Naval Postgraduate School

About: Naval Postgraduate School is a education organization based out in Monterey, California, United States. It is known for research contribution in the topics: Tropical cyclone & Nonlinear system. The organization has 5246 authors who have published 11614 publications receiving 298300 citations. The organization is also known as: NPS & U.S. Naval Postgraduate School.

Emissions from Ships with respect to Their Effects on Clouds

Abstract: Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as ‘‘ship tracks.’’ Airborne measurements are used to derive emission factors of SO 2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were ;15‐89 and ;2‐25 g kg21 of fuel burned, respectively. By contrast a steam turbine‐powered ship burning high-grade navy distillate fuel had an SO2 emission factor of ; 6gk g 21. Various types of ships, burning both MFO and navy distillate fuel, emitted from ;4 3 1015 to 2 3 1016 total particles per kilogram of fuel burned (;4 3 1015‐1.5 3 1016 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (;0.03‐0.05 mm) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius ;0.02 mm). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine‐powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis. The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO 2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN. The fluxes of heat and water vapor from ships are estimated to be ;2‐22 MW and;0.5‐1.5 kg s21, respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.

Probabilistic noninterference in a concurrent language

Abstract: The authors previously give a type system that guarantees that well-typed multi-threaded programs are possibilistically noninterfering. If thread scheduling is probabilistic, however, then well-typed programs may have probabilistic timing channels. They describe how they can be eliminated without making the type system more restrictive. They show that well-typed concurrent programs are probabilistically noninterfering if every total command with a high guard executes atomically. The proof uses the concept of a probabilistic state of a computation, following the work of Kozen (1981).

The Presidents' Day cyclone of 18-19 February 1979 - Influence of upstream trough amplification and associated tropopause folding on rapid cyclogenesis

Abstract: The Presidents' Day cyclone of 18-19 February, 1979 is analyzed based on conventional radiosonde data, infrared and visible satellite imagery, water vapor images and ozone measurement The well-known synoptic-scale characteristics of the PJ-trough system are described, and evidence for the development of the tropopause fold are presented Processes contributing to the formation of the fold are discussed in terms of an evaluation of the Sawyer-Eliassen circulation equation and a diagnostic evaluation of the ageostrophic winds and vertical motion near the polar jet streak The documentation of stratospheric extrusions and their possible role in cyclogenesis is reviewed, and Eulerian and Lagrangian diagnostics are used to establish a connection between the tropopause fold associated with the polar jet streak and rapid cyclogenesis along the East Coast Conservation of potential vorticity expressed in isentropic coordinates is used as a constraint from which to view cyclogenesis

Freshening of the upper ocean in the Arctic: Is perennial sea ice disappearing?

Abstract: During the Surface Heat Budget of the Arctic (SHEBA) deployment in October, 1997, multiyear ice near the center of the Beaufort Gyre was anomalously thin The upper ocean was both warmer and less saline than in previous years The salinity deficit in the upper 100 m, compared with the same region during the Arctic Ice Dynamics Joint Experiment (AIDJEX) in 1975, is equivalent to surface input of about 24 m of fresh water Heat content has increased by 67 MJ m−2 During AIDJEX the change in salinity over the melt season implied melt equivalent to about 08 m of fresh water As much as 2 m of freshwater input may have occurred during the 1997 summer, possibly resulting from decreased ice concentration from changes in atmospheric circulation early in the summer , in the classic albedo-feedback scenario Unchecked, the pattern could lead to a significantly different sea-ice regime in the central Arctic