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On the Prediction of Stratospheric Balloon Trajectories: Improving Winds with Mesoscale Simulations

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第8期33卷 1629-1647页

作者： Jewtoukoff, Valerian Plougonven, Riwal Hertzog, Albert Snyder, Chris Romine, Glen Ecole Polytech CNRS Lab Meteorol Dynam Palaiseau France Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA Penn State Univ Dept Meteorol 406 Walker Bldg University Pk PA 16802 USA

Safety compliance issues for operational studies of the atmosphere with balloons require quantifying risks associated with descent and developing strategies to reduce the uncertainties at the location of the touchdown point. Trajectory forecasts are typically computed from weather forecasts produced by an operational center, for example, the European Centre for Medium-Range Weather Forecasts. This study uses past experiments to investigate strategies for improving these forecasts. Trajectories for open stratospheric balloon (OSB) short-term flights are computed using mesoscale simulations with the Weather and Research Forecasting (WRF) Model initialized with ECMWF operational forecasts and are assimilated with radio soundings using the Data Assimilation Research Testbed (DART) ensemble Kalman filter, for three case studies during the Strapolete 2009 campaign in Sweden. The results are very variable: in one case, the error in the final simulated position is reduced by 90% relative to the forecast using the ECMWF winds, while in another case the forecast is hardly improved. Nonetheless, they reveal the main source of forecasting error: during the ceiling phase, errors due to unresolved inertia gravity waves accumulate as the balloon continuously experiences one phase of a wave for a few hours, whereas they essentially average out during the ascent and descent phases, when the balloon rapidly samples through whole wave packets. This sensitivity to wind during the ceiling phase raises issues regarding the feasibility of such forecasts and the observations that would be needed. The ensemble spread is also analyzed, and it is noted that the initial ensemble perturbations should probably be improved in the future for better forecasts.

关键词： Circulation/ Dynamics Ensembles Forecasting Kalman filters Lagrangian circulation/transport Mathematical and statistical techniques Mesoscale forecasting observational techniques and algorithms Radiosonde observations

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The Occurrence, Drivers, and Implications of Submesoscale Eddies on the Martha's Vineyard Inner Shelf

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JOURNAL OF PHYSICAL OCEANOGRAPHY 2016年第9期46卷 2645-2662页

作者： Kirincich, Anthony Woods Hole Oceanog Inst Woods Hole MA 02543 USA

The occurrence, drivers, and implications of small-scaleO(2-5) kmdiameter coherent vortices, referred to as submesoscale eddies, over the inner shelf south ofMartha's Vineyard, Massachusetts, are examined using high-frequency (HF), radar-based, high-resolution (400m) observations of surface currents. Within the 300 km(2) study area, eddies occurred at rates of 1 and 4 day(-1) in winter and summer, respectively. Most were less than 5 h in duration, smaller than 4 km in diameter, and rotated less than once over their lifespan;60% of the eddies formed along the eastern edge of study area, adjacent toWasque Shoal, and moved westward into the interior, often with relative vorticity greater than f. Eddy generation was linked to vortex stretching on the ebb and flood tide as well as the interaction of the spatially variable tide and the wind-driven currents;however, these features had complex patterns of surface divergence and stretching. Eddies located away from Wasque Shoal were related to the movement of wind-driven surface currents, as wind direction controlled where eddies formed as well as density effects. Using an analysis of particles advected within the radar-based surface currents, the observed eddies were found to be generally leaky, losing 60%-80% of particles over their lifespan, but stillmore retentive than the background flow. As a result, the combined translation and rotational effects of the observed eddies were an important source of lateral exchange for surface waters over the inner shelf.

关键词： Geographic location/entity Continental shelf/slope Circulation/ Dynamics Currents Eddies observational techniques and algorithms Radars/Radar observations

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Remotely Sensed Land Skin Temperature as a Spatial Predictor of Air Temperature across the Conterminous United States

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JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY 2016年第7期55卷 1441-1457页

作者： Oyler, Jared W. Dobrowski, Solomon Z. Holden, Zachary A. Running, Steven W. Univ Montana Div Biol Sci Missoula MT 59812 USA Univ Montana Montana Forest & Conservat Expt Stn Montana Climate Off Missoula MT 59812 USA Univ Montana Coll Forestry & Conservat Missoula MT 59812 USA Univ Montana US Forest Serv Reg 1 Missoula MT 59812 USA Univ Montana Dept Geog Missoula MT 59812 USA Univ Montana Dept Ecosyst & Conservat Sci Numer Terradynam Simulat Grp Missoula MT 59812 USA Penn State Univ Earth & Environm Syst Inst 2217 EES Bldg University Pk PA 16802 USA

