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1
Knuteson, R. O., H. E. Revercomb, F. A. Best, N. C. Ciganovich, R. G. Dedecker, T. P. Dirkx, S. C. Ellington, et al. "Atmospheric Emitted Radiance Interferometer. Part I: Instrument Design." Journal of Atmospheric and Oceanic Technology 21, no. 12 (December 1, 2004): 1763–76. http://dx.doi.org/10.1175/jtech-1662.1.
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Abstract A ground-based Fourier transform spectrometer has been developed to measure the atmospheric downwelling infrared radiance spectrum at the earth's surface with high absolute accuracy. The Atmospheric Emitted Radiance Interferometer (AERI) instrument was designed and fabricated by the University of Wisconsin Space Science and Engineering Center (UW-SSEC) for the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program. This paper emphasizes the key features of the UW-SSEC instrument design that contribute to meeting the AERI instrument requirements for the ARM Program. These features include a highly accurate radiometric calibration system, an instrument controller that provides continuous and autonomous operation, an extensive data acquisition system for monitoring calibration temperatures and instrument health, and a real-time data processing system. In particular, focus is placed on design issues crucial to meeting the ARM requirements for radiometric calibration, spectral calibration, noise performance, and operational reliability. The detailed performance characteristics of the AERI instruments built for the ARM Program are described in a companion paper.
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Knuteson, R. O., H. E. Revercomb, F. A. Best, N. C. Ciganovich, R. G. Dedecker, T. P. Dirkx, S. C. Ellington, et al. "Atmospheric Emitted Radiance Interferometer. Part II: Instrument Performance." Journal of Atmospheric and Oceanic Technology 21, no. 12 (December 1, 2004): 1777–89. http://dx.doi.org/10.1175/jtech-1663.1.
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Abstract The Atmospheric Emitted Radiance Interferometer (AERI) instrument was developed for the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program by the University of Wisconsin Space Science and Engineering Center (UW-SSEC). The infrared emission spectra measured by the instrument have the sensitivity and absolute accuracy needed for atmospheric remote sensing and climate studies. The instrument design is described in a companion paper. This paper describes in detail the measured performance characteristics of the AERI instruments built for the ARM Program. In particular, the AERI systems achieve an absolute radiometric calibration of better than 1% (3σ) of ambient radiance, with a reproducibility of better than 0.2%. The knowledge of the AERI spectral calibration is better than 1.5 ppm (1σ) in the wavenumber range 400– 3000 cm−1.
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Cheng, Anne Ru, Tim Hau Lee, Hsin I. Ku, and Yi Wen Chen. "Quality Control Program for Real-Time Hourly Temperature Observation in Taiwan." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 953–76. http://dx.doi.org/10.1175/jtech-d-15-0005.1.
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AbstractThis paper introduces a quality control (QC) program for the real-time hourly land surface temperature observation developed by the Central Weather Bureau in Taiwan. There are three strategies involved. The first strategy is a range check scheme that inspects whether the observation falls inside the climatological limits of the station to screen out the obvious outliers. Limits are adjusted according to the station’s elevation. The second strategy is a spatial check scheme that scrutinizes whether the observation falls inside the derived confidence interval, according to the data from the reference stations and the correlations among the stations, to judge the reliability of the data. The scheme is specialized, as it employs the theorems of unbiased and minimum error estimators to determine the weights. The performance evaluation results show that the new method is in theory superior to the spatial regression test (You et al.). The third strategy is a temporal check scheme that examines whether the temperature difference of two successive observations exceeds the temperature variation threshold for judging the rationality of the data. Different thresholds are applied for the data observed in different times under different rainfall conditions. Procedurally, the observation must pass the range check first and then go through the spatial or the temporal check. The temporal check is applied only when the spatial check is unavailable. Post-examinations of the data from 2014 show that the QC program is able to filter out most of the significant errors.
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Roemmich, Dean, Jeffrey T. Sherman, Russ E. Davis, Kyle Grindley, Michael McClune, Charles J. Parker, David N. Black, et al. "Deep SOLO: A Full-Depth Profiling Float for the Argo Program." Journal of Atmospheric and Oceanic Technology 36, no. 10 (October 2019): 1967–81. http://dx.doi.org/10.1175/jtech-d-19-0066.1.
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AbstractDeployment of Deep Argo regional pilot arrays is underway as a step toward a global array of 1250 surface-to-bottom profiling floats embedded in the upper-ocean (2000 m) Argo Program. Of the 80 active Deep Argo floats as of July 2019, 55 are Deep Sounding Oceanographic Lagrangian Observer (SOLO) 6000-m instruments, and the rest are composed of three additional models profiling to either 4000 or 6000 m. Early success of the Deep SOLO is owed partly to its evolution from the Core Argo SOLO-II. Here, Deep SOLO design choices are described, including the spherical glass pressure housing, the hydraulics system, and the passive bottom detection system. Operation of Deep SOLO is flexible, with the mission parameters being adjustable from shore via Iridium communications. Long lifetime is a key element in sustaining a global array, and Deep SOLO combines a long battery life of over 200 cycles to 6000 m with robust operation and a low failure rate. The scientific value of Deep SOLO is illustrated, including examples of its ability (i) to observe large-scale spatial and temporal variability in deep ocean temperature and salinity, (ii) to sample newly formed water masses year-round and within a few meters of the sea floor, and (iii) to explore the poorly known abyssal velocity field and deep circulation of the World Ocean. Deep SOLO’s full-depth range and its potential for global coverage are critical attributes for complementing the Core Argo Program and achieving these objectives.
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Tridon, Frédéric, Alessandro Battaglia, Pavlos Kollias, Edward Luke, and Christopher R. Williams. "Signal Postprocessing and Reflectivity Calibration of the Atmospheric Radiation Measurement Program 915-MHz Wind Profilers." Journal of Atmospheric and Oceanic Technology 30, no. 6 (June 1, 2013): 1038–54. http://dx.doi.org/10.1175/jtech-d-12-00146.1.
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Abstract The Department of Energy Atmospheric Radiation Measurement (ARM) Program has recently initiated a new research avenue toward a better characterization of the transition from cloud to precipitation. Dual-wavelength techniques applied to millimeter-wavelength radars and a Rayleigh reference have a great potential for rain-rate retrievals directly from dual-wavelength ratio measurements. In this context, the recent reconfiguration of the ARM 915-MHz wind profilers in a vertically pointing mode makes these instruments the ideal candidate for providing the Rayleigh reflectivity/Doppler velocity reference. Prior to any scientific study, the wind profiler data must be carefully quality checked. This work describes the signal postprocessing steps that are essential for the delivery of high-quality reflectivity and mean Doppler velocity products—that is, the estimation of the noise floor from clear-air echoes, the absolute calibration with a collocated disdrometer, the dealiasing of Doppler velocities, and the merging of the different modes of the wind profiler. The improvement added by the proposed postprocessing is confirmed by comparison with a high-quality S-band profiler deployed at the ARM Southern Great Plains site during the Midlatitude Continental Convective Clouds Experiment. With the addition of a vertically pointing mode and with the postprocessing described in this work in place, besides being a key asset for wind research wind profilers observations may therefore become a centerpiece for rain studies in the years to come.
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Leeper, Ronald D., Jared Rennie, and Michael A. Palecki. "Observational Perspectives from U.S. Climate Reference Network (USCRN) and Cooperative Observer Program (COOP) Network: Temperature and Precipitation Comparison." Journal of Atmospheric and Oceanic Technology 32, no. 4 (April 2015): 703–21. http://dx.doi.org/10.1175/jtech-d-14-00172.1.
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AbstractThe U.S. Cooperative Observer Program (COOP) network was formed in the early 1890s to provide daily observations of temperature and precipitation. However, manual observations from naturally aspirated temperature sensors and unshielded precipitation gauges often led to uncertainties in atmospheric measurements. Advancements in observational technology (ventilated temperature sensors, well-shielded precipitation gauges) and measurement techniques (automation and redundant sensors), which improve observation quality, were adopted by NOAA’s National Climatic Data Center (NCDC) into the establishment of the U.S. Climate Reference Network (USCRN). USCRN was designed to provide high-quality and continuous observations to monitor long-term temperature and precipitation trends, and to provide an independent reference to compare to other networks. The purpose of this study is to evaluate how diverse technological and operational choices between the USCRN and COOP programs impact temperature and precipitation observations. Naturally aspirated COOP sensors generally had warmer (+0.48°C) daily maximum and cooler (−0.36°C) minimum temperatures than USCRN, with considerable variability among stations. For precipitation, COOP reported slightly more precipitation overall (1.5%) with network differences varying seasonally. COOP gauges were sensitive to wind biases (no shielding), which are enhanced over winter when COOP observed (10.7%) less precipitation than USCRN. Conversely, wetting factor and gauge evaporation, which dominate in summer, were sources of bias for USCRN, leading to wetter COOP observations over warmer months. Inconsistencies in COOP observations (e.g., multiday observations, time shifts, recording errors) complicated network comparisons and led to unique bias profiles that evolved over time with changes in instrumentation and primary observer.
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Tokay, Ali, Leo Pio D’Adderio, David B. Wolff, and Walter A. Petersen. "Development and Evaluation of the Raindrop Size Distribution Parameters for the NASA Global Precipitation Measurement Mission Ground Validation Program." Journal of Atmospheric and Oceanic Technology 37, no. 1 (January 2020): 115–28. http://dx.doi.org/10.1175/jtech-d-18-0071.1.
