{"id":219848,"date":"2016-06-29T19:30:18","date_gmt":"2016-06-29T22:30:18","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/en\/?p=219848"},"modified":"2016-06-29T20:07:46","modified_gmt":"2016-06-29T23:07:46","slug":"the-hidden-seeds-of-rain","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/the-hidden-seeds-of-rain\/","title":{"rendered":"The hidden seeds of rain"},"content":{"rendered":"
\"Rain

FABIO COLOMBINI<\/span>Rain cloud in a clean-atmosphere region over the forest: aerosols concentrated near the topFABIO COLOMBINI<\/span><\/p><\/div>\n

The answer is now becoming clearer for a question that has