Showing papers in "Journal of Atmospheric and Oceanic Technology in 1995"
TL;DR: The Oklahoma mesonet as discussed by the authors is a joint project of Oklahoma State University and the University of Oklahoma, which is used to measure air temperature, humidity, barometric pressure, wind speed and direction, rainfall, solar radiation, and soil temperatures.
Abstract: The Oklahoma mesonet is a joint project of Oklahoma State University and the University of Oklahoma. It is an automated network of 108 stations covering the state of Oklahoma. Each station measures air temperature, humidity, barometric pressure, wind speed and direction, rainfall, solar radiation, and soil temperatures. Each station transmits a data message every 15 min via a radio link to the nearest terminal of the Oklahoma Law Enforcement Telecommunications System that relays it to a central site in Norman, Oklahoma. The data message comprises three 5-min averages of most data (and one 15-min average of soil temperatures). The central site ingests the data, runs some quality assurance tests, archives the data, and disseminates it in real time to a broad community of users, primarily through a computerized bulletin board system. This manuscript provides a technical description of the Oklahoma mesonet including a complete description of the instrumentation. Sensor inaccuracy, resolution, height ...
668 citations
TL;DR: In this article, the authors proposed a method based on the solution of a constrained weighted least-squares problem and maximized the smoothness of the resulting salinitypotential temperature diagram.
Abstract: Hydrographic data, be it raw or highly averaged observational data, contain substantial regions having vertical density inversions. An algorithm is described that minimally modifies such data so that the resulting hydrographic casts have vertical buoyancy frequency profiles larger than a specified lower bound. The method underlying the algorithm is based on the solution of a constrained weighted least-squares problem and maximizes the smoothness of the resulting salinity-potential temperature diagram. Examples are provided that demonstrate the effectiveness of the technique in minimally altering hydrographic data only in the immediate vicinity of the data that do not already satisfy the buoyancy frequency constraint. A modified equation of state, identical in form to the international equation of state of seawater but written in terms of potential rather than in situ temperature, is also provided, enabling rapid computation of the thermal expansion and saline contraction coefficients.
408 citations
TL;DR: In this paper, an improved method for the measurement of the ice water content (IWC) of cirrus cloud using a total water content probe is described, which resolves anomalies in the earlier measurements that were due to the assumption of saturation with respect to ice everywhere within cloud.
Abstract: This note describes an improved method for the measurement of the ice water content (IWC) of cirrus cloud using a total water content probe. A previous version of this technique assumed that the air in cloud-containing regions was saturated with respect to ice. This assumption has now been replaced with measurements of the water vapor content from a fast-response Lyman-α fluorescence water vapor sensor. The improved measurement of the vapor phase resolves anomalies in the earlier measurements that were due to the assumption of saturation with respect to ice everywhere within cloud. The comparison of IWC measurements made by this new method with those from a 2D optical array probe is greatly improved. The new measurements may now be used to provide much more stringent tests of the algorithms used for the derivation of crystal mass from measured size in 2D probe data.
400 citations
TL;DR: In this paper, the authors used six Global Positioning System (GPS) receivers for 1 month at sites in Colorado, Kansas, and Oklahoma to measure atmospheric water vapor and tested the accuracy of the method for meteorological applications.
Abstract: Atmospheric water vapor was measured with six Global Positioning System (GPS) receivers for 1 month at sites in Colorado, Kansas, and Oklahoma. During the time of the experiment from 7 May to 2 June 1993, the area experienced severe weather. The experiment, called “GPS/STORM,” used GPS signals to sense water vapor and tested the accuracy of the method for meteorological applications. Zenith wet delay and precipitable water (PW) were estimated, relative to Platteville, Colorado, every 30 min at five sites. At three of these five sites the authors compared GPS estimates of PW to water vapor radiometer (WVR) measurements. GPS and WVR estimates agree to 1–2 mm rms. For GPS/STORM site spacing of 500–900 km, high-accuracy GPS satellite orbits are required to estimate 1–2-mm-level PW. Broadcast orbits do not have sufficient accuracy. It is possible, however, to estimate orbit improvements simultaneously with PW. Therefore, it is feasible that future meteorological GPS networks provide near-real-time hig...
