scholarly journals Diffusion from a point source using power law of wind speed

MAUSAM ◽  
2021 ◽  
Vol 64 (2) ◽  
pp. 351-356
Author(s):  
KHALEDS.M. ESSA ◽  
REFAATA.R. GHOBRIAL
Keyword(s):  
Wind Speed ◽  
Point Source ◽  
Power Law ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Urban Atmosphere ◽  
Field Observations

bl 'kks/k i= esa ,d 'kgjh ok;q eaMy dks ,d lzksr fcUnq eku dj inkFkZ ds folj.k ds fy, ,d ekWMy laLFkkfir fd;k x;k gSA blds fiPNd dks ,d ifjHkkf"kr voLFkk ekuk x;k gS tgk¡ bldh lkanzrk 'kwU; gks tkrh gSA LFkkf;Ro Jsf.k;ksa dh miyC/k rduhdksa }kjk ikoj ykW dk mi;ksx djrs gq, m/okZ/kj iou vi:i.k dks vkdfyr fd;k x;k gSA bl ekWMy esa vkdfyr lkanzrkvksa dh rqyuk vUos"k.kdrkZvksa ds QhYM izs{k.kksa ls izkIr fd, x, fu"d"kksZa ds lkFk dh xbZ gSA In the present paper, a model for the diffusion of material from a point source in an urban atmosphere is incorporated. The plume is assumed to have a well-defined edge at which the concentration falls to zero. The vertical wind shear is estimated using power law, by employing most of the available techniques of stability categories. The concentrations estimated from the model were compared favorably with the field observations of investigators.

Clear-Air Turbulence Near the Jet-Stream Maxima *

1955 ◽  
Vol 36 (2) ◽  
pp. 53-60 ◽  
Author(s):  
Leroy H. Clem
Keyword(s):  
Wind Speed ◽  
Physical Model ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Stability Conditions ◽  
Jet Stream ◽  
Air Turbulence ◽  
Helical Vortices ◽  
High Level

The development of turbo-jet aircraft has made high-level clear air turbulence a major problem for aviation interests. This paper emphasizes the association of the majority of this turbulence with the pronounced vertical wind shear in and near the maximum wind speed centers that move along the jet stream. A physical model is proposed as a possible explanation of clear air turbulence, the associated cirrus bands and wind streaks in the jet maxima. This model is supported by an analogy drawn with similar low-level phenomena studied by Woodcock and others. The model can explain distribution of these features in the horizontal by means of helical vortices which are dependent upon proper vertical wind shear and stability conditions. The observed multiple layers in the vertical are also explained by this model. It is believed that the reason why most of the clear-air turbulence is found near the jet-stream maxima is simply because the necessary shear and stability conditions associated with this turbulence are most frequently fulfilled in that region.

The World's Strongest Winds as Revealed by Tateno Relay-Method Soundings

1959 ◽  
Vol 40 (7) ◽  
pp. 343-347 ◽  
Author(s):  
H. Arakawa
Keyword(s):  
Wind Speed ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Maximum Wind Speed ◽  
Directional Distribution ◽  
Maximum Wind ◽  
The World

Upper winds over Japan during the winter are known to be stronger than at any other place in the world. Here, analysis for the Tateno relay-method soundings over three winters is presented. Frequency of maximum wind speed in 1000-m intervals of height and in 10-m-per-sec intervals of speed and directional distribution of maximum wind speed are given. Strong vertical wind-shear data observed are also studied.

scholarly journals Environmental sensitivities of shallow-cumulus dilution – Part 2: Vertical wind profile

2021 ◽  
Author(s):  
Sonja Drueke ◽  
Daniel J. Kirshbaum ◽  
Pavlos Kollias
Keyword(s):  
Wind Speed ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Dilution Effect ◽  
Cloud Layer ◽  
Vertical Wind ◽  
Exposure Effect ◽  
The Core ◽  
Shallow Cumulus ◽  
Cloud Core

