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 & Boundary layer. 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.

Eddy covariance measurements and parameterisation of traffic related particle emissions in an urban environment

Abstract: Urban aerosol sources are important due to the health effects of particles and their potential impact on climate. Our aim has been to quantify and parameterise the urban aerosol source number flux F (particles m-2 s-1), in order to help improve how this source is represented in air quality and climate models. We applied an aerosol eddy covariance flux system 118.0 m above the city of Stockholm. This allowed us to measure the aerosol number flux for particles with diameters >11 nm. Upward source fluxes dominated completely over deposition fluxes in the collected dataset. Therefore, the measured fluxes were regarded as a good approximation of the aerosol surface sources. Upward fluxes were parameterised using a traffic activity (TA) database, which is based on traffic intensity measurement. The footprint (area on the surface from which sources and sinks affect flux measurements, located at one point in space) of the eddy system covered road and building construction areas, forests and residential areas, as well as roads with high traffic density and smaller streets. We found pronounced diurnal cycles in the particle flux data, which were well correlated with the diurnal cycles in traffic activities, strongly supporting the conclusion that the major part of the aerosol fluxes was due to traffic emissions. The emission factor for the fleet mix in the measurement area EFfm=1.4±0.1×1014 veh-1 km-1 was deduced. This agrees fairly well with other studies, although this study has an advantage of representing the actual effective emission from a mixed vehicle fleet. Emission from other sources, not traffic related, account for a F0=14±18×106 m-2 s-1. The urban aerosol source flux can then be written as F=EFfmTA+F0. In a second attempt to find a parameterisation, the friction velocity U* normalised with the average friction velocity has been included, F=EF. This parameterisation results in a somewhat reduced emission factor, 1.3×1014 veh-1 km-1. When multiple linear regression have been used, two emission factors are found, one for light duty vehicles EFLDV=0.3±0.3×1014 veh-1 km-1 and one for heavy-duty vehicles, EFHDV=19.8±4.0×1014 veh-1 km-1, and F0=18±16×106 m-2 s-1. The results show that during weekdays ~70?80% of the emissions came from HDV.

Slow Speed Flight Control of Autonomous Underwater Vehicles: Experimental Results with NPS AUV II

Abstract: Proceedings of the Second (1992) International Offshore and Polar Engineering Conference San Francisco, USA, 14-19 June 1992

Integrating security into the curriculum

Abstract: Computer security can be used as a vehicle to achieve accreditation goals for computer science and engineering programs, while at the same time engaging students with relevant, exciting topics. The authors' approach, based on educational outcomes, illustrates that security topics can contribute to an engineering program by fostering all skills required to produce graduates capable of critical thinking.

Clear-Column Radiative Closure During ACE-Asia: Comparison of Multiwavelength Extinction Derived from Particle Size and Composition with Results from Sun Photometry

Abstract: From March to May 2001, aerosol size distributions and chemical compositions were measured using differential mobility analyzers (DMA), an aerodynamic particle sizer (APS), Micro-Orifice Uniform Deposit Impactors (MOUDI), and denuder samplers onboard the Twin Otter aircraft as part of the Aerosol Characterization Experiment (ACE)-Asia campaign. Of the 19 research flights, measurements on four flights that represented different aerosol characteristics are analyzed in detail. Clear-column radiative closure is studied by comparing aerosol extinctions predicted using in situ aerosol size distribution and chemical composition measurements to those derived from the 14-wavelength NASA Ames Airborne Tracking Sun photometer (AATS-14). In the boundary layer, pollution layers, and free troposphere with no significant mineral dust present, aerosol extinction closure was achieved within the estimated uncertainties over the full range of wavelengths of AATS-14. Aerosol extinctions predicted based on measured size distributions also reproduce the wavelength dependence derived from AATS-14 data. Considering all four flights, the best fit lines yield Predicted/Observed ratios in boundary and pollution layers of 0.97 ± 0.24 and 1.07 ± 0.08 at λ = 525 nm and 0.96 ± 0.21 and 1.08 ± 0.08 at λ = 1059 nm, respectively. In free troposphere dust layers, aerosol extinctions predicted from the measured size distributions were generally smaller than those derived from the AATS-14 data, with Predicted/Observed ratios of 0.65 ± 0.06 and 0.66 ± 0.05 at 525 and 1059 nm, respectively. A detailed analysis suggests that the discrepancy is likely a result of the lack of the knowledge of mineral dust shape as well as variations in aerosol extinction derived from AATS-14 data when viewing through horizontally inhomogeneous layers.

The downstream impact of tropical cyclones on a developing baroclinic wave in idealized scenarios of extratropical transition

Abstract: The interaction of a tropical cyclone with a developing baroclinic wave is investigated in an idealized scenario of extratropical transition (ET). The impact of ET is examined by comparing and analyzing two numerical baroclinic-wave experiments: a traditional experiment in which baroclinic development is excited by a localized upper-level perturbation on a realistic jet profile and an experiment in which, additionally, a model tropical cyclone is inserted south of the jet at the initial time. ET occurs in a wavy upper-level flow while baroclinic surface systems are still weak. The characteristic direct impact of ET on the midlatitude flow is the formation of a distinct jet streak and the amplification of a ridge–trough couplet in the adjacent downstream region. The subsequent rapid cyclogenesis downstream is a direct consequence of these upper-level flow modifications. This faster and stronger development constitutes the amplification of the leading edge of downstream development. Both the upper-level wave pattern and the surface development are subsequently amplified in the region further downstream. The formation of the ridge adjacent to the intensified downstream cyclone is analyzed in detail to elucidate the next stage in the downstream dispersion of the ET impact. Ridge-building in the ET scenario exhibits characteristics distinct from those in the life-cycle experiment. Wave breaking, feedback from the modified low-level frontal structure and diabatic processes all contribute to the high-amplitude wave pattern downstream of ET. The downstream impact of ET is highly sensitive to the initial storm location and intensity. The considerable amplification of the leading edge found in the reference experiment is the most widespread and rapidly propagating impact. We thus speculate that this leading edge represents an optimal location of the midlatitude circulation, where ET can lead to the most significant impact on the downstream flow. Copyright © 2010 Royal Meteorological Society