The Role of Convectively Generated Gravity Waves on Convective Initiation: A Case Study

Abstract A case study of a convection initiation (CI) event involving a mesoscale gravity wave is presented. This severe convection event occurred in east China on 5 June 2009. High-frequency automatic weather station (AWS) data, visible satellite data, and Doppler radar data were combined to depict the features of the gravity wave and the development of several convection centers. The gravity wave was manifested by a surface pressure dip and surface wind shift propagating westward away from the early convection. The pressure dip propagated at a speed of >30 m s−1, which is comparable with that in previous observational studies of convectively generated gravity waves. A special focus is on the initiation of a deep convection cell in Anhui Province, which resulted in 25 deaths. Surface observations showed two precursors before CI, including a convergence line and wind shift at the eastern end of the convergence line. High-resolution numerical simulations with the Weather Research and Forecasting (WRF) Model were used to examine the structure of the gravity waves and forecast CI processes. The model reproduced the observed features of the gravity wave and the precursors before CI. Three-dimensional model results showed that CI occurred at the intersection between a convergence line and the gravity wave. The relationships between the wind shift and the pressure drop are consistent with polarization relation in ducted gravity waves. As the updraft of the gravity wave intersected with the convergence line, the low-level updraft strengthened and led to CI. The gravity wave, which had stronger updraft than downdraft, suggested a positive contribution to CI.

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Performance Evaluation of Sub-Grid Orographic Parameterization in the WRF Model over Complex Terrain in Central Asia

Atmosphere ◽

10.3390/atmos11111164 ◽

2020 ◽

Vol 11 (11) ◽

pp. 1164

Author(s):

Huoqing Li ◽

Junjian Liu ◽

Hailiang Zhang ◽

Chenxiang Ju ◽

Junjie Shi ◽

...

Keyword(s):

Wind Speed ◽

Central Asia ◽

Gravity Wave ◽

Gravity Waves ◽

Surface Wind ◽

Wrf Model ◽

Wave Drag ◽

Near Surface ◽

Upper Level ◽

Orographic Drag

The terrain of Central Asia is complex and rugged over mountains. Consequently, wind speed is overestimated over mountains and plains when using the Weather Research Forecast (WRF) model in winter. To solve this problem, three different simulations (named as control simulation (CRTL), gravity waves (GWD), and flow-blocking drag (FBD), respectively) were designed to investigate the impact of sub-grid orography (gravity waves and flow-blocking drag) on wind forecasts. The results illustrated that near-surface wind-speed overestimations were alleviated when sub-grid orographic drag was used in GWD, though the upper-level wind fields at 500 hPa were excessively reduced compared to CRTL. Thus, we propose eliminating the gravity wave breaking at the upper level to improve upper-level wind underestimations and surface wind speeds at the same time. The sub-grid orographic drag stress of the vertical profile over mountains was reduced when only the flow-blocking drag was retained in FBD. This alleviated underestimations of the upper-level wind speed and near-surface wind, which both have the same positive effects as the gravity wave and flow-blocking total. The mean bias and root mean squared error reduced by 32.76% and 9.39%, respectively, compared to CRTL. Moreover, the temperature and specific humidity in the lower troposphere were indirectly improved. The results of the study demonstrate that it is better to remove sub-grid orographic gravity wave drag when using the gravity wave drag scheme of the WRF model.

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Gravity Wave Investigations over Comandante Ferraz Antarctic Station in 2017: General Characteristics, Wind Filtering and Case Study

Atmosphere ◽

10.3390/atmos11080880 ◽

2020 ◽

Vol 11 (8) ◽

pp. 880

Author(s):

Gabriel Augusto Giongo ◽

José Valentin Bageston ◽

Cosme Alexandre Oliveira Barros Figueiredo ◽

Cristiano Max Wrasse ◽

Hosik Kam ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Phase Speed ◽

Propagation Direction ◽

Small Scale ◽

Wave Source ◽

Medium Scale ◽

Reliable Source ◽

The Fourier Transform

This work presents the characteristics of gravity waves observed over Comandante Ferraz Antarctic Station (EACF: 62.1° S, 58.4° W). A total of 122 gravity waves were observed in 34 nights from March to October 2017, and their parameters were obtained by using the Fourier Transform spectral analysis. The majority of the observed waves presented horizontal wavelength ranging from 15 to 35 km, period from 5 to 20 min, and horizontal phase speed from 10 to 70 ± 2 m·s−1. The propagation direction showed an anisotropic condition, with the slower wave propagating mainly to the west, northwest and southeast directions, while the faster waves propagate to the east, southeast and south. Blocking diagrams for the period of April–July showed a good agreement between the wave propagation direction and the blocking positions, which are eastward oriented while the waves propagate mainly westward. A case study to investigate wave sources was conducted for the night of 20–21 July, wherein eight small-scale and one medium-scale gravity waves were identified. Reverse ray tracing model was used to investigate the gravity wave source, and the results showed that six among eight small-scale gravity waves were generated in the mesosphere. On the other hand, only two small-scale waves and the medium-scale gravity wave had likely tropospheric or stratospheric origin, however, they could not be associated with any reliable source.

