Showing papers in "Journal of Atmospheric and Oceanic Technology in 2000"
TL;DR: In this article, a prototype optical disdrometer is presented, which is easy to handle, robust, and low cost, allowing a cluster of instruments to investigate the spatial and temporal fine-scale structure of precipitation, and it provides reliable detection of the range of small drops.
Abstract: The characteristics of a prototype optical disdrometer are presented. Particles are detectable in the diameter range from 0.3 to 30 mm having velocities of up to 20 m s−1. Advantages of the new system are (i) it is easy to handle, robust, and low cost, allowing a cluster of instruments to investigate the spatial and temporal fine-scale structure of precipitation; (ii) it provides reliable detection of the range of small drops; and (iii) it allows the possibility of snow measurements. Results of rain measurements are compared with data from a Joss–Waldvogel disdrometer and a Hellmann rain gauge. Furthermore, some snow measurements are presented and compared with results of a research spectrometer. The overall agreement is good. The repeatability of particle size estimation was checked in the diameter range between 1.4 and 8.0 mm and yielded a standard deviation of less than 5%. For drop velocities the standard deviation varies between 25% (0.3-mm drops) and 10% (5-mm drops). The optical disdromete...
521 citations
TL;DR: In this paper, the authors developed an algorithm for ground-based polarimetric radars that is derived from those used for the spaceborne rain radar of TRMM (Tropical Rainfall Measurement Mission).
Abstract: The algorithm developed in this paper for ground-based polarimetric radars is derived from those used for the spaceborne rain radar of TRMM (Tropical Rainfall Measurement Mission)—the so-called rain profiling algorithms. The characteristic of this type of algorithm is to be nonlocal, that is, the full rain profile along the radar beam is derived from the reflectivity profile. However, to be stable such algorithms require an external constraint. In TRMM, the constraint is the total path attenuation derived from the observation of the ocean surface, which is used as a reference target. In the present algorithm, the external constraint is provided by the differential phase shift ΦDP between H and V polarizations. This is the reason for calling this new algorithm ZPHI. The inverse model on which ZPHI is based is a set of three power law relationships between A and Ze, KDP and A, and R and A, respectively (A, specific attenuation; Ze, equivalent reflectivity; R, rainfall rate). Each of these relations...
437 citations
TL;DR: In this article, a model that provides an efficient approximation to sea ice thermodynamics for climate studies is presented, where the brine content of the upper ice is represented with a variable heat capacity as is done in more physically based models.
Abstract: A model is presented that provides an efficient approximation to sea ice thermodynamics for climate studies. Semtner’s three-layer framework is used, but the brine content of the upper ice is represented with a variable heat capacity as is done in more physically based models. A noniterative fully implicit time-stepping scheme is used for calculation of ice temperature. The results of the new model are compared to those of Semtner’s original model.
400 citations
TL;DR: A fuzzy logic and neuro-fuzzy system for classification of hydrometeor type based on polarimetric radar measurements is described, which is more advantageous than a simple neural network or a fuzzy logic classifier because it is more transparent and can learn the parameter of the system from the past data.
Abstract: A fuzzy logic and neuro-fuzzy system for classification of hydrometeor type based on polarimetric radar measurements is described in this paper. The hydrometeor classification system is implemented by using fuzzy logic and a neural network, where the fuzzy logic is used to infer hydrometeor type, and the neural network learning algorithm is used for automatic adjustment of the parameters of the fuzzy sets in the fuzzy logic system according to prior knowledge. Five radar measurements, namely, horizontal reflectivity ( ZH), differential reflectivity (ZDR), differential propagation phase shift ( KDP), correlation coefficient [rHV(0)], and linear depolarization ratio (LDR), and corresponding altitude, have been used as input variables to the neuro-fuzzy network. The output of the neuro-fuzzy system is one of the many possible hydrometeor types: 1) drizzle, 2) rain, 3) dry and low density snow, 4) dry and high-density crystals, 5) wet and melting snow, 6) dry graupel, 7) wet graupel, 8) small hail, 9) large hail, and 10) a mixture of rain and hail. The neuro-fuzzy classifier is more advantageous than a simple neural network or a fuzzy logic classifier because it is more transparent (instead of a ‘‘black box’’) and can learn the parameter of the system from the past data (unlike a fuzzy logic system). The hydrometeor classifier has been applied to several case studies and the results are compared against in situ observations.