289 citations
TL;DR: Rainfall algorithms developed for the DMSP Special Sensor Microwave/Imager are presented and then “calibrated” against ground-based radar measurements to develop instantaneous rain-rate retrieval algorithms, including both scattering- and emission-based algorithms.
Abstract: Rainfall algorithms developed for the DMSP Special Sensor Microwave/Imager are presented and then “calibrated” against ground-based radar measurements to develop instantaneous rain-rate retrieval algorithms. These include both scattering- and emission-based algorithms. Radar data from Japan, the United States, and the United Kingdom have been used in the investigation. Because of the difficulties in accurately matching the satellite and radar measurements in both time and space, an approach where both measurements are grouped in 1 mm h−1 rain-rate bins provides a much more accurate set of measurements to be used in the derivation of coefficients for instantaneous rain-rate retrieval. Both linear and nonlinear relationships are developed, with the nonlinear fits being more accurate and supported by model simulations. An application of the derived instantaneous rain-rate relationships to an independent case is presented, with approximately a 10% error for the scattering algorithm when compared with...
284 citations
TL;DR: In this article, almost 1000 microstructure profiles from two separate groups on two separate ships using different instrumentation, signal processing, and calibration procedures were compared for a 3.5-day time period at 0°, 140°W and within 11 km of each other.
Abstract: Almost 1000 microstructure profiles from two separate groups on two separate ships using different instrumentation, signal processing, and calibration procedures were compared for a 3.5-day time period at 0°, 140°W and within 11 km of each other. Systematic bias in the estimates of ϵ is less than a factor of 2, which is within estimates of the cumulative uncertainties in the measurement of ϵ. Although there is no evidence for strong gradients in mean currents, water properties, or surface meteorology, occasional hourly averages of ϵ differ by several factors of 10. Both groups observed periods where ϵ estimates exceeded those of the other group by large factors. The authors believe that the primary reason for these large differences is natural variability, which appears to be greater in the meridional direction than in the zonal direction.
252 citations
TL;DR: In this article, an iterative range filtering technique was proposed to separate the differential propagation phase and differential backscatter phase under a wider variety of conditions than is possible with a simple range filter.
Abstract: Copolar differential phase is composed of two components, namely, differential propagation phase and differential backscatter phase. To estimate specific differential phase KDP, these two phase components must first be separated when significant differential backscatter phase is present. This paper presents an iterative range filtering technique that can separate these phase components under a wider variety of conditions than is possible with a simple range filter. This technique may also be used when estimating hail signals from range profiles of dual-frequency reflectivity ratios.
230 citations
TL;DR: In this paper, an algorithm was developed that classifies precipitating clouds into either stratiform, mixed stratiform/convective, deep convective, or shallow convective clouds by analyzing the vertical structure of reflectivity, velocity, and spectral width derived from measurements made with the vertical beam of a 915-MHz Doppler wind profiler.
Abstract: An algorithm has been developed that classifies precipitating clouds into either stratiform, mixed stratiform/convective, deep convective, or shallow convective clouds by analyzing the vertical structure of reflectivity, velocity, and spectral width derived from measurements made with the vertical beam of a 915-MHz Doppler wind profiler. The precipitating clouds classified as stratiform and convective clouds match the physical and radar properties deduced by Doppler weather radars in the GATE and EMEX programs. The mixed stratiform/convective cloud category is a hybrid regime containing a melting-layer signature associated with stratiform clouds yet is turbulent above the melting level similar to convective clouds. Shallow convective clouds have hydrometeors confined entirely below the melting level implying that warm rain processes are occurring exclusively. The algorithm is illustrated by classifying precipitating clouds from 10 months of observations at Manus Island (2°S, 147°E) in the western...
209 citations
TL;DR: In this article, the performance of a 94-GHz radar is evaluated for a variety of cloud conditions, and a physically relevant study of beam extinction and backscattering by clouds is attempted by modeling cloud drop size distributions with a gamma distribution over a range of number concentrations, particle mean diameters, and distribution shape factors; cloud liquid water contents and mean drop size diameters reported in the literature are analyzed in this paper.
