Assessment of Conditional Symmetric Instability from Global Reanalysis Data

Abstract Slantwise convection, the process by which moist symmetric instability is released, has often been linked to banded clouds and precipitation, especially in frontal zones within extratropical cyclones. Studies also suggest that the latent heat release associated with slantwise convection can lead to a spinup of surface frontogenesis, which can enhance the rapid intensification of extratropical cyclones. However, most of these studies considered only local areas or short time durations. In this study, we provide a novel statistical investigation of the global climatology of the potential occurrence of slantwise convection, in terms of conditional symmetric instability, and its relationship with precipitating systems. Using the 6-hourly ERA-Interim, two different indices are calculated, namely, slantwise convective available potential energy (SCAPE) and vertically integrated extent of realizable symmetric instability (VRS), to assess the likelihood of occurrence of slantwise convection around the globe. The degree of association is quantified between these indices and the observed surface precipitation as well as the cyclone activity. The susceptibility of midlatitude cyclones to slantwise convection at different stages of their life cycle is also investigated. As compared to the nonexplosive cyclone cases, the time evolution of SCAPE and VRS within rapidly deepening cyclones exhibit higher values before, and a more significant drop after, the onset of rapid intensification, supporting the idea that the release of symmetric instability might contribute to the intensification of storms.

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Conditional Symmetric Instability: A Theory for Rainbands within Extratropical Cyclones

Mesoscale Meteorology — Theories, Observations and Models ◽

10.1007/978-94-017-2241-4_12 ◽

1983 ◽

pp. 231-245 ◽

Cited By ~ 2

Author(s):

Kerry A. Emanuel

Keyword(s):

Extratropical Cyclones ◽

Symmetric Instability ◽

Conditional Symmetric Instability

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Severe weather in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere system

10.5194/egusphere-egu2020-4968 ◽

2020 ◽

Author(s):

Paul Prikryl ◽

Vojto Rušin ◽

Pavel Šťastný ◽

Maroš Turňa ◽

Martina Zeleňáková

Keyword(s):

Solar Wind ◽

High Speed ◽

Coronal Holes ◽

Lower Thermosphere ◽

Severe Weather ◽

Lower Atmosphere ◽

Extratropical Cyclones ◽

Rapid Intensification ◽

Rainfall Events ◽

Slantwise Convection

Tropical and extratropical cyclones can intensify into the most destructive weather systems that have significant societal and economic impacts. Rapid intensification of such weather systems has been examined in the context of solar wind coupling to the magnetosphere-ionosphere-atmosphere (MIA) system. It has been shown [1,2] that explosive extratropical cyclones and rapid intensification of tropical cyclones tend to follow arrivals of high-speed solar wind when the MIA coupling is strongest. The coupling generates atmospheric gravity waves (AGWs) that propagate from the high-latitude lower thermosphere both upward and downward [3,4]. In the upper atmosphere, AGWs are observed as traveling ionospheric disturbances. In the lower atmosphere, they can reach the troposphere and be ducted [4] to low latitudes. Despite significantly reduced wave amplitude, but subject to amplification upon over-reflection in the upper troposphere, these AGWs can trigger/release moist instabilities leading to convection and latent heat release, which is the energy driving the storms. The release of conditional symmetric instability is known to initiate slantwise convection producing rain/snow bands in extratropical cyclones. Severe weather, including severe winter storms, heavy snowfall and rainfall events, have been examined in the context of MIA coupling [5]. The results indicate a tendency of significant weather events, particularly if caused by low pressure systems in winter, to follow arrivals of solar wind high-speed streams from coronal holes. In the present paper we review the published results and provide further evidence to support them. This includes the occurrence of heavy rainfall events and flash floods, as well as the rapid intensification of recent hurricanes and typhoons, with the goal to identify sources of AGWs at high latitudes that may play a role in triggering convective bursts potentially leading to such events.[1] Prikryl P., et al., J. Atmos. Sol.-Terr. Phys., 149, 219&#8211;231, 2016.[2] Prikryl P., et al., J. Atmos. Sol.-Terr. Phys., 183, 36&#8211;60, 2019.[3] Prikryl P., et al., Ann. Geophys., 23, 401&#8211;417, 2005.[4] Mayr H.G., et al., J. Geophys. Res., 89, 10929&#8211;10959, 1984.[5] Prikryl P., et al., J. Atmos. Sol.-Terr. Phys., 171, 94&#8211;110, 2018.