337 citations
TL;DR: The process of developing high quality data in one network, the Oklahoma Mesonetwork (Mesonet), is detailed in this paper, which consists of an instrument laboratory, field visits, automated computer routines, and manual inspection.
Abstract: High quality data sources are critical to scientists, engineers, and decision makers alike. The models that scientists develop and test with quality-assured data eventually become used by a wider community, from policy makers’ long-term strategies based upon weather and climate predictions to emergency managers’ decisions to deploy response crews. The process of developing high quality data in one network, the Oklahoma Mesonetwork (Mesonet) is detailed in this manuscript. The Oklahoma Mesonet quality-assurance procedures consist of four principal components: an instrument laboratory, field visits, automated computer routines, and manual inspection. The instrument laboratory ensures that all sensors that are deployed in the network measure up to high standards established by the Mesonet Steering Committee. Routine and emergency field visits provide a manual inspection of the performance of the sensors and replacement as necessary. Automated computer routines monitor data each day, set data flags a...
260 citations
TL;DR: In this paper, two deep-layer tropospheric temperature products, one for the lower troposphere (T2LT) and another for the mid-troposphere, are derived from the observations of channel 2 of the microwave sounding unit on National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites.
Abstract: Two deep-layer tropospheric temperature products, one for the lower troposphere (T2LT) and one for the midtroposphere (T2, which includes some stratospheric emissions), are based on the observations of channel 2 of the microwave sounding unit on National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites. Revisions to version C of these datasets have been explicitly applied to account for the effects of orbit decay (loss of satellite altitude) and orbit drift (east–west movement). Orbit decay introduces an artificial cooling in T2LT, while the effects of orbit drift introduce artificial warming in both T2LT and T2. The key issues for orbit drift are 1) accounting for the diurnal cycle and 2) the adjustment needed to correct for spurious effects related to the temperature of the instrument. In addition, new calibration coefficients for NOAA-12 have been applied. The net global effect of these revisions (version D) is small, having little impact on the year-to-year anomalies. T...
249 citations
TL;DR: The steps taken by the National Severe Storms Laboratory (NSSL) to develop open system hardware to facilitate upgrades to the WSR-88D (NEXRAD) radar and improve identification of the type of precipitation and its quantitative measure are reported on.
Abstract: This paper reports on the steps taken by the National Severe Storms Laboratory (NSSL) to 1) develop open system hardware to facilitate upgrades to the WSR-88D (NEXRAD) radar and 2) improve identification of the type of precipitation and its quantitative measure. An engineering evaluation is made to determine if the WSR-88D antenna assembly with minimum modification could be used in a polarimetric mode. The polarimetric characteristics and radiation patterns of a research WSR-88D are briefly discussed. Considerations for the choice of polarimetric basis and design options are described. A polarimetric scheme employing simultaneous transmission of horizontally (H) and vertically (V) polarized waves is suggested for the WSR-88D, which eliminates an expensive, high-power switch. A theoretical evaluation is performed to determine the effects that feed alignment, drop canting, and backscatter depolarization have on the measurements of polarimetric parameters made with simultaneous transmission and rece...
245 citations
TL;DR: In this article, a wavelet analysis is applied to airborne infrared lidar data to obtain an objective determination of boundaries in aerosol backscatter that are associated with boundary layer structure.
Abstract: Wavelet analysis is applied to airborne infrared lidar data to obtain an objective determination of boundaries in aerosol backscatter that are associated with boundary layer structure. This technique allows high-resolution spatial variability of planetary boundary layer height and other structures to be derived in complex, multilayered atmospheres. The technique is illustrated using data from four different lidar systems deployed on four different field campaigns. One case illustrates high-frequency retrieval of the top of a strongly convective boundary layer. A second case illustrates the retrieval of multiple layers in a complex, stably stratified region of the lower troposphere. The method is easily modified to allow for varying aerosol distributions and data quality. Two more difficult cases, data that contain a great deal of instrumental noise and a cloud-topped convective layer, are described briefly. The method is also adaptable to model analysis, as is shown via application to large eddy ...
