Gulf Stream trajectories measured with free-drifting buoys

Also published as: Journal of Physical Oceanography 11 (1981): 999-1010During 1975-78, 35 free-drifting buoys measured surface currents in the Gulf Stream region. The buoy trajectories trace numerous paths of the Stream and show that the Stream is strongly influenced by the New England Seamounts. This influence is manifested as 1) a quasi-permanent, 100 km, southeastward deflection of the Stream and the frequent occurrence of a ring meander over the seamounts; 2) large-amplitude meanders beginning at the seamounts and extending eastward; and 3) small, 20 km diameter eddies which appear to be generated locally by individual seamounts. A chart of the mean temperature field at a depth of 450 m agrees with several of the patterns seen in the buoy trajectories. West of the seamounts, the mean path of the Gulf Stream is eastward; over the seamounts, the path turns sharply northeastward and the isotherms in the Stream abruptly diverge.Prepared for the Office of Naval Research under Contract N000 14-74-C- 0262; NR 083-004 and for the National Science Foundation under Grant OCE 78-18017

Upwind dynamic soaring of albatrosses and UAVs

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Progress in Oceanography 130 (2015): 146-156, doi:10.1016/j.pocean.2014.11.002.Albatrosses have been observed to soar in an upwind direction using what is called here an upwind mode of dynamic soaring. The upwind mode is modeled using the dynamics of a two-layer Rayleigh cycle in which the lower layer has zero velocity and the upper layer has a uniform wind speed of W. The upwind mode consists of a climb across the wind-shear layer headed upwind, a 90° turn and descent across the wind- shear layer perpendicular to the wind, followed by a 90° turn into the wind. The increase of airspeed gained from crossing the wind-shear layer headed upwind is balanced by the decrease of airspeed caused by drag. Results show that a wandering albatross can soar over the ocean in an upwind direction at a mean speed of 8.4 m/s in a 3.6 m/s wind, which is the minimum wind speed necessary for sustained dynamic soaring. The main result is that an albatross can soar upwind much faster that the wind speed. The upwind dynamic soaring mode of a possible robotic albatross UAV (Unmanned Aerial Vehicle) is also modeled using a Rayleigh cycle. Maximum possible airspeeds are approximately equal to 9.5 times the wind speed of the upper layer. In a wind of 10 m/s, the maximum possible upwind (56 m/s) and across-wind (61 m/s) components of UAV velocity over the ocean result in a diagonal upwind velocity of 83 m/s. In sufficient wind, a UAV could, in principle, use fast diagonal speeds to rapidly survey large areas of the ocean surface and the marine boundary layer. Limitations to achieving such fast travel velocity are discussed and suggestions are made for further studies.Financial support was provided by the F. Livermore Trust and Woods Hole Oceanographic Institution emeritus funds

Da Vinci’s observations of soaring birds

Author Posting. © American Institute of Physics, 2017. This article is posted here by permission of American Institute of Physics for personal use, not for redistribution. The definitive version was published in Physics Today 70, no. 11 (2017): 78, doi:10.1063/PT.3.3773.With only a minimal flapping, the wandering albatross can circumnavigate the globe. During its peregrinations over the Southern Ocean, the seabird exploits wind shear—the gradient of wind speed—to extract energy for its sustained flight. That same maneuver, called dynamic soaring, is used by pilots of radio-controlled gliders. In flights that take advantage of the shear associated with wind blowing over mountain ridges, the gliders reach air speeds of an astonishing 500 mph. Engineers are currently developing autonomous unmanned vehicles that can use the technique to supplement different sources of energy for sustained flight over the oceans. Possible applications include environmental monitoring, surveillance, and search and rescue.2018-11-0

Agulhas leakage into the Atlantic estimated with subsurface floats and surface drifters

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 54 (2007): 1361-1389, doi:10.1016/j.dsr.2007.04.010.Surface drifters and subsurface floats drifting at depths near 800 m were used to study the pathways of warm salty Indian Ocean water leaking into the South Atlantic that is a component of the upper limb of the Atlantic meridional overturning circulation. Four drifters and 5 floats drifted from the Agulhas Current directly into the Benguela Current. Others looped for various amounts of time in Agulhas rings and cyclones, which translated westward into the Atlantic contributing a large part of Indian Ocean leakage. Agulhas rings translated into the Benguela Current where they slowly decayed. Some large blob-like Agulhas rings with irregular shapes were found in the southeastern Cape Basin. Drifter trajectories suggest these rings become more circular with time eventually evolving into the circular rings observed west of the Walvis Ridge. Agulhas cyclones, which form on the north side of the Agulhas south of Africa, translated southwestward (to 6°E) and contributed water to the southern Cape Basin. A new discovery is a westward extension from the mean Agulhas retroflection measured by westward drifting floats near 41ºS out to at least 5ºW with some floats as far west as 25ºW. The Agulhas extension appears to split the South Atlantic Current into two branches and to transport Agulhas water westward where it is mixed and blended with eastward-flowing water from the western Atlantic. The blended mixture flows northeastward in the northern branch of the South Atlantic Current and into the Benguela Current. Agulhas leakage transport was estimated from drifters and floats to be at least 15 Sv in the upper 1,000 m, which is equivalent to the transport of the upper layer meridional overturning circulation. It is suggested that the major component of the upper layer overturning circulation in the Atlantic is Agulhas leakage.Funds for this research were provided by National Science Foundation grants OCE-0236654 to the Woods Hole Oceanographic Institution and OCE-0236527 to the Woods Hole Research Center