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The diurnal cycle of rainfall over New Guinea in convection-permitting WRF simulations

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-18327-2015 ◽

2015 ◽

Vol 15 (13) ◽

pp. 18327-18363 ◽

Cited By ~ 2

Author(s):

M. E. E. Hassim ◽

T. P. Lane ◽

W. W. Grabowski

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Diurnal Cycle ◽

Regional Scale ◽

Wrf Model ◽

Evolutionary Process ◽

New Guinea ◽

Squall Line ◽

Land Breeze ◽

North East

Abstract. In this study, we examine the diurnal cycle of rainfall over New Guinea using a series of convection-permitting numerical simulations with the Weather Research and Forecasting (WRF) model. We focus our simulations on a period of suppressed regional-scale conditions (February 2010) during which local diurnal forcings are maximised. Additionally, we focus our study on the occurrence and dynamics of offshore propagating convective systems that contribute to the observed early-morning rainfall maximum north-east of New Guinea. In general, modelled diurnal precipitation shows good agreement with satellite-observed rainfall, albeit with some timing and intensity differences. The simulations also reproduce the occurrence and variability of overnight convection that propagate offshore as organised squall lines north-east of New Guinea. The occurrence of these offshore systems is largely controlled by background conditions. Days with offshore propagating convection have more middle tropospheric moisture, larger CAPE and greater low-level moisture convergence. Convection has similar characteristics over the terrain on days with and without offshore propagation. The offshore propagating convection manifests via a multi-stage evolutionary process. First, scattered convection over land, which is remnant of the daytime maximum, moves towards the coast and becomes re-organised near the region of coastal convergence associated with the land breeze. The convection then moves offshore in the form of a squall line at ~5 m s−1. In addition, cool anomalies associated with gravity waves generated by precipitating land convection propagate offshore at a dry hydrostatic gravity wave speed (of ~15 m s−1), and act to destabilise the coastal/offshore environment prior to the arrival of the squall line. Although the gravity wave does not appear to initiate the convection or control its propagation, it should contribute to its longevity and maintenance. The results highlight the importance of terrain and coastal effects along with gravity waves in contributing to the diurnal cycle over the Maritime Continent, especially the offshore precipitation maxima adjacent to quasi-linear coastlines.

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Weather Features Associated with Aircraft Icing Conditions: A Case Study

The Scientific World JOURNAL ◽

10.1155/2014/279063 ◽

2014 ◽

Vol 2014 ◽

pp. 1-18 ◽

Cited By ~ 10

Author(s):

Sergio Fernández-González ◽

José Luis Sánchez ◽

Estíbaliz Gascón ◽

Laura López ◽

Eduardo García-Ortega ◽

...

Keyword(s):

Gravity Waves ◽

Atmospheric Stability ◽

Wrf Model ◽

Atmospheric Temperature ◽

Weather Research And Forecasting ◽

Synoptic Situation ◽

Aircraft Icing ◽

Ice Nuclei ◽

Humidity Profiles

In the context of aviation weather hazards, the study of aircraft icing is very important because of several accidents attributed to it over recent decades. On February 1, 2012, an unusual meteorological situation caused severe icing of a C-212-200, an aircraft used during winter 2011-2012 to study winter cloud systems in the Guadarrama Mountains of the central Iberian Peninsula. Observations in this case were from a MP-3000A microwave radiometric profiler, which acquired atmospheric temperature and humidity profiles continuously every 2.5 minutes. A Cloud Aerosol and Precipitation Spectrometer (CAPS) was also used to study cloud hydrometeors. Finally, ice nuclei concentration was measured in an isothermal cloud chamber, with the goal of calculating concentrations in the study area. Synoptic and mesoscale meteorological conditions were analysed using the Weather Research and Forecasting (WRF) model. It was demonstrated that topography influenced generation of a mesolow and gravity waves on the lee side of the orographic barrier, in the region where the aircraft experienced icing. Other factors such as moisture, wind direction, temperature, atmospheric stability, and wind shear were decisive in the appearance of icing. This study indicates that icing conditions may arise locally, even when the synoptic situation does not indicate any risk.

