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Rajul E. Pandya and Dale R. Durran

Abstract

The dynamical processes that determine the kinematic and thermodynamic structure of the mesoscale region around 2D squall lines are examined using a series of numerical simulations. The features that develop in a realistic reference simulation of a squall line with trailing stratiform precipitation are compared to the features generated by a steady thermal forcing in a “dry” simulation with no microphysical parameterization. The thermal forcing in the dry simulation is a scaled and smoothed time average of the latent heat released and absorbed in and near the leading convective line in the reference simulation. The mesoscale circulation in the dry simulation resembles the mesoscale circulation in the reference simulation and around real squall lines; it includes an ascending front-to-rear flow, a midlevel rear inflow, a mesoscale up- and downdraft, an upper-level rear-to-front flow ahead of the thermal forcing, and an upper-level cold anomaly to the rear of the thermal forcing. It is also shown that a steady thermal forcing with a magnitude characteristic of real squall lines can produce a cellular vertical velocity field as the result of the nonlinear governing dynamics. An additional dry simulation using a more horizontally compact thermal forcing demonstrates that the time-mean thermal forcing from the convective leading line alone can generate a mesoscale circulation that resembles the circulation in the reference simulation and around real squall lines.

The ability of this steady thermal forcing to generate the mesoscale circulation accompanying squall lines suggests that this circulation is the result of gravity waves forced primarily by the low-frequency components of the latent heating and cooling in the leading line. The gravity waves in the dry and reference simulation produce a perturbed flow that advects diabatically lifted air from the leading line outward. In the reference simulation, this leads to the development of leading and trailing anvils, while in the dry simulation this produces a pattern of vertically displaced air that is similar to the distribution of cloud in the reference simulation. Additional numerical simulations, in which either the thermal forcing or large-scale environmental conditions were varied, reveal that the circulation generated by the thermal forcing shows a greater sensitivity to variations in the thermal forcing than to variations in the large-scale environment. Finally, it is demonstrated that the depth of the thermal forcing in the leading convective line, not the height of the tropopause, is the primary factor determining the height of the trailing anvil cloud.

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Rajul E. Pandya, Dale R. Durran, and Morris L. Weisman

Abstract

Midlatitude squall lines are typically trailed by a large region of stratiform cloudiness and precipitation with significant mesoscale flow features, including an ascending front to rear flow; a descending rear inflow jet; line-end vortices; and, at later times, mesoscale convective vortices. The present study suggests that the mesoscale circulation in the trailing stratiform region is primarily determined by the time-mean pattern of heating and cooling in the leading convective line. Analysis of the line-normal circulation shows that it develops as thermally generated gravity waves spread away from the leading line. Midlevel line-end vortices are the result of diabatically driven tilting of horizontal vorticity generated by the time-mean thermal forcing. In the presence of the Coriolis force, a symmetric thermal forcing generates an asymmetric stratiform circulation and a pattern of vertical displacement that resembles the comma-shaped stratiform anvil observed in real systems; this suggests that asymmetries in the cloud and circulation behind midlatitude squall lines are not necessarily the result of asymmetries in the convective leading line.

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R. E. Pandya, D. R. Smith, M. K. Ramamurthy, P. J. Croft, M. J. Hayes, K. A. Murphy, J. D. McDonnell, R. M. Johnson, and H. A. Friedman

The 11th American Meteorological Society (AMS) Education Symposium was held from 13 to 15 January 2002 in Orlando, Florida, as part of the 82nd Annual Meeting of the AMS. The theme of the symposium was “creating opportunities in educational outreach in the atmospheric and related sciences.” Drawing from traditional strengths in meteorology and numerous national recommendations, the presentations and posters of the symposium highlighted three opportunities for reform. These opportunities build on partnerships between diverse educational stakeholders, efforts to make science education more like scientific practice, and strategies that place the atmospheric sciences within a larger, multidisciplinary context that includes oceanography, hydrology, and earth-system science.

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Rajul E. Pandya, David R. Smith, Donna J. Charlevoix, Genene M. Fisher, Shirley T. Murillo, Kathleen A. Murphy, Diane M. Stanitski, and Thomas M. Whittaker
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Rajul E. Pandya, David R. Smith, Donna J. Charlevoix, Wayne Hart, Marianne J. Hayes, Shirley T. Murillo, Kathleen A. Murphy, Diane M. Stanitski, and Thomas M. Whittaker
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Rajul E. Pandya, David R. Smith, Donna J. Charlevoix, Susan Q. Foster, Robert Hart, Marianne J. Hayes, Marjorie McGuirk, Shirley T. Murillo, Kathleen A. Murphy, Diane M. Stanitski, and Thomas M. Whittaker
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R. H. Moss, S. Avery, K. Baja, M. Burkett, A. M. Chischilly, J. Dell, P. A. Fleming, K. Geil, K. Jacobs, A. Jones, K. Knowlton, J. Koh, M. C. Lemos, J. Melillo, R. Pandya, T. C. Richmond, L. Scarlett, J. Snyder, M. Stults, A. Waple, J. Whitehead, D. Zarrilli, J. Fox, A. Ganguly, L. Joppa, S. Julius, P. Kirshen, R. Kreutter, A. McGovern, R. Meyer, J. Neumann, W. Solecki, J. Smith, P. Tissot, G. Yohe, and R. Zimmerman
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R. H. Moss, S. Avery, K. Baja, M. Burkett, A. M. Chischilly, J. Dell, P. A. Fleming, K. Geil, K. Jacobs, A. Jones, K. Knowlton, J. Koh, M. C. Lemos, J. Melillo, R. Pandya, T. C. Richmond, L. Scarlett, J. Snyder, M. Stults, A. M. Waple, J. Whitehead, D. Zarrilli, B. M. Ayyub, J. Fox, A. Ganguly, L. Joppa, S. Julius, P. Kirshen, R. Kreutter, A. McGovern, R. Meyer, J. Neumann, W. Solecki, J. Smith, P. Tissot, G. Yohe, and R. Zimmerman

Abstract

As states, cities, tribes, and private interests cope with climate damages and seek to increase preparedness and resilience, they will need to navigate myriad choices and options available to them. Making these choices in ways that identify pathways for climate action that support their development objectives will require constructive public dialogue, community participation, and flexible and ongoing access to science- and experience-based knowledge. In 2016, a Federal Advisory Committee (FAC) was convened to recommend how to conduct a sustained National Climate Assessment (NCA) to increase the relevance and usability of assessments for informing action. The FAC was disbanded in 2017, but members and additional experts reconvened to complete the report that is presented here. A key recommendation is establishing a new nonfederal “climate assessment consortium” to increase the role of state/local/tribal government and civil society in assessments. The expanded process would 1) focus on applied problems faced by practitioners, 2) organize sustained partnerships for collaborative learning across similar projects and case studies to identify effective tested practices, and 3) assess and improve knowledge-based methods for project implementation. Specific recommendations include evaluating climate models and data using user-defined metrics; improving benefit–cost assessment and supporting decision-making under uncertainty; and accelerating application of tools and methods such as citizen science, artificial intelligence, indicators, and geospatial analysis. The recommendations are the result of broad consultation and present an ambitious agenda for federal agencies, state/local/tribal jurisdictions, universities and the research sector, professional associations, nongovernmental and community-based organizations, and private-sector firms.

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