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Patricia M. Dare and Philip J. Smith

Abstract

Eddy kinetic energy budgets are presented for both moist and dry 48 h forecasts and corresponding observations of a developing, winter extratropical cyclone. Forecasts are from the Drexel-NCAR Limited Area Mesoscale Prediction System initialized at 1200 GMT 9 January 1975. Observations consist of North American rawinsonde data objectively analyzed to the model grid. The energetics quantities are calculated for both model and observed data on a domain including most of the contiguous United States and southern Canada for times corresponding to the model initialization and the 12, 24, 36 and 48 h forecasts.

Results show that the eddy kinetic energy content is dominated by the jet stream development for both model and observed data, with maxima flanking the trough at approximately 300 mb. The area-averaged, vertically-integrated eddy kinetic energy content is approximately 25% greater for the model initialization than the observations. The excess is localized in the jet maximum west of the trough, where geostrophic first-guess values are retained during initialization in place of missing winds. The increased kinetic energy west of the trough may be a factor in the excessive upper-air wave development predicted in the 24 h forecast and in the southeastward displacement of the cyclone system in the latter half of the forecast. Despite the larger initial eddy kinetic energy content, both models predict only a doubling of the integrated value, whereas the observed value tripled.

The observed increase in eddy kinetic energy content primarily results from an upper-tropospheric surplus of the source due to horizontal flux convergence over the sinks, generation and dissipation. The inability of the models to produce the observed increase in eddy kinetic energy is consistent with the underprediction of the horizontal flux convergence. The predicted flux values are affected by model boundary errors which are expected to propagate into the domain at the rate of 20 to 30° longitude per day. This implies the influence of boundary errors on the flux maximum associated with the western jet core as early as the 24 h forecast. Generation by cross-contour flow tends to be negatively correlated with the horizontal flux convergence, but also is affected by latent heat release. Latent heat release is found to enhance positive generation in both the observed and moist model results as compared to the dry model results.

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Song Chin Lin and Philip J. Smith

Abstract

Diabatic heating by latent heat release and longwave radiation and corresponding generation of available potential energy have been computed for a tornado-producing cyclone system. Also, the contributions of two subareas, encompassing the immediate cyclone vicinity and the convection area, to the cyclone system generation are examined applying the concepts of limited region baroclinic and barotropic generation.

Heating values, which are dominated by convective latent heat release, are generally in good agreement with observed weather features and cyclone development. The resulting positive cyclone system generation is comparable with previous studies and is strongly influenced by the contributions made by the two subareas. In turn, the latter are dominated by their. barotropic components, indicating that the heating fields in these subareas contribute more effectively to increasing or maintaining the baroclinicity of the cyclone system than of the subareas themselves.

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Matthew J. Carrier, Hans E. Ngodock, Philip Muscarella, and Scott Smith

Abstract

The assimilation of surface velocity observations and their impact on the model sea surface height (SSH) is examined using an operational regional ocean model and its four-dimensional variational data assimilation (4DVAR) analysis component. In this work, drifter-derived surface velocity observations are assimilated into the Navy’s Coastal Ocean Model (NCOM) 4DVAR in weak-constraint mode for a Gulf of Mexico (GoM) experiment during August–September 2012. During this period the model is trained by assimilating surface velocity observations (in a series of 96-h assimilation windows), which is followed by a 30-day forecast through the month of October 2012. A free-run model and a model that assimilates along-track SSH observations are also run as baseline experiments to which the other experiments are compared. It is shown here that the assimilation of surface velocity measurements has a substantial impact on improving the model representation of the forecast SSH on par with the experiment that assimilates along-track SSH observations directly. Finally, an assimilation experiment is done where both along-track SSH and velocity observations are utilized in an attempt to determine if the observation types are redundant or complementary. It is found that the combination of observations provides the best SSH forecast, in terms of the fit to observations, when compared to the previous experiments.

