Vertical Wind Profiles Research Articles

Observational study on thermodynamic and kinematic structures of Typhoon Vicente (2012) at landfall

Severe Typhoon Vicente was the strongest tropical cyclone (TC) that has attacked Hong Kong (HK) since 1999. This paper presents a comprehensive observational study on this windstorm during its landfall, based on in-situ measurements from weather radars, radiosonde balloons, wind profilers and other ground-based devices at various meteorological stations in HK. Both its thermodynamic and kinematic structures are investigated to explore the TC characteristics at landfall. The results of this study reflected that the vortex extended to the tropopause around 16 km. Vertical profiles of pressure deficit below TC outflow layer depicted a linear distribution pattern with respect to isobar-expressed altitude, with a slope increasing almost linearly with increasing surface pressure deficit. The inner and outer rainband regions were respectively dominated by stratiform and convective precipitations, and the inner region was vertically separated into two discriminatory layers by the melting layer located at 5.4 km. The sea-air contrast temperature varied noticeably during the landfall process, with an increase of 1–1.5 °C in the TC inner region where sea-air flux exchange strengthened distinctly compared to that at outer areas.Vertical wind profiles from balloons showed that horizontal wind speed and wind direction experienced a sharp change around the tropopause, above which flow motions were dominated by the anti-cyclone of Tibetan high. The inflow layer depth was found on the order of 2 km, compared to 1–2 km for the atmospheric mixing layer depth. The gradient height, recognized via the maximum horizontal wind, was in the range of 0.5–2.5 km which decreased with decreasing radii prior to landfall. Examination of the results from wind profilers over marine, urban and rugged terrain showed that the wind structures in the TC boundary layer (TCBL) depended upon storm-relative position and underlying terrain features. Vertical profiles of marine winds in the inner rainband region demonstrated a jet feature, with mean speed being logarithmical with height in the lowest 1 km. TCBL winds above rugged areas were influenced severely by topographic effects. The low-level wind maximum, or the gradient speed, changed insignificantly above different sites.

Vertical observation and analysis on rapid formation and evolutionary mechanisms of a prolonged haze episode over central-eastern China

To clarify the rapid formation and evolutionary mechanisms of an extremely severe and persistent haze and fog (HF) episode that occurred in central-eastern China from Dec 20 to 25, 2015, a novel campaign was conducted and vertical profiles of wind, temperature, light extinction coefficient (LEC) and PM2.5 concentration were used to analyze the rapid formation and evolutionary mechanisms of this HF episode. The substantial downward transportation of regional pollution from high layers and stagnant weather conditions favorable for the local pollution accumulation were the two main causes of the rapid increase in pollutant concentration. Southwest wind speeds of 4m/s between 300 and 600m and obvious downward flows were observed, whereas the southwest wind speeds were low below 300m, and strong temperature inversion with intensity of 4.5°C/100m expanded vertically to a height of 600m. Two peaks of PM2.5 concentration were observed at 200 and 700m, corresponding to 235 and 215μg/m3, respectively. The frequent change in wind direction and wind speeds resulted in the fluctuation of PM2.5 concentration. The turbulence within lower layers of the troposphere was enhanced by easterly and northerly winds which decreased the pollution level; however, the strength and stretching height of the winds were insufficient to fully clear the air of pollutants. The PM2.5 concentration revealed 2-high concentration layers in the vertical direction. The maximum concentration layer was below 100m, while the second high-concentration layer was at 400m.

Upper limit for wind shear in stably stratified conditions expressed in terms of a bulk Richardson number

Profile measurements of wind and potential temperature from a land site (obtained by a RASS for several years) and an offshore site (obtained at the meteorological mast on the research platform FINO 1 for one year) are used to analyse the temporal evolution of wind speed and wind shear under statically stable conditions, especially in situations with low-level jets. In both cases a bulk Richardson number is calculated from the data. Data analysis indicates that there seems to exist a lower bound for the bulk Richardson number during stable stratification which is greater than zero. At this lower bound the flow reaches its maximum possible vertical wind shear. Even larger shear would then mean production of new turbulence which in turn would reduce the shear. Therefore, at this lower bound, the flow is in equilibrium between production and depletion of turbulence characterized by an equilibrium Richardson number. This equilibrium Richardson number is found here at about 0.1 for the land site and 0.04 for the marine site. For situations where maximum shear occurs, this shear can be compared to the shear described by the logarithmic vertical wind profile law for stable stratification. This allows the derivation of relations for the equilibrium Richardson number and the constant in the correction term of the logarithmic wind law in terms of the stratification parameter z∕L* and the surface roughness zT for temperature.

