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  • Author or Editor: Bruce C. Macdonald x
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Bruce C. Macdonald and Elmar R. Reiter


Cases of explosive cyclogenesis (“bombs”) were identified over the central and eastern United States and were compared with nonexplosive cyclone development in the same region. The tendency equations for vorticity and geopotential thickness, and a modified divergence equation were used to find signatures of distinction between these two types of cyclogenesis, whose recognition might improve forecasting skills.

Bombs tend to show a marked decrease of vorticity with height during their incipient and explosive stages, whereas regular cyclones reveal only weak vertical vorticity gradients in the troposphere. The low-tropospheric spin-up in bombs precedes significantly that in the upper troposphere. Preexisting low-tropospheric vorticity maxima are associated with low-level jet streaks.

Whereas regular cyclones possess an ill-defined level of nondivergence (i.e., a broad region between 800 and 400 mb, of divergence values close to zero), incipient bombs have a well-marked zero-divergence level near 500 mb, associated with a sharp maximum of rising motions.

We observed a marked increase in large-scale latent beat release between the incipient and the explosive phases of bomb development. The convective component of latent beating shows a distinct maximum in the incipient phase of bombs and a decrease which continues through the explosive and mature phases. Regular cyclones show much less heating and much less change between the phases of development than is observed with the bombs. Static stability reveals little change as the bomb grows and mature. There also is little difference between the stability associated with bombs and regular cyclones.

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Armin Sorooshian, Bruce Anderson, Susanne E. Bauer, Rachel A. Braun, Brian Cairns, Ewan Crosbie, Hossein Dadashazar, Glenn Diskin, Richard Ferrare, Richard C. Flagan, Johnathan Hair, Chris Hostetler, Haflidi H. Jonsson, Mary M. Kleb, Hongyu Liu, Alexander B. MacDonald, Allison McComiskey, Richard Moore, David Painemal, Lynn M. Russell, John H. Seinfeld, Michael Shook, William L. Smith Jr, Kenneth Thornhill, George Tselioudis, Hailong Wang, Xubin Zeng, Bo Zhang, Luke Ziemba, and Paquita Zuidema


We report on a multiyear set of airborne field campaigns (2005–16) off the California coast to examine aerosols, clouds, and meteorology, and how lessons learned tie into the upcoming NASA Earth Venture Suborbital (EVS-3) campaign: Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE; 2019–23). The largest uncertainty in estimating global anthropogenic radiative forcing is associated with the interactions of aerosol particles with clouds, which stems from the variability of cloud systems and the multiple feedbacks that affect and hamper efforts to ascribe changes in cloud properties to aerosol perturbations. While past campaigns have been limited in flight hours and the ability to fly in and around clouds, efforts sponsored by the Office of Naval Research have resulted in 113 single aircraft flights (>500 flight hours) in a fixed region with warm marine boundary layer clouds. All flights used nearly the same payload of instruments on a Twin Otter to fly below, in, and above clouds, producing an unprecedented dataset. We provide here i) an overview of statistics of aerosol, cloud, and meteorological conditions encountered in those campaigns and ii) quantification of model-relevant metrics associated with aerosol–cloud interactions leveraging the high data volume and statistics. Based on lessons learned from those flights, we describe the pragmatic innovation in sampling strategy (dual-aircraft approach with combined in situ and remote sensing) that will be used in ACTIVATE to generate a dataset that can advance scientific understanding and improve physical parameterizations for Earth system and weather forecasting models, and for assessing next-generation remote sensing retrieval algorithms.

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