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BAINS BEYOND THE TROPICS. 297
CHAPTER XVIL
RAINS BEYOND THE TROPICS.—WINTER RAINS.—RAINS OP SPRING AND
AUTUMN.—SUMMER RAINS.—RAINS OP THE POLAR REGIONS.
To the north and south of the zone of the trade-winds, the rains, like
the winds, present much less regularity than in the region of the-equatorial calms, both in the quantity of rain that falls and in the time and duration of the rainy season. It is in the northern hemisphere especially that
the precipitation of rain is accomplished in an unequal manner, for the
surface is there more varied than anywhere £lse by the contours of continents, scattered islands, inland seas, and chains of mountains, which lie
parallel, oblique, or transverse to the winds. Thus it is very difficult in
many countries to discover the general order in which the rains succeed
each other; and so long as conscientious observations have not been made
during any series of years, uncertainty must prevail in this respect.
However, the registers kept at the various meteorological stations of
the northern hemisphere are already sufficient to show what is the normal
distribution of the rains on this side of the Tropic of Cancer. To the
north of the variable limit where the trade-winds commence, and as high
as a latitude of forty degrees, the rains fall almost exclusively during the
winter. Around the basin of the Tyrrhenian Sea, and on the coasts of
Western Europe, they are distributed throughout the year, but it is especially in autumn that the greatest precipitation of moisture takes place;
more to the north it is the summer which is the especial rainy season;
finally, in polar countries it is in the winter that the condensation of the
clouds produces the most rain and snow.
The direction ofthe winds is the true cause of this unequal distribution
ofthe rain-fall according to the various parts ofthe year; for beyond the
equatorial zone most of the showers are, so to speak, not formed on the
spot by the condensation of the ascending vapors, but are brought from
afar by the currents ofthe atmosphere. During the winter of the northern hemisphere the whole system of trade-winds is attracted to the south,
following the sun, and consequently the aerial counter-currents which return toward the Arctic pole can descend again to the surface of the globe
in the neighborhood of the Tropic of Cancer.* The vapors with which
these winds are charged are then condensed into rain in consequence of
the mingling ofthe air which carries them with other and colder atmospheric masses; this is the rainy season. But when the sun approaches
the equator, bringing with it toward the north the entire system of winds,
the counter trade-winds ofthe south-west can not then approach the surface except toward the middle of the temperate zone. The sky becomes
* See above, p. 232.
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000324 |
| Type | Books/Pamphlets |
| Transcript | BAINS BEYOND THE TROPICS. 297 CHAPTER XVIL RAINS BEYOND THE TROPICS.—WINTER RAINS.—RAINS OP SPRING AND AUTUMN.—SUMMER RAINS.—RAINS OP THE POLAR REGIONS. To the north and south of the zone of the trade-winds, the rains, like the winds, present much less regularity than in the region of the-equatorial calms, both in the quantity of rain that falls and in the time and duration of the rainy season. It is in the northern hemisphere especially that the precipitation of rain is accomplished in an unequal manner, for the surface is there more varied than anywhere £lse by the contours of continents, scattered islands, inland seas, and chains of mountains, which lie parallel, oblique, or transverse to the winds. Thus it is very difficult in many countries to discover the general order in which the rains succeed each other; and so long as conscientious observations have not been made during any series of years, uncertainty must prevail in this respect. However, the registers kept at the various meteorological stations of the northern hemisphere are already sufficient to show what is the normal distribution of the rains on this side of the Tropic of Cancer. To the north of the variable limit where the trade-winds commence, and as high as a latitude of forty degrees, the rains fall almost exclusively during the winter. Around the basin of the Tyrrhenian Sea, and on the coasts of Western Europe, they are distributed throughout the year, but it is especially in autumn that the greatest precipitation of moisture takes place; more to the north it is the summer which is the especial rainy season; finally, in polar countries it is in the winter that the condensation of the clouds produces the most rain and snow. The direction ofthe winds is the true cause of this unequal distribution ofthe rain-fall according to the various parts ofthe year; for beyond the equatorial zone most of the showers are, so to speak, not formed on the spot by the condensation of the ascending vapors, but are brought from afar by the currents ofthe atmosphere. During the winter of the northern hemisphere the whole system of trade-winds is attracted to the south, following the sun, and consequently the aerial counter-currents which return toward the Arctic pole can descend again to the surface of the globe in the neighborhood of the Tropic of Cancer.* The vapors with which these winds are charged are then condensed into rain in consequence of the mingling ofthe air which carries them with other and colder atmospheric masses; this is the rainy season. But when the sun approaches the equator, bringing with it toward the north the entire system of winds, the counter trade-winds ofthe south-west can not then approach the surface except toward the middle of the temperate zone. The sky becomes * See above, p. 232. |
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