scholarly journals Investigation of Meteorological Conditions Favourable for Formation of Thunderstorm Occurred Over Bangladesh Through Simulation by WRF-ARW Model

2020 ◽  
Vol 68 (1) ◽  
pp. 71-77
Author(s):  
Dewan Abdul Quadir ◽  
Towhida Rashid ◽  
Shammi Akhter ◽  
MN Ahasan
Keyword(s):  
Wrf Model ◽  
Cumulus Cells ◽  
Meteorological Conditions ◽  
Mitigation Strategies ◽  
The North ◽  
Outer Domain ◽  
Westerly Winds ◽  
Arw Model ◽  
Strong Winds ◽  
East West

Investigation of meteorological conditions favorable for formation of pre-monsoon thunderstorm over Bangladesh has been conducted by simulating a selected thunderstorm case using ARW dynamic core of WRF model (WRF-ARW). A multi-cell thunderstorm formed on 30-03-2018 over the northwestern tip of Bangladesh and adjacent territories of India and moved south-southeast wards with its highest development at 09:30 UTC was selected for this study. The chosen case of thunderstorm has 3 distinct cells of which 2 cells have the width of over 100 km each and the third one located in the eastern Bangladesh and had the width of 50 km. A WRF ARW model has been applied to examine the atmospheic characteristics favorabe for genesis of selected case run in a double nested domain of resolution of 9x9 km2 in the outer domain and 3 3 km2in the inner domain.  The analysis of the geopotential height field of 925 hPa level generated by WRF model at different hours of 31 March 2018 clearly indicates favourable condition with pockets of micro lows and their progression towards central to southeastern Bangladesh. The strong winds blowing from Bay of Bengal along an anticyclone over the Bay brings sufficient moisture to the north. The southerly winds meet the easterly and also westerly winds providing strong low level convergence which favors the convective activities forming cumulus cells. The orography of foothills may also enhance the convections. The wind in the upper tropospheric winds attains jet speed over these areas. The distribution of divergence and vorticity in the 925 hPa level shows the evolution of system. The distribution of precipitation shows that the spatial patterns were well captured. Vertical velocity has been plotted along the vertical-horizontal plane oriented in the east-west direction across a high rainfall cell. This shows that the highest development of narrow vertical cell extends up to 100 hPa level. Following the temporal evolution of the system, it is seen that the highest development delayed by around 2 hours. Some mitigation strategies in respect of thunderstorms and associated lighting are also discussed. Dhaka Univ. J. Sci. 68(1): 71-77, 2020 (January)

scholarly journals Mechanism of Daytime Strong Winds on the Northern Slopes of Himalayas, near Mount Everest: Observation and Simulation

2018 ◽  
Vol 57 (2) ◽  
pp. 255-272 ◽  
Author(s):  
Fanglin Sun ◽  
Yaoming Ma ◽  
Zeyong Hu ◽  
Maoshan Li ◽  
Gianni Tartari ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Monsoon Season ◽  
Meteorological Data ◽  
Mount Everest ◽  
The North ◽  
China Academy ◽  
Westerly Winds ◽  
Meteorological Observations ◽  
Strong Winds ◽  
Academy Of Sciences

AbstractThe seasonal variability of strong afternoon winds in a northern Himalayan valley and their relationship with the synoptic circulation were examined using in situ meteorological data from March 2006 to February 2007 and numerical simulations. Meteorological observations were focused on the lower Rongbuk valley, on the north side of the Himalayas (4270 m MSL), where a wind profile radar was available. In the monsoon season (21 May–4 October), the strong afternoon wind was southeasterly, whereas it was southwesterly in the nonmonsoon season. Numerical simulations were performed using the Weather Research and Forecasting Model to investigate the mechanism causing these afternoon strong winds. The study found that during the nonmonsoon season the strong winds are produced by downward momentum transport from the westerly winds aloft, whereas those during the monsoon season are driven by the inflow into the Arun Valley east of Mount Everest. The air in the Arun Valley was found to be colder than that of the surroundings during the daytime, and there was a horizontal pressure gradient from the Arun Valley to Qomolangma Station (QOMS), China Academy of Sciences, at the 5200-m level. This explains the formation of the strong afternoon southeasterly wind over QOMS in the monsoon season. In the nonmonsoon season, the colder air from Arun Valley is confined below the ridge by westerly winds associated with the subtropical jet.

scholarly journals Global variations of local asymmetry in glacier altitude: separation of north–south and east–west components

2005 ◽  
Vol 51 (174) ◽  
pp. 469-482 ◽  
Author(s):  
Ian S. Evans ◽  
Nicholas J. Cox
Keyword(s):  
The Arctic ◽  
Equilibrium Line Altitude ◽  
Height Range ◽  
The North ◽  
Regional Trends ◽  
Strong Winds ◽  
The Tropics ◽  
New Evidence ◽  
North And South ◽  
East West