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AbstractThe National Aeronautics and Space Administration Global Precipitation Measurement (GPM) mission ground validation program uses dual-polarization radar moments to estimate raindrop size distribution (DSD) parameters, the mass-weighted mean drop diameter Dmass, and normalized intercept parameter NW, to validate the GPM Core Observatory–derived DSD parameters. The disdrometer-based Dmass and NW are derived through empirical relationships between Dmass and differential reflectivity ZDR, and between NW, reflectivity ZH, and Dmass. This study employs large datasets collected from two-dimensional video disdrometers (2DVD) during six different field studies to derive the requisite empirical relationships. The uncertainty of the derived Dmass(ZDR) relationship is evaluated through comparisons of 2DVD-calculated and ZDR-estimated Dmass, where ZDR is calculated directly from 2DVD observations. Similarly, the uncertainty of the NW(ZH, Dmass) relationship is evaluated through 2DVD-calculated and Dmass and ZH-estimated NW, where Dmass and ZH are directly calculated from 2DVD observations. This study also presents the sensitivity of Dmass(ZDR) relationships to climate regime and to disdrometer type after developing three additional Dmass(ZDR) relationships from second-generation Particle Size Velocity (PARSIVEL2) disdrometer (P2) observations collected in the Pacific Northwest, in Iowa, and at Kwajalein Atoll in the tropical Pacific Ocean. The application of P2-derived Dmass(ZDR) relationship based on precipitation in the northwestern United States to P2 observations collected over the tropical ocean resulted in the highest error among comparisons of the three datasets.
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Demaria, Eleonora M. C., David C. Goodrich, and Kenneth E. Kunkel. "Evaluating the Reliability of the U.S. Cooperative Observer Program Precipitation Observations for Extreme Events Analysis Using the LTAR Network." Journal of Atmospheric and Oceanic Technology 36, no. 3 (March 2019): 317–32. http://dx.doi.org/10.1175/jtech-d-18-0128.1.
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AbstractThe detection and attribution of changes in precipitation characteristics relies on dense networks of rain gauges. In the United States, the COOP network is widely used for such studies even though there are reported inconsistencies due to changes in instruments and location, inadequate maintenance, dissimilar observation time, and the fact that measurements are made by a group of dedicated volunteers. Alternately, the Long-Term Agroecosystem Research (LTAR) network has been consistently and professionally measuring precipitation since the early 1930s. The purpose of this study is to compare changes in extreme daily precipitation characteristics during the warm season using paired rain gauges from the LTAR and COOP networks. The comparison, done at 12 LTAR sites located across the United States, shows underestimation and overestimation of daily precipitation totals at the COOP sites compared to the reference LTAR observations. However, the magnitude and direction of the differences are not linked to the underlying precipitation climatology of the sites. Precipitation indices that focus on extreme precipitation characteristics match closely between the two networks at most of the sites. Our results show consistency between the COOP and LTAR networks with precipitation extremes. It also indicates that despite the discrepancies at the daily time steps, the extreme precipitation observed by COOP rain gauges can be reliably used to characterize changes in the hydrologic cycle due to natural and human causes.
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Martini, Kim I., David J. Murphy, Raymond W. Schmitt, and Nordeen G. Larson. "Corrections for Pumped SBE 41CP CTDs Determined from Stratified Tank Experiments." Journal of Atmospheric and Oceanic Technology 36, no. 4 (April 2019): 733–44. http://dx.doi.org/10.1175/jtech-d-18-0050.1.
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AbstractSea-Bird Scientific SBE 41CP CTDs are used on autonomous floats in the global Argo ocean observing program to measure the temperature and salinity of the upper ocean. While profiling, the sensors are subject to dynamic errors as they profile through vertical gradients. Applying dynamic corrections to the temperature and conductivity data reduces these errors and improves sensor accuracy. A series of laboratory experiments conducted in a stratified tank are used to characterize dynamic errors and determine corrections. The corrections are adapted for Argo floats, and recommendations for future implementation are presented.
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Seaman, Curtis J., Yoo-Jeong Noh, Steven D. Miller, Andrew K. Heidinger, and Daniel T. Lindsey. "Cloud-Base Height Estimation from VIIRS. Part I: Operational Algorithm Validation against CloudSat." Journal of Atmospheric and Oceanic Technology 34, no. 3 (March 2017): 567–83. http://dx.doi.org/10.1175/jtech-d-16-0109.1.
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AbstractThe operational VIIRS cloud-base height (CBH) product from the Suomi–National Polar-Orbiting Partnership (SNPP) satellite is compared against observations of CBH from the cloud profiling radar (CPR) on board CloudSat. Because of the orbits of SNPP and CloudSat, these instruments provide nearly simultaneous observations of the same locations on Earth for a ~4.5-h period every 2–3 days. The methodology by which VIIRS and CloudSat observations are spatially and temporally matched is outlined. Based on four 1-month evaluation periods representing each season from June 2014 to April 2015, statistics related to the VIIRS CBH retrieval performance have been collected. Results indicate that when compared against CloudSat, the VIIRS CBH retrieval does not meet the error specifications set by the Joint Polar Satellite System (JPSS) program, with a root-mean-square error (RMSE) of 3.7 km for all clouds globally. More than half of all matching VIIRS pixels and CloudSat profiles have CBH errors exceeding the 2-km error requirement. Underscoring the significance of these statistics, it is shown that a simple estimate based on a constant cloud geometric thickness of 2 km outperforms the current operational CBH algorithm. It was found that the performance of the CBH product is impacted by the accuracy of upstream retrievals [primarily cloud-top height (CTH)] and the a priori information used by the CBH retrieval algorithm. However, even when CTH errors were small, CBH errors still exceed the JPSS program error specifications with an RMSE of 2.3 km.
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Chen, Maosi, John Davis, and Wei Gao. "A New Cloud Screening Algorithm for Ground-Based Direct-Beam Solar Radiation." Journal of Atmospheric and Oceanic Technology 31, no. 12 (December 1, 2014): 2591–605. http://dx.doi.org/10.1175/jtech-d-14-00095.1.
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Abstract Cloud screening of direct-beam solar radiation is an essential step for in situ calibration and atmospheric properties retrieval. The internal cloud screening module of a Langley analysis program [Langley Analyzer (LA)] used by the U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Program (UVMRP) is used for screening the uncalibrated direct-beam measurements and for deriving Langley offset voltages for calibration of the UV version of the Multifilter Rotating Shadowband Radiometer (UV-MFRSR). The current LA cloud screening module utilizes data from extended clear-sky periods and tends to ignore shorter periods that typify periods of broken cloudiness, and as a result, fewer values are generated for sites with higher frequencies of cloudy days (cloudy sites). A new cloud screening algorithm is presented that calculates the total optical depth (TOD) difference between a target point and pairs of points, and identifies the target as cloudy if the mean TOD difference exceeds a certain threshold. The screening is an iterative process that finishes when no new cloudy points are found. The result at a typical clear/sunny site shows that values from partly cloudy days are consistent with those from cloud-free days, when the new method is employed. The new cloud screening algorithm picks up significantly more values at cloudy sites. The larger decrease of the annual mean value of at cloudy sites than at relatively clear sites suggests the potential for improving calibration accuracy at cloudy sites. The results also show that the new cloud screening method is capable of detecting clear points in short clear windows and in transitional regions.
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Miller, Steven D., Cynthia L. Combs, Stanley Q. Kidder, and Thomas F. Lee. "Assessing Moonlight Availability for Nighttime Environmental Applications by Low-Light Visible Polar-Orbiting Satellite Sensors." Journal of Atmospheric and Oceanic Technology 29, no. 4 (April 1, 2012): 538–57. http://dx.doi.org/10.1175/jtech-d-11-00192.1.
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Abstract The next-generation U.S. polar-orbiting environmental satellite program, the Joint Polar Satellite System (JPSS), promises unprecedented capabilities for nighttime remote sensing by way of the day/night band (DNB) low-light visible sensor. The DNB will use moonlight illumination to characterize properties of the atmosphere and surface that conventionally have been limited to daytime observations. Since the moon is a highly variable source of visible light, an important question is where and when various levels of lunar illumination will be available. Here, nighttime moonlight availability was examined based on simulations done in the context of Visible/Infrared Imager Radiometer Suite (VIIRS)/DNB coverage and sensitivity. Results indicate that roughly 45% of all JPSS-orbit [sun-synchronous, 1330 local equatorial crossing time on the ascending node (LTAN)] nighttime observations in the tropics and midlatitudes would provide levels of moonlight at crescent moon or greater. Two other orbits, 1730 and 2130 LTAN, were also considered. The inclusion of a 2130 LTAN satellite would provide similar availability to 1330 LTAN in terms of total moonlit nights, but with approximately a third of those nights being additional because of this orbit’s capture of a different portion of the lunar cycle. Nighttime availability is highly variable for near-terminator orbits. A 1-h shift from the 1730 LTAN near-terminator orbit to 1630 LTAN would nearly double the nighttime availability globally from this orbit, including expanded availability at midlatitudes. In contrast, a later shift to 1830 LTAN has a negligible effect. The results are intended to provide high-level guidance for mission planners, algorithm developers, and various users of low-light applications from these future satellite programs.
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Caicedo, Vanessa, Ruben Delgado, Ricardo Sakai, Travis Knepp, David Williams, Kevin Cavender, Barry Lefer, and James Szykman. "An Automated Common Algorithm for Planetary Boundary Layer Retrievals Using Aerosol Lidars in Support of the U.S. EPA Photochemical Assessment Monitoring Stations Program." Journal of Atmospheric and Oceanic Technology 37, no. 10 (October 1, 2020): 1847–64. http://dx.doi.org/10.1175/jtech-d-20-0050.1.
