RESEARCH

Atmospheric Aerosol and Cloud Optical Properties Clouds and aerosols is a fundamental component of the Earth's atmosphere and play a important role in the radiation budget since their physical and optical properties affect the scattering and absorption processes of solar radiation. Clouds act on atmospheric radiation processes by reflecting incoming sunlight back into space and by trapping thermal radiation emitted from the Earth’s surface. Aerosols can act to either cool or warm the atmosphere. Cooling occurs when aerosols scatter incoming sun radiation back into space, whereas warming occurs due to the absorption of the incoming sunlight. Aerosol particles can also act as cloud condensation nuclei (CCN) affecting the concentration, size and lifetime of clouds. One of the main challenges in the atmospheric sciences lies in acquiring more accurate knowledge about aerosol and cloud properties and how their interactions can affect climate model. Since 2001, when the first Lidar system was installed in Metropolitan Area of São Paulo (MASP), LEAL has been conducted several studies in order to improve our understanding on the vertical distribution of aerosol and their optical properties due the local pollution and the role of MASP on global climate changes scenario.

Aerosols are transported by the airflows during the time they are suspended in the atmosphere. The transport of aerosol can be in local scale within short distance and in global scale, covering large distances, such as the transport of Saharan dust across the Atlantic ocean to the American continent. Satellite measurement can improve the understanding of aerosol properties on global scale, and ground-based measurement can improve our understanding in local scale. Combining both type of measurements we can are able to improve our understanding on the aerosol transport events, the changes on optical properties of aerosol, and also determine the sources, the sinks and the resident time of aerosols on the atmosphere. LEAL has apply Lidar measurements, in synergy with several satellite data and air masses trajectories models to understanding the aerosol transportation events, especially to monitoring the biomass burning aerosol transportation from Amazon and the North and Central region of Brazil to the São Paulo, and determine the impacts of local pollution due these events. LEAL lab is also coordinating a project to install a Depolarization Lidar at Natal - Rio Grande do Norte, in colaboration with Universidade Federal do Rio Grande do Norte - UFRN, UNiversidade de Granada - Espanha e o Instituto de Óptica de Moscow, in order to measure and study Saharan dust transportation across the Atlantic ocean to South America.

The measurement and understanding of the impact of Cirrus clouds in climate is very complex due their influence on both Earth's incoming and its outgoing solar radiation, with their variable radiative and optical properties affecting both the cooling and heating of Earth’s atmosphere. Some properties of this type of clouds are very interesting on the scientific point of view such as the influence of cloud shapes and sizes due the presence of ice crystals or the presence of liquid water at temperatures below the freezing point, their composition, shape, distribution, altitude of top and base. Measurements with ground-based systems, especially with Lidar systems can help to improve our knowledge of cirrus clouds properties on local scale. Combining these measurements with satellite data we are able to understand the optical and physical properties also on global scale, and all these information can contribute to understand the whole contribution of cirrus clouds on the radiation budget process. LEAL has applied a methodology to study the physical and optical properties of Cirrus clouds on the Southern Hemisphere.

The Planetary Boundary Layer (PBL) is the region of troposphere, which feels the direct influence of the activities developed at the surface in short interval time such as one hour or less. The exchange of energy between the surface and atmosphere influences the PBL stability and it can increase or decrease it level of turbulence, which can interfere in pollutants dispersion or imprisonment process in this layer. Because that, studies about PBL became very important for a better understanding of how this process can influence the everyday life.The PBL is an important factor in several fields, from analysis about air quality until modeling. However, monitoring the PBL evolution is a complex problem, because few instruments can provide continuous atmospheric measurements with enough spatial and temporal resolution. Inside this scenario Lidar systems appear as an important tool, because it complies with all these capabilities. Since 2010 LEAL has been conducted some studies in order to understanding the PBL dynamics and his influence on the pollution dispersion or events of strong pollution concentrations.

One of the main challenges in the atmospheric sciences lies in acquiring more accurate knowledge about aerosol and cloud properties and how their interactions can affect climate model predictions. In the last decades, several remote sensing platforms, space-borne, aircraft and ground-based measurement systems have been developed or improved to conduct studies of aerosol and cloud optical properties on local and global scales, as well as to provide the scientific basis for understanding the Earth's climate system. Most of our current understanding of aerosol influences in climate change processes has been developed from the study of horizontal distributions of aerosols derived from space-based remote sensor measurements. Validation of satellite data products via intercomparison with independent measurements is essential to the production of a high quality dataset. Since 2007 LEAL has been conducted some studies in the validation processes of satellite data, such as CALIPSO satellite, in collaboration with the NASA Langley Research Center, and AEOLUS, EarthCARE and Copernicus-Sentinel 5 satellites from European Space Agency-ESA.