scholarly journals Simulation of severe storms of tornadic intensity over Indo-Bangla region

MAUSAM ◽  
2021 ◽  
Vol 67 (2) ◽  
pp. 479-492
Author(s):  
SOMESHWAR DAS ◽  
MD. NAZRUL ISLAM ◽  
MOHAN K. DAS
Keyword(s):  
Convective Motion ◽  
Dew Point ◽  
Wind Fields ◽  
Low Level ◽  
Westerly Jet ◽  
Severe Thunderstorms ◽  
Surface Data ◽  
Arw Model ◽  
Upper Level ◽  
Tornadic Storms

Many severe thunderstorms of tornadic intensity were reported in the northwestern parts of Bangladesh during 30 August to 14 September, 2008. Two among them occurred at Nilphamari and Kurigram districts on 30th August, and at Nilphamari district on 3rd September. The tornadic storms are studied based on a field survey, surface data, radar and satellite observations and model simulations. Low level moisture influx by southerly flow from the Bay of Bengal coupled with an upper level westerly jet stream causing intense instability and shear in the wind fields triggered a series of storms for two weeks. The exact time and locations of the storms are investigated by using the hourly precipitation data retrieved from a S-band radar of Bangladesh Meteorological Department (BMD) located at Dhaka. Subsequently, the storms are simulated by using the WRF-ARW model on double nested domains at 9 and 3 km horizontal resolutions based on 6 hourly FNL analyses and boundary conditions of NCEP.  Among the typical characteristics of the storms, the CAPE, Storm-Relative Environment Helicity (SREH), Bulk Richardson Number Shear (BRNSHR), dew point depression, and potential vorticity are studied. Results show that while there are differences of 2-3 hours between the observed and simulated time of the storms, the distances between observed and simulated locations of the storms are several tens of kilometers. The maximum CAPE is generally above 2400 J kg-1. The maximum amount of vorticity transferred by directional shear in the storm updraft (helicity) due to convective motion simulated by the model is 766 m2 sec-2, and the highest value of BRNSHR that define the region in which low-level mesocyclogenesis is more likely is 168 m2 sec-2 among the 2 cases, which is generally supposed to produce rotating storms according to the prescribed range.  

scholarly journals A Background Investigation of Tornado Activity across the Southern Cumberland Plateau Terrain System of Northeastern Alabama

2018 ◽  
Vol 146 (12) ◽  
pp. 4261-4278 ◽  
Author(s):  
Anthony W. Lyza ◽  
Kevin R. Knupp
Keyword(s):  
Wind Profile ◽  
Cumberland Plateau ◽  
Activity Maximum ◽  
Low Level ◽  
Terrain Effects ◽  
Surface Data ◽  
Tennessee Valley ◽  
Profile Changes ◽  
Tornadic Storms

Abstract The effects of terrain on tornadoes are poorly understood. Efforts to understand terrain effects on tornadoes have been limited in scope, typically examining a small number of cases with limited observations or idealized numerical simulations. This study evaluates an apparent tornado activity maximum across the Sand Mountain and Lookout Mountain plateaus of northeastern Alabama. These plateaus, separated by the narrow Wills Valley, span ~5000 km2 and were impacted by 79 tornadoes from 1992 to 2016. This area represents a relative regional statistical maximum in tornadogenesis, with a particular tendency for tornadogenesis on the northwestern side of Sand Mountain. This exploratory paper investigates storm behavior and possible physical explanations for this density of tornadogenesis events and tornadoes. Long-term surface observation datasets indicate that surface winds tend to be stronger and more backed atop Sand Mountain than over the adjacent Tennessee Valley, potentially indicative of changes in the low-level wind profile supportive to storm rotation. The surface data additionally indicate potentially lower lifting condensation levels over the plateaus versus the adjacent valleys, an attribute previously shown to be favorable for tornadogenesis. Rapid Update Cycle and Rapid Refresh model output indicate that Froude numbers for the plateaus in tornadic environments are likely supportive of enhanced low-level flow over the plateaus, which further indicates the potential for favorable wind profile changes for tornado production. Examples of tornadic storms rapidly acquiring increased low-level rotation while reaching the plateaus of northeast Alabama are presented. The use of this background to inform the VORTEX-SE 2017 field campaign is discussed.

scholarly journals On the general circulation of the atmosphere around Colombia

2020 ◽  
Vol 44 (172) ◽  
pp. 857-875
Author(s):  
Oscar José Mesa-Sánchez ◽  
Julián David Rojo-Hernández
Keyword(s):  
South America ◽  
General Circulation ◽  
Rain Gauge ◽  
Kelvin Wave ◽  
Wind Fields ◽  
Low Level ◽  
Heating Source ◽  
The Pacific ◽  
Northern South America ◽  
Upper Level

