Characterising the properties of the atmospheric emission at Teide Observatory in the 10--20,GHz range with QUIJOTE data

QUIJOTE is a cosmic microwave background (CMB) experiment composed of two telescopes, QT1 and QT2, located at the Teide Observatory (OT) in Tenerife, Spain. The multifrequency instrument (MFI) (2012–2018), installed on QT1, observed the sky at four frequency bands, namely 11, 13, 17, and 19,GHz, with an angular resolution of one degree. Its successor, the Second Multifrequency Instrument (MFI2), began operations in early 2024 and operates in the same frequency bands. This paper has two main goals. First, we characterise the atmospheric conditions at the Teide Observatory. Second, we carry out an empirical characterisation of the atmospheric turbulence using observations from both QUIJOTE MFI and MFI2. This work has implications for both atmospheric physics and CMB observations, and can be used for future reanalyses of MFI data or in the preparation for upcoming instruments such as the Tenerife Microwave Spectrometer (TMS). We used data from GPS antennas, the STELLA observatory, and radio soundings to derive median profiles and distributions of key atmospheric parameters in the period 2012--2018. We then analysed MFI data to compute atmospheric structure functions at 17 and 19,GHz. Using the full MFI database, we studied the correlation properties of the atmospheric signal by calculating the cross-correlation function of the time-ordered data between horns operating at the same frequency. Finally, we used MFI2 observations to study the atmospheric power spectrum and compared it to the determination of the structure function based on MFI data. The water vapour density profile above the observatory can be well described by an exponential decay law, with a characteristic half-height of about 1000,m. Median values of precipitable water vapour (PWV) in the 2012--2018 period are 3.3,mm, with a 25th percentile of 2.1,mm. For high PWV conditions, we find that the structure function estimated with MFI data is consistent with the Kolmogorov turbulence model. The slope of the power spectrum of the atmospheric emission also seems consistent with the prediction of this model, although within a range of frequencies limited by the outer scale and by the instrument noise. Furthermore, through the study of the coherence length in the correlation function, we confirmed that atmospheric conditions remain stable for a period of about 1--2 hours. These results show that the Teide Observatory has an atmospheric behaviour comparable to that of the Atacama Cosmology Telescope (ACT) site, although with higher integrated precipitable water vapour due to its lower altitude.