scholarly journals Tornadogenesis in a Quasi-linear Convective System over Kanto Plain in Japan: A Numerical Case Study

2021 ◽  
Author(s):  
Eigo Tochimoto ◽  
Hiroshi Niino
Keyword(s):  
Numerical Simulation ◽  
Pressure Gradient ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Gradient Force ◽  
Convective System ◽  
Data Set ◽  
Low Level ◽  
Budget Analysis ◽  
Low Level Jet

AbstractThe environmental characteristics and formation process of a tornado spawned by a quasi-linear convective system (QLCS) over Kanto Plain, Japan, are examined using observations, a reanalysis data set, and a high-resolution numerical simulation with a horizontal grid spacing of 50 m. The QLCS environment responsible for tornadogenesis was characterized by small convective available potential energy and large storm-relative environmental helicity due to strong vertical shear associated with a low-level jet. The strong low-level jet was associated with a large zonal pressure gradient between two meridionally aligned extratropical cyclones and a synoptic-scale high-pressure system to the east. The numerical simulation reproduced the tornado in the central part of the QLCS. Before the tornadogenesis, three mesovortices developed that were meridionally aligned at 500 m height, and a rear inflow jet (RIJ) associated with relatively cold air originated from aloft and developed in the west side of the QLCS, while descending from rear to front. Tornadogenesis occurred in the southernmost mesovortex at the northern tip of the RIJ. This mesovortex induces strong low-level updrafts through vertical pressure gradient force. A circulation analysis and vorticity budget analysis for the mesovortex show that environmental crosswise vorticity in the forward inflow region east of the QLCS played a significant role in the formation of the mesovortex. The circulation analysis for the tornado shows that frictional effects contribute to the increase of circulation associated with the tornado. Moreover, environmental shear associated with horizontal and vertical shear of the horizontal wind also contribute to the circulation of the tornado.

scholarly journals The Structure, Evolution, and Dynamics of a Nocturnal Convective System Simulated Using the WRF-ARW Model

2017 ◽  
Vol 145 (8) ◽  
pp. 3179-3201 ◽  
Author(s):  
Benjamin T. Blake ◽  
David B. Parsons ◽  
Kevin R. Haghi ◽  
Stephen G. Castleberry
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Vertical Shear ◽  
Structure Evolution ◽  
Cold Pool ◽  
Density Current ◽  
Convective System ◽  
Low Level ◽  
Arw Model ◽  
Low Level Jet

Previous studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central United States. Forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate. This study utilized the WRF-ARW Model to simulate a nocturnal mesoscale convective system that occurred over the southern Great Plains on 3–4 June 2013. A low-level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer. The storm was elevated and associated with bores that assisted in the maintenance of the system. Three-dimensional variations in the system’s structure were found along the cold pool, which were examined using convective system dynamics and wave theory. Shallow lifting occurred on the southern flank of the storm. Conversely, the southeastern flank had deep lifting, with favorable integrated vertical shear over the layer of maximum CAPE. The bore assisted in transporting high-CAPE air toward its LFC, and the additional lifting by the density current allowed for deep convection to occur. The bore was not coupled to the convective system and it slowly pulled away, while the convection remained in phase with the density current. These results provide a possible explanation for how convection is maintained at night in the presence of a low-level jet and a stable boundary layer, and emphasize the importance of the three-dimensionality of these systems.

scholarly journals Mechanisms of Convection Initiation in the Southwestern Xinjiang, Northwest China: A Case Study

Atmosphere ◽  
2020 ◽  
Vol 11 (12) ◽  
pp. 1335
Author(s):  
Abuduwaili Abulikemu ◽  
Jie Ming ◽  
Xin Xu ◽  
Xiaoyong Zhuge ◽  
Yuan Wang ◽  
...  
Keyword(s):  
Wrf Model ◽  
Northwest China ◽  
Radiative Heating ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Convective System ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Budget Analysis ◽  
Convection Initiation

