Passage Of Extratropical Cyclones Research Articles

Surface Impacts of Springtime Extratropical Cyclones over the Bohai Sea and Yellow Sea, East Asia

Extratropical cyclones (ETCs) are active in spring over East Asia, and their surface impacts are crucial to northeast China, the Korean Peninsula, and Japan. In this study, a total of 215 continental ETCs crossing the Bohai Sea and Yellow Sea have been identified and tracked by applying an objective algorithm to the 850 hPa relative vorticity fields from the European Centre for Medium-range Weather Forecasts interim reanalysis (ERA-Interim) in March to May from 1979 to 2018. These ETCs were then classified into three groups by considering their geographical positions of cyclogenesis and cyclone tracks. Cluster 1 refers to the commonly named Mongolian cyclones that firstly travel southeastward and then recurve eastward. These ETCs are usually associated with a southward cold wave from Siberia and Mongolia resulting in decreasing temperature and reduced moisture uptake. The ETCs in cluster 2 mainly originate over the North China Plain, the leeside of the Loess Plateau, and Taihang Mountain, while ETCs in cluster 3 originate around southwest and central China. Greater moisture uptake occurred in the warmer region of these cyclones. The surface impacts of ETCs in clusters 2 and 3 were similar although their tracks were different. The passage of ETCs in clusters 2 and 3 across the Bohai Sea and Yellow Sea was associated with a period of lower tropospheric warming followed by a period of cooling. Extreme ETCs in all the three clusters could induce strong winds, and the risk of a storm surge was higher along the west and south coasts of the Bohai Sea and the west coast of the Korean Peninsula.

Formation of Wind Gusts in an Extratropical Cyclone in Light of Doppler Lidar Observations and Large-Eddy Simulations

AbstractDamaging gusts in windstorms are represented by crude subgrid-scale parameterizations in today’s weather and climate models. This limitation motivated the Wind and Storms Experiment (WASTEX) in winter 2016–17 in the Upper Rhine Valley over southwestern Germany. Gusts recorded at an instrumented tower during the passage of extratropical cyclone “Thomas” on 23 February 2017 are investigated based on measurements of radial wind with ≈70-m along-beam spacing from a fast-scanning Doppler lidar and realistic large-eddy simulations with grid spacings down to 78 m using the Icosahedral Nonhydrostatic model. Four wind peaks occur due to the storm onset, the cold front, a precipitation line, and isolated showers. The first peak is related to a sudden drop in dewpoint and results from the downward mixing of a low-level jet and a dry layer within the warm sector characterized by extremely high temperatures for the season. While operational convection-permitting forecasts poorly predict the storm onset overall, a successful ensemble member highlights the role of upstream orography. Lidar observations reveal the presence of long-lasting wind structures that result from a combination of convection- and shear-driven instability. Large-eddy simulations contain structures elongated in the wind direction that are qualitatively similar but too coarse compared to the observed ones. Their size is found to exceed the effective model resolution by one order of magnitude due to their elongation. These results emphasize the need for subkilometer-scale measuring and modeling systems to improve the representation of gusts in windstorms.

Overview and first results of the Wind and Storms Experiment (WASTEX): a field campaign to observe the formation of gusts using a Doppler lidar

Abstract. Wind gusts are responsible for most damages in winter storms over central Europe, but capturing their small scale and short duration is a challenge for both models and observations. This motivated the Wind and Storms Experiment (WASTEX) dedicated to investigate the formation of gusts during the passage of extratropical cyclones. The field campaign took place during the winter 2016–2017 on a former waste deposit located close to Karlsruhe in the Upper Rhine Valley in southwest Germany. Twelve extratropical cyclones were sampled during WASTEX with a Doppler lidar system performing vertical scans in the mean wind direction and complemented with a Doppler C-band radar and a 200 m instrumented tower. First results are provided here for the three most intense storms and include a potential sting jet, a unique direct observation of a convective gust and coherent boundary-layer structures of strong winds.