Abstract: The performance of a 94-GHz radar is evaluated for a variety of cloud conditions. Descriptions of the radar hardware, signal processing, and calibration provide an overview of the radar's capabilities. An important component of the signal processing is the application of two cloud-mask schemes to the data to provide objective estimates of cloud boundaries and to detect significant returns that would otherwise be discarded if a simple threshold method for delectability was applied to the return power. Realistic profiles of atmospheric pressure, temperature, and water vapor are used in a radiative transfer model to address clear-sky attenuation. A physically relevant study of beam extinction and backscattering by clouds is attempted by modeling cloud drop size distributions with a gamma distribution over a range of number concentrations, particle mean diameters, and distribution shape factors; cloud liquid water contents and mean drop size diameters reported in the literature are analyzed in this c...
182 citations
TL;DR: In this article, several polarimetric radar estimators of rain rate R and rainwater content M were examined using a gamma drop size distribution (DSD) simulation and a radar wavelength of 11 cm.
Abstract: Several polarimetric radar estimators of rain rate R and rainwater content M are examined. The accuracy of the estimators is analyzed using a gamma drop size distribution (DSD) simulation and a radar wavelength of 11 cm. The estimators that use combined measurements of specific differential phase KDP and differential reflectivity ZDR are superior to the estimators of R and M obtained from reflectivity factors Zh and Zv at orthogonal polarizations or KDP only. The standard deviation of the R(KDP, ZDR) estimate is 2–3 times less than for the best of the R(Zh, Zv) estimators. The statistical accuracy of the M(KDP, ZDR) estimator is at least 1.5–2 times better than for the M(Zh, Zv) estimator. Cumulative rainfalls obtained with the estimators are compared with accumulations recorded with 42 rain gauges in the Little Washita River basin. Biases, errors, and reasons for the superior performance of the R(KDP, ZDR) estimator are explained in terms of the microphysical processes in the squall line that co...
149 citations
TL;DR: In this paper, a method for Doppler spectral processing more readily identifies the profiler radar return signals from the atmosphere in the presence of contamination, e.g., from bird echoes, ground clutter, and radio frequency interference.
Abstract: This method for Doppler spectral processing more readily identifies the profiler radar return signals from the atmosphere in the presence of contamination, e.g., from bird echoes, ground clutter, and radio frequency interference. Profiler radars measure winds in the atmosphere by using backscatter (i) from refractive index fluctuations in clear air due to turbulence or (ii) from precipitation such as rain or snow. These radars also receive contaminating radar returns from ground clutter (e.g., from vehicles, power lines, and trees) and from fliers (e.g., aircraft, insects, and birds). In general, the radar return signals from the atmosphere have statistical and physical properties different from those properties for the contaminating radar returns. This new method uses these differences to eliminate or reduce contamination in radar Doppler spectra for estimation of atmospheric winds.
TL;DR: In this article, a practical technology based on moored subsea instrumentation has been developed to measure the draft of polar pack ice, which exploits the complementary capabilities of an iceprofiling sonar designed and built for the application and of a commercially available acoustic Doppler sonar.
Abstract: A practical technology based on moored subsea instrumentation has been developed to measure the draft of polar pack ice. The technology exploits the complementary capabilities of an ice-profiling sonar designed and built for the application and of a commercially available acoustic Doppler sonar. The former instrument observes the zenithal range of sea ice passing through its single narrow sonar beam, while the latter observes the radial motion of the ice along its four inclined beams. The sequence of ranges obtained by the ice-profiling sonar is combined with supplementary observations of hydrostatic pressure to yield a sequence of ice draft versus time; the sequence of Doppler speeds provides ice velocity that can be integrated to obtain displacement; by combining the draft and displacement sequences the profile of draft versus position is obtained. The foremost practical problem in calibration is establishing the temporal variation in the zero-draft reference. The technology is well suited to u...
TL;DR: In this paper, the authors examined the calibration characteristics of the NASA/GSFC Raman water vapor lidar during three field experiments that occurred between 1991 and 1993 and found that the lidar water vapor profiles were calibrated using relative humidity profiles measured by AIR and Vaisala radiosondes.
Abstract: This paper examines the calibration characteristics of the NASA/GSFC Raman water vapor lidar during three field experiments that occurred between 1991 and 1993. The lidar water vapor profiles are calibrated using relative humidity profiles measured by AIR and Vaisala radiosondes. The lidar calibration computed using the AIR radiosonde, which uses a carbon hygristor to measure relative humidity, was 3%–5% higher than that computed using the Vaisala radiosonde, which uses a thin film capacitive element. These systematic differences were obtained for relative humidities above 30% and so cannot be explained by the known poor low relative humidity measurements associated with the carbon hygristor. The lidar calibration coefficient was found to vary by less than 1% over this period when determined using the Vaisala humidity data and by less than 5% when using the AIR humidity data. The differences between the lidar relative humidity profiles and those measured by these radiosondes are also examined. Th...
