Clifford F. Mass

DOES INCREASING HORIZONTAL RESOLUTION PRODUCE MORE SKILLFUL FORECASTS? The Results of Two Years of Real-Time Numerical Weather Prediction over the Pacific Northwest

This paper examines the impacts of increasing horizontal resolution on the performance of mesoscale numerical weather prediction models. A review of previous studies suggests that decreasing grid spacing to approximately 10 km or less generally produces more realistic mesoscale structures, with particular benefits for orographically and diurnally driven flows. There have been only a few long-term objective verification studies of high-resolution forecasts, and these studies suggest, perhaps deceptively, that there are diminishing returns as horizontal grid spacing decreases below approximately 10 km. A multiyear objective verification of the University of Washington MM5 real-time forecasting system compares the realism of predicted surface parameters at 36-, 12-, and 4-km grid spacing over western Washington state for periods up to 48 h. Traditional verification statistics (such as mean absolute, bias, and root-mean-square error) are calculated by interpolating model forecasts to the observation sites. Fo...

Stratospheric Vacillation Cycles

Abstract A quasi-geostrophic β-plane channel model is used to study wave-mean flow interaction in the stratosphere. The zonal mean circulation in the model is driven by differential radiative heating (parameterized in terms of a “Newtonian cooling”) and by horizontal eddy heat fluxes due to vertically propagating planetary waves excited by steady forcing at the lower boundary. We find that for sufficiently low-amplitude wave forcing the response is a steady stratospheric circulation very close to radiative equilibrium conditions. However, when the wave forcing is raised beyond a critical amplitude (typically of order 150 m) the response is no longer steady; rather, the mean zonal flow and eddy components oscillate quasi-periodically. We conclude that oscillations in stratospheric long waves do not necessarily reflect oscillating tropospheric forcing but may occur even in the presence of steady forcing.

Aspects of Effective Mesoscale, Short-Range Ensemble Forecasting

Abstract This study developed and evaluated a short-range ensemble forecasting (SREF) system with the goal of producing useful, mesoscale forecast probability (FP). Real-time, 0–48-h SREF predictions were produced and analyzed for 129 cases over the Pacific Northwest. Eight analyses from different operational forecast centers were used as initial conditions for running the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5). Model error is a large source of forecast uncertainty and must be accounted for to maximize SREF utility, particularly for mesoscale, sensible weather phenomena. Although inclusion of model diversity improved FP skill (both reliability and resolution) and increased dispersion toward statistical consistency, dispersion remained inadequate. Conversely, systematic model errors (i.e., biases) must be removed from an SREF since they contribute to forecast error but not to forecast uncertainty. A grid-based, 2-week, runnin...

Volcanic dust, sunspots, and temperature trends

The extent to which two often proposed external causes of climatic change, volcanic dust and variations in the solar constant correlated with variable sunspot activity, might account for the general patterns of surface temperature variation since A.D. 1600 are examined. The consequences of a simple climatic model are discussed. 32 references. (BJG)

Initial Results of a Mesoscale Short-Range Ensemble Forecasting System over the Pacific Northwest

Abstract Motivated by the promising results of global-scale ensemble forecasting, a number of groups have attempted mesoscale, short-range ensemble forecasting (SREF), focusing mainly over the eastern half of the United States. To evaluate the performance of mesoscale SREF over the Pacific Northwest and to test the value of using different initial analyses as a means of ensemble forecast generation, a five-member mesoscale SREF system was constructed in which the Pennsylvania State University–National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) was run with initializations and forecast boundary conditions from major operational centers. The ensemble system was evaluated over the Pacific Northwest from January to June 2000. The model verification presented in this study considers only near-surface weather variables, especially the observed 10-m wind direction. The ensemble mean forecast displays lower mean absolute wind direction errors than the component ensemble members when av...

Evaluation of MM5 and Eta-10 Precipitation Forecasts over the Pacific Northwest during the Cool Season

Abstract Precipitation forecasts from the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and NCEP’s 10-km resolution Eta Model (Eta-10) are verified over the Pacific Northwest in order to show the effects of increasing horizontal resolution, the spatial variations in model skill across the region, and the relative differences in performance between the two modeling systems. The MM5 is verified at 36- and 12-km resolution for 9 December 1996 through 30 April 1997 using approximately 150 cooperative observer and National Weather Service precipitation sites across the Pacific Northwest. A noticeable improvement in bias, equitable threat, and root-mean-square (rms) error scores occurs as the horizontal resolution is increased. The spatial distribution of bias and equitable threat scores across Washington and Oregon indicate that the 12-km MM5 generates too much precipitation along the steep windward slopes and not enough precipitation in the lee of major barriers....

MM5 Precipitation Verification over the Pacific Northwest during the 1997–99 Cool Seasons*

Abstract Precipitation forecasts from the Pennsylvania State University–National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) are verified for the 1997–98 and 1998–99 cool seasons over the Pacific Northwest. The MM5 precipitation at 36-, 12-, and 4-km horizontal resolution is compared with over 250 NOAA cooperative observer, snow telemetry (SNOTEL), avalanche, and National Weather Service sites in order to evaluate the effects of increasing horizontal resolution and to document spatial variations in model skill. A noticeable improvement in bias, equitable threat, and root-mean-square (rms) error scores occurs as horizontal resolution is increased from 36- to 12-km resolution; however, going from 12- to 4-km resolution improvements in skill are restricted to the heavy precipitation events (>5.08 cm in 24 h). For light to moderate precipitation events, both the 12- and 4-km domains have significant overprediction over the upper windward slopes of the higher terrain. In contrast, fo...

A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations.

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

Improvement of Microphysical Parameterization through Observational Verification Experiment

Abstract Despite continual increases in numerical model resolution and significant improvements in the forecasting of many meteorological parameters, progress in quantitative precipitation forecasting (QPF) has been slow. This is attributable in part to deficiencies in the bulk microphysical parameterization (BMP) schemes used in mesoscale models to simulate cloud and precipitation processes. These deficiencies have become more apparent as model resolution has increased. To address these problems requires comprehensive data that can be used to isolate errors in QPF due to BMP schemes from those due to other sources. These same data can then be used to evaluate and improve the microphysical processes and hydrometeor fields simulated by BMP schemes. In response to the need for such data, a group of researchers is collaborating on a study titled the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE). IMPROVE has included two field campaigns carried out in th...

Major Volcanic Eruptions and Climate: A Critical Evaluation

Abstract This paper examines whether major volcanic eruptions of the past century have had a significant impact on surface land and ocean temperatures surface pressure and precipitation. Both multieruption composites and individual eruption time series are constructed and analyzed. Included in this work is an attempt to remove one source of interannual variability the El Nino/Southern Oscillation (ENSO). These exercises indicate that only the largest eruptions (in terms of producing a stratospheric dust cloud) are suggested in the climatic record. Removing the ENSO signal in the composite and individual eruption series enhances the apparent volcanic effect of the largest eruptions. No volcanic signal is obvious in pressure and precipitation records.