Joseph B. Olson

A North American Hourly Assimilation and Model Forecast Cycle: The Rapid Refresh

AbstractThe Rapid Refresh (RAP), an hourly updated assimilation and model forecast system, replaced the Rapid Update Cycle (RUC) as an operational regional analysis and forecast system among the suite of models at the NOAA/National Centers for Environmental Prediction (NCEP) in 2012. The need for an effective hourly updated assimilation and modeling system for the United States for situational awareness and related decision-making has continued to increase for various applications including aviation (and transportation in general), severe weather, and energy. The RAP is distinct from the previous RUC in three primary aspects: a larger geographical domain (covering North America), use of the community-based Advanced Research version of the Weather Research and Forecasting (WRF) Model (ARW) replacing the RUC forecast model, and use of the Gridpoint Statistical Interpolation analysis system (GSI) instead of the RUC three-dimensional variational data assimilation (3DVar). As part of the RAP development, modif...

Multiseason Verification of the MM5. Part I: Comparison with the Eta Model over the Central and Eastern United States and Impact of MM5 Resolution

Abstract This paper describes the multiseason verification of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and the National Centers for Environmental Prediction (NCEP) Eta Model over the eastern two-thirds of the United States and surrounding coastal waters during the cool (1 November–31 March) and warm (1 May–30 September) seasons from the autumn of 1999 through the summer of 2001. Verification statistics are calculated by interpolating model forecasts to the observation sites. The horizontal and vertical distributions of model errors are presented as are the diurnal and intraseasonal trends. During the cool season, both the MM5 and Eta have a low-level cool and moist bias over land, a significant surface warm bias over water, and surface winds that are too strong over land to the east of the Rockies and too weak over water. The low-level cool and moist bias is maximized during the day, and the cool bias is largest during late winter. D...

Multiseason Verification of the MM5. Part II: Evaluation of High-Resolution Precipitation Forecasts over the Northeastern United States

Abstract This paper evaluates the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) precipitation forecasts over the northeastern United States to show the effects of increasing resolution, the spatial variations in model skill, and the impact of convective parameterizations on the MM5 precipitation forecasts. The MM5 is verified during the cool seasons (November–March) of 1999–2001 and the warm season (May–September) of 2000 using approximately 500 cooperative observer and National Weather Service precipitation sites. During the cool season, the 12-km MM5 produces excessive precipitation immediately downwind of the Great Lakes and along the windward slopes of the Appalachians and too little precipitation in the lee of the barrier. The 36-km MM5 has slightly more skill than at 12-km grid spacing for the light to moderate thresholds, while the 12-km precipitation forecasts are slightly better on average for the heavy precipitation events. During t...

Using SAR Remote Sensing, Field Observations, and Models to Better Understand Coastal Flows in the Gulf of Alaska

Abstract The steeply rising coastal terrain of southeast Alaska can produce a wide variety of terrain-induced flows such as barrier jets, gap flows, and downslope wind storms. This study uses a combination of satellite remote sensing, field observations, and modeling to improve our understanding of the dynamics of these flows. After examining several thousand synthetic aperture radar (SAR) high-resolution wind speed images over the Gulf of Alaska, several subclasses of barrier jets were identified that do not fit the current conceptual model of barrier jet development. This conceptual model consists of an acceleration and turning of the ambient cross-barrier flow into the along-barrier direction when the ambient low-level flow is blocked by terrain; however, the SAR imagery showed many barrier jet cases with significant flow variability in the along-coast direction as well as evidence for the influence of cold, dry continental air exiting the gaps in coastal terrain. A subclass of jets has been observed w...

The Wind Forecast Improvement Project (WFIP): A Public–Private Partnership Addressing Wind Energy Forecast Needs

AbstractThe Wind Forecast Improvement Project (WFIP) is a public–private research program, the goal of which is to improve the accuracy of short-term (0–6 h) wind power forecasts for the wind energy industry. WFIP was sponsored by the U.S. Department of Energy (DOE), with partners that included the National Oceanic and Atmospheric Administration (NOAA), private forecasting companies (WindLogics and AWS Truepower), DOE national laboratories, grid operators, and universities. WFIP employed two avenues for improving wind power forecasts: first, through the collection of special observations to be assimilated into forecast models and, second, by upgrading NWP forecast models and ensembles. The new observations were collected during concurrent year-long field campaigns in two high wind energy resource areas of the United States (the upper Great Plains and Texas) and included 12 wind profiling radars, 12 sodars, several lidars and surface flux stations, 184 instrumented tall towers, and over 400 nacelle anemome...

