Heat And Freshwater Controlling Processes On The Northern Gulf Of Alaska Shelf

Thesis (Ph.D.) University of Alaska Fairbanks, 2009We examined conditions and processes that control the distribution of heat and freshwater on the northern Gulf of Alaska (GOA) shelf. Cross-shelf heat gradients are weak throughout the year, while salinity gradients are substantial due to the impact of coastal freshwater runoff. Outer shelf water properties are influenced by large anticyclonic eddies, while the inner and middle shelves may be regulated by wind and freshwater runoff dynamics around the Alaska Coastal Current (ACC). On the outer shelf, anticyclonic eddies propagate from the eastern GOA southwestward along the continental slope, where they favor on-shelf (off-shelf) transport of saline and nutrient-rich (fresh and iron-rich) waters Certain along-shelf locations are identified where low-salinity coastal waters are found near the shelfbreak within reach of eddies and may be regions of enhanced cross-shelf freshwater transport. The eddies have lifetimes of ~5 years and increase in size and sea level anomaly west of the Seward Line, which implies more vigorous eddy cross-shelf exchange in the northwestern GOA. By comparison, on the inner shelf the heat and freshwater distribution is dominated by large coastal river runoff, which forces the ACC and controls the vertical distribution of temperatures through stratification. In May 2007, the coastal GOA revealed some of the lowest ocean temperatures since the early 1970s, initiated by strong atmospheric cooling and reduced coastal runoff in November 2006. Stepwise regression shows that 81% of the variability of deep temperatures is explained by salinity stratification and air-sea heat fluxes. Weak baroclinic flow in May 2007 likely aided the cooling through reduced along-shore heat transport. A more detailed examination of heat transport indicated that along-shore heat flux convergence in the ACC may re-supply 10-35% of the heat removed by air-sea fluxes throughout the coastal GOA cooling season, while the annual mean cross-shore heat flux convergence is insignificant. Spatial gradients show increasing heat fluxes from off- to on-shore and from east to west. The cross-shore gradients result from wind speed gradients due to ageostrophic near-shore wind jets near coastal mountains, while the along-shore gradients result from larger-scale pressure systems. While the ACC advects coastal freshwater around the GOA shelf its waters are subjected to disproportional heat loss west of the Seward Line

The impact of tides on mixing and freshwater export in the Laptev Sea

The vast and shallow Laptev Sea shelf is seasonally ice covered and receives large amounts of freshwater runoff from the Lena River. This shelf is an important export region for sea ice and freshwater to the Arctic basin, and features strong vertical and horizontal gradients which separate the saline basin waters from the fresh coastal waters. Processes promoting shear instabilities and diapycnal mixing are therefore of interest for physical and biogeochemical properties. The Laptev Sea shelf features considerable shear in under-ice currents largely dominated by the baroclinicity in semidiurnal tides. We present an investigation into semidiurnal tides based on year-round oceanographic moorings from different locations across the Laptev Sea shelf. Harmonic analysis of ADCP records shows a strong depth-dependence in the clockwise tidal currents that can be linked to stratification and further shows large spatial and seasonal variability of tides. Total current magnitudes are stronger on the outer than on the inner shelf, and tides overall explain >80% of the current’s variance throughout the year. On the inner shelf, tides play a comparatively greater role under sea ice (40-70%) than during open water periods (20-50%) when wind-induced inertial motions dominate. The ADCP records are further complemented by two cross-shelf microstructure transects which show episodes of intense turbulent kinetic energy dissipation in the pycnocline following the alignment of the semidiurnally rotating shear-vector and the surface forcing, hence underlining the potential influence of tides on diapycnal mixing. Our results highlight the potential of tides to vertically transport freshwater, heat and nutrients, and provide some first order insights into how the physical environment of this shelf may change with changing sea ice conditions

Baroclinic tides and their possible impact on bottom boundary layer evolution and vertical mixing in the Laptev Sea

3 consecutive years of moored ADCP and bottom temperature and salinity records at a ∼40 m deep location on the Laptev Sea shelf show strongly amplified internal tides with a period of ∼14 days during two highly stratified winters of 2009 and 2010, while no internal tides were identified during winter of 2008 when conditions were barotropic. The observations likely result from the combined effect of stratification induced by the Lena river freshwater plume (2009) or near-bottom inflow of denser waters (2010) with the proximity of the critical latitude of the M2 tide. The high velocity core found 10-15 m above the bottom during spring tide cycles appears to migrate upward in the water column, which suggests that the bottom boundary layer thickness increases due to shear instability beneath the pycnocline. This potentially has important consequences on the vertical distribution of heat and freshwater in the water column. In addition, measurements show that nutrients are available in near-bottom waters while depleted near the surface, hence upward mixing of nutrients by baroclinic tide-induced turbulence in winter may be a key mechanism for the success of the spring bloom. Currently, one-dimensional numerical experiments are performed to verify the suggested mechanisms and to further investigate the impact of baroclinic tides on bottom boundary layer evolution and water column stability in the Laptev Sea

