Richard Swinbank

Dynamics and predictability of large-scale, high-impact weather and climate events

In recent years, a significant number of high-impact weather and extreme climate events have inflicted catastrophic property damage, and loss of human life, around the world, and hindered socio-economic development. Improving simulation and prediction nof these events is an increasingly important requirement of npublic meteorological services. n nBased largely on an International Commission on Dynamical nMeteorology (ICDM) workshop, this timely volume covers a range of important research issues related to extreme events. Dynamical linkages between these extremes and various atmospheric and ocean phenomena are examined, including Atlantic Multi-decadal, North Atlantic, and Madden–Julian Oscillations, Annular Modes, Tropical cyclones, and Asian monsoons. This book also examines the predictability nof high-impact weather and extreme climate events on nmultiple time scales. Highlighting recent research and new advances in the field, this book enhances understanding of dynamical and physical processes associated with these events, to help Managers and policy makers make informed decisions to manage risk and prevent or mitigate disasters. It also provides guidance on future research directions for experts and young scientists. n nWritten by leading researchers in weather and climate nextremes, this comprehensive volume is ideal for professionals and policy makers working in disaster prevention and mitigation, and is a key resource for graduate students and academic researchers in atmospheric science, meteorology, climate science, and weather forecasting.

Western North American extreme heat, associated large-scale synoptic-dynamics, and performance by a climate model

Generally speaking, North American extreme hot spells are associated with large scale displacements of air masses, placing unusually warm air where it is not normally found. Examples are numerous and occur over a wide range of time scales. A lengthy heat wave affected the central United States from JuneAugust during the summer of 1980 (Karl and Quayle, 1981; Namias, 1982). An intermediate time scale event, 16-26 July 2006,affected California (and subsequently other regions of North America to the east and north Gershunov et al., 2009) Events shorter than three days, more properly called hot spells, are also of interest though three days is a commonly-used minimum period (Grotjahn and Faure, 2008, Bumbaco et al., 2013). In each case, the displacement of the hot air mass is reflected in the geopotential height fields and hence the winds. So the displacement results in a large scale pattern for several primary meteorological variables. These large scale meteorological patterns (LSMPs) will be a focus of this Chapter.

Secondary eyewall formation in tropical cyclones

Secondary eyewall formation (SEF), and the subsequent eyewall replacement cycle, are often observed in intense tropical cyclones (TCs), and its association with short-term changes in TC intensity and structure has been widely documented from aircraft observations and satellite imagery (Willoughby et al., 1982, Black and Willoughby, 1992, Willoughby and Black, 1996, Houze et al., 2006, 2007, Hawkins and Helveston, 2008, Kossin and Sitkowski, 2009, Kuo et al., 2009, Didlake and Houze, 2011, Sitkowski et al., 2011, Bell et al., 2012, Hence and Houze, 2012). A double-eyewall TC contains two concentric quasi-circular deep convective rings (inner and outer TC eyewalls) with a nearly cloud-free region (moat) between them. In most such cases, the outer eyewall is established later, with characteristics similar to the inner eyewall. A localized maximum swirling wind is often present in the outer eyewall, with its scope confined to the lower troposphere. Taking the example of a model simulation of Typhoon Sinlaku (2008), constructed by Wu et al. (2012), Fig. 13.1 demonstrates such flow characteristics in a concentric eyewall TC. For cases undergoing an eyewall replacement cycle, during which a TC usually weakens and enlarges, the inner eyewall gradually dissipates, while the outer eyewall later becomes the new primary eyewall. More recently, it has been shown that SEF is preceded by a broadening tangential wind field with small radial gradients in the storm’s outer-core region, serving as a precursory flow characteristic for SEF (Wu et al., 2012, Huang et al., 2012; hereafter WH12). Considering such temporary, but pronounced, changes in storm intensity and structure, and the lack of skill in predicting concentric-eyewall events, SEF remains an important research issue and forecast priority for the understanding of TC intensity/structure evolution. This review provides an updated summary and discussion of the literature concerned with our current understanding of the favorable conditions for, and potential mechanisms of, SEF. Because of limited or discontinuous spatial/temporal coverage of observations, studies of SEF mechanisms have mostly been based on numerical simulations. The remainder of this article is organized as follows. Section 13.2 describes the possible roles of various environmental conditions in SEF. Having considered the environmental factors that are conducive to SEF, Section 13.3 introduces a variety of internal dynamical processes suggested for SEF, such as the axisymmetrization process, energy accumulation through vortex Rossby wave activities, beta-skirt-induced energy cascade, unbalanced responses to boundary layer dynamics, and balanced response to convective heating. Finally, in Section 13.4, the merits and caveats of the various dynamical interpretations are discussed, and the remaining unresolved issues are addressed to provide guidance for future SEF research.