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LARRY L. WENDELL

Abstract

Techniques are developed to utilize wind data from a network of stations to study mesoscale flow patterns and transport in the lower planetary boundary layer. The data sample for this study is hourly averaged wind data for the year 1969 from 21 stations over the Upper Snake River Plain of southeastern Idaho. Examination of 6-hourly wind field plots for the entire year reveals a strong correlation of the flow patterns with a topographic variation of relatively minor amplitude. Plots of patterns of trajectories of hypothetical “particles” released once an hour from a single location for the entire year are typed according to season and release period during the day. These patterns provide an estimate of a transport climatology; a climatology not available from a wind rose at the source. Evidence is presented that demonstrates that estimates of transport from the source wind can be seriously in error due to marked spatial variations in the flow.

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S-K. Kao and Larry L. Wendell

Abstract

The wavenumber-frequency spectra of the kinetic energy of the zonal and meridional components of the motion at 100, 200 and 500 mb, at 20, 40, 60 and 8ON, show a definite spectral domain of wave activities in the atmosphere. In middle latitudes, the spectral domain is oriented from a region of low wavenumbers and low frequencies to a region of high wavenumbers and negative frequencies designated for waves moving from west to east. In high latitudes, the domain of wave activities is confined to a region of low wavenumbers and low frequencies. In low latitudes, however, there exist two domains, one similar to that in the middle latitude and the other occurring in a narrow band centered near zero frequency in the medium wavenumber range.

The frequency spectra of the kinetic energy of the zonal motion show similar distributions at all levels and seasons, and are approximately proportional to the minus first power of the frequency in low latitudes but are proportional to the minus second power of the frequency in high latitudes. The wavenumber spectra of the zonal motion a1so show similar distributions at all levels and seasons, and are approximately proportional to the minus third power of the wavenumber in the high wavenumber range. The wavenumber spectra of the meridional motion show an energy peak in the wavenumber range k = 4–10. Again, in the high wavenumber range, the power spectra of the meridional motion are approximately proportional to the minus third power of the wavenumber.

The mean kinetic energy of the zonal motion shows a maximum near 4ON at all levels and seasons, except at 100 mb in the summer where it occurs near 20N. The distribution of the mean kinetic energy of the moving waves indicates a definite shift in the region of wave activities with height; the maximum wave activity occurs near 60N in the troposphere, near 4ON at the tropopause level, and near 6ON in the stratosphere. In winter, the mean kinetic energy of the meridional motion shows a great deal of energy in high latitudes, caused primarily by the winter instability of the polar vortex in the stratosphere.

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G. E. Start, C. R. Dickson, and L. L. Wendell

Abstract

An accelerated field measurements program was conducted to quantify atmospheric diffusion within a deep, steep-walled canyon in rough, mountainous terrain. Two principle objectives were pursued: impaction of plumes upon elevated terrain, and diffusion of gases within the canyon versus diffusion over flat, open terrain. Oil fog flow visualizations provided qualitative information; quantitative diffusion measurements were obtained using sulfur hexafluoride gas with analysis by highly sensitive gas phase coulometric techniques. Eleven 45 to 60 min gaseous tracer releases were conducted.

Stability-category-related differences in canyon diffusion versus flat terrain diffusion were found. Daytime lapse conditions showed little difference. Neutral stability tests showed five times greater dilution for canyon axial concentrations; strong inversion tests resulted in canyon plume centerline dilutions fifteen times greater than calculations using parameters derived for flat terrain. Plume effluents frequently impacted against elevated terrain.

Enhanced mechanical turbulence associated with gradient wind-flows near the mountain tops, density flows originating in side canyons, and turbulent wakes from pronounced terrain irregularities within the canyon are believed to be some of the additional physical mechanisms affecting plume dilutions in Huntington Canyon.

The present results should be relevant, at least qualitatively, to similar deep, steep-walled canyons. They should not be applied indiscriminantly to sites with less extreme topography. Additional measurements are needed at sites in less rugged terrain.

Highly buoyant plumes may require special study since buoyancy may be in competition with postulated effects from the enhanced mechanical turbulence observed within the rough terrain setting.

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J. C. Barnard, L. L. Wendell, and V. R. Morris

Abstract

The output of pulsed and AC output anemometers suffer from discretization noise when such anemometers are sampled at fast rates (>1 Hz). This paper describes the construction of an optimal filter designed to reduce this noise. By comparing the filtered output from an AC output cup anemometer with a nearby cup anemometer whose output is free from discretization noise, it is shown that the filter significantly reduces the noise. Wind speed time series obtained from the two anemometers are quite similar. Next, deconvolution is applied to the filtered time series to account for the anemometer response. Spectra from the deconvolved time series and a time series measured by a nearby sonic anemometer are compared, and for high-speed flows the spectra from the two instruments match quite well. The time series are also very similar; however, the cup anemometer generally cannot respond to the quick bursts of speed seen by the sonic anemometer. The filtering and deconvolution methods presented here are most appropriate for the high-speed flows relevant to wind energy studies. These methods make it possible to use inexpensive, rugged cup anemometers to measure a high-speed, turbulent wind field up to a frequency of about 5 Hz.