The effect of extreme weather conditions on commercial fishing activities and vessel incidents in Atlantic Canada

Extreme weather factors, a key aspect of the commercial fishing operating environment, can present danger to fish harvesters and fishing vessels. The extreme environmental conditions in Atlantic Canada, most often associated with the passage of extratropical cyclones and icy waters, can be characterized using wind speed, precipitation, air and sea surface temperature, Laplacian of pressure, and ice presence over the study area. This research aims to identify the extreme weather conditions that may affect fishing activity levels and fishing incidents. Negative Binomial Regression, Zero-Inflated Negative Binomial Regression, Fractional Logit Regression, and Random Parameters Negative Binomial Regression were applied to recognize patterns in historical fishing activity levels, incident data, and extreme weather factors in Atlantic Canada. The results suggest that there is a strong relationship between the studied weather factors and fishing activity levels overall (extreme weather conditions usually result in decreased fishing activity levels in the study area). Furthermore, different weather factors can have different effects on various vessel sizes. Wind speed is a significant factor in determining fishing activity levels for vessels smaller than 45 feet; but activity levels of vessels larger than 45 feet are only affected by ice presence. There are correlations between harsh weather factors and fishing incidents with respect to activity levels. More specifically, incident rates (i.e. number of fishing incidents over fishing activity levels) increase with low air temperature, ice presence, strong winds, and high Laplacian of pressure. These results can help mariners and fisheries management to make more informed decisions with respect to fishing safety.

Can the CMIP5 models represent winter frontal precipitation?

Much of the day-to-day variability of rainfall in the midlatitudes is controlled by the passage of extratropical cyclones and their related fronts. A good representation of fronts and their associated rainfall in climate models is essential to have confidence in future projections of midlatitude precipitation. An objective front identification method has been applied to the data from ERA-Interim and 18 Coupled Model Intercomparison Project, version 5 (CMIP5) models and the fronts linked with daily precipitation estimates to investigate how winter front-related precipitation is represented in the models. While the front frequency is well represented, the frequency of frontal precipitation is too high and the intensity is too low, thus adding little bias to the rainfall total. Although the intensity of the modeled frontal precipitation is too low, the intensity of other precipitation is even lower; thus, the ratio of frontal precipitation to total precipitation is higher in the models than in the reanalysis.

A Climatology of Cold Air Outbreaks and Their Impact on Air–Sea Heat Fluxes in the High-Latitude South Pacific

AbstractA climatology of cold air outbreaks (CAOs) in the high latitudes of the South Pacific and an analysis of the dynamical mechanisms leading to their formation are presented. Two major and distinct regions with frequent CAOs from autumn to spring are identified: one in the Ross Sea and another in the Amundsen and Bellingshausen Seas. Using an objective method to attribute CAOs to extratropical cyclones, it is shown that about 80% of the CAOs occur in association with the cyclonic flow induced by the passage of extratropical cyclones. Based on kinematic backward trajectories it is quantified that more than 40% of the air masses leading to CAOs originate from Antarctica and descend substantially, with the Ross Ice Shelf corridor as the major pathway. CAO trajectories descending from Antarctica differ from those originating over sea ice by a much lower specific humidity, stronger diabatic cooling, and much more intense adiabatic warming, while potential vorticity evolves similarly in both categories. In winter, CAOs are the major contributor to the net turbulent heat flux off the sea ice edge and CAO frequency strongly determines its interannual variation. Wintertime variations of the frequency of extratropical cyclones are strongly imprinted on the frequency of CAOs and the net turbulent heat and freshwater fluxes. In particular, much of the precipitation associated with the passage of extratropical cyclones is compensated by intense evaporation in cyclone-induced CAOs. This highlights the dominant role of the extratropical storm track in determining the variability of the buoyancy flux forcing of the Southern Ocean.

The relationship between clouds and dynamics in Southern Hemisphere extratropical cyclones in the real world and a climate model

AbstractThe representation of clouds over the Southern Ocean in contemporary climate models remains a major challenge. A major dynamical influence on the structure of clouds is the passage of extratropical cyclones. They exert significant dynamical influences on the clouds in the dynamically active frontal regions as well as in the dynamically suppressed regions ahead and behind the cyclones. A cyclone compositing methodology is applied to a reanalysis and vertical profiles of cloudiness from CloudSat/CALIPSO to quantify the relationship between clouds and dynamics in extratropical cyclones over the Southern Ocean. It is found that the range of cloud fraction, vertical motion, and relative humidity changes considerably with height. There is a strong quasi‐linear relationship between the three variables which changes with altitude. After establishing the observed relationships, the methodology is applied to the Australian Community Climate and Earth System Simulator to evaluate the model's ability to simulate the identified cloud‐dynamics relationships. While the model is able to qualitatively reproduce the overall cloud structure, the circulation around the cyclone is generally too weak. As a result, the model fails to represent the observed cloud to dynamics relationship. This wrong relationship in the model leads to a misrepresentation of the cloud field manifested as either an error in the cloud fraction or as simulating the “right” clouds for the “wrong” reason. The result underscores the importance of relationship‐oriented model evaluation techniques over simple right or wrong assessments.

