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David A. Barber and Larry J. Mahrt

Abstract

Rawinsonde observations taken during the National Hail Research Experiment are analyzed by multiple-linear regression techniques to study the influence of environmental factors on hailstorm severity. The latter is inferred from integrated radar returns. The roles of mixed-layer flow and thermodynamic properties as well as upper tropospheric kinematic properties are emphasized. The low-level properties are found to be more important discriminators of storm severity over the High Plains.

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David A. Barber, Jerry M. Davis, and Allen J. Riordan

Abstract

A substantial decline in North American cyclone and anticyclone activity has been documented by several recent studies based on counts of disturbance tracks. An independent method of assessing long-term trends in synoptic-scale activity based on sequential spectral analysis of station pressure is suggested. The efficacy of this approach is supported by previous studies relating the spatial distribution of variance of band-pass filtered pressures to preferred cyclone tracks. However, examples of a preliminary application of the spectral method to three widely separated stations using approximately 30 years of winter data fail to reveal any significant long-term trends in the variance of pressure for synoptic-scale time periods.

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Alex D. Crawford, Erika A. P. Schreiber, Nathan Sommer, Mark C. Serreze, Julienne C. Stroeve, and David G. Barber

Abstract

Lagrangian detection and tracking algorithms are frequently used to study the development, distribution, and trends of extratropical cyclones. Past research shows that results from these algorithms are sensitive to both spatial and temporal resolutions of the gridded input fields, with coarser resolutions typically underestimating cyclone frequency by failing to capture weak, small, and short-lived systems. The fifth-generation atmospheric reanalysis from the European Centre for Medium-Range Weather Forecasts (ERA5) offers finer resolution, and, therefore, more precise information regarding storm locations and development than previous global reanalyses. However, our sensitivity tests show that using ERA5 sea level pressure fields at their finest-possible resolution does not necessarily lead to better cyclone detection and tracking. If a common number of nearest neighbors is used when detecting minima in sea level pressure (like past studies), finer spatial resolution leads to noisier fields that unrealistically break up multicenter cyclones. Using a common search distance instead (with more neighbors at finer resolution) resolves the issue without smoothing inputs. Doing this also makes cyclone frequency, life span, and average depth insensitive to refining spatial resolution beyond 100 km. Results using 6- and 3-h temporal resolutions have only minor differences, but using 1-h temporal resolution with a maximum allowed propagation speed of 150 km h−1 leads to unrealistic track splitting. This can be counteracted by increasing the maximum propagation speed, but modest sensitivity to temporal resolution persists for several cyclone characteristics. Therefore, we recommend caution if applying existing algorithms to temporal resolutions finer than 3 h and careful evaluation of algorithm settings.

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