The mechanism of convection initiation (CI) occurring in the Southwest Xinjiang, Northwest China is investigated using quantitative budget analysis of vertical momentum for the first time. The Weather Research and Forecasting (WRF) model is used to reproduce and analyze the CI events. The observations showed that many CIs occurred continuously, with an intense mesoscale convective system eventually forming. The overall features of the CIs were well captured by the simulation. Lagrangian vertical momentum budgets, in which the vertical acceleration was decomposed into dynamic and buoyant components, were performed along the backward trajectories of air parcels within two convective cells. The results showed that the buoyant acceleration is the major contributor in both the slow and rapid lifting period of the CI, while the dynamic acceleration also showed a considerably positive effect only during the rapid lifting period. The buoyant acceleration during the slow lifting period was due to the warm advection generated by the radiative heating near the mountainous area on the south side of Tarim Basin in the afternoon. The buoyant acceleration during the rapid lifting period was from the latent heat release within the convective cell. Further decomposition of the dynamic acceleration showed that the vertical twisting related to the vertical shear of horizontal wind almost completely dominated the dynamic acceleration, while the horizontal curvature and extension showed very weak contribution. These findings provide some new insights into the roles of buoyant and dynamic forcing in the mechanism of CI in Southwest Xinjiang.

Mechanisms of the Great Plains Low-Level Jet as Simulated in an AGCM

2007 ◽  
Vol 64 (2) ◽  
pp. 532-547 ◽  
Author(s):  
Xianan Jiang ◽  
Ngar-Cheung Lau ◽  
Isaac M. Held ◽  
Jeffrey J. Ploshay
Keyword(s):  
Simple Model ◽  
Pressure Gradient ◽  
Great Plains ◽  
Gradient Force ◽  
Inertial Oscillation ◽  
Pressure Gradient Force ◽  
Surface Cooling ◽  
Vertical Diffusion ◽  
Low Level ◽  
Low Level Jet

Abstract A model diagnosis has been performed on the nocturnal Great Plains low-level jet (LLJ), which is one of the key elements of the warm season regional climate over North America. The horizontal–vertical structure, diurnal phase, and amplitude of the LLJ are well simulated by an atmospheric general circulation model (AGCM), thus justifying a reevaluation of the physical mechanisms for the formation of the LLJ based on output from this model. A diagnosis of the AGCM data confirms that two planetary boundary layer (PBL) processes, the diurnal oscillation of the pressure gradient force and of vertical diffusion, are of comparable importance in regulating the inertial oscillation of the winds, which leads to the occurrence of maximum LLJ strength during nighttime. These two processes are highlighted in the theories for the LLJ proposed by Holton (1967) and Blackadar (1957). A simple model is constructed in order to study the relative roles of these two mechanisms. This model incorporates the diurnal variation of the pressure gradient force and vertical diffusion coefficients as obtained from the AGCM simulation. The results reveal that the observed diurnal phase and amplitude of the LLJ can be attributed to the combination of these two mechanisms. The LLJ generated by either Holton’s or Blackadar’s mechanism alone is characterized by an unrealistic meridional phase shift and weaker amplitude. It is also shown that the diurnal phase of the LLJ exhibits vertical variations in the PBL, more clearly at higher latitudes, with the upper PBL wind attaining a southerly peak several hours earlier than the lower PBL. The simple model demonstrates that this phase tilt is due mainly to sequential triggering of the inertial oscillation from upper to lower PBL when surface cooling commences after sunset. At lower latitudes, due to the change of orientation of prevailing mean wind vectors and the longer inertial period, the inertial oscillation in the lower PBL tends to be interrupted by strong vertical mixing in the following day, whereas in the upper PBL, the inertial oscillation can proceed in a low-friction environment for a relatively longer duration. Thus, the vertical phase tilt initiated at sunset is less evident at lower latitudes.

scholarly journals On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

2019 ◽  
Author(s):  
Étienne Vignon ◽  
Olivier Traullé ◽  
Alexis Berne
Keyword(s):  
Pressure Gradient ◽  
Vertical Structure ◽  
East Antarctica ◽  
Radiosonde Data ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Ice Shelves ◽  
Low Level ◽  
Humidity Profiles