234 citations
TL;DR: In this paper, the authors derive expressions for correcting second-through fourth-order moments of measured variables that are contaminated by random uncorrelated noise and apply them to an artificially produced time series as well as measurements from two upward-pointing ground-based lidar systems.
Abstract: The authors derive expressions for correcting second- through fourth-order moments of measured variables that are contaminated by random uncorrelated noise. These expressions are then tested by applying them to an artificially produced time series as well as measurements from two upward-pointing ground-based lidar systems:a differential absorption lidar that measures water vapor density and a high-resolution Doppler lidar that measures vertical wind velocity. Both sets of measurements were obtained in a convective boundary layer, and contain sufficient noise to significantly affect measurements of second- and fourth-order moments (as well as integral scale and skewness) throughout the boundary layer. It is shown that the corrections derived here can be used to obtain useful measurements of these moments from instruments such as lidars, which are inherently noisy. The authors also obtain information on higher-order moments of the noise as well as the correlation between noise and atmospheric measu...
191 citations
TL;DR: In this paper, a simple technique for fitting spectra that is applicable to any problem of adjusting a theoretical spectral form to fit observations is described, based on direct application of the maximum likelihood approach.
Abstract: A simple technique for fitting spectra that is applicable to any problem of adjusting a theoretical spectral form to fit observations is described. All one needs is a functional form for the theoretical spectrum and an estimate for the instrumental noise spectrum. The method, based on direct application of the maximum likelihood approach, has several advantages over other fitting techniques. 1) It is unbiased in comparison with other least squares or cost function–based approaches. 2) It is insensitive to dips and wiggles in the spectrum, due to the small number of fitted parameters. It is also robust because the range of wavenumbers used in the fit is held fixed, and the built-in noise model forces the routine to ignore the spectrum as it gets down toward the noise level. 3) The method provides a theoretical estimate for error bars on the fitted Batchelor wavenumber, based on how broad or narrow the likelihood function is in the vicinity of its peak. 4) Statistical quantities that indicate how w...
166 citations
TL;DR: In this paper, the Air-Sea Interaction Spar (ASIS) is deployed for sea trials in the waters off Miami, Florida; in the northeastern region of the Gulf of Mexico; and in the northwestern Mediterranean.
Abstract: This paper describes a new, compact buoy, the Air–Sea Interaction Spar (ASIS), capable of reliably and accurately measuring directional wave spectra, atmospheric surface fluxes, and radiation in the the open ocean. The ASIS buoy is a stable platform and has low flow disturbance characteristics in both atmospheric and oceanic surface boundary layers. The buoy has been deployed for sea trials in the waters off Miami, Florida; in the northeastern region of the Gulf of Mexico; and in the northwestern Mediterranean. The acquired measurements of directional wave spectra, momentum and heat fluxes, and profile data—as well as general meteorological and oceanographic parameters—obtained from the buoy are well suited for enhancing research on air–water interfacial processes, wave dynamics, remote sensing, and gas transfer. In this paper the design is described and the performance of the buoy using field data is characterized.
TL;DR: In this article, a series of microphysical laboratory experiments studying the hydrodynamics of single bubbles were conducted to measure the variation of rise velocity, VB, with temperature, T, and radius, r.
Abstract: A series of microphysical laboratory experiments studying the hydrodynamics of single bubbles were conducted to measure the variation of rise velocity, VB, with temperature, T, and radius, r. Bubbles with an equivalent spherical radius between 377 and 4500 μm were studied for T varying between 0° and 40°C. While for nonoscillating bubbles VB increases with T; due to the significance of oscillations, VB decreases with T for oscillating bubbles, in conjunction with an increase in trajectory oscillations with T. Using observations from this study and data from other researchers, a three-part parameterization of VB(r, T) is proposed with transitions at Re = 1 and the onset of oscillations, where Re is the Reynolds number. The T for the transition to oscillatory behavior was found to vary linearly with r. An empirical parameterization of VB(r, T) for oscillatory and nonoscillatory bubbles that correctly incorporates the effect of T is presented.
