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  • Author or Editor: C. E. Anderson x
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S. A. Vay
,
B. E. Anderson
,
K. L. Thornhill
, and
C. H. Hudgins

Abstract

Results are reported from an experiment conducted aboard the NASA DC-8 research aircraft to determine whether cabin air vented upstream of investigator's inlets had potentially contaminated ambient air samples obtained aboard the aircraft during previous airborne scientific expeditions. For the study, three multiport inlet rakes were mounted in windows downstream of an exhaust vent in locations forward, above, and aft of the right wing. These were used to make impact pressure measurements for determining boundary layer thickness (δ) as well as to collect ambient air samples at various distances outward from the airframe. The fraction of cabin air in the samples was determined by doping the vent air with a metered amount of CO2, then monitoring air at the inlet ports for differential CO2 enhancements. Data were collected at altitudes ranging from the surface to 12 km, at various indicated airspeeds, pitch and yaw angles, and during vertical ascents and descents. Results indicate that δ varies from about 13 to 37 cm and depends on inlet position, as well as the aircraft velocity, altitude, and pitch angle. The CO2-doped vent air was observed to mix throughout the depth of the boundary layer, but to be confined vertically to a narrow stream so that its interception by any particular inlet probe was highly dependent upon the aircraft-indicated airspeed and pitch angle. The inlet located forward of the wing was the most highly impacted, as samples collected there contained up to 0.8% cabin air at cruise altitudes under typical aircraft operating conditions. The implications of these findings on previous datasets are discussed, and a modified formula for calculating δ values appropriate for the DC-8 is proposed.

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C. W. Fairall
,
P. O. G. Persson
,
E. F. Bradley
,
R. E. Payne
, and
S. P. Anderson

Abstract

The calibration and accuracy of the Eppley precision infrared radiometer (PIR) is examined both theoretically and experimentally. A rederivation of the fundamental energy balance of the PIR indicates that the calibration equation in common use in the geophysical community today contains an erroneous factor of the emissivity of the thermopile. If a realistic value (0.98) for the emissivity is used, then this leads to errors in the total flux of 5–10 W m−2. The basic precision of the instrument is found to be about 1.5% of the total IR irradiance when the thermopile voltage and both dome and case temperatures are measured. If the manufacturer’s optional battery-compensated output is used exclusively, then the uncertainties increase to about 5% of the total (20 W m−2). It is suggested that a modern radiative transfer model combined with radiosonde profiles can be used as a secondary standard to improve the absolute accuracy of PIR data from field programs. Downwelling IR fluxes calculated using the Rapid Radiative Transfer Model (RRTM), from 55 radiosondes ascents in cloud-free conditions during the Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment field program, gave mean agreement within 2 W m−2 of those measured with a shipborne PIR. PIR data from two sets of instrument intercomparisons were used to demonstrate ways of detecting inconsistencies in thermopile-sensitivity coefficients and dome-heating correction coefficients. These comparisons indicated that pairs of PIRs are easily corrected to yield mean differences of 1 W m−2 and rms differences of 2 W m−2. Data from a previous field program over the ocean indicate that pairs of PIRs can be used to deduce the true surface skin temperature to an accuracy of a few tenths of a kelvin.

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L. A. Sromovsky
,
J. R. Anderson
,
F. A. Best
,
J. P. Boyle
,
C. A. Sisko
, and
V. E. Suomi

Abstract

An untended instrument to measure ocean surface heat flux has been developed for use in support of field experiments and the investigation of heat flux parameterization techniques. The sensing component of the Skin-Layer Ocean Heat Flux Instrument (SOHFI) consists of two simple thermopile heat flux sensors suspended by a fiberglass mesh mounted inside a ring-shaped surface float. These sensors make direct measurements within the conduction layer, where they are held in place by a balance between surface tension and float buoyancy. The two sensors are designed with differing solar absorption properties so that surface heat flux can be distinguished from direct solar irradiance. Under laboratory conditions, the SOHFI measurements agree well with calorimetric measurements (generally to within 10%). Performance in freshwater and ocean environments is discussed in a companion paper.

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L. A. Sromovsky
,
J. R. Anderson
,
F. A. Best
,
J. P. Boyle
,
C. A. Sisko
, and
V. E. Suomi

Abstract

The Skin-Layer Ocean Heat Flux Instrument (SOHFI) described by Sromovsky et al. (Part I, this issue) was field-tested in a combination of freshwater and ocean deployments. Solar irradiance monitoring and field calibration techniques were demonstrated by comparison with independent measurements. Tracking of solar irradiance diurnal variations appears to be accurate to within about 5% of full scale. Preliminary field tests of the SOHFI have shown reasonably close agreement with bulk aerodynamic heat flux estimates in freshwater and ocean environments (generally within about 20%) under low to moderate wind conditions. Performance under heavy weather suggests a need to develop better methods of submergence filtering. Ocean deployments and recoveries of drifting SOHFI-equipped buoys were made during May and June 1995, during the Combined Sensor Program of 1996 in the western tropical Pacific region, and in the Greenland Sea in May 1997. The Gulf Stream and Greenland Sea deployments pointed out the need for design modifications to improve resistance to seabird attacks. Better estimates of performance and limitations of this device require extended intercomparison tests under field conditions.

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A. B. White
,
M. L. Anderson
,
M. D. Dettinger
,
F. M. Ralph
,
A. Hinojosa
,
D. R. Cayan
,
R. K. Hartman
,
D. W. Reynolds
,
L. E. Johnson
,
T. L. Schneider
,
R. Cifelli
,
Z. Toth
,
S. I. Gutman
,
C. W. King
,
F. Gehrke
,
P. E. Johnston
,
C. Walls
,
D. Mann
,
D. J. Gottas
, and
T. Coleman

Abstract

During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount concern to California, where aging water supply and flood protection infrastructures are challenged by increased standards for urban flood protection, an unusually variable weather regime, and projections of climate change. Additionally, there are inherent conflicts between releasing water to provide flood protection and storing water to meet requirements for the water supply, water quality, hydropower generation, water temperature and flow for at-risk species, and recreation. To improve reservoir management and meet the increasing demands on water, improved forecasts of precipitation, especially during extreme events, are required. Here, the authors describe how California is addressing their most important and costliest environmental issue—water management—in part, by installing a state-of-the-art observing system to better track the area’s most severe wintertime storms.

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