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AbstractA unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for implementation under the redesigned U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval method using the Haar wavelet covariance transform. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late-afternoon transition times, critical to air quality model prediction and when retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used, and retrievals for nocturnal stable layers, residual layers, and mixing layers were assessed. Overall good agreement was found for all comparisons, with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable-layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual-layer heights and mixing-layer comparisons revealed overall good correlations with radiosonde heights (square of correlation coefficients r2 ranging from 0.89 to 0.96, and bias ranging from approximately −131 to +63 m for the residual layer and r2 from 0.88 to 0.97 and bias from −119 to +101 m for the mixing layer).
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Davison, Jennifer L. "A Filter for Removing Sidelobe Artifacts in Bragg Scattering Layer (BSL) Analysis for S-Band Radar." Journal of Atmospheric and Oceanic Technology 32, no. 7 (July 2015): 1289–97. http://dx.doi.org/10.1175/jtech-d-15-0033.1.
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AbstractThe local environment during the joint Atmospheric Radiation Measurement Program (ARM) Madden–Julian oscillation (MJO) Investigation Experiment (AMIE)–Cooperative Indian Ocean Experiment on Intraseasonal Variability in Year 2011 (CINDY2011)–Dynamics of the MJO (DYNAMO) field experiments caused frequent occurrences of sidelobe artifacts in the NCAR S-Pol radar dataset. Although generally low in radar reflectivity factor value (less than 5 dBZ), this contamination still proved problematic for Bragg scattering layer (BSL) analysis, generating numerous false BSL edge detections. In this paper, a statistical filtering technique is developed that effectively removes these false BSL edge detections, utilizing a new version of BSL analysis based on range–height indicator (RHI) data instead of plan position indicator data.
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Tirelli, Cecilia, Simone Ceccherini, Nicola Zoppetti, Samuele Del Bianco, Marco Gai, Flavio Barbara, Ugo Cortesi, Jukka Kujanpää, Yu Huan, and Rossana Dragani. "Data Fusion Analysis of Sentinel-4 and Sentinel-5 Simulated Ozone Data." Journal of Atmospheric and Oceanic Technology 37, no. 4 (April 2020): 573–87. http://dx.doi.org/10.1175/jtech-d-19-0063.1.
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AbstractThe complete data fusion method, generalized to the case of fusing profiles of atmospheric variables retrieved on different vertical grids and referred to different true values, is applied to ozone profiles retrieved from simulated measurements in the ultraviolet, visible, and thermal infrared spectral ranges for the Sentinel-4 and Sentinel-5 missions of the Copernicus program. In this study, the production and characterization of combined low Earth orbit (Sentinel-5) and geostationary Earth orbit (Sentinel-4) fused ozone data is performed. Fused and standard products have been compared and a performance assessment of the generalized complete data fusion is presented. The analysis of the output products of the complete data fusion algorithm and of the standard processing using quality quantifiers demonstrates that the generalized complete data fusion algorithm provides products of better quality when compared with standard products.
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Schmid, Paul, and Dev Niyogi. "A Method for Estimating Planetary Boundary Layer Heights and Its Application over the ARM Southern Great Plains Site." Journal of Atmospheric and Oceanic Technology 29, no. 3 (March 1, 2012): 316–22. http://dx.doi.org/10.1175/jtech-d-11-00118.1.
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Abstract A new objective method to determine the height of the planetary boundary layer (PBL) is presented here. PBL heights are computed using the statistical variance and kurtosis of dewpoint and virtual potential temperature differences measured from radio soundings at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) program at the Southern Great Plains (SGP) site. These heights are compared with those derived from lidar, also on the site, and with gridded model data from the North American Regional Reanalysis (NARR). A climatology of mean heights in the early (1800 UTC) and late (0000 UTC) afternoon from 2002 to 2010 is presented to show the effectiveness of the method. Future work using the new method include producing an observational climatology of PBL heights and understanding the aerosol loading within the PBL as well as a better understanding of the coupling between the surface and free atmosphere.
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Chu, Peter C., Robin T. Tokmakian, Chenwu Fan, and L. Charles Sun. "Optimal Spectral Decomposition (OSD) for Ocean Data Assimilation." Journal of Atmospheric and Oceanic Technology 32, no. 4 (April 2015): 828–41. http://dx.doi.org/10.1175/jtech-d-14-00079.1.
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AbstractOptimal spectral decomposition (OSD) is applied to ocean data assimilation with variable (temperature, salinity, or velocity) anomalies (relative to background or modeled values) decomposed into generalized Fourier series, such that any anomaly is represented by a linear combination of products of basis functions and corresponding spectral coefficients. It has three steps: 1) determination of the basis functions, 2) optimal mode truncation, and 3) update of the spectral coefficients from innovation (observational increment). The basis functions, depending only on the topography of the ocean basin, are the eigenvectors of the Laplacian operator with the same lateral boundary conditions as the assimilated variable anomalies. The Vapnik–Chervonkis dimension is used to determine the optimal mode truncation. After that, the model field updates due to innovation through solving a set of a linear algebraic equations of the spectral coefficients. The strength and weakness of the OSD method are demonstrated through a twin experiment using the Parallel Ocean Program (POP) model.
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Bruserud, Kjersti, and Sverre Haver. "Uncertainties in Current Measurements in the Northern North Sea." Journal of Atmospheric and Oceanic Technology 34, no. 4 (April 2017): 855–76. http://dx.doi.org/10.1175/jtech-d-16-0192.1.
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AbstractA met–ocean measurement program of waves and current profiles at five locations in the northern North Sea was performed over a period of approximately 5 years. Despite quality control, the measured current speed data contained more noise than expected and large discrepancies were observed between overlapping current speed data measured by different current profilers at the same locations and water depths. Some of the noise and discrepancies can be explained by the influence from surface waves. The current measurements from instruments attached to a surface buoy indicated that these suffered from the influence of surface waves. Further investigations of the uncertainties in current speed data were carried out through three phases of a current verification study, where both additional current measurements and data analysis were done. Comparisons of overlapping measured current speed showed large deviations, suggesting that the accuracy of current measurements is not as good as the user expects. These presented results are in contrast to previous studies of overlapping current measurements.
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Zhang, Jun A., Joseph J. Cione, Evan A. Kalina, Eric W. Uhlhorn, Terry Hock, and Jeffrey A. Smith. "Observations of Infrared Sea Surface Temperature and Air–Sea Interaction in Hurricane Edouard (2014) Using GPS Dropsondes." Journal of Atmospheric and Oceanic Technology 34, no. 6 (June 2017): 1333–49. http://dx.doi.org/10.1175/jtech-d-16-0211.1.
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AbstractThis study highlights infrared sensor technology incorporated into the global positioning system (GPS) dropsonde platforms to obtain sea surface temperature (SST) measurements. This modified sonde (IRsonde) is used to improve understanding of air–sea interaction in tropical cyclones (TCs). As part of the Sandy Supplemental Program, IRsondes were constructed and then deployed during the 2014 hurricane season. Comparisons between SSTs measured by collocated IRsondes and ocean expendables show good agreement, especially in regions with no rain contamination. Surface fluxes were estimated using measurements from the IRsondes and AXBTs via a bulk method that requires measurements of SST and near-surface (10 m) wind speed, temperature, and humidity. The evolution of surface fluxes and their role in the intensification and weakening of Hurricane Edouard (2014) are discussed in the context of boundary layer recovery. The study’s result emphasizes the important role of surface flux–induced boundary layer recovery in regulating the low-level thermodynamic structure that is tied to the asymmetry of convection and TC intensity change.
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Li, Feili, M. Susan Lozier, and William E. Johns. "Calculating the Meridional Volume, Heat, and Freshwater Transports from an Observing System in the Subpolar North Atlantic: Observing System Simulation Experiment." Journal of Atmospheric and Oceanic Technology 34, no. 7 (July 2017): 1483–500. http://dx.doi.org/10.1175/jtech-d-16-0247.1.
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AbstractA transbasin monitoring array from Labrador to Scotland was deployed in the summer of 2014 as part of the Overturning in the Subpolar North Atlantic Program (OSNAP). The aim of the observing system is to provide a multiyear continuous measure of the Atlantic meridional overturning circulation (AMOC) and the associated meridional heat and freshwater transports in the subpolar North Atlantic. Results from the array are expected to improve the understanding of the variability of the subpolar transports and the nature and degree of the AMOC’s latitudinal dependence. In this present work, the measurements of the OSNAP array are described and a suite of observing system simulation experiments in an eddy-permitting numerical model are used to assess how well these measurements will estimate the fluxes across the OSNAP section. The simulation experiments indicate that the OSNAP array and calculation methods will adequately capture the mean and temporal variability of the overturning circulation and of the heat and freshwater transports across the subpolar North Atlantic.
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Lumpkin, Rick, Nikolai Maximenko, and Mayra Pazos. "Evaluating Where and Why Drifters Die*." Journal of Atmospheric and Oceanic Technology 29, no. 2 (February 1, 2012): 300–308. http://dx.doi.org/10.1175/jtech-d-11-00100.1.
