Defense
Student: Jorge Rosas Santana
Program: Meteorology
Tiltle: “Os efeitos 3D das nuvens sobre a radiação solar em superfície e variação das propriedades das nuvens em dois sítios característicos do Brasil”
Advisor: Profa. Dra. Marcia Akemi Yamasoe - IAG/USP
Judging Comitee:
- Profa. Dra. Marcia Akemi Yamasoe (orientadora)
- Prof. Dr. Pedro Leite da Silva Dias – IAG/USP
- Prof. Dr. Alexandre Lima Correia –IF/USP
- Prof. Dr. Fernando Ramos Martins - UNIFESP - Campus Santos (por videoconferência)
- Prof. Dr. José Vanderlei Martins – UMBC
Abstract:
Effective cloud optical depth (ECOD) retrievals were conducted for the period of
2012-2018 for two important regions: the Metropolitan Area of São Paulo (MASP)
and around a preserved rainforest, in the Amazon, representing an urban and a
pristine environment, respectively. Additionally, the impact of 3D cloud effects on
shortwave radiation at the surface was evaluated using various cloud field
geometries. The study highlights the importance and the multifunctionality of
Multifilter Rotating Shadowband Radiometers (MFRSR), which enable ECOD
estimation and also allowing the development of ancillary algorithms to classify
different retrieval scenarios, including overcast conditions and sun-disk blocked by
clouds. The evaluation of methodologies confirms the feasibility of classifying
overcast conditions using MFRSR and if the sun-disk is clear or cloudy. tatistical
differences in ECOD between the Amazon (mean value of 31.1) and São Paulo
(mean value of 32.8) were observed throughout the entire period. The most
significant differences occurred in spring, with a mean ECOD of 27.8 in the Amazon
and 35.7 in São Paulo. Those differences probably can be attributed to changes in
microphysical properties of the clouds, due to the combination of moisture
convection with aerosol particles transported from other regions during the biomass
burning season. A case study of the transport of aerosol from biomass burning
toward São Paulo revealed strong radiative impacts with solar irradiance dropping
to 0 and estimated ECOD values as high as 300. In addition, the cloud radiative
effects at the surface was 7% stronger on the biomass burning day as compared to
other overcast days. The 3D effects of cloud fields were assessed using 3D
simulations and compared with 1D simulations of Individual Pixel Approximations
(IPA). For this purpose, we used various 3D clouds geometries, such as a single
cuboid cloud, stochastic stratocumulus clouds and near-realistic cumulus clouds
from Large Eddy Simulations (LES) in the Amazon. The cloud fields were used as
input for the Monte Carlo code for the physically correct tracing of photons in
cloudy atmospheres (MYSTIC), a state of art of 3D radiative transfer model. Results
showed the complexity of the 3D effects mainly influenced by the solar geometry,
cloud optical depth, cloud thickness, and surface albedo. Using one cuboid cloud,
strong impacts of the surface albedo and the cloud thickness were observed. While
the increase of surface albedo helped to increase the positive values of the 3D
effects, the increase of cloud thickness enhanced the effect of shadowing,
contributing to more negative values of 3D effects. n general, for cloud fields
analyzed, the 3D effects on the global downward irradiance were negative, as
observed in cuboid cloud fields (minimum of -40 % at optically thick clouds) and
LES simulations (minimum of -16 %), but shallow stochastics stratocumulus clouds
exhibited positive values (maximum of 10 %). Variations in cloud fraction, solar
geometry, and ECOD were also identified as key mechanisms driving the 3D effects
in broken cloud fields.
Keywords: cloud optical depth; 3D radiative transfer;clouds, ground-based measurements.