Assessment of formulas for clear sky downwelling longwave irradiance in the Arctic.

Pace G., Calì Quaglia F., Ciardini V., Di Bernardino A., Di Iorio T., Iaccarino A., Meloni D., Muscari G., Scarchilli C., di Sarra A.
  Martedì 12/09   09:00 - 13:30   Aula F3 - Maria Telkes   IV - Geofisica e fisica dell'ambiente   Presentazione
Ground-based high-resolution observations of downward longwave irradiance (DLI), surface temperature, water vapour surface partial pressure and column amount and zenith sky infrared radiance in the atmospheric window are regularly obtained at the Thule High Arctic Atmospheric Observatory (THAAO, $76.5^{\circ}$N, $68.8^{\circ}$W), North-West Greenland. These datasets from 2017 and 2018 are used to assess the performance of different empirical formulas to infer clear sky DLI. Seventeen different formulas to estimate DLI have been tested against the THAAO dataset, using the originally determined coefficients. Formulas which combine information on total column water vapour and surface temperature appear to perform better than others, with a mean bias with respect to the measured DLI smaller than 1 W/m${}^{2}$ and a root mean squared error around 6 W/m$^2$. The bias displays a significant improvement when the coefficients of the different formulas are calculated using the THAAO dataset. The presence of two full years of data allows the investigation of the inter-annual variability, and the use of different years for the determination of the coefficients and the evaluation of results.