Movement of Large Convective Rainstorms in Relation to Winds Aloft

1958 ◽  
Vol 39 (3) ◽  
pp. 129-136 ◽  
Author(s):  
C. W. Newton ◽  
Sey Katz
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Rainfall Data ◽  
Squall Lines ◽  
Hourly Rainfall ◽  
The Difference ◽  
Strong Winds

By means of hourly rainfall data from the Hydroclimatic Network, the motions of large rainstorms, of the kind associated with squall lines, are examined in relation to the winds aloft. Very little correlation is found between the speed of movement of the rainstorms and the wind speed at any level, although the fastest moving storms were associated with strong winds aloft. Significant correlation is found between direction of motion of rainstorms, and wind direction at 700 mb or higher levels. On the average, the rainstorms move with an appreciable component toward right of the wind direction. The difference between these results, and those from other studies based on small precipitation areas, is ascribed to propagation. The mechanism involved is discussed briefly.

scholarly journals Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

2013 ◽  
Vol 7 (1) ◽  
pp. 175-217 ◽  
Author(s):  
N. Champollion ◽  
G. Picard ◽  
L. Arnaud ◽  
E. Lefebvre ◽  
M. Fily
Keyword(s):  
Wind Speed ◽  
Satellite Data ◽  
Wind Direction ◽  
Near Infrared ◽  
Microwave Remote Sensing ◽  
Passive Microwave ◽  
Infrared Photography ◽  
Surface Mass ◽  
Prevailing Direction ◽  
Strong Winds

Abstract. Hoar crystals episodically cover the snow surface in Antarctica and affect the roughness and reflective properties of the air-snow interface. However, little is known about their evolution and the processes responsible for their development and disappearance despite a probable influence on the surface mass balance and energy budget. To investigate hoar evolution, we use continuous observations of the surface by in-situ near-infrared photography and by passive microwave remote sensing at Dome C in Antarctica. From the photography data, we retrieved a daily indicator of the presence/absence of hoar crystals using a texture analysis algorithm. The analysis of this 2-yr long time series shows that Dome C surface is covered almost half of the time by hoar. The development of hoar crystals takes a few days and seems to occur whatever the meteorological conditions. In contrast, the disappearance of hoar is rapid (a few hours) and coincident with either strong winds or with moderate winds associated with a change in wind direction from Southwest (the prevailing direction) to Southeast. From the microwave satellite data, we computed the polarisation ratio (i.e. horizontal over vertical polarised brightness temperatures), an indicator known to be sensitive to hoar in Greenland. Photography data and microwave polarisation ratio are correlated, i.e. high values of polarisation ratio which theoretically correspond to low snow density values near the surface are associated with the presence of hoar crystals in the photography data. Satellite data over nearly ten years (2002–2011) confirm that a strong decrease of the polarisation ratio (i.e. signature of hoar disappearance) is associated with an increase of wind speed or a change in wind direction from the prevailing direction. The photography data provides, in addition, evidence of interactions between hoar and snowfall. Further adding the combined influence of wind speed and wind direction results in a complex picture of the snow-atmosphere interactions in Antarctica which deserves further quantification and modelling.

scholarly journals Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite

2013 ◽  
Vol 7 (4) ◽  
pp. 1247-1262 ◽  
Author(s):  
N. Champollion ◽  
G. Picard ◽  
L. Arnaud ◽  
E. Lefebvre ◽  
M. Fily
Keyword(s):  
Wind Speed ◽  
Satellite Data ◽  
Wind Direction ◽  
Near Infrared ◽  
Microwave Remote Sensing ◽  
Passive Microwave ◽  
Infrared Photography ◽  
Surface Mass ◽  
Prevailing Direction ◽  
Strong Winds

Abstract. Hoar crystals episodically cover the snow surface in Antarctica and affect the roughness and reflective properties of the air–snow interface. However, little is known about their evolution and the processes responsible for their development and disappearance despite a probable influence on the surface mass balance and energy budget. To investigate hoar evolution, we use continuous observations of the surface by in situ near-infrared photography and by passive microwave remote sensing at Dome C in Antarctica. From the photography data, we retrieved a daily indicator of the presence/absence of hoar crystals using a texture analysis algorithm. The analysis of this 2 yr long time series shows that Dome C surface is covered almost half of the time by hoar. The development of hoar crystals takes a few days and seems to occur whatever the meteorological conditions. In contrast, the disappearance of hoar is rapid (a few hours) and coincident with either strong winds or with moderate winds associated with a change in wind direction from southwest (the prevailing direction) to southeast. From the microwave satellite data, we computed the polarisation ratio (i.e. horizontal over vertical polarised brightness temperatures), an indicator known to be sensitive to hoar in Greenland. Photography data and microwave polarisation ratio are correlated, i.e. high values of polarisation ratio which theoretically correspond to low snow density values near the surface are associated with the presence of hoar crystals in the photography data. Satellite data over nearly ten years (2002–2011) confirm that a strong decrease of the polarisation ratio (i.e. signature of hoar disappearance) is associated with an increase of wind speed or a change in wind direction from the prevailing direction. The photography data provides, in addition, evidence of interactions between hoar and snowfall. Further adding the combined influence of wind speed and wind direction results in a complex picture of the snow–atmosphere interactions in Antarctica which deserves further quantification and modelling.

