Meeting Summaries

Abstract

THE NEXT-GENERATION NWP MODELS.The meeting provided a good opportunity for various scientists to describe recent modeling improvements. At the Japan Meteorological Agency (JMA), the improved nonhydrostatic model has led to the better prediction of heavy rainfall in Japan. That was the conclusion of Kazuo Saito of the Meteoro- PROBLEMATIC ISSUES. Problems with physics parameterizations in the models that emerged during the workshop include the following: resolution dependency of each physical process, deterministic versus stochastic approaches, and use of observations.Resolution dependency of physics. Physical parameterization schemes developed at one scale may no longer be valid at smaller scales, because computer power increases and grid sizes decrease. Cumulus schemes are a current example, and PBL schemes may be another in the future. Chun stated that GWDC was needed in mesoscale models as long as the need for a cumulus parameterization scheme was valid. Hong stated that parameterized convection could still be useful even at grid sizes of a few kilometers because it helps initiate mesoscale circulation. Dudhia and Lee stated that 4-km grid spacing could be sufficient for microphysics alone in strongly forced midlatitude convective systems. Even with 5-km grid spacing, a convective parameterization is required to properly simulate convective rains and keep radiation and convection in equilibrium. Based on the CRM results and data assimilation issues in high resolutions, Tao argued that 3 km might be the cutoff for cumulus schemes. Hong stated that PBL and shallow convection might be valid with a coarser resolution than is needed for LES. Work at NCAR has shown that the PBL scheme might still give reasonable results at 50-250-m grid sizes by suppressing resolved eddies, thereby eliminating the problem of double counting. Tao said we should separately decide which schemes to apply at various scales (5, 3 km, etc.), while Chen pointed out the need to develop new schemes that gradually change with scale.Deterministic versus ensemble versus stochastic approaches. Deterministic approaches to modeling imply refinement of parameterizations, addition of complexity, and superparameterization, whereas an ensemble approach can be based on uncertainties in initial conditions or physics schemes. Meanwhile, stochastic approach incorporates randomness, such as Grell's ensemble cumulus approach, the PDF approach, or random number uses. For a given computing resource the choice can be as simple as deciding whether to use high-resolution deterministic or lower-resolution ensemble approaches. A recent convection workshop (Tao et al. 2003) found a need to improve ID schemes, a need for multimoment approaches in these schemes, and considered superparameterization a promising approach. Hong pointed out that ensemble means produce better large-scale patterns (such as 500-hPa height), but deterministic method produces better precipitation, such as heavy rain. Hong stated that a stochastic approach might be able to combine advantages ...

Making the Case for Improved Structural Design: Tornado Outbreaks of 2011

“…The dynamics of the tornado vortex and theoretical models are available in the literature (Bengtsson and Lighthill 1982;Davies-Jones 1986;Lewellen et al 1979), and Lewellen (1993) provided a thorough review of these and other models. Knowledge of tornado interaction with structural systems has been improving in recent years through the efforts of scientists collecting data during the passage of tornadoes (Kosiba and Wurman 2010;Kosiba et al 2008;Lee and Wurman 2005;Kosiba et al 2005) and from related surface observations of winds and forensic investigations of the damage following these events (Karstens et al 2010;Coulbourne 2008;Building Performance Assessment Team 1999;Minor et al 1978;Kikitsu and Sarkar 2010). Although tornado occurrences are most associated with weather conditions in the midwestern United States, they are a global natural hazard occurring on most continents (Chmielewski et al 2011;Bienkiewicz 2008;Budek et al 2006).…”

Regional Thermodynamic Characteristics Distinguishing Long- and Short-Duration Freezing Rain Events over North America

“…One of the greatest challenges forecasters face during the winter is predicting the phase of precipitation (e.g., Ralph et al 2005). Forecasting freezing rain is particularly difficult, as it forms under very similar conditions to ice pellets yet is considerably more hazardous.…”

Evaluation of ABL parametrization schemes in the COSMO, a regional non-hydrostatic atmospheric model over an inhomogeneous environment

“…These processes can be characterized as complex physical and dynamical interactions dominated by turbulent transport and mixing. The turbulent motion responsible for this interaction is generally very small scale and totally sub grid and therefore needs to be parametrized in numerical weather prediction (NWP) models (Deardorff 1972;Troen and Mahrt 1986;Pielke 2002;Teixeira et al 2003;Lee and Hong 2005). The basic role of an ABL parametrization scheme is to provide the coupling with the surface through the determination of turbulent fluxes and their vertical diffusion, to give realistic forecasts of near surface parameters such as temperature, specific humidity and wind and to provide input to the cloud and convection schemes (Pielke 2002;Teixeira et al 2003).…”

“…With the development of highresolution atmospheric models used for the NWP, requirements for accurate ABL parametrization schemes have dramatically increased, making them a key element in the weather and climate predictions, as well as in several other environmental applications, such as pollutant dispersion and biometeorology (Yamartino and Wiegand 1986;Nielsen-Gammon et al 2010;Hu et al 2010). Despite a considerable progress in the prediction of synoptic weather conditions through atmospheric models, the errors and uncertainties associated with the ABL parametrization schemes in the NWP model simulations remain one of the primary sources of inaccuracies, especially for the tropics where small-scale cumulus convection dominate (Basu et al 1998(Basu et al , 1999Lee and Hong 2005;Pleim 2007a, b;Shah et al 2010). One of the major challenges of modelling the ABL processes through parametrization is the prediction of the temporal variation of vertical and horizontal structures in response to the influence of the major processes acting in the atmosphere and at the Earth's surface.…”