K. Oceanic Weather [Background] [Survey
of Issues and Techniques] 1. Background Beginning in 2001 and continuing into 2002, RAP began a new program of applied research and product development that addresses an international need for better nowcasts and forecasts of flight conditions and weather-related aviation hazards in data-sparse oceanic regions. The program is sponsored by the FAA Aviation Weather Research Program, and is motivated by recognition that the weather information that supports air traffic managers, pilots and dispatchers along oceanic routes is generally less informative and less timely than that typically available for continental routes. This forecast information gap is largely due to the lack of surface, rawinsonde, radar and other observational data over the remote oceans. This lack of information critically limits analyses of current weather and forecast model data assimilation in these regions. Of course, limitations in the spatial and temporal resolution and physics of global forecast models (covering oceanic regions) vs. regional forecast models (covering continental regions) also play a significant role in the information gap, as do other factors. Key factors that degrade the timeliness of weather information for oceanic regions include limited frequency of global forecast model runs (currently four per day for the NOAA/NCEP AVN global aviation model), and limited means to receive in-flight weather information updates in current transport aircraft. Development and testing of new approaches to the nowcasting and forecasting of aviation-critical weather conditions in oceanic regions is the responsibility of the Oceanic Weather Product Development Team (OWPDT), composed of scientists and engineers from RAP, the Naval Research Laboratory at Monterey (NRL), MIT Lincoln Laboratory (MIT/LL), and the NOAA Aviation Weather Center (AWC). RAP's T. Lindholm is the overall lead for the team effort, while P. Herzegh serves as scientific lead. The OWPDT will address development of improved wind field information and the diagnosis and nowcasting of aviation-critical phenomena such as convection, flight-level turbulence, volcanic ash, and in-flight airframe icing. Verification of the performance of the resulting weather information products will be an integral part of the development process. As work progresses, the team will collaborate closely with communications and weather information services to help conceive and support methodologies for operational dissemination of oceanic weather products to pilots, dispatchers, controllers and other end users in industry and government. Further project information, including the current Seven-Year Scientific Plan and real-time weather displays, is maintained on the OWPDT website (see Figure 1 below).
Figure 1. OWPDT website: http://www.rap.ucar.edu/projects/owpdt/
2. Survey of Issues and Techniques The OWPDT continued to survey existing information, products, analysis techniques, and emerging technologies to support: (1) the formulation of working priorities; (2) strategies for research and product development; and (3) identification of other groups and individuals whose collaboration can advance our objectives. Established strategies will be continually updated and revised as appropriate. The oceanic weather team maintains a close liaison with end-user groups to establish and refine priorities for weather product development and geographic coverage. Primary contacts include pilots, weather analysts, and dispatchers associated with commercial transport airlines; air traffic controllers; and working committees sponsored by government and professional aviation organizations. Results to date have underscored the importance of diagnosing and forecasting convective hazards and turbulence (all types) on upper-level flight routes. Aircraft icing, while not a significant problem at typical en route flight levels, can be a critical factor affecting extended twin-engine operations at lower altitudes. The North Pacific and Gulf of Mexico regions emerge as the current top priorities to receive early implementation of oceanic weather products. The North Atlantic region will soon follow, driven by the results of hazard climatology studies that indicate a high occurrence of moderate or greater clear air turbulence encounters by commercial airliners. J. Hawkins (NRL), T. Tsui (NRL), and Herzegh and are working on improving wind information available both for general flight planning and as input to support the diagnosis of convection and turbulence. The current development strategy is being led by Hawkins and will utilize satellite winds derived from the tracking of upper-level features evident in the IR imagery of water vapor provided by geostationary weather satellites and the lower-level cloud images evident in visible imagery. T. Lindholm, P. Herzegh, R. Sharman, and F. Mosher (AWC) continued to study the aviation threat posed by volcanic ash emissions and identified strategies to improve the current infrastructure for detecting, forecasting, and communicating expected ash dispersion along oceanic flight routes. Results suggest that improved detection, dispersion calculation techniques, and dissemination infrastructure are matters of high priority to aviation operators, particularly in the Pacific Rim and Central America regions. International partnerships with Volcanic Ash Advisory Centers are being fostered which in turn will assist the team in formulating a long-term strategy to address the problem. 3. Continuing Steps Toward a Convective Nowcast Product Significant progress was made toward refining the cloud top height depiction, considered by the OWPDT as the first step of developing a true convective diagnosis and nowcasting capability. This product is the first to be linked onto the OWPDT web site for three oceanic regions-North Pacific, South/Central Pacific, and the Gulf of Mexico. Collaboration between NRL and NCAR resulted in the development and implementation of an algorithm that maps infrared cloud top temperature to aircraft flight level and corrects for non-standard atmospheric conditions. Global atmospheric model sounding data are used as the basis for the correction. Errors without this correction were shown to be as much as 8,000 ft. Airline flight crews, dispatch, and air traffic management continue to provide positive usability feedback to the OWPDT. RAP OWPDT has made good progress on an expert system that diagnoses convection, the next step in the convective hazard product development. C. Kessinger will be running a prototype expert system framework in the laboratory early in FY03. G. Blackburn continued to reformat, ingest, and archive global atmospheric data sets to support further expert system development. The team plans to integrate global lightning data as the first data element in the expert system. RAP and NRL continued to collaborate on development and coding of a cloud classification scheme, which will become the first diagnostic element. In summary, the NRL cloud classification system uses a growing set of expert-classified images (on the order of 5000-6000) as a training data set for automated code which processes GOES data and classifies cloud imagery into one of fifteen daytime cloud classes (Figure 2). Meanwhile, NRL continued to enhance global spot wind diagnostics that use water vapor and infrared satellite imagery, which will be used as a means to advect convection for an initial convective nowcasting capability. All of these experimental products are or will shortly be running in the laboratory for evaluation and initial verification purposes.