The average annual precipitation in the Pacific coast of Colombia ranges from 8,000 to 13,000 mm. The annual average (1960-2018) in Puerto López (Cauca) rain gauge (77°14’56.3”W, 2°50’43.0”N) is 13.159 mm making it, probably, the rainiest place on the Earth. Such a large amount of precipitation also means a sizeable diabatic heating source over western Colombia, which is responsible for driving the circulation in northern South America and Mesoamerica from mid-March to the end of November. We applied a simple conceptual model to study the heat-induced circulation. Our results indicated that the heating source over western Colombia produces a steady, low-level westerly inflow as a result of a half planetary wave propagating over Mesoamerica and the far eastern Pacific that generates two cyclonical flows. On the east side of the heating source, a Kelvin wave generates a low-level easterly flow from the tropical Atlantic Ocean and the Northern Amazon and Orinoco basins in a Walker-type circulation. This Rossby and Kelvin patterns create information pathways, which, in their turn, dominate the low- and upper-level wind fields. Documented observations about the atmosphere’s general circulation over northern South America and Mesoamérica are consistent enough to support the assertion that a set of waves trapped in the tropics induced by a heating source explains the circulation over Colombia and its surroundings.

Meso β-Scale Thunderstorm/Environment Interactions During AVE-SESAME V (20–21 May 1979)

1983 ◽  
Vol 64 (10) ◽  
pp. 1144-1156 ◽  
Author(s):  
Henry E. Fuelberg ◽  
Matthew F. Printy
Keyword(s):  
Lower Stratosphere ◽  
Lower Troposphere ◽  
The Other ◽  
Atmospheric Variability ◽  
Feedback Mechanisms ◽  
Low Level ◽  
Severe Thunderstorms ◽  
Other Hand ◽  
Upper Level ◽  
Rawinsonde Data

Meso β-scale rawinsonde data from the Atmospheric Variability Experiment-Severe Environmental Storms and Mesoscale Experiment (AVE-SESAME) V period (20–21 May 1979) are used to diagnose atmospheric variability in the environment of a convective area. As the storms developed, temperatures increased in the upper stratosphere; however, cooling was observed nearer to the surface and in the lower stratosphere. Height rises above 400 mb produced a mesohigh over the convective area that was most pronounced near 200 mb. Weaker height falls occurred in the lower troposphere. Wind patterns underwent especially interesting fluctuations. North of the convective area, upper-level winds increased significantly during storm development. Southeast of the convection, however, winds near 200 mb decreased approximately 50% during a 3 h period coinciding with the most active storms. On the other hand, winds at 400 mb almost doubled during the same 3 h period. Strong low-level convergence, upper-level divergence, and ascending motion developed after storm initiation. Much more detailed study is required to understand this fascinating case. However, many of the current findings about the meso β-scale storm environment are consistent with those previously attributed to feedback mechanisms from severe thunderstorms.

scholarly journals Polarimetric Radar Characteristics of Tornadogenesis Failure in Supercell Thunderstorms

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 581
Author(s):  
Matthew Van Den Broeke
Keyword(s):  
Polarimetric Radar ◽  
Low Level ◽  
Supercell Storms ◽  
Supercell Thunderstorms ◽  
Near Term ◽  
Tornadic Storms ◽  
Differential Reflectivity

Many nontornadic supercell storms have times when they appear to be moving toward tornadogenesis, including the development of a strong low-level vortex, but never end up producing a tornado. These tornadogenesis failure (TGF) episodes can be a substantial challenge to operational meteorologists. In this study, a sample of 32 pre-tornadic and 36 pre-TGF supercells is examined in the 30 min pre-tornadogenesis or pre-TGF period to explore the feasibility of using polarimetric radar metrics to highlight storms with larger tornadogenesis potential in the near-term. Overall the results indicate few strong distinguishers of pre-tornadic storms. Differential reflectivity (ZDR) arc size and intensity were the most promising metrics examined, with ZDR arc size potentially exhibiting large enough differences between the two storm subsets to be operationally useful. Change in the radar metrics leading up to tornadogenesis or TGF did not exhibit large differences, though most findings were consistent with hypotheses based on prior findings in the literature.

