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Alexandru Rap, Satyajit Ghosh, and Michael H. Smith

Abstract

This paper presents a novel method based on the application of interpolation techniques to the multicomponent aerosol–cloud parameterization for global climate modeling. Quantifying the aerosol indirect effect still remains a difficult task, and thus developing parameterizations for general circulation models (GCMs) of the microphysics of clouds and their interactions with aerosols is a major challenge for climate modelers. Three aerosol species are considered in this paper—namely sulfate, sea salt, and biomass smoke—and a detailed microphysical chemical parcel model is used to obtain a dataset of points relating the cloud droplet number concentration (CDNC) to the three aerosol input masses. The resulting variation of CDNC with the aerosol mass has some nonlinear features that require a complex but efficient parameterization to be easily incorporated into GCMs. In bicomponent systems, simple interpolation techniques may be sufficient to relate the CDNC to the aerosol mass, but with increasing components, simple methods fail. The parameterization technique proposed in this study employs either the modified Shepard interpolation method or the Hardy multiquadrics interpolation method, and the numerical results obtained show that both methods provide realistic results for a wide range of aerosol mass loadings. This is the first application of these two interpolation techniques to aerosol–cloud interaction studies.

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Richard A. Dare, David H. Smith, and Michael J. Naughton

Abstract

A meteorological ensemble prediction system that represents uncertainties in both initial conditions and model formulations is coupled with a modified version of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. This coupled dispersion ensemble prediction system (DEPS) is used to generate a 24-member ensemble forecast of the dispersion of the volcanic ash cloud produced by the 13 February 2014 eruption of Kelut, Indonesia. Uncertainties in the volcanic ash source are not represented. For predictions up to 12 h from the start of the eruption, forecasts from the deterministic control member and from the DEPS both show very good qualitative agreement with satellite observations. By 18–24 h the DEPS forecast shows better qualitative agreement with observations than does the deterministic forecast. Although composited fields such as the ensemble mean and probability present information concisely, experiments here show that it is very important to also consider results from individual member forecasts in order to identify features that may be underrepresented. For example, an area of relatively high ash concentration that was forecast by most of the members was not particularly evident in the composited fields because the location of this feature was highly variable between member forecasts. To fully understand a DEPS forecast, it is necessary to consider both atmospheric column load and concentration fields, individual member forecasts, and a range of thresholds in computing and interpreting probabilities.

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Margaret J. Yelland, Peter K. Taylor, Ian E. Consterdine, and Michael H. Smith

Abstract

Consideration of the inertial dissipation method for routine wind stress estimation suggests that the most significant errors are likely to be changes in height of the airflow before reaching the anemometers, and errors in estimating the true wind, due either to flow distortion-induced errors in the relative wind estimate or errors in estimating the ship's speed relative to the water. The results from four anemometers—Solent sonic and Kaijo Denki sonic anemometers, and R.M. Young propeller-vane and bivane anemometers—mounted on the foremast of a research ship were compared. The mean bias between the four anemometers in the friction velocity estimates was less than 3% (rms scatter 6%–12%). In contrast the bias and scatter for the drag coefficient was 17%–27% due to flow distortion-induced errors in estimating the true wind speed. It is concluded that, with a reasonably well-exposed anemometer, wind stress can be determined to 5% or better by the dissipation method whereas errors in the bulk aerodynamic method are likely to be between 20% and 30%.

The data from the two sonic anemometers showed the best correlation; the Solent sonic, a relatively new instrument, was comparable in performance to the Kaijo Denki. Comparisons of the two propeller anemometers typically showed twice the scatter compared to the sonic values. Overcorrection for the propeller response at low wind speeds resulted in spuriously high drag coefficient values for wind speeds below 10 m s−1. In contrast, the sonic anemometer data showed no change in the slope of the drag coefficient to wind speed relationship at low wind speed.

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Martin K. Hill, Barbara J. Brooks, Sarah J. Norris, Michael H. Smith, Ian M. Brooks, and Gerrit de Leeuw

Abstract

The Compact Lightweight Aerosol Spectrometer Probe (CLASP) is an optical particle spectrometer capable of measuring size-resolved particle concentrations in 16 user-defined size bins spanning diameters in the range 0.24 < D < 18.5 μm at a rate of 10 Hz. The combination of its compact nature and lightweight and robust build allows for deployment in environments and locations where the use of the larger, heavier, more traditional instrumentation would prove awkward or impossible. The high temporal resolution means it is particularly suited to direct measurements of aerosol fluxes via the eddy covariance technique. CLASP has been through an extended evolutionary development. This has resulted in an instrument whose performance characteristics are well established.