TL;DR: In this paper, an automated technique for the rejection of contaminated data in historical datasets, based on thresholding high values of rnoment-level reflectivity and spectral width, is shown to be effective.
Abstract: Winds measured with 915- and 404-MHz wind profilers are frequently found to have nonrandom errors as large as 15 m s−1 when compared to simultaneously measured rawinsonde winds. Detailed studies of these errors which occur only at night below about 4 km in altitude and have a pronounced seasonal pattern, indicate that they are due to the wind profilers' detection of migrating songbirds (passerines). Characteristics of contaminated data at various stages of data processing are described, including raw time series, individual spectra, averaged spectra, 30- or 60-s moments, 3- or 6-min winds, and hourly averaged winds. An automated technique for the rejection of contaminated data in historical datasets, based on thresholding high values of rnoment-level reflectivity and spectral width, is shown to be effective. Techniques designed for future wind profiter data acquisition systems are described that show promise for rejecting bird echoes, with the additional capability of being able to retrieve the t...
TL;DR: An approach based on the analysis of an image sequence to detect temperature fronts in a sea surface temperature image and the location of the fronts obtained by applying various methods to the SST images is compared to the in situ measures of the Gulf Stream position.
Abstract: This paper presents an approach based on the analysis of an image sequence to detect temperature fronts in a sea surface temperature image. The multi-image edge detection algorithm starts by applying a single-image edge detection algorithm to the sequence of images under study. Next, fronts or portions of fronts, which were detected in neighboring images by the single-image algorithm and which match features in the current image, are identified as persistent. The coordinates of these persistent fronts are then passed to the single-image edge detection algorithm so that additional fronts can be detected. The performance of the multi-image edge detection algorithm, of various single-image algorithms, and of a human expert are evaluated on a set of 98 images. For that purpose, the location of the fronts obtained by applying various methods to the SST images is compared to the in situ measures of the Gulf Stream position. With respect to both quality and the number of detected edges, the multi-image ...
TL;DR: In this paper, two independent radar methods for estimating the turbulent eddy dissipation rate ϵ are applied to a common dataset, and the results are compared, and encouraging similarities are found both in the magnitude and shape of the measured profiles, though differences are also found.
Abstract: Two independent radar methods for estimating the turbulent eddy dissipation rate ϵ are applied to a common dataset, and the results are compared. The first method estimates ϵ from backscattered power and relies on the effects of turbulent mixing of atmospheric refractive index gradients. It requires additional measurements of temperature and humidity from a balloon sounding. The second makes use of broadening of the backscattered Doppler spectrum by turbulent motions. The turbulent eddy dissipation rate ϵ is a measure of the energy cascade through scales of inertial subrange turbulence. Data were collected with the Millstone Hill UHF radar in Westford, Massachusetts, and with Cross-chain Loran Atmospheric Sounding System thermodynamic soundings launched from Hanscom Field about 25 km away. Encouraging similarities are found both in the magnitude and shape of the measured profiles, though differences are also found. Some differences may be explained by characteristics of the measurement techniques...
TL;DR: In this article, a relatively straightforward method for efficiently reducing the ERS-1 orbit error using Topex/Postidon data is presented. The method is based on a global minimization of TOPEX/Poscidon-ERS-1 (TP-E) dual crossover differences.
Abstract: This paper presents a relatively straightforward method for efficiently reducing the ERS-1 orbit error using Topex/Postidon data. The method is based on a global minimization of Topex/Poscidon-ERS-1 (TP-E) dual crossover differences. The TP-E crossover differences give an estimate of the ERS-1 radial orbit error almost directly, leading to a geometric estimation of orbit error. Smoothing cubic-spline functions are then used to obtain a continuous estimation of the orbit error over time. The splines can also be adjusted to minimize the ERS-1-ERS-1 (E-E) crossover differences. This allows a better estimation of the orbit error, especially poleward of 66° where no TP-E crossovers are available. The method was successfully applied to the final TP and ERS-1 datasets [i.e., the TP GDRs (geophysical data records) and the ERS-1 OPRs (ocean products)]. The authors used one full 35-day ERS-1 cycle and five TP cycles concurrent with ERS-1 data. Only crossovers with time differences lm than 5 days are used i...
