Seasonal and intraseasonal variability of precipitable water vapour in the Chajnantor plateau, Chile

Abstract

The Chajnantor plateau is located in the Atacama Desert at over 4800 m above sea level. The plateau features a large fraction of days during the year where dry and stable atmospheric conditions predominate. The suitability of the type of astronomy observations routinely made at sites across the Chajnantor region at different times of the year depends on the variability of atmospheric water vapour. In this work, we study seasonal and intraseasonal variability associated with periods of large and low precipitable water vapour (PWV) in the Chajnantor region over 32 years. We establish large‐scale conditions favourable for above‐ and below‐normal PWV for each of the four seasons. We also explore whether intraseasonal PWV variations are related to the Madden–Julian Oscillation (MJO). Below‐normal PWV in winter, spring, and autumn seasons was found associated with mostly zonal 500‐hPa winds, which advect drier than normal air from the anticyclone over the eastern portions of the southeast (SE) Pacific Ocean. In summer, periods with below‐normal PWV were found to have anomalously south‐westerly winds at mid‐levels, also indicating transport of anomalously dry air from the stable SE Pacific. In winter, spring, and autumn seasons, above‐normal PWV was generally associated with north‐westerly mid‐tropospheric wind anomalies, indicating advection of above‐normal PWV from the subtropical and tropical regions of the SE Pacific Ocean. Above‐normal PWV conditions in summer were associated with nearly calm winds at 500 hPa. Months and phases of the MJO for the most extreme anomalies of PWV for each season agreed well with the seasonal anomalies. Furthermore, three independent reanalysis data sets generally agreed on MJO phases associated with largest positive and negative PWV anomalies. This agreement provides evidence for the first time that the MJO modulates the PWV content over the Atacama Desert.

Twenty years of precipitable water vapor measurements in the Chajnantor area

“…The results from Figure 9 are also consistent with the results from Marín et al (2017). These authors used the Climate Forecast System Reanalysis (CFSR) (Saha et al 2010) as source for the PWV data for Chajnantor and the APEX radiometer data (2006 to 2010) to validate the analysis.…”

“…In addition, we find the median values for the extreme months of January and August, with a 50th percentile value for each condition of 2.56 mm and 0.72 mm, respectively. The results from Figure 9 are also consistent with the results from Marín et al (2017). These authors used the Climate Forecast System Reanalysis (CFSR) (Saha et al 2010) as source for the PWV data for Chajnantor and the APEX radiometer data (2006 to 2010) to validate the analysis.…”

“…These authors used the Climate Forecast System Reanalysis (CFSR) (Saha et al 2010) as source for the PWV data for Chajnantor and the APEX radiometer data (2006 to 2010) to validate the analysis. In Marín et al (2017), the authors argued about a connection between the Madden-Julian Oscillation (MJO) pattern and the variability of the PWV at Chajnantor. Given that the MJO starts in the western Pacific Ocean and develops through the east sometimes reaching the South American coast, we believe a study of the MJO could be used as a tool to predict wet events in Chajnantor.…”

“…Delgado et al (1999); Radford et al (2008) derived a conversion scheme to obtain PWV from radiometric measurements of the 183 GHz water emission line, while longer-term climatology studies in the Chajnantor area were presented in Bustos et al (2000); Otárola et al (2005Otárola et al ( , 2019. Estimates and forecasts of PWV for the Chajnantor area using the Geostationary Operational Environmental Satellite (GOES) were presented in Marín Article number, page 1 of 10 arXiv:2007.04262v1 [astro-ph.IM] 8 Jul 2020, and in addition, seasonal and intraseasonal variations for PWV were studied in Marín et al (2017). In Holdaway et al (2004), the relationship between global warming and PWV for the area was studied in a period of six years with inconclusive results.…”

A 68 ka precipitation record from the hyperarid core of the Atacama Desert in northern Chile

“…The complexity of atmospheric circulation systems over western South America and the eastern South Pacific is postulated to have a strong impact on the moisture supply to the Atacama Desert (e.g. Marin and Barrett, 2017;. As the Atacama Desert is subdivided into two precipitation zones, local climates are spatially influenced either by summer or by winter rainfall (Houston, 2006b; see dashed line in Fig.…”