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Abstract NOAA ’s Global Drifter Program (GDP) manages a global array of ~1250 active satellite-tracked surface drifting buoys (“drifters”) in collaboration with numerous national and international partners. To better manage the drifter array and to assess the performance of various drifter manufacturers, it is important to discriminate between drifters that cease transmitting because of internal failure and those that cease because of external factors such as running aground or being picked up. An accurate assessment of where drifters run aground would also allow the observations to be used to more accurately simulate the evolution of floating marine debris and to quantify globally which shores are most prone to the deposit of marine debris. While the drifter Data Assembly Center of the GDP provides a metadata file that includes cause of death, the identified cause for most drifters is simply “quit transmitting.” In this study it is shown that a significant fraction of these drifters likely ran aground or were picked up, and a statistical estimate that each drifter ran aground or was picked up is derived.
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Lumpkin, Rick, Semyon A. Grodsky, Luca Centurioni, Marie-Helene Rio, James A. Carton, and Dongkyu Lee. "Removing Spurious Low-Frequency Variability in Drifter Velocities." Journal of Atmospheric and Oceanic Technology 30, no. 2 (February 1, 2013): 353–60. http://dx.doi.org/10.1175/jtech-d-12-00139.1.
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Abstract Satellite-tracked drifting buoys of the Global Drifter Program have drogues, centered at 15-m depth, to minimize direct wind forcing and Stokes drift. Drogue presence has historically been determined from submergence or tether strain records. However, recent studies have revealed that a significant fraction of drifters believed to be drogued have actually lost their drogues, a problem that peaked in the mid-2000s before the majority of drifters in the global array switched from submergence to tether strain sensors. In this study, a methodology is applied to the data to automatically reanalyze drogue presence based on anomalous downwind ageostrophic motion. Results indicate that the downwind slip of undrogued drifters is approximately 50% higher than previously believed. The reanalyzed results no longer exhibit the dramatic and spurious interannual variations seen in the original data. These results, along with information from submergence/tether strain and transmission frequency variations, are now being used to conduct a systematic manual reevaluation of drogue presence for each drifter in the post-1992 dataset.
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Hashimoto, Taishi, Koji Nishimura, Masaki Tsutsumi, Kaoru Sato, and Toru Sato. "A User Parameter-Free Diagonal-Loading Scheme for Clutter Rejection on Radar Wind Profilers." Journal of Atmospheric and Oceanic Technology 34, no. 5 (May 2017): 1139–53. http://dx.doi.org/10.1175/jtech-d-16-0058.1.
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AbstractThis paper presents a novel method for the automatic determination of the diagonal-loading level for robust adaptive beamforming on radar wind profilers. This method balances the degradation of the signal-to-interference ratio with that of the signal-to-noise ratio to maximize the detectability of the backscattered signals. Because radial wind velocities are usually estimated from the first moment of the spectrum of backscattered echoes, both the residual ground clutter and any increase in noise level degrade the detectability of atmospheric echoes. The proposed algorithm evaluates the power spectral density of the residual clutter and increased noise to determine the optimal diagonal-loading level by balancing these two factors. The results of numerical simulation show that, without the need to specify any user parameters, the proposed algorithm is stable and more effective at maximizing the signal-to-interference ratio than the conventional norm-constrained diagonal-loading approach. The stability and clutter suppression capability of the proposed algorithm are examined using data from the Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent Scatter Radar.
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Hashimoto, Taishi, Akinori Saito, Koji Nishimura, Masaki Tsutsumi, Kaoru Sato, and Toru Sato. "First Incoherent Scatter Measurements and Adaptive Suppression of Field-Aligned Irregularities by the PANSY Radar at Syowa Station, Antarctic." Journal of Atmospheric and Oceanic Technology 36, no. 9 (September 2019): 1881–88. http://dx.doi.org/10.1175/jtech-d-18-0175.1.
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The Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent Scatter (PANSY) radar is a large atmospheric radar located at the Antarctic Syowa Station (69.01°S, 39.59°E). The PANSY radar performed the first incoherent scatter (IS) measurements in the Antarctic region in 2015. Several specific observations were undertaken in 2017 including a 24-h observation of the ionosphere using a peripheral antenna array to suppress interference from the field-aligned irregularities (FAIs). This paper presents the preliminary results derived from the IS measurements using the PANSY radar and the adaptive signal processing techniques to suppress FAIs. The norm-constrained and directionally constrained minimization of power (NC-DCMP) algorithm was applied to the 24-h ionosphere observations by the PANSY radar with a weighting applied to the directional constraint based on the gain differences of the subarrays. When compared with the conventional nonadaptive approach, the number of usable power profiles was increased by about 24% by the gain-weighted NC-DCMP algorithm, suggesting its effectiveness for FAI clutter suppression in ionosphere observations. Furthermore, detection of FAIs using the dedicated antenna array was found valuable in assessing the reliability of estimations of electron density based on VHF-band IS radar data.
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Kottayil, Ajil, Stefan A. Buehler, Viju O. John, Larry M. Miloshevich, M. Milz, and G. Holl. "On the Importance of Vaisala RS92 Radiosonde Humidity Corrections for a Better Agreement between Measured and Modeled Satellite Radiances." Journal of Atmospheric and Oceanic Technology 29, no. 2 (February 1, 2012): 248–59. http://dx.doi.org/10.1175/jtech-d-11-00080.1.
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Abstract A study has been carried out to assess the importance of radiosonde corrections in improving the agreement between satellite and radiosonde measurements of upper-tropospheric humidity. Infrared [High Resolution Infrared Radiation Sounder (HIRS)-12] and microwave [Advanced Microwave Sounding Unit (AMSU)-18] measurements from the NOAA-17 satellite were used for this purpose. The agreement was assessed by comparing the satellite measurements against simulated measurements using collocated radiosonde profiles of the Atmospheric Radiation Measurement (ARM) Program undertaken at tropical and midlatitude sites. The Atmospheric Radiative Transfer Simulator (ARTS) was used to simulate the satellite radiances. The comparisons have been done under clear-sky conditions, separately for daytime and nighttime soundings. Only Vaisala RS92 radiosonde sensors were used and an empirical correction (EC) was applied to the radiosonde measurements. The EC includes correction for mean calibration bias and for solar radiation error, and it removes radiosonde bias relative to three instruments of known accuracy. For the nighttime dataset, the EC significantly reduces the bias from 0.63 to −0.10 K in AMSU-18 and from 1.26 to 0.35 K in HIRS-12. The EC has an even greater impact on the daytime dataset with a bias reduction from 2.38 to 0.28 K in AMSU-18 and from 2.51 to 0.59 K in HIRS-12. The present study promises a more accurate approach in future radiosonde-based studies in the upper troposphere.
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Piecuch, Christopher G., and Tatiana A. Rynearson. "Quantifying Dispersal and Connectivity of Surface Waters Using Observational Lagrangian Measurements." Journal of Atmospheric and Oceanic Technology 29, no. 8 (August 1, 2012): 1127–38. http://dx.doi.org/10.1175/jtech-d-11-00172.1.
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Abstract Probability distribution functions of displacement are central to Lagrangian statistics and the study of fluid dispersal. A method for computing marginal probability distributions of passive tracer dispersal from Lagrangian observations is developed. Using a pseudotrack approach, probability distributions for the domain of occupation and transit time are developed, complimenting more frequently used bulk statistics for average transit time and overall crossing probability. To demonstrate application of this technique to observations, likelihoods and time scales of dispersal from the Gulf Stream to the Azores are quantified using World Ocean Circulation Experiment (WOCE) Surface Velocity Program (SVP) near-surface drifter data for the years 1992–2008. Over observable time scales, the transit of a particle in the near-surface ocean from the Gulf Stream to the Azores occurs across a spectrum of time scales, from tens to hundreds of days, with an overall likelihood of 42% ± 4% and a mean time scale of 321 ± 41 days. The exclusion of measurements from drifters released after 1 January 2004 (which have been shown to potentially exhibit bias) slightly increases the overall likelihood of connection (49% ± 6%), consistent with recent surface current shifts in the northern North Atlantic, and increases the mean connection time scale (371 ± 52 days), potentially reflecting spurious acceleration of drifters in recent years. The method presented is general and applicable to a wide range of applications in physical and ecological oceanography.
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Senocak, Inanc, Micah Sandusky, Rey DeLeon, Derek Wade, Kyle Felzien, and Marianna Budnikova. "An Immersed Boundary Geometric Preprocessor for Arbitrarily Complex Terrain and Geometry." Journal of Atmospheric and Oceanic Technology 32, no. 11 (November 2015): 2075–87. http://dx.doi.org/10.1175/jtech-d-14-00023.1.
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AbstractThere is a growing interest to apply the immersed boundary method to compute wind fields over arbitrarily complex terrain. The computer implementation of an immersed boundary module into an existing flow solver can be accomplished with minor modifications to the rest of the computer program. However, a versatile preprocessor is needed at the first place to extract the essential geometric information pertinent to the immersion of an arbitrarily complex terrain inside a 3D Cartesian mesh. Errors in the geometric information can negatively impact the correct implementation of the immersed boundary method as part of the solution algorithm. Additionally, the distance field from the terrain is needed to implement various subgrid-scale turbulence models and to initialize wind fields over complex terrain. Despite the popularity of the immersed boundary method, procedures used in the geometric preprocessing stage have received less attention. The present study found that concave and convex regions of complex terrain are particularly challenging to process with existing procedures discussed in the literature. To address this issue, a geometric preprocessor with a distance field solver was presented, and the solver demonstrated its versatility for arbitrarily complex geometry, terrain, and urban environments. The distance field solver uses the initial distance field at the immersed boundaries and propagates it to the rest of the domain by solving the Eikonal equation with the fast sweeping method.
