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R. A. McCormick and C. Xintaras

Abstract

Diurnal variations of carbon monoxide concentrations and traffic density, exemplified in the literature as common for urban areas, were observed at “curb-side” studies in Nashville, Tenn., and Cincinnati, Ohio.

A new technique is suggested for evaluating the effect of changes in traffic density on CO concentrations which may be useful for urban planning purposes and for appreciating the role wind speed can play to modify these assessments.

Peak to mean ratios of CO concentrations at Cincinnati were in the same range, 2:1–3:1, as those reported in single-source experiments in open terrain in which the source and receptor were located at the same height. In both cities, the decrease of the average ratios, χ τ/χ 60, (maximum short-period CO concentrations within the hour to the mean value over the hour) with increasing τ, proceeds at a somewhat slower rate for τ > 3 min than in single source cases. Multiple and indefinite sources of CO in the immediate area of the urban sampling sites undoubtedly account for this by providing an atmosphere which is never entirely free of CO contamination.

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G. C. McCormick, L. E. Allan, and A. Hendry

Abstract

Measurements of the backscatter matrix, including phase, have been made at 2.86 GHz on blocks of ice intended to approximate oblate and prolate spheroids with axial ratios of 0.6 and 0.8. For 2.5<ka<4.5 respective cancellation ratios in the order of 0 and 5 dB were obtained compared with Rayleigh values of 19 and 25 dB. The relevance of these and other polarization characteristics for the identification of hail is considered with examples from Ku-band radar observations.

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H. C. Yi, N. J. McCormick, and R. Sanchez

Abstract

Radiative transfer algorithms are developed to estimate the optical thickness of clouds using an irradiance detector located above, deep within, and beneath a cloud. Both monodirectional and diffuse illumination cases are considered. For each detector position, one algorithm is derived from asymptotic radiative transfer theory and another is derived from transport-corrected diffusion theory. The algorithms for an above-cloud or below- cloud detector with monodirectional illumination can be utilized without radiative transfer calculations and are much less sensitive to the phase function than a related algorithm for an above-cloud detector that requires measurements of downward and upward radiances.

Radiative transfer calculations with the FN method are used to numerically test the above-cloud detector algorithms for monodirectional illumination for the Haze-L and Fair Weather Cumulus cloud models. Both algorithms show good agreement with the FN results for optically thick clouds; the transport-corrected diffusion algorithm also agrees with the FN method for optically thin clouds, but is less accurate for intermediate cloud thicknesses than the asymptotic algorithm.

An error analysis for the above-cloud detector algorithms is included that confirms the difficulty of estimating the optical thickness if the surface albedo is close to an “exclusion” albedo, which is the irradiance ratio for a semi-infinite cloud for the transport-corrected diffusion algorithm or a value close to it for the asymptotic algorithm. A sensitivity analysis provides a means to estimate retrieval ranges for the algorithms and it shows that these ranges dramatically increase as the cloud absorption decreases. The useful retrieval range generally tends to be broader for non-normal incident illumination directions. The general trends of the sensitivity analysis also are applicable to the estimation of optical thickness using the bidirectional reflection function.

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A. Hendry, G. C. McCormick, and B. L. Barge

Abstract

Measurements are presented of the extent to which a common alignment of hydrometeors exists in various forms of precipitation. The observations, obtained with circularly-polarized radars situated at Penhold, Alberta and Ottawa, Ontario, were made at wavelengths of 10.4 and 1.82 cm respectively. Good agreement between results obtained at these two wavelengths was found for observations made on similar classes of precipitation. The degree of preferred alignment is high (typically 75%) in moderate or heavy rain; the presence of ice-phase hydrometeors is usually associated with a low degree of orientation. The degree of orientation, in conjunction with other parameters, is useful for the identification of the precipitation particles. Limitations on its usefulness imposed by propagation effects and by multiple scattering are discussed briefly.

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E. C. Flowers, R. A. McCormick, and K. R. Kurfis

Abstract

Five years of turbidity measurements from a network of stations in the United States are analyzed. Measurements are made with the Volz sunphotometer; the instrumentits calibration, and its use are described. The relationship of these measurements to those of Linke and Ångström is briefly discussed. Analysis of the data indicates the following: 1) an annual mean pattern of low turbidity (near 0.05) over the western plains and Rocky Mountains and high turbidity (near 0.14) in the east; 2) observed minimum turbidity near 0.02; 3) an annual cycle of low turbidity in winter and high in summer; 4) lowest turbidity in continental polar air masses and highest in maritime tropical; and 5) no noticeable lowering of turbidity following precipitation.

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G. S. Kent, C. R. Trepte, U. O. Farrukh, and M. P. McCormick

Abstract

Aerosol extinction data obtained by the Stratospheric Aerosol Measurement II (SAM II) satellite instrument during the 1979/80 Northern Hemisphere winter season have been analyzed in relation to the cyclonic polar vortex. A synoptic approach has been employed to study the behavior of aerosol extinction ratio and optical depth between altitudes of 8 and 30 km as a tracer of mean atmospheric motions in and near the polar vortex. As the polar vortex intensifies, a gradient of extinction ratio is established across the polar-night jet stream, which is associated with subsidence within the vortex. Maximum subsidence occurs at the center of the vortex. Calculated descent rates relative to isentropic surfaces are of the order of 8 × 10−4 m s−1 near 20 km, at the center of the vortex between September and December. Below an altitude of 14 km, taken as the base of the vortex, and outside the vortex, horizontal movements occur freely, masking any systematic vertical motions. Extinction enhancements by polar stratospheric clouds and changes produced by sudden warmings in the second half of winter have prevented a similar study for this period. An estimate of the aerosol mass transferred downward through the base of the vortex for the entire season is 7000 tonnes. Comparison of the inferred stratospheric motions with earlier studies using radioactive tracers shows good agreement.

