Surface Wind Direction Research Articles

台風シミュレーション・システムの開発と風向別最大風速の評価

The basic wind speed for a long-span bridge was examined using GIS-based typhoon simulation system. First, the recorded typhoons which generated strong wind at the proposed bridge site were extracted from the typhoon data by the Japan Meteorological Agency, and probabilistic models expressing the characteristics of the typhoons were created. Next, the surface wind speed and direction were calculated using the Meng's formula, and they were examined by comparing with wind observation records at the site. Based on these results, the probability distributions of the annual maximum wind speed for every 16-divided wind direction were computed by the Monte-Carlo method. Various analyses were efficiently performed making the best use of the functions of GIS.

Identification of sources and estimation of emission profiles from highly time-resolved pollutant measurements in Tampa, FL

Aerosol slurry samples were collected at 30-min intervals for sequential 1-month periods at each of two sites (Sydney and “Dairy”) in the Tampa Bay area during the 2002 Bay Regional Atmospheric Chemistry Experiment using the University of Maryland Semicontinuous Elements in Aerosol Sampler-II (SEAS-II). More than 500 samples, believed to be affected by plumes from local utility and industrial sources, were selected for electrothermal atomic absorption spectrophotometric analyses for elemental markers (Al, Fe, Cr, Cu, Mn, Pb, Se, As, Ni, Zn and Cd) based on excursions in SO 2 and NO x measurements. Correlation of short-term excursions in metals and SO 2, and surface wind directions observed between May 23 and 26th, 2002, revealed the influence of an animal feed supplements production facility (AFS), 17 km upwind at a station angle of 81°, for which emissions had not previously been detected by standard monitoring methods. Emission “profiles” for this source were developed, separately, from the time series data and by using principle components analysis (PCA) and positive matrix factorization (PMF). In addition, a local dust component was evident in Al and Fe concentration profiles during periods of elevated wind speeds and was resolved by PCA/PMF. Similarly, large but brief 1.5-h excursions in Zn (maximum, 403 ng m −3), Cd, and Pb on May 17th were correlated with winds from the direction of an incinerator (station angle, 250°) 17 km from Sydney. Lastly, large excursions in As concentrations (maximum, 86 ng m −3) observed (May 4th and 5th at Sydney and November 2nd and 3rd at the Dairy) were used to locate previously unrecognized sources, tentatively associated with combustion/production of pressure-treated lumber. Profiles developed directly from the time series data were in the range of those derived from PCA-PMF (AFS); and those for the incinerator, with previously published values.

Vicarious calibration of the third and fourth Stokes parameters of Windsat measurements

Microwave observations made at the third and fourth Stokes parameters can be used to determine the surface wind direction over oceans. However, due to their smaller amplitudes (less than 3 K at the third Stokes parameter and 1 K at the fourth Stokes parameter), the absolute calibration to these measurements becomes crucial. A new methodology is developed in this study to calibrate the Windsat third and fourth Stokes parameters through tropical rain forest measurements over the Amazon and central Africa. It is found that the Windsat fourth Stokes parameter at 18 GHz has biases of the order of 0.5 K, which could severely affect the wind vector retrievals.

Can synthetic aperture radars be used to estimate hurricane force winds?

We compare wind fields retrieved from a RADARSAT‐I synthetic aperture radar (SAR) image acquired over Hurricane Ivan on September 10, 2004 using the C‐band geophysical model functions Cmod4 and its newest version Cmod5. Cmod4 has previously been shown to yield very good wind field estimates under low and moderate wind conditions. Wind directions obtained from streaks imaged by the SAR, that are well aligned with the mean surface wind direction are used to invert both algorithms to obtain estimates of the wind speed on scales of 1 km. These estimates are compared with predictions from a high‐resolution tropical cyclone model as well as local in situ data. It is found that the SAR wind speeds using Cmod5 agree reasonably well, while those from Cmod4 significantly under predict the measured wind speeds near the hurricane eye wall that reach values as high as 60 m s−1.