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David R. Smith, Lisa M. Bastiaans, Robert S. Weinbeck, Michael J. Passow, Phillip J. Smith, Nezette N. Rydell, H. Patricia Warthan, Timothy C. Spangler, and Alexander E. MacDonald

In recognition of the educational efforts throughout the atmospheric and oceanic science communities, the American Meteorological Society (AMS) has instituted an annual forum called the Symposium on Education. The third such symposium was held this year in conjunction with the 74th Annual Meeting in Nashville, Tennessee. The theme of this year's symposium was “Preparing for the Twenty-First Century.” Thirty-one oral presentations and 26 poster presentations summarized a variety of educational programs or examined issues of importance for both the precollege and university levels. In addition, there was a panel discussion on future directions for the undergraduate degree in the atmospheric and marine sciences. One interesting aspect of this year's symposium was a joint session with the 10th International Conference on Interactive Information and Processing Systems for Meteorology, Oceanography, and Hydrology on new technologies for the classroom. Over 200 people representing a wide spectrum of the Society attended one or more of the sessions in this two-day conference, where they increased their awareness of the educational initiatives of members and institutions associated with the AMS.

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Adrian A. Ritchie Jr., Matthew R. Smith, H. Michael Goodman, Ronald L. Schudalla, Dawn K. Conway, Frank J. LaFontaine, Don Moss, and Brian Motta

Abstract

Antenna temperatures and the corresponding geolocation data from the five sources of the Special Sensor Microwave/Imager data from the Defense Meteorological Satellite Program F11 satellite have been characterized. Data from the Fleet Numerical Meteorology and Oceanography Center (FNMOC) have been compared with data from other sources to define and document the differences resulting from different processing systems. While all sources used similar methods to calculate antenna temperatures, different calibration averaging techniques and other processing methods yielded temperature differences. Analyses of the geolocation data identified perturbations in the FNMOC and National Environmental Satellite, Data and Information Service data. The effects of the temperature differences were examined by generating rain rates using the Goddard Scattering Algorithm. Differences in the geophysical precipitation products are directly attributable to antenna temperature differences.

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Robert A. Massom, Sharon E. Stammerjohn, Raymond C. Smith, Michael J. Pook, Richard A. Iannuzzi, Neil Adams, Douglas G. Martinson, Maria Vernet, William R. Fraser, Langdon B. Quetin, Robin M. Ross, Yuko Massom, and H. Roy Krouse

Abstract

Exceptional sea ice conditions occurred in the West Antarctic Peninsula (WAP) region from September 2001 to February 2002, resulting from a strongly positive atmospheric pressure anomaly in the South Atlantic coupled with strong negative anomalies in the Bellingshausen–Amundsen and southwest Weddell Seas. This created a strong and persistent north-northwesterly flow of mild and moist air across the WAP. In situ, satellite, and NCEP–NCAR Reanalysis (NNR) data are used to examine the profound and complex impact on regional sea ice, oceanography, and biota. Extensive sea ice melt, leading to an ocean mixed layer freshening and widespread ice surface flooding, snow–ice formation, and phytoplankton growth, coincided with extreme ice deformation and dynamic thickening. Sea ice dynamics were crucial to the development of an unusually early and rapid (short) retreat season (negative ice extent anomaly). Strong winds with a dominant northerly component created an unusually compact marginal ice zone and a major increase in ice thickness by deformation and over-rafting. This led to the atypical persistence of highly compact coastal ice through summer. Ecological effects were both positive and negative, the latter including an impact on the growth rate of larval Antarctic krill and the largest recorded between-season breeding population decrease and lowest reproductive success in a 30-yr Adélie penguin demographic time series. The unusual sea ice and snow cover conditions also contributed to the formation of a major phytoplankton bloom. Unexpectedly, the initial bloom occurred within compact sea ice and could not be detected in Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) ocean color data. This analysis demonstrates that sea ice extent alone is an inadequate descriptor of the regional sea ice state/conditions, from both a climatic and ecological perspective; further information is required on thickness and dynamics/deformation.

