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METEOROLOGY FOR MARINERS

224

Extreme Eastern Part of the Ocean

The currents here, including those of the Arafura Sca, are not wcll known, owing to the scarcity of observations. Eastwards of Christmas Island, between the parallcls of about io°s and I2°s, there is a prcdominance of wcstcriy sets during most of the ycar and they form the most casterly part of the Eąuatorial Current.

NORTH PACIFIC OCEAN

Main Circulation

The main circulation of the North Pacific resemblcs that of the North Atlantic. Obscrvations are inadcquatc to give detailed information about the currents ovcr largc parts of this ocean, owing to its size and the limited shipping tracks. This especially applies to the middlc longitudcs, both ncar the equator and in the variable currcnt region further north.

The Southern part of the main circulation is formed by the west-going North Equatorial Current. Immediatcly south of this the Equatorial Counter-current flows eastwards across the ocean, but its limits are not cxactly known and they may be subjcct to some scasonal variation. During the latter half of the year the Southern limit appears to be nearer the cquator in the west tlian in central or eastern longitudes. Over most of the ocean the counter-current is usually found between latitudes 4⁰ or 5°n and 8° or io°n. The South Equatorial Current, the northern limit of which reaches to about latitudc 4⁰ or 5°n, is described under the South Pacific.

The North Equatorial Current has no defined northern limit. This west-going current lessens in strength as the prcdominance of trade winds deereases, until it is lost in the variable current region lying to the northwards. The latitude to which some predominance of westerly currcnt extends appears to vary with the scason. In mid ocean it is between latitude 20°n and 24°n in winter and in about latitudc 30°n in the late summer or autumn.

The Equatorial Counter-current flows eastwards throughout the ycar across the wholc ocean. During March to Novcmber, this counter-current is formed by the rccurving of the South Equatorial Current northwards and part of the North Equatorial Current southwards down the east coasts of the Philippines. In Decembcr to February the North Equatorial Current is the only source of the counter-current. During these months the South Equatorial Current, north of the equator, turns south in about longitudes i40°E to I50°e and finally south-eastwards, and thus makes no contribution to the counter-current. In all seasons part of the North Equatorial Currcnt enters the Celebes Sea and emerges in a north-eastcrly dircction to join the counter-current. The counter-current appears to be strongest in its most westerly portion, from northwards of Halmahera (between New Guinea and Celebes) to about longitudc I45°e.

To continue the main circulation, a considerablc part of the water from the North Equatorial Current turns north-eastwards when east of Luzon and flows up the east coast of Taiwan to form the Kuro Shio, a warm current corrc-sponding to the Gulf Strcam of the North Atlantic. Southwards of the Japanese Islands the Kuro Shio flows north-eastwards. This current then fans out to form the North Pacific Current, which sets eastwards across the ocean toward the North American coast. It is joined by cold water from the Bering Sca, flowing down the east coast of Kamchatka and turning south-east and then east.

CURRENT CIRCULATIONS OF THE OCE ANS    225

The whole forms a broad belt of variable current with a predominance of eastcrly sets, filling most of the arca between latitudes 35°n and 50°n, across the ocean. The coldcr part of this is known as the Aleutian Current and in the middlc longitudes of the ocean is found northwards of about latitudc 45°n.

Water fans out to the south-cast and south from the Southern part of the North Pacific Current, and passes into the central region of variablc currents. Eastwards of about longitude i5o°w the remainder of the North Pacific Current and the bulk of the Aleutian Currcnt tum southwards and south-westwards and finally merge with the North Equatorial Current. Near the coast this southward current is called the California Current.

The California Current docs not actually mcct the coast; from November to February a rclatively cool counter-current, known as the Davidson Current, runs northwards, elose inshorc, to at least latitude 48°n. During the rest of the year the space between the California Current and the coast is filled by irregular current eddies.

In the extreme eastern part of the Equatorial Counter-current, seasonal variations occur off the Central American coast and numerous eddies are formed, which scem to vary from year to year. In most months the counter-current will be met between latitudes 5°n and io°N, and it generally turns north and north-west along the Central American coast, finally to enter the North Equatorial Current. Early in the year part of the counter-current branches south and enters the South Pacific.

Associated Regions

Northern Part of the Ocean

The Bering Sea currents are not wcll known, but therc is a counter-clockwise circulation round the coasts, northwards on the east and southwards on the west side. The cold southward current flows along the east coast of Kamchatka as the Kamchatka Current, and then past the Kurii Islands whcrc it is known as the Oya Shio.¹ The Oya Shio continues along the east coast of the main Japanese island of Honshu, until it meets the northern edge of the Kuro Shio in about latitude 36°n. The Oya Shio thus corresponds to the Labrador Current of the North Atlantic. (See Chaptcr 8—Yisibility—north-west Pacific, for the frequency of fog in this arca.) It is joincd by water emerging through Tsugaru Kaikyó. Water fans out south-east and east all along the course of the current, from Kamchatka southwards. The rcsultant easterly current flows parallel and adjacent to the North Pacific Current and forms the Aleutian Current. The morę northerly part of this, as it approaches the American coast, sets north-cast and then north-west past Queen Charlotte Islands and along the coast of south-cast Alaska. This is the Alaska Current. It follows the Gulf of Alaska coastline to set to the westwards across the head of the gulf and then along the south coasts of the Aleutian Islands. West of longitude i55°w to i6o°w, some water recurvcs from the Alaska Current to the south and south-cast and rcjoins the east-going Aleutian Current; the remainder recurves northwards and enters the Bering Sea and thence it turns north-eastwards and later northwards to form the east side of the Bering Sea circulation, referred to prcviously.

1

The whole of the cold current from the Bering Sca is sometimes referred to as the Oya Shio, especially by American writers.