scholarly journals An account of low level wind shear over Chennai airport - Part I : Observation and forecasting aspects

MAUSAM ◽  
2021 ◽  
Vol 61 (1) ◽  
pp. 19-34
Author(s):  
R. SURESH
Keyword(s):  
Wind Shear ◽  
Richardson Number ◽  
General Belief ◽  
Low Level ◽  
Time Period ◽  
Period Of Occurrence

Low level wind shear (LLWS) is an aviation hazard. LLWS cases reported by the air crews over Chennai airport from 1987 to 2007 (barring 1992 and 1993 during which period no report is readily available for analysis) have been analysed threadbare. The most favourable time / period of occurrence of LLWS have been documented which has prophylactic value to issue LLWS alert in current weather reports. Richardson number and turbulence index (TI) have been computed for the reported cases of LLWS and the efficacies of these thermodynamical indices have been documented. There were cases of active moderate / severe LLWS cases lasting even beyond 10 hrs duration in contrary to the general belief that LLWS is a short lived phenomenon. The urgency / necessity of having a sizeable LLWS database to devise a suitable warning strategy have been highlighted.

scholarly journals Low Level Jet Wind Shear in the Sahel

2013 ◽  
Vol 11 ◽  
pp. 1-10
Author(s):  
Saïdou Madougou ◽  
Frederique Saïd ◽  
Bernard Campistron ◽  
Fadel Kebe Cheikh
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Shear Direction ◽  
Low Level ◽  
Aircraft Navigation ◽  
Time Period ◽  
Wind Profiler Radar ◽  
Low Level Jet ◽  
Wind Shears ◽  
Uhf Wind Profiler

In the Sahel, a vertical wind shear appears in the dry and in the wet seasons. In Niamey, Niger, during the dry season, the period of strong shears is clearly linked to the Nocturnal Low Level Jet (LLJ) since it occurs in a narrow time period around 06H00 UTC at 60% of the cases reach shears which require an alert to the pilots (higher than 4 ms-1 per 100 m). The majority of cases occur during the night with a wind shear direction between 90 and 150° per 100 m, which is shown that it is dangerous for aircraft. In Bamako, Mali, high wind shears represent (higher than 4 ms-1 per 100 m) only 16-22% of the cases and can occur at any time of the day. There are, however, 8% of the cases, the whole day long, when the wind shear can reach more than 6 ms-1 per 100 m. Most of the wind shear directions are also between 0 and 90° per 100 m during the night. This is why the Agency for the safety of aircraft navigation in Africa and Madagascar (ASECNA) has put in 2004 at Bamako airport an UHF wind profiler radar for monitoring nocturnal strong Low Level Jet wind shear which occur regularly in this airport.

scholarly journals An account of low level wind shear over Chennai airport - Part II : Turbulence and eddy dissipation

MAUSAM ◽  
2021 ◽  
Vol 60 (3) ◽  
pp. 325-342
Author(s):  
R. SURESH
Keyword(s):  
Wind Shear ◽  
Three Dimensional ◽  
Civil Aviation ◽  
Atmospheric Conditions ◽  
Velocity Data ◽  
Mean Power ◽  
General Belief ◽  
Low Level ◽  
International Civil Aviation Organisation ◽  
Radial Velocity Data

In-flight reports on Low Level Wind Shear (LLWS) received from aircrafts are used to issue wind shear alerts for all subsequent landing aircrafts as per standing guidelines of International Civil Aviation Organisation (ICAO). In this paper, winds reported by aircrafts at 1000 and 1800 ft. are used to validate the wind estimated from DWR measured radial wind data employing standard algorithms. Turbulence indices and parameters have been computed independently using conventional (RS/RW) upper air data, aircraft measured winds and DWR estimated winds and compared these with wind shear induced turbulence reported by aircrews. Mean power law (wind escalation law) profiles in the boundary layer have been arrived at for unstable and stable atmospheric conditions.                   Three dimensional shear (3DS) upto 600 m a.g.l. has been worked out from DWR measured radial velocity data and compared with wind shear computed from RS/RW and aircraft measured winds and DWR estimated winds. It is found that 3DS values of more than 16 * 10-3 s-1 predict well the occurrence of moderate turbulence. Contrary to the general belief that wind shear is a short lived phenomenon which may last for a few minutes only, it has been observed that incidences of LLWS and induced moderate turbulence lasting more than 10 hrs are not at all uncommon over Chennai aircraft.

