Josep Calbó is member of the Scientific Committee of the 7th International Conference on Meteorology and Climatology of the Mediterranean, held in Palma from 4 to 6 March 2019. In addition, Babak Jahani, Aarón Enríquez-Alonso, Josep Calbó and Josep-Abel González participate in this conference with an oral presentation and a poster.

Babak Jahani and his PhD advisor, Dr. Calbó, participate with an oral presentation entitled “Radiative Transfer Simulation of Clouds and Aerosols in the Transition Zone: Weather Research and Forecasting Model (WRF)”. In this research, the authors state that solar radiation is a key component of the Earth atmosphere system, which controls a number of natural processes on the planet Earth. Furthermore, the amount of solar radiation reaching the Earth surface is mainly affected by the aerosols and clouds properties, which are two particular cases of a single phenomenon, i.e. a suspension of particles in the air. The differences between the radiative characteristics of cloud and aerosol are well known. However, in many cases the characteristics of the suspension are on the border between those corresponding to a cloud and those corresponding to an atmospheric aerosol (twilight or transition zone). As a result, it is hard to define the suspended particles as either aerosol or cloud. So that, this study aims to assess the ability of a number of radiative transfer parameterizations included in the Weather Research and Forecasting Model (WRF) in simulating the radiative effect of the suspended particles in the transition zone, by applying a sensitivity analysis approach. To this aim, several radiation parameterizations of WRF (New Goddard, RRTMG, FLG, …) were isolated from the whole model and were applied to perform simulations under either “cloud” or “aerosol” modes, for different values of (i) cloud optical thicknesses resulted from different sizes of ice crystals, liquid droplets, cloud height, mixing ratios and (ii) different aerosol optical thicknesses combined with various aerosol types. The optical thickness under both aerosol and cloud modes was considered to vary between 0.1 and 2, which is a common range of optical thickness for twilight zone. The analyzed results consisted of shortwave broadband global, beam and diffuse irradiances at the Earth surface.

On the other hand, Dr. Enríquez-Alonso, Dr. Calbó and Dr. González participate with the poster entitled “A method for the study of nocturnal clouds from images in the visible: implementation and validation in Girona”. In this work, the authors explain that clouds play an important role in the global energy balance as they reflect a large fraction of shortwave radiation and at the same time absorb and emit longwave radiation. However, large uncertainties remain about the climatology and long-term trends of clouds, as well as about their response and feedbacks to the anthropogenic forcing. In this work, night-time whole-sky images in the visible range, taken with an all-sky camera (SONA from Sieltec SL) are analyzed. During the night, both the Moon (when it’s present) and the artificial light coming from the ground act as sources of light that illuminate the clouds and allow to differentiate them in the images taken by the camera. An automatic image analysis method is implemented by establishing criteria in intensity and the ratio of red to blue components in each pixel, to be able to estimate the total cloud cover. In the second part of the work, this method is applied to the images taken in Girona by the SONA camera, with a temporal resolution of one minute, which generates approximately 400.000 images from June 2016 to May 2018. With this, the evolution of the nocturnal cloudiness during two years is presented. As longwave radiation highly correlates with total cloudiness, measurements from a pyrgeometer have been used to validate the estimations of nocturnal cloud cover. The use of the images to obtain an estimation of the cloud base height was also explored, by using ceilometer data as additional information.

These studies have been conducted within the framework of the “Clouds, Radiation to the Atmosphere and Climate” research line.