TL;DR: In this article, a transportable multiple-wavelength lidar is presented, which is used for the profiling of optical and physical aerosol properties, and the combined beam can be directed into the atmosphere from −90° to +90° zenith angle by means of a turnable mirror unit.
Abstract: A transportable multiple-wavelength lidar is presented, which is used for the profiling of optical and physical aerosol properties. Two Nd:YAG and two dye lasers in combination with frequency-doubling crystals emit simultaneously at 355, 400, 532, 710, 800, and 1064 nm. A beam-combination unit aligns all six laser beams onto one optical axis. Hence the same air volume is observed by all six beams. The combined beam can be directed into the atmosphere from −90° to +90° zenith angle by means of a turnable mirror unit. From the simultaneous detection of the elastic-backscatter signals and of the Raman signals backscattered by nitrogen molecules at 387 and 607 nm and by water vapor molecules at 660 nm, vertical profiles of the six backscatter coefficients between 355 and 1064 nm, of the extinction coefficients, and of the extinction-to-backscatter ratio at 355 and 532 nm, as well as of the water vapor mixing ratio, are determined. The optical thickness between the lidar and a given height can be retr...
TL;DR: In this paper, the satellite-based optical transient detector (OTD) was used for preliminary validation of the U.S. National Lightning Detection Network (NLDN).
Abstract: Lightning data from the U.S. National Lightning Detection Network (NLDN) are used to perform preliminary validation of the satellite-based Optical Transient Detector (OTD). Sensor precision, accuracy, detection efficiency, and biases of the deployed instrument are considered. The sensor is estimated to have, on average, about 20–40-km spatial and better than 100-ms temporal accuracy. The detection efficiency for cloud-to-ground lightning is about 46%–69%. It is most likely slightly higher for intracloud lightning. There are only marginal day/night biases in the dataset, although 55- or 110-day averaging is required to remove the sampling-based diurnal lightning cycle bias.
TL;DR: In this paper, simple bulk formulas that include the effects of dynamic stability are developed to provide wind stress, and latent and sensible heat fluxes at the air-sea interface in general circulation models (GCMs).
Abstract: Efficient and computationally inexpensive simple bulk formulas that include the effects of dynamic stability are developed to provide wind stress, and latent and sensible heat fluxes at the air–sea interface in general circulation models (GCMs). In these formulas the exchange coefficients for momentum and heat (i.e., wind stress drag coefficient, and latent and sensible heat flux coefficients, respectively) have a simple polynomial dependence on wind speed and a linear dependence on the air–sea temperature difference that are derived from a statistical analysis of global monthly climatologies according to wind speed and air–sea temperature difference intervals. Using surface meteorological observations from a central Arabian Sea mooring, these formulas are shown to yield air–sea fluxes on daily timescales that are highly accurate relative to those obtained with the standard algorithm used by the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE), where the ...
TL;DR: In this paper, the authors used a state-of-the-art, third-generation wave model to evaluate the marine surface wind fields produced in the National Centers for Environmental Protection-National Center for Atmospheric Research (NCEP-NCAR) Reanalysis (NRA) project.
Abstract: This paper uses a state-of-the-art, third-generation wave model to evaluate the marine surface wind fields produced in the National Centers for Environmental Protection–National Center for Atmospheric Research (NCEP–NCAR) Reanalysis (NRA) project. Three alternative NRA wind fields were initially considered by assessing the resulting wave hindcasts against wave measurements in the North Atlantic Ocean. The surface 10-m wind field was found to be the most skillful and was selected for further analysis. While the wind fields from the NRA were found to be at least as skillful as the best of the analyses produced by operational Numerical Weather Prediction centers, they had significant deficiencies when compared to kinematically analyzed wind fields carried out in detailed hindcast studies. Storm peak wave heights in extratropical storms were systematically underestimated at higher sea states due to underestimation of peak wind speeds in major jet streak features propagating about intense extratropica...
