Rain shadow effect

Because of the ready solubility of sodium nitrate, it has been argued that it exists to such an extent in the Atacama as it is drier than any of the other deserts in the world. Sub-tropical subsiding air, the upwelling of cold offshore waters, and the rain-shadow effect of the Andes, create this aridity. The most intense aridity occurs in northern Chile, which receives less than 10 mm of rainfall per annum. Indeed, some stations, such as Calama, receive on average less than 2 mm. The climate station at Quillagua (mean annual rainfall 0.05 mm) can lay claim to be the driest place on Earth (Middleton, 2001). 

In the UK rain comes mainly from the moist south-westerly winds and from the many depressions which cross fiom west to east. Western areas receive much more rain than eastern areas this is partly due to the west to east movement of the rain-bearing air and also becanse most of the high land is along the western side of the country. As the moistnre-laden air rises over this high gronnd it is cooled, its ability to hold moistnre decreases and this moisture is deposited as rain. On the leeward (sheltered) side of the mountain the air is drier and warmer. This is sometimes known as a rain shadow effect. 

The aridity in north-western and especially coastal Peru, and all the way south to Chile, is due to (a) a constant temperature inversion generated in large part by the cool north-flowing Humboldt current which prevents precipitation in the coastal region and (b) the influence of subtropical atmospheric subsidence and the rain-shadow effect of the Andean cordillera, which prevents humid air from the Amazon reaching the Pacific coastline (Hartley, 2003 Rundel et al., 1991). In the inter-Andean valleys the rain-shadow effect caused by the eastern Andean cordilleras is, however, the most important aridity-producing factor (Troll, 1952). 

FIGURE 12.2 Illustration of the effects of topography on biological communities. A mass of warm moist air forced to rise over a mountain range deposits rain and snow providing water that enables a produetive community to thrive. On the other side of the range, a rain shadow creates drought eonditions in whieh the productivity is low, and a much different community exists. 

In addition to technical investigations (avoidance of glare and shadows), further tests should be performed in order to allow for a more comprehensive assessment of the suitability of CMS in trucks. Tests should include a broad range of weather conditions (rain, fog, snow and at night) and investigate the effect of familiarization with the CMS. This test would help to confirm the present statements of the subjects, e.g. with regard to the size and position of the monitors. 

---