Finding upper-level sets in cellular surface data using echelons and saTScan

2006 ◽  
Vol 13 (4) ◽  
pp. 379-390 ◽  
Author(s):  
Wayne L. Myers ◽  
Koji Kurihara ◽  
Ganapati P. Patil ◽  
Ryan Vraney
Keyword(s):  
Level Sets ◽  
Surface Data ◽  
Upper Level

scholarly journals Simulasi Kontrol 2 Pompa Supplay Air Bersih Menggunakanrelay Change Over Dan Floatless Level Switch (Sebagai Modul Praktek Mahasiswa Ps Teknik Pendingin Dan Tata Udara)

2018 ◽  
Vol 4 (1) ◽  
pp. 10-16
Author(s):  
Sudirman Sudirman ◽  
I Nyoman Gede Baliarta
Keyword(s):  
Water Level ◽  
Level Control ◽  
Low Level ◽  
Upper Level ◽  
Underground Tank

Sistem supplay air bersih pasti ada dipasang disuatu gedung. Tujuan dari penelitian ini adalah untuk menciptakan modul praktek mahasiswa Program Studi Teknik Pendingin  dalam mata Kuliah Praktek Utility Gedung dan BAS. Sehingga kompetensi mahasiswa tentang utility gedung, khususnya dibidang system pompa supplai air bersih bisa tercapai dengan lebih mudah. Modul praktek ini menggunakan 2 buah pompa, 2 buah tangki air, 1 sebagai tangki sebagai tangki underground tank dan 1 lagi sebagai tower tank. Menggunakan WLC (water level control) untuk mengontrol hidup mati pompa berdasarkan level  air pada tangki tower. Dan menggunakan Relay Change over untuk merubah pompa on duty secara otomatis. Hasil uji kerja alat simulasi ini, saat level air pada tangki tower low level, Pompa 1 akan hidup sampai level air mencapai upper level dan akan Off, secara otomatis Relay change over merubah pompa on duty dari Pompa 1 ke Pompa 2. Pada saat level air mencapai low level lagi di tangki tower, yang hidup adalah Pompa 2.

scholarly journals Seasonal Variations of the Synoptic-Scale Transient Eddy Activity and Polar Front Jet over East Asia

2010 ◽  
Vol 23 (12) ◽  
pp. 3222-3233 ◽  
Author(s):  
Xuejuan Ren ◽  
Xiuqun Yang ◽  
Cuijiao Chu
Keyword(s):  
East Asia ◽  
Seasonal Variations ◽  
East Asian ◽  
Polar Front ◽  
Transient Eddy ◽  
Synoptic Scale ◽  
Wind Fields ◽  
The North ◽  
Upper Level ◽  
Polar Front Jet

Abstract Seasonal variations of the synoptic-scale transient eddy activity (STEA) and the jet streams over East Asia are examined through analysis of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data. Extracted from the 6-hourly upper-level wind fields, the distribution of the jet core numbers exhibits a distinct geographical border for the East Asian subtropical jet (EASJ) and the East Asian polar front jet (EAPJ) at the latitudes of the northern Tibetan Plateau (TP). In the cool seasons, two branches of the STEA and low-level baroclinicity exist over the East Asian landmass, accompanied by the two-jet state of the EASJ and EAPJ. In the warm seasons, a single jet pattern of the EASJ along the north flank of the TP is accompanied by the weakened STEA over the mid- to high latitudes of East Asia. Further analysis shows two distinct features of the seasonal variations of the STEA over East Asia, compared with that over the North Pacific. First, during the transitional period of April–June, the main STEA band over East Asia migrates northward dramatically, in conjunction with the EAPJ shifting in the same direction. Second, both the upper-level STEA and the lower-level baroclinicity poleward of the TP are prosperous in spring. The relationship between the STEA, baroclinicity, vertical wind shear, and static stability in the EAPJ region in different seasons is further investigated. It is found that in addition to the time-mean wind fields, the rapid increase in the sensible heat flux poleward side of the TP region in spring and the associated boundary layer processes are partially responsible for the spring prosperity of the local baroclinicity and the STEA.

Scale sensitivity of the Gill circulation, Part II: Off-equatorial case

2021 ◽  
Author(s):  
Gilles Bellon ◽  
Beatriz Reboredo
Keyword(s):  
Diabatic Heating ◽  
Dynamical Response ◽  
Plane Case ◽  
Horizontal Scale ◽  
Overturning Circulation ◽  
Low Level ◽  
Heating Source ◽  
Horizontal Extent ◽  
Westerly Jet ◽  
Tropospheric Heating

Abstract We investigate the steady dynamical response of the atmosphere on the equatorial β-plane to a steady, localized, mid-tropospheric heating source. Following Part I which investigates the case of an equatorial diabatic heating, we explore the sensitivity of the Gill circulation to the latitudinal location of the heating, together with the sensitivity to its horizontal scale. Again, we focus on characteristics of the response which would be particularly important if the circulation interacted with the hydrologic and energy cycles: overturning circulation and low-level wind. In the off-equatorial case, the intensity of the overturning circulation has the same limit as in the equatorial case for small horizontal extent of the diabatic heating, which is also the limit in the f-plane case. The decrease in this intensity with increasing horizontal scale of the diabatic heating is slightly faster in the off-equatorial case than in the equatorial case, which is due to the increase of rotational winds at the expense of divergent winds. The low-level westerly jet is more intense than in the equatorial case, with larger maximum wind and eastward mass transport that tend to infinity for small horizontal extent of the diabatic heating. In terms of spatial characteristics, this jet has a similar latitudinal extent as in the equatorial case but, unlike in the equatorial case, it extends further equatorward than poleward of the diabatic-heating center. It also extends further eastward than in the equatorial case.