Airborne infrared low level wind shear predictor

1984 ◽  
Author(s):  
P. KUHN ◽  
R. KURKOWSKI
Keyword(s):  
Wind Shear ◽  
Low Level

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

Atmosphere ◽  
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.

scholarly journals An Observational Study of Mesoscale Convective Systems with Heavy Rainfall over the Korean Peninsula

2006 ◽  
Vol 21 (2) ◽  
pp. 125-148 ◽  
Author(s):  
Hyung Woo Kim ◽  
Dong Kyou Lee
Keyword(s):  
Observational Study ◽  
Korean Peninsula ◽  
Wind Shear ◽  
Heavy Rainfall ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Mesoscale Convective Systems ◽  
Low Level ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract A heavy rainfall event induced by mesoscale convective systems (MCSs) occurred over the middle Korean Peninsula from 25 to 27 July 1996. This heavy rainfall caused a large loss of life and property damage as a result of flash floods and landslides. An observational study was conducted using Weather Surveillance Radar-1988 Doppler (WSR-88D) data from 0930 UTC 26 July to 0303 UTC 27 July 1996. Dominant synoptic features in this case had many similarities to those in previous studies, such as the presence of a quasi-stationary frontal system, a weak upper-level trough, sufficient moisture transportation by a low-level jet from a tropical storm landfall, strong potential and convective instability, and strong vertical wind shear. The thermodynamic characteristics and wind shear presented favorable conditions for a heavy rainfall occurrence. The early convective cells in the MCSs initiated over the coastal area, facilitated by the mesoscale boundaries of the land–sea contrast, rain–no rain regions, saturated–unsaturated soils, and steep horizontal pressure and thermal gradients. Two MCSs passed through the heavy rainfall regions during the investigation period. The first MCS initiated at 1000 UTC 26 July and had the characteristics of a supercell storm with small amounts of precipitation, the appearance of a mesocyclone with tilting storm, a rear-inflow jet at the midlevel of the storm, and fast forward propagation. The second MCS initiated over the upstream area of the first MCS at 1800 UTC 26 July and had the characteristics of a multicell storm, such as a broken areal-type squall line, slow or quasi-stationary backward propagation, heavy rainfall in a concentrated area due to the merging of the convective storms, and a stagnated cluster system. These systems merged and stagnated because their movement was blocked by the Taebaek Mountain Range, and they continued to develop because of the vertical wind shear resulting from a low-level easterly inflow.

scholarly journals Low-Level Wind Shear Identification along the Glide Path at BCIA by the Pulsed Coherent Doppler Lidar

Atmosphere ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 50
Author(s):  
Hongwei Zhang ◽  
Xiaoying Liu ◽  
Qichao Wang ◽  
Jianjun Zhang ◽  
Zhiqiang He ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Direction ◽  
Small Scale ◽  
Observation Data ◽  
Doppler Lidar ◽  
Low Level ◽  
Glide Path ◽  
Coherent Doppler Lidar ◽  
Scanning Strategies ◽  
Meteorological Phenomenon

Low-level wind shear is usually to be a rapidly changing meteorological phenomenon that cannot be ignored in aviation security service by affecting the air speed of landing and take-off aircrafts. The lidar team in Ocean University of China (OUC) carried out the long term particular researches on the low-level wind shear identification and regional wind shear inducement search at Beijing Capital International Airport (BCIA) from 2015 to 2020 by operating several pulsed coherent Doppler lidar (PCDL) systems. On account of the improved glide path scanning strategy and virtual multiple wind anemometers based on the rang height indicator (RHI) modes, the small-scale meteorological phenomenon along the glide path and/or runway center line direction can be captured. In this paper, the device configuration, scanning strategies, and results of the observation data are proposed. The algorithms to identify the low-level wind shear based on the reconstructed headwind profiles data have been tested and proved based on the lidar data obtained from December 2018 to January 2019. High spatial resolution observation data at vertical direction are utilized to study the regional wind shear inducement at the 36L end of BCIA under strong northwest wind conditions.

