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Andrew J. Weinheimer

Abstract

The solution of the electrostatic boundary value problem for a point charge inside an infinite cylinder is applied to sensors employed in the measurement of charge on precipitation. With these devices the charge induced on a cylindrical segment is measured and must then be related to the actual charge on the particle. This induced charge depends upon the axis ratio of the cylindrical segment and upon the location of the point charge. Here the fractional induced charge is computed for a number of cases: 1) point charge at the centers of cylindrical segments of various axis ratios; 2) point charges moving along the axes of cylinders with axis ratios of 0.25, 0.5, 1.0, and 2.0; and 3) charges moving parallel to but off of the axis of a cylinder with an axis ratio of 1.0. In addition, the effect of the measuring electronics is computed for certain cases. Numerical results such as these will find application in the design of charge sensors, and in some cases may even suffice for their calibration.

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Andrew J. Weinheimer

Abstract

The measured drag forces on cylinders and disks obtained by Jayaweera and Cottis and by Kajikawa are compared with those computed for Stokes flow around equivalent spheroids. For both the disks and cylinders, comparisons an made both for flow parallel to and perpendicular to the solids' symmetry axes. The ratios of measured to Stokes drag forces range from 0.59 to 1.14 and cover Reynolds numbers ranging from 1.6 × 10−3 to 2.0 × 10−1. Thus these results allow for the convenient calculation, using the Stokes drag expression, of the terminal velocities of ice crystals falling in the atmosphere with major dimensions of up to a few tens of microns.

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Andrew J. Weinheimer

Abstract

The magnitude of the electro-optical Kerr effect in the atmosphere is assessed with an eye toward employing it in the measurement of humidity and electric fields. For various conditions, the birefringence of air is computed along with the attendant phase shift for light waves with polarizations parallel and perpendicular to a static electric field. For most cases this phase shift and its variation are so small as to render the proposed measurements unfeasible. This is based on an assumed resolution of 2 × 10−8 for measured values of phase shift.

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Andrew J. Weinheimer
and
Ronald L. Schwiesow

Abstract

An ultraviolet-absorption hygrometer for airborne use was designed and tested. Here the principles of operation, the design, and the results of the first test flights are presented. The motivation for the new design is to overcome the shortcomings of existing Lyman-α devices. To solve the problem of source drift, a second optical path is employed as a reference. To address the problem of window contamination, a second ultraviolet wavelength is used. In addition, detector offsets are measured and subtracted from the signals. The flight data clearly demonstrate the value of both the reference detector and the second wavelength.

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Andrew J. Weinheimer
and
Charles A. Knight

Abstract

A new explanation is proposed for the rare Scheiner's halo, observed in the sky at an angle of 28° from the sun or moon. The existing explanation invokes the presence in the atmosphere of the cubic form of ice, ice Ic. However, extensive laboratory work has not demonstrated that ice Ic can form under conditions found in the atmosphere. We point out an alternative, that polycrystals of ice Ih (the ordinary hexagonal polymorph), in which specific orientation relations exist between adjacent crystals, are another possible cause of Scheiner's halo. Polycrystals with the appropriate orientation relation are not uncommon in the atmosphere, but concentrations sufficient to produce optical effects are expected to be rare. There appears to be no decisive evidence to rule out either of these explanations.

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L. Jay Miller
,
Carl G. Mohr
, and
Andrew J. Weinheimer

Abstract

Periodic sampling of the Doppler radar return signal at the pulse repetition frequency causes measured velocities to be ambiguous (folded) when true meteorological velocities along the radial direction exceed the Nyquist or folding value. Furthermore, mean radial velocity estimates become more uncertain as the spatial variability of velocity increases or the returned signal strength decreases. These data have conventionally been prepared for such uses as multiple-Doppler radar wind synthesis by unfolding and editing them in the sampling domain (range-azimuth-elevation spherical coordinates).