Abstract. This second part of a numerical study on shallow-cumulus dilution focuses on the sensitivity of cloud dilution to changes in the vertical wind profile. Insights are obtained through large-eddy simulations of maritime and continental cloud fields. In these simulations, the speed of the initially uniform geostrophic wind, and the strength of geostrophic vertical wind shear in the cloud and subcloud layer are varied. Increases in the cloud-layer vertical wind shear (up to 9 m/s/km) lead to 40–50 % larger cloud-core dilution rates compared to their respective unsheared counterparts. When the background wind speed, on the other hand, is enhanced by up to 10 m/s and subcloud-layer vertical wind shear develops or is initially prescribed, the dilution rate decreases by up to 25 %. The sensitivities of the dilution rate are linked to the updraft strength and the properties of the entrained air. Increases in the wind speed or vertical wind shear result in lower vertical velocities across all sets of experiments with stronger reductions in the cloud-layer wind shear simulation (27–47 %). Weaker updrafts are exposed to mixing with the drier surrounding air for a longer time period, allowing more entrainment to occur (i.e., the "core exposure effect"). However, reduced vertical velocities, in concert with increased cloud-layer turbulence, also assist in widening the humid shell surrounding the cloud cores, leading to entrainment of more humid air (i.e., the "core-shell dilution effect"). In the experiments with cloud-layer vertical wind shear, the core exposure effect dominates and the cloud-core dilution increases with increasing shear. Conversely, when the wind speed is increased and subcloud-layer vertical wind shear develops or is imposed, the core-shell dilution effect dominates to induce a purifying effect. The sensitivities are generally stronger in the maritime simulations, where weaker sensible heat fluxes lead to narrower, more tilted, and, therefore, more suppressed cumuli when cloud-layer shear is imposed. Moreover, in the experiments with subcloud wind shear, the weaker baseline turbulence in the maritime case allows for a larger turbulence enhancement, resulting in a widening of the transition zones between the cores and their environment, leading to the entrainment of more humid air.

scholarly journals Environmental sensitivities of shallow-cumulus dilution – Part 2: Vertical wind profile

2021 ◽  
Vol 21 (18) ◽  
pp. 14039-14058
Author(s):  
Sonja Drueke ◽  
Daniel J. Kirshbaum ◽  
Pavlos Kollias
Keyword(s):  
Wind Speed ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Dilution Effect ◽  
Cloud Layer ◽  
Vertical Wind ◽  
Exposure Effect ◽  
The Core ◽  
Shallow Cumulus ◽  
Cloud Core

Abstract. This second part of a numerical study on shallow-cumulus dilution focuses on the sensitivity of cloud dilution to changes in the vertical wind profile. Insights are obtained through large-eddy simulations of maritime and continental cloud fields. In these simulations, the speed of the initially uniform geostrophic wind and the strength of geostrophic vertical wind shear in the cloud and subcloud layer are varied. Increases in the cloud-layer vertical wind shear (up to 9 ms-1km-1) lead to 40 %–50 % larger cloud-core dilution rates compared to their respective unsheared counterparts. When the background wind speed, on the other hand, is enhanced by up to 10 m s−1 and subcloud-layer vertical wind shear develops or is initially prescribed, the dilution rate decreases by up to 25 %. The sensitivities of the dilution rate are linked to the updraft strength and the properties of the entrained air. Increases in the wind speed or vertical wind shear result in lower vertical velocities across all sets of experiments with stronger reductions in the cloud-layer wind shear simulation (27 %–47 %). Weaker updrafts are exposed to mixing with the drier surrounding air for a longer time period, allowing more entrainment to occur (i.e., the “core-exposure effect”). However, reduced vertical velocities, in concert with increased cloud-layer turbulence, also assist in widening the humid shell surrounding the cloud cores, leading to entrainment of more humid air (i.e., the “core–shell dilution effect”). In the experiments with cloud-layer vertical wind shear, the core-exposure effect dominates and the cloud-core dilution increases with increasing shear. Conversely, when the wind speed is increased and subcloud-layer vertical wind shear develops or is imposed, the core–shell dilution effect dominates to induce a buffering effect. The sensitivities are generally stronger in the maritime simulations, where weaker sensible heat fluxes lead to narrower, more tilted, and, therefore, more suppressed cumuli when cloud-layer shear is imposed. Moreover, in the experiments with subcloud wind shear, the weaker baseline turbulence in the maritime case allows for a larger turbulence enhancement, resulting in a widening of the transition zones between the cores and their environment, leading to the entrainment of more humid air.

scholarly journals Observation of Jet Stream Winds during NAWDEX and Characterization of Systematic Meteorological Analysis Errors

2020 ◽  
Vol 148 (7) ◽  
pp. 2889-2907 ◽  
Author(s):  
Andreas Schäfler ◽  
Ben Harvey ◽  
John Methven ◽  
James D. Doyle ◽  
Stephan Rahm ◽  
...  
Keyword(s):  
Wind Speed ◽  
North Atlantic ◽  
Wind Shear ◽  
Forecast Error ◽  
Vertical Wind Shear ◽  
Weather Forecast ◽  
Vertical Wind ◽  
Jet Stream ◽  
The North ◽  
The North Atlantic