A Comparison of Vertical Atmospheric Wind Profiles Obtained from Monostatic Sodar and Unmanned Aerial Vehicle–Based Acoustic Tomography

AbstractThe natural sound generated by an unmanned aerial vehicle is used in conjunction with tomography to remotely sense the virtual temperature and wind profiles of the atmosphere in a horizontal plane up to an altitude of 1200 m and over a baseline of 600 m. Sound fields recorded on board the aircraft and by an array of microphones on the ground are compared and converted to sound speed estimates for the ray paths intersecting the intervening medium. Tomographic inversion is then used to transform these sound speed values into two-dimensional profiles of virtual temperature and wind vector, which enables the atmosphere to be visualized and monitored over time. The wind vector and temperature estimates are compared to measurements taken by a collocated midrange Doppler sodar and sensors on board the aircraft. Large-eddy simulations of daytime atmospheric boundary layers and error models of the tomographic inversion and sodar are also used to assess the magnitude and nature of anticipated differences. Both the simulations and field trials data show similar levels of correspondence between the tomographically derived and independently observed measurements.

Effects of simplified atmospheric profiles on short range infrasound propagation

Meteorological profiles strongly influence the propagation of infrasound signals. Much of the infrasound literature has focused on long-range (>250 km) propagation; however, there is interest in short-range (<150 km) propagation from an infrastructure monitoring standpoint. Therefore, understanding the effects of meteorological profiles is crucial. This paper focuses on simplified vertical temperature and wind profiles up to 20 km altitude and their effect on an infrasonic signal emanating from an arbitrary point source. A wide-angle, finite-element PE model that correctly handles discontinuities in wavenumber is used for calculating transmission loss. A large number of simulations were performed to investigate the effect that temperature and wind profiles in different layers of the atmosphere have on surface transmission loss and to assess the sensitivity of varying these profiles. A discussion of the results of these simulations are presented as well as an overview of temperature profiles used in this study.

Quality assessment of VVP winds from Indian Doppler weather radars: a data assimilation perspective

This study demonstrates the data assimilation perspective of vertical profiles of winds derived from the Doppler weather radar (DWR) data using the volume velocity processing (VVP) technique. The VVP information from the nine Indian DWR stations is used in this study. The winds from the Indian DWR network are assessed for their quality based on the National Center for Medium Range Weather Forecasting unified model (NCUM). This paper describes the quality of DWR VVP winds, preprocessing of VVP wind data, and their use in NCUM 4 D-Var assimilation systems. The VVP winds are compared against an NCUM background (short forecast) to understand the observation bias. Comparison of VVP winds is also made with colocated radiosonde wind observations. The VVP winds show less bias when compared against model background especially in the region of strong wind flow. The correlation between the observations and the model background is greater than 0.7 for most of the radars. The VVP winds provide reasonably accurate estimates of the vertical wind structure in the troposphere over radar locations, which can be effectively used in the numerical weather prediction system.

Dropsonde Observations of Total Integrated Water Vapor Transport within North Pacific Atmospheric Rivers

Abstract Aircraft dropsonde observations provide the most comprehensive measurements to date of horizontal water vapor transport in atmospheric rivers (ARs). The CalWater experiment recently more than tripled the number of ARs probed with the required measurements. This study uses vertical profiles of water vapor, wind, and pressure obtained from 304 dropsondes across 21 ARs. On average, total water vapor transport (TIVT) in an AR was 4.7 × 108 ± 2 × 108 kg s−1. This magnitude is 2.6 times larger than the average discharge of liquid water from the Amazon River. The mean AR width was 890 ± 270 km. Subtropical ARs contained larger integrated water vapor (IWV) but weaker winds than midlatitude ARs, although average TIVTs were nearly the same. Mean TIVTs calculated by defining the lateral “edges” of ARs using an IVT threshold versus an IWV threshold produced results that differed by less than 10% across all cases, but did vary between the midlatitudes and subtropical regions.