TL;DR: In this article, the authors evaluate properties of techniques typically used for such objective analysis and propose the isotropic Gaussian or Barnes-type weight function with constant smoothing parameter.
Abstract: The spherical geometry of weather radar scans results in a data distribution wherein datapoint separation in one coordinate direction and/or in one part of the analysis domain can differ widely from that in another. Objective analysis of the nonuniform radar data to a uniform Cartesian grid is desirable for many diagnostic purposes. For the benefit of the diagnostic data analyst as well as of users of these analyses, the authors evaluate properties of techniques typically used for such objective analysis. This is done partly through theoretical consideration of the properties of the schemes, but mostly by empirical testing. In terms of preservation of the phase and amplitude of the input data, predictability of the degree of smoothing and filtering, and relative insensitivity to input data unsteadiness or spatial characteristic, the isotropic Gaussian or Barnes-type weight function with constant smoothing parameter appears to be the most desirable of the schemes considered. Modification of this s...
TL;DR: The ground-based water vapor observing system based on the measurement of GPS signal delays caused by water vapor in the atmosphere was developed by the National Oceanic and Atmospheric Administrations (NOAA) Forecast Systems Laboratory (FSL) and Environmental Technology Laboratory (ETL) in collaboration with the University NAVSTAR Consortium, University of Hawaii, Scripps Institution of Oceanography, and NOAA's National Geodetic Survey (NGS) Laboratory as discussed by the authors.
Abstract: The need for a reliable, low-cost observing system to measure water vapor in the atmosphere is incontrovertible. Experiments have shown the potential for using Global Positioning System (GPS) receivers to measure total precipitable water vapor accurately at different locations and times of year and under all weather conditions. The National Oceanic and Atmospheric Administrations’s (NOAA) Forecast Systems Laboratory (FSL) and Environmental Technology Laboratory (ETL), in collaboration with the University NAVSTAR Consortium, University of Hawaii, Scripps Institution of Oceanography, and NOAA’s National Geodetic Survey (NGS) Laboratory, are addressing this need by developing a ground-based water vapor observing system based on the measurement of GPS signal delays caused by water vapor in the atmosphere. The NOAA GPS Integrated Precipitable Water Vapor (NOAA GPS–IPW) network currently has 35 continuously operating stations and is expected to expand into a 200-station demonstration network by 2004. T...
TL;DR: In this article, a disdrometer that provides information on raindrop size distribution, terminal velocity, and shape using video imaging technology is investigated, where two video cameras are enclosed in a large box and provide images of the passing drops.
Abstract: The authors investigate a disdrometer that provides information on raindrop size distribution, terminal velocity, and shape using video imaging technology. Two video cameras are enclosed in a large box and provide images of the passing drops. The box modifies the air flow, and this in turn affects the drop trajectories, causing some of the drops to miss the sensing area in the instrument’s opening. The authors investigate the distortion of the trajectories using numerical simulation methods of computational fluid dynamics. This approach enables the authors to quantify the effects of wind velocity and direction on the instrument’s measurement of drop size distribution. The results of the study lead to the conclusion that the shape of the enclosure of the instrument causes errors in the detection of the small drops. Small drops can get caught in a vortex that develops over the inlet. Some of them end up being counted more than once as they cross the sensing area while others are carried away and no...
TL;DR: In this paper, a discussion of the response of these instruments to varying environmental conditions, including the magnitude and variability of the irradiance being measured, is presented, and it is found that different conditions, commonly occurring in field experiments, affect the thermal balance and temperature gradients within the instrument in a variety of ways.
Abstract: Pyranometers are reliable, economical radiometers commonly used to measure solar irradiances at the surface in a long-term, monitoring mode. This paper presents a discussion of the response of these instruments to varying environmental conditions, including the magnitude and variability of the irradiance being measured. It is found that different conditions, commonly occurring in field experiments, affect the thermal balance and temperature gradients within the instrument in a variety of ways. Such an effect results in variable offset systematic errors whose origin and magnitude are investigated in laboratory and field experiments. It is shown that these offset errors are proportional to the difference between the fourth power of the dome and detector temperatures, following closely the Stefan–Boltzmann radiation law. Results of field experiments are presented for daytime and nighttime operation over a variety of atmospheric conditions ranging from clear to heavy overcast and rain. All measuremen...