scholarly journals 2.5D Flexible Wind Sensor Using Differential Plate Capacitors

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 3101
Author(s):  
Yu Wan ◽  
Zhenxiang Yi
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Parallel Plate ◽  
Electrode Array ◽  
Copper Electrode ◽  
Windward Side ◽  
Leeward Side ◽  
Electrode Layer ◽  
Young’S Moduli ◽  
Speed Up

In this paper, a novel 2.5-dimensional (2.5D) flexible wind sensor is proposed based on four differential plate capacitors. This design consists of a windward pillar, two electrode layers, and a support layer, which are all made of polydimethylsiloxane (PDMS) with different Young’s moduli. A 2 mm × 2 mm copper electrode array is located on each electrode layer, forming four parallel plate capacitors as the sensitive elements. The wind in the xy-plane tilts the windward pillar, decreasing two capacitances on the windward side and increasing two capacitances on the leeward side. The wind in the z-axis depresses the windward pillar, resulting in an increase of all four capacitances. Experiments demonstrate that this sensor can measure the wind speed up to 23.9 m/s and the wind direction over the full 360° range of the xy-plane. The sensitivities of wind speed are close to 4 fF·m−1·s and 3 fF·m−1·s in the xy-plane and z-axis, respectively.

Climate Conditions at Perennially Ice-Covered Lake Untersee, East Antarctica

2015 ◽  
Vol 54 (7) ◽  
pp. 1393-1412 ◽  
Author(s):  
Dale T. Andersen ◽  
Christopher P. McKay ◽  
Victor Lagun
Keyword(s):  
Wind Speed ◽  
Austral Summer ◽  
Solar Flux ◽  
East Antarctica ◽  
Daily Maximum ◽  
Mean Annual Temperature ◽  
Secondary Source ◽  
Climate Conditions ◽  
Wind Speeds ◽  
Strong Winds

AbstractIn November 2008 an automated meteorological station was established at Lake Untersee in East Antarctica, producing a 5-yr data record of meteorological conditions at the lake. This dataset includes five austral summer seasons composed of December, January, and February (DJF). The average solar flux at Lake Untersee for the four years with complete solar flux data is 99.2 ± 0.6 W m−2. The mean annual temperature at Lake Untersee was determined to be −10.6° ± 0.6°C. The annual degree-days above freezing for the five years were 9.7, 37.7, 22.4, 7.0, and 48.8, respectively, with summer (DJF) accounting for virtually all of this. For these five summers the average DJF temperatures were −3.5°, −1.9°, −2.2°, −2.6°, and −2.5°C. The maximum (minimum) temperatures were +5.3°, +7.6°, +5.7°, +4.4°, and +9.0°C (−13.8°, −12.8°, −12.9°, −13.5°, and −12.1°C). The average of the wind speed recorded was 5.4 m s−1, the maximum was 35.7 m s−1, and the average daily maximum was 15 m s−1. The wind speed was higher in the winter, averaging 6.4 m s−1. Summer winds averaged 4.7 m s−1. The dominant wind direction for strong winds is from the south for all seasons, with a secondary source of strong winds in the summer from the east-northeast. Relative humidity averages 37%; however, high values will occur with an average period of ~10 days, providing a strong indicator of the quasi-periodic passage of storms across the site. Low summer temperatures and high wind speeds create conditions at the surface of the lake ice resulting in sublimation rather than melting as the main mass-loss process.

scholarly journals Initial-Condition Sensitivities and the Predictability of Downslope Winds

2009 ◽  
Vol 66 (11) ◽  
pp. 3401-3418 ◽  
Author(s):  
Patrick A. Reinecke ◽  
Dale R. Durran
Keyword(s):  
Wave Breaking ◽  
Initial Conditions ◽  
Static Stability ◽  
Synoptic Scale ◽  
Wind Speeds ◽  
Downslope Winds ◽  
First Case ◽  
Downslope Wind ◽  
The Difference ◽  
Strong Winds