Comparison and Application of Two Kinds Vertical Wind Profile Data Part II:The Characteristics of Wind Profiles under Different Weather Conditions Related to Rainfall

Comparison and Application of Two Kinds Vertical Wind Profile Data Part II:The Characteristics of Wind Profiles under Different Weather Conditions Related to Rainfall

Properties of a Martian local dust storm in Atlantis Chaos from OMEGA/MEX data

In this study we present the analysis of the dust properties of a local storm imaged in the Atlantis Chaos region on Mars by the OMEGA imaging spectrometer on March 2nd, 2005. We use the radiative transfer model MITRA to study the dust properties at solar wavelengths between 0.5 µm and 2.5 µm and infer the connection between the local storm dynamics and the topography.We retrieve maps of effective grain radius (reff), optical depth at 9.3 µm (τ9.3) and top altitude (ta) of the dust layer. Our results show that large particles (reff = 1.6 µm) are gathered in the centre of the storm (lat = 33.5° S; lon = 183.5° W), where the optical depth is maximum (τ9.3 > 7.0) and the top altitude exceeds 18 km. Outside the storm, we obtain τ9.3 < 0.2, in agreement with the estimates derived from global climate models (GCM).We speculate that a low thermal inertia region at the western border of Atlantis Chaos is a possible source of the dust storm. Moreover, we find evidence that topography plays a role in confining the local storm in Atlantis Chaos. The vertical wind component from the GCM does not provide any hint for the triggering of dust lifting. On the other hand, the combination of the horizontal and vertical wind profiles suggests that the dust, once lifted, is pushed eastward and then downward and gets confined within the north-east ridge of Atlantis Chaos.From our results, the thickness of the dust layer collapsed on the surface ranges from about 1 µm at the storm boundaries up to more than 100 µm at its centre. We verify that a layer of dust thicker than 1 µm, deposited on the surface, can prevent the detection of mafic absorption features. However, such features are still present in OMEGA data of Atlantis Chaos registered after the storm. Hence, we deduce that, once the storm is over, the dust deposited on an area larger than the one where it has been observed.

Vertical wind profiles for typhoon, monsoon and thunderstorm winds

The vertical profiles of mean wind speed within the atmospheric boundary layer have always been a focus of attention in wind engineering. In particular, the characteristics of wind speed profiles associated with different wind phenomena are of great significance in many engineering fields. Hence, this study presents a comparative analysis on the wind profile characteristics in connection with typhoon, monsoon and thunderstorm winds respectively, in which the wind profiles are constructed by synchronizing the wind measurements taken from a surface cup-anemometer and a Doppler radar profiler equipped at a coastal weather station in Hong Kong. For each type of wind phenomenon, the shape of the wind speed profiles is examined, and the fitting parameters contained in the logarithmic-law and the power-law model are derived. In addition, some other characteristic parameters associated with the wind speed profiles, such as wind shear coefficient and gust factor, etc, are determined as well to enhance the understanding of the characteristics of wind profiles in connection with different wind phenomena.

Least Squares Fitting of Computational Fluid Dynamics Results to Measured Vertical Wind Profiles

Microscale numerical modeling is currently the main tool used in wind industry to assess local wind resources. This paper presents a systematic procedure to adjust computational fluid dynamics (CFD) predicted wind profiles to experimental measurements in order to minimize their differences. It can be applied when wind measurements are available. Data from ten masts with several measurement heights from the well-known Bolund hill experiment provided the observed wind profiles. Simulated profiles were calculated with windsim CFD model for the aforementioned site. Speed-up correction factors were defined through the least squares method to cross-correlate each mast as reference to all the others inside the Bolund hill domain. After, the observed and the adjusted wind profiles at the same position were compared. Moreover, root mean square errors (RMSEs) were used as a metric to evaluate the estimations and the ability of each position to be predicted and predictor. Results have shown that the quality of the adjustment process depends on the flow characteristics at each position related to the incoming wind direction. Most affected positions, i.e., when the airflow overcomes the Bolund hill escarpment, present the less accurate wind profile estimations. The reference mast should be installed upstream of the potential wind turbines' locations and after the main local characteristics of topographical changes.