Using Sun Glint to Check the Relative Calibration of Reflected Spectral Radiances

Abstract Observations of sunlight reflected from regions of sun glint are used to check the relative calibration of spectral radiances obtained with imaging radiometers. Reflectances at different wavelengths for sun-glint regions are linearly related. Provided that the atmosphere is reasonably transparent at the wavelengths, the aerosol burden is reasonably light, 0.64-μm optical depth less than 0.2; the particles constituting the aerosol are reasonably large, as is the case for marine aerosols; and the solar zenith angle is less than about 35°, the linear relationships between reflectances at different wavelengths are rather insensitive to the factors that govern the reflectances themselves. The relationships are remarkably insensitive to atmospheric composition, surface wind speed and direction, illumination, and viewing geometry. The slopes and offsets of the linear relationships are used to assess the relative accuracies of the calibrations of the different channels. Such assessments would appear to be attractive for checks on the in-flight performance of aircraft-borne imaging radiometers. Here, observations of reflectances at 0.64, 0.84, 1.6, and 2.1 μm for regions of sun glint obtained with the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) instruments are shown to be consistent with each other. Observations of the 0.64- and 1.6-μm reflectances for the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) instrument are shown to be inconsistent with the MODIS observations, the VIRS 1.6-μm gain appearing to be too low by 9%. The 0.64-, 0.84-, and 1.6-μm reflectances obtained with the NOAA-16 and NOAA-17 Advanced Very High Resolution Radiometers (AVHRRs) for December 2002 are shown to be inconsistent with each other and inconsistent with the MODIS observations. Based on observations of the extensive ice sheets of Antarctica, the NOAA-16 0.64-μm gain is found to be too low by 5% and that for the 0.84-μm reflectance is too low by 12%; the NOAA-17 0.64-μm gain is found to be accurate (within 2%), but the 0.84-μm gain is too low by 15%. With the gains adjusted, the 0.64- and 0.84-μm reflectances obtained for regions of sun glint with the AVHRRs are consistent with each other and consistent with the Terra and Aqua MODIS observations. These results suggest that the gain for the NOAA-16 AVHRR 1.6-μm reflectance is accurate (within 1%) and that for the NOAA-17 AVHRR is too low by 5%. All of the observations were made with the AVHRR in the low-reflectance (high gain) mode. The accuracy of these assessments is expected to be about 5%.

Wind- and Wave-Field Measurements Using Marine X-Band Radar-Image Sequences

This paper describes two algorithms for the retrieval of high-resolution wind and wave fields from radar-image sequences acquired by a marine X-band radar. The wind-field retrieval algorithm consists of two parts. In the first part, wind directions are extracted from wind-induced streaks, which are approximately in line with the mean surface wind direction. The methodology is based on the retrieval of local gradients from the mean radar backscatter image and assumes the surface wind direction to be oriented normal to the local gradient. In the second part, wind speeds are derived from the mean radar cross section. Therefore, the dependence of the radar backscatter on the wind vector and imaging geometry has to be determined. Such a relationship is developed by using neural networks (NNs). For the verification of the algorithm, wind directions and speeds from nearly 3300 radar-image sequences are compared to in situ data from a colocated wind sensor. The wave retrieval algorithm is based on a methodology that, for the first time, enables the inversion of marine radar-image sequences to an elevation-map time series of the ocean surface without prior calibration of the acquisition system, and therefore, independent of external sensors. The retrieved ocean-surface elevation maps are validated by comparison of the resulting radar-derived significant wave heights, with the significant wave heights acquired from three colocated in situ sensors. It is shown that the accuracy of the radar-retrieved significant wave height is consistent with the accuracy of the in situ sensors.

Impact of Island-Induced Clouds on Surface Measurements: Analysis of the ARM Nauru Island Effect Study Data