AbstractNorth–south and east–west differences in firn-line altitude, equilibrium-line altitude or middle altitudes of glaciers can be separated by regression on the cosine and sine of glacier aspect (accumulation area azimuth). Allowing for regional trends in altitude, the north–south differences expected from radiation and shade effects can be reliably quantified from World Glacier Inventory (WGI) data. The north–south differences are greater in sunnier climates, mid-latitudes and steeper relief. Local altitude differences between north- and south-facing glaciers are commonly 70–320 m. Such asymmetry is near-universal, although weak in the Arctic and tropics. East–west contrasts are less, and found mainly in the tropics and areas most exposed to strong winds. Altitude, latitude, glacier gradient and height range, calculable from most of the WGI data, are potential controls on the degree of north–south contrast, as well as surrogates for climatic controls (temperature, precipitation, radiation and cloudiness). An asymmetric sine–cosine power model is developed to describe the variation of north–south contrast with latitude. Multiple regression over 51 regions shows altitude and latitude to be the strongest controls of this contrast. Aspect–altitude analysis for former glaciers provides new evidence of cloudiness.

Lake-Effect Snowbands in Baroclinic Environments

2019 ◽  
Vol 34 (6) ◽  
pp. 1657-1674
Author(s):  
Daniel T. Eipper ◽  
Steven J. Greybush ◽  
George S. Young ◽  
Seth Saslo ◽  
Todd D. Sikora ◽  
...  
Keyword(s):  
Horizontal Resolution ◽  
Societal Impact ◽  
Contrasting Cases ◽  
The North ◽  
Dominant Band ◽  
Lake Effect ◽  
Strong Winds ◽  
Representative Member ◽  
Insight Into ◽  
East West

Abstract Lake-effect snowstorms are often observed to manifest as dominant bands, commonly produce heavy localized snowfall, and may extend large distances inland, resulting in hazards and high societal impact. Some studies of dominant bands have documented concomitant environmental baroclinity (i.e., baroclinity occurring at a scale larger than the width of the parent lake), but the interaction of this baroclinity with the inland structure of dominant bands has been largely unexplored. In this study, the thermodynamic environment and thermodynamic and kinematic structure of simulated dominant bands are examined using WRF reanalyses at 3-km horizontal resolution and an innovative technique for selecting the most representative member from the WRF ensemble. Three reanalysis periods are selected from the Ontario Winter Lake-effect Systems (OWLeS) field campaign, encompassing 185 simulation hours, including 155 h in which dominant bands are identified. Environmental baroclinity is commonly observed during dominant-band periods and occurs in both the north–south and east–west directions. Sources of this baroclinity are identified and discussed. In addition, case studies are conducted for simulation hours featuring weak and strong along-band environmental baroclinity, resulting in weak and strong inland extent, respectively. These contrasting cases offer insight into one mechanism by which along-band environmental baroclinity can influence the inland structure and intensity of dominant bands: in the case with strong environmental baroclinity, inland portions of this band formed under weak instability and therefore exhibit slow overturning, enabling advection far inland under strong winds, whereas the nearshore portion forms under strong instability, and the enhanced overturning eventually leads to the demise of the inland portion of the band.

scholarly journals The Quinault Blowdown: A Microscale Wind Event Driven by a Mountain-Wave Rotor

2019 ◽  
Vol 100 (6) ◽  
pp. 977-986
Author(s):  
Clifford F. Mass ◽  
Robert Conrick ◽  
Nicholas Weber ◽  
Joseph P. Zagrodnik
Keyword(s):  
High Resolution ◽  
Wrf Model ◽  
High Amplitude ◽  
Strong Wind ◽  
Mountain Wave ◽  
The North ◽  
Wave Rotors ◽  
Wind Event ◽  
Strong Shear ◽  
Strong Winds

AbstractOn 27 January 2018, a highly localized, strong wind event occurred along the north shore of Lake Quinault, Washington. The resulting loss of large old-growth trees in a roughly 0.5-km2 region led to blocked roads and power outages. Nearby surface stations did not record anomalous winds, and no tree damage was reported in the surrounding region. Based on public accounts and a nearby seismometer, it appears that the strong winds lasted less than 10 min. Surface and aerial damage surveys showed that the trees fell from a different direction (northerly) than the synoptic or mesoscale f low (southwesterly to southeasterly). Based on high-resolution Weather Research and Forecasting (WRF) Model simulations, it appears that the damaging northerly winds were the result of a strong atmospheric rotor produced by a high-amplitude mountain wave. A simulation with 148-m grid spacing produced a rotor at the same time and location as the treefalls. Synoptic analysis and the high-resolution simulation showed that moderately strong southeasterly flow and a stable layer associated with the approaching occluded front interacted with a ∼750-m-high upstream mountain ridge to produce the mountain wave and associated rotor circulation. The combination of an inversion and strong shear at and above the upstream ridge were outliers in a climatology of soundings from the nearby Quillayute rawinsonde site, suggesting that such intense mountain-wave rotors are unusual in this valley.

