The Pacific Landfalling Jets
27 January 2000
(Contact: Dr. Martin Ralph, NOAA/Environmental Technology Lab., Marty.Ralph@noaa.gov)
a) Overarching goal
To develop and test methods to improve short-term (0-24 h) forecasts of damaging weather on the U. S. West Coast in landfalling winter storms emerging from the data sparse Pacific Ocean. PACJET is designed to be a next step toward attaining this goal. It is envisioned as part of a long-term effort that combines analysis, a series of focused field experiments, development of new products and tools for operational forecasting, and exploration of physical processes that contribute to the linkage between seasonal-to-interannual climate variability (e.g., ENSO) and extreme coastal weather events.
b) Time and location of PACJET
10 January 2001 to 5 March 2001
From 300 km inland to 1000 km offshore of the U.S. West Coast from Southern California to Washington State. This covers the area between the coast and the central Pacific domain sampled by the Winter Storm Reconnaissance program (Figs. 1 and 2).
PACJET addresses short-term weather prediction along the US West Coast during winter, focusing on quantitative precipitation forecasting. It builds on experience gained from CALJET, an earlier west coast experiment performed during the strong El Niño of 1997/98. CALJET aided flood forecasting (Fig. 3), studied the utility of new observations, and explored the relationship between El Niño and extreme coastal storms. PACJET expands the area covered by CALJET and targets the coastal zone, which is an area of extreme societal vulnerability for which forecasts are typically less accurate than normal, and thus is a problem of great interest to NOAA. PACJET directly links core USWRP objectives on quantitative precipitation forecasting (QPF) and Optimal Observing Systems to this difficult but important problem.
The strategy is based on applying research techniques and technology development over several years to address specific forecast problems, such as flood warnings, high wind warnings, and marine warnings. An ongoing series of focused field experiments is envisioned over the coming years to test new instruments, data assimilation techniques and operational tools that emerge from analysis of the previous experiments, and to develop a strategy to anticipate the nature of extreme weather events linked to climate variability (e.g., ENSO).
d) Societal impacts and forecast user input
#Input at PACJET Workshop 9/99.
2. Linkages to national and NOAA priorities
3. The strategy for PACJET and for addressing West Coast short-term prediction
This section briefly summarizes the experimental goals, which attempt to balance basic and applied research with operational applications development.
b) Operational applications development:
4. PACJET and the linkage between climate variability and extreme weather events
Although it is becoming well established that large-scale climate variability such as ENSO can modulate seasonal-to-interannual variations in regional climate, in the case of extreme precipitation it is the specifics of each storm that determine many of the societal impacts of these climate anomalies. PACJET explores this linkage in the following ways:
5. Data assimilation studies to improve short-term west coast weather prediction
The evaluation of data impact and the use of different models will allow investigation of several issues that are important to short-term QPF and wind prediction over the US west coast. First, it will enable comparisons to be made between forecasts/simulations from different models through verification against specialized field experiment data, so that the performance of each model in coastal wind and precipitation prediction will be evaluated. Second, the difference in the forecasts/simulations revealed by the evaluation of data impact will provide information on the sensitivity of coastal predictions to perturbations in the model physics and initial/boundary conditions. Third, it will provide a unique opportunity to test the concept of mesoscale ensemble forecast for coastal weather prediction. Last, it provides a test bed for future improvement and development of an optimal data assimilation strategy for coastal weather prediction.
Data assimilation for coastal prediction is extremely challenging because conventional observations are sparse in the eastern Pacific. The initialization of a model for very short-range prediction over the US west coast requires optimal assimilation of information from unconventional data sets, such as those from satellite and targeted observation missions. There are several techniques available for assimilating unconventional data, but each technique has its advantages and disadvantages that vary with different operational settings and instrumentation. Thus, the variety of instruments that will be applied in PACJET makes it a valuable opportunity to tackle issues regarding the superiority of one technique over the other for short-range prediction over the US west coast, and to reveal the statistics and sensitivity that are critical for optimizing data assimilation.
