Operations Updates

ARM Climate Research Facility Operations Update - April 30, 2004

This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).

Second Phase of AIRS Validation Exercise Completed; Third Phase In Progress

Jimmy Ivanoff, lead operator at the North Slope of Alaska ACRF locale, launches a radiosonde during Phase II of the AIRS validation activity.

Phase II of the ARM Program's special series of radiosonde flights, coordinated with overpasses of the National Aeronautics and Space Administration's "Aqua" satellite, began in September, 2003 at all three of the ARM Climate Research Facility (ACRF) locales. Because ARM is the only program that can provide ongoing, consistent, and coordinated research-grade radiosonde data from stations located in the arctic, mid-latitudes, and the tropics, the global distribution of the ACRF was a key factor for scientists involved in validating the Atmospheric Infrared Sounder (AIRS), one of the instruments onboard Aqua. Consisting of two flights per overpass - the first timed so one radiosonde is near the tropopause (10-18 km depending on the site and season) while the second radiosonde is near the surface - ACRF operators successfully concluded the series of 90 sampling events in March 2004.

Because AIRS is intended to measure profiles of atmospheric temperature and humidity, using ARM's radiosonde observations is an extremely important activity for evaluating the satellite sensor's performance. Sampling for Phase III of the program, which again includes 90 sampling events at each ACRF locale, began in April 2004.

The Tale of the Tapes - No More Boxes of Data!

In October 1997, the ARM Program entered into a contract with the University of Alaska-Fairbanks to obtain image data covering ACRF's North Slope of Alaska (NSA) locale. Image data taken by an advanced very high resolution radiometer (AVHRR) are collected by a satellite receiver at Fairbanks and, up until February 2004, were stored on 4mm tapes. These boxes were then shipped by the boxful to the ACRF External Data Center every six months. Once at the External Data Center, the data was processed into standard "hierarchical data format" or HDF files and transferred to the ACRF Data Archive for use by ARM researchers. All data from 1997 through 2003 is now available in the Archive, but the delay and logistics involved with the tape storage and transfer process led to a troublesome gap in providing timely information to ARM users.

Taking advantage of a pause in satellite data reception at the NSA, the ACRF operations team put in place a strategy to upgrade the AVHRR data transfer process. With improvements to the internet connection in Alaska in recent years, it is now capable of transmitting the full complement of AVHRR data electronically. By changing the data delivery mode from labor-intensive and cumbersome tapes to near real-time (daily) delivery via a file server, both time and costs in this operations area have been significantly decreased.

Upgrades to Raman Lidar Backup Laser Improve Reliability

The Raman Lidar is an active, ground-based laser remote sensing instrument that measures vertical profiles of water-vapor mixing ratio and several cloud- and aerosol-related quantities.

In March 2004, upgrades to a second (backup) laser for the Raman Lidar at the ACRF Southern Great Plains (SGP) locale were completed, concluding a complex effort that began more than a year ago. Upgrades included required modification to the optical layout of the lidar system, several changes to the laser head by the vendor (for compatibility with existing power supply equipment), the addition of a larger heat exchanger, and a second pump in the laser cooling system. This upgrade is expected to significantly improve the reliability of the Raman Lidar system. Now, if one laser fails, SGP personnel can bring the second laser on-line in a few minutes, rather than waiting days for the laser vendor to travel to the SGP and make repairs.

In preparation for the upgrade, an entirely new air handling system was installed in the SGP lidar shelter last summer. The new air handling equipment includes a much higher capacity air conditioner, new HEPA filtration, and an entirely new air distribution system to achieve more uniform distribution of the airflow in the shelter to avoid warm zones. Because of these improvements, the lidar will be able to operate satisfactorily during the hottest days of the Oklahoma summer, when ambient temperatures exceed 100 °F.

Arctic Winter Water Vapor IOP Completed

Following four weeks of data acquisition, the Arctic Winter Water Vapor Intensive Operational Period (IOP) at the ACRF North Slope of Alaska (NSA) locale was completed the weekend of April 9, 2004. In collaboration with the National Oceanic and Atmospheric Administration's Environmental Technology Laboratory (ETL), the major goal of this IOP was to demonstrate that millimeter wavelength radiometers can substantially improve water vapor observations during arctic winters at the NSA and other high latitude research sites. Supplemental goals included forward modeling studies over a broad frequency range, demonstration of recently-developed calibration techniques, and application of infrared cloud imaging techniques. In addition, because the surface conditions at NSA in March are similar to those that are found at high altitudes at lower latitudes, the effort was particularly useful for studying parts of the thermal infrared spectrum that are normally opaque at the other ACRF sites.

A new radiosonde launch mezzanine (lower-right inset), adjacent to the Duplex that houses the site data systems and visitor living quarters, is a recent upgrade at ACRF's North Slope of Alaska locale.

During the IOP, both the ARM MicroWave Radiometer and MicroWave Radiometer Profiler, as well as ETL's Ground-based Scanning Radiometer, yielded excellent data over a range of conditions. Angular scanned and calibrated radiometer data ranging from 22 to 380 GHz were taken. Precipitable water vapor varied more than an order of magnitude from 1 to 10 mm, and surface temperatures varied from -10 to -40 C. Data plots from the cloud radar and the depolarization micropulse lidar indicate that clearly identifiable conditions of clear, liquid, mid-level ice, and mixed phase clouds were present during the IOP. High quality thermal images of the atmosphere were also taken throughout the IOP.