Remotely sensed land skin temperature (LST) is increasingly being used to improve gridded interpolations of near-surface air temperature. The appeal of LST as a spatial predictor of air temperature rests in the fact that it is an observation available at spatial resolutions fine enough to capture topoclimatic and biophysical variations. However, it remains unclear if LST improves air temperature interpolations over what can already be obtained with simpler terrain-based predictor variables. Here, the relationship between LST and air temperature is evaluated across the conterminous United States (CONUS). It is found that there are significant differences in the ability of daytime and nighttime observations of LST to improve air temperature interpolations. Daytime LST mainly indicates finescale biophysical variation and is generally a poorer predictor of maximum air temperature than simple linear models based on elevation, longitude, and latitude. Moderate improvements to maximum air temperature interpolations are thus limited to specific mountainous areas in winter, to coastal areas, and to semiarid and arid regions where daytime LST likely captures variations in evaporative cooling and aridity. In contrast, nighttime LST represents important topoclimatic variation throughout the mountainous western CONUS and significantly improves nighttime minimum air temperature interpolations. In regions of more homogenous terrain, nighttime LST also captures biophysical patterns related to land cover. Both daytime and nighttime LST display large spatial and seasonal variability in their ability to improve air temperature interpolations beyond simpler approaches.

关键词： observational techniques and algorithms Climate classification/regimes Remote sensing Surface observations Models and modeling Interpolation schemes Applications Mountain meteorology

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Radiometric Comparison of 1.6-μm CO₂ Absorption Band of Greenhouse Gases Observing Satellite (GOSAT) TANSO-FTS with Suomi-NPP VIIRS SWIR Band

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第7期33卷 1443-1453页

作者： Uprety, Sirish Cao, Changyong Colorado State Univ Cooperat Inst Res Atmosphere 1375 Campus Delivery Ft Collins CO 80523 USA NOAA Ctr Satellite Applicat & Res NESDIS College Pk MD USA

An atmospheric CO2 increase has become a progressively important global concern in recent past decades. Since the 1950s, the Keeling curve has documented the atmospheric CO2 increase as well as seasonal variations, which also intrigued scientists to develop new methods for global CO2 measurements from satellites. One of the dedicated satellite missions is the CO2 measurement in the 1.6-mu m shortwave infrared spectra by the Greenhouse Gases Observing Satellite (GOSAT) Thermal and Near Infrared Sensor for Carbon Observations-Fourier Transform Spectrometer (TANSO-FTS) instrument. While this spectral region has unique advantages in detecting lower-trophosphere CO2, there are many challenges because it relies on accurate measurements of reflected solar radiance from Earth's surface. Therefore, the calibration of the TANSO-FTS CO2 has a direct impact on the CO2 retrievals and its long-term trends. Coincidently, the Suomi-NPP Visible Infrared Imaging Radiometer Suite (VIIRS) 1.6-mu m band spectrally overlaps with the TANSO-FTS CO2 band, and both satellites are in orbit with periodical simultaneous nadir overpass measurements. This study performs an intercomparison of VIIRS and the TANSO-FTS CO2 band in an effort to evaluate and improve the radiometric consistency. Understanding the differences provides feedback on how well the GOSAT TANSO-FTS is performing over time, which is critical to ensure a well-calibrated, stable, and bias-free CO2 product.

关键词： Instrumentation/sensors observational techniques and algorithms Remote sensing

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Airborne Radar Observations of Lake-Effect Snowbands over the New York Finger Lakes

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MONTHLY WEATHER REVIEW 2016年第10期144卷 3895-3914页

作者： Bergmaier, Philip T. Geerts, Bart Univ Wyoming Dept Atmospher Sci 1000 East Univ Ave Laramie WY 82071 USA

The vast majority of lake-effect snow research throughout the years has focused on the North American Great Lakes since they are often associated with strong lake-effect events that produce heavy downstream snowfall. This study investigates a lake-effect snow event that instead occurred over two smaller lakes, the New York Finger Lakes, which are just 0(5) km wide and 0(50) km long. A pair of well-defined snow bands that formed over Seneca and Cayuga Lakes, the two largest of the Finger Lakes, were sampled from above by a vertically pointing Doppler radar and lidar on board the University of Wyoming King Air (UWKA). With typical widths matching the widths of the lakes, and depths of less than 1000 m, the long lake-axis-parallel bands were actually quite intense for their size. For example, updrafts of 2-3 m s(-1) or greater within the band cores were common, and reflectivity occasionally exceeded 5 dBZ. Airborne dual Doppler data show that both bands were sometimes accompanied by a well-defined thermally driven secondary circulation. Lidar data reveal that the Cayuga Lake band contained significantly more liquid water than the band over Seneca Lake, which was composed mainly of ice. Dissipating lake-effect ice clouds, carried downstream from Lake Ontario toward Seneca Lake, likely seeded the emerging convection over Seneca Lake, resulting in an accelerated depletion of liquid in the Seneca Lake band via more efficient snow growth.