The tropical cyclone response to changing wind shear using the method of time‐varying point‐downscaling

AbstractPrevious studies using idealized numerical simulations to understand the tropical cyclone (TC) response to time‐varying wind shear have applied instantaneous changes in the TC environment. This was typically accomplished by pausing the simulation, constructing a new environmental vertical wind profile, rebalancing the mass field, and then restarting the simulation. A new modeling framework allows for smoothly transitioning environmental wind states: time‐varying point‐downscaling (TVPDS). TVPDS uses large‐scale relaxation to smoothly transition between different vertical profiles of environmental wind (and/or temperature and moisture) while coordinating the point‐downscaling method such that the environment remains in balance. TVPDS simulations of quasi steady state, moderately intense (∼50 m s−1) TCs show that the response to increasing wind shear is a steady reduction in intensity without recovery to the preshear intensity. These results, which are consistent with the typical evolution of real TCs, stand in contrast to some previous studies that found a recovery to prestorm intensity after an initial weakening due to increased shear. TVPDS simulations also show that the rate at which the TC weakens depends on how rapidly the environment transitions to greater shear. Analyses of surface fluxes, regions of convection, and other variables are presented to determine how time‐varying shear affects TCs. Finally, TVPDS simulations of TCs transitioning from environments characterized by high‐shear into low‐shear environments show that a similar but opposite response occurs.

Potential of collocated radiometer and wind profiler observations for monsoon studies

Collocated observations from microwave radiometer and wind profiler are used in a pilot study during the monsoon period to derive information on the thermodynamics and winds and association with rainfall characteristics. These instruments were operated throughout the monsoon season of 2015. Continuous vertical profiles of winds, temperature and humidity show significant promise for understanding the low-level jet, its periodicity and its association with moisture transport, clouds and precipitation embedded within the monsoon large-scale convection. Observations showed mutually beneficial in explaining variability that are part of the low frequency oscillations and the diurnal variability during monsoon. These observations highlight the importance of locally driven convective systems, in the presence of weak moisture transport over the area. The episodic moisture convergence showed a periodicity of 9 days which matches with the subsequent convection and precipitation and thermodynamic regimes. Inferences from the diurnal cycle of moisture transport and the convective activity, relationship with the low-level jet characteristics and thermodynamics are also illustrated.

Quality and Impact of Indian Doppler Weather Radar Wind Profiles: A Diagnostic Study

In the tropics, efficient weather forecasts require high-quality vertical profiles of winds to overcome improper coupling of mass and wind fields and balance relationships in the region. The India Meteorological Department (IMD) operates the network of Doppler Weather Radar (DWR) in microwave frequencies (S-band or C-band) at various locations in India. The National Centre for Medium Range Weather Forecasting (NCMRWF) receives the volume velocity processing (VVP) wind profiles from all DWRs through the Global Telecommunication System (GTS) network in near real time. The radar VVP wind is a mean horizontal wind derived at different heights from radial velocities suitable for numerical weather prediction applications. Three numerical experiments, CNTL (without VVP winds), 3DVAR and HYBRID with the assimilation of VVP winds by means of 3-dimensional variational (3dvar) and hybrid data assimilation systems were conducted using the NCMRWF Global Forecast System (NGFS) model. This study had two objectives: (1) quality assessment of VVP winds and (2) investigation of the impact of VVP wind profiles on NGFS model forecast. The quality of VVP wind profiles was assessed against the NGFS model background and radiosonde wind profiles. The absolute values of zonal and meridional wind observation minus background (O−B) increased with the pressure for all DWRs. All radars exhibited the accepted (rejected) ratio as a decreasing (increasing) function of pressure. The resemblance between the zonal and meridional O−B statistics for 3DVAR and HYBRID experiments is apparently remarkable. The accepted VVP winds and radiosonde winds in both experiments (3DVAR and HYBRID) were consistent. The correlation coefficient (R) was higher at Patna (Patiala) for zonal (meridional) winds in the 3DVAR experiment and at Patna (Jaipur) in the HYBRID experiment. At Chennai, the R value was lower in both the experiments for both wind components. However, because of the assimilation of VVP winds by means of 3dvar, the root-mean-square error (RMSE) of zonal and meridional winds improved by approximately 2–3% up to the day 5 forecast in the analysis performed below 700 hPa. Further improvement in RMSE by approximately 5% was observed in both the wind components because of the hybrid data assimilation. The zonal and meridional wind RMSEs in the HYBRID (3DVAR) experiment improved by ≈5 (3)% compared with the 3DVAR (CNTL) experiment.