Abstract. Eight years of high-resolution radiosonde data at nine Antarctic stations are analysed to provide the first large scale characterization of the fine scale vertical structure of the low troposphere up to 3 km of altitude over the coastal margins of East Antarctica. Radiosonde data show a large spatial variability of wind, temperature and humidity profiles, with different features between stations in katabatic regions (e.g., Dumont d'Urville and Mawson stations), stations over two ice shelves (Neumayer and Halley stations) and regions with complex orography (e.g., Mc Murdo). At Dumont d'Urville, Mawson and Davis stations, the yearly median wind speed profiles exhibit a clear low-level katabatic jet. During precipitation events, the low-level flow generally remains of continental origin and its speed is even reinforced due to the increase in the continent- ocean pressure gradient. Meanwhile, the relative humidity profiles show a dry low troposphere, suggesting the occurence of low-level sublimation of precipitation in katabatic regions but such a phenomenon does not appreciably occur over the ice-shelves near Halley and Neumayer. Although ERA-Interim and ERA5 reanalyses assimilate radiosoundings at most stations considered here, substantial – and sometimes large – low-level wind and humidity biases are revealed but ERA5 shows overall better performances. A free simulation with the regional model Polar WRF (at a 35-km resolution) over the entire continent shows too strong and too shallow near-surface jets in katabatic regions especially in winter. This may be a consequence of an understimated coastal cold air bump and associated sea-continent pressure gradient force due to the coarse 35 km resolution of the Polar WRF simulation. Beyond documenting the vertical structure of the low troposphere over coastal East-Antarctica, this study gives insights into the reliability and accuracy of two major reanalysis products in this region on the Earth and it raises the difficulty of modeling the low-level flow over the margins of the ice sheet with a state-of-the-art climate model.

scholarly journals Comparison of Simulated Tropical Cyclone Intensity and Structures Using the WRF with Hydrostatic and Nonhydrostatic Dynamical Cores

Atmosphere ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 483 ◽  
Author(s):  
Fujun Qi ◽  
Jianfang Fei ◽  
Zhanhong Ma ◽  
Jinrong Chen ◽  
Xiaogang Huang ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Wrf Model ◽  
Vertical Motion ◽  
Radial Pressure ◽  
Momentum Equation ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Dynamical Core ◽  
Budget Analysis ◽  
Perturbation Pressure

This study explored the influence of choosing a nonhydrostatic dynamical core or a hydrostatic dynamical core in the weather research and forecasting (WRF) model on the intensity and structure of simulated tropical cyclones (TCs). A comparison of cloud-resolving simulations using each core revealed significant differences in the TC simulations. In comparison with the nonhydrostatic simulation, the hydrostatic simulation produced a stronger and larger TC, associated with stronger convective activity. A budget analysis of the vertical momentum equation was conducted to investigate the underlying mechanisms. Although the hydrostatic dynamical core was used, the vertical motion was not in strict hydrostatic balance because of the existence of the vertical perturbation pressure gradient force, local buoyancy force, water loading, and sum of the Coriolis and diffusion effects. The contribution of the enhanced vertical perturbation pressure gradient force was found to be more important for stronger upward acceleration in the eyewall in the hydrostatic simulation than in the nonhydrostatic simulation. This is because it leads to intensified convection in the eyewall that releases more latent heat, which induces a larger low-level radial pressure gradient and inflow motion, and eventually leads to a stronger storm.

A Modeling Study of a Low-Level Jet along the Yun-Gui Plateau in South China

2016 ◽  
Vol 55 (1) ◽  
pp. 41-60 ◽  
Author(s):  
Ming-Yang He ◽  
Hong-Bo Liu ◽  
Bin Wang ◽  
Da-Lin Zhang
Keyword(s):  
South China ◽  
Large Scale ◽  
Model Simulation ◽  
Three Dimensional ◽  
Radiative Heating ◽  
Horizontal Wind ◽  
Maximum Speed ◽  
Pressure System ◽  
Low Level ◽  
Low Level Jet

AbstractIn this study, the three-dimensional structures and diurnal evolution of a typical low-level jet (LLJ) with a maximum speed of 24 m s−1 occurring in the 850–800-hPa layer are examined using both large-scale analysis and a high-resolution model simulation. The LLJ occurred on the eastern foothills of the Yun-Gui Plateau in south China from 1400 LST 29 June to 1400 LST 30 June 2003. The effects of surface radiative heating, topography, and latent heat release on the development of the LLJ case are also studied. Results show that a western Pacific Ocean subtropical high and a low pressure system on the respective southeast and northwest sides of the LLJ provide a favorable large-scale mean pressure pattern for the LLJ development. The LLJ reaches its peak intensity at 850 hPa near 0200 LST with wind directions veering from southerly before sunset to southwesterly at midnight. A hodograph at the LLJ core shows a complete diurnal cycle of the horizontal wind with a radius of 5.5 m s−1. It is found that in an LLJ coordinates system the along-LLJ geostrophic component regulates the distribution and 65% of the intensity of LLJ, whereas the ageostrophic component contributes to the clockwise rotation, thus leading to the formation and weakening of the LLJ during night- and daytime, respectively. Numerical sensitivity experiments confirm the surface radiative heating as the key factor in determining the formation of the nocturnal LLJ. The existence of the Yun-Gui Plateau, and the downstream condensational heating along the mei-yu front play secondary roles in the LLJ formation.