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Kluver, Daria, Tom Mote, Daniel Leathers, Gina R. Henderson, Weihan Chan, and David A. Robinson. "Creation and Validation of a Comprehensive 1° by 1° Daily Gridded North American Dataset for 1900–2009: Snowfall." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 857–71. http://dx.doi.org/10.1175/jtech-d-15-0027.1.
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AbstractThis study details the creation of a gridded snowfall dataset for North America, with focus on the quality of the interpolated product. Daily snowfall amounts from National Weather Service Cooperative Observer Program stations and Meteorological Service of Canada surface stations are interpolated to 1° by 1° grids from 1900 to 2009 and examined for data record length and quality. The interpolation is validated spatially and temporally through the use of stratified sampling and k-fold cross-validation analyses. Interpolation errors average around 0.5 cm and range from less than 0.01 to greater than 2.5 cm. For most locations, this is within the measurement sensitivity. Grid cells with large variations in elevation experience higher errors and should be used with caution. A new gridded snowfall climatology is presented based on in situ observations that capture seasonal and interannual variability in monthly snowfall over most of the North American land area from 1949 to 2009. The Community Collaborative Rain, Hail and Snow Network is used as an independent set of point data that is compared to the gridded product. Errors are mainly in the form of the gridded data underestimating snowfall compared to the point data. The spatial extent, temporal length, and resolution of the dataset are unprecedented with regard to observational snowfall products and will present new opportunities for examining snowfall across North America.
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Sadikni, Remon, Nils H. Schade, Axel Andersson, Annika Jahnke-Bornemann, Iris Hinrichs, Lydia Gates, Birger Tinz, and Detlef Stammer. "The KLIWAS North Sea Climatology. Part I: Processing of the Atmospheric Data." Journal of Atmospheric and Oceanic Technology 35, no. 1 (January 2018): 111–26. http://dx.doi.org/10.1175/jtech-d-17-0044.1.
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AbstractClimatological reference data serve as validation of regional climate models, as the boundary condition for the model runs, and as input for assimilation systems used by reanalyses. Within the framework of the interdisciplinary research program Climate Water Navigation (KLIWAS): Impacts of Climate Change on Waterways and Navigation of the German Federal Ministry of Transport and Digital Infrastructure, a new climatology of the North Sea and adjacent regions was developed in an joint effort by the Federal Maritime and Hydrographic Agency, the German Weather Service [Deutscher Wetterdienst (DWD)], and the Integrated Climate Data Center (ICDC) of the University of Hamburg. Long-term records of monthly and annual mean 2-m air temperature, dewpoint temperature, and sea level pressure data from 1950 to 2010 were calculated on a horizontal 1° × 1° grid. All products were based on quality-controlled data from DWD’s Marine Data Centre. Correction methods were implemented for each parameter to reduce the sampling error resulting from the sparse coverage of observations in certain regions. Comparisons between sampling error estimates based on ERA-40 and the climatology products show that the sampling error was reduced effectively. The climatologies are available for download on the ICDC’s website and will be updated regularly regarding new observations and additional parameters. An extension to the Baltic Sea is in progress.
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Cook, Werner E., and J. Scott Greene. "Gridded Monthly Rainfall Estimates Derived from Historical Atoll Observations." Journal of Atmospheric and Oceanic Technology 36, no. 4 (April 2019): 671–87. http://dx.doi.org/10.1175/jtech-d-18-0140.1.
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AbstractTo provide an analysis tool for areal rainfall estimates, 1° gridded monthly sea level rainfall estimates have been derived from historical atoll rainfall observations contained in the Pacific Rainfall (PACRAIN) database. The PACRAIN database is a searchable repository of in situ rainfall observations initiated and maintained by the University of Oklahoma and supported by a research grant from the National Oceanic and Atmospheric Administration (NOAA)/Climate Program Office/Ocean Observing and Monitoring. The gridding algorithm employs ordinary kriging, a standard geostatistical technique, and selects for nonnegative estimates and for local estimation neighborhoods yielding minimum kriging variance. This methodology facilitates the selection of fixed-size neighborhoods from available stations beyond simply choosing the closest stations, as it accounts for dependence between estimator stations. The number of stations used for estimation is based on bias and standard error exhibited under cross estimation. A cross validation is conducted, comparing estimated and observed rains, as well as theoretical and observed standard errors for the ordinary kriging estimator. The conditional bias of the kriging estimator and the predictive value of kriging standard errors, with respect to observed standard errors, are discussed. Plots of the gridded rainfall estimates are given for sample El Niño and La Niña cases and standardized differences between the estimates produced here and the merged monthly rainfall estimates published by the Global Precipitation Climatology Project (GPCP) are shown and discussed.
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Zhao, Mengnan, Rui M. Ponte, Ou Wang, and Rick Lumpkin. "Using Drifter Velocity Measurements to Assess and Constrain Coarse-Resolution Ocean Models." Journal of Atmospheric and Oceanic Technology 38, no. 4 (April 2021): 909–19. http://dx.doi.org/10.1175/jtech-d-20-0159.1.
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AbstractProperly fitting ocean models to observations is crucial for improving model performance and understanding ocean dynamics. Near-surface velocity measurements from the Global Drifter Program (GDP) contain valuable information about upper-ocean circulation and air–sea fluxes on various space and time scales. This study explores whether GDP measurements can be used for usefully constraining the surface circulation from coarse-resolution ocean models, using global solutions produced by the consortium for Estimating the Circulation and Climate of the Ocean (ECCO) as an example. To address this problem, a careful examination of velocity data errors is required. Comparisons between an ECCO model simulation, performed without any data constraints, and GDP and Ocean Surface Current Analyses Real-Time (OSCAR) velocity data, over the period 1992–2017, reveal considerable differences in magnitude and pattern. These comparisons are used to estimate GDP data errors in the context of the time-mean and time-variable surface circulations. Both instrumental errors and errors associated with limitations in model physics and resolution (representation errors) are considered. Given the estimated model–data differences, errors, and signal-to-noise ratios, our results indicate that constraining ocean-state estimates to GDP can have a substantial impact on the ECCO large-scale time-mean surface circulation over extensive areas. Impact of GDP data constraints on the ECCO time-variable circulation would be weaker and mainly limited to low latitudes. Representation errors contribute substantially to degrading the data impacts.
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Bouali, Marouan, and Alexander Ignatov. "Adaptive Reduction of Striping for Improved Sea Surface Temperature Imagery from Suomi National Polar-Orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS)." Journal of Atmospheric and Oceanic Technology 31, no. 1 (January 1, 2014): 150–63. http://dx.doi.org/10.1175/jtech-d-13-00035.1.
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Abstract The Suomi National Polar-Orbiting Partnership (S-NPP) satellite was successfully launched on 28 October 2011. It carries five new-generation instruments, including the Visible Infrared Imaging Radiometer Suite (VIIRS). The VIIRS is a whiskbroom radiometer that scans the surface of the earth using a rotating telescope assembly, a double-sided half-angle mirror, and 16 individual detectors. Substantial efforts are being made to accurately calibrate all detectors in orbit. As of this writing, VIIRS striping is reduced to levels below those seen in corresponding Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) bands and meets the program specifications and requirements. However, the level 2 SST products derived from level 1 sensor data records (SDRs) thermal emissive bands still show residual striping. These artifacts reduce the accuracy of SST measurements and adversely affect cloud masking and the output of downstream applications, such as thermal front detection. To improve the quality of SST imagery derived from the VIIRS sensor, an adaptive algorithm was developed for operational use within the National Environmental Satellite, Data, and Information Service (NESDIS)’s SST system. The methodology uses a unidirectional quadratic variational model to extract stripe noise from the observed image prior to nonlocal filtering. Evaluation of the algorithm performance over an extended dataset demonstrates a significant improvement in the Advanced Clear-Sky Processor for Oceans (ACSPO) VIIRS SST image quality, with normalized improvement factors (NIF) varying between 5% and 25%.
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Turner, D. D., R. A. Ferrare, V. Wulfmeyer, and A. J. Scarino. "Aircraft Evaluation of Ground-Based Raman Lidar Water Vapor Turbulence Profiles in Convective Mixed Layers." Journal of Atmospheric and Oceanic Technology 31, no. 5 (May 2014): 1078–88. http://dx.doi.org/10.1175/jtech-d-13-00075.1.
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AbstractHigh temporal and vertical resolution water vapor measurements by Raman and differential absorption lidar systems have been used to characterize the turbulent fluctuations in the water vapor mixing ratio field in convective mixed layers. Since daytime Raman lidar measurements are inherently noisy (due to solar background and weak signal strengths), the analysis approach needs to quantify and remove the contribution of the instrument noise in order to derive the desired atmospheric water vapor mixing ratio variance and skewness profiles. This is done using the approach outlined by Lenschow et al.; however, an intercomparison with in situ observations was not performed.Water vapor measurements were made by a diode laser hygrometer flown on a Twin Otter aircraft during the Routine Atmospheric Radiation Measurement (ARM) Program Aerial Facility Clouds with Low Optical Water Depths Optical Radiative Observations (RACORO) field campaign over the ARM Southern Great Plains (SGP) site in 2009. Two days with Twin Otter flights were identified where the convective mixed layer was quasi stationary, and hence the 10-s, 75-m data from the SGP Raman lidar could be analyzed to provide profiles of water vapor mixing ratio variance and skewness. Airborne water vapor observations measured during level flight legs were compared to the Raman lidar data, demonstrating good agreement in both variance and skewness. The results also illustrate the challenges of comparing a point sensor making measurements over time to a moving platform making similar measurements horizontally.