scholarly journals The Effect of the Balcones Escarpment on Three Cases of Extreme Precipitation in Central Texas

2015 ◽  
Vol 144 (1) ◽  
pp. 119-138 ◽  
Author(s):  
Erik R. Nielsen ◽  
Russ S. Schumacher ◽  
Alexandra M. Keclik
Keyword(s):  
Extreme Precipitation ◽  
Wrf Model ◽  
Extreme Rainfall ◽  
Flood Damage ◽  
Mitigation Strategies ◽  
Atmospheric Conditions ◽  
The North ◽  
Local Topography ◽  
Central Texas ◽  
Balcones Escarpment

Abstract The proximity to the Gulf of Mexico and local topography makes central Texas particularly prone to heavy precipitation and deadly flood events. Specifically, the Balcones Escarpment, located in central Texas, creates extremely favorable hydrologic characteristics for damaging floods. Urban centers such as San Antonio and Austin, Texas, are located along this terrain feature and have suffered at times, even with mitigation strategies, catastrophic flood damage. While the hydrologic effects of the Balcones Escarpment are well known, the meteorological impacts are uncertain. The purpose of this study is to evaluate the effect of the Balcones Escarpment in three cases of extreme precipitation in which the rainfall was maximized near the escarpment. Numerical simulations for each event were run at convection-allowing grid spacing using the Weather Research and Forecasting (WRF) Model and were used as control runs. Then, the Balcones Escarpment was removed by moving the associated terrain gradient to the north and west. The removal of the Balcones Escarpment did not change the overall characteristics of any of the three rainfall events, with the spatial pattern and magnitude of precipitation similar between the control and terrain-modified simulations. However, the location of the maximum precipitation was slightly, but consistently, shifted to the north and west. These results show that the overall atmospheric conditions are much more important for determining the intensity and occurrence of extreme rainfall in central Texas than the local topography, but the Balcones Escarpment can cause subtle hydrologically important changes in the location of the maximum accumulation.

scholarly journals A Low frequency Southern Sky Survey Using the Mauritius Radio Telescope

2002 ◽  
Vol 199 ◽  
pp. 25-31
Author(s):  
N. Udaya Shankar
Keyword(s):  
Radio Telescope ◽  
Low Frequency ◽  
Fourier Synthesis ◽  
North East ◽  
The North ◽  
Sky Survey ◽  
Correlation Receiver ◽  
Complex Correlation ◽  
Right Ascension ◽  
East West

The Mauritius Radio Telescope (MRT) is a Fourier synthesis instrument which has been built to fill the gap in the availability of deep sky surveys at low radio frequencies in the southern hemisphere. It is situated in the north-east of Mauritius at a southern latitude of 20°.14 and an eastern longitude of 57°.73. The aim of the survey with the MRT is to contribute to the database of southern sky sources in the declination range −70° ≤ δ ≤ −10°, covering the entire 24 hours of right ascension, with a resolution of 4' × 4'.6sec(δ + 20.14°) and a point source sensitivity of 200 mJy (3σ level) at 151.5 MHz.MRT is a T-shaped non-coplanar array consisting of a 2048 m long East-West arm and a 880 m long South arm. In the East-West arm 1024 fixed helices are arranged in 32 groups and in the South arm 16 trolleys, with four helices on each, which move on a rail are used. A 512 channel, 2-bit 3-level complex correlation receiver is used to measure the visibility function. At least 60 days of observing are required for obtaining the visibilities up to the 880 m spacing. The calibrated visibilities are transformed taking care of the non-coplanarity of the array to produce an image of the area of the sky under observation.This paper will describe the telescope, the observations carried out so far, a few interesting aspects of imaging with this non-coplanar array and present results of a low resolution survey (13' × 18') covering roughly 12 hours of right ascension, and also present an image with a resolution of 4' × 4'.6sec(δ + 20.14°) made using the telescope.

scholarly journals Future Changes in Tropical Cyclone and Easterly Wave Characteristics over Tropical North America

Oceans ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 429-447
Author(s):  
Christian Dominguez ◽  
James M. Done ◽  
Cindy L. Bruyère
Keyword(s):  
North America ◽  
North Atlantic Ocean ◽  
Mitigation Strategies ◽  
Track Density ◽  
Caribbean Region ◽  
Tropical Cyclogenesis ◽  
Future Scenarios ◽  
Southern Mexico ◽  
The North ◽  
The Future