Abstract An Atmospheric Radiation and Cloud Station (ARCS) was established on the island of Nauru by the Atmospheric Radiation Measurement (ARM) Program. Analysis of the Nauru99 field experiment data indicated that measurements at the ARCS were affected by a cloud plume that was induced by diurnal heating of the island. During the Nauru Island Effects Study, instrumentation was installed at a second site to develop criteria for identifying when the cloud plume occurs and to quantify its effect on ARCS measurements. The plume directional heading and frequency of occurrence are affected by the large-scale tropical circulation. During the present study, in which an El Niño was developing, Nauru was in a region of active convection, and easterly trade winds were not dominant; plumes were observed in 25% of satellite images, and only one-half of the observed plumes were downwind of the ARCS site. Surface wind direction, surface air temperature, and downwelling solar radiation at the two sites were used to identify periods when the cloud plume affected surface measurements. Differences in low-cloud frequency and surface radiation between plume-affected and non-plume-affected periods were examined. Existence of the cloud plume increased the average low-cloud frequency of occurrence from 20% to 35%, decreased the average downwelling shortwave radiation by 50–60 W m−2, and increased the average downwelling longwave radiation by 5–10 W m−2. Installing a suite of surface meteorological instruments and a global shortwave radiometer at a second site will allow for the long-term quantification of the cloud plume effect on the radiation field at the ARCS site.

Measurement of Ocean Surface Winds Using Synthetic Aperture Radars

A methodology for retrieving high-resolution ocean surface wind fields from satellite-borne synthetic aperture radar (SAR) data is introduced and validated. The algorithms developed are suited for ocean SAR data, which were acquired at the C band of either vertical (VV) or horizontal (HH) polarization in transmission and reception. Wind directions are extracted from wind-induced streaks that are visible in SAR images of the ocean at horizontal scales greater than 200 m. These wind streaks are very well aligned with the mean surface wind direction. To extract the orientation of these streaks, two algorithms are introduced, which are applied either in the spatial or spectral domain. Ocean surface wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR images, together with the local SAR-retrieved wind direction. Therefore, several C-band models (CMOD IFR2, CMOD4, and CMODS) are available, which were developed for VV polarization, and have to be extended for HH polarization. To compare the different algorithms and C-band models as well as demonstrate their applicability, SAR-retrieved wind fields are compared to numerical-model results considering advanced SAR (ASAR) data from Environmental Satellite (ENVISAT), a European satellite.

A high time resolution study of boundary layer ozone chemistry and dynamics over the Arctic Ocean near Alert, Nunavut

During the field campaign “Out On The Ice” (OOTI) in the spring of 2004 at Alert, Nunavut (N82°30′, W62°19′) an event occurred where surface ozone (O3) and reactive bromine species in the boundary layer showed dramatic changes on a timescale of minutes and a spatial scale of a few kilometers. In apparent direct response to changes in surface wind speed and direction, surface O3 mole fractions of >30 nmol.mol−1 replaced stable, O3 depleted boundary layer conditions for about 5 hours. High time resolved (seconds to minutes) chemical and meteorological observations on the ice and on land, as well as synoptic weather maps and routine radiosonde data are used to constrain the unfolding of the event. It is hypothesized that the bromine oxide (BrO) distribution in the troposphere over the frozen ocean features a maximum in a narrow transition layer that separates the boundary layer from free tropospheric air above.

The acoustic heartbeat of Hurricane Juan

When Hurricane Juan made landfall in Nova Scotia, Canada in September 2003, meteorological and acoustical measurements were made independently. The meteorological data yielded surface wind speeds and directions while wind gust frequencies and noise from damage events were extracted from the acoustical data. By establishing a timeline for damage-related noise using acoustics, greater insight into when and how damage occurred near the audio recording site became possible. Examples of wind-induced damage to local maple and spruce trees are used to illustrate the value of acoustics in high-wind storm events like hurricanes.

The atmospheric circulation and dust activity in different orbital epochs on Mars