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Structural and Environmental Characteristics of Extratropical Cyclones Associated with Tornado Outbreaks in the Warm Sector: An Idealized Numerical Study

Monthly Weather Review ◽

10.1175/mwr-d-16-0107.1 ◽

2016 ◽

Vol 145 (1) ◽

pp. 117-136 ◽

Cited By ~ 6

Author(s):

Eigo Tochimoto ◽

Hiroshi Niino

Keyword(s):

Numerical Study ◽

Convective Available Potential Energy ◽

Environmental Parameters ◽

Reanalysis Data ◽

Extratropical Cyclones ◽

Horizontal Shear ◽

Sensitivity Experiment ◽

Moist Processes ◽

Tornado Outbreaks ◽

Composite Study

Abstract To clarify the effects of the horizontal shear of the jet stream on the structure and environment of extratropical cyclones that are accompanied by tornado outbreaks (OCs) and those that are not (NOCs), two idealized numerical experiments are performed. The experiments (OC-CTL and NOC-CTL) adopt the basic states taken from the corresponding composites of reanalysis data (JRA-55), except that the humidity field in both cases is taken from the OC composite. The simulated cyclone in OC-CTL exhibits a more meridionally elongated structure and stronger low-level wind in the southeast quadrant of the cyclone center, resulting in larger values of storm relative environmental helicity (SREH) than those in NOC-CTL. These results are consistent with the characteristics of the cyclones found for OCs and NOCs in the authors’ composite study. The distributions of surface-based convective available potential energy (SBCAPE) show no notable differences between OC-CTL and NOC-CTL, while those of CAPE based on the most unstable air parcel (MUCAPE) show some differences. A sensitivity experiment without moist processes such as condensation heating and evaporative cooling shows that the differences in the cyclone structure and environmental parameters between OCs and NOCs can be qualitatively explained by the dry dynamics. However, inclusion of moist processes results in notably larger differences.

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Geographic Shift and Environment Change of U.S. Tornado Activities in a Warming Climate

Atmosphere ◽

10.3390/atmos12050567 ◽

2021 ◽

Vol 12 (5) ◽

pp. 567

Author(s):

Zuohao Cao ◽

Huaqing Cai ◽

Guang J. Zhang

Keyword(s):

Wind Shear ◽

Convective Available Potential Energy ◽

Geographic Location ◽

Reanalysis Data ◽

Cyclonic Circulation ◽

Upward Motion ◽

Environment Change ◽

Low Level ◽

High Event ◽

The U.S

Even with ever-increasing societal interest in tornado activities engendering catastrophes of loss of life and property damage, the long-term change in the geographic location and environment of tornado activity centers over the last six decades (1954–2018), and its relationship with climate warming in the U.S., is still unknown or not robustly proved scientifically. Utilizing discriminant analysis, we show a statistically significant geographic shift of U.S. tornado activity center (i.e., Tornado Alley) under warming conditions, and we identify five major areas of tornado activity in the new Tornado Alley that were not identified previously. By contrasting warm versus cold years, we demonstrate that the shift of relative warm centers is coupled with the shifts in low pressure and tornado activity centers. The warm and moist air carried by low-level flow from the Gulf of Mexico combined with upward motion acts to fuel convection over the tornado activity centers. Employing composite analyses using high resolution reanalysis data, we further demonstrate that high tornado activities in the U.S. are associated with stronger cyclonic circulation and baroclinicity than low tornado activities, and the high tornado activities are coupled with stronger low-level wind shear, stronger upward motion, and higher convective available potential energy (CAPE) than low tornado activities. The composite differences between high-event and low-event years of tornado activity are identified for the first time in terms of wind shear, upward motion, CAPE, cyclonic circulation and baroclinicity, although some of these environmental variables favorable for tornado development have been discussed in previous studies.

