Precipitable water vapour forecasting: a tool for optimizing IR observations at Roque de los Muchachos Observatory

Abstract

We validate the Weather Research and Forecasting (WRF) model for precipitable water vapour (PWV) forecasting as a fully operational tool for optimizing astronomical infrared (IR) observations at Roque de los Muchachos Observatory (ORM). For the model validation we used GNSS-based (Global Navigation Satellite System) data from the PWV monitor located at the ORM. We have run WRF every 24 h for near two months, with a horizon of 48 hours (hourly forecasts), from 2016 January 11 to 2016 March 4. These runs represent 1296 hourly forecast points. The validation is carried out using different approaches: performance as a function of the forecast range, time horizon accuracy, performance as a function of the PWV value, and performance of the operational WRF time series with 24-and 48-hour horizons. Excellent agreement was found between the model forecasts and observations, with R = 0.951 and R = 0.904 for the 24-and 48-h forecast time series respectively. The 48-h forecast was further improved by correcting a time lag of 2 h found in the predictions. The final errors, taking into account all the uncertainties involved, are 1.75 mm for the 24-h forecasts and 1.99 mm for 48 h. We found linear trends in both the correlation and RMSE of the residuals (measurements − forecasts) as a function of the forecast range within the horizons analysed (up to 48 h). In summary, the WRF performance is excellent and accurate, thus allowing it to be implemented as an operational tool at the ORM.

Local Monitoring of Atmospheric Transparency from the NASA MERRA-2 Global Assimilation System

“…The reliability of local interpolation of 3-D variables from global data in the context of abrupt orography could also be further assessed by combining local probes with a mesoscale weather forecast algorithm to control the assimilated profiles. Such forecast algorithms have already be used successfully by Pérez-Jordán et al (2018) at La Palma Roque de los Muchachos Observatory to predict PWV content at millimeter level precision and sub-millimeter accuracy.…”

Forecasting water vapour above the sites of ESO’s Very Large Telescope (VLT) and the Large Binocular Telescope (LBT)

“…This will allow the possibility to plan in advance service-mode observations and match the science targets of a specific observing program with the corresponding optimal weather conditions, thus maximizing the scientific output of an observatory. A few studies already tried to apply mesoscale models to PWV forecast on astronomical sites (Giordano et al 2013;Pozo et al 2016;Perez-Jordan et al 2018).…”