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WRF model and ASAR-retrieved 10 m wind field comparison in a case study over Eastern Mediterranean Sea

Advances in Science and Research ◽

10.5194/asr-4-83-2010 ◽

2010 ◽

Vol 4 (1) ◽

pp. 83-88 ◽

Cited By ~ 1

Author(s):

M. M. Miglietta ◽

S. Zecchetto ◽

F. De Biasio

Keyword(s):

Boundary Layer ◽

Mediterranean Sea ◽

Wind Field ◽

Eastern Mediterranean ◽

Surface Wind ◽

Wrf Model ◽

Eastern Mediterranean Sea ◽

Area Of Interest ◽

Crete Island

Abstract. In Synthetic Aperture Radar (SAR) imagery, signatures of coherent atmospheric structures, due to sea surface roughness modulation by surface winds, are usually well detected. In the present study, the wind field derived from the Envisat Advanced SAR (ASAR) sensor has been analyzed and compared with those simulated with a regional atmospheric model in a case study over an area located in the eastern Mediterranean Sea, extending southward and eastward of Crete island. This is a region subject to complex wind patterns, due to the interaction of the almost steady northerly Etesian wind with the orography of the islands in the region. The ASAR Wide Swath Mode images provide datasets at resolutions exceptionally high compared to model data, appropriate for investigating the mesoscale phenomena on the marine atmospheric boundary layer and to retrieve the surface wind field. The latter has been obtained with a methodology based on the 2-D Continuous Wavelet Transform, suitable to isolate the backscatter patterns on the base of energy and scale considerations. Numerical simulations with the Weather Research and Forecasting (WRF) model have been performed using three 2-way nested domains, the inner one covering the area of interest with a resolution of 1 km. Several simulations, using different diffusion and boundary layer parameterization schemes, have been performed in a case study corresponding to mountain lee waves detected in the ASAR image. The 10 m winds resulting from the numerical experiments have been compared to those retrieved from the ASAR, both quantitatively and qualitatively, in order to analyze the correspondence of observed and simulated wind structures.

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Influence of the cloud-level neutral layer on the vertical propagation of topographically generated gravity waves on Venus

Earth Planets and Space ◽

10.1186/s40623-019-1106-7 ◽

2019 ◽

Vol 71 (1) ◽

Author(s):

Takeru Yamada ◽

Takeshi Imamura ◽

Tetsuya Fukuhara ◽

Makoto Taguchi

Keyword(s):

Layer Thickness ◽

Gravity Wave ◽

Local Time ◽

Gravity Waves ◽

Analytical Approach ◽

Wave Activity ◽

Neutral Layer ◽

Low Latitudes ◽

Vertical Propagation ◽

The Waves

AbstractThe reason for stationary gravity waves at Venus’ cloud top to appear mostly at low latitudes in the afternoon is not understood. Since a neutral layer exists in the lower part of the cloud layer, the waves should be affected by the neutral layer before reaching the cloud top. To what extent gravity waves can propagate vertically through the neutral layer has been unclear. To examine the possibility that the variation of the neutral layer thickness is responsible for the dependence of the gravity wave activity on the latitude and the local time, we investigated the sensitivity of the vertical propagation of gravity waves on the neutral layer thickness using a numerical model. The results showed that stationary gravity waves with zonal wavelengths longer than 1000 km can propagate to the cloud-top level without notable attenuation in the neutral layer with realistic thicknesses of 5–15 km. This suggests that the observed latitudinal and local time variation of the gravity wave activity should be attributed to processes below the cloud. An analytical approach also showed that gravity waves with horizontal wavelengths shorter than tens of kilometers would be strongly attenuated in the neutral layer; such waves should originate in the altitude region above the neutral layer.

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Characterisation and Life Cycle Assessment of Pervious Concrete with Recycled Concrete Aggregates

Crystals ◽

10.3390/cryst11020209 ◽

2021 ◽

Vol 11 (2) ◽

pp. 209

Author(s):

Adilson C. Paula Junior ◽

Cláudia Jacinto ◽

Thaís M. Oliveira ◽

Antonio E. Polisseni ◽

Fabio M. Brum ◽

...

Keyword(s):

Environmental Performance ◽

Treatment Plant ◽

Recycled Concrete ◽

Pervious Concrete ◽

Recycled Aggregate ◽

Recycled Aggregates ◽

Positive Contribution ◽

Concrete Aggregates ◽

Recycled Concrete Aggregates

The search for environmental preservation and conservation of natural resources gives rise to new concepts and viable technical solutions on the path to sustainable development. In this context, this study’s main objective is to analyse the influence of recycled concrete aggregates (RCAs) on the development of pervious concrete, whose use as a floor covering represents an excellent device to mitigate the urban soil sealing phenomena. For this, mechanical and hydraulic tests were carried out, in addition to microstructural analyses and the assessment of its environmental performance. The results obtained were compared to reference studies also involving the incorporation of recycled aggregates. A pilot-scale case study was conducted, involving a parking space lined with pervious concrete moulded “in situ”. In laboratory tests, permeability coefficients and mechanical strengths compatible with the literature and above the normative limit for light traffic were found. The case study demonstrated higher permeability than in the laboratory, but the flexural strength was lower, being indicated only for pedestrian traffic. The environmental assessment showed that the RCA represents a positive contribution to the environmental performance of pervious concrete. Still, attention should be given to the recycled aggregate transport distance between the concrete plant and the RCA treatment plant.