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James D. Irish, Wendell S. Brown, and Thomas L. Howell

Abstract

Geophysical signals are often intermittent, having statistics which vary with time. Optimal sampling of these signals requires a so-called “conditional sampling” scheme, a technique which changes the sampling program to match the time scales of the processes of interest. To optimize the limited tape storage capacity of remote oceanographic instruments, a conditional sampling scheme has been implemented using the computational power of microprocessor-controlled instruments, and several deployments have been made with various configurations of the conditional sampling algorithm. This algorithm monitors short-term changes in the energy of an incoming signal within a designated high-frequency band (by digital filtering techniques) and compares the resulting intensity with the longer term statistics of the signal. If the energy exceeds an intensity defined as critical according to some criteria, then an “event” is declared and the data are recorded at a higher than normal rate for the duration of the event. When the statistics of the expected signals are not well known, and criteria cannot be predetermined with confidence, an “adaptive” technique is required whereby the instrument makes an in situ determination of the critical intensity level for each signal based on the statistics of that signal.

Several deployments of the conditional sampling instruments have been made which demonstrate the operation of the technique. In Massachusetts Bay, a burst of high-frequency internal wave energy was identified and recorded by the adaptive critical algorithm applied to a moored temperature sensor array. On the northern California shelf, salinity was calculated in situ from moored temperature and conductivity sensors, and the resulting salinity time series conditionally sampled to identify salinity events as separate from temperature or pressure events.

Conditional sampling techniques may not be optimum for exploratory work. However, where the processes and expected signals are intermittent and have a specific signature, then the use of a conditional sampling technique can make more efficient use of the limited storage capacity of remote instrumentation.

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S-K. Kao, C. Y. Tsay, and Larry L. Wendell

Abstract

The wavenumber-frequency spectra of the meridional transport of angular momentum at 100, 200 and 500 mb, at 20, 40, 60 and 80N, show that there exist definite spectral domains of wave interactions between the zonal and meridional velocities at various latitudes. In the middle latitudes near 40N, the spectral band of the meridional transport of angular momentum is oriented from a region of low wavenumbers and low frequencies to a region of high wavenumbers and negative frequencies designated for eastward-moving waves. In low latitudes, however, the spectral band is confined to a narrow band centered near zero frequency.

An analysis of the linear and nonlinear contributions to the meridional transport of angular momentum in various wavenumber-frequency domains indicates that in the mid-troposphere the primary contribution to the nonlinear interactions always involves the interactions of the spectral domain of concern with the mean zonal flow and the stationary planetary waves. It is also found that except in the domain of low-frequency, eastward-moving cyclone waves the following characteristics are in common. 1) the meridional transport of angular momentum is directed toward the north pole; 2) the resultant of the nonlinear interactions due to the longitudinal convergence of the transport provides a poleward flux of angular momentum in the domains of eastward-moving waves, but provides an equatorward transport in the domains of westward-moving waves; 3) the resultant of the nonlinear interactions due to the latitudinal convergence of the transport generally contributes a poleward transport of angular momentum in the domains of westward-moving waves, but contributes an equatorward transport in the domains of eastward-moving waves; 4) the ageostrophic effect always counteracts the nonlinear interactions due to the longitudinal convergence of the transport of angular momentum; and 5) the effects of eddy and molecular stress forces generally work against the ageostrophic effect.

The frequency spectra of the meridional transport of angular momentum indicate that: 1) in the summer most of the transport is accomplished by the moving waves, the eastward-moving waves contributing to most of the poleward transport, and the westward-moving waves to the equatorward transport; 2) in the winter most of the transport is accomplished by the stationary waves, and both the eastward- and westward- moving waves contribute to the poleward transport of angular momentum.

The wavenumber spectra of the transport of angular momentum indicate that in both the summer and winter seasons waves of practically all wavelengths in low and middle latitudes contribute to the poleward transport of angular momentum. In high latitudes, however, only the very long waves contribute to the equatorward transport of angular momentum.

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S. Kinne, T. P. Ackerman, M. Shiobara, A. Uchiyama, A. J. Heymsfield, L. Miloshevich, J. Wendell, E. Eloranta, C. Purgold, and R. W. Bergstrom

Abstract

Measurements from the FIRE 1991 cirrus cloud field experiment in the central United States are presented and analyzed.