关键词： Circulation/ Dynamics Lake effects Mesoscale processes Snowbands observational techniques and algorithms Aircraft observations Lidars/Lidar observations Radars/Radar observations

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Spectral Characteristics of Instrumental and Climate Model Surface Temperatures

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JOURNAL OF CLIMATE 2016年第4期29卷 1253-1268页

作者： Fredriksen, Hege-Beate Rypdal, Kristoffer Univ Tromso Dept Math & Stat Hansine Hansens Vei 54 N-9037 Tromso Norway

The spatiotemporal temperature variability for several gridded instrumental and general circulation climate model data is characterized, contrasting power spectra of local and global temperatures, land and sea temperatures, and temperatures of different regions. There is generally a high degree of agreement between the spectral characteristics of instrumental and climate model data. All but the equatorial spectra exhibit a power-law shape and are hence more consistent with the spectra expected from long-memory processes than from short-memory processes. The power-law exponent beta of the spectra is a measure of memory, or persistence, of the temperatures and is observed to be about twice as large for global temperature than for local temperatures. However, there are large variations, in particular between land and sea surface temperatures. This is shown by estimates of the spectra for different regions and global maps of beta. It is also demonstrated that global spectra are related to local spectra via teleconnections between local temperatures.

关键词： Model output statistics Spectral analysis/models/distribution observational techniques and algorithms Oceanic variability Surface observations Interannual variability Interdecadal variability Variability Models and modeling

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Optimization of the Cross-Correlation Algorithm for Two-Component Wind Field Estimation from Single Aerosol Lidar Data and Comparison with Doppler Lidar

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JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 2016年第1期33卷 81-101页

作者： Hamada, Masaki Derian, Pierre Mauzey, Christopher F. Mayor, Shane D. Calif State Univ Chico 400 W First St Chico CA 95929 USA

Numerical and field experiments were conducted to test an optimized cross-correlation algorithm (CCA) for the remote sensing of two-component wind vectors from horizontally scanning elastic backscatter lidar data. Each vector is the result of applying the algorithm to a square and contiguous subset of pixels (an interrogation window) in the lidar scan area. Synthetic aerosol distributions and flow fields were used to investigate the accuracy and precision of the technique. Results indicate that in neutral static stability, when the mean flow direction over the interrogation window is relatively uniform, the random error of the estimates increases as the mean wind speed and turbulence intensity increases. In convective conditions, larger errors may occur as a result of the cellular nature of convection and the dramatic changes in wind direction that may span the interrogation window. Synthetic fields were also used to determine the significance of various image processing and numerical steps used in the CCA. Results show that an iterative approach that dynamically reduces the block size provides the largest performance gains. Finally, data from a field experiment conducted in 2013 in Chico, California, are presented. Comparisons with Doppler lidar data indicate excellent agreement for the 10-min mean wind velocity computed over a set of 150 h: the root-mean-square deviations (and slopes) for the u and v components are 0.36 m s(-1) (0.974) and 0.37 m s(-1) (0.991), respectively, with correlation coefficients R-2 > 0.99.

关键词： Circulation/ Dynamics Turbulence Atm/Ocean Structure/ Phenomena Boundary layer Wind observational techniques and algorithms algorithms Lidars/Lidar observations Remote sensing

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Probabilistic Forecasts of Mesoscale Convective System Initiation Using the Random Forest Data Mining Technique

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WEATHER AND FORECASTING 2016年第2期31卷 581-599页

作者： Ahijevych, David Pinto, James O. Williams, John K. Steiner, Matthias Natl Ctr Atmospher Res POB 3000 Boulder CO 80307 USA Weather Co Andover MA USA

A data mining and statistical learning method known as a random forest (RF) is employed to generate 2-h forecasts of the likelihood for initiation of mesoscale convective systems (MCS-I). The RF technique uses an ensemble of decision trees to relate a set of predictors [in this case radar reflectivity, satellite imagery, and numerical weather prediction (NWP) model diagnostics] to a predictand (in this case MCS-I). The RF showed a remarkable ability to detect MCS-I events. Over 99% of the 550 observed MCS-I events were detected to within 50 km. However, this high detection rate came with a tendency to issue false alarms either because of premature warning of an MCS-I event or in the continued elevation of RF forecast likelihoods well after an MCS-I event occurred. The skill of the RF forecasts was found to increase with the number of trees and the fraction of positive events used in the training set. The skill of the RF was also highly dependent on the types of predictor fields included in the training set and was notably better when a more recent training period was used. The RF offers advantages over high-resolution NWP because it can be run in a fraction of the time and can account for nonlinearly varying biases in the model data. In addition, as part of the training process, the RF ranks the importance of each predictor, which can be used to assess the utility of new datasets in the prediction of MCS-I.