Nocturnal Destabilization Associated with the Summertime Great Plains Low-Level Jet

2020 ◽  
Vol 148 (11) ◽  
pp. 4641-4656
Author(s):  
Thomas R. Parish ◽  
Richard D. Clark ◽  
Todd D. Sikora
Keyword(s):  
Great Plains ◽  
The United States ◽  
Temperature Gradients ◽  
Gradient Force ◽  
Wind Component ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Low Level ◽  
Temperature Advection ◽  
Low Level Jet

AbstractThe Great Plains low-level jet (LLJ) has long been associated with summertime nocturnal convection over the central Great Plains of the United States. Destabilization effects of the LLJ are examined using composite fields assembled from the North American Mesoscale Forecast System for June and July 2008–12. Of critical importance are the large isobaric temperature gradients that become established throughout the lowest 3 km of the atmosphere in response to the seasonal heating of the sloping Great Plains. Such temperature gradients provide thermal wind forcing throughout the lower atmosphere, resulting in the establishment of a background horizontal pressure gradient force at the level of the LLJ. The attendant background geostrophic wind is an essential ingredient for the development of a pronounced summertime LLJ. Inertial turning of the ageostrophic wind associated with LLJ provides a westerly wind component directed normal to the terrain-induced orientation of the isotherms. Hence, significant nocturnal low-level warm-air advection occurs, which promotes differential temperature advection within a vertical column of atmosphere between the level just above the LLJ and 500 hPa. Such differential temperature advection destabilizes the nighttime troposphere above the radiatively cooled near-surface layer on a recurring basis during warm weather months over much of the Great Plains and adjacent states to the east. This destabilization process reduces the convective inhibition of air parcels near the level of the LLJ and may be of significance in the development of elevated nocturnal convection. The 5 July 2015 case from the Plains Elevated Convection at Night field program is used to demonstrate this destabilization process.

A Numerical Simulation of the Mei-Yu Front and the Associated Low Level Jet

1990 ◽  
Vol 118 (7) ◽  
pp. 1408-1428 ◽  
Author(s):  
L. C. Chou ◽  
C-P. Chang ◽  
R. T. Williams
Keyword(s):  
Numerical Simulation ◽  
Low Level ◽  
Low Level Jet

scholarly journals Low-Level Easterly Winds Blowing through the Tsugaru Strait, Japan. Part II: Numerical Simulation of the Event on 5–10 June 2003

2012 ◽  
Vol 140 (6) ◽  
pp. 1779-1793 ◽  
Author(s):  
Teruhisa Shimada ◽  
Masahiro Sawada ◽  
Weiming Sha ◽  
Hiroshi Kawamura
Keyword(s):  
Pressure Gradient ◽  
Air Temperature ◽  
Temperature Difference ◽  
Diurnal Variations ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
The West ◽  
Low Level ◽  
Tsugaru Strait ◽  
Mutsu Bay

Abstract This paper investigates the structures of and diurnal variations in low-level easterly winds blowing through the Tsugaru Strait and Mutsu Bay on 5–10 June 2003 using a numerical weather prediction model. Cool air that accompanies prevailing easterly winds owing to the persistence of the Okhotsk high intrudes into the strait and the bay below 500 m during the nighttime and retreats during the daytime. This cool-air intrusion and retreat induce diurnal variations in the winds in the east inlet of the strait, in Mutsu Bay, and in the west exit of the strait. In the east inlet, a daytime increase in air temperature within the strait produces a large air temperature difference with the inflowing cool air, and the resulting pressure gradient force accelerates the winds. The cool air flowing into Mutsu Bay is heated over land before entering the bay during the daytime. The resulting changes in cool-air depth and in pressure gradient force strengthen the daytime winds. In the west exit, local pressure gradient force perturbations are induced by the air temperature difference between warm air over the Japan Sea and cool air within the strait, and by variations in the depth of low-level cool air. The accelerated winds in the west exit extend southwestward in close to geostrophic balance during the daytime and undergo a slight anticyclonic rotation to westerly during the nighttime owing to the dominance of the Coriolis effect.

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