Atmospheric circulation over the Bolivian Altiplano during ... - CDAM

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1594M. VUILLE4.2. Austral winter (JJA)Precipitation events in austral winter are rare in the Altiplano and the recorded amounts are sometimesvery dubious (Vuille and Ammann, 1997). In addition, the Southern Oscillation tends to peak duringaustral summer, and exhibits less extreme values during the winter months. Accordingly it is no surprisethat precipitation data from the stations near Nevado Sajama show no relationship with the SouthernOscillation during austral winter months (JJA, not shown). Changes in the atmospheric circulationbetween HIGH and LOW index phases are also less pronounced and the patterns generally less consistentbetween the analysed records. Therefore, only results from the radiosonde analysis are presented here.Most obvious are the increased temperatures (Figure 14(d)) and the vertically expanded troposphere(increase in geopotential height, Figure 14(c)) during LOW as compared to HIGH, consistent with resultsby Aceituno (1989), who reports that the atmospheric response during LOW periods in austral winter isFigure 11. As in Figure 10 but for wind field (m s −1 )Copyright © 1999 Royal Meteorological Society Int. J. Climatol. 19: 1579–1600 (1999)
BOLIVIAN DRY AND WET PERIODS AND CIRCULATION 1595Figure 12. As in Figure 10 but for air temperature (°C)in broad agreement with the response in austral summer. Lima is the only station which does not agreewith this pattern, featuring slightly decreased (increased) geopotential height values and lower (higher)mid-tropospheric temperatures during LOW (HIGH). The wind pattern shows a less evident picture,featuring reduced zonal wind components over the southern stations Salta and Antofagasta (weakerwesterlies) in the upper and middle troposphere during LOW as compared to HIGH, while the samecomponent is enhanced over Lima and La Paz (Figure 14(a)). The significance of these anomalieshowever, varies widely, depending on station and pressure level. The response of the meridional windcomponent is more consistent, featuring positive anomalies (weakened northerly winds) during LOW ascompared to HIGH over the entire area, although not significant at all levels (Figure 14(b)). The specifichumidity is higher during LOW than during HIGH over Antofagasta, Salta, and La Paz, while Limaagain shows a different behaviour with higher values during HIGH (Figure 14(e)). In general variationsin the atmospheric circulation over the Altiplano during austral winter show a rather weak relationshipto the Southern Oscillation. Interannual variability during austral winter might more likely be determinedby other factors, such as the strength and frequency of extra-tropical waves (frontal systems and cut-offlow pressure systems) originating in the Pacific and penetrating into the Altiplano region.Copyright © 1999 Royal Meteorological Society Int. J. Climatol. 19: 1579–1600 (1999)
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Page 22: 1600M. VUILLEFuenzalida, H.P. and R

Atmospheric circulation over the Bolivian Altiplano during ... - CDAM

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