Three-Dimensional Idealized Simulations of Barrier Jets along the Southeast Coast of Alaska

Abstract Three-dimensional idealized simulations using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) down to 6-km grid spacing were performed in order to understand how different ambient conditions (wind speed and direction, stability, and inland cold pool) and terrain characteristics impact barrier jets along the southeastern Alaskan coast. The broad inland terrain of western North America is important in Alaskan jet development, since it rotates the impinging flow cyclonically (more coast parallel) well upstream of the coast, thus favoring more low-level flow blocking while also adding momentum and width to the barrier jet. Near the steep coastal terrain, the largest wind speed enhancement factor (1.9–2.0) in the terrain-parallel direction relative to the ambient onshore-directed wind speed occurs at relatively low Froude numbers (Fr ∼ 0.3–0.4). These low Froude numbers are associated with (10–15 m s−1) ambient wind speeds and wind directions orientated 30°–45° from terra...

A Modified Approach to Initialize an Idealized Extratropical Cyclone within a Mesoscale Model

Abstract A technique for initializing realistic idealized extratropical cyclones for short-term (0–72 h) numerical simulations is described. The approach modifies select methods from two previous studies to provide more control over the initial cyclone structure. Additional features added to the technique include 1) deformation functions to initialize more realistic low-level fronts, tropopause structure, and enhanced jet maximum at upper levels; 2) a barotropic shear function to help develop different cyclone and frontal geometries; and 3) damping functions to create an isolated baroclinic wave in the horizontal; therefore, the initialized cyclone is not influenced by the domain boundaries for relatively short simulations. Since this procedure allows for control of the initialized cyclone structures, it may be useful for studies of frontal and cyclone interaction with topography and mesoscale predictability. The initialization system produces a variety of basic states and synoptic disturbances, ranging f...

A Performance Comparison between Multiphysics and Stochastic Approaches within a North American RAP Ensemble

AbstractA stochastic parameter perturbation (SPP) scheme consisting of spatially and temporally varying perturbations of uncertain parameters in the Grell–Freitas convective scheme and the Mellor–Yamada–Nakanishi–Niino planetary boundary scheme was developed within the Rapid Refresh ensemble system based on the Weather Research and Forecasting Model. Alone the stochastic parameter perturbations generate insufficient spread to be an alternative to the operational configuration that utilizes combinations of multiple parameterization schemes. However, when combined with other stochastic parameterization schemes, such as the stochastic kinetic energy backscatter (SKEB) scheme or the stochastic perturbation of physics tendencies (SPPT) scheme, the stochastic ensemble system has comparable forecast performance. An additional analysis quantifies the added value of combining SPP and SPPT over an ensemble that uses SPPT only, which is generally beneficial, especially for surface variables. The ensemble combining a...

The POWER Experiment: Impact of Assimilation of a Network of Coastal Wind Profiling Radars on Simulating Offshore Winds in and above the Wind Turbine Layer

AbstractDuring the summer of 2004 a network of 11 wind profiling radars (WPRs) was deployed in New England as part of the New England Air Quality Study (NEAQS). Observations from this dataset are used to determine their impact on numerical weather prediction (NWP) model skill at simulating coastal and offshore winds through data-denial experiments. This study is a part of the Position of Offshore Wind Energy Resources (POWER) experiment, a Department of Energy (DOE) sponsored project that uses National Oceanic and Atmospheric Administration (NOAA) models for two 1-week periods to measure the impact of the assimilation of observations from 11 inland WPRs. Model simulations with and without assimilation of the WPR data are compared at the locations of the inland WPRs, as well as against observations from an additional WPR and a high-resolution Doppler lidar (HRDL) located on board the Research Vessel Ronald H. Brown (RHB), which cruised the Gulf of Maine during the NEAQS experiment. Model evaluation in the ...

Assessment of NWP Forecast Models in Simulating Offshore Winds through the Lower Boundary Layer by Measurements from a Ship-Based Scanning Doppler Lidar

AbstractEvaluation of model skill in predicting winds over the ocean was performed by comparing retrospective runs of numerical weather prediction (NWP) forecast models to shipborne Doppler lidar measurements in the Gulf of Maine, a potential region for U.S. coastal wind farm development. Deployed on board the NOAA R/V Ronald H. Brown during a 2004 field campaign, the high-resolution Doppler lidar (HRDL) provided accurate motion-compensated wind measurements from the water surface up through several hundred meters of the marine atmospheric boundary layer (MABL). The quality and resolution of the HRDL data allow detailed analysis of wind flow at heights within the rotor layer of modern wind turbines and data on other critical variables to be obtained, such as wind speed and direction shear, turbulence, low-level jet properties, ramp events, and many other wind-energy-relevant aspects of the flow. This study will focus on the quantitative validation of NWP models’ wind forecasts within the lower MABL by com...