Climate dynamics along the arid northern coast of Chile: The 1997–1998 Dinámica del Clima de la Región de Antofagasta (DICLIMA) experiment

Abstract

[1] The DICLIMA field experiment was designed to test and quantify the hypothesis of an afternoon enhancement of the coastal subsidence in the extremely arid northern Chile because of solar heating over the west slope of the Andes. Ten-day campaigns near Antofagasta (23°S) were carried out in January 1997, July 1997, and January 1998. Significant diurnal cycles in temperature, mixing ratio, and wind from about 1000 to 4000 m above sea level were observed. This layer was decoupled from the marine boundary layer circulation below by the subsidence inversion when its base was under the average height of the coastal mountain range. The solar heating cycle over the Andes and associated circulation resulted in a mean afternoon zonal divergence above the subsidence inversion base of about 30 Â 10 À6 s À1 , exceeding by a factor of 5 typical subtropical west coast divergences. The corresponding early morning convergence was particularly intense during the austral winter experiment. In spite of the very strong El Niño conditions that prevailed during the July 1997 and January 1998 experiments, the overwhelming control that radiation exerts on the daily cycles of the atmospheric circulation over the west slope of the Andes seems to guarantee the general validity of the results.

Climate change along the arid coast of northern Chile

“…Cloudiness along the coastal desert of northern Chile is mostly associated with a persistent low-level SCu cloud deck that is capped by the TIL described in the previous section (Rutllant et al, 1998;Rutllant et al, 2003;Garreaud et al, 2008;Muñoz and Zamora, 2011). These predominant low-level clouds were reported in 95 and 75% of the hourly observations at Antofagasta and Arica, respectively, during the period 1986-1993.…”

“…The sharp temperature increase within the inversion layer hinders the vertical development of clouds, while the steep coastal mountain range largely impedes its movement inland. Reduced insolation beneath the SCu layer in the coastal area further contributes to preservation of sea surface and air temperatures below the corresponding latitudinal means (Rutllant et al, 2003). Along with the relatively low temperature, high atmospheric humidity and reduced solar radiation, the Camanchaca plays a key role for the subsistence of vegetation along this hyperarid coastal region.…”

“…The relatively cold surface water associated with the Humboldt Current and the intense coastal upwelling forced by the persistent SEPArelated southerly wind along the coast further contributes to the high stability of the atmosphere. Finally, the barrier effect of the massive mountain range of the Andes prevents the advection of moist air from the Amazon basin, while intensified subsidence in the troposphere linked to the sea-land contrast (Rutllant and Ulriksen, 1979;Rutllant et al, 1998Rutllant et al, , 2003 contributes significantly to the preservation of a hyperarid environment in the immediate vicinity of the ocean. Annual precipitation in the coastal area of northern Chile is extremely low, varying from ca 1 mm in the northern part (Iquique, Arica) to about 80 mm at the southern fringe of the arid region (Figure 1).…”

“…that separates the well-mixed humid marine air from the warmer and much drier subsiding air aloft (Rutllant and Ulriksen, 1979;Rutllant et al, 2003;Garreaud and Muñoz, 2004;Muñoz and Zamora, 2011). A persistent stratocumulus (SCu) cloud deck forms in the upper part of the MBL, generating heavy fog (locally known as Camanchaca) at places where the coastal escarpment intercepts the clouds (Figure 3).…”

Southeast Pacific stratocumulus clouds, precipitation and boundary layer structure sampled along 20° S during VOCALS-REx

“…At Iquique, there is a strong diurnal cycle with slope flows that can diffuse the inversion structure, as observed by Rutllant et al (2003) 300 km to the south. Slightly offshore (e.g.…”