TL;DR: In this paper, an improved algorithm for the generation of gridded window brightness temperatures is presented, which takes window brightness, temperatures from multiple satellites, both geostationary and polar orbiting, which have already been navigated and normalized radiometrically to the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer.
Abstract: An improved algorithm for the generation of gridded window brightness temperatures is presented. The primary data source is the International Satellite Cloud Climatology Project, level B3 data, covering the period from July 1983 to the present. The algorithm takes window brightness, temperatures from multiple satellites, both geostationary and polar orbiting, which have already been navigated and normalized radiometrically to the National Oceanic and Atmospheric Administration’s Advanced Very High Resolution Radiometer, and generates 3-hourly global images on a 0.5° by 0.5° latitude–longitude grid. The gridding uses a hierarchical scheme based on spherical kernel estimators. As part of the gridding procedure, the geostationary data are corrected for limb effects using a simple empirical correction to the radiances, from which the corrected temperatures are computed. This is in addition to the application of satellite zenith angle weighting to downweight limb pixels in preference to nearer-nadir p...
TL;DR: In this article, a nonintrusive remote sensing method to measure water level is examined, which relies on the fact that water is a good reflector of radio frequency energy, thus, a readily detectable interference pattern is formed as the satellite moves through its orbit.
Abstract: A nonintrusive remote sensing method to measure water level is examined. It relies on the fact that water is a good reflector of radio frequency energy, thus, on a satellite-to-ground path when the satellite is near the horizon, a readily detectable interference pattern is formed as the satellite moves through its orbit. Provided that the elevation angles from the ground-based receiver to the satellite are small enough for good reflection but not so small that atmospheric refractive effects contribute, the shape of this interference pattern is strongly related to the geometry of propagation. Results from interferometric observations of Global Positioning System (GPS) satellite signals are presented for two sets of measurements where the receiving antenna varied from 7 to 10 m above the nominal water surface. These results, compared to in situ or nearby tide gauges, show that water level is measured to an accuracy of about 12 cm. A GPS receiver, a laptop computer, and a clear over-water path to th...
TL;DR: In this article, the uncertainties associated with implementing data collection procedures while using different in-water optical instruments and deployment methods were quantified using data from multiple cruises, including the use of a portable light source and intercomparisons to monitor the stability of the field radiometers, alternative methods for acquiring reference measurements, and different techniques for making inwater profiles.
Abstract: The primary objective of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project is to produce waterleaving radiances within an uncertainty of 5% in clear-water regions, and chlorophyll a concentrations within 35% over the range of 0.05‐50 mg m23. Any global mission, like SeaWiFS, requires validation data from a wide variety of investigators. This places a significant challenge on quantifying the total uncertainty associated with the in situ measurements, because each investigator follows slightly different practices when it comes to implementing all of the steps associated with collecting field data, even those with a prescribed set of protocols. This study uses data from multiple cruises to quantify the uncertainties associated with implementing data collection procedures while using different in-water optical instruments and deployment methods. A comprehensive approach is undertaken and includes (a) the use of a portable light source and in-water intercomparisons to monitor the stability of the field radiometers, (b) alternative methods for acquiring reference measurements, and (c) different techniques for making in-water profiles. Three optical systems had quadrature sum uncertainties sufficiently small to ensure a combined uncertainty for the spaceborne and in situ measurements within a total 5% vicarious calibration budget. A free-fall profiler using (relatively inexpensive) modular components performed best (2.7% quadrature sum uncertainty), although a more sophisticated (and comparatively expensive) profiler using integral components was very close and only 0.5% higher. A relatively inexpensive system deployed with a winch and crane was also close, but ship shadow contamination increased the quadrature sum uncertainty to approximately 3.4%.
TL;DR: In this paper, a case study in which coincident 35-and 94-GHz radars located at Chilbolton, England, were used to measure crystal size in cirrus clouds was presented.