Examining Terrain Effects on an Upstate New York Tornado Event Utilizing a High-Resolution Model Simulation

2021 ◽  
Author(s):  
Luke J. LeBel ◽  
Brian H. Tang ◽  
Ross A. Lazear
Keyword(s):  
New York ◽  
High Resolution ◽  
Wind Shear ◽  
Model Simulation ◽  
Wrf Model ◽  
Severe Weather ◽  
Streamwise Vorticity ◽  
Low Level ◽  
Severe Convection ◽  
The Impact

AbstractThe complex terrain at the intersection of the Mohawk and Hudson valleys of New York has an impact on the development and evolution of severe convection in the region. Specifically, previous research has concluded that terrain-channeled flow in the Mohawk and Hudson valleys likely contributes to increased low-level wind shear and instability in the valleys during severe weather events such as the historic 31 May 1998 event that produced a strong (F3) tornado in Mechanicville, New York.The goal of this study is to further examine the impact of terrain channeling on severe convection by analyzing a high-resolution WRF model simulation of the 31 May 1998 event. Results from the simulation suggest that terrain-channeled flow resulted in the localized formation of an enhanced low-level moisture gradient, resembling a dryline, at the intersection of the Mohawk and Hudson valleys. East of this boundary, the environment was characterized by stronger low-level wind shear and greater low-level moisture and instability, increasing tornadogenesis potential. A simulated supercell intensified after crossing the boundary, as the larger instability and streamwise vorticity of the low-level inflow was ingested into the supercell updraft. These results suggest that terrain can have a key role in producing mesoscale inhomogeneities that impact the evolution of severe convection. Recognition of these terrain-induced boundaries may help in anticipating where the risk of severe weather may be locally enhanced.

Assessing the influence of complex terrain on severe convective environments in northeastern Alabama

2021 ◽  
Author(s):  
Branden Katona ◽  
Paul Markowski
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Spatial Distributions ◽  
Convective Storm ◽  
Self Organizing Maps ◽  
Low Level ◽  
Wind Regimes

AbstractStorms crossing complex terrain can potentially encounter rapidly changing convective environments. However, our understanding of terrain-induced variability in convective stormenvironments remains limited. HRRR data are used to create climatologies of popular convective storm forecasting parameters for different wind regimes. Self-organizing maps (SOMs) are used to generate six different low-level wind regimes, characterized by different wind directions, for which popular instability and vertical wind shear parameters are averaged. The climatologies show that both instability and vertical wind shear are highly variable in regions of complex terrain, and that the spatial distributions of perturbations relative to the terrain are dependent on the low-level wind direction. Idealized simulations are used to investigate the origins of some of the perturbations seen in the SOM climatologies. The idealized simulations replicate many of the features in the SOM climatologies, which facilitates analysis of their dynamical origins. Terrain influences are greatest when winds are approximately perpendicular to the terrain. In such cases, a standing wave can develop in the lee, leading to an increase in low-level wind speed and a reduction in vertical wind shear with the valley lee of the plateau. Additionally, CAPE tends to be decreased and LCL heights are increased in the lee of the terrain where relative humidity within the boundary layer is locally decreased.

scholarly journals Comparison of convective parameters derived from ERA5 and MERRA2 with rawinsonde data over Europe and North America