Sensitivity analysis of WRF model PBL schemes in simulating boundary-layer variables in southern Italy: An experimental campaign

The sensitivity of boundary layer variables to five (two non-local and three local) planetary boundary-layer (PBL) parameterization schemes, available in the Weather Research and Forecasting (WRF) mesoscale meteorological model, is evaluated in an experimental site in Calabria region (southern Italy), in an area characterized by a complex orography near the sea. Results of 1km×1km grid spacing simulations are compared with the data collected during a measurement campaign in summer 2009, considering hourly model outputs.Measurements from several instruments are taken into account for the performance evaluation: near surface variables (2m temperature and relative humidity, downward shortwave radiation, 10m wind speed and direction) from a surface station and a meteorological mast; vertical wind profiles from Lidar and Sodar; also, the aerosol backscattering from a ceilometer to estimate the PBL height.Results covering the whole measurement campaign show a cold and moist bias near the surface, mostly during daytime, for all schemes, as well as an overestimation of the downward shortwave radiation and wind speed. Wind speed and direction are also verified at vertical levels above the surface, where the model uncertainties are, usually, smaller than at the surface. A general anticlockwise rotation of the simulated flow with height is found at all levels. The mixing height is overestimated by all schemes and a possible role of the simulated sensible heat fluxes for this mismatching is investigated. On a single-case basis, significantly better results are obtained when the atmospheric conditions near the measurement site are dominated by synoptic forcing rather than by local circulations.From this study, it follows that the two first order non-local schemes, ACM2 and YSU, are the schemes with the best performance in representing parameters near the surface and in the boundary layer during the analyzed campaign.

Prototype campaign assessment of disturbance‐induced tree loss effects on surface properties for atmospheric modeling

AbstractChanges in large‐scale vegetation structure triggered by processes such as deforestation, wildfires, and tree die‐off alter surface structure, energy balance, and associated albedo—all critical for land surface models. Characterizing these properties usually requires long‐term data, precluding characterization of rapid vegetation changes such as those increasingly occurring in the Anthropocene. Consequently, the characterization of rapid events is limited and only possible in a few specific areas. We use a campaign approach to characterize surface properties associated with vegetation structure. In our approach, a profiling LiDAR and hemispherical image analyses quantify vegetation structure and a portable mast instrumented with a net radiometer, wind–humidity–temperature stations in a vertical profile, and soil temperature–heat flux characterize surface properties. We illustrate the application of our approach in two forest types (boreal and semiarid) with disturbance‐induced tree loss. Our prototype characterizes major structural changes associated with tree loss, changes in vertical wind profiles, surface roughness energy balance partitioning, a proxy for NDVI (Normalized Differential Vegetation Index), and albedo. Multi‐day albedo estimates, which differed between control and disturbed areas, were similar to tower‐based multi‐year characterizations, highlighting the utility and potential of the campaign approach. Our prototype provides general characterization of surface and boundary‐layer properties relevant for land surface models, strategically enabling preliminary characterization of rapid vegetation disturbance events.

Climate Forecasts at the Centro de Lançamento de Alcântara using the Climate Model RegCM4

This study uses climate modeling (RegCM4 Climate Model) to provide a wind forecast average behavior at low levels, close to the surface. The model was used to generate an estimate of the average vertical wind profile lasting 5 months, from August to December 2015, attempting to observe intra-seasonal variations, with the presence of persistence in the wind field. The results of climate modeling of the wind profile near the surface have the great potential for great operational significance during launch campaigns at the Centro de Lancamento de Alcântara. Three average results were generated for the month of November 2015, while operating in Sao Lourenco. A dynamical downscaling nested with global models with RCP4.5 and RCP8.5, using 3 different global conditions initialization datasets. It used subsets with the models from the Met Office Hadley Centre (HadGEM2-ES), the Centre National de Recherches Meteorologiques (CNRM-CM5), and the Commonwealth Scientific and Industrial Research Organization CSIRO-Mk3.6), making a downscaling with the RegCM4 Climate Model for the Centro de Lancamento de Alcântara region. The results are preliminary but show great potential. Since the RegCM4 Climate Model can show variations of high and low intensity, its temporal frequency in the average vertical wind profile and the duration of temporal variation are of the order of 3 – 5 days. The RegCM4 Climate Model had better results with the one from the Met Office Hadley Centre, HadGEM2-ES, when it was qualitatively compared with observational data (ERA Interim Model) of the campaign period and reanalysis data.