Abstract: Results are presented from a case study in which coincident 35- and 94-GHz radars located at Chilbolton, England, were used to measure crystal size in cirrus clouds. In the presence of larger crystals the 94-GHz radar scatters sufficiently beyond the Rayleigh regime that the difference in reflectivity factor measured by the two can be directly related to size. This enables more accurate estimation of ice water content than would be possible using a single radar. The small crystals at the top of the cloud scatter in the Rayleigh regime at both wavelengths, which provides a valuable method of calibration, but also means that sizing is not possible in this part of the cloud. Ice water content and median volume diameter were derived and compared with the analyses of the U.K. Meteorological Office Unified Model. The smallest measurable median volume diameter in this case study was around 200 μm, although it is believed that with both radars sensitive down to −35 dBZ, it should be possible to measure m...
TL;DR: In this article, a set of battery-powered temperature dataloggers (HOBO H8 Pro from Onset Computer, Bourne, Massachusetts) were selected for laboratory calibration.
Abstract: Recent advances in electronics miniaturization have allowed the commercial development of sensor/datalogger combinations that are sufficiently inexpensive and appear to be sufficiently accurate to deploy in measurement arrays to resolve local atmospheric structure over periods of weeks to months. As part of an extended wintertime field experiment in the Columbia Basin of south-central Washington, laboratory and field tests were performed on one such set of battery-powered temperature dataloggers (HOBO H8 Pro from Onset Computer, Bourne, Massachusetts). Five loggers were selected for laboratory calibration. These were accurate to within 0.26°C over the range from −5° to +50°C with a resolution of 0.04°C or better. Sensor time constants were 122 ± 6 s. Sampling intervals can be varied over a wide range, with onboard data storage of more than 21 000 data points. Field experiences with a set of 15 dataloggers are also described. The loggers appear to be suitable for a variety of meteorological applic...
TL;DR: In this article, two histograms (a single image and a multi-image method) and one gradient algorithm were tested for the occurrence of two types of errors: (a) the detection of false fronts and (b) the failure to detect fronts observed in in situ data.
Abstract: Sea surface temperature (SST) fronts detected in Advanced Very High Resolution Radiometer (AVHRR) data using automated edge-detection algorithms were compared to fronts found in continuous measurements of SST made aboard a ship of opportunity. Two histograms (a single-image and a multi-image method) and one gradient algorithm were tested for the occurrence of two types of errors: (a) the detection of false fronts and (b) the failure to detect fronts observed in the in situ data. False front error rates were lower for the histogram methods (27%‐28%) than for the gradient method (45%). Considering only AVHRR fronts for which the SST gradient along the ship track was greater than 0.18 Ck m 21, error rates drop to 14% for the histogram methods and 29% for the gradient method. Missed front error rates were lower using the gradient method (16%) than the histogram methods (30%). This error rate drops significantly for the histogram methods (5%‐10%) if fronts associated with small-scale SST features (,10 km) are omitted from the comparison. These results suggest that frontal climatologies developed from the application of automated edge-detection methods to long time series of AVHRR images provide acceptably accurate statistics on front occurrence.
TL;DR: In this article, the authors used Lagrangian drifter data to improve the accuracy of predicted trajectories in oceanic flows by assimilating velocity data from the surrounding drifters into a Gauss-Markov model for particle motion.