Tropical Cyclones (TCs) and Easterly Waves (EWs) are the most important phenomena in Tropical North America. Thus, examining their future changes is crucial for adaptation and mitigation strategies. The Community Earth System Model drove a three-member regional model multi-physics ensemble under the Representative Concentration Pathways 8.5 emission scenario for creating four future scenarios (2020–2030, 2030–2040, 2050–2060, 2080–2090). These future climate runs were analyzed to determine changes in EW and TC features: rainfall, track density, contribution to seasonal rainfall, and tropical cyclogenesis. Our study reveals that a mean increase of at least 40% in the mean annual TC precipitation is projected over northern Mexico and southwestern USA. Slight positive changes in EW track density are projected southwards 10° N over the North Atlantic Ocean for the 2050–2060 and 2080–2090 periods. Over the Eastern Pacific Ocean, a mean increment in the EW activity is projected westwards across the future decades. Furthermore, a mean reduction by up to 60% of EW rainfall, mainly over the Caribbean region, Gulf of Mexico, and central-southern Mexico, is projected for the future decades. Tropical cyclogenesis over both basins slightly changes in future scenarios (not significant). We concluded that these variations could have significant impacts on regional precipitation.

scholarly journals Optimal design of the solar tracking system of parabolic trough concentrating collectors

2020 ◽  
Vol 15 (4) ◽  
pp. 613-619
Author(s):  
Li Kong ◽  
Yunpeng Zhang ◽  
Zhijian Lin ◽  
Zhongzhu Qiu ◽  
Chunying Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Solar Radiation ◽  
Tracking System ◽  
Low Cost ◽  
Parabolic Trough ◽  
The North ◽  
Tracking Mode ◽  
Solar Tracking ◽  
East West

Abstract The present work aimed to select the optimum solar tracking mode for parabolic trough concentrating collectors using numerical simulation. The current work involved: (1) the calculation of daily solar radiation on the Earth’s surface, (2) the comparison of annual direct solar radiation received under different tracking modes and (3) the determination of optimum tilt angle for the north-south tilt tracking mode. It was found that the order of solar radiation received in Shanghai under the available tracking modes was: dual-axis tracking > north-south Earth’s axis tracking > north-south tilt tracking (β = 15°) > north-south tilt tracking (β = 45) > north-south horizontal tracking > east-west horizontal tracking. Single-axis solar tracking modes feature simple structures and low cost. This study also found that the solar radiation received under the north-south tilt tracking mode was higher than that of the north-south Earth’s axis tracking mode in 7 out of 12 months. Therefore, the north-south tilt tracking mode was studied separately to determine the corresponding optimum tilt angles in Haikou, Lhasa, Shanghai, Beijing and Hohhot, respectively, which were shown as follows: 18.81°, 27.29°, 28.67°, 36.21° and 37.97°.

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

scholarly journals Q fever in South Australia: an outbreak in a meat-works

1962 ◽  
Vol 60 (1) ◽  
pp. 1-20 ◽  
Author(s):  
Margaret D. Beech ◽  
A. E. Duxbury ◽  
Peter Warner
Keyword(s):  
Q Fever ◽  
South Australia ◽  
Meteorological Conditions ◽  
American Continent ◽  
North American Continent ◽  
The Past ◽  
The North ◽  
Epidemiological Features ◽  
Very High ◽  
Abattoir Workers

This paper consists of an epidemiological study of 52 cases of Q fever occurring in metropolitan Adelaide in 1957 and also a description of the results of a survey of 516 sera obtained from abattoir workers.The only case occurring outside the abattoirs was a dairy farmer who probably became infected while visiting the abattoirs. If this were so the incubation period (35 days) of his disease would have been exceptionally long.The general features of the outbreak, which lasted several months, differed from those on the North American continent in that the latter occurred explosively within a few days with very high attack rates. The situation in the Adelaide abattoirs is similar to that in Brisbane, where the disease appears to be endemic. However, unlike in Adelaide, cases are commonly recognized outside the abattoirs in Brisbane.In the abattoirs the disease affected mainly inspectors, those working on killing beef, and those working on offal. Mutton workers were not so severely affected. However, all these groups had similar incidences of low titre antibodies suggesting that in the past Q fever spread equally in all killing departments. In departments not directly associated with slaughtering the incidence both of cases in 1957 and low titre antibodies was relatively small.It was suggested that the epidemiological features of Q fever in Adelaide could be explained by the irregular appearance of animals from infected herds situated perhaps in Queensland—a known endemic area. Perhaps the appearance of such animals in the Adelaide abattoirs might be governed by meteorological conditions such that they were prevented from going to the ordinarily most convenient slaughterhouse.

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