Operations Updates
ARM Climate Research Facility Operations Update - May 31, 2005
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
Rain in the Plain Falls Mainly on the... Farm?
Understanding the microphysics (size, shape, velocity) of heavy precipitation is important for scientists to accurately estimate rainfall rate and for improving these parameterizations in models that predict weather. Between May and June, the ACRF Southern Great Plains (SGP) site is hosting a joint field campaign for scientists from the National Center for Atmospheric Research (NCAR), the National Oceanic and Atmospheric Administration (NOAA), and the University of Oklahoma that involves daily precipitation measurements using a video disdrometer. A disdrometer is an instrument used to measure the drop size distribution and velocity of falling precipitation. Some disdrometers can distinguish between rain and graupel (solid precipitation such as hail, sleet, and snow pellets). Newer disdrometers that use microwave or laser technologies are sensitive enough to analyze individual snowflakes.
Almost hidden by orange caution fencing, this upward looking 2D video disdrometer is collecting precipitation data at Kessler Farm, near the SGP's Purcell Boundary Facility.
In late April, an NCAR 2D video disdrometer was installed at Kessler Farm near SGP's Purcell Boundary Facility, next to a disdrometer used by NOAA's National Severe Storms Laboratory (NSSL). In addition to the surface observation area, the Purcell Boundary Facility provides scientists with the internet connection, power, and workspace needed to record their research. Goals of this 2-month campaign are to accurately measure characteristics of precipitating particles using 2D video disdrometer technology.
The National Weather Service uses 2D video disdrometers for dual-polarization measurements. Polarization measurements are important for discriminating between radar signals that bounce off of symmetrical versus irregular shapes (i.e., rain drops versus snow or ice crystals). The Weather Service radars (WSR-88Ds) will be upgraded with dual-polarization capability in the next five to seven years, which will provide polarization radar measurements and allow scientists to remotely study precipitation microphysics from instruments located throughout the United States. Accurate in-situ measurements are important for verifying and understanding polarization radar capabilities. Disdrometer observations obtained during the field campaign will be used to verify polarimeter radar measurements from an NSSL dual-polarization radar located about 30 km away, in the same field of view. In addition, the data will be used to develop data retrieval algorithms, to study rain microphysics, and to derive improved parameterization schemes for National Weather Prediction models.
History Tool Records Changes to Datastreams
As the name implies, a "datastream" is a continuous record of a specific type of data that is collected and saved in a time series. Occasionally, modifications are needed to update or correct a datastream. Knowing the history of changes to a datastream is a critical issue for ACRF data users. Recognizing this need, the ACRF Data Management Facility (DMF) created a tool to record the history of every datastream for every instrument from every ACRF site since the beginning of the ARM Program.
The History of Datastream tool looks for changes to the data object design (DOD) files weekly and creates a history link for DODs that have changed. By selecting "history," users will have access to the old DOD file and a file outlining the differences.
Each day, the DMF processes approximately 1875 datastreams from 287 instrument systems and delivers them to the Data Archive. These datastreams contain netCDF (network Common Data Form) files, which is the standard file format for ACRF measurement collection. Each datastream has a specific netCDF structure that is defined and managed by a data object design (DOD) file. Historically, the metadata within the DODs were revised and overwritten whenever a change occurred, with no record of the change saved for reference. Not anymore!
In March, the History of Datastream tool began providing information on changes to the metadata, and when the changes occurred—a historical record—for all the datastreams available at the DMF. Once a week, the tool scans the current DOD files, identifies any changes, and adds a link to "history" (see figure) for each DOD impacted. This information is available from the ARM netCDF File Header Description webpage by selecting the instrument or value-added product's DOD. Soon, ACRF's Data Archive and External Data Center (XDC) will begin using the History of Datastream tool to help build a historical record of datastream changes since the sites first began collecting data, as well as to maintain a history of datastream changes in the future.