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Kevin J. Noone, Doug W. Johnson, Jonathan P. Taylor, Ronald J. Ferek, Tim Garrett, Peter V. Hobbs, Philip A. Durkee, Kurt Nielsen, Elisabeth Öström, Colin O’Dowd, Michael H. Smith, Lynn M. Russell, Richard C. Flagan, John H. Seinfeld, Lieve De Bock, René E. Van Grieken, James G. Hudson, Ian Brooks, Richard F. Gasparovic, and Robert A. Pockalny

Abstract

A case study of the effects of ship emissions on the microphysical, radiative, and chemical properties of polluted marine boundary layer clouds is presented. Two ship tracks are discussed in detail. In situ measurements of cloud drop size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside-cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to remotely sensed measurements of cloud radiative properties.

The authors examine the processes behind ship track formation in a polluted marine boundary layer as an example of the effects of anthropogenic particulate pollution on the albedo of marine stratiform clouds.

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Kevin J. Noone, Elisabeth Öström, Ronald J. Ferek, Tim Garrett, Peter V. Hobbs, Doug W. Johnson, Jonathan P. Taylor, Lynn M. Russell, Richard C. Flagan, John H. Seinfeld, Colin D. O’Dowd, Michael H. Smith, Philip A. Durkee, Kurt Nielsen, James G. Hudson, Robert A. Pockalny, Lieve De Bock, René E. Van Grieken, Richard F. Gasparovic, and Ian Brooks

Abstract

The effects of anthropogenic particulate emissions from ships on the radiative, microphysical, and chemical properties of moderately polluted marine stratiform clouds are examined. A case study of two ships in the same air mass is presented where one of the vessels caused a discernible ship track while the other did not. In situ measurements of cloud droplet size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to measurements of cloud radiative properties. The differences between the aerosol in the two ship plumes are discussed;these indicate that combustion-derived particles in the size range of about 0.03–0.3-μm radius were those that caused the microphysical changes in the clouds that were responsible for the ship track.

The authors examine the processes behind ship track formation in a moderately polluted marine boundary layer as an example of the effects that anthropogenic particulate pollution can have in the albedo of marine stratiform clouds.

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Armin Sorooshian, Bruce Anderson, Susanne E. Bauer, Rachel A. Braun, Brian Cairns, Ewan Crosbie, Hossein Dadashazar, Glenn Diskin, Richard Ferrare, Richard C. Flagan, Johnathan Hair, Chris Hostetler, Haflidi H. Jonsson, Mary M. Kleb, Hongyu Liu, Alexander B. MacDonald, Allison McComiskey, Richard Moore, David Painemal, Lynn M. Russell, John H. Seinfeld, Michael Shook, William L. Smith Jr, Kenneth Thornhill, George Tselioudis, Hailong Wang, Xubin Zeng, Bo Zhang, Luke Ziemba, and Paquita Zuidema

Abstract

We report on a multiyear set of airborne field campaigns (2005–16) off the California coast to examine aerosols, clouds, and meteorology, and how lessons learned tie into the upcoming NASA Earth Venture Suborbital (EVS-3) campaign: Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE; 2019–23). The largest uncertainty in estimating global anthropogenic radiative forcing is associated with the interactions of aerosol particles with clouds, which stems from the variability of cloud systems and the multiple feedbacks that affect and hamper efforts to ascribe changes in cloud properties to aerosol perturbations. While past campaigns have been limited in flight hours and the ability to fly in and around clouds, efforts sponsored by the Office of Naval Research have resulted in 113 single aircraft flights (>500 flight hours) in a fixed region with warm marine boundary layer clouds. All flights used nearly the same payload of instruments on a Twin Otter to fly below, in, and above clouds, producing an unprecedented dataset. We provide here i) an overview of statistics of aerosol, cloud, and meteorological conditions encountered in those campaigns and ii) quantification of model-relevant metrics associated with aerosol–cloud interactions leveraging the high data volume and statistics. Based on lessons learned from those flights, we describe the pragmatic innovation in sampling strategy (dual-aircraft approach with combined in situ and remote sensing) that will be used in ACTIVATE to generate a dataset that can advance scientific understanding and improve physical parameterizations for Earth system and weather forecasting models, and for assessing next-generation remote sensing retrieval algorithms.

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