Contrary to what one might expect after centuries of exploration, the charting of Neptune's Realm is not complete. It is still an ongoing process; indeed, there is an explosion in the amount and kind of new information now available. Up until the mid-1970s there was a delay of weeks, if not months, for the data acquired by mariners to reach cartographers. Then, more time was needed to collate the material, engrave new plates, print, and finally dispense charts to the waiting public. Now, satellites commonly circle over our globe, taking photographs and measuring many of the ocean's characteristics with special sensors. Much of this material is then organized and transformed by computer. Data that at one time was too transitory in nature to be disseminated in a timely fashion is instantly accessible electronically. Commercial shippers, commercial fishermen, research scientists, and recreational sailors all benefit from this new era in marine cartography. Note: all of the images in this section of the exhibition are reproduced here by the permission of their generating organizations. Note that those organizations d not necessarily archive their daily or monthly maps of sea surface temperature, etc. The URLs provided with each image point to the websites of the organizations and to their current images and not to the actual images reproduced. The URLs were correct as of 27 September 2000.
Throughout the centuries, mariners have used their knowledge of the ocean currents to plan speedy voyages. This body of knowledge grew slowly; dependent on many voyages over the years before general patterns were discerned. Today, Government agencies continuously monitor all the major cold water and warm water currents of the ocean with great accuracy. Each meander and eddy of the Gulf Stream is mapped almost as quickly as it develops. The procedure for defining these currents is no different than that used by Benjamin Franklin--differences in water temperature are measured. Today, however, instead of a thermometer being placed in the ocean to record temperature (as Franklin used), satellite infrared imagery and altimetry, combined with color enhancement. Chart T1, shows a portion of the Gulf Stream in the northwest quadrant of the Atlantic Ocean. Note how sharply the stream's north wall is confined, and how the banks of Cape Hatteras deflect the stream eastward. Nantucket Shoals and Georges Bank prevent any incursion of the Gulf Stream's warm water into the Gulf of Maine. Two warm water eddies, circulating clockwise, have broken off the main stream, and can be seen east of Chesapeake Bay and southeast of Cape Cod. The white blotches on the picture are the result of cloud cover preventing the sensing of temperature.
Chart T2 is of the same area covered by chart T1. Here, isobars of like temperature are depicted, and their numerical value given in degrees centigrade. Though lacking the drama of the color image, it nonetheless has its own beauty, and shows water temperature more precisely.
Canada Space Agency's Centre for Remote Sensing provided these two images of worldwide sea surface temperature, taken on January 13, 1999. It is particularly interesting that the internet site from which these pictures were obtained enables the viewer to participate as cartographer by selecting the parameters, and modifying the view.
From NOAA Coastwatch Northeast Node come images T5 and T5a of sea surface temperature in the Gulf of Maine. One can retrieve archived photos made daily for the past several years.
NOAA Coastwatch Northeast Node
Gulf of Maine Sea Surface Temperature, Thumbnails, 5 August 1999
original image: http://rossby.sr.unh.edu/test/thumbnails/aug99/aug05.html
Gulf of Maine Home Page (with archive)
The importance of changes in sea surface temperature was dramatically thrust into general public awareness by the 1997-1998 El Niño phenomenon. Oscillations in the locus of normal water temperatures in the equatorial Pacific, along with attendant changes in sea level height and wind patterns, are normal occurrences. Periodically, these changes become exaggerated; when they do they result in the condition called El Niño, characterized by unusually warm temperatures along the west coast of North America at the equator, and its corollary, La Niña, with abnormally cold temperatures there. When these anomalous conditions occur, climate systems around the entire globe are affected. In some areas the result is excessive rainfall with destructive flooding, in others, severe drought producing extensive forest fires. Commercial fishermen are also affected. Higher water temperatures reduce the supply of nutrients, which in turn, adversely affects marine ecosystems and fish populations. Normally, easterly tradewinds pile up warm surface water in the western part of the Pacific, resulting in a higher sea level there. On maps T6 and T6a the La Niña condition of cool water (indicated in blue and purple) off the coast of South America is clearly apparent. Satellite measurements that made these maps include the height and temperature of the sea, with incredible accuracy. The red areas are four inches above normal, and the purple areas seven inches below normal. Differences in height as seemingly insignificant as these nevertheless affect the heat temperature of surface waters.
