Sting Jet Research Articles

Sting Jets in Simulations of a Real Cyclone by Two Mesoscale Models

AbstractThe existence of sting jets as a potential source of damaging surface winds during the passage of extratropical cyclones has recently been recognized. However, there are still very few published studies on the subject. Furthermore, although it is known that other models are capable of reproducing sting jets, in the published literature only one numerical model [the Met Office Unified Model (MetUM)] has been used to numerically analyze these phenomena. This article aims to improve our understanding of the processes that contribute to the development of sting jets and show that model differences affect the evolution of modeled sting jets. A sting jet event during the passage of a cyclone over the United Kingdom on 26 February 2002 has been simulated using two mesoscale models, namely the MetUM and the Consortium for Small Scale Modeling (COSMO) model, to compare their performance. Given the known critical importance of vertical resolution in the simulation of sting jets, the vertical resolution of both models has been enhanced with respect to their operational versions. Both simulations have been verified against surface measurements of maximum gusts, satellite imagery, and Met Office operational synoptic analyses, as well as operational analyses from the ECMWF. It is shown that both models are capable of reproducing sting jets with similar, though not identical, features. Through the comparison of the results from these two models, the relevance of physical mechanisms, such as evaporative cooling and the release of conditional symmetric instability, in the generation and evolution of sting jets is also discussed.

A climatology of mid-tropospheric mesoscale strong wind events as observed by the MST radar, Aberystwyth

Continuous sounding of the troposphere by the NERC Mesosphere-Stratosphere-Troposphere (MST) wind profiling radar, mid-Wales, since late 1997 provides a unique dataset with which to study the mesoscale wind field of the mid-troposphere over the United Kingdom. A wind speed probability density function (PDF) generated from 7 years of data is used to design a feature-finding algorithm to identify mesoscale strong wind events in the radar dataset. The resulting 117 events form a climatology of mesoscale strong wind features at mid-tropospheric heights over the British Isles, defined as peak wind speeds at or above the top 1% of the PDF, wind speeds exceeding the top 5% for at least 1 h, and extending over at least 1 km in depth. Plotting the location of the peak winds of these features on schematic charts of the Norwegian and Shapiro–Keyser models of cyclogenesis show these to be mainly warm sector and cold frontal in nature, with smaller numbers of tropopause folds and sting jets. Wind roses indicate a prevailing westerly direction for mid-tropospheric winds generally, but the strong wind events are distinctly different: cold frontal and warm sector events prevail from the south to southwest, tropopause folds from the northwest and sting jets from the west. The wider applicability of the results to the British Isles is established through comparison with radiosonde data from five sites covering the British Isles. Copyright © 2010 Royal Meteorological Society

Major Extratropical Cyclones of the Northwest United States: Historical Review, Climatology, and Synoptic Environment

Abstract The northwest United States is visited frequently by strong midlatitude cyclones that can produce hurricane-force winds and extensive damage. This article reviews these storms, beginning with a survey of the major events of the past century. A climatology of strong windstorms is presented for the area from southern Oregon to northern Washington State and is used to create synoptic composites that show the large-scale evolution associated with such storms. A recent event, the Hanukkah Eve Storm of December 2006, is described in detail, with particular attention given to the impact of the bent-back front/trough and temporal changes in vertical stability and structure. The discussion section examines the general role of the bent-back trough, the interactions of such storms with terrain, and the applicability of the “sting jet” conceptual model. A conceptual model of the evolution of Northwest windstorm events is presented.

The Sting Jet in a Simulated Extratropical Cyclone

The sting jet (SJ), distinguished from warm and cold conveyor belt jets, has significant impacts on our society and economy through producing damaging surface winds. The purpose of this study is to confirm two scientific hypotheses on the SJ through diagnosing the idealized numerical simulation. It is confirmed that the SJ exists and produces severe surface winds in the simulated extratropical cyclone with explosively deepening and formation of the bent-back front. It is shown that strong winds in the SJ with a speed of about 30 m s-1 are first appeared in a cloud free zone. It is further demonstrated that the SJs are located at the tip of the bent-back front and the cloud head, and to the south/southwest of the surface low center. These features are in good agreement with observations. It is also confirmed that conditional symmetric instability (CSI) exists and is associated with the strengthening of the SJs at and after the mature stage of the simulated extratropical cyclone.

Wind profiler observations of a sting jet

AbstractSome of the most damaging surface winds experienced in midlatitude cyclonic storms have been attributed to a phenomenon known as a sting jet. Previous studies have deduced how sting jets develop from their midtropospheric origin, but there have been no direct observations of these wind features in the midtroposphere. During Windstorm Jeanette on 27 October 2002, the tip of the storm's cloud head passed over a VHF wind profiler at Aberystwyth, Wales, allowing the structure of a sting jet to be measured with high spatial and temporal resolution. These observations showed a multiple slantwise structure to the sting jet region, with two tails of increased winds that persisted after the passing of the cloud head aloft. Simulations by the Met Office Unified Model (UM) showed that the slantwise structure followed θw surfaces, and that the sting jet descended along θ surfaces as it passed over the UK, accelerating and drying during its descent. The horizontal and vertical scales of the observed structures are compatible with slantwise convection releasing conditional symmetric instability within the cloud head. Further observations of the sting jet were obtained by a UHF wind profiler at Cardington in Eastern England, where the sting jet had merged with the cold conveyor belt circulating around the storm. An unstable temperature profile in the lowest kilometre over Cardington enabled damaging gusts of strong winds to be brought to the surface in convective plumes; however, this strong vertical mixing was not represented correctly in the UM. Copyright © 2009 Royal Meteorological Society

The sting at the end of the tail: Model diagnostics of fine‐scale three‐dimensional structure of the cloud head

AbstractThis is the second in a series of papers on ‘the sting at the end of the tail’—a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent‐back front of an extratropical cyclone. In the first paper the sting phenomenon was identified from a purely observational study of the great storm of October 1987. In the present paper an observationally validated forecast run from a high‐resolution numerical weather prediction model is used to examine the evolving three‐dimensional structure of the sting phenomenon. It is shown that the damaging surface winds in the October 1987 storm were due to a well‐defined mesoscale ‘sting jet’ (SJ), identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hPa. There is evidence of multiple mesoscale slantwise circulations, and the SJ appears to form within the descending part of these circulations. Air within the SJ descends to the 900 hPa level over a period of about 4 h, during which time it accelerates from less than 20 to above 45 m s−1 with extremes greater than 50 m s−1. Although the wet‐bulb potential temperature of air in the SJ remains constant during its descent to 900 hPa, evaporation leads to a reduction of up to 5 K or more in dry‐bulb potential temperature in some parts of the jet. The SJ is situated behind the primary cold front, and is distinct from the associated warm‐conveyor‐belt low‐level jet; it is also distinct from the cold‐conveyor‐belt low‐level jet which remains below and behind it as the SJ skirts the bent‐back front. © Crown copyright, 2005.