First cloud census of Brazil has been completed

Findings of experiments were described in a cover article of the Bulletin of the American Meteorological Society. The goal is to improve models that can predict extreme weather events.

By Karina Toledo

Agência FAPESP – To more precisely predict extreme events such as storms or simulate scenarios of climate change effects, we need to know more about the physical processes that occur inside clouds and define the variation among factors such as the size of raindrops, the proportion of layers of water and ice, and how electrical discharges function.

For this purpose, a series of data collection campaigns were conducted between 2010 and 2014 in six Brazilian cities: Alcântara (in the state of Maranhão), Fortaleza (Ceará), Belém (Pará), São José dos Campos (São Paulo), Santa Maria (Rio Grande do Sul) and Manaus (Amazonas) under the scope of a FAPESP thematic project headed by Luiz Augusto Toledo Machado of the National Institute for Space Research (INPE). These campaigns included participation by researchers from the University of São Paulo (USP) and several meteorology institutions in Brazil, which hosted the experiments.

The principal findings of the initiative, known as the “CHUVA Project”, were described in an article featured on the cover of the Bulletin of the American Meteorological Society, a high-impact journal in the field of meteorology.

According to Machado, the regions selected for field research represent the various precipitation regimes found in Brazil. “It is important to make this regional characterization so that the mathematical models can make high-resolution predictions, in other words, on a scale of just a few kilometers,” the researcher said.

A common set of instruments, which includes dual-polarization cloud radar, was used at the various sites so that the measurements could be compared and parameterized for modeling purposes.

The dual-polarization, radar together with other instruments, sends horizontal and vertical waves whose reflections indicate the shape of the ice crystals and the raindrops, helping explain the composition of the clouds and the mechanisms of formation and intensification of electrical discharges during storms. They also collected data such as temperature, humidity and aerosol composition.

Separate additional experiments were also conducted in each of the six cities. In the case of Alcântara, where data collection occurred in March 2010, the experiment focused on the development of algorithms to estimate precipitation for the Global Precipitation Measurement (GPM), an international satellite mission launched in February 2014 by NASA (the U.S. space agency) and the Japanese Aerospace Exploration Agency (JAXA).

“The main challenge in that region is estimating precipitation from what are known as warm clouds, which contain no ice crystals. They are commonly found in Brazil’s semi-arid Northeastern region,” Machado explained.

Because these clouds have no ice, the rain in the clouds goes undetected by the microwave sensors that equip the satellites normally used to measure precipitation, resulting in imprecise data.

Measurements of warm clouds conducted by radar in Alcântara compared with measurements made by satellite indicated that the volume of water present in the clouds had been underestimated by more than 50%.

In Fortaleza, where data were collected in April 2011, a partnership was established with the civil defense system to test a real-time open access storm prediction method known as Observation System for Severe Weather (SOS Chuva).

“We used the data that were being collected by radar and put them in real-time within a geographical information system. That way, it’s possible to make predictions for the next two hours, knowing where heavy rainfall and lightning are at any given time and how the situation will change in 20-30 minutes. We also added a flood map that allows us to predict areas that could flood if water were to rise one meter, for example,” Machado said.

The researcher said that the experiment was so successful that the team decided to repeat it in later campaigns. “SOS Chuva is contributing towards reducing the vulnerability of the population to climate extremes because it offers information not only to civil defense agencies but also to citizens,” he said.

In June 2011, the data collection campaign was conducted in Belém, where researchers used a GPS network of instruments to estimate the amount of water in the atmosphere. The results are expected to be published soon. They also launched weather balloons capable of flying for periods of 10 hours to collect atmospheric data. “The objective was to understand the flow of vapor from the Atlantic Ocean that produces rain in the Amazon,” Machado explained.

From November 2011 to March 2012, the São José dos Campos campaign was conducted. It focused on studying lightning and atmospheric electricity. A set of lightning detection networks was used in partnership with the National Oceanic and Atmospheric Administration (NOAA), a U.S. federal agency, and the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT).

“Data were collected to develop algorithms for the electrical discharge sensors of the third-generation geostationary satellites that are to be launched by NOAA and EUMETSAT this decade. Another objective was understanding how clouds start to change before the first electrical discharge occurs, as a way to predict when lightning will occur,” Machado explained.

Mathematical models for predicting extreme weather events were tested in Santa Maria from November to December 2012, in partnership with Argentine researchers. According to Machado, the region that encompasses southern Brazil and northern Argentina experiences the most severe storms in the world.

“The results showed that the models are still not precise enough to effectively predict the occurrence of these extreme events. In 2017, we will conduct a similar experiment called Lightning in northern Argentina,” Machado explained.

GOAmazon

The two intensive data collection operations conducted in Manaus – the first from February through March 2014 and the second from September through October 2014 – had not yet taken place when the article was submitted for publication.

The campaign was conducted under the scope of the Green Ocean Amazon project and included two aircraft flying at different altitudes to monitor the pollution plume emitted by the Manaus metropolitan region. The goal was to determine the interaction between the pollutants and the compounds emitted by the forest, as well as its impact on the cloud properties (read more about it at: http://agencia.fapesp.br/20157). Data from the campaign are still being analyzed.

In commenting on the main differences found in the various Brazilian regions, Machado points to the South and Southeastern regions, which present larger raindrops and a more developed mixed cloud layer that contains water in both liquid and solid states. This, according to the researcher, is the main reason for the higher incidence of electrical discharges in these locations.

In contrast, the clouds over the Amazon region have a top layer of ice – over 20 kilometers high – that is better developed than that of other regions. The coastal regions, such as Alcântara and Fortaleza, have a higher number of warm clouds, which contain almost no electrical discharges.

“This was the first updated cloud census performed in Brazil. The information will serve as a basis for testing and developing new models capable of describing cloud formation in detail, using high-resolution spatial and temporal resolution,” the researcher concluded.