TL;DR: The IMET (improved meteorology) system for ships and buoys and the key elements of the program that led to its development are described in this article, where the system improves the ability to measure mean meteorological variables, including wind velocity, barometric pressure, incoming shortwave and longwave radiation, air temperature, sea surface temperature, humidity, and precipitation.
Abstract: The recently developed IMET (improved meteorology) system for ships and buoys and the key elements of the program that led to its development are described. The system improves the ability to measure mean meteorological variables, including wind velocity, barometric pressure, incoming shortwave and longwave radiation, air temperature, sea surface temperature, humidity, and precipitation, from both types of platforms. Extensive laboratory and field tests of a variety of sensors were conducted to investigate and document their stability, accuracy, and reliability. Modular electronics were developed so that each sensor in the system communicated digitally, returning calibrated values to a central data recorder. IMET systems have been deployed on buoys in the Atlantic and Pacific Oceans and on research vessels. The history of the program, reasons for the choice of the present sensor suite, the design of the sensor modules, a description of the data acquisition system, and examples of data collected w...
TL;DR: In this article, a new monthly climatology is derived by exploiting the statistical interpolation method to provide an improved weighted estimate of the tropical ocean thermal structure, and a statistical forecast based on the previous analysis and the new monthly climate model is presented.
Abstract: This study demonstrates techniques that lead to improved use of ocean thermal information and more useful and informative products for monitoring variability in the tropical oceans. The method is based on statistical interpolation and is illustrated using analyses for the 20°C isotherm depth over the Pacific and Indian Oceans. A new monthly climatology is derived by exploiting the statistical interpolation method to provide an improved weighted estimate. The new climatology is shown to better represent key aspects of the tropical ocean thermal structure. A statistical forecast based on the previous analysis and climatology significantly improves the analysis product, both in a qualitative sense and as judged by quantitative measures of the skill of the forecast and of the estimated error of the analysis. Both the new climatology and the statistical forecasting scheme are interpreted as strategies for delivering enhanced information to the analysis system. A series of 10-day analyses are presented...
TL;DR: In this paper, the quality and vertical correlation scales of high-frequency (HF) radar-derived ocean surface current measurements from an Ocean Surface Current Radar (OSCR) are assessed by comparing surface to subsurface current observations from 11 June to 8 July 1993 at directional discus buoys DW and DE, each instrumented with a three-axis ultrasonic current meter at the 13.8- and 9.5-m depths, respectively.
Abstract: The quality and vertical correlation scales of high-frequency (HF) radar-derived ocean surface current measurements from an ocean surface current radar (OSCR) are assessed by comparing surface to subsurface current observations from 11 June to 8 July 1993 at directional discus buoys DW and DE, each instrumented with a three-axis ultrasonic current meter at the 13.8- and 9.5-m depths, respectively. A dual-station OSCR mapped the current fields at 20-min intervals at a horizontal resolution of 1.2 km over a 30 km × 44 km domain inshore of the Gulf Stream using the HF (25.4 MHz) mode. Over a 27-day experimental period, surface current observations were acquired 97% of the time extending to the maximum theoretical range of 44 km. Linear regression analyses indicated a bias of 2–4 cm s−1 and slopes of O(1). While there were periods when the daily averaged complex correlation coefficients were highly correlated (>0.8), periods of low correlation (<0.3) are explained in terms of vertical phase differenc...
TL;DR: In this paper, a technique for deriving tropospheric water vapor and cloud liquid water, as well as temperature, from a suite of ground-based sensors is presented, which includes a dual-channel microwave radiometer, a ceilometer, and a radio acoustic sounding system (RASS).
Abstract: A technique is presented for deriving tropospheric water vapor and cloud liquid water, as well as temperature, from a suite of ground-based sensors. Included in the suite are a dual-channel microwave radiometer, a ceilometer, a radio acoustic sounding system (RASS), and conventional surface meteorological instruments. A linear statistical inversion algorithm, combined with a data classification technique, is applied to retrieve water vapor and cloud liquid water profiles. The linear statistical inversion algorithm is also applied to derive temperature profiles from RASS virtual temperature measurements and surface meteorological parameters. A physical retrieval algorithm is then applied to retrieve integrated water vapor and liquid water. Finally, these two algorithms are coupled in a two-step iteration process. The technique is evaluated by comparing retrieved quantities with radiosonde measurements and by comparing this technique with the traditional technique based solely on dual-channel micro...
