Comparison of the simulated microwave cloudy radiances using ARTS and RTTOV-SCAT

V. GALLIGANI

Conferencia; International TOVS Study Conference-XXI; 2017

This paper discusses ongoing work to compare the fast operational model RTTOV with the physics based, research model, ARTS under cloudy conditions to intercompare their scattering solvers. The simulations discussed in this paper correspond to simple scenario, where clear-sky, rain-only cloudy and snow-only cloudy conditions from a realistic deep convection case are modelled. The simulation discussed analyse the behaviour of the radiative transfer models to different parameters, such as the scattering properties, the zenith angle, or the cloud mass contents. Under clear sky conditions where both ARTS and RTTOV use the same water vapour absorption model, differences were shown to be below 1.5 K for nadir simulations. An analysis of the sensitivity of these simulations to zenith angle showedlarger differences for zenith angles higher than 45 degrees. For cloudy conditions, the sensitivity of the ARTS simulations to MC miniter, and RT4 nstreams and quadrature type were tested for rain-only and snow only simulations, using the soft sphere approach and 3 habits from the Liu (2008) DDA database for the latter. Using the soft-sphere approximation a strong sensitivity in the differences between RTTOV and ARTS cloud signals were shown as a function of zenith angle, but these differences remain constant with snow water level fraction. The contrary is observed using DDA habits.There is no zenith angle sensitivity in the differences between RTTOV and ARTS, but there are differences as a function of snow water level fraction for all DDA habits.