus efforts to improve convection-resolving models need to address both processes.
A joint MAPP-NGGPS Webinar as part of the OneNOAA Seminar Series: Sources of Predictability at Subseasonal to Seasonal Time Scales
Frédéric Vitart (European Centre for Medium-Range Weather Forecasts (ECMWF)), Cristiana Stan (George Mason University), Antje Weisheimer (University of Oxford & ECMWF) presented May 24, 2017
Winter forecast skill: teleconnections from the tropics and a case study for winter 2015/16
Adam Scaife (Met Office) presented March 8, 2017
Abstract:
Part 1: Skillful climate predictions of the winter North Atlantic Oscillation and Arctic Oscillation out to a few months ahead have recently been demonstrated, but the source of this predictability remains largely unknown. Here we investigate the role of the tropics in this predictability. We show high levels of skill in tropical rainfall predictions, particularly over the Pacific but also the Indian and Atlantic Ocean. Rainfall fluctuations in these regions are associated with clear signatures in the atmospheric circulation that are approximately symmetric about the equator in boreal winter. We show how these patterns can be explained as steady poleward propagating linear Rossby waves emanating from just a few key source regions and that predicted tropical rainfall explains a significant fraction of the predicted variation of the winter North Atlantic Oscillation.
Part 2: The northern winter of 2015/16 gave rise to the strongest El Niño event since 1997/8. Central and eastern Pacific sea surface temperature anomalies exceeded three degrees and closely resembled the strong El Niño in winter of 1982/3. A second feature of this winter was a strong westerly phase of the Quasi-Biennial Oscillation and very strong winds in the stratospheric polar night jet. At the surface, intense extratropical circulation anomalies occurred in both the North Pacific and North Atlantic that were consistent with known teleconnections to the observed phases of ENSO and the QBO. The North Atlantic Oscillation was very positive in the early winter period (Nov-Dec) but the flow was blocked in late winter. Initialised climate predictions were able to capture these signals at seasonal lead times. This case study adds to the evidence that north Atlantic circulation exhibits predictability on seasonal timescales, and we show that even aspects of the sub-seasonal evolution were predicted in this case.
Sub-seasonal prediction of aerosols fields and impact on meteorology using the ECMWF's coupled Ensemble Prediction System
Angela Benedetti and Fréderic Vitart (ECMWF) presented February 8, 2016
Abstract:
Recent years have seen the rise of global operational atmospheric composition models for several applications including climate monitoring, provision of boundary conditions for regional air quality forecasting, and energy sector applications, to mention a few. Typically global forecasts are provided in the medium-range up to five days ahead. In this work we investigate the feasibility of sub-seasonal to seasonal prediction of aerosols using the ECMWF’s coupled Ensemble Prediction System. The motivation of this study is also to investigate the impact of the aerosol direct effect on meteorological variables such as winds, temperature and precipitation. A comparison between a run with fully prognostic and interactive aerosols and a control run using the current operational set-up will be presented. Aerosol forecast fields at the weekly/monthly scales will also be presented and compared with corresponding analysis to assess their quality.