A general circulation model is used to evaluate changes to the circulation and dust transport in the martian atmosphere for a range of past orbital conditions. A dust transport scheme, including parameterized dust lifting, is incorporated within the model to enable passive or radiatively active dust transport. The focus is on changes which relate to surface features, as these may potentially be verified by observations. Obliquity variations have the largest impact, as they affect the latitudinal distribution of solar heating. At low obliquities permanent CO 2 ice caps form at both poles, lowering mean surface pressures. At higher obliquities, solar insolation peaks at higher summer latitudes near solstice, producing a stronger, broader meridional circulation and a larger seasonal CO 2 ice cap in winter. Near-surface winds associated with the main meridional circulation intensify and extend polewards, with changes in cap edge position also affecting the flow. Hence the model predicts significant changes in surface wind directions as well as magnitudes. Dust lifting by wind stress increases with obliquity as the meridional circulation and associated near-surface winds strengthen. If active dust transport is used, then lifting rates increase further in response to the larger atmospheric dust opacities (hence circulation) produced. Dust lifting by dust devils increases more gradually with obliquity, having a weaker link to the meridional circulation. The primary effect of varying eccentricity is to change the impact of varying the areocentric longitude of perihelion, l, which determines when the solar forcing is strongest. The atmospheric circulation is stronger when l aligns with solstice rather than equinox, and there is also a bias from the martian topography, resulting in the strongest circulations when perihelion is at northern winter solstice. Net dust accumulation depends on both lifting and deposition. Dust which has been well mixed within the atmosphere is deposited preferentially over high topography. For wind stress lifting, the combination produces peak net removal within western boundary currents and southern midlatitude bands, and net accumulation concentrated in Arabia and Tharsis. In active dust transport experiments, dust is also scoured from northern midlatitudes during winter, further confining peak accumulation to equatorial regions. As obliquity increases, polar accumulation rates increase for wind stress lifting and are largest for high eccentricities when perihelion occurs during northern winter. For dust devil lifting, polar accumulation rates increase (though less rapidly) with obliquity above o = 25 ° , but increase with decreasing obliquity below this, thus polar dust accumulation at low obliquities may be increasingly due to dust lifted by dust devils. For all cases discussed, the pole receiving most dust shifts from north to south as obliquity is increased.

Spatial patterns of the urban heat island in Zaragoza (Spain)

Spatial patterns of the urban heat island (UHI) in Zaragoza (Spain) were determined by Principal Component Analysis (VARIMAX rotation) of air temperature in the city, and mapped using GIS. The 3 components extracted accounted for 92.9% of the total variance. Principal component (PC) 1 accounted for the most general patterns of UHI, PC2 showed a shift of warm areas to the SE and PC3 a shift to the NW. A rotated component matrix was used to identify correlations between each component and daily maps. The spatial patterns indicated by PC2 and PC3 were determined by surface wind direction. The displacement of warm areas to the SE (PC2) was greater during NW winds while the shift to the NW (PC3) was produced mainly by SE winds.

Ocean wind fields retrieved from the advanced synthetic aperture radar aboard ENVISAT

In this paper an algorithm is presented which enables high-resolution ocean surface wind fields to be retrieved from the advanced synthetic aperture radar (ASAR) data acquired by the European remote sensing satellite ENVISAT. Wind directions are extracted from wind-induced streaks that are visible in ASAR images at scales above 200 m and that are approximately in line with the mean surface wind direction. Wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated ASAR images, together with the local ASAR-retrieved wind direction. Therefore the empirical C-band model CMOD4, which describes the dependency of the NRCS on wind and image geometry, is used. CMOD4 is a semi-empirical model, which was originally developed for the scatterometer of the European remote sensing satellites ERS-1 and 2 operating at C-band with vertical polarization. Consequently, CMOD4 requires modification when applied to ASAR images that were acquired with horizontal polarization in transmitting and receiving. This is performed by considering the polarization ratio of the NRCS. To demonstrate the applicability of the algorithm, wind fields were computed from several ENVISAT ASAR images of the North Sea and compared to atmospheric model results of the German weather service.

High-resolution simulation of volcanic sulfur dioxide dispersion over the Miyake Island

