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This work is the first comprehensive study of the climate at the major ridge of the Andes in South Ecuador and North Peru. The data sets used for this purpose are data from own measurements, existing data from the national weather stations and NCEP Reanalysis data. A particular feature of this dissertation is the elaborate and innovative graphical methods of presenting both measured and model data. The Andes of South Ecuador pose a significant, perpendicular barrier to a quasi-permanent easterly mid-level jet stream. Orographic uplift at the eastbound slopes deprives the air masses of a large share of its moisture load. The nearly incessant interception of moisture makes the highest ridge of this section of the Andes, the Cordillera Real, a true climate divide that separates humid climates upwind from semiarid and arid climates downwind. The outstanding topographic and climate setup produces a row of surprising weather extremes. Wind speed during easterly trades reaches mean monthly values of up to 15 m/s. In austral winter, mean daily speed of up to 24 m/s has been observed; gusts have reached >28 m/s (10 Bft). Predominantly advective and wind-enhanced rainfall mounts to over 6,000 mm/year in the summit regions. Within a range of only 30 km, local rain totals of probably even up to 8.000 mm/year are contrasted by barely 300 mm/year in the rain shadow. Very clear skies, cloud radiative effects and the high sun position result in a very intensive light climate. Global irradiance of unprecedented absolute magnitudes of over 1800 W/m2 has been measured. Intermittent northern and southern meridional air flow along the eastern slopes of the Andes produce outstanding weather extremes in the region as well. The northern variant, associated with El Veranillo del Nino, comes along with fair weather, aridity and high air temperatures. Key feature of this weather situation is a dynamic, along-barrier LLJ. The southern current is less dynamic but by spanning >70 degrees of latitude (>8000 km) an unmatched climatic disturbance. It transports maritime sub polar air from the southern hemisphere to north of the equator, causing e.g. cold and pressure extremes and record low radiation budgets in tropical latitudes.