1. Background

Near mid-year, RAP began leadership of a new program of applied research and product development that addresses international need for better nowcasts and forecasts of flight conditions and weather-related aviation hazards in data-sparse oceanic regions. The program is funded by the FAA Aviation Weather Research Program, and is motivated by recognition that the weather information that supports 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 sparseness of surface, rawinsonde, radar and other observational data over the remote oceans, as this sparseness 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 provisions to receive in-flight weather information updates in current transport aircraft.

Work to develop and test new approaches to the nowcasting and forecasting of aviation-critical weather conditions in oceanic regions is the responsibility of a new collaborative team comprised of principals 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 provides overall management of the team effort, while P. Herzegh serves as scientific lead. The team 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.

Work to date has begun a survey of critical issues and techniques (Sec. 2 below) and has yielded first steps toward an oceanic convective nowcast product (Sec. 3). Further project information including the current Seven-Year Scientific Plan is maintained on the Oceanic Weather project website.

2. Survey of Issues and Techniques

The oceanic weather team has initially undertaken a survey of existing information, products, analysis techniques, and emerging technologies to support (i) the formulation of working priorities, (ii) strategies for research and product development, and (iii) identification of other groups and individuals whose collaboration can advance our objectives. Both this initial survey and the related planning of development strategies will continue well into the coming year. Thereafter, established strategies will be continually updated and revised as appropriate.

Lindholm is conducting a continuing survey of end-user needs to establish priorities for weather product development and geographic coverage. His 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 better defining the incursion of deep oceanic convection on upper-level flight routes. Associated aviation hazards include severe turbulence (the leading cause of in-flight injuries), damaging hail, and lightning strikes. Aircraft icing, while not a significant problem at uppermost 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.

J. Hawkins (NRL), T. Tsui (NRL), and P. Herzegh and are working to define a strategy for improvement of wind information available both for general flight planning and as input to support the diagnosis of convective evolution and turbulence. The emerging development strategy will be 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.

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T. Lindholm, P. Herzegh, R. Sharman, and F. Mosher (AWC) are working to better understand the aviation threat posed by volcanic ash emissions and the current infrastructure for detecting, forecasting, and communicating expected ash dispersion across oceanic flight routes. As shown by the time composite of NOAA Advanced Very High Resolution Radiometer (AVHRR) satellite data in Figure K1 (a product of research by Schneider et al. at Michigan Technological University), ash cloud dispersion can yield a potential aviation hazard over thousands of km. Survey results indicate that improved specificity in current and forecast ash plume boundaries is a matter of high priority to aviation operators in the Pacific Rim and Central America regions. The oceanic weather team is exploring pathways toward more accurate plume detection, dispersion modeling, and improved integration of ash nowcast/forecast results with other advisory information.

Figure K1: Time composite of ash cloud imagery from the Mt. Spurr, Alaska, eruption as determined from Advanced Very High Resolution Radiometer data analyzed and displayed by Michigan Technological University.

Figure K2: Sample Pacific region cloud top height field (in ft.) representative of the RAP V1.0 prototype cloud top product currently available on the Oceanic Weather website.


3. Initial Steps Toward a Convective Nowcast Product

Pursuit of a product leading to an operational nowcast of convection over the oceans is proceeding along several lines. RAP's D. Johnson, N. Rehak, and G. Blackburn have developed a first-cut prototype web display of cloud top height for the Pacific region as shown in Figure K2 and in real time via the Internet in the Oceanic Weather prototype cloud top product. Pilots and dispatchers use this V1.0 prototype to aid identification of broad regions of deep convection and associated incursions to flight-level air routes. Cloud top height is determined by converting satellite-observed cloud-top temperatures (from IR imagery) to pressure heights (which correspond to the height reference used for aircraft navigation) using a simple, non-varying standard atmosphere conversion. Johnson has begun a short-term V1.1 upgrade to the product which substitutes seasonally and latitudinally varying climatological mean temperature soundings for the standard atmosphere sounding utilized in the V1.0 prototype. NRL's J. Hawkins is working with D. Johnson and RAP scientist C. Kessinger to plan and implement a V2.0 upgrade to the prototype, which would substitute time and place representative soundings from the AVN global model in place of the climatological mean soundings used in the V1.1 product. T. Tsui and J. Hawkins have recently outlined a similar NRL cloud top height product utilizing sounding data from the NOGAPS global forecast model. The relative performance of the V1.1 and V2.0 products will be evaluated in the coming year.

C. Kessinger has taken parallel steps to merge additional data and analysis methodologies with the cloud top height product to bring more specific definition to the location of peak convective activity, severity, and life-cycle evolution of the convective regions broadly identified by the V1.1 and V2.0 products described. Near-term steps include work toward automated analysis of mesoscale and cloud-scale satellite imagery features to derive information on cloud type, apparent movement, and growth/decay rates of regions of active convection. Current collaboration with scientist E. Marshall of MIT/LL will bring (in the coming year) a methodology for parallel use of lightning data derived from NASA's Tropical Rainfall Measuring Mission (TRMM) low earth orbit satellite and (possibly) DoD geostationary satellites to further define sub-regions of active, deep convection. Collaboration with M. Mosher of AWC will further develop and incorporate a satellite-based methodology he has developed for identifying regions of active convection.

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