An alternative method of locally (to the output grid point) unfolding the unedited radial velocities during their linear interpolation to a regular Cartesian grid is presented. The method preserves the spatial discontinuities of order twice the Nyquist value associated with velocity folding. A nondimensional velocity quality parameter is also computed which serves to identify interpolated values that contain too much variance to be reliable. Editing of radar data is thereby postponed until all radar data are mapped to the analysis coordinate system. This allows for iterative global unfolding and multiple-Doppler synthesis of complicated convective storm flow patterns. The resolution of folding in such flow fields may require more information than is usually available from single radar radial velocity fields in spherical coordinates. Further, the amount of data that must be subsequently manipulated is reduced about ten-fold in the process of interpolation.

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Christopher P. Loughner
,
Maria Tzortziou
,
Melanie Follette-Cook
,
Kenneth E. Pickering
,
Daniel Goldberg
,
Chinmay Satam
,
Andrew Weinheimer
,
James H. Crawford
,
David J. Knapp
,
Denise D. Montzka
,
Glenn S. Diskin
, and
Russell R. Dickerson

Abstract

Meteorological and air-quality model simulations are analyzed alongside observations to investigate the role of the Chesapeake Bay breeze on surface air quality, pollutant transport, and boundary layer venting. A case study was conducted to understand why a particular day was the only one during an 11-day ship-based field campaign on which surface ozone was not elevated in concentration over the Chesapeake Bay relative to the closest upwind site and why high ozone concentrations were observed aloft by in situ aircraft observations. Results show that southerly winds during the overnight and early-morning hours prevented the advection of air pollutants from the Washington, D.C., and Baltimore, Maryland, metropolitan areas over the surface waters of the bay. A strong and prolonged bay breeze developed during the late morning and early afternoon along the western coastline of the bay. The strength and duration of the bay breeze allowed pollutants to converge, resulting in high concentrations locally near the bay-breeze front within the Baltimore metropolitan area, where they were then lofted to the top of the planetary boundary layer (PBL). Near the top of the PBL, these pollutants were horizontally advected to a region with lower PBL heights, resulting in pollution transport out of the boundary layer and into the free troposphere. This elevated layer of air pollution aloft was transported downwind into New England by early the following morning where it likely mixed down to the surface, affecting air quality as the boundary layer grew.

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Mary C. Barth
,
Christopher A. Cantrell
,
William H. Brune
,
Steven A. Rutledge
,
James H. Crawford
,
Heidi Huntrieser
,
Lawrence D. Carey
,
Donald MacGorman
,
Morris Weisman
,
Kenneth E. Pickering
,
Eric Bruning
,
Bruce Anderson
,
Eric Apel
,
Michael Biggerstaff
,
Teresa Campos
,
Pedro Campuzano-Jost
,
Ronald Cohen
,
John Crounse
,
Douglas A. Day
,
Glenn Diskin
,
Frank Flocke
,
Alan Fried
,
Charity Garland
,
Brian Heikes
,
Shawn Honomichl
,
Rebecca Hornbrook
,
L. Gregory Huey
,
Jose L. Jimenez
,
Timothy Lang
,
Michael Lichtenstern
,
Tomas Mikoviny
,
Benjamin Nault
,
Daniel O’Sullivan
,
Laura L. Pan
,
Jeff Peischl
,
Ilana Pollack
,
Dirk Richter
,
Daniel Riemer
,
Thomas Ryerson
,
Hans Schlager
,
Jason St. Clair
,
James Walega
,
Petter Weibring
,
Andrew Weinheimer
,
Paul Wennberg
,
Armin Wisthaler
,
Paul J. Wooldridge
, and
Conrad Ziegler

Abstract

The Deep Convective Clouds and Chemistry (DC3) field experiment produced an exceptional dataset on thunderstorms, including their dynamical, physical, and electrical structures and their impact on the chemical composition of the troposphere. The field experiment gathered detailed information on the chemical composition of the inflow and outflow regions of midlatitude thunderstorms in northeast Colorado, west Texas to central Oklahoma, and northern Alabama. A unique aspect of the DC3 strategy was to locate and sample the convective outflow a day after active convection in order to measure the chemical transformations within the upper-tropospheric convective plume. These data are being analyzed to investigate transport and dynamics of the storms, scavenging of soluble trace gases and aerosols, production of nitrogen oxides by lightning, relationships between lightning flash rates and storm parameters, chemistry in the upper troposphere that is affected by the convection, and related source characterization of the three sampling regions. DC3 also documented biomass-burning plumes and the interactions of these plumes with deep convection.

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