4. Initial Steps Toward an Integrated Oceanic Turbulence Product Research addressing the high altitude turbulence hazard for remote regions focused on two areas. First, to enhance our understanding of the hazard from a meteorological point of view, the team is studying a large historical data base of pilot reports over areas of the globe with dense air traffic, as well as well-documented accident reports. Preliminary results of ongoing work to define a climatology of moderate or greater (MOG) turbulence as reported by pilots along routes across the North Atlantic and North Pacific indicate the rate of occurrence in the North Atlantic to be considerably higher than for over the North Pacific (after normalizing MOG report volume by the total number of reports received). Fall/winter occurrence (Oct-Mar) is significantly greater than spring/summer (Apr-Sep) occurrence. Further, in the North Atlantic, eastbound flights show higher rates of MOG turbulence than westbound flights. The east/west difference is unexplained, but early ideas involve possible differences in the east vs. west flight tracks established to take advantage of (or avoid, for westbound flights) the jet stream. The climatology of the region suggests that clear air turbulence is the hazard of interest. Additional studies addressed the convective-induced turbulence hazard potential in the Gulf of Mexico and South/Central Pacific. Using flight data from a severe turbulence encounter over the CONUS, detailed simulations dramatically showed the potential effect of environmental conditions on the generation, propagation, and breaking of gravity waves induced by thunderstorms. Figure 3 below shows potential temperature perturbations induced by the cloud near the cloud top at three distinct times during the cloud's evolution. The sequence shows an upshear propagation, steepening, overturning, and breaking of gravity waves produced as the cloud penetrates the stratosphere. The breaking region extends easily through a depth of 2 km above the cloud top.
The OWPDT runs a version of a global Integrated Turbulence Forecast Algorithm (ITFA) through the collaborative efforts of B. Sharman and the Turbulence PDT. Similar to the CONUS ITFA in place today, the global system uses full resolution model forecast grids to compute selected diagnostic parameters, and uses PIREPs information to weight the diagnostics. The weighted sum of these diagnostics will serve as the first instance of a probabilistic indicator of the occurrence of MOG turbulence as a function of position and time. Please refer to the Turbulence PDT section for a sample image and further description of the global ITFA. 5. Volcanic Ash The volcanic ash effort primarily focused on researching the current global effort addressing the hazard and surveying the capabilities of various Volcanic Ash Advisory Centers (VAACs) relative to the needs of operational users. T. Lindholm participated in a Spring Volcanic Ash Workshop sponsored by the NWS, USGS, and various user groups. It was clear that capability improvement needs to focus on three major areas: volcanic eruption detection, ash dispersion and particle characterization, and collaborative alert generation and dissemination. There is considerable work going on in these areas, very little of which is integrated into a national capability. That is where RAP can contribute, in particular for the Anchorage and Washington VAACs, which are part of the FAA/NWS infrastructure. Lindholm also visited the Australian Bureau of Meteorology and observed the progress being made by the Darwin VAAC. Darwin has a much more directed effort that integrates seismic sensing, satellite observations, interactive and connected display systems, and an improved dispersion model that together equates to a true regional capability. RAP's development work will be somewhat modeled after the Darwin process, perhaps starting with a simple graphical dissemination system linked to the OW website in FY03.
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