High-speed dynamic soaring

Author Posting. © B2Streamlines.com, 2012. This article is posted here by permission of B2Streamlines.com for personal use, not for redistribution. The definitive version was published in R/C Soaring Digest 29, no. 4 (2012): 36-49.Dynamic soaring uses the gradient of wind velocity (wind shear) to gain energy for energy-neutral flight. Recently, pilots of radiocontrolled gliders have exploited the wind shear associated with fast winds blowing over mountain ridges to achieve very fast speeds, reaching a record of 487 mph in January 2012. A relatively simple two-layer model of dynamic soaring was developed to investigate factors that enable such fast speeds. The optimum period and diameter of a glider circling across a thin wind-shear layer predict maximum glider airspeed to be around 10 times the wind speed of the upper layer (assuming a maximum lift/drag of around 30). The optimum circling period can be small ~1.2 seconds in fast dynamic soaring at 500 mph, which is difficult to fly in practice and results in very large load factors ~100 times gravity. Adding ballast increases the optimum circling period toward flyable circling periods of 2-3 seconds. However, adding ballast increases stall speed and the difficulty of landing without damage. The compressibility of air and the decreasing optimum circling period with fast speeds suggest that record glider speeds will probably not increase as fast as they have during the last few years and will probably level out below a speed of 600 mph

High-speed robotic albatross : unmanned aerial vehicle powered by dynamic soaring

Author Posting. © B2Streamlines.com, 2012. This article is posted here by permission of B2Streamlines.com for personal use, not for redistribution. The definitive version was published in R/C Soaring Digest 29, no. 6 (2012): 4-18.Wandering albatrosses exploit the vertical gradient of wind velocity (wind shear) above the ocean to gain energy for long distance dynamic soaring with a typical airspeed of 36 mph. In principle, albatrosses could soar much faster than this in sufficient wind, but the limited strength of their wings prevents a much faster airspeed. Recently, pilots of radio-controlled (RC) gliders have exploited the wind shear associated with winds blowing over mountain ridges to achieve very fast glider speeds, reaching a record of 498 mph in March 2012. A relatively simple two-layer model of dynamic soaring predicts maximum glider airspeed to be around 10 times the wind speed of the upper layer (assuming zero wind speed in the lower layer). This indicates that a glider could soar with an airspeed of around 200 mph in a wind speed of 20 mph, much faster than an albatross. It is proposed that recent highperformance RC gliders and their pilots’ expertise could be used to develop a high-speed robotic albatross UAV (Unmanned Aerial Vehicle), which could soar over the ocean like an albatross, but much faster than the bird. This UAV could be used for various purposes such as surveillance, search and rescue, and environmental monitoring. A first step is for pilots of RC gliders to demonstrate high-speed dynamic soaring over the ocean in realistic winds and waves

Nantucket whalers and the Franklin-Folger chart of the Gulf Stream

Author Posting. © The Author(s), 2018. This article is posted here by permission of Nantucket Historical Association for personal use, not for redistribution. The definitive version was published in Historic Nantucket 68, no. 1 (2018): 17-24.Also includes: The search for the “lost” Franklin-Folger chart by Philip L. Richardso

Surface velocity in the equatorial oceans (20N-20S) calculated from historical ship drifts

Ship drift velocity observations were used to calculate and plot monthly mean and yearly mean velocities in 2° latitude by 5° longitude boxes for the Atlantic, Pacific, and Indian Oceans. The vector maps shown here provide a visualization of the mean and seasonally varying currents.Funding was provided by the National Science Foundation through grant Number OCE 87-16509

The Impact of Land Fragmentation on Beef Cattle Inventory

Many groups have discussed with alarm the impact of agricultural land conversion to non-agricultural uses. This research indicates little evidence that beef cow inventory has been negatively affected by land fragmentation. Average acres per transaction, total transactions, or a fragmentation index did not have an important effect on cattle inventory.Land Economics/Use, Livestock Production/Industries,

Reconstructing Columbus’s first transatlantic track and landfall using climatological winds and currents

An article in the November 1986 National Geographic magazine examined the question of Columbus's first landfall in the Americas. The author, Luis Marden, was the first to quantitatively include the effects of the winds and currents in reconstructing the transoceanic portion of the voyage. There seemed, however, to be two major weaknesses in his analysis. First, the leeway effect on the ship by the wind was ignored for that portion of the voyage west of 40W, the whole second half of the voyage. Second, currents from pilot charts were used with the corresponding speed determined by the prevailing current. We sought to reanalyze the track using the leeway effect for the whole transatlantic track and using more appropriate average vector velocities of the current. Using climatological winds and currents we found the island of San Salvador (Watling Island) to be the most likely site of the first landfall of Columbus. This paper discusses the effects of wind, current, leeway, and magnetic variation on the determination of the landfall.Funding was provided in part by the National Science Foundation under grant Number DCE 85-14885