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A little help from my friends: how purchasing gains influence in complex business-to-business services: the case of legal

Journal of Business and Industrial Marketing ◽

10.1108/jbim-01-2015-0006 ◽

2017 ◽

Vol 32 (2) ◽

pp. 206-217 ◽

Cited By ~ 1

Author(s):

Wendy L. Tate ◽

Lisa M. Ellram ◽

Ulrich Schmelzle

Keyword(s):

Supplier Management ◽

Positive Contribution ◽

Business Service ◽

Case Study Method ◽

Business Services ◽

Content Type ◽

Additional Costs ◽

Service Procurement ◽

Business To Business

Purpose The purpose of this research is to develop an understanding of how purchasing can become meaningfully involved in complex business-to-business service purchases. Design/methodology/approach A single in-depth case study method of an exemplar organization was applied to better understand the purchasing function’s role in adding to the value proposition in complex, non-traditional business-to-business service purchases. Findings Powerful allies or advocates can mediate purchasing involvement in service procurement. However, once the involvement is initiated, purchasing must make a positive contribution with respect to the specific needs and expectations of the budget owner to retain its influence. Research limitations/implications This research extends institutional theory to show how powerful allies or advocates can mediate purchasing involvement in the complex services spend. Practical implications This study describes the potential impact of purchasing’s involvement in complex services spend and highlights the opportunities for purchasing managers to improve supplier management and drive out additional costs. Originality/value For the business practitioner, this research provides evidence regarding how individual functions can gain influence in the organization. A conceptual model describes the meaningful involvement of purchasing in complex business-to-business service purchases.

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The nonlinear effects on the characteristics of gravity wave packets: dispersion and polarization relations

Annales Geophysicae ◽

10.1007/s00585-000-1316-z ◽

2000 ◽

Vol 18 (10) ◽

pp. 1316-1324 ◽

Cited By ~ 13

Author(s):

S.-D. Zhang ◽

F. Yi ◽

J.-F. Wang

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Middle Atmosphere ◽

Wave Packets ◽

Nonlinear Effects ◽

Wave Theory ◽

Nonlinear Propagation ◽

Waves And Tides ◽

Time Variations ◽

Isothermal Atmosphere

Abstract. By analyzing the results of the numerical simulations of nonlinear propagation of three Gaussian gravity-wave packets in isothermal atmosphere individually, the nonlinear effects on the characteristics of gravity waves are studied quantitatively. The analyses show that during the nonlinear propagation of gravity wave packets the mean flows are accelerated and the vertical wavelengths show clear reduction due to nonlinearity. On the other hand, though nonlinear effects exist, the time variations of the frequencies of gravity wave packets are close to those derived from the dispersion relation and the amplitude and phase relations of wave-associated disturbance components are consistent with the predictions of the polarization relation of gravity waves. This indicates that the dispersion and polarization relations based on the linear gravity wave theory can be applied extensively in the nonlinear region.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

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GRAVITY-WAVE DETECTORS AS PROBES OF EXTRA DIMENSIONS

International Journal of Modern Physics D ◽

10.1142/s0218271805007905 ◽

2005 ◽

Vol 14 (12) ◽

pp. 2347-2353 ◽

Cited By ~ 1

Author(s):

CHRIS CLARKSON ◽

ROY MAARTENS

Keyword(s):

Black Holes ◽

String Theory ◽

Gravity Wave ◽

Gravity Waves ◽

Extra Dimensions ◽

State Of The Art ◽

Three Dimensional ◽

Observable Universe ◽

Dimensional Spacetime ◽

Higher Dimensional

If string theory is correct, then our observable universe may be a three-dimensional "brane" embedded in a higher-dimensional spacetime. This theoretical scenario should be tested via the state-of-the-art in gravitational experiments — the current and upcoming gravity-wave detectors. Indeed, the existence of extra dimensions leads to oscillations that leave a spectroscopic signature in the gravity-wave signal from black holes. The detectors that have been designed to confirm Einstein's prediction of gravity waves, can in principle also provide tests and constraints on string theory.

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