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Sijia Lou, Yang Yang, Hailong Wang, Jian Lu, Steven J. Smith, Fukai Liu, and Philip J. Rasch

ABSTRACT

El Niño–Southern Oscillation (ENSO) is the leading mode of Earth’s climate variability at interannual time scales with profound ecological and societal impacts, and it is projected to intensify in many climate models as the climate warms under the forcing of increasing CO2 concentration. Since the preindustrial era, black carbon (BC) emissions have substantially increased in the Northern Hemisphere. But how BC aerosol forcing may influence the occurrence of the extreme ENSO events has rarely been investigated. In this study, using simulations of a global climate model, we show that increases in BC emissions from both the midlatitudes and Arctic weaken latitudinal temperature gradients and northward heat transport, decrease tropical energy divergence, and increase sea surface temperature over the tropical oceans, with a surprising consequential increase in the frequency of extreme ENSO events. A corollary of this study is that reducing BC emissions might serve to mitigate the possible increasing frequency of extreme ENSO events under greenhouse warming, if the modeling result can be translated into the climate in reality.

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Philip Muscarella, Matthew J. Carrier, Hans Ngodock, Scott Smith, B. L. Lipphardt Jr., A. D. Kirwan Jr., and Helga S. Huntley

Abstract

The Lagrangian predictability of general circulation models is limited by the need for high-resolution data streams to constrain small-scale dynamical features. Here velocity observations from Lagrangian drifters deployed in the Gulf of Mexico during the summer 2012 Grand Lagrangian Deployment (GLAD) experiment are assimilated into the Naval Coastal Ocean Model (NCOM) 4D variational (4DVAR) analysis system to examine their impact on Lagrangian predictability. NCOM-4DVAR is a weak-constraint assimilation system using the indirect representer method. Velocities derived from drifter trajectories, as well as satellite and in situ observations, are assimilated. Lagrangian forecast skill is assessed using separation distance and angular differences between simulated and observed trajectory positions. Results show that assimilating drifter velocities substantially improves the model forecast shape and position of a Loop Current ring. These gains in mesoscale Eulerian forecast skill also improve Lagrangian forecasts, reducing the growth rate of separation distances between observed and simulated drifters by approximately 7.3 km day−1 on average, when compared with forecasts that assimilate only temperature and salinity observations. Trajectory angular differences are also reduced.

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Matthew J. Carrier, Hans Ngodock, Scott Smith, Gregg Jacobs, Philip Muscarella, Tamay Ozgokmen, Brian Haus, and Bruce Lipphardt

Abstract

Eulerian velocity fields are derived from 300 drifters released in the Gulf of Mexico by The Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) during the summer 2012 Grand Lagrangian Deployment (GLAD) experiment. These data are directly assimilated into the Navy Coastal Ocean Model (NCOM) four-dimensional variational data assimilation (4DVAR) analysis system in a series of experiments to investigate their impact on the model circulation. The NCOM-4DVAR is a newly developed tool for data analysis, formulated for weak-constraint data assimilation based on the indirect representer method. The assimilation experiments take advantage of this velocity data along with other available data sources from in situ and satellite measurements of surface and subsurface temperature and salinity. Three different experiments are done: (i) A nonassimilative NCOM free run, (ii) an assimilative NCOM run that utilizes temperature and salinity observations, and (iii) an assimilative NCOM run that uses temperature and salinity observations as well as the GLAD velocity observations. The resulting analyses and subsequent forecasts are compared to assimilated and future GLAD velocity and temperature/salinity observations to determine the performance of each experiment and the impact of the GLAD data on the analysis and the forecast. It is shown that the NCOM-4DVAR is able to fit the observations not only in the analysis step, but also in the subsequent forecast. It is also found that the GLAD velocity data greatly improves the characterization of the circulation, with the forecast showing a better fit to future GLAD observations than those experiments without the velocity data included.

