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Lee Harrison

Abstract

The submicron aerosol of metropolitan Seattle was segregated into CCN and non-CCN fractions by a high-flux thermal diffusion cloud chamber in series with a dichotomous separator. Each segregated fraction of the five-hour daily sample was deposited on a filter, and analyzed for mass, optical absorption, sulfate and nitrate. Results are presented in context with the meteorological record. A new finding of this study is that the mean non-CCN mass fraction of the submicron aerosol was greater than 50%. The sulfate, nitrate, and optical absorption partitioned between the CCN and non-CCN fractions. The mean ratio of optical absorption to mass concentration suggests that both the non-CCN and CCN fractions contain soot. The CCN optical absorption and sulfate concentration am modulated by rainfall events.

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Lee Harrison and Halstead Harrison

Abstract

We describe a thermal diffusion cloud chamber operated in series with an aerodynamic dichotomous separator that can segregate aerosol particles by their abilities to nucleate cloud droplets. The apparatus takes advantage of compensating gradients in flow velocities and supersaturations to operate with an effective aperture of 70 cm2 and high flow rates (up to 50 L min−1) to produce narrow distributions of 4–5 μm diameter droplets grown from those particles which would nucleate clouds at a range of supersaturations from 0 to 1%. Subsequent aerodynamic separation of these large droplets from unactivated smaller aerosol particles is achieved with efficiencies exceeding 90%, by mass, at a supersaturation of 0.64% (+0, −0.3%).

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Qilong Min and Lee C. Harrison

Abstract

A quasi-linear retrieval was developed to profile moderately thin atmospheres using a high-resolution O2 A-band spectrometer. The retrieval is explicitly linear with respect to single scattering; the multiple-scattering contribution is treated as a perturbation. The properties of the linear inversion, examined using singular value decomposition of the kernel function, demonstrate the impacts of instrument specifications, such as resolution, out-of-band rejection, and signal-to-noise ratio, on information content. A system with 0.5 cm−1 resolution, signal-to-noise ratio of 100:1, and out-of-band floor of 10−3 has four independent pieces of information.

A fast radiative transfer model was developed to compute the multiple-scattering perturbation, in which multiple scattering is calculated at 16 different O2 absorption depths to synthesize the O2 A band. The linear system is then solved using Tikhonov's regularization with inequality constraints. Tests with synthetic data, including noise, of O2 A-band retrievals illustrate that this algorithm is accurate and fast for retrieving aerosol profiles. The errors are less than 10% for the integrated total optical depth for the cases tested. It is shown that instruments with the needed performance are practical.

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T. Connor Nelson, Lee Harrison, and Kristen L. Corbosiero

Abstract

The newly developed Expendable Digital Dropsondes (XDDs) allow for high spatial and temporal resolution observations of the kinematic and thermodynamic structures in tropical cyclones (TCs). It is important to evaluate both the temporal and spatial autocorrelations within the recorded data to address concerns about spatial interpolation, statistical significance of individual data points, and launch-rate spatial requirements for future dropsonde studies in TCs. Data from 437 XDDs launched into Hurricanes Marty (27–28 September), Joaquin (2–5 October), and Patricia (20–23 October) during the 2015 Tropical Cyclone Intensity (TCI) experiment are used to compute temporal and spatial autocorrelations for vertical velocity, temperature, horizontal wind speed, and equivalent potential temperature. All of the examined variables had temporal autocorrelation scales between approximately 10 and 40 s, with most between 20 and 30 s. Most of the spatial autocorrelation scales were estimated to be 3–10 km. The temporal autocorrelation scales for vertical velocity, horizontal wind speed, and equivalent potential temperature were correlated with updraft depth. Vertical velocity usually had the smallest mean, and median, temporal and estimated spatial autocorrelation scales of approximately 20 s and 3–6 km, respectively. The estimated horizontal scales are below the median sounding spacing and suggest that an increase in the launch rate of the XDDs by a factor of 3–4 from the TCI sampling rate is needed to adequately depict TC kinematics and structure in transects of soundings. The results also indicate that current temporal sampling rates are adequate to depict TC kinematics and structure in a single sounding.

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T. Connor Nelson, Lee Harrison, and Kristen L. Corbosiero

Abstract

The newly developed expendable digital dropsonde (XDD) allows for high spatial and temporal resolution data collection in tropical cyclones (TCs). In 2015, a total of 725 XDDs were launched into Hurricanes Marty (27–28 September), Joaquin (2–5 October), and Patricia (20–23 October) as part of the Tropical Cyclone Intensity (TCI) experiment. These dropsondes were launched from a NASA WB-57 at altitudes above 18 km, capturing the full depth of the TCs to the tropopause. This study documents the vertical velocity distributions observed in TCI using the XDDs and examines the distributions altitudinally, radially, and azimuthally. The strongest mean or median XDD-derived vertical velocities observed during TCI occurred in the upper levels and within the cores of the three TCs. There was little azimuthal signal in the vertical velocity distribution, likely due to sampling asymmetries and noise in the data. Downdrafts were strongest in Joaquin, while updrafts were strongest in Patricia, especially within the eyewall on 23 October. Patricia also had an impressive low-level (<2 km) updraft that exceeded 10 m s−1 associated with a shallow, overturning, radial circulation in the secondary eyewall.