TL;DR: A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06-2.0-micrometer-diameter range in flights following the eruption of Mount Pinatubo in 1991 as mentioned in this paper.
Abstract: A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06-2.0-micrometer-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.
TL;DR: In this article, the authors present the first simultaneous measurements of calibrated acoustic returns and turbulent microstructure collected in a set of 20m tall billows collected from Admiralty Inlet, a salt-stratified tidal channel near Puget Sound.
Abstract: Acoustic backscatter has produced spectacular images of internal ocean processes for nearly two decades, but interpretation of the images remains ambiguous because several mechanisms can generate measurable backscatter. The authors present what is thought to be the first simultaneous measurements of calibrated acoustic returns and turbulent microstructure, collected in a set of 20-m-tall billows. The observations are from Admiralty Inlet, a salt-stratified tidal channel near Puget Sound. Scattering due to turbulent microstructure alone is strong enough to explain the measured backscatter at specific sites within the billows. Existing formulations underestimate the strength of acoustic backscatter from turbulent microstructure. Due to a misinterpretation of the high-wavenumber temperature spectrum, some previous formulations underestimate the differential Scattering cross section (σ) when scattering from the viscous-convective subrange. Also, the influence of salinity on refractive-index fluctuati...
TL;DR: In this article, the angular and range weighting functions of the radar measurement are modeled using Gaussian approximations to give the so-called weighted illuminated areas for various sizes of radar resolution volume.
Abstract: The aim of the present study is to characterize mountain returns measured with a ground-based weather radar operating in a mountainous region. A computation code based on the use of a digitized terrain model is developed for calculating the areas illuminated by the radar beam. Partial and total screening effects am accounted for in the calculation. The angular and range weighting functions of the radar measurement am modeled using Gaussian approximations to give the so-called weighted illuminated areas for various sizes of the radar resolution volume. Radar measurements are compared to the computed illuminated areas in order to determine the average backscattering coefficient of partly grass-covered, partly forested mountains: 87% of the measured time-averaged mountain return variance is explained by the computed values when the 15-dB resolution volume is considered. Additional geometrical information, provided by the calculated angles of incidence, is accounted for to yield a linear σ(dB)0(α) mo...
TL;DR: In this paper, the authors established thresholds separating regimes for which Rayleigh scattering from precipitation is likely to dominate over Bragg scattering from clear air for several common radar wind profiler frequencies.
Abstract: Thresholds separating regimes for which Rayleigh scattering from precipitation is likely to dominate over Bragg scattering from clear air are established for several common radar wind profiler frequencies The thresholds are first determined for radar reflectivity factor Z based on observed values of the structure parameter Cn2 in the troposphere These thresholds for Z are then transformed to thresholds for modal terminal velocities V* of rain and snow for exponential particle size distributions Measurements at 915,404, and 50 MHz in stratiform rain help substantiate the applicability of the calculated thresholds, even though fall velocities, rather than V*, are measured Because the V* thresholds for rain at wind profiler frequencies (ie, >25–56 m s−1 at 404 MHz) are substantially greater than typical vertical air motions outside convective cells, profiler-observed radial vertical velocities are a robust indicator of the presence of rain in profiler data Although snow can also often be id
TL;DR: In this article, a high-performance liquid chromatographic analytical technique has been developed for the separation of hydrogen peroxide and low molecular weight organic hydroperoxides using post-column derivatization using an enzymatic reaction with p-hydroxyphenylacelic acid to form a fluorescent dimer.
Abstract: A high-performance liquid chromatographic analytical technique has been developed for the separation of hydrogen peroxide and low molecular weight organic hydroperoxides. A total of 10 C1–C3 organic hydroperoxides have been separated. The detection system is based on postcolumn derivatization using an enzymatic reaction with p-hydroxyphenylacelic acid to form a fluorescent dimer. The detection limit for the technique is 9 × 10−8 M for hydrogen peroxide and 2 × 10−8 M for other hydroperoxides. This paper details the optimization of the analytical technique, examining column characteristics and the chemistry of the analytical reaction.