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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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Thomas Jung, Neil D. Gordon, Peter Bauer, David H. Bromwich, Matthieu Chevallier, Jonathan J. Day, Jackie Dawson, Francisco Doblas-Reyes, Christopher Fairall, Helge F. Goessling, Marika Holland, Jun Inoue, Trond Iversen, Stefanie Klebe, Peter Lemke, Martin Losch, Alexander Makshtas, Brian Mills, Pertti Nurmi, Donald Perovich, Philip Reid, Ian A. Renfrew, Gregory Smith, Gunilla Svensson, Mikhail Tolstykh, and Qinghua Yang

Abstract

The polar regions have been attracting more and more attention in recent years, fueled by the perceptible impacts of anthropogenic climate change. Polar climate change provides new opportunities, such as shorter shipping routes between Europe and East Asia, but also new risks such as the potential for industrial accidents or emergencies in ice-covered seas. Here, it is argued that environmental prediction systems for the polar regions are less developed than elsewhere. There are many reasons for this situation, including the polar regions being (historically) lower priority, with fewer in situ observations, and with numerous local physical processes that are less well represented by models. By contrasting the relative importance of different physical processes in polar and lower latitudes, the need for a dedicated polar prediction effort is illustrated. Research priorities are identified that will help to advance environmental polar prediction capabilities. Examples include an improvement of the polar observing system; the use of coupled atmosphere–sea ice–ocean models, even for short-term prediction; and insight into polar–lower-latitude linkages and their role for forecasting. Given the enormity of some of the challenges ahead, in a harsh and remote environment such as the polar regions, it is argued that rapid progress will only be possible with a coordinated international effort. More specifically, it is proposed to hold a Year of Polar Prediction (YOPP) from mid-2017 to mid-2019 in which the international research and operational forecasting communites will work together with stakeholders in a period of intensive observing, modeling, prediction, verification, user engagement, and educational activities.

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AIRS

Improving Weather Forecasting and Providing New Data on Greenhouse Gases

MOUSTAFA T. CHAHINE, THOMAS S. PAGANO, HARTMUT H. AUMANN, ROBERT ATLAS, CHRISTOPHER BARNET, JOHN BLAISDELL, LUKE CHEN, MURTY DIVAKARLA, ERIC J. FETZER, MITCH GOLDBERG, CATHERINE GAUTIER, STEPHANIE GRANGER, SCOTT HANNON, FREDRICK W. IRION, RAMESH KAKAR, EUGENIA KALNAY, BJORN H. LAMBRIGTSEN, SUNG-YUNG LEE, JOHN Le MARSHALL, W. WALLACE MCMILLAN, LARRY MCMILLIN, EDWARD T. OLSEN, HENRY REVERCOMB, PHILIP ROSENKRANZ, WILLIAM L. SMITH, DAVID STAELIN, L. LARRABEE STROW, JOEL SUSSKIND, DAVID TOBIN, WALTER WOLF, and LIHANG ZHOU

The Atmospheric Infrared Sounder (AIRS) and its two companion microwave sounders, AMSU and HSB were launched into polar orbit onboard the NASA Aqua Satellite in May 2002. NASA required the sounding system to provide high-quality research data for climate studies and to meet NOAA's requirements for improving operational weather forecasting. The NOAA requirement translated into global retrieval of temperature and humidity profiles with accuracies approaching those of radiosondes. AIRS also provides new measurements of several greenhouse gases, such as CO2, CO, CH4, O3, SO2, and aerosols.

The assimilation of AIRS data into operational weather forecasting has already demonstrated significant improvements in global forecast skill. At NOAA/NCEP, the improvement in the forecast skill achieved at 6 days is equivalent to gaining an extension of forecast capability of six hours. This improvement is quite significant when compared to other forecast improvements over the last decade. In addition to NCEP, ECMWF and the Met Office have also reported positive forecast impacts due AIRS.

AIRS is a hyperspectral sounder with 2,378 infrared channels between 3.7 and 15.4 μm. NOAA/NESDIS routinely distributes AIRS data within 3 hours to NWP centers around the world. The AIRS design represents a breakthrough in infrared space instrumentation with measurement stability and accuracies far surpassing any current research or operational sounder..The results we describe in this paper are “work in progress,” and although significant accomplishments have already been made much more work remains in order to realize the full potential of this suite of instruments.

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