El Nino/La Nina Watch
Measuring the Ocean's Height and Temperature
http://www.jpl.nasa.gov.elnino/ (has archive)
Image provided by TOPEX/Poseidon; Courtesy of NASA/JPL/California Institute of Technology
This shows predictions of sea surface temperature predictions for the equatorial Pacific made in December of 1998. In the top two panels, covering the months of March through August, cold water anomalies are predicted to dominate the scene. In the fall, however, they will begin to degrade and break up.
The latest sea surface temperature maps (T8) are available on line. Not only can one see what is happening at the moment, but through time-lapse animation loops it is possible to view transitory changes as they occur over the course of a year. The introduction of the element of time is a major revolution in cartography. Changes in temperature over the entire equatorial Pacific Ocean during the course of a year can currently be seen.
This composite map shows land temperatures, sea temperatures, ice fields at the poles, and cloud cover with their altitudes, in June 1996.
Every spring icebergs calve off the Greenland glacier and drift into the Labrador Sea where they are carried south along the coast of Labrador and Newfoundland by the Labrador Current. When they reach southeast Newfoundland their path splits to either side of the Grand Banks. At this point they are now far enough south to pose a serious threat to trans-oceanic shipping. Environment Canada Ice Centre, in conjunction with the U.S. Coast Guard International Ice Patrol, issues daily bulletins of the distribution and limits of icebergs between latitudes 40°N and 52°N, and longitudes 39°W and 57°W. Ships transiting this region report all sightings of icebergs, sea surface temperature, and weather. This information, along with satellite observations is used to produce charts of iceberg locations. Radar is an unreliable means of detecting icebergs. Since they are only composed of water, albeit in a solid state, radar signals tend to pass right through icebergs, rather than reflecting off them. With varying degrees of clarity, radar will pick up icebergs only if their surface is particularly corrugated or rough, or if a large amount of gravel is embedded in them. On March 6, 1998, solid sea ice extends northward from Bonavista Bay along the Newfoundland and Labrador shore. In open water, seaward of the ice, the number of icebergs is too great to show. No radar targets (ships) are present at this time. East of the Grand Banks there are ten icebergs and two smaller chunks of ice, called growlers. Unless icebergs become trapped in bays along the coast, or ground out on the edge of the banks, they continue moving southward with the Labrador Current until they encounter the Gulf Stream. There, they rapidly melt in the warm waters. On rare occasions, a few, either due to their great size, or the benefit of a particularly strong cold-water eddy, survive this barrier. In 1926, one iceberg reached to within 150 nautical miles of Bermuda, and icebergs have been sighted as far east as the Azores, 900 miles off the coast of Portugal.
Plotting where icebergs are likely to be in the near future is as important as knowing their position at the moment. Though ocean currents are the major force controlling their movement, strong winds, and wave motion also have an effect. To monitor these influences, buoys dropped from planes transmit via VHF radio a continuous record of the buoy's latitude and longitude, as well as a reading of the sea surface temperature. From this information detailed charts of the currents are made, allowing prediction of the most likely direction the icebergs will take. On both charts, note the weakness of currents directly over the shallow Grand Banks and Flemish Cap.
The topography of the ocean floor, and the flow of the Labrador Current with its interaction with the warm water of the Gulf Stream, are readily apparent in this chart of iceberg distribution in the North Atlantic. The turquoise line represents the 100 fathom curve.