scholarly journals Analysis of Possible Triggering Mechanisms of Severe Thunderstorms in the Tropical Central Andes of Peru, Mantaro Valley

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 301 ◽  
Author(s):  
J.L. J.L. ◽  
A.S. A.S. ◽  
S. S. ◽  
D. D. ◽  
E. E. ◽  
...  
Keyword(s):  
Central Andes ◽  
The South ◽  
The West ◽  
Subtropical Anticyclone ◽  
Low Level ◽  
The Andes ◽  
Severe Thunderstorms ◽  
Westerly Winds ◽  
Moisture Fluxes ◽  
Triggering Mechanisms

The aim of the present study is to analyze the triggering mechanisms of three thunderstorms (TSs) associated with severe rainfall, hail and lightening in the tropical central Andes of Peru, specifically above the Huancayo observatory (12.04 ∘ S, 75.32 ∘ W, 3313 m a.s.l.) located in the Mantaro valley during the spring-summer season (2015–2016). For this purpose, we used a set of in-situ pluviometric observations, satellite remote sensing data, the Compact Meteorological Ka-Band Cloud Radar (MIRA-35C), the Boundary Layer Tropospheric Radar and downscaling model simulations with the Weather Research and Forecasting (WRF) Model (resolutions: 18 km, 6 km and 2 km), and the Advance Regional Prediction System (ARPS) (resolution: 0.5 km) models in order to analyze the dynamic of the atmosphere in the synoptic, meso and local scales processes that control the occurrence of the three TS events. The results show that at synoptic scale, the TSs are characterized by the southern displacement of the South-east Pacific Subtropical Anticyclone up to latitudes higher than 35 ∘ S, by the weakening and south-eastern displacement of the Bolivian high–North east low system and by the intrusion of westerly winds along the west side of the central Andes at upper and medium levels of the atmosphere. At meso-scale, apparently, two important moisture fluxes from opposite directions are filtered through the passes along the Andes: one from the north-west and the other from the south-east directions converge and trigger the deep convection into the Mantaro valley. These moisture fluxes are generated by the intrusion of the sea-breeze from the Pacific ocean along the west of the Andes coupling with upper and middle westerly winds and by the thermally induced moisture fluxes coming from the South American low level jet at the east side of the Andes. At the local scale, there is a low-level conditional instability in the previous hours as well as during the occurrence of the TSs above the Huancayo observatory. In addition, the simulation results indicated the possibility of generation of inertial gravity waves in the Amazon basin, associated with geostrophic adjustment which transports energy and moisture into the central Andes plateau and consequently intensifies the thunderstorms above the Mantaro valley.

scholarly journals Evaluation of Two Cloud-Resolving Models Using Bin or Bulk Microphysics Representation for the HyMeX-IOP7a Heavy Precipitation Event

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1177
Author(s):  
Diana Arteaga ◽  
Céline Planche ◽  
Christina Kagkara ◽  
Wolfram Wobrock ◽  
Sandra Banson ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Sensitivity Study ◽  
Precipitation Event ◽  
Convective System ◽  
Wind Fields ◽  
Massif Central ◽  
Surface Precipitation ◽  
Low Level

The Mediterranean region is frequently affected in autumn by heavy precipitation that causes flash-floods or landslides leading to important material damage and casualties. Within the framework of the international HyMeX program (HYdrological cycle in Mediterranean EXperiment), this study aims to evaluate the capabilities of two models, WRF (Weather Research and Forecasting) and DESCAM (DEtailed SCAvenging Model), which use two different representations of the microphysics to reproduce the observed atmospheric properties (thermodynamics, wind fields, radar reflectivities and precipitation features) of the HyMeX-IOP7a intense precipitating event (26 September 2012). The DESCAM model, which uses a bin resolved representation of the microphysics, shows results comparable to the observations for the precipitation field at the surface. On the contrary, the simulations made with the WRF model using a bulk representation of the microphysics (either the Thompson scheme or the Morrison scheme), commonly employed in NWP models, reproduce neither the intensity nor the distribution of the observed precipitation—the rain amount is overestimated and the most intense cell is shifted to the East. The different simulation results show that the divergence in the surface precipitation features seems to be due to different mechanisms involved in the onset of the precipitating system: the convective system is triggered by the topography of the Cévennes mountains (i.e., south-eastern part of the Massif Central) in DESCAM and by a low-level flux convergence in WRF. A sensitivity study indicates that the microphysics properties have impacted the thermodynamics and dynamics fields inducing the low-level wind convergence simulated with WRF for this HyMeX event.

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