ETL Installs Meteorological Equipment In Time for Record Breaking Storm
20th Dec, 2002Contact: Marty Ralph
Although this year's edition of the Pacific Land-falling Jets Experiment (PACJET) is not slated to begin until January 10, 2003, engineers and technical staff from NOAA/ETL worked diligently to get important meteorological equipment installed prior to December's record breaking storms on the West Coast. This effort was accelerated due to requests from NWS forecasters who were anticipating that potentially dangerous conditions would develop, and due to the potential value of the research data for studies of "extreme events and their link to climate variability." The forecaster's concern was expressed during consultations with ETL on research results from CALJET data during the floods of 1997/98. Among several relevant results, those analyses confirmed that major flooding had occurred when a low-level jet of 70 kt intensity struck the coast, an intensity that was predicted by the AVN (NCEP's Aviation forecast model) model for last week's storms as well as was observed by the profiler array installed by ETL.
The meteorological equipment at most of the sites consists of a 915-MHz Doppler wind profiling radar with a radio acoustic sounding system for temperature profiling and a 10-m meteorological tower that provides near surface meteorological data including rainfall accumulation. The wind profiler continuously monitors the winds well above the surface, which are closely correlated to the flooding rains measured in the coastal mountains, as indicated by Neiman et al. (2002). The wind profiler also provides a measurement of the snow level in the atmosphere, which is an important parameter for river basin forecasting (e.g., White et al. 2002) as well as for transportation and tourism in the Sierra Nevada Mountains. Four profiler sites were installed along the coast of California to complement the profiler network already in place from other studies (see image on website), and have already proven useful to NWS operational forecasters.
At one of the rainiest locations in the coastal mountains, near the town of Cazadero, California, NOAA/ETL deployed a vertically pointing 2875-MHz radar along with a 10-m meteorological tower. This radar provides information about the physical processes contributing to orographic rainfall enhancement. NOAA/ETL has obtained a winter season radar climatology from this location dating back to the last strong El Ni�o experienced during the winter of 1997-98. "With this formidable start, the seasonal rainfall [measured at the Cazadero site] could surpass what we measured in ?97-?98!" exclaimed Paul Neiman, a research meteorologist with NOAA/ETL.
In January, NOAA/ETL, the University of Washington, and the Desert Research Institute of the University of Nevada will deploy additional instrumentation, including an X-band scanning, polarimetric radar; various types of rain gauges; and raindrop disdrometers at a coastal location approximately 25 km north of Bodega Bay, California (see image on website). The X-band radar will provide low-level radar reflectivity and Doppler velocity surveillance scans over the ocean and along the coastline to help fill important gaps in the operational observing network. The primary research objective motivating the deployment of this additional instrumentation is to gain a better understanding of the microphysical processes that are affected by the coastal topography. Together with the Cazadero site, the coastal site will provide an excellent laboratory to study orographic effects. This overall effort reflects an investment in hydrometeorological research at ETL, and a parallel effort to test new forecast techniques. This follows the approach outlined by a team developing a Hydrometeorological Testbed concept that will enable NOAA to attain its GPRA goals in hydrology and hydrometeorology.
Highlights from December 8-16, 2002:
- 8 Dec. Equipment installed at Cazadero (coastal mountains)
- 13-14 Dec. 1st storm hits coast: 13 inches of rain falls in 40 hours, soils become saturated, rivers crest just below flood stage, winds gust to 70 knots.
- 15-16 Dec. 2nd storm hits coast: 6 inches of rain falls in 12 hours (77-h storm total reaches 20 inches at Cazadero and other sites), rivers reach flood stage, wind gusts exceed hurricane intensity, widespread power outages, ocean waves exceed 30 feet.
Publications
Neiman, P.J., F.M. Ralph, A.B. White, D.E. Kingsmill, and P.O.G. Persson, 2002: The statistical relationship between upslope flow and rainfall in California's coastal mountains: Observations during CALJET, Mon. Wea. Rev., 130, 1468-1492.
White, A.B., D.J. Gottas, E.T. Strem, F.M. Ralph, and P.J. Neiman, 2002: An automated brightband height detection algorithm for use with Doppler radar spectral moments. J. Atmos. Oceanic Technol., 19, 687-697.