A few specific approaches that are envisioned include:
Quasi-real-time evaluation of data impact using operational models and NWS verification
Real-time use of experimental models
Post-experiment research on optimal data assimilation techniques for mesoscale QPF and probabilistic QPF
Predictability on the mesoscale
6. Status of the PACJET experiment as of January 2000
This list of organizations is based mostly on participation at the PACJET Planning Workshop that was conducted in Sept. 1999 in Monterey, CA, and represents a core group likely to participate in PACJET.
Science and operations groups:
Forecast user groups:
Mesoscale modeling groups who have indicated likely involvement in PACJET:
8. Payoffs of PACJET and a long-term effort to improve short-range west coast forecasting
Workshop to Explore Applications of a Field Experiment (PacJet)
to 0-24 h West Coast Winter Weather Forecasting
Experience gained during the recent California Land-falling Jets Experiment (CALJET) indicates that real-time use of experimental data from the coast to 1000 km offshore can aid in issuing coastal weather warnings. In particular, the Monterey forecast office of the National Weather Service (NWS) used CALJET research aircraft measurements of the strength of a low-level jet in an approaching storm to help issue a flash flood warning that gave 6 h lead time for a record-breaking flash flood in the region. It has also been shown recently by NCEP that insertion of CALJET aircraft data in storms roughly 24 h before they made land-fall led to improvement in the 24-h operational numerical weather predictions in all of the 5 cases tested. In addition, operational and research profiler networks on the U. S. west coast are now providing real-time monitoring of the coastal environment, albeit fewer are now available than in recent years. In particular, coastal wind profilers provide a real-time view of weather phenomena, such as blocking and barrier jets along the coast that can modify the location of precipitation maxima.
These results, along with other research, have motivated the preliminary design of a follow-on experiment referred to as PacJet. A planning letter has been submitted for use of two NOAA research aircraft and NOAA's state-of-the-art research vessel (the Ron Brown) off the west coast of the United States during the winter of 2000/2001. In addition, data from numerous wind profilers that will be deployed in this region for air quality research will also be available for use. Although the experimental design will be modeled after our 1998 El Niño experience, the location of the experiment may be adjusted depending on threats assessments provided several months ahead of time based on seasonal-to-interannual forecasts (i.e., El Niño and La Niña). The value of seasonal-to-interannual forecasts and forecast uncertainty will also be discussed.
We invite your participation in a workshop aimed to provide recommendations from the operational weather forecasting community along the US west coast that can aid directly in the detailed design of the field program. The emphasis will be on 0-24 h forecasting of land-falling Pacific winter storms, covering the area from roughly 200 km inland to 1000 km offshore. Illustrations of atmospheric, hydrologic, and ocean sea state forecasting issues are encouraged. This input, combined with the basic research objectives, will set the priorities for the experiment. The concept for this meeting emerged from a joint session of the CALJET Workshop and the National Weather Service Western Region Marine Forecasters Training Course in May 1999 where marine forecasters indicated that such data could be very useful, and provided several novel recommendations on what would be useful and why.
The experimental objectives identified thus far have been developed out of priorities established in several reports by NOAA, the National Weather Service, the U.S. Weather Research Program (USWRP), and the National Research Council which include research aimed at:
Session A: Introduction
Summary of experience gained from CALJET and two recent central Pacific observing programs. Description of preliminary design for PacJet and how input from this meeting can affect the experiment.
Session B: Illustrate forecast problems and needs
To bring out the most important areas where experimental data could aid in operational forecasting, presentation of case studies by the forecasting community are requested. These case studies are intended to illustrate where additional coastal, inland, and offshore data (up to 1000 km offshore) could be of most value. These examples should focus on the winter season along the U. S. west coast, on the region from roughly 200 km inland to 1000 km offshore, and on the 0-24 h forecast time window. Illustrations of atmospheric, hydrologic, and ocean sea state forecasting issues are encouraged. It is anticipated that each forecaster or Science Operations Officer would use about 20-30 min to illustrate their region's forecast problems. This is enough time to see in depth what the problems are and to discuss them. This is the heart of the workshop and will form the basis for the recommendations developed the next morning in session C. See http://www7.etl.noaa.gov/programs/CALJET/index.html for a description of CALJET.