Historical variability of the density stratification in the Laptev Sea

The Laptev Sea is a key region for sea ice formation and export to the inner Arctic. During winter, wind-ice-dynamics repeatedly produce open water areas (polynyas) with extensive heat fluxes, sea ice formation and water mass modification. In summer, the oceanic processes are strongly influenced by the enormous freshwater discharge of Siberian rivers. All this influences the density distribution. We therefore present a comprehensive analysis of the historical temperature and salinity data which is episodically available since around 1910. The variability of the density stratification is important for mixing across the water column

Známky a medaile k výročím Jednoty českých matematiků a fyziků

summary:The article describes the postal stamps and the memorial medals emitted at the occasion of the anniversaries of the Union of Czech Mathematicians and Physicists

Study of a Hybrid Propulsion System with Turbine Engine

Diplomová práce řeší návrh sériového hybridního pohonného sytému s turbohřídelovým motorem pro kategorii ultralehkých letounů. V práci je uveden přehled základních hybridních technologií, možná uspořádání a jejich výhody a nevýhody. Součástí je přehled realizovaných projektů hybridních a elektrických ultralehkých letounů. Samotný návrh hybridního systému zahrnuje výběr vhodného elektromotoru, akumulátorů, invertoru a dalších komponent. Podstatnou částí práce je předběžný návrh turbohřídelového motoru, včetně výpočtu tepelného oběhu a předběžného návrhu všech hlavních komponent, to je vstupního ústrojí, kompresoru, spalovací komory, turbíny a výstupního ústrojí. V závěru je porovnání navrženého hybridního pohonu s nejběžnějším spalovacím motorem Rotax.The diploma thesis solves a serial hybrid propulsion system with a turboshaft engine for category of ultralight aircrafts. The thesis gives an overview of basic hybrid technologies, possible arrangements and their advantages and disadvantages. It also includes an overview of implemented projects of hybrid and electric ultralight aircrafts. The design of the hybrid system itself includes the selection of a suitable electric motor, accumulators, inverter and the other components. An essential part of the thesis is a preliminary design of a turboshaft engine, including the calculation of cycle of a thermal engine and a preliminary design of all the main components, i.e. the input, compressor, combustion chamber, turbine and output. In conclusion there is a comparison of the proposed hybrid engine with the most common combustion engine Rotax

Assessing Cloud Segmentation in the Chromacity Diagram of All-Sky Images

Open Access.--This article belongs to the Special Issue Remote Sensing of CloudsAll-sky imaging systems are currently very popular. They are used in ground-based meteorological stations and as a crucial part of the weather monitors for autonomous robotic telescopes. Data from all-sky imaging cameras provide important information for controlling meteorological stations and telescopes, and they have specific characteristics different from widely-used imaging systems. A particularly promising and useful application of all-sky cameras is for remote sensing of cloud cover. Post-processing of the image data obtained from all-sky imaging cameras for automatic cloud detection and for cloud classification is a very demanding task. Accurate and rapid cloud detection can provide a good way to forecast weather events such as torrential rainfalls. However, the algorithms that are used must be specifically calibrated on data from the all-sky camera in order to set up an automatic cloud detection system. This paper presents an assessment of a modified k-means++ color-based segmentation algorithm specifically adjusted to the WILLIAM (WIde-field aLL-sky Image Analyzing Monitoring system) ground-based remote all-sky imaging system for cloud detection. The segmentation method is assessed in two different color-spaces (L*a*b and XYZ). Moreover, the proposed algorithm is tested on our public WMD database (WILLIAM Meteo Database) of annotated all-sky image data, which was created specifically for testing purposes. The WMD database is available for public use. In this paper, we present a comparison of selected color-spaces and assess their suitability for the cloud color segmentation based on all-sky images. In addition, we investigate the distribution of the segmented cloud phenomena present on the all-sky images based on the color-spaces channels. In the last part of this work, we propose and discuss the possible exploitation of the color-based k-means++ segmentation method as a preprocessing step towards cloud classification in all-sky images. © 2020 by the authors.This work was supported by the Grant Agency of the Czech Technical University in Prague, Grant No. SGS20/179/OHK3/3T/13, "Modern Optical Imaging Systems with Non-linear Point Spread Function and Advanced Algorithms for Image Data Processing", and by the Grant Agency of the Czech Republic, Grant No. 20-10907S, "Meteor clusters: An evidence for fragmentation of meteoroids in interplanetary space". Martin Blazek acknowledges funding under Fellowship Number PTA2016-13192-I and financial support from the State Agency for Research of the Spanish MCIUthrough the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709).Peer reviewe