TL;DR: In this paper, a method was described to improve the instrument depth measurements using the binned backscattered energy profile near the surface, and the accuracy of the depth estimates was significantly better than 0.5 m.
Abstract: Surface data obtained from 153-kHz acoustic Doppler current profilers deployed in the Greenland Sea at about 350-m depth during the winter of 1988/89 were investigated under several aspects. First a method is described to improve the instrument depth measurements using the binned backscattered energy profile near the surface. The accuracy of the depth estimates is found to be significantly better than 0.5 m. Further, improvements of wind speed estimates were found by using the ambient noise in the 150-kHz band in favor of the surface backscattered energy as suggested by Schott. Limitations of the ambient sound method at low wind speeds are presented when thermal noise overwhelms the wind-induced noise. Finally, a method to detect the presence of sea ice above the ADCP is presented by cross correlating the surface backscatter strength and the magnitudes of all Doppler velocity components. The resulting time series of ice concentration are in overall good agreement with Special Sensor Microwave/Ima...
TL;DR: In this paper, a computerized method for calculating the sky view factor from fish-eye lens photographic negatives is presented, where images are scanned and stored on CD ROM, each CD holding 100 images.
Abstract: A computerized method for calculating the sky view factor from fish-eye lens photographic negatives is presented. The images are scanned and stored on CD ROM, each CD holding 100 images. The images can be retrieved at very high resolutions of up to 2048 × 3072 pixels for one 24 mm × 36 mm negative. The calculations include corrections for lens projection distortion and restrictions in field of view. They are compared to standard methods of calculating the sky view factor. For applications of the sky view factor where the effective infrared radiation is of interest, a method to account for zenith angular variation in atmospheric transmissivity to infrared radiation is presented.
TL;DR: In this article, a scan-by-scan analysis of the earth's surface reflectivity and velocity is used to correct for errors in navigation and radar pointing angles, including errors in aircraft altitude, aircraft speed and drift, aircraft vertical velocity, aircraft pitch and roll, radar ranging error, and error in antenna spin angle.
Abstract: The development of airborne Doppler radars for atmospheric sciences research has vastly improved the ability to measure atmospheric storms. This paper addresses a new technique for improving airborne Doppler radar data quality. Assuming the earth's surface is flat and still, the technique uses the airborne radar measurements of the earth's surface reflectivity and velocity to correct for errors in navigation and radar pointing angles. The methodology makes use of the helical scanning adopted in the existing systems onboard the two National Oceanic and Atmospheric Administration P3 aircraft and on the National Center for Atmospheric Research Electra aircraft (ELDORA/ASTRAIA radar). On the basis of a scan-by-scan analysis, it is shown that this methodology has the potential to retrieve most of the navigation errors, including errors in aircraft altitude, aircraft speed and drift, aircraft vertical velocity, aircraft pitch and roll, radar ranging error, and error in antenna spin angle. The methodolo...
TL;DR: An HPLC (high-performance liquid chromatography) method was developed to quantify hydrogen peroxide, methyl hydroperoxide, and peroxyaectic acid in the atmosphere as mentioned in this paper.
Abstract: An HPLC (high-performance liquid chromatography) method was developed to quantify hydrogen peroxide, methyl hydroperoxide. Hydroxymethyl hydroperoxide, ethyl hydroperoxide, and peroxyaectic acid in the atmosphere. Gas-phase hydroperoxides are collected in aqueous solution using a continuous-flow glass scrubbing coil and then analyzed by an HPLC postcolumn derivatization system. The detection system is based on fluorescence, produced by the product of the reaction of hydroperoxides with peroxidase and p-hydroxyphenylacetic acid. Reproducibilities are better than 3% for all hydroperoxides in aqueous concentrations of 1 × 10−7–6 × 10−7 M. Detection limits in aqueous concentration are 1.2 × 10−9 M for hydrogen peroxide, 1.5 × 10−9 M for hydroxymethyl hydroperoxide, 2.9 × 10−9 M for methyl hydroperoxide, 16 × 10−9 M for peroxyaectic acid, and 19 × 10−9 M for ethyl hydroperoxide. Corresponding gas-phase detection limits are 5 PPtv for hydrogen peroxide, 7 pptv for hydroxymethyl hydroperoxide, 13 pptv f...