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Lund, Björn, Hans C. Graber, Katrin Hessner, and Neil J. Williams. "On Shipboard Marine X-Band Radar Near-Surface Current ‘‘Calibration’’." Journal of Atmospheric and Oceanic Technology 32, no. 10 (October 2015): 1928–44. http://dx.doi.org/10.1175/jtech-d-14-00175.1.
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AbstractThe ocean wave signatures within conventional noncoherent marine X-band radar (MR) image sequences can be used to derive near-surface current information. On ships, an accurate near-real-time record of the near-surface current could improve navigational safety. It could also advance understanding of air–sea interaction processes. The standard shipboard MR near-surface current estimates were found to have large errors (of the same order of magnitude as the signal) that are associated with ship speed and heading. For acoustic Doppler current profilers (ADCPs), ship heading errors are known to induce a spurious cross-track current that is proportional to the ship speed and the sine of the error angle. Conventional mechanical gyrocompasses are very reliable heading sensors, but they are too inaccurate for shipboard ADCPs. Within the ADCP community, it is common practice to correct the gyrocompass measurements with the help of multiantenna carrier-phase differential GPS systems. This study shows how a similar multiantenna GPS-based ship heading correction technique stands to improve the accuracy of MR near-surface current estimates. Changes to the standard MR near-surface current retrieval method that are necessary for high-quality results from ships are also introduced. MR and ADCP data collected from R/V Roger Revelle during the Impact of Typhoons on the Ocean in the Pacific (ITOP) program in 2010 are used to demonstrate the MR currents’ accuracy and reliability.
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Scovell, Robert, and Hassan al-Sakka. "A Point Cloud Method for Retrieval of High-Resolution 3D Gridded Reflectivity from Weather Radar Networks for Air Traffic Management." Journal of Atmospheric and Oceanic Technology 33, no. 3 (March 2016): 461–79. http://dx.doi.org/10.1175/jtech-d-15-0051.1.
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AbstractA prototype high-resolution (1 km, 5 min) multiradar 3D gridded reflectivity product, including a suite of derived 2D vertical column products, has been developed for the Single European Skies Air Traffic Management Research program. As part of this, a new method for mapping radar data to grid points is being used, based on the concept of a binary space partitioning (BSP) tree that treats radar data as a set of points in a 3D point cloud. This allows the resulting analysis to be based on a complete picture of the nearby data from overlapping radars and can easily adapt to irregular grid configurations. This method is used with a Barnes successive corrections technique to retrieve finescale features while avoiding problems of undersmoothing in data-sparse regions. This has been tested using 3D domains enclosing the terminal maneuvering areas surrounding Paris, France, and London, United Kingdom, and using reflectivity plan position indicator scan data from the French and U.K. operational networks, encoded using the standard European Operational Programme for the Exchange of Weather Radar Information (OPERA) Data Information Model format. Quantitative intercomparisons between the new method, in various configurations; a high-resolution version of an existing method, in operational use at Météo-France; and a method that was developed by the National Oceanic and Atmospheric Administration for use with the Weather Surveillance Radar-1998 Doppler radar network, have been done using simulated radar scans derived from 3D synthetic radar reflectivity fields in stratiform and convective regimes.
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Crosby, Sean C., Bruce D. Cornuelle, William C. O’Reilly, and Robert T. Guza. "Assimilating Global Wave Model Predictions and Deep-Water Wave Observations in Nearshore Swell Predictions." Journal of Atmospheric and Oceanic Technology 34, no. 8 (August 2017): 1823–36. http://dx.doi.org/10.1175/jtech-d-17-0003.1.
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AbstractNearshore wave predictions with high resolution in space and time are needed for boating safety, to assess flood risk, and to support nearshore processes research. This study presents methods for improving regional nearshore predictions of swell-band wave energy (0.04–0.09 Hz) by assimilating local buoy observations into a linear wave propagation model with a priori guidance from global WAVEWATCH III (WW3) model predictions. Linear wave propagation, including depth-induced refraction and shoaling, and travel time lags, is modeled with self-adjoint backward ray tracing techniques. The Bayesian assimilation yields smooth, high-resolution offshore wave directional spectra that are consistent with WW3, and with offshore and local buoy observations. Case studies in the Southern California Bight (SCB) confirm that the nearshore predictions at independent (nonassimilated) buoy sites are improved by assimilation compared with predictions driven with WW3 or with a single offshore buoy. These assimilation techniques, valid in regions and frequency bands where wave energy propagation is mostly linear, use significantly less computational resources than nonlinear models and variational methods, and could be a useful component of a larger regional assimilation program. Where buoy locations have historically been selected to meet local needs, these methods can aid in the design of regional buoy arrays by quantifying the regional skill improvement for a given buoy observation and identifying both high-value and redundant observations. Assimilation techniques also identify likely forward model error in the Santa Barbara Channel, where permanent observations or model corrections are needed.
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Dushaw, Brian D. "Ocean Acoustic Tomography in the North Atlantic." Journal of Atmospheric and Oceanic Technology 36, no. 2 (January 30, 2019): 183–202. http://dx.doi.org/10.1175/jtech-d-18-0082.1.
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Abstract An objective mapping exercise simulating observations of temperature in the North Atlantic Ocean was used to assess the resolution capabilities of ocean acoustic tomography in combination with Argo floats. A set of basis functions for a basinwide area was obtained from a singular value decomposition of a covariance derived from an ocean state estimate. As demonstrated by the formal uncertainty estimates from the objective maps, Argo and tomography are complementary measurements. In several examples, each separately obtained uncertainty for determining large-scale monthly average temperature of about 50% of prior (resolved 75% of variance), while when both data were employed, uncertainties were reduced to about 25% of prior (resolved 94% of variance). Possible tomography configurations range from arrays that span specific regions to line arrays that supplement existing observations to arrays that span the Atlantic basin. A basinwide array consisting of two acoustic sources and seven receivers can be used to significantly reduce the uncertainties of estimated broad-scale temperature. An optimal observing system study would comprise simulated measurements in combination with data assimilation techniques and numerical ocean modeling. This objective map study, however, showed that the addition of tomography to the existing observing system could substantially reduce the uncertainties for estimated large-scale temperature. To the extent that tomography offers a 50% reduction in uncertainty at a fraction of the cost of the Argo program, it is a cost-effective contribution to the ocean observing system.
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Williams, Skylar S., Timothy J. Wagner, and Ralph A. Petersen. "Examining the Compatibility of Aircraft Moisture Observations and Operational Radiosondes." Journal of Atmospheric and Oceanic Technology 38, no. 4 (April 2021): 859–72. http://dx.doi.org/10.1175/jtech-d-20-0053.1.
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AbstractThe addition of moisture observations via the Water Vapor Sensing System (WVSS) from about 150 aircraft available operationally through the World Meteorological Organization (WMO) Aircraft Meteorological Data Relay (AMDAR) program now provides highly reliable thermodynamic profiles of the troposphere. The nearly 900 profiles available daily provide greater temporal and spatial density than the operational radiosonde network over many parts of the United States. Previous studies comparing WVSS reports with specially collocated radiosondes have documented the quality and consistency of the WVSS observations. These studies, however, have been limited for short periods at a single location. This study expands on the earlier evaluations by using operational U.S. radiosondes from 2015 in a variety of locations, seasons, and climates. Comparison profiles at radiosonde sites were calculated in pressure layers and then interpolated to terrain-following sigma coordinates to account for the differences in elevations of comparison sites and provide a better means of integrating the higher vertical resolution of AMDAR observations taken in the boundary layer. Overall, systematic differences between the WVSS and radiosondes are smallest just above the surface, with the WVSS observations being slightly moister than the radiosondes aloft, with WVSS reports being moister during ascent than descent—possibly the result of small hysteresis effects. Standard deviations averaged 1.3 g kg−1 near the surface over the yearlong period. Differences varied by season and region. Overall, the results indicate that WVSS observations are compatible with radiosonde reports and can be used with high confidence to fill temporal and spatial data gaps.
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Thadathil, Pankajakshan, C. C. Bajish, Swadhin Behera, and V. V. Gopalakrishna. "Drift in Salinity Data from Argo Profiling Floats in the Sea of Japan*." Journal of Atmospheric and Oceanic Technology 29, no. 1 (January 1, 2012): 129–38. http://dx.doi.org/10.1175/jtech-d-11-00018.1.
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Abstract In drift analysis of salinity sensors, one major problem is the difficulty in delineating sensor drift from water mass changes. In the present study, a new method is proposed for finding sensor drift that is free from water mass changes. The efficiency of this new method in finding out possible drift in the Argo salinity is demonstrated in the Sea of Japan (SOJ) by using the “near-linear” subsurface salinity structure of the SOJ. The new method is based on the time–space decorrelation scale. The salinity difference between two neighboring observations within the time–space decorrelation scale (SALD) is used to find out possible drift. Neighboring observations within the time–space decorrelation scale are referred to as matchups. The SALD derived from matchups between Argo floats and shipboard CTD observations from the SOJ shows linear drift. Although all four selected floats (5 yr completed) from the SOJ show linear drift (<0.001 PSS yr−1), the drift alone is not so significant to affect the objective of the Argo program in understanding climate variability. In the SOJ, SALD identified salinity error other than drift in good quality data that are flagged by the Argo delayed-mode quality control (ADMQC) method. Therefore, SALD could be used as an effective additional tool in the Argo data quality control. To examine the applicability of SALD in open ocean regions, in addition to confined basins such as SOJ, SALD was applied successfully to detect salinity error in Argo data from the subtropical North Pacific (SNP).
