WinterTime

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Objective: We asked whether women self-reporting the recommended consumption of vitamin D from milk and multivitamins would be less likely to have low wintertime 25-hydroxyvitamin D (25(OH)D) levels.

Conclusions and relevance: Among healthy children aged 1 to 5 years, daily administration of 2000 IU compared with 400 IU of vitamin D supplementation did not reduce overall wintertime upper respiratory tract infections. These findings do not support the routine use of high-dose vitamin D supplementation in children for the prevention of viral upper respiratory tract infections.

(a) The topography of central Chile and geographical locations referred to in the text. Black dots mark the locations of precipitation gauges. Crosses indicate the Andean river gauges. The stars show the locations of the Qunitero and Santo Domingo radiosonde sites. The large white circle indicates the approximate location and size of the city of Santiago. The black line that marks the boundary between darker and lighter topographic shading is the 2500-m elevation contour, which is at the approximate mean height of the wintertime snow line. The border with Argentina (gray line) roughly follows the main divide of the Andes. The dashed line west of the Chilean coast indicates the reference (d = 0) used to calculate the horizontal axes of the plots in Fig. 4. Groups A and S refer to the rain gauge station groups used in section 6. The map inset in the top left shows the location of central Chile (black rectangle) in South America. (b) The mean topography along a 10-km-wide section at 33.35°S.

(a) RW and (b) Rf over the southeast Pacific Ocean derived from SSM/I rain-rate estimates. Here Rw is the mean wintertime precipitation between 1993 and 2002, and Rf is the percentage of days in which precipitation was recorded over this time period (again winter only). The box indicates the location of central Chile. The dashed line, determined subjectively, indicates the region where the continent appears to begin to influence the rainfall pattern. (c) The maximum height of the South American topography as a function of latitude smoothed to an effective resolution of 0.25°.

The strong seasonality of precipitation in central Chile results from the wintertime retreat of the South Pacific anticyclone that prevails over the region during summer (Saavedra and Foppiano 1992), exposing the region to sporadic frontal rainstorms embedded within baroclinic disturbances crossing the continent to the south. There are several major storms each winter that have a large variability in both the intensity and spatial distribution of the precipitation produced. Rutllant and Fuenzalida (1991) found that the presence of blocking anticyclones in the Bellingshausen Sea (60°S, 90°W) favors precipitation in central Chile by driving midlatitude cyclones well northward of their usual trajectories. Over interannual time scales, annual precipitation in central Chile shows a striking range (between 100 and 700 mm in Santiago), with wet (dry) years having a well-documented association with the El Niño (La Niña) phases of the Southern Oscillation (e.g., Aceituno 1988; Montecinos et al. 2000; Montecinos and Aceituno 2003; Grimm et al. 2000; amongst others).

While the synoptic-scale and climatological forcing of precipitation in central Chile have been reasonably well studied, comparatively little has been documented on the local forcing. Given the complex, high-altitude topography of the region, which includes not only the impressive Andes Cordillera (mountain range), but also a coastal mountain range and central basin, orographic precipitation processes may exert strong control over local rainfall patterns (e.g., Smith 1979; Banta 1990; Houze 1993). In the city of Mendoza, Argentina (33°S, 69°W), situated at a similar latitude and altitude to Santiago on the eastern side of the Andes, the wintertime precipitation amounts to only about 70 mm, less than a quarter of that in Santiago. Thus, in the broadest sense, the Andes of central Chile exhibit a rainfall pattern typical of midlatitude mountain ranges: a rainier zone on the upwind side and drier region in the lee (Roe 2005). Nonetheless, the shape of the rainfall distribution across the Andes, the extent of their upstream influence, and the existence of rainfall enhancement or shadow zones related to the coastal topography is not well known. This is in part due to the difficulty of obtaining long-term precipitation records in the inaccessible terrain, particularly at higher altitudes where the surface is snow covered during winter.

In this study wintertime precipitation in central Chile was examined using daily observations from precipitation gauge, radiosonde, and SSM/I passive microwave radiometer over a 10-winter period from 1993 to 2002. 781b155fdc