Abstract: The predictability of particle trajectories in oceanic flows is investigated in the context of a primitive equation, idealized, double-gyre ocean model. This study is motivated not only by the fact that this is an important conceptual problem but also by practical applications, such as searching for objects lost at sea, and ecological problems, such as the spreading of pollutants or fish larvae. The original aspect of this study is the use of Lagrangian drifter data to improve the accuracy of predicted trajectories. The prediction is performed by assimilating velocity data from the surrounding drifters into a Gauss‐Markov model for particle motion. The assimilation is carried out using a simplified Kalman filter. The performance of the prediction scheme is quantified as a function of a number of factors: 1) dynamically different flow regimes, such as interior gyre, western boundary current, and midlatitude jet regions; 2) density of drifter data used in assimilation; and 3) uncertainties in the knowledge of the mean flow field and the initial conditions. The data density is quantified by the number of data per degrees of freedom NR, defined as the number of drifters within the typical Eulerian space scale from the prediction particle. The simulations indicate that the actual World Ocean Circulation Experiment sampling (1 particle/[5 83 58 ]o rNR K 1) does not improve particle prediction, but predictions improve significantly when NR k 1. For instance, a coverage of 1 particle/ [1 83 18 ]o rNR ; O(1) is already able to reduce the errors of about one-third or one-half. If the sampling resolution is increased to 1 particle/[0.5 83 0.58] or 1 particle/[0.25 83 0.258 ]o rNR k 1, reasonably accurate predictions (rms errors of less than 50 km) can be obtained for periods ranging from one week (western boundary current and midlatitude jet regions) to three months (interior gyre region). Even when the mean flow field and initial turbulent velocities are not known accurately, the information derived from the surrounding drifter data is shown to compensate when NR . 1. Theoretical error estimates are derived that are based on the main statistical parameters of the flow field. Theoretical formulas show good agreement with the numerical results, and hence, they may serve as useful a priori estimates of Lagrangian prediction error for practical applications.
TL;DR: In this article, a new algorithm was developed to classify populations of binary (black and white) images of cloud particles collected with Particle Measuring Systems (PMS) Optical Array Probes (OAPA).
Abstract: A new algorithm was developed to classify populations of binary (black and white) images of cloud particles collected with Particle Measuring Systems (PMS) Optical Array Probes (OAPA). The algorithm classifies images into four habit categories: ‘‘spheres,’’ ‘‘irregulars,’’ ‘‘needles,’’ and ‘‘dendrites.’’ The present algorithm derives the particle habits from an analysis of dimensionless ratios of simple geometrical measures such as the x and y dimensions, perimeter, and image area. For an ensemble of images containing a mixture of different habits, the distribution of a particular ratio will be a linear superposition of basis distributions of ratios of the individual habits. The fraction of each habit in the ensemble is found by solving the inverse problem. One of the advantages of the suggested scheme is that it provides recognition analysis of both ‘‘complete’’ and ‘‘partial’’ images, that is, images that are completely or partially contained within the sample area of the probe. The ability to process ‘‘partial’’ images improves the statistics of the recognition by approximately 50% when compared with retrievals that use ‘‘complete’’ images only. The details of this algorithm are discussed in this study.
TL;DR: The authors present a new differential reflectivity ( ZDR) calibration technique and data examples collected in different polarization modes for the CSU‐CHILL National Radar Facility’s S-band polarimetric research radar.
Abstract: The subject of this paper is the Colorado State University‐University of Chicago‐Illinois State Water Survey (CSU‐CHILL) National Radar Facility’s S-band polarimetric research radar. Key features of this system include polarization agility (provided by the dual-transmitter, dual-receiver design), a recently updated signal processor, and a low (234 dB, two way) integrated cross-polar ratio (ICPR 2) antenna system. After reviewing the technical description of the radar, the authors present a new differential reflectivity ( ZDR) calibration technique and data examples collected in different polarization modes. Although the CSU‐CHILL radar is transportable, it can also be operated in a dual-Doppler configuration with the CSU‐Pawnee radar, an 11-cm Doppler radar system situated 48 km north of the CSU‐CHILL Greeley field site. Used together, these radars provide three-dimensional kinematic and hydrometeor information in precipitating cloud systems.
TL;DR: The Kipp & Zonen NR-Lite as discussed by the authors is a newly designed domeless net radiometer designed for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project, which was rigorously field tested for over eight months during 1998.
Abstract: The Kipp & Zonen NR-Lite is a newly designed domeless net radiometer. In preparation for the Oklahoma Atmospheric Surface-layer Instrumentation System (OASIS) Project, the NR-Lite was rigorously field tested for over eight months during 1998. Seven NR-Lites were compared to an Eppley four-component PSP/PIR net radiometer system, a Kipp & Zonen four-component CNR1, and a REBS Q*7.1. Measurement problems associated with calibration, precipitation, cosine response, and wind-induced error were examined. Results conclude that the NR-Lite is well-suited for experiments where remote, long-term measurements of net radiation are required.