The first part focuses on cirrus microphysical properties. Aircraft 2D-probe in situ data at different cloud altitudes were evaluated for cirrus cases on four different days. Also presented are simultaneous data samples from balloonborne videosondes. Only these balloonsondes could detect the smaller crystals. Their data suggest (at least for midlatitude altitudes below 10 km) that ice crystals smaller than 15 μm in size are rare and that small ice crystals not detected by 2D-probe measurements are radiatively of minor importance, as overlooked 2D-probe crystals account for about 10% of the total extinction.

The second part focuses on the link between cirrus cloud properties and radiation. With cloud macrophysical properties from surface remote sensing added to the microphysical data and additional radiation measurements at the surface, testbeds for radiative transfer models were created. To focus on scattering processes, model evaluations were limited to the solar radiative transfer by comparing calculated and measured transmissions of sunlight at the surface.

Comparisons under cloud-free conditions already reveal a model bias of about +45 W m−2 for the hemispheric solar downward broadband flux. This discrepancy, which is (at least in part) difficult to explain, has to be accounted for in comparisons involving clouds.

Comparisons under cirrus cloud conditions identify as the major obstacle in cirrus solar radiative transfer modeling the inability of one-dimensional radiative transfer models to account for horizontal inhomogeneities. The successful incorporation of multidimensional radiative transfer effects will depend not only on better models but critically on the ability to measure and to define characteristic inhomogeneity scales of cloud fields.

The relative minor error related to the microphysical treatment is in part a reflection of the improved understanding on solar scattering on ice crystals over the last decade and of the available wealth on ice-crystal size and shape data for this study. In absence of this information, uncertainties from microphysical cirrus model assumptions will remain high.

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Elisabeth Andrews, Patrick J. Sheridan, John A. Ogren, Derek Hageman, Anne Jefferson, Jim Wendell, Andrés Alástuey, Lucas Alados-Arboledas, Michael Bergin, Marina Ealo, A. Gannet Hallar, András Hoffer, Ivo Kalapov, Melita Keywood, Jeongeun Kim, Sang-Woo Kim, Felicia Kolonjari, Casper Labuschagne, Neng-Huei Lin, AnneMarie Macdonald, Olga L. Mayol-Bracero, Ian B. McCubbin, Marco Pandolfi, Fabienne Reisen, Sangeeta Sharma, James P. Sherman, Mar Sorribas, and Junying Sun

Abstract

To estimate global aerosol radiative forcing, measurements of aerosol optical properties are made by the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL)’s Global Monitoring Division (GMD) and their collaborators at 30 monitoring locations around the world. Many of the sites are located in regions influenced by specific aerosol types (Asian and Saharan desert dust, Asian pollution, biomass burning, etc.). This network of monitoring stations is a shared endeavor of NOAA and many collaborating organizations, including the World Meteorological Organization (WMO)’s Global Atmosphere Watch (GAW) program, the U.S. Department of Energy (DOE), several U.S. and foreign universities, and foreign science organizations. The result is a long-term cooperative program making atmospheric measurements that are directly comparable with those from all the other network stations and with shared data access. The protocols and software developed to support the program facilitate participation in GAW’s atmospheric observation strategy, and the sites in the NOAA/ESRL network make up a substantial subset of the GAW aerosol observations. This paper describes the history of the NOAA/ESRL Federated Aerosol Network, details about measurements and operations, and some recent findings from the network measurements.

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Qing Wang, Denny P. Alappattu, Stephanie Billingsley, Byron Blomquist, Robert J. Burkholder, Adam J. Christman, Edward D. Creegan, Tony de Paolo, Daniel P. Eleuterio, Harindra Joseph S. Fernando, Kyle B. Franklin, Andrey A. Grachev, Tracy Haack, Thomas R. Hanley, Christopher M. Hocut, Teddy R. Holt, Kate Horgan, Haflidi H. Jonsson, Robert A. Hale, John A. Kalogiros, Djamal Khelif, Laura S. Leo, Richard J. Lind, Iossif Lozovatsky, Jesus Planella-Morato, Swagato Mukherjee, Wendell A. Nuss, Jonathan Pozderac, L. Ted Rogers, Ivan Savelyev, Dana K. Savidge, R. Kipp Shearman, Lian Shen, Eric Terrill, A. Marcela Ulate, Qi Wang, R. Travis Wendt, Russell Wiss, Roy K. Woods, Luyao Xu, Ryan T. Yamaguchi, and Caglar Yardim

Abstract

The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.

Open access