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Mark A. Donelan, Fred W. Dobson, Hans C. Graber, Niels Madsen, and Cyril McCormick

Abstract

The design and implementation on a Small Waterline Area Twin Hull (SWATH) vessel of a complete system for measuring the directional distribution of wind waves and the concomitant fluctuations of air pressure and wind speed immediately above them are described. Data taken with the system on board the Canadian Coast Guard Ship Frederick G. Creed during the 1999 Shoaling Waves Experiment (SHOWEX) are used to calculate the wave-supported fluxes of momentum and energy between the air and the sea.

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P.B. Russell, M.P. McCormick, T.J. Swissler, W.P. Chu, J.M. Livingston, W.H. Fuller, J.M. Rosen, D.J. Hofmann, L.R. McMaster, D.C. Woods, and T.J. Pepin

Abstract

We show results from the first set of measurements conducted to validate extinction data from the satellite sensor SAM II. Dustsonde-measured number density profiles and lidar-measured backscattering profiles for two days are converted to extinction profiles using the optical modeling techniques described in the companion Paper I (Russell et al., 1981). At heights ∼2 km and more above the tropopause, the dustsonde data are used to restrict the range of model size distributions, thus reducing uncertainties in the conversion process. At all heights, measurement uncertainties for each sensor are evaluated, and these are combined with conversion uncertainties to yield the total uncertainty in derived data profiles.

The SAM II measured, dustsonde-inferred, and lidar-inferred extinction profiles for both days are shown to agree within their respective uncertainties at all heights above the tropopause. Near the tropopause, this agreement depends on the use of model size distributions with more relatively large particles (radius ≳0.6 μm) than are present in distributions used to model the main stratospheric aerosol peak. The presence of these relatively large particles is supported by measurements made elsewhere and is suggested by in situ size distribution measurements reported here. These relatively large particles near the tropopause are likely to have an important bearing on the radiative impact of the total stratospheric aerosol.

The agreement in this experiment supports the validity of the SAM II extinction data and the SAM II uncertainty estimates derived from an independent error analysis. Recommendations are given for reducing the uncertainties of future correlative experiments.

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R. A Anthes, P. A Bernhardt, Y. Chen, L. Cucurull, K. F. Dymond, D. Ector, S. B. Healy, S.-P. Ho, D. C Hunt, Y.-H. Kuo, H. Liu, K. Manning, C. McCormick, T. K. Meehan, W J. Randel, C. Rocken, W S. Schreiner, S. V. Sokolovskiy, S. Syndergaard, D. C. Thompson, K. E. Trenberth, T.-K. Wee, N. L. Yen, and Z Zeng

The radio occultation (RO) technique, which makes use of radio signals transmitted by the global positioning system (GPS) satellites, has emerged as a powerful and relatively inexpensive approach for sounding the global atmosphere with high precision, accuracy, and vertical resolution in all weather and over both land and ocean. On 15 April 2006, the joint Taiwan-U.S. Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3, hereafter COSMIC) mission, a constellation of six microsatellites, was launched into a 512-km orbit. After launch the satellites were gradually deployed to their final orbits at 800 km, a process that took about 17 months. During the early weeks of the deployment, the satellites were spaced closely, offering a unique opportunity to verify the high precision of RO measurements. As of September 2007, COSMIC is providing about 2000 RO soundings per day to support the research and operational communities. COSMIC RO data are of better quality than those from the previous missions and penetrate much farther down into the troposphere; 70%–90% of the soundings reach to within 1 km of the surface on a global basis. The data are having a positive impact on operational global weather forecast models.

With the ability to penetrate deep into the lower troposphere using an advanced open-loop tracking technique, the COSMIC RO instruments can observe the structure of the tropical atmospheric boundary layer. The value of RO for climate monitoring and research is demonstrated by the precise and consistent observations between different instruments, platforms, and missions. COSMIC observations are capable of intercalibrating microwave measurements from the Advanced Microwave Sounding Unit (AMSU) on different satellites. Finally, unique and useful observations of the ionosphere are being obtained using the RO receiver and two other instruments on the COSMIC satellites, the tiny ionosphere photometer (TIP) and the tri-band beacon.

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M. P. McCormick, D. M. Winker, E. V. Browell, J. A. Coakley, C. S. Gardner, R. M. Hoff, G. S. Kent, S. H. Melfi, R. T. Menzies, C. M. R. Piatt, D. A. Randall, and J. A. Reagan

The Lidar In-Space Technology Experiment (LITE) is being developed by NASA/Langley Research Center for a series of flights on the space shuttle beginning in 1994. Employing a three-wavelength Nd:YAG laser and a 1-m-diameter telescope, the system is a test-bed for the development of technology required for future operational spaceborne lidars. The system has been designed to observe clouds, tropospheric and stratospheric aerosols, characteristics of the planetary boundary layer, and stratospheric density and temperature perturbations with much greater resolution than is available from current orbiting sensors. In addition to providing unique datasets on these phenomena, the data obtained will be useful in improving retrieval algorithms currently in use. Observations of clouds and the planetary boundary layer will aid in the development of global climate model (GCM) parameterizations. This article briefly describes the LITE program and discusses the types of scientific investigations planned for the first flight.

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