Sea Land Currents and Mountain Ranges

When very humid air masses coming from the sea meet a mountain range and are forced to rise, very intensive precipitation can occur, often reaching record levels. The best-known case is the precipitation at Cherrapunji in the Khasi mountains in the approaches to the Himalayas. Massive amounts of precipitation fall due to the interplay of the summer monsoon and the effect induced by the mountains. The other precipitation extremes shown in Table 1 are also a consequence of humid ocean air flowing against mountains. In addition to these examples, one can say that the windward side of mountain ranges near the sea are in general characterized by high levels of precipitation (examples are the Cordilleras (Canada, South Chile), the Scandinavian mountains, the Alps, and the Tsaratanana massif on Madagascar). These regions are mostly not large in

Table 1 Extremes of precipitation

Value

Kind of extreme Location (mm)

Highest annual sum Debundscha, Cameroun (Africa) 10287

Lloro, Colombia (America) 13299

Cherrapunji, India (Asian) 26461

Bellender Ker, Queensland (Australia) 8 636

Crkvice, Croatia (Europe) 4 648

Highest monthly sum Cherrapunji, India 9300

Highest daily sum Cilaos, La Reunion 1 870

Highest annual sum of snow fall Paradise, Mt. Rainier, Washington, USA 31 100

Highest snow cover Sierra Nevada, California, USA 11 455

300 250

E 200

50 0

300 250

E 200

50 0

9 10 11 12

Figure 6 Monthly mean of precipitation, Singapore, 1°17' N, 103°50' E (annual sum = 2423 mm).

9 10 11 12

Figure 6 Monthly mean of precipitation, Singapore, 1°17' N, 103°50' E (annual sum = 2423 mm).

450

400

350

F

300

c o

250

.2

200

a

o

150

¡u

Ol

100

50

10 11 12

6 7 Month

10 11 12

Figure 7 Monthly mean of precipitation, Darwin, 12°28' S, 130°50' E (annual sum = 1630 mm).

extent, but their annual sums are significant (Sitka, Canada: 2454 mm; Bergen, Norway: 1958 mm). The example of Hawaii shows that when humid air masses are forced to rise through meeting a mountain barrier, high values for precipitation can also be produced even in the trade-wind zone which is otherwise comparatively dry due to inversion. The 1569 m high Mt. Waialeale on Hawaii shows a mean annual sum of 11 684 mm.

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