Abstract The sensitivity of downslope wind forecasts to small changes in initial conditions is explored by using 70-member ensemble simulations of two prototypical windstorms observed during the Terrain-Induced Rotor Experiment (T-REX). The 10 weakest and 10 strongest ensemble members are composited and compared for each event. In the first case, the 6-h ensemble-mean forecast shows a large-amplitude breaking mountain wave and severe downslope winds. Nevertheless, the forecasts are very sensitive to the initial conditions because the difference in the downslope wind speeds predicted by the strong- and weak-member composites grows to larger than 28 m s−1 over the 6-h forecast. The structure of the synoptic-scale flow one hour prior to the windstorm and during the windstorm is very similar in both the weak- and strong-member composites. Wave breaking is not a significant factor in the second case, in which the strong winds are generated by a layer of high static stability flowing beneath a layer of weaker mid- and upper-tropospheric stability. In this case, the sensitivity to initial conditions is weaker but still significant. The difference in downslope wind speeds between the weak- and strong-member composites grows to 22 m s−1 over 12 h. During and one hour before the windstorm, the synoptic-scale flow exhibits appreciable differences between the strong- and weak-member composites. Although this case appears to be more predictable than the wave-breaking event, neither case suggests that much confidence should be placed in the intensity of downslope winds forecast 12 or more hours in advance.

scholarly journals Surface gas pollutants in Lhasa, a highland city of Tibet – current levels and pollution implications

2014 ◽  
Vol 14 (19) ◽  
pp. 10721-10730 ◽  
Author(s):  
L. Ran ◽  
W. L. Lin ◽  
Y. Z. Deji ◽  
B. La ◽  
P. M. Tsering ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Fossil Fuels ◽  
Trace Gases ◽  
Early Morning ◽  
Current Status ◽  
Urban Site ◽  
Large Variability ◽  
Mixing Ratios ◽  
Low Wind Speed

Abstract. Through several years of development, the city of Lhasa has become one of the most populated and urbanized areas on the highest plateau in the world. In the process of urbanization, current and potential air quality issues have been gradually concerned. To investigate the current status of air pollution in Lhasa, various gas pollutants including NOx, CO, SO2, and O3, were continuously measured from June 2012 to May 2013 at an urban site (29.40° N, 91.08° E, 3650 m a.s.l.). The seasonal variations of primary gas pollutants exhibited a peak from November to January with a large variability. High mixing ratios of primary trace gases almost exclusively occurred under low wind speed and showed no distinct dependence on wind direction, implying local urban emissions to be predominant. A comparison of NO2, CO, and SO2 mixing ratios in summer between 1998 and 2012 indicated a significant increase in emissions of these gas pollutants and a change in their intercorrelations, as a result of a substantial growth in the demand of energy consumption using fossil fuels instead of previously widely used biomass. The pronounced diurnal double peaks of primary trace gases in all seasons suggested automobile exhaust to be a major emission source in Lhasa. The secondary gas pollutant O3 displayed an average diurnal cycle of a shallow flat peak for about 4–5 h in the afternoon and a minimum in the early morning. Nighttime O3 was sometimes completely consumed by the high level of NOx. Seasonally, the variations of O3 mixing ratios displayed a low valley in winter and a peak in spring. In autumn and winter, transport largely contributed to the observed O3 mixing ratios, given its dependence on wind speed and wind direction, while in spring and summer photochemistry played an important role. A more efficient buildup of O3 mixing ratios in the morning and a higher peak in the afternoon was found in summer 2012 than in 1998. An enhancement in O3 mixing ratios would be expected in the future and more attention should be given to O3 photochemistry in response to increasing precursor emissions in this area.

Numerical Investigation of Thermal Flow Field of Air-Cooled Condensers for Yongshou Plant

2012 ◽  
Vol 248 ◽  
pp. 391-394
Author(s):  
Wen Zhou Yan ◽  
Wan Li Zhao ◽  
Qiu Yan Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Speed ◽  
Power Plant ◽  
Flow Field ◽  
Wind Direction ◽  
Rotational Speed ◽  
Power Plants ◽  
Thermal Flow ◽  
Air Cooled Condensers

By using the computational fluid dynamics code, FLUENT, Numerically simulation is investigated for Youngshou power plant. Under the constant ambient temperature, the effects of different wind speed and wind direction on the thermal flow field are qualitatively considered. It was found that when considering about the existing and normally operating power plants, the thermal flow field is more sensitive to wind direction and wind speed. Based on the above results, three improved measures such as: increasing the wind-wall height and accelerating the rotational speed of the fans near the edge of the ACC platform and lengthen or widen the platform are developed to effectively improving the thermal flow field, and enhanced the heat dispersal of ACC.

What can idealized storm surge simulations tell us about worst case scenarios?

