Since the 1560s, Spanish ships have taken advantage of the North Pacific westerlies and northeast trade winds (Deblieu 51). The Acapulco Galleon leaves Acapulco with Spanish silver and gold, and takes the trade wind route to the Philippines. Then the Manila Galleon leaves Manila with Chinese silk, heads north along the coast of Japan (taking advantage of the northward Kuroshio current) and turns east as soon as it encounters the westerlies, making landfall off the coast of Upper or Lower California, and returns to Acapulco on the southward California current.
The southeast trades of the South Pacific were used, much earlier, by the ancient Polynesians. Their ships sailed best on a "reaching" course-one with the wind off the beam, and they expanded northeast from southeast Asia and Australia. (Watson 91).
Finally, Norse exploration of Iceland and Greenland was made possible by their exploitation of the polar easterlies. (Deblieu 50).
The desired routes are described in sailing directions composed by governments and trading companies. While these are nominally kept secret, the precautions are ineffectual. For example, the Dutch learned the Portuguese monsoon routes because the Portuguese allowed Dutchmen to serve as sailors on their ships.
Wind Meteorology in Grantville Literature
The Grantville encyclopedias and school earth science textbooks will put this information into perspective. That is, they will explain the physical mechanisms that create the westerlies, the trade winds, etc. However, they aren't likely to provide detailed information about the spatial extent of these prevailing wind regions, the average wind speed, or the steadiness of the wind direction.
Monsoon systems are characterized by prevailing wind patterns that reverse twice a year. There are monsoon systems in both the Indian and Pacific Oceans. EB2002CD/"Indian Ocean" explains that the monsoon zone extends north from 10° S, and that in May-October it experiences the wet southwest monsoon with wind speeds up to 24 knots (28 miles per hour), and in November-April the dry northeast monsoon. The term southwest monsoon is something of a misnomer as there's a west wind over the Arabian Sea and a south wind over the Bay of Bengal. The monsoon season begins over the Arabian Sea first. Also note that during the changeovers (October and March-May), there may be "desultory breezes with no strong prevailing patterns" (EB2002CD/"India," "Climate").
EB2002CD/"Monsoon" warns that "At the poleward limit of a monsoon system, the winds shift sharply. In India, for example, the monsoon blows from the southwest in July-August, while north of India the winds are from the east. Over northern Australia the monsoon comes from the northwest in January-February, and at the southern limit the winds again become easterly."
Another monsoon system affects both southeast Asia and northern Australia. Its northern limit is about 25° N. In South China and the Philippines, the trade winds prevail in October-April and southwest monsoon winds in May-September. The summer monsoon is stronger over Vietnam and Thailand, but monsoon winds are weak over Indonesia. Northern Australia experiences northwest summer (November-April) monsoons and winter (May-September) southeast monsoons, but even in summer there are periods of southeast trade winds. (EB2002CD/"Climate").
Another essay notes that monsoon winds of the East China Sea blow from the southeast in summer and from the north in winter (EB2002CD/"China Sea"), but says nothing about their strength. Even less information is given about the monsoons of the South China Sea; essentially just that they exist.
In the Sea of Japan, further north, we are informed that the northwest monsoon prevails December (or September) to March, and the south(east) monsoon in summer (or, more broadly, mid-April to early September). (EB2002CD/"Japan, Sea of"; "Japan").
There are also small monsoonal systems in West Africa and Central America. (EB2002CD/"Climate").
EB11/"Trade Winds" says, "The area of their greatest influence may be taken to extend from about 3° to 35° N., and from the equator to 28° S., though these belts are actually somewhat narrower at any given season, as the whole system of surface winds over the globe moves north and south following the sun."
EB2002CD/"Wind" (my surrogate for the EB2000) says that the trade wind is a "very steady wind that blows westward and toward the equator from the subtropical high-pressure belts at latitudes near 30° N and 30° S toward the intertropical convergence zone. It is stronger and more consistent over the oceans than over land and produces fairly clear skies that make trade-wind islands popular tourist resorts. Its average speed is about 5 to 6 m per second (11 to 13 miles per hour). "
Some further information is provided in EB2002CD/"Pacific Ocean: Climate": "The obliquity of the ecliptic . . . limits the seasonal shifting of the Pacific trade-wind belts to about 5° of latitude. The easterly winds . . . tend to be strongest in the eastern Pacific. . . . The average wind speed of the Pacific trade winds is about 13 knots (15 miles per hour). The weather in the trade-wind belts is normally fine, with relatively little cloud cover. . . ."
There is also a southeast trade wind zone in the Indian Ocean, between 10° and 30° S; the winds are strongest June-September. EB2002CD/"Indian Ocean."
EB11/"Climate and Climatology" comments that the westerlies "are much less regular than the trades. They vary greatly in velocity in different regions and in different seasons, and are stronger in winter than in summer." Note that the southern hemisphere westerlies are more reliable: " Between latitudes 40° and 60° S the " brave west winds " blow with a constancy and velocity found in the northern hemisphere only on the oceans, and then in a modified form."
To this, EB2002CD/"Atlantic Ocean" adds, "the prevailing westerlies of mid-latitudes, . . . are found to be half as strong and about 10° farther north in latitude over the North Atlantic in summer than in winter. "
It continues, "In latitudes 15° to 30° N the North Atlantic is characterized by prevailing high pressure with an attendant lack of intense storms and severe weather." This, of course, is a reference to the Variables (Horse Latitudes).
The essay continues, "Over the South Atlantic the belt of prevailing westerlies extends from about 40° S almost to Antarctica, and the South Atlantic high-pressure area is centered around 30° S. . . ."
With regard to wind conditions in the polar regions, EB2002CD/"Atmospheric Circulation" informs us that "Poleward of 60° N and 60° S, the winds generally blow westward and equatorward as the polar easterlies. In the northern polar regions, where water and land are interspersed, the polar easterlies give way in summer to variable winds."
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The North Marion High School in Mannington has the McGraw-Hill Encyclopedia of Science and Technology (1977)(McGHEST); I checked the 2002 edition and hopefully the relevant points are the same. McGHEST/"Atmosphere" provides a formula for the geostrophic wind (the wind resulting from the balancing of pressure gradient force and Coriolis force; this is dominant above about one kilometer, except near the equator. It also explains how the north-south temperature difference can cause winds aloft to be more westerly than those at the surface ("thermal wind"). McGHEST/"Wind" states that the trade winds run from 30° equatorward, and the westerlies from 30-35° to 55-60°. In winter, it says that these have mean speeds of 15 knots, and in summer, half that. And it says that these systems move poleward in summer and equatorward in winter. McGHEST/"Wind Power" provides a formula for the power of the wind.