Estimating and forecasting the precipitable water vapor from GOES satellite data at high altitude sites

Abstract

In this work, we describe a method to estimate the precipitable water vapor (PWV) from Geostationary Observational Environmental Satellite (GOES) data at high altitude sites. The method was applied at Atacama Pathfinder Experiment (APEX) and Cerro Toco sites, located above 5000 m altitude in the Chajnantor plateau, in the north of Chile. It was validated using GOES-12 satellite data over the range 0-1.2 mm since submillimeter/millimeter astronomical observations are only useful within this PWV range. The PWV estimated from GOES and the Final Analyses (FNL) at APEX for 2007 and 2009 show root mean square error values of 0.23 mm and 0.36 mm over the ranges 0-0.4 mm and 0.4-1.2 mm, respectively. However, absolute relative errors of 51% and 33% were shown over these PWV ranges, respectively. We recommend using high-resolution thermodynamic profiles from the Global Forecast System (GFS) model to estimate the PWV from GOES data since they are available every three hours and at an earlier time than the FNL data. The estimated PWV from GOES/GFS agrees better with the observed PWV at both sites during night time. The largest errors are shown during daytime. Short-term PWV forecasts were implemented at both sites, applying a simple persistence method to the PWV estimated from GOES/GFS. The 12 h and 24 h PWV forecasts evaluated from August to October 2009 indicates that 25% of them show a very good agreement with observations whereas 50% of them show reasonably good agreement with observations. Transmission uncertainties calculated for PWV estimations and forecasts over the studied sites are larger over the range 0-0.4 mm than over the range 0.4-1.2 mm. Thus, the method can be used over the latter interval with more confidence.

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

“…Middle‐ and upper‐tropospheric westerly winds predominate from May to October (Figure ) and are linked to the northward displacement of the subtropical westerly jet stream, which brings dry mid‐troposphere air to the region, favouring clear skies and stable atmospheric conditions. The circulation anomalies during these months are mainly due to transient midlatitude disturbances embedded in the mean westerly flow (Garreaud et al ., ; Garreaud, ), which seems to be related to short periods of above‐normal PWV values (Marín et al ., , ). In summer months (December–February), low‐latitude easterly winds extend southward associated with a westward and southward displacement of the mean anticyclone (Figure ), reaching latitudes poleward of 20°S, and these winds are associated with thunderstorm formation (Garreaud, ).…”

“…The Chajnantor plateau is located in the Atacama Desert at over 4800 m above sea level, centred about 20 km from the Bolivia border and 80 km from the Argentina border ( Figure 1). The plateau features a large fraction of days during the year where dry and stable atmospheric conditions predominate (Giovanelli et al, 2001;Peterson et al, 2003;Radford, 2011;Marín et al, 2015;Rondanelli et al, 2015). For this reason, a number of telescopes that operate at the submillimetre and millimetre range have been installed there [e.g.…”

The Innsbruck/ESO sky models and telluric correction tools

“…As already shown by us in [1] and independently at the Pierre Auger facilities by [10], a properly adapted GDAS model already gives a very good description. This can be now further improved including the grid refinements down to 1 km resolution described by [15]. But moreover fitting by only a few spectral lines provides a nearly perfect profile and improves significantly this input of the GDAS profiles (interpolation in space 1 • × 1 • and time 3 h ).…”

“…radiometer measurements [4]. A new access is the exact recalculation of the forecast by a nested grids down to a resolution of 1 km and using the complete ground topography around the site [15]. We plan to implement this soon.…”

Atmospheric conditions at Cerro Armazones derived from astronomical data

“…Furthermore, this allows characterizing a site for its homogeneity and asymmetries in the water vapour content caused by dominating local ground layer air streams, for example, which is important for observations with the E-ELT in the infrared spectral bands. An even more sophisticated solution was presented recently, using local refinement calculations around the site (Lascaux et al 2015;Chacón et al 2011;Marín et al 2015). The numerical weather prediction models, in particular those running at high horizontal and vertical resolution, require extensive computing time, and they are not always readily available to support the operations and astronomical observations program.…”