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Wang, Yunheng, Youngsun Jung, Timothy A. Supinie, and Ming Xue. "A Hybrid MPI–OpenMP Parallel Algorithm and Performance Analysis for an Ensemble Square Root Filter Designed for Multiscale Observations." Journal of Atmospheric and Oceanic Technology 30, no. 7 (July 1, 2013): 1382–97. http://dx.doi.org/10.1175/jtech-d-12-00165.1.
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Abstract A hybrid parallel scheme for the ensemble square root filter (EnSRF) suitable for parallel assimilation of multiscale observations, including those from dense observational networks such as those of radar, is developed based on the domain decomposition strategy. The scheme handles internode communication through a message passing interface (MPI) and the communication within shared-memory nodes via Open Multiprocessing (OpenMP) threads. It also supports pure MPI and pure OpenMP modes. The parallel framework can accommodate high-volume remote-sensed radar (or satellite) observations as well as conventional observations that usually have larger covariance localization radii. The performance of the parallel algorithm has been tested with simulated and real radar data. The parallel program shows good scalability in pure MPI and hybrid MPI–OpenMP modes, while pure OpenMP runs exhibit limited scalability on a symmetric shared-memory system. It is found that in MPI mode, better parallel performance is achieved with domain decomposition configurations in which the leading dimension of the state variable arrays is larger, because this configuration allows for more efficient memory access. Given a fixed amount of computing resources, the hybrid parallel mode is preferred to pure MPI mode on supercomputers with nodes containing shared-memory cores. The overall performance is also affected by factors such as the cache size, memory bandwidth, and the networking topology. Tests with a real data case with a large number of radars confirm that the parallel data assimilation can be done on a multicore supercomputer with a significant speedup compared to the serial data assimilation algorithm.
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Reverdin, G., S. Morisset, H. Bellenger, J. Boutin, N. Martin, P. Blouch, J. Rolland, F. Gaillard, P. Bouruet-Aubertot, and B. Ward. "Near–Sea Surface Temperature Stratification from SVP Drifters." Journal of Atmospheric and Oceanic Technology 30, no. 8 (August 1, 2013): 1867–83. http://dx.doi.org/10.1175/jtech-d-12-00182.1.
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Abstract This study describes how the hull temperature (Ttop) measurements from multisensor surface velocity program (SVP) drifters can be combined with other measurements to provide quantitative information on near-surface vertical temperature stratification during large daily cycles. First, Ttop is compared to the temperature measured at 17 -cm depth from a float tethered to the SVP drifter. These 2007–12 SVP drifters present a larger daily cycle by 1%–3% for 1°–2°C daily cycle amplitudes, with a maximum difference close to the local noon. The difference could result from flow around the SVP drifter in the presence of temperature stratification in the top 20 cm of the water column but also from a small influence of internal drifter temperature on Ttop. The largest differences were found for small drifters (Technocean) for very large daily cycles, as expected from their shallower measurements. The vertical stratification is estimated by comparing these hull data with the deeper T or conductivity C measurements from Sea-Bird sensors 25 (Pacific Gyre) to 45 cm (MetOcean) below the top temperature sensor. The largest stratification is usually found near local noon and early afternoon. For a daily cycle amplitude of 1°C, these differences with the upper level are in the range of 3%–5% of the daily cycle for the Pacific Gyre drifters and 6%–10% for MetOcean drifters with the largest values occurring when the midday sun elevation is lowest. The relative differences increase for larger daily cycles, and the vertical profiles become less linear. These estimated stratifications are well above the uncertainty on Ttop.
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Wagner, Timothy J., David D. Turner, Larry K. Berg, and Steven K. Krueger. "Ground-Based Remote Retrievals of Cumulus Entrainment Rates." Journal of Atmospheric and Oceanic Technology 30, no. 7 (July 1, 2013): 1460–71. http://dx.doi.org/10.1175/jtech-d-12-00187.1.
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Abstract While fractional entrainment rates for cumulus clouds have typically been derived from airborne observations, this limits the size and scope of available datasets. To increase the number of continental cumulus entrainment rate observations available for study, an algorithm for retrieving them from ground-based remote sensing observations has been developed. This algorithm, called the Entrainment Rate In Cumulus Algorithm (ERICA), uses the suite of instruments at the Southern Great Plains (SGP) site of the U.S. Department of Energy's Atmospheric Radiation Measurement Program (ARM) Climate Research Facility as inputs into a Gauss–Newton optimal estimation scheme, in which an assumed guess of the entrainment rate is iteratively adjusted through intercomparison of modeled cloud attributes to their observed counterparts. The forward model in this algorithm is the explicit mixing parcel model (EMPM), a cloud parcel model that treats entrainment as a series of discrete entrainment events. A quantified value for the uncertainty in the retrieved entrainment rate is also returned as part of the retrieval. Sensitivity testing and information content analysis demonstrate the robust nature of this method for retrieving accurate observations of the entrainment rate without the drawbacks of airborne sampling. Results from a test of ERICA on 3 months of shallow cumulus cloud events show significant variability of the entrainment rate of clouds in a single day and from one day to the next. The mean value of 1.06 km−1 for the entrainment rate in this dataset corresponds well with prior observations and simulations of the entrainment rate in cumulus clouds.
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Kollias, Pavlos, Nitin Bharadwaj, Kevin Widener, Ieng Jo, and Karen Johnson. "Scanning ARM Cloud Radars. Part I: Operational Sampling Strategies." Journal of Atmospheric and Oceanic Technology 31, no. 3 (March 1, 2014): 569–82. http://dx.doi.org/10.1175/jtech-d-13-00044.1.
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Abstract The acquisition of scanning cloud radars by the Atmospheric Radiation Measurement (ARM) program and research institutions around the world generates the need for developing operational scan strategies for cloud radars. Here, the first generation of sampling strategies for the scanning ARM cloud radars (SACRs) is presented. These scan strategies are designed to address the scientific objectives of ARM; however, they introduce an initial framework for operational scanning cloud radars. While the weather community uses scan strategies that are based on a sequence of scans at constant elevations, the SACR scan strategies are based on a sequence of scans at constant azimuth. This is attributed to the cloud geometrical properties, which are vastly different from the rain and snow shafts that are the primary targets of precipitation radars; the need to cover the cone of silence; and the scanning limitations of the SACRs. A “cloud surveillance” scan strategy is introduced that is based on a sequence of horizon-to-horizon range–height indicator (RHI) scans that sample the hemispherical sky (HS) every 30° azimuth (HSRHI). The HSRHI scan strategy is complimented with a low-elevation plan position indicator (PPI) scan. The HSRHI and PPI are repeated every 30 min to provide a static view of the cloud conditions around the SACR location. Between the HSRHI and PPI scan strategies, other scan strategies are introduced depending on the cloud conditions. In the future, information about the atmospheric cloud state will be used in a closed-loop process to optimize the selection of the SACR scan strategy.
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Kollias, Pavlos, Ieng Jo, Paloma Borque, Aleksandra Tatarevic, Katia Lamer, Nitin Bharadwaj, Kevin Widener, Karen Johnson, and Eugene E. Clothiaux. "Scanning ARM Cloud Radars. Part II: Data Quality Control and Processing." Journal of Atmospheric and Oceanic Technology 31, no. 3 (March 1, 2014): 583–98. http://dx.doi.org/10.1175/jtech-d-13-00045.1.
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Abstract The scanning Atmospheric Radiation Measurement (ARM) Program cloud radars (SACRs) are the primary instruments for documenting the four-dimensional structure and evolution of clouds within a 20–30-km radius of the ARM fixed and mobile sites. Here, the postprocessing of the calibrated SACR measurements is discussed. First, a feature mask algorithm that objectively determines the presence of significant radar returns is described. The feature mask algorithm is based on the statistical properties of radar receiver noise. It accounts for atmospheric emission and is applicable even for SACR profiles with few or no signal-free range gates. Using the nearest-in-time atmospheric sounding, the SACR radar reflectivities are corrected for gaseous attenuation (water vapor and oxygen) using a line-by-line absorption model. Despite having a high pulse repetition frequency, the SACR has a narrow Nyquist velocity limit and thus Doppler velocity folding is commonly observed. An unfolding algorithm that makes use of a first guess for the true Doppler velocity using horizontal wind measurements from the nearest sounding is described. The retrieval of the horizontal wind profile from the hemispherical sky range–height indicator SACR scan observations and/or nearest sounding is described. The retrieved horizontal wind profile can be used to adaptively configure SACR scan strategies that depend on wind direction. Several remaining challenges are discussed, including the removal of insect and second-trip echoes. The described algorithms significantly enhance SACR data quality and constitute an important step toward the utilization of SACR measurements for cloud research.
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André, Xavier, Bertrand Moreau, and Serge Le Reste. "Argos-3 Satellite Communication System: Implementation on the Arvor Oceanographic Profiling Floats." Journal of Atmospheric and Oceanic Technology 32, no. 10 (October 2015): 1902–14. http://dx.doi.org/10.1175/jtech-d-14-00219.1.