关键词： Physical Meteorology and Climatology Convective storms observational techniques and algorithms Data mining Mathematical and statistical techniques Statistical techniques Forecasting Forecasting techniques Models and modeling Nonlinear models

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Stratocumulus Cloud Clearings and Notable Thermodynamic and Aerosol Contrasts across the Clear-Cloudy Interface

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第3期73卷 1083-1099页

作者： Crosbie, Ewan Wang, Zhen Sorooshian, Armin Chuang, Patrick Y. Craven, Jill S. Coggon, Matthew M. Brunke, Michael Zeng, Xubin Jonsson, Haflidi Woods, Roy K. Flagan, Richard C. Seinfeld, John H. Univ Arizona Dept Atmospher Sci Tucson AZ 85721 USA Univ Arizona Dept Chem & Environm Engn Tucson AZ 85721 USA Univ Calif Santa Cruz Earth & Planetary Sci Santa Cruz CA 95064 USA CALTECH Dept Chem Engn Pasadena CA 91125 USA Naval Postgrad Sch Ctr Interdisciplinary Remotely Piloted Aircraft S Monterey CA USA

Data from three research flights, conducted over water near the California coast, are used to investigate the boundary between stratocumulus cloud decks and clearings of different sizes. Large clearings exhibit a diurnal cycle with growth during the day and contraction overnight and a multiday life cycle that can include oscillations between growth and decay, whereas a small coastal clearing was observed to be locally confined with a subdiurnal lifetime. Subcloud aerosol characteristics are similar on both sides of the clear-cloudy boundary in the three cases, while meteorological properties exhibit subtle, yet important, gradients, implying that dynamics, and not microphysics, is the primary driver for the clearing characteristics. Transects, made at multiple levels across the cloud boundary during one flight, highlight the importance of microscale (similar to 1 km) structure in thermodynamic properties near the cloud edge, suggesting that dynamic forcing at length scales comparable to the convective eddy scale may be influential to the larger-scale characteristics of the clearing. These results have implications for modeling and observational studies of marine boundary layer clouds, especially in relation to aerosol-cloud interactions and scales of variability responsible for the evolution of stratocumulus clearings.

关键词： Aircraft observations Atm/Ocean Structure/ Phenomena North Pacific Ocean Thermodynamics Physical Meteorology and Climatology Cloud cover observational techniques and algorithms Aerosols Boundary layer Geographic location/entity

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Development and Analysis of a Long-Term, Global, Terrestrial Land Surface Temperature Dataset Based on HIRS Satellite Retrievals

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JOURNAL OF CLIMATE 2016年第10期29卷 3589-3606页

作者： Siemann, Amanda L. Coccia, Gabriele Pan, Ming Wood, Eric F. Princeton Univ Dept Civil & Environm Engn E-208 E Quad Princeton NJ 08544 USA

Land surface temperature (LST) is a critical state variable for surface energy exchanges as it is one of the controls on emitted radiation at Earth's surface. LST also exerts an important control on turbulent fluxes through the temperature gradient between LST and air temperature. Although observations of surface energy balance components are widely accessible from in situ stations in most developed regions, these ground-based observations are not available in many underdeveloped regions. Satellite remote sensing measurements provide wider spatial coverage to derive LST over land and are used in this study to form a high-resolution, long-term LST data product. As selected by the Global Energy and Water Exchanges project (GEWEX) Data and Assessments Panel (GDAP) for development of internally consistent datasets, the High Resolution Infrared Radiation Sounder (HIRS) data are used for the primary satellite observations because of the data record length. The final HIRS-consistent, hourly, global, 0.5 degrees resolution LST dataset for clear and cloudy conditions from 1979 to 2009 is developed through merging the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) LST estimates with the HIRS retrievals using a Bayesian postprocessing procedure. The Baseline Surface Radiation Network (BSRN) observations are used to validate the HIRS retrievals, the CFSR LST estimates, and the final merged LST dataset. An intercomparison between the original retrievals and CFSR LST datasets, before and after merging, is also presented with an analysis of the datasets, including an error assessment of the final LST dataset.

关键词： Physical Meteorology and Climatology Surface temperature observational techniques and algorithms Satellite observations

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