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Robert M. Cunningham

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Robert M. Cunningham

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Robert M. Cunningham
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Robert M. Cunningham
and
Frederick Sanders

Abstract

The afternoon of 30 December 1962 saw the nearly simultaneous arrival at Grand Manan (an island in the Bay of Fundy) of an intense cold front, accompanied by northwesterly gales and snow, and an intense small cyclonic vortex, producing a mild southeasterly gale. Surprisingly, the cold front arrived first, having advanced over the preceding 9 hours against a geostrophic flow increasing from a few meters per second to about 40 m s−1. The mild air returned for about 2 h as the vortex passed across the Grand Manan prior to the final arrival of the mass of cold air. The frontal oscillation was marked by temperature changes from 3°C to −9°C to 3°C to −12°C, within 6 h. There was only a single, strongly defined, low-pressure center.

A simplistic model of the ageostrophic response to geostrophic frontogenetical forcing, neglecting the effects of friction and stratification, shows more than enough ageostrophic flow to account for the observations. Comparison with physically more satisfying models supports the conclusion that this anomalous frontal behavior was the consequence of ageostrophic response to geostrophic forcing acting on an already-intense horizontal temperature gradient, exacerbated by the coincidental approach of an intense cyclone. This comparison also indicates, however, that semigeostrophic theory is not quantitatively reliable when applied to even moderately strong fronts in the real atmosphere.

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Capt. Edward J. Dolezel, A.C.
,
Robert M. Cunningham
, and
Robert E. Katz

This paper presents a non-technical survey of the research being done on the meteorological aspects of aircraft icing. The organization of the program and functions of four installations in the U. S. are indicated. After a short qualitative discussion of the flow around cylinders, several new specialized instruments are described, and some of the theory developed to interpret their data is treated briefly.

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Lindsey M. Richardson
,
Jeffrey G. Cunningham
,
W. David Zittel
,
Robert R. Lee
,
Richard L. Ice
,
Valery M. Melnikov
,
Nicole P. Hoban
, and
Joshua G. Gebauer

Abstract

Studies have shown that echo returns from clear-air Bragg scatter (CABS) can be used to detect the height of the convective boundary layer and to assess the systematic differential reflectivity (Z DR) bias for a radar site. However, these studies did not use data from operational Weather Surveillance Radar-1988 Doppler (WSR-88D) or data from a large variety of sites. A new algorithm to automatically detect CABS from any operational WSR-88D with dual-polarization capability while excluding contamination from precipitation, biota, and ground clutter is presented here. Visual confirmation and tests related to the sounding parameters’ relative humidity slope, refractivity gradient, and gradient Richardson number are used to assess the algorithm. Results show that automated detection of CABS in operational WSR-88D data gives useful Z DR bias information while omitting the majority of contaminated cases. Such an algorithm holds potential for radar calibration efforts and Bragg scatter studies in general.

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Lindsey M. Richardson
,
W. David Zittel
,
Robert R. Lee
,
Valery M. Melnikov
,
Richard L. Ice
, and
Jeffrey G. Cunningham

Abstract

Clear-air Bragg scatter (CABS) is a refractivity gradient return generated by turbulent eddies that operational Weather Surveillance Radar-1988 Doppler (WSR-88D) systems can detect. The randomly oriented nature of the eddies results in a differential reflectivity (Z DR) value near 0 dB, and thus CABS can be used as an assessment of Z DR calibration in the absence of excessive contamination from precipitation or biota. An automated algorithm to estimate Z DR bias from CABS was developed by the Radar Operations Center and can be used to assess the calibration quality of the dual-polarized WSR-88D fleet. This technique supplements existing Z DR bias assessment tools, especially the use of other external targets, such as light rain and dry snow.

The estimates of Z DR bias from CABS using a 1700–1900 UTC time window were compared to estimates from the light rain and dry snow methods. Output from the automated CABS algorithm had approximately the same amount of bias reported as the light rain and dry snow estimates (within ±0.1 dB). As the 1700–1900 UTC time window appeared too restrictive, a modified version of the algorithm was tested to detect CABS diurnally on a volume-by-volume basis (continuous monitoring). Continuous monitoring resulted in a two- to fourfold increase in the number of days with CABS detections. Results suggest estimates from CABS are viable for many sites throughout the year and provide an important addition to existing bias estimation techniques.

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M. Susan Lozier
,
Sheldon Bacon
,
Amy S. Bower
,
Stuart A. Cunningham
,
M. Femke de Jong
,
Laura de Steur
,
Brad deYoung
,
Jürgen Fischer
,
Stefan F. Gary
,
Blair J. W. Greenan
,
Patrick Heimbach
,
Naomi P. Holliday
,
Loïc Houpert
,
Mark E. Inall
,
William E. Johns
,
Helen L. Johnson
,
Johannes Karstensen
,
Feili Li
,
Xiaopei Lin
,
Neill Mackay
,
David P. Marshall
,
Herlé Mercier
,
Paul G. Myers
,
Robert S. Pickart
,
Helen R. Pillar
,
Fiammetta Straneo
,
Virginie Thierry
,
Robert A. Weller
,
Richard G. Williams
,
Chris Wilson
,
Jiayan Yang
,
Jian Zhao
, and
Jan D. Zika

Abstract

For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.

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