Sea breeze

About: Sea breeze is a research topic. Over the lifetime, 2544 publications have been published within this topic receiving 55651 citations.

Shoreline Processes near Barrow, Alaska: A Comparison of the Normal and the Catastrophic

Abstract: The normal average yearly net transport of sediment along the Alaska coast west of Pt Barrow to the NE is 10,000 yd³, to the east of Barrow, 9,500 yd³. An Oct 1963 storm with gusts of up to 75 mi/hr, over an ice-free ocean, produced 10-ft waves and a storm surge of 11-12 ft; it moved >200,000 yd³ sediment, caused coastal flooding and >$3 million damage. If climate is warming, such storms can be expected more frequently. The normal daily tide at Barrow is about 6 in (except in storm) and an additional monthly variation of about 5 in. Storm tides of several feet are caused by rise of sea level under a low pressure area and by onshore wind. Ice damps waves and wave-generated currents. Freeze-up occurs 2 Sept- 19 Dec, breakup 17-23 July. Even when considered open and navigable, the water may have scattered ice near Barrow and sea ice a few mi offshore, which would act as a damper of waves. The northern Alaska coast is one of transgression, with the recent dominant action of coastal submergence. The gravel along beaches cannot be replaced by natural processes without a large amount of erosion. It should be left in place as protection.

Numerical modelling of the offshore extent of sea breezes

Abstract: Two- and three-dimensional versions of a nonlinear atmospheric model were used to investigate environmental controls on the offshore influence of sea-breeze circulations. The temperature of the water surface relative to the atmospheric temperature had a small effect when the water was colder than the overlying air, and a greater effect when the water temperature was high enough to create convective mixing in the planetary boundary layer over the water. Ambient thermal stratification, including elevated inversions with thermal stratification similar to trade wind inversions, had a small influence. The predicted offshore extent of the sea breeze was substantially affected by latitude. The effects of both ambient stratification and latitude were generally consistent with predictions of linear theory. Prevailing synoptic winds were also found to have a significant effect on the sea breeze offshore, with offshore influence greatly suppressed by onshore large-scale flow. Curvature of the coastline produces slightly stronger winds offshore for a concave coast than for a convex coast. The subsidence offshore also extends further over the water for a concave coast than for a convex coast. The model predictions were compared with previous investigations which used linear theory. It was found that the present results agreed with the linear theory of R. Rotunno with regard to the effects of latitude and ambient thermal stability. Linear theory is less suitable for explaining the effects of water temperature, owing to the simplified treatment of turbulent exchange necessary for a tractable linear model.

Tropical Rainfall Measuring Mission observation and regional model study of precipitation diurnal cycle in the New Guinean region

Abstract: [1] The diurnal cycle of precipitation in the New Guinean region is studied on the basis of satellite observations from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) measurements and regional atmospheric model simulations. The study focuses on the effects of both the land-sea breeze and the orographic forcing on the diurnal evolution of precipitation during the rainy season (January–March) in the region. The 7-year TRMM PR data composite reveals several distinct features of the precipitation diurnal cycle in the region. Precipitation bands develop in the inland coastal region in the late morning to early afternoon and migrate inland from both northeast and southwest sides of the New Guinean Island following the inland penetration of the sea-breeze fronts. A separate convective rainband develops over the central mountain ridge in the early afternoon as a result of the development of the upslope winds due to the elevated surface warming over the mountain in the morning hours. This mountain ridge rainband intensifies and becomes the dominant rainband as the coastal rainbands associated with the sea-breeze fronts weaken during the late afternoon and the early evening. In the midnight to the early morning the rainband over the mountaintop weakens as downslope winds develop and splits into two rainbands, propagating away from the mountain ridge, one to the north and one to the south, and weakens over the lowland some distance away from the coasts. Meanwhile a coastal rainband develops offshore on each side of the island in the late evening to midnight and remains strong through early morning before it migrates offshore. As a result, the rainfall rate peaks in the late afternoon to early evening in most land areas except for in the lowland regions between the coastlines and the mountain where the rainfall rate peaks during the midnight, while the rainfall rate peaks in the late evening to early morning in most coastal regions offshore. The distribution of the diurnal amplitude shows two maxima: one over the mountains and the other in the coastal regions offshore. Convective rainfall rate peaks in the late afternoon while stratiform rainfall rate peaks in the midnight to early morning. The latter dominates the large diurnal amplitude over the mountain areas in the early morning. The above broad features are simulated reasonably well in a control experiment with a high-resolution regional atmospheric model. A sensitivity experiment with the terrain removed is conducted to elucidate the role of orographic forcing in the diurnal evolution of both the local circulation and rainfall patterns. The results show that the orographic forcing affects the diurnal precipitation through three major processes. First, the orography increases the moisture convergence at low levels by blocking and deflecting the mean flow. Second, the upslope winds help initiate convection in the afternoon at the mountaintop. Finally, the deep convection over the mountain acts as a source of propagating gravity waves, which help initiate rainbands in the coastal regions offshore in the late evening to early morning. Implication of the results is discussed.

Floating Offshore Wind Turbines: Responses in a Seastate Pareto Optimal Designs and Economic Assessment

Abstract: Wind is the fastest growing renewable energy source, increasing at an annual rate of 25% with a worldwide installed capacity of 74 GW in 2007. The vast majority of wind power is generated from onshore wind farms. Their growth is however limited by the lack of inexpensive land near major population centers and the visual pollution caused by large wind turbines. Wind energy generated from offshore wind farms is the next frontier. Large sea areas with stronger and steadier winds are available for wind farm development and 5MW wind turbine towers located 20 miles from the coastline are invisible. Current offshore wind turbines are supported by monopoles driven into the seafloor at coastal sites a few miles from shore and in water depths of 10–15m. The primary impediment to their growth is visual pollution and the prohibitive cost of seafloor mounted monopoles in larger water depths. This paper presents a fully coupled dynamic analysis of floating wind turbines that enables a parametric design study of floating wind turbine concepts and mooring systems. Pareto optimal designs are presented that possess a favorable combination of nacelle acceleration, mooring system tension and displacement of the floating structure supporting a five megawatt wind turbine. All concepts are selected so that they float stably while in tow to the offshore wind farm site and prior to their connection to the mooring system. A fully coupled dynamic analysis is carried out of the wind turbine, floater and mooring system in wind and a sea state based on standard computer programs used by the offshore and wind industries. The results of the parametric study are designs that show Pareto fronts for mean square acceleration of the turbine versus key cost drivers for the offshore structure that include the weight of the floating structure and the static plus dynamic mooring line tension. Pareto optimal structures are generally either a narrow deep drafted spar, or a shallow drafted barge ballasted with concrete. The mooring systems include both tension leg and catenary mooring systems. In some of the designs, the RMS acceleration of the wind turbine nacelle can be as low as 0.03 g in a sea state with a significant wave height of ten meters and water depths of up to 200 meters. These structures meet design requirements while possessing a favorable combination of nacelle accleration, total mooring system tension and weight of the floating structure. Their economic assessment is also discussed drawing upon a recent financial analysis of a proposed offshore wind farm.Copyright © 2008 by ASME