2021 ◽  
Author(s):  
Elin Andrée ◽  
Jian Su ◽  
Martin Drews ◽  
Morten Andreas Dahl Larsen ◽  
Asger Bendix Hansen ◽  
...  
Keyword(s):  
Wind Speed ◽  
Sea Level ◽  
North Sea ◽  
Wind Direction ◽  
Water Levels ◽  
Sea Levels ◽  
The North ◽  
The North Sea ◽  
Sea Coast ◽  
North Sea Coast

<p>The potential impacts of extreme sea level events are becoming more apparent to the public and policy makers alike. As the magnitude of these events are expected to increase due to climate change, and increased coastal urbanization results in ever increasing stakes in the coastal zones, the need for risk assessments is growing too.</p><p>The physical conditions that generate extreme sea levels are highly dependent on site specific conditions, such as bathymetry, tidal regime, wind fetch and the shape of the coastline. For a low-lying country like Denmark, which consists of a peninsula and islands that partition off the semi-enclosed Baltic Sea from the North Sea, a better understanding of how the local sea level responds to wind forcing is urgently called for.</p><p>We here present a map for Denmark that shows the most efficient wind directions for generating extreme sea levels, for a total of 70 locations distributed all over the country’s coastlines. The maps are produced by conducting simulations with a high resolution, 3D-ocean model, which is used for operational storm surge modelling at the Danish Meteorological Institute. We force the model with idealized wind fields that maintain a fixed wind speed and wind direction over the entire model domain. Simulations are conducted for one wind speed and one wind direction at a time, generating ensembles of a set of wind directions for a fixed wind speed, as well as a set of wind speeds for a fixed wind direction, respectively.</p><p>For each wind direction, we find that the maximum water level at a given location increases linearly with the wind speed, and the slope values show clear spatial patterns, for example distinguishing the Danish southern North Sea coast from the central or northern North Sea Coast. The slope values are highest along the southwestern North Sea coast, where the passage of North Atlantic low pressure systems over the shallow North Sea, as well as the large tidal range, result in a much larger range of variability than in the more sheltered Inner Danish Waters. However, in our simulations the large fetch of the Baltic Sea, in combination with the funneling effect of the Danish Straits, result in almost as high water levels as along the North Sea coast.</p><p>Although the wind forcing is completely synthetic with no spatial and temporal structure of a real storm, this idealized approach allows us to systematically investigate the sea level response at the boundaries of what is physically plausible. We evaluate the results from these simulations by comparison to peak water levels from a 58 year long, high resolution ocean hindcast, with promising agreement.</p>

Analysis for the Effect of Wind Barrier on Reducing Wind Velocity across a Bridge

2012 ◽  
Vol 256-259 ◽  
pp. 2739-2742
Author(s):  
Ji Hong Bi ◽  
Peng Lu ◽  
Jian Wang ◽  
Chun Bao
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Speed ◽  
Wind Velocity ◽  
Efficient Design ◽  
Wind Barrier ◽  
Strong Winds

A bridge, which is located in the route of typhoon, is considered how to assure normal traffic use against strong winds. As one of the measures, wind barrier is proposed to be set on both sides of the bridge section for reducing wind velocity across it. In this study, an analysis by using CFX, a computational fluid dynamics program, is carried out to investigate the effects of wind barrier. The speed of wind is assumed as 60m/s. To find out an efficient design of the boards, different porosity ratios(r) of the boards is assumed for comparison. The result shows that wind barrier could reduce the wind speed across the bridge effectively.

scholarly journals Bayesian Model Averaging for Wind Speed Ensemble Forecasts Using Wind Speed and Direction

2017 ◽  
Vol 32 (6) ◽  
pp. 2217-2227 ◽  
Author(s):  
Siri Sofie Eide ◽  
John Bjørnar Bremnes ◽  
Ingelin Steinsland
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Bayesian Model Averaging ◽  
Weather Prediction ◽  
Model Averaging ◽  
Strong Wind ◽  
Ensemble Forecasts ◽  
Wind Speeds ◽  
Low Wind Speeds ◽  
The One

Abstract In this paper, probabilistic wind speed forecasts are constructed based on ensemble numerical weather prediction (NWP) forecasts for both wind speed and wind direction. Including other NWP variables in addition to the one subject to forecasting is common for statistical calibration of deterministic forecasts. However, this practice is rarely seen for ensemble forecasts, probably because of a lack of methods. A Bayesian modeling approach (BMA) is adopted, and a flexible model class based on splines is introduced for the mean model. The spline model allows both wind speed and wind direction to be included nonlinearly. The proposed methodology is tested for forecasting hourly maximum 10-min wind speeds based on ensemble forecasts from the European Centre for Medium-Range Weather Forecasts at 204 locations in Norway for lead times from +12 to +108 h. An improvement in the continuous ranked probability score is seen for approximately 85% of the locations using the proposed method compared to standard BMA based on only wind speed forecasts. For moderate-to-strong wind the improvement is substantial, while for low wind speeds there is generally less or no improvement. On average, the improvement is 5%. The proposed methodology can be extended to include more NWP variables in the calibration and can also be applied to other variables.

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