Session C: Develop set of recommendations
Combine input from the forecasting community with that from the research team concerning the capabilities and limitations of new observing systems and strategies, to develop a detailed set of recommendations for use in designing PacJet.
Tuesday 31 August 1999
Session A: CALJET Experience and PACJET Planning
Session Chair: Warren Blier, Science and Operations Officer, NWSFO Monterey, CA
9:00 AM Introduction and meeting objectives
9:05 AM "What was CALJET and what have we learned from it?" (Ralph)
9:25 AM "Can targeted dropsonde deployments improve coastal storm forecasts?" (Toth)
9:45 AM "PACJET: Preliminary plans, candidate observing systems, and status" (Ralph)
10:00 AM "Special PacJet Satellite Products" (Velden/Ralph)
10:10 AM "Studying Surface Wind Fields in Oceanic Storms with SSM/I, Scatterometer, and SAR data (Walter)
10:20 AM "Geostationary and Polar Orbiting Satellite Data during PacJet" (Dostalek)
10:35-11:00 AM Break
11:00 AM "RUC Mesoscale Modeling Runs for PacJet" (Benjamin)
11:15 AM "Quasi-operational mesoscale modeling in California: Application to PacJet" (Miller/Schmidt)
11:30 AM "Sea state prediction with coupled mesoscale models: PacJet as a test bed?" (Wilczak)
11:45 AM "NOAA's Coastal Forecast System and SAFESEAS" (Contorno)
12:00 Noon "The THORPEX Experiment" (Langland)
Session B: Illustrate forecast problems and needs
Session Chair: Brad Colman, Science and Operations Officer, NWSFO, Seattle, WA
1:20 PM "The NWS Quantitative Precipitation Forecast Process Assessment" (Reynolds)
1:40 PM "NCEP/Hydrometeorological Prediction Center QPF Skill and its Relationship to Numerical Weather Prediction, Can PacJet Improve the Models?" (Reynolds)
2:00 PM "How CNRFC fits into the QPF process and how we use the QPF" (Rhea/Strem)
2:20 PM "How the Sacramento Flood Control System Works," (Roos)
2:40 PM "NCEP Marine Prediction Center Overview of Operations and Critical Forecast Problems" (Partain)
3:00-3:45 PM Break
3:45 PM "Impacts of Winter Season Pacific Storms on Southern California" Oxnard (Danielson)
4:00 PM "Perspectives from the Hanford NWS Forecast office" (Greiss)
4:15 PM "Winter Hydrometeorological Concerns at WFO Sacramento" (Cunningham)
4:30 PM "Perspectives from the Monterey NWS Forecast Office" (Blier)
4:45 - 5:15 PM Discussion "Needs and opportunities for improvement"
5:15 PM Session B ends for the day. Session B continues Wednesday morning.
Wednesday 1 September
Session B Continued
Session Chair: Wendell Nuss and Doug Miller, Naval Postgraduate School, Monterey, CA
8:30 AM "Perspectives from the Eureka NWS Forecast Office" (Nordquist)
8:45 AM "Perspectives from the Seattle NWS Forecast Office" (Colman)
9:00 AM Tom Maruyama, San Mateo County Emergency Management
9:15 AM Neal O'Haire, California Governor's Office of Emergency Services, Coastal Region
9:30 AM "Perspectives from a Television Broadcast Meteorologist" (Lynn)
9:45-10:15 AM Break
Session C: Synthesis and Recommendations
Session Chair: Marty Ralph, NOAA/Environmental Technology Laboratory, Boulder, CO
10:15 AM - 12:00 Noon Discussion
What are the key forecast issues?