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Peter Black, Lee Harrison, Mark Beaubien, Robert Bluth, Roy Woods, Andrew Penny, Robert W. Smith, and James D. Doyle

Abstract

The High-Definition Sounding System (HDSS) is an automated system deploying the expendable digital dropsonde (XDD) designed to measure wind and pressure–temperature–humidity (PTH) profiles, and skin sea surface temperature (SST) within and around tropical cyclones (TCs) and other high-impact weather events needing high sampling density. Three experiments were conducted to validate the XDD.

On two successive days off the California coast, 10 XDDs and 14 Vaisala RD-94s were deployed from the navy’s Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft over offshore buoys. The Twin Otter made spiral descents from 4 km to 60 m at the same descent rate as the sondes. Differences between successive XDD and RD-94 profiles due to true meteorological variability were on the same order as the profile differences between the spirals, XDDs, and RD-94s. XDD SST measured via infrared microradiometer, referred to as infrared skin SST (SSTir), and surface wind measurements were within 0.5°C and 1.5 m s−1, respectively, of buoy and Twin Otter values.

A NASA DC-8 flight launched six XDDs from 12 km between ex-TC Cosme and the Baja California coast. Repeatability was shown with good agreement between features in successive profiles. XDD SSTir measurements from 18° to 28°C and surface winds agreed well with drifting buoy- and satellite-derived estimates.

Excellent agreement was found between PTH and wind profiles measured by XDDs deployed from a NASA WB-57 at 18-km altitude offshore from the Texas coast and NWS radiosonde profiles from Brownsville and Corpus Christi, Texas. Successful XDD profiles were obtained in the clear and within precipitation over an offshore squall line.

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Bruce A. Wielicki, Bruce R. Barkstrom, Edwin F. Harrison, Robert B. Lee III, G. Louis Smith, and John E. Cooper

Clouds and the Earth's Radiant Energy System (CERES) is an investigation to examine the role of cloud/radiation feedback in the Earth's climate system. The CERES broadband scanning radiometers are an improved version of the Earth Radiation Budget Experiment (ERBE) radiometers. The CERES instruments will fly on several National Aeronautics and Space Administration Earth Observing System (EOS) satellites starting in 1998 and extending over at least 15 years. The CERES science investigations will provide data to extend the ERBE climate record of top-of-atmosphere shortwave (SW) and longwave (LW) radiative fluxes. CERES will also combine simultaneous cloud property data derived using EOS narrowband imagers to provide a consistent set of cloud/radiation data, including SW and LW radiative fluxes at the surface and at several selected levels within the atmosphere. CERES data are expected to provide top-of-atmosphere radiative fluxes with a factor of 2 to 3 less error than the ERBE data. Estimates of radiative fluxes at the surface and especially within the atmosphere will be a much greater challenge but should also show significant improvements over current capabilities.

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Joseph T. Schaefer, James P. Travers, Thomas A. Heffner, A. Dale Eubanks, Armando L. Garza, Lans P. Rothfusz, Walter A. Rogers, Sylvia K. Graff, James T. Skeen, Kenneth Haydu, and M. Lee Harrisons

The National Weather Service sponsored a workshop on aviation weather on 10–12 December 1991, in Kansas City, Missouri. The theme of the workshop was the improvement of service to the aviation community through the application of technology and advanced forecast techniques. The 150-plus people who attended the workshop included a cross section of operational forecasters, pilots, research meteorologists, and representatives of the aviation industry. The workshop included sessions on user requirements, operational procedures, and the impacts of new technology on the forecast products. There were also four “hands-on” laboratory sessions where participants produced various types of aviation weather products. The interaction between the user community and working-level forecasters made the workshop a unique event.

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Alberto Troccoli, Pierre Audinet, Paolo Bonelli, Mohammed S. Boulahya, Carlo Buontempo, Peter Coppin, Laurent Dubus, John A. Dutton, Jane Ebinger, David Griggs, Sven-Erik Gryning, Don Gunasekera, Mike Harrison, Sue Ellen Haupt, Trevor Lee, Pascal Mailier, Pierre-Philippe Mathieu, Roberto Schaeffer, Marion Schroedter-Homscheidt, Rong Zhu, and John Zillman
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Anand Gnanadesikan, Keith W. Dixon, Stephen M. Griffies, V. Balaji, Marcelo Barreiro, J. Anthony Beesley, William F. Cooke, Thomas L. Delworth, Rudiger Gerdes, Matthew J. Harrison, Isaac M. Held, William J. Hurlin, Hyun-Chul Lee, Zhi Liang, Giang Nong, Ronald C. Pacanowski, Anthony Rosati, Joellen Russell, Bonita L. Samuels, Qian Song, Michael J. Spelman, Ronald J. Stouffer, Colm O. Sweeney, Gabriel Vecchi, Michael Winton, Andrew T. Wittenberg, Fanrong Zeng, Rong Zhang, and John P. Dunne

Abstract

The current generation of coupled climate models run at the Geophysical Fluid Dynamics Laboratory (GFDL) as part of the Climate Change Science Program contains ocean components that differ in almost every respect from those contained in previous generations of GFDL climate models. This paper summarizes the new physical features of the models and examines the simulations that they produce. Of the two new coupled climate model versions 2.1 (CM2.1) and 2.0 (CM2.0), the CM2.1 model represents a major improvement over CM2.0 in most of the major oceanic features examined, with strikingly lower drifts in hydrographic fields such as temperature and salinity, more realistic ventilation of the deep ocean, and currents that are closer to their observed values. Regional analysis of the differences between the models highlights the importance of wind stress in determining the circulation, particularly in the Southern Ocean. At present, major errors in both models are associated with Northern Hemisphere Mode Waters and outflows from overflows, particularly the Mediterranean Sea and Red Sea.

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