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Characteristics of Extratropical Cyclones That Cause Tornadoes in Italy: A Preliminary Study

Atmosphere ◽

10.3390/atmos12020180 ◽

2021 ◽

Vol 12 (2) ◽

pp. 180

Author(s):

Eigo Tochimoto ◽

Mario Marcello Miglietta ◽

Leonardo Bagaglini ◽

Roberto Ingrosso ◽

Hiroshi Niino

Keyword(s):

Environmental Conditions ◽

Convective Available Potential Energy ◽

Static Stability ◽

Extratropical Cyclones ◽

Cool Season ◽

Southeastern Us ◽

Different Seasons ◽

The Difference ◽

Upper Level ◽

Strong Evaporation

Characteristics of extratropical cyclones that cause tornadoes in Italy are investigated. Tornadoes between 2007 and 2016 are analyzed, and statistical analysis of the associated cyclone structures and environments is performed using the JRA-55 reanalysis. Tornadoes are distributed sporadically around the cyclone location within a window of 10° × 10°. The difference in the cyclone tracks partially explains the seasonal variability in the distribution of tornadoes. The highest number of tornadoes occur south of the cyclone centers, mainly in the warm sector, while a few are observed along the cold front. Composite mesoscale parameters are examined to identify the environmental conditions associated with tornadoes in different seasons. Potential instability is favorable to tornado development in autumn. The highest convective available potential energy (CAPE) in this season is associated with relatively high-temperature and humidity at low-levels, mainly due to the strong evaporation over the warm Mediterranean Sea. Upper-level potential vorticity (PV) anomalies and the associated cold air reduce the static stability above the cyclone center, mainly in spring and winter. On average, the values of CAPE are lower than for US tornadoes and comparable with those occurring in Japan, while storm relative helicity (SREH) is comparable with US tornadoes and higher than Japanese tornadoes, indicating that the environmental conditions for Italian tornadoes have peculiar characteristics. Overall, the conditions emerging in this study are close to the high-shear, low-CAPE environments typical of cool-season tornadoes in the Southeastern US.

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Using satellite and reanalysis data to evaluate the representation of latent heating in extratropical cyclones in a climate model

Climate Dynamics ◽

10.1007/s00382-016-3204-6 ◽

2016 ◽

Vol 48 (7-8) ◽

pp. 2255-2278 ◽

Cited By ~ 17

Author(s):

Matt Hawcroft ◽

Helen Dacre ◽

Richard Forbes ◽

Kevin Hodges ◽

Len Shaffrey ◽

...

Keyword(s):

Climate Model ◽

Reanalysis Data ◽

Extratropical Cyclones ◽

Latent Heating

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Trend analysis of extratropical cyclones in long-term ERA5 data series (1950-2019)

10.5194/egusphere-egu21-8703 ◽

2021 ◽

Author(s):

Richard Blender ◽

Alexia Karwat ◽

Christian Franzke

Keyword(s):

Nearest Neighbor ◽

Climate Extremes ◽

Reanalysis Data ◽

Nearest Neighbor Search ◽

Data Series ◽

Extratropical Cyclones ◽

Weather Forecasts ◽

Neighbor Search ◽

Weather And Climate

Extratropical cyclones are the primary natural hazards affecting Europe. With the release of ERA5 reanalysis data from 1950-1978 by the European Centre for Medium-Range Weather Forecasts (ECMWF), new opportunities have arisen to investigate mid-latitude cyclones in terms of climatic features and trends in longer and higher resolution. We analyze cyclones by nearest neighbor search in 1000 hPa geopotential height minima in different high resolutions for different minimum life-times. We find an intensification of North Atlantic cyclones in 1950-2019. Short-lived cyclones grow in radius and depth. In the Mediterranean, however, long-lived cyclones have weakened; but traveled also further in 1950-2019. Additionally, we illustrate relations between cyclone tracks, radii and correlated weather and climate extremes.

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