What experimental data would be most useful?
How should the data be made available?
Should training be considered just before the experiment?
How to best assess operational impact, both NWP and real-time?
Noon Workshop ends.
A Scanning Radar Altimeter for use on a P-3 During PACJET
The Scanning Radar Altimeter (SRA) [1, 2] and its predecessor, the Surface Contour Radar (SCR) [3, 4] were designed primarily to measure the energetic portion of the directional wave spectrum by generating a topographic map of the sea surface. The measurement geometry is shown in Figure A.1A. The SRA sweeps a radar beam of 1o half_power width (two_way) across the aircraft ground track from _22o (off_nadir to the left side of the aircraft) to +22o (off_nadir to the right side of the aircraft), simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 points spaced across the swath at 0.7o incidence angle intervals. These slant ranges are multiplied by the cosine of the incidence angles (including the effect of aircraft roll attitude) to determine the vertical distance from the aircraft to the sea surface. Subtracting these distances from the aircraft height produces the sea surface height. The SRA produced these raster scan lines of wave topography at the rate of 10 Hz.
Figure A.1B shows a surface elevation profile extracted from the middle of the SRA swath during a flight into hurricane Bonnie on 24 August 98 at 1.5 km altitude. The crest-to-trough height of the highest wave is almost 18 m. This wave was the highest in the 10 km segment of grey-scale coded SRA wave topography data shown in Figure A.1C. The SRA swath width was 1.2 km and the wave image is in proportion. The aircraft was traveling toward the north and the image shows the general spatial variation the waves in the predominantly northwest propagating swell wave field 150 km north of the hurricane Bonnie eye.
Figure A.1D shows the directional wave spectrum generated from the SRA topography of Figure A.1C. The significant wave height (SWH) was 9.1 m. The nine contours are linearly distributed between 10% and 90% of the peak spectral density. The three solid circles indicate wavelengths of 100, 200, and 300 m. This spectrum was quite narrow and its peak corresponded to a 300 m wavelength wave propagating toward 330o. The long arrow indicates the wind at that location, which was blowing toward 258o at 40 m/s. There were wind-driven waves propagating in the downwind direction, but their energy density was below the 10% level of the spectral peak. Figure A.1F shows a 10-km segment of gray_scale-coded wave topography measured while the aircraft was traveling toward the southeast about 30 km south and 40 km east of the eye. The image has been rotated about 45o clockwise from its original track orientation. The time sequence of the data progresses from top to bottom.
Figure A.1E shows the directional wave spectrum generated from the SRA data of Figure A.1F. The SWH was 6.7 m and the wave system was bimodal with approximately the same energy in waves propagating almost at right angles to each other. The wind at this location was also about 40 m/s, but toward 22o. Waves of about 140 m wavelength propagated toward 28o, nearly aligned with the wind. The spectral peak of the swell system corresponded to waves of 200 m wavelength propagating toward 315o.
 Walsh, E. J., L. K. Shay, H.C. Graber, A.Guillaume, D. Vandemark, D. E. Hines, R. N. Swift, and J. F. Scott, "Observations of Surface Wave_Current Interaction During SWADE," The Global Atmosphere and Ocean System, 5, 99_124, Gordon and Breach Science Publishers SA, 1996.
 Parsons, C., and Walsh, E.J., "Off_Nadir Altimetry," IEEE Trans. Geosci. Remote Sens., 27, 215_224, 1989.
 Walsh, E. J., D. W. Hancock, D. E. Hines, R. N. Swift, and J. F. Scott, "An Observation of the Directional Wave Spectrum Evolution from Shoreline to Fully Developed," J. Phys. Oceanogr., 19(5), 670_690, 1989.
 Walsh, E. J., D. W. Hancock, D. E. Hines, R. N. Swift, and J. F. Scott, "Directional Wave Spectra Measured with the Surface Contour Radar," J. Phys. Oceanogr., 15(5), 566_592, 1985.