The earth's seasons are produced by its annual orbit around the sun, while the rotation of the earth on its axis is responsible for the alternation of night and day; both influence wind regimes of the earth. Within the major general flow of air about the planet are numerous smaller masses of air, all in constant motion, both horizontally and vertically. This flow, at the same time creates changes in pressure, with concomitant low pressure and high pressure cells. Everything is in motion, everything flowing, trying to reach some state of equilibrium. Wind, pressure, temperature, and the amount of moisture in the air, are all interrelated and part of one large cyclical pattern. To understand that basic pattern is to understand its variations, which, in turn, is to understand weather. Charted here is one moment (midnight, GMT of Aug. 31, 1996) in this continually shifting pattern of pressure cells and winds. The Bermuda/Azores high pressure system that dominates weather patterns in the North Atlantic is clearly visible as a broad band extending from the Azores to Ireland. In its center the winds are light and variable. Winds move outward and clockwise from high pressure cells. Since Maine lies in the northwest quadrant of this system, the predominant summertime winds are from the southwest. Three migratory lows--a large, weak low just off the coast of Africa, another east of Puerto Rico, and a third, deeper low off the coast of Florida--will move westward with the Northeast Trade Winds. Another low of 998 millibars, southeast off the tip of Greenland, will move eastward with the prevailing Westerlies. In low pressure cells, winds move inward toward the center, and counterclockwise. Note the tightly compressed isobars between the low off Greenland and the Bermuda/Azores high, where winds reach 45 knots. Similar wind speeds are present around the low pressure cell east of Florida. On the Beaufort Wind Scale, 45 knots is Force 9, and called a strong gale, producing wave heights of 23 to 32 feet.
Ocean going vessels rely on hourly updated charts, and up to 7 day forecasts of global marine wind and wave conditions to help determine either the fastest route, or the route least costly in fuel consumption. Wave heights are graphically depicted by the use of color, and wave direction is shown with arrows. An intense low pressure cell east of Newfoundland dominates the Atlantic Ocean scene. Although the two apple-green areas south of Iceland, and west of Ireland, appear innocuous, nevertheless, with their wave heights of 15 feet, they would be of concern to fishing vessels.
The ultimate winds mariners in the North Atlantic must contend with are tropical cyclones, more commonly called hurricanes. Spawned in the warm equatorial waters, most often near the coast of Africa, they begin life as a weather disturbance--thunderstorms and strong surface winds. Fed by latent heat released from the water vapor, they are given a spin by the Coriolis force,* and when other conditions are proper they increase in strength. When the winds in these storms reach a constant speed of 74 miles per hour or more, they are termed hurricanes; their greatest wind speed can be too high to be recorded. Pushed westward by the flow of upper atmosphere winds (10-40,000 feet) cyclones eventually die out when they reach land, or when their path takes them into the colder waters of the North Atlantic, where they are robbed of their warm-water source of energy. Hurricanes at sea have the power to destroy any vessel unfortunate enough to come within its range; upon mainland coasts and islands, they leave a path of destruction and death. During the time of early exploration and colonization in the New World, hurricanes have been responsible for events that changed the emerging balance of power. Had the ability existed then to chart hurricanes and predict their path, France, instead of Spain, might have controlled the southeast coast of North America. In 1564, French Huguenots established Fort Caroline, near present-day Jacksonville, Florida--the first European settlement on the mainland of North America. Without warning, in September of the following year, a hurricane dispersed France's fleet and destroyed most of its vessels. This left the Spanish fleet, under command of Pedro Menedez de Avila, to capture Fort Caroline. And in 1640 a Dutch fleet would have survived to attack Havana, as originally planned, and Cuba would not have been relinquished to the Spaniards. The seventeen ships, with 2,000 troops of Lord Willoughby (Governor of Barbados) was almost totally lost to a hurricane in 1666, allowing the control of Guadeloupe to be taken by the French. *The Coriolis force is the deflection of a moving body relative to the earth's surface, produced by the earth's rotation. This causes winds in the northern hemisphere to be deflected to the right. This accounts for direction in circulation for both water and major air currents. On August 26th, 1996, three hurricanes at one time are seen proceeding toward the Caribbean; from west to east they are Edouard, showing the classical spiral-shaped cloud mass and a well defined eye, Fran, and Gustav. Hurricane Edouard started as a tropical wave in western Africa on Aug 17-18 with typical thunderstorms and squalls. Upon entering the Atlantic southeast of the Cape Verde Islands it increased in strength, and by noon (GMT) on August 22nd strengthened into a hurricane. Its highest wind speed, reported on August 28th was 163 MPH.
An active hurricane season in 1996 is evident by this tracking chart of all hurricanes for that year. Not all have their origin in the far eastern part of the North Atlantic; some begin life in the warm waters of the Carribean or the Gulf of Mexico.