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AbstractThe scientific community observes the ocean for applications in the fields of oceanography and climate research. To recover in situ data, more than 3000 profiling floats are operated in the framework of the Argo program. Each float performs cycles between the sea surface and a depth of 2000 m. Scientific data are gathered while the float is traveling upward from the depths of the oceans and are then transmitted via a satellite communication system at the end of each cycle. During its time at the surface, mainly dedicated to transmissions, the float is vulnerable and subject to drift, which limits its use in many studies. Moreover, transmission times are becoming longer due to a trend toward high-resolution or multisensor profiles. Consequently, the transmission system embedded in the profiling floats had to evolve.Argos-3 is the latest generation of the Argos satellite communication system. It has been designed to allow instruments to transmit more data in a small time budget and as an alternative to Iridium, already implemented on profiling floats in restrictive applications.This study aims to evaluate the implementation of Argos-3 on Arvor profiling floats. Tests were carried out first in the laboratory, before being implemented on the Arvor float and deployed at sea. This study proves that the high-data-rate mode suffered from European electromagnetic noise, which is incompatible with this application. The interactive low-data-rate mode was successfully qualified; it is capable of transmitting an entire dataset in a few minutes, compared to 8–10 h for the previous Argos-2 system.
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Organelli, Emanuele, Hervé Claustre, Annick Bricaud, Catherine Schmechtig, Antoine Poteau, Xiaogang Xing, Louis Prieur, Fabrizio D’Ortenzio, Giorgio Dall’Olmo, and Vincenzo Vellucci. "A Novel Near-Real-Time Quality-Control Procedure for Radiometric Profiles Measured by Bio-Argo Floats: Protocols and Performances." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 937–51. http://dx.doi.org/10.1175/jtech-d-15-0193.1.
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AbstractAn array of Bio-Argo floats equipped with radiometric sensors has been recently deployed in various open ocean areas representative of the diversity of trophic and bio-optical conditions prevailing in the so-called case 1 waters. Around solar noon and almost every day, each float acquires 0–250-m vertical profiles of photosynthetically available radiation and downward irradiance at three wavelengths (380, 412, and 490 nm). Up until now, more than 6500 profiles for each radiometric channel have been acquired. As these radiometric data are collected out of an operator’s control and regardless of meteorological conditions, specific and automatic data processing protocols have to be developed. This paper presents a data quality-control procedure aimed at verifying profile shapes and providing near-real-time data distribution. This procedure is specifically developed to 1) identify main issues of measurements (i.e., dark signal, atmospheric clouds, spikes, and wave-focusing occurrences) and 2) validate the final data with a hierarchy of tests to ensure a scientific utilization. The procedure, adapted to each of the four radiometric channels, is designed to flag each profile in a way compliant with the data management procedure used by the Argo program. Main perturbations in the light field are identified by the new protocols with good performances over the whole dataset. This highlights its potential applicability at the global scale. Finally, the comparison with modeled surface irradiances allows for assessing the accuracy of quality-controlled measured irradiance values and identifying any possible evolution over the float lifetime due to biofouling and instrumental drift.
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Le Reste, Serge, Vincent Dutreuil, Xavier André, Virginie Thierry, Corentin Renaut, Pierre-Yves Le Traon, and Guillaume Maze. "“Deep-Arvor”: A New Profiling Float to Extend the Argo Observations Down to 4000-m Depth." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 1039–55. http://dx.doi.org/10.1175/jtech-d-15-0214.1.
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AbstractThe international Argo program, consisting of a global array of more than 3000 free-drifting profiling floats, has now been monitoring the upper 2000 m of the ocean for several years. One of its main proposed evolutions is to be able to reach the deeper ocean in order to better observe and understand the key role of the deep ocean in the climate system. For this purpose, Ifremer has designed the new “Deep-Arvor” profiling float: it extends the current operational depth down to 4000 m, and measures temperature and salinity for up to 150 cycles with CTD pumping continuously and 200 cycles in spot sampling mode. High-resolution profiles (up to 2000 points) can be transmitted and data are delivered in near–real time according to Argo requirements. Deep-Arvor can be deployed everywhere at sea without any preballasting operation and its light weight (~26 kg) makes its launching easy. Its design was done to target a cost-effective solution. Predefined spots have been allocated to add an optional oxygen sensor and a connector for an extra sensor. Extensive laboratory tests were successful. The results of the first at-sea experiments showed that the expected performances of the operational prototypes had been reached (i.e., to perform up to 150 cycles). Meanwhile, the industrialization phase was completed in order to manufacture the Deep-Arvor float for the pilot experiment in 2015. This paper details all the steps of the development work and presents the results from the at-sea experiments.
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Fairall, C. W., Sergey Y. Matrosov, Christopher R. Williams, and E. J. Walsh. "Estimation of Rain Rate from Airborne Doppler W-Band Radar in CalWater-2." Journal of Atmospheric and Oceanic Technology 35, no. 3 (March 2018): 593–608. http://dx.doi.org/10.1175/jtech-d-17-0025.1.
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ABSTRACTThe NOAA W-band radar was deployed on a P-3 aircraft during a study of storm fronts off the U.S. West Coast in 2015 in the second CalWater (CalWater-2) field program. This paper presents an analysis of measured equivalent radar reflectivity factor Zem profiles to estimate the path-averaged precipitation rate and profiles of precipitation microphysics. Several approaches are explored using information derived from attenuation of Zem as a result of absorption and scattering by raindrops. The first approach uses the observed decrease of Zem with range below the aircraft to estimate column mean precipitation rates. A hybrid approach that combines Zem in light rain and attenuation in stronger rain performed best. The second approach estimates path-integrated attenuation (PIA) via the difference in measured and calculated normalized radar cross sections (NRCSm and NRCSc, respectively) retrieved from the ocean surface. The retrieved rain rates are compared to estimates from two other systems on the P-3: a Stepped Frequency Microwave Radiometer (SFMR) and a Wide-Swath Radar Altimeter (WSRA). The W-band radar gives reasonable values for rain rates in the range 0–10 mm h−1 with an uncertainty on the order of 1 mm h−1. Mean profiles of Zem, raindrop Doppler velocity, attenuation, and precipitation rate in bins of rain rate are also computed. A method for correcting measured profiles of Zem for attenuation to estimate profiles of nonattenuated profiles of Ze is examined. Good results are obtained by referencing the surface boundary condition to the NRCS values of PIA. Limitations of the methods are discussed.
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Wick, Gary A., Terrence F. Hock, Paul J. Neiman, Holger Vömel, Michael L. Black, and J. Ryan Spackman. "The NCAR–NOAA Global Hawk Dropsonde System." Journal of Atmospheric and Oceanic Technology 35, no. 8 (August 2018): 1585–604. http://dx.doi.org/10.1175/jtech-d-17-0225.1.
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AbstractA new remotely controlled Airborne Vertical Atmospheric Profiling System (AVAPS) dropsonde system has been developed for and deployed on the NASA Global Hawk (GH) unmanned aircraft. Design, fabrication, and operation of the system was led by the National Center for Atmospheric Research (NCAR) with support from the National Oceanic and Atmospheric Administration (NOAA) Unmanned Aircraft Systems (UAS) Program. The system has employed the NCAR Research Dropsonde 94 (NRD94) dropsonde, a smaller and lighter version of the standard RD94 dropsonde deployed from manned aircraft but with virtually identical sensors. The dropsondes provide in situ atmospheric profiles of temperature, pressure, and humidity at a 2-Hz data rate, and wind speed and direction at 4 Hz. The system is capable of carrying up to 90 dropsondes and can support eight simultaneous soundings. Operation from the GH means that the dropsondes can be deployed from altitudes up to 19.8 km during flights in excess of 24-h duration. The dropsonde launch is commanded directly by an operator on the ground in coordination with the aircraft commander. Over 2700 total dropsondes have been deployed from the GH during four major campaigns since 2011. Data are processed in near–real time and have been employed by forecasters, for assimilation in numerical weather prediction models, and in diverse research studies. Intercomparison studies suggest the performance of the GH NRD94 dropsondes is similar to those deployed from manned aircraft. This paper describes the components and operation of the system and illustrates its unique capabilities through highlights of data application to research on the Arctic atmosphere, atmospheric rivers, and tropical cyclones.
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Tornow, F., H. W. Barker, Velázquez Blázquez, C. Domenech, and J. Fischer. "EarthCARE’s Broadband Radiometer: Uncertainties Associated with Cloudy Atmospheres." Journal of Atmospheric and Oceanic Technology 35, no. 11 (November 2018): 2201–11. http://dx.doi.org/10.1175/jtech-d-18-0083.1.
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AbstractThe Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) satellite’s Broadband Radiometer (BBR) consists of three telescopes and a rotating chopper drum (CD). Together they yield alternating measurements of total wave (TW; 0.25 to >50 μm) and shortwave (SW; 0.25–4 μm) radiances with point spread functions that translate to 0.6-km-diameter pixels. The mission requires that SW and TW radiances be averaged over 100-km2 domains. Correspondingly, the average longwave (LW) radiances are the differences between TW and SW averages. It is shown that impacts on domain-average nadir radiances resulting from alternating samples of TW and SW signals for realistic cloudy atmospheres are sensitive to the variance of cloudy-sky radiances, CD rotation rate, and along-track length of averaging domains. Over domains measuring 5 × 21 km2 and at a 50% rotation rate, uncertainties reached up to 3.2 and 4.1 W m−2 sr−1 for SW and TW radiances, respectively. The BBR’s design allows for in-flight alteration of the CD rate. An approximate method is provided for estimating SW and LW uncertainties resulting from the CD rate. While the nominal rotation rate meets EarthCARE’s mission requirements, reducing below 75% of that rate will lead to uncertainties for domain-average LW radiances that will often exceed mission requirements. This could be mitigated by increasing the size of averaging domains but that would compromise the BBR’s role in EarthCARE’s radiative closure assessment program. Uncertainties for off-nadir radiances are largely free of impacts arising from changes to the CD rotation rate.