WV

The Water Vapor IOP was conducted as a follow-up to a predecessor IOP on water vapor held in September 1996. This IOP relied heavily on both ground-based guest and CART instrumentation and in-situ aircraft and tethered sonde/kite measurements. Primary operational hours were from 6 p.m. Central until at least midnight, with aircraft support normally from about 9 p.m. until midnight when available. However, many daytime measurements were made to support this IOP. The first Water Vapor IOP primarily concentrated on the atmosphere's lowest kilometer. This IOP concentrated not only there but also on atmospheric layers up to 12 kilometers. A key goal of each Water Vapor IOPs was to reduce the uncertainties in water vapor observations integral to ARM spectroscopic analyses that contribute to better radiative transfer calculations for climate models. Each saw an assemblage of a wide array of both remote and in situ sampling platforms for observing water vapor profiles and precipitable water to ultimately learn how to best measure and characterize water vapor. Establishment of absolute calibration techniques and stability characterization for the CART Raman lidar was another prime goal of these IOPs. Specific IOP objectives during fall 1997 included 1) evaluation of absolute calibration standards, 2) characterization of the accuracy of the routine CART water vapor measurements, 3) calibration of the CART Raman lidar independent of the BBSS, and 4) evaluation of methodologies for synthesizing more accurate measurements. Guest ground-based instrumentation included the NASA/GSFC scanning Raman lidar, NOAA/CIRES microwave and infrared radiometers, Los Alamos National Laboratory (LANL) tethered balloon system with chilled mirror hygrometers, NOAA tethered kite and balloon system with chilled mirror hygrometers, ARM chilled mirror hygrometers at the 25- and 60-m levels on the 60-m tower and at the THWAPS (adjacent to BBSS launch station), NOAA GPS, capable of inferring integrated precipitable water vapor, University of Wisconsin AERI-00 and AERIbago, and NASA/Ames 6-channel tracking sunphotometer and two MICROTOPS hand-held sunphotometers. Critical ARM instrumentation for this IOP included the BBSS with dual sonde capability, Raman lidar, MWR, 60-m tower sensors, AERI, SMOS, MFRSR, and MPL. All five IOP aircraft platforms were important for the Water Vapor IOP because each carried either a chilled mirror hygrometer (Citation, King Air, Gulfstream, and Twin Otter) and/or a frost-point hygrometer (Citation, Altus). Thus, every aircraft flight made during the Integrated IOP had benefit for the Water Vapor IOP. In addition, the DOE 7-channel microwave radiometer (DoER) and the 5-channel millimeter-wave imaging radiometer (MIR) were flown on the Twin Otter to support microwave radiometer comparisons. The Citation and King Air flew special nighttime missions in direct support of the Water Vapor IOP. These flights, carrying the highly precise hygrometers, were coordinated especially with operations of the two Raman lidars, tethered systems, and dual package BBSS launches. In all, the Citation performed five such nighttime missions (September 17, 25, 30; October 1, 3), while the King Air participated in two (September 27; October 3). The evening of October 3 saw both aircraft flying in support of this IOP. A special wingtip-to-wingtip flight mission involving the King Air and Gulfstream-1 on September 29 afforded comparison of both the chilled mirror and wind sensors on those aircraft. Also, the joint flights of the Citation and King Air on the evening of October 3 allowed similar comparisons to be made between sensors on those two aircraft. A substantial 2:00 p.m. Central meeting was held each day at the Central Facility to discuss/display results from the previous day/night and to make plans for the upcoming evening. A good deal of decision making was made based on which instrument(s) were/were not performing as anticipated. Data is being analyzed by the IOP's scientific focus groups throughout the rest of 1997 and early 1998 in anticipation of water vapor meetings at both the IRF Workshop in January 1998 and the ARM Science Team Meeting in March 1998. Decisions will then be made as to when and how to conduct a third Water Vapor IOP.