Abstract After severe eruptions of the volcano at Miyake Island in August 2000, a large amount of volcanic gas was released into the atmosphere. To simulate flows and dispersion of sulfur dioxide (SO 2 ) over Miyake Island, a set of numerical models was developed. The multi-nesting method was adopted to reflect a realistic meteorological field and to sufficiently resolve the flow over the island with a diameter of 8 km. The outermost model was the Regional Spectral Model (RSM) of the Japan Meteorological Agency (JMA) with a horizontal grid size of 10 km. Finer atmospheric structure was simulated with the nonhydrostatic model jointly developed by the Meteorological Research Institute and the Numerical Prediction Division of JMA (MRI/NPD-NHM) with grid intervals of 2 km, 400 m and 100 m. Realistic topography of the island was represented in the innermost model. The Lagrangian particle method was applied to the dispersion model, which is driven by the meteorological field of the 100 m grid MRI/NPD-NHM. The random walk procedure was used to represent the turbulent diffusion. The model was verified in four cases. Simulated SO 2 concentrations agreed well with observed concentrations at a monitoring station including temporal variation. Under a large synoptic change, however, accurate prediction became difficult. Further numerical experiments have been done to investigate characteristics of the flow and the distribution of SO 2 . Steady inflows, classified according to the surface wind speed and direction, were assumed. Simulated SO 2 distribution on the ground apparently depends on the surface wind. Under relatively weak inflow, there is a large diurnal change in SO 2 distribution, affected by the thermally induced flow. SO 2 gas is widely spread downstream in the nighttime but hardly reaches the coastal area in the daytime. On the other hand, SO 2 gas steadily reached the downstream coast with little diurnal variation under the stronger inflow. Ground temperature, as well as the static stability of the inflow, also influences downstream wind, turbulent diffusivity and SO 2 distribution.

황사의 확산예측을 위한 기상정보의 시간해상도에 관한 수치연구

In order to predict air pollution and Yellow-sand dispersion precisely, it is necessary to clarify the sensitivity of meteorological field input interval. Therefore numerical experiment by atmospheric dynamic model(RAMS) and atmospheric dispersion model(PDAS) was performed for evaluating the effect of temporal and spatial resolution of meteorological data on particle dispersion. The results are as follows: 1) Base on the result of RAMS simulation, surface wind direction and speed can either synchronize upper wind or not. If surface wind and upper wind do not synchronize, precise prediction of Yellow-sand dispersion is strongly associated with upwelling process of sand of particle. 2) There is no significant discrepance in distribution of particle under usage of difference temporal resolution of meteorological information at early time of simulation, but the difference of distribution of particles become large as time goes by. 3) There is little difference between calculated particles distributions in dispersion experiments with high temporal resolution of meteorological data. On the other hand, low resolution of meteorological data occur the quantitative difference of particle density and there is strong tendency to the quantitative difference.

Measuring Surface Wind Direction by Monostatic HF Ground-Wave Radar at the Eastern China Sea

The extraction of full wind vectors from data obtained by single-site (monostatic) high-frequency ground-wave radar (HFGWR) is an ongoing challenge because of the inherent directional ambiguities. Here, a new algorithm for resolving the ambiguity of wind direction from monostatic data is presented. The true wind direction is determined by minimizing the sum of the difference among three wind directions derived from three different radar look angles. The wind directions estimated by applying the algorithm to data obtained from the OSMAR2000 HFGWR situated at the Eastern China Sea are compared with values obtained from ship-borne instrumentation. The mean difference between the ground-truthed values and those obtained from the radar data is approximately 20/spl deg/. The distance limit for wind direction sensing using the OSMAR2000 is about 200 km, which is the range for which signal-to-noise ratios typically exceed about 23 dB in the relevant first-order portions of the backscatter spectra.

Aerosol spectral optical depths and size characteristics at a coastal industriallocation in India - effect of synoptic and mesoscale weather

Abstract. The aerosol spectral optical depths at ten discrete channels in the visible and near IR bands, obtained from a ground-based passive multi-wavelength solar radiometer at a coastal industrial location, Visakhapatnam, on the east coast of India, are used to study the response of the aerosol optical properties and size distributions to the changes in atmospheric humidity, wind speed and direction. It is observed that during high humidity conditions, the spectral optical depths show about 30% higher growth factors, and the size distributions show the generation of a typical new mode around 0.4 microns. The surface wind speed and direction also indicate the formation of new particles when the humid marine air mass interacts with the industrial air mass. This is interpreted in terms of new particle formation and subsequent particle growth by condensation and self-coagulation. The results obtained on the surface-size segregated aerosol mass distribution from a co-located Quartz Crystal Microbalance during different humidity conditions also show a large mass increase in the sub-micron size range with an increase in atmospheric humidity, indicating new particle formation at the sub-micron size range.