Keeping well to the northeast of the Caribbean Islands, Edouard headed west until north of Hispaniola, then turned to take a more northerly course. The track of hurricane Edouard (T18), and its potential for landfall on the northeast coast of North America, were fully charted. The actual course taken by Edouard was fairly consistent with the predictions, thus allowing ships at sea to seek timely refuge. Though Edouard never touched the mainland coast, it came close enough to produce gusts of hurricane force at Nantucket, and unofficially, wind gusts of 80 MPH at Marthas Vinyard and 77 MPH on Cape Cod. By September 1st, Edouard was centered east of the Chesapeake (T18b). It was downgraded to a tropical storm two days later as it approached the coast of Nova Scotia, and finally expired when well east of Newfoundland. In the six days between August 26th and September 1st, Edouard traveled over 2,100 nautical miles.
NOAA, National Hurricane Center
Edouard Advisory #43, 1 September 1996
Probability that center of Edouard will pass within 75 statute miles during the 72 hours starting at 5AM EDT Sun Sept 1 1996
Hurricane Edouard, 1 September 1996
Three years later, Tropical Storm Dennis whose track is shown here in black, intensified to become a hurricane when it reached 71°W. The red track shows not only the predicted path of Dennis, but the indication that it will intensify to reach wind gusts of 123 MPH by August 28th. Compare this chart with the color enhanced satellite image (T19a) of Dennis, and the global weather chart (T22) produced by the University of Hawaii, all three downloaded from the Internet on August 25th.
Hurricane Mitch (T20) in 1998 was one of the deadliest in history, with wind speeds reaching a peak of 180 MPH. Over 9,000 lives were lost in Honduras and Nicaragua. In Honduras alone, 50% of the agricultural crop was wiped out, 70,000 houses destroyed or damaged, and 92 bridges made impassable, isolating communities and preventing aid from reaching them. The loss of life and extensive damage came not from the force of Mitch's winds, which were diminished once over land, but the very slow rate of movement as it hovered there. This produced 35.89 inches of rain, causing flash floods and mudslides. The image here was produced from data received from the Geostationary Operational Environmental Satellite-8 (GOES-8) and the Polar Orbiting Environmental Satellites (POES) NOAA-12 and NOAA-14.
After Mitch's destructive path through Honduras, Nicaragua, and the Yucatan (T21), it curved back toward the northeast and gained strength from the warm water of the Gulf of Mexico. Cutting across the southern tip of Florida, it generated five tornados, then re-entered the Atlantic and lost its strength. The track charted covers the period from October 22nd to November 5th.
This composite global view (T22) of temperature, visible cloud, and water vapor was produced by the University of Hawaii at Manoa, Department of Meteorology. Using infrared photographs received from a GOES satellite, the image is color enhanced to clearly distinguish temperatures of various features. Compare the colors of mid-range temperatures here, with those in the center of Hurricane Dennis on chart T18c; in the center of Dennis, temperatures are in the 167° to 176° Fahrenheit range. GOES satellites are geostationary, that is, they orbit the earth at the same speed as the earth's orbit, thus allowing the view to be kept constant.
Except for the position of the upper atmosphere jet streams (available on other web sites), everything the mariner, or landsman, needs to forecast the weather is present on chart T23, produced by the University of Hawaii. All the elements (temperature, visible cloud, and water vapor) are rendered in a grey scale, instead of color, on the left side of the chart so as not to obscure other information. Barometric pressure--with isobars (e.g. 1020) and identification of high (H) and low (L) pressure cells, wind direction and speeds, a latitude and longitude grid, and outlines of land, all come together on this composite chart. Hurricane Dennis is visible north of Hispaniola at 23.1°N, 72.8°W; Hurricane Cindy is farther east at 18.6°N, 45.3°W; and the more loosely organized Tropical Storm is Emily at 8°N, 53°W. With all the information now available, there is still an element of unpredictability in the science of meteorology. No better advice can be given today than that of the Greek philosopher, Aratus Solensis, in his treatise on weather signs written 2300 years ago. "Make light of none of the warnings. It is a good rule to look for sign confirming sign. When two point the same way, forecast with hope. When three point the same way, forecast with confidence."