Inversion Build-Up and Cold-Air Outflow in a Small Alpine Sinkhole

Semi-idealized model simulations are made of the nocturnal cold-air pool development in the approximately 1-km wide and 100–200-m deep Grunloch basin, Austria. The simulations show qualitatively good agreement with vertical temperature and wind profiles and surface measurements collected during a meteorological field expedition. A two-layer stable atmosphere forms in the basin, with a very strong inversion in the lowest part, below the approximate height of the lowest gap in the surrounding orography. The upper part of the stable layer is less strongly stratified and extends to the approximate height of the second-lowest gap. The basin atmosphere cools most strongly during the first few hours of the night, after which temperatures decrease only slowly. An outflow of air forms through the lowest gap in the surrounding orography. The outflow connects with a weak inflow of air through a gap on the opposite sidewall, forming a vertically and horizontally confined jet over the basin. Basin cooling shows strong sensitivity to surface-layer characteristics, highlighting the large impact of variations in vegetation and soil cover on cold-air pool development, as well as the importance of surface-layer parametrization in numerical simulations of cold-air-pool development.

Observing and Modeling the Vertical Wind Profile at Multiple Sites in and above the Amazon Rain Forest Canopy

We analyzed the vertical wind profile measured at six experimental tower sites in dense forest in the Amazon Basin and examined how well two simple models can reproduce these observations. In general, the vertical wind profile below the canopy is strongly affected by the forest structure. From the forest floor to 0.65h (where h = 35 m is the average height of the forest canopy for sites considered), the wind profile is approximately constant with height with speeds less than 1 ms−1. Above 0.65 to 2.25h, the wind speed increases with height. Testing these data with the Yi and Souza models showed that each was able to reproduce satisfactorily the vertical wind profile for different experimental sites in the Amazon. Using the Souza Model, it was possible to use fewer input variables necessary to simulate the profile.

What is the Required Level of Details to Represent the Impact of the Built Environment on Energy Demand?

A full coupling between a CFD code, a thermo-radiative model and a building energy simulation model enables Solene-microclimat software to calculate both building thermal behavior and urban microclimate with the retroaction of buildings on microclimate. However, this full coupling is time consuming and it is legitimate to wonder if it is always necessary to perform such detailed simulations. In the framework of the MERUBBI project, simulations were carried out to answer this question. A set of simulations was designed to explore different kinds of configurations: three cities in France (Nantes, Paris and Strasbourg), three levels of density (from an isolated building to an implementation in the dense city center) and three kinds of buildings (an individual house in Paris, a residential building in Nantes and an office building in Strasbourg). To study the sensitivity of energy demand to the coupling detail, for each thermal flux at the external surfaces of the building, several levels of details were taken into account. For the impact of wind on convection, three modalities were considered: a constant convective heat transfer coefficient, calculated from the wind velocity at 10m; a convective heat transfer coefficient calculated from a vertical wind profile; a convective heat transfer coefficient calculated from the local wind velocity simulated with a CFD code. For the impact of air temperature on convection, two modalities are considered the use of the temperature measured at the nearest meteorological station; a local temperature calculated with the CFD simulation. For the impact of long-wave radiative exchanges, three modalities: the building exchanges with the sky without taking into account the masks of the environment and the long-wave radiative exchanges with the other surfaces; the building exchanges with the sky, taking into account the mask effects but not the exchanges with the surrounding surfaces; long-wave exchanges are taken into account with all kinds of surfaces in function of view factors. For the impact of short-wave radiations, two modalities: only direct and diffuse solar fluxes are taken into account; inter-reflections are considered. The results indicate that if the calculation of air temperature and convective heat transfer coefficient have few impacts in all the cases, the way of calculating long-wave and short wave radioactive fluxes has to be carefully considered, in winter as in summer. More detailed recommendations are given according to the density of the site in which the building will be implemented.