Modelling tropical cyclone over-water wind and pressure fields

A parametric wind field model and an interactive computer tool are used to develop time histories of 2D wind field (surface wind speed and direction) during the 64 historical tropical cyclones that threatened the east coast of Queensland, Australia, during the 33 years (1969–2002) after the advent of meteorological satellite data for the region. These wind fields are suitable to be applied to applications such as wave, storm surge and circulation modelling. The parametric wind field model includes a double vortex and a representation of the synoptic winds in which the tropical cyclone is embedded. The process used all easily accessible meteorological data, including wind speeds, directions and pressures to determine the best-fit wind fields. Detailed comparisons between model and measurements for three individual storms are shown. These highlight the difficulties associated with fitting the parametric model to the very sparse measurements. If the storm did not pass close to a measurement station, then estimates of parameter values for radius of the storm and spatial shape of the wind field make the calibration process difficult and subjective. Nevertheless, results from the whole ensemble show that the modelled wind fields are unbiased with very good error statistics. These calibrations provide information for the distributions of values for radius of maximum winds and Holland B, parameters for which data are nonexistent in the Coral Sea region. An example of the use of the calibrated wind fields for the forcing of storm surge and wave models shows a very accurate comparison between modelled and measured surge and waves.

Retrieval of Ocean Surface Wind Speed and Wind Direction Using Reflected GPS Signals

Global positioning system (GPS) signals reflected from the ocean surface can be used for various remote sensing purposes. Some possibilities include measurements of surface roughness characteristics from which the rms of wave slopes, wind speed, and direction could be determined. In this paper, reflected GPS measurements that were collected using aircraft with a delay mapping GPS receiver are used to explore the possibility of determining ocean surface wind speed and direction during flights to Hurricanes Michael and Keith in October 2000. To interpret the GPS data, a theoretical model is used to describe the correlation power of the reflected GPS signals for different time delays as a function of geometrical and sea-roughness parameters. The model employs a simple relationship between surface-slope statistics and both a wind vector and wave age or fetch. Therefore, for situations when this relationship holds there is a possibility of indirectly measuring the wind speed and the wind direction. Wind direction estimates are based on a multiple-satellite nonlinear least squares solution. The estimated wind speed using surface-reflected GPS data collected at wind speeds between 5 and 10 m s−1 shows an overall agreement of better than 2 m s−1 with data obtained from nearby buoy data and independent wind speed measurements derived from TOPEX/Poseidon, European Remote Sensing (ERS), and QuikSCAT observations. GPS wind retrievals for strong winds in the close vicinity to and inside the hurricane are significantly less accurate. Wind direction agreement with QuikSCAT measurements appears to be at the 30° level when the airplane has both a stable flight level and a stable flight direction. Discrepancies between GPS retrieved wind speeds/directions and those obtained by other means are discussed and possible explanations are proposed.

Diatom oxygen isotopes in pro-glacial lake sediments from northern Sweden: a 5000 year record of atmospheric circulation

We use a pro-glacial oxygen isotope record of diatom silica (δ 18O diatom) and a sedimentary proxy for glacier fluctuations to determine centennial–millennial scale climate change during the last 5000 years in northern Sweden. We show that the lake water isotopic composition predominantly reflects the isotopic composition of the precipitation. Superimposed on a general depletion trend of 3.5‰ over the past 5000 years we found that the isotopic composition of precipitation became depleted (>1‰ excursions) during four occasions centered at 4400, 3000, 2000, and after 1200 cal yr BP. Climate simultaneously sustained a positive glacier mass balance, that caused the catchment glacier to advance. A persistent change in the atmospheric circulation pattern could potentially have caused the registered changes in δ 18O diatom because different air masses hold characteristic δ 18O signatures of their precipitation. The glacier mass balance primarily responds to the influence of summer temperature on ablation. We suggest that the most likely cause for the recorded changes in both these proxies is a steadily increasing but fluctuating dominance of colder and δ 18O depleted air masses from the north/northeast during the past 5000 years. The δ 18O diatom depletion and glacier events all occur at times of relative ice-rafted-debris maxima in the North Atlantic, consistent with cold conditions and changes in surface wind directions. Our results confirm that changes towards a predominance of north/northeasterly winds occurred at these time intervals.