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.

Fatalities Associated with Nonconvective High-Wind Events in the United States

Abstract A database was compiled for the period 1980–2005 to assess the threat to life in the conterminous United States from nonconvective high-wind events. This study reveals the number of fatalities from these wind storms, their cause, and their unique spatial distributions. While tornadoes continue to cause the most wind-related fatalities per year, nonconvective high winds (defined as phenomena such as downslope and gap winds, gradient winds, dust storms, and winds associated with midlatitude cyclones) have the potential to fatally injure more people than thunderstorm or hurricane winds. Nonconvective wind fatalities occur more frequently in vehicles or while boating. Fatalities are most common along the West Coast and Northeast in association with passing extratropical cyclones, with fewer fatalities observed in the central United States despite this region’s susceptibility for high-wind gusts. A combination of physical and social vulnerabilities is suggested as the cause for the unique fatality distribution found. More than 83% of all nonconvective wind fatalities are associated with the passage of extratropical cyclones.

Distribution of Precipitating Clouds up to the Meso-.ALPHA. Scale in Radar Echo Composite Charts over Japan.

A radar echo composite chart (RECC) displays precipitation intensity levels in 5 × 5-km grids for a composite region of digitized radars covering more than 2 × 106 km2. Each continuous precipitation cluster in a RECC is considered a precipitating cloud (p-cloud). At around 400 km, the distribution of the horizontal scale (S) for p-clouds changes. At scales smaller than 400 km, the distribution decreases smoothly with scale. In the distributions of S and maximum precipitation intensity (A) for p-clouds, there is a peak at between 400 and 1,000 km and about 45 mm/h throughout the year. This peak results from large-scale p-clouds accompanying macro-β and meso-α-scale disturbances. From June to September over land, precipitation is concentrated at scales between 15 and 200 km and intensities exceeding 8 mm/h. This distribution results from cumulus-scale p-clouds, which include a variety of convective clouds initiated by boundary-layer processes. A third type of p-cloud, caused by air-sea interactions, appears with the cold northwesterly flow that follows the passage of extratropical cyclones, especially in winter. This type dominates the weaker intensity side of the cumulusscale p-clouds between 5 and 200 km in the precipitation distribution.

特集 日本の小氷期 日記天候記録から推定した小氷期後半の夏期気温変動

Many historical documents suggest that the climate of the Little Ice Age in Japan was cool and moist, especially in summer. Among these summers, the 1780s and 1830s might have been cooler and wetter, because severe famines due to the lack of rice production occurred frequently. The 1810s is also of great interest for the reason that this decade includes 1816 which is famous for the year without a summer in Western Europe and Eastern North America.An attempt was made to reconstruct summer temperature variations and variabilities during the Little Ice Age, especialy for the period 1771-1840, based on the daily weather records of old diaries in Japan. Comparison of summer temperatures and rainfall frequencies for the recent instrumental period reveals that they are closely related in terms of the causes for hot/cool summers over East Asia. In general, a hot and dry summer is brought by the continuous sunny weather conditiones under the influence of North Pacific High. By contrast, cool and wet summer is connected with the rainy weather conditiones caused by the passage of extratropical cyclones and polar fronts.By analyzing the correlations between the number of rainy days and the grid temperature data in August for recent years, linear regression equations were derived. Using these equations, August temperatures in Northeastern Japan and Central Japan were calculated. As a result, the 1770s, the early 1810s and the late 1830s were cool, on the other hand, the late 1790s and the late 1810s to the early 1820s were relatively warm. In Central Japan, the early 1810s and the late 1820s were somewhat cool. Reconstructed temperature series in Central Japan indicates large year-to-year variabilities for the whole period.