2020 ◽  
pp. 1-55
Author(s):  
Mateusz Taszarek ◽  
Natalia Pilguj ◽  
John T. Allen ◽  
Victor Gensini ◽  
Harold E. Brooks ◽  
...  
Keyword(s):  
North America ◽  
Great Plains ◽  
Wind Shear ◽  
Extreme Values ◽  
Absolute Error ◽  
Coastal Zones ◽  
Opposite Pattern ◽  
The Balkans ◽  
Low Level ◽  
Lapse Rates

AbstractIn this study we compared 3.7 mln rawinsonde observations from 232 stations over Europe and North America with proximal vertical profiles from ERA5 and MERRA2 to examine how well reanalysis depicts observed convective parameters. Larger differences between soundings and reanalysis are found for thermodynamic theoretical parcel parameters, low-level lapse rates and low-level wind shear. In contrast, reanalysis best represents temperature and moisture variables, mid-tropospheric lapse rates, and mean wind. Both reanalyses underestimate CAPE, low-level moisture and wind shear, particularly when considering extreme values. Overestimation is observed for low-level lapse rates, mid-tropospheric moisture and the level of free convection. Mixed-layer parcels have overall better accuracy when compared to most-unstable, especially considering convective inhibition and lifted condensation level. Mean absolute error for both reanalyses has been steadily decreasing over the last 39 years for almost every analyzed variable. Compared to MERRA2, ERA5 has higher correlations and lower mean absolute errors. MERRA2 is typically drier and less unstable over central Europe and the Balkans, with the opposite pattern over western Russia. Both reanalyses underestimate CAPE and CIN over the Great Plains. Reanalyses are more reliable for lower elevations stations and struggle along boundaries such as coastal zones and mountains. Based on the results from this and prior studies we suggest that ERA5 is likely one of the most reliable available reanalysis for exploration of convective environments, mainly due to its improved resolution. For future studies we also recommend that computation of convective variables should use model levels that provide more accurate sampling of the boundary-layer conditions compared to less numerous pressure levels.

scholarly journals A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima

2015 ◽  
Vol 15 (6) ◽  
pp. 8479-8523
Author(s):  
C.-C. Wang ◽  
H.-C. Kuo ◽  
R. H. Johnson ◽  
C.-Y. Lee ◽  
S.-Y. Huang ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Extreme Rainfall ◽  
Vertical Wind ◽  
Cold Pool ◽  
Rear Side ◽  
Gradient Force ◽  
Typhoon Morakot ◽  
Low Level ◽  
Pressure Perturbations

Abstract. This paper investigates the formation and evolution of deep convection inside the east–west oriented rainbands associated with a low-level jet (LLJ) in Typhoon Morakot (2009). With typhoon center to the northwest of Taiwan, the westerly LLJ was resulted from the interaction of typhoon circulation with the southwest monsoon flow, which supplied the water vapor for the extreme rainfall (of ~1000 mm) over southwestern Taiwan. The Cloud-Resolving Storm Simulator with 1 km grid spacing was used to simulate the event, and it successfully reproduced the slow-moving rainbands, the embedded cells, and the dynamics of merger and back-building (BB) on 8 August as observed. Our model results suggest that the intense convection interacted strongly with the westerly LLJ that provided reversed vertical wind shear below and above the jet core. Inside mature cells, significant dynamical pressure perturbations (pd') are induced with positive (negative) pd' at the western (eastern) flank of the updraft near the surface and a reversed pattern aloft (>2 km). This configuration produced an upward directed pressure gradient force (PGF) to the rear side and favors new development to the west, which further leads to cell merger as the mature cells slowdown in eastward propagation. The strong updrafts also acted to elevate the jet and enhance the local vertical wind shear at the rear flank. Additional analysis reveals that the upward PGF there is resulted mainly by the shearing effect but also by the extension of upward acceleration at low levels. In the horizontal, the upstream-directed PGF induced by the rear-side positive pd' near the surface is much smaller, but can provide additional convergence for BB development upstream. Finally, the cold-pool mechanism for BB appears to be not important in the Morakot case, as the conditions for strong evaporation in downdrafts do not exist.

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