Abstract Observations across the North Atlantic jet stream with high vertical resolution are used to explore the structure of the jet stream, including the sharpness of vertical wind shear changes across the tropopause and the wind speed. Data were obtained during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) by an airborne Doppler wind lidar, dropsondes, and a ground-based stratosphere–troposphere radar. During the campaign, small wind speed biases throughout the troposphere and lower stratosphere of only −0.41 and −0.15 m s−1 are found, respectively, in the ECMWF and Met Office analyses and short-term forecasts. However, this study finds large and spatially coherent wind errors up to ±10 m s−1 for individual cases, with the strongest errors occurring above the tropopause in upper-level ridges. ECMWF and Met Office analyses indicate similar spatial structures in wind errors, even though their forecast models and data assimilation schemes differ greatly. The assimilation of operational observational data brings the analyses closer to the independent verifying observations, but it cannot fully compensate for the forecast error. Models tend to underestimate the peak jet stream wind, the vertical wind shear (by a factor of 2–5), and the abruptness of the change in wind shear across the tropopause, which is a major contribution to the meridional potential vorticity gradient. The differences are large enough to influence forecasts of Rossby wave disturbances to the jet stream with an anticipated effect on weather forecast skill even on large scales.

scholarly journals Asymmetric Hurricane Boundary Layer Structure from Dropsonde Composites in Relation to the Environmental Vertical Wind Shear

2013 ◽  
Vol 141 (11) ◽  
pp. 3968-3984 ◽  
Author(s):  
Jun A. Zhang ◽  
Robert F. Rogers ◽  
Paul D. Reasor ◽  
Eric W. Uhlhorn ◽  
Frank D. Marks
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Mixed Layer ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Asymmetric Structure ◽  
Layer Depth ◽  
Tangential Wind ◽  
Hurricane Boundary Layer

Abstract This study investigates the asymmetric structure of the hurricane boundary layer in relation to the environmental vertical wind shear in the inner core region. Data from 1878 GPS dropsondes deployed by research aircraft in 19 hurricanes are analyzed in a composite framework. Kinematic structure analyses based on Doppler radar data from 75 flights are compared with the dropsonde composites. Shear-relative quadrant-mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to decrease with decreasing radius, consistent with previous axisymmetric analyses. There is still a clear separation between the kinematic and thermodynamic boundary layer heights. Both the thermodynamic mixed layer and height of maximum tangential wind speed are within the inflow layer. The inflow layer depth is found to be deeper in quadrants downshear, with the downshear right (DR) quadrant being the deepest. The mixed layer depth and height of maximum tangential wind speed are alike at the eyewall, but are deeper outside in quadrants left of the shear. The results also suggest that air parcels acquire equivalent potential temperature θe from surface fluxes as they rotate through the upshear right (UR) quadrant from the upshear left (UL) quadrant. Convection is triggered in the DR quadrant in the presence of asymmetric mesoscale lifting coincident with a maximum in θe. Energy is then released by latent heating in the downshear left (DL) quadrant. Convective downdrafts bring down cool and dry air to the surface and lower θe again in the DL and UL quadrants. This cycling process may be directly tied to shear-induced asymmetry of convection in hurricanes.

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 Atlantic Hurricanes and Climate Change. Part II: Role of Thermodynamic Changes in Decreased Hurricane Frequency

2013 ◽  
Vol 26 (21) ◽  
pp. 8513-8528 ◽  
Author(s):  
Megan S. Mallard ◽  
Gary M. Lackmann ◽  
Anantha Aiyyer
Keyword(s):  
Case Studies ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Effect Of Temperature ◽  
Physical Processes ◽  
Thermodynamic Conditions ◽  
Atlantic Hurricanes ◽  
Reduced Activity

Abstract A method of downscaling that isolates the effect of temperature and moisture changes on tropical cyclone (TC) activity was presented in Part I of this study. By applying thermodynamic modifications to analyzed initial and boundary conditions from past TC seasons, initial disturbances and the strength of synoptic-scale vertical wind shear are preserved in future simulations. This experimental design allows comparison of TC genesis events in the same synoptic setting, but in current and future thermodynamic environments. Simulations of both an active (September 2005) and inactive (September 2009) portion of past hurricane seasons are presented. An ensemble of high-resolution simulations projects reductions in ensemble-average TC counts between 18% and 24%, consistent with previous studies. Robust decreases in TC and hurricane counts are simulated with 18- and 6-km grid lengths, for both active and inactive periods. Physical processes responsible for reduced activity are examined through comparison of monthly and spatially averaged genesis-relevant parameters, as well as case studies of development of corresponding initial disturbances in current and future thermodynamic conditions. These case studies show that reductions in TC counts are due to the presence of incipient disturbances in marginal moisture environments, where increases in the moist entropy saturation deficits in future conditions preclude genesis for some disturbances. Increased convective inhibition and reduced vertical velocity are also found in the future environment. It is concluded that a robust decrease in TC frequency can result from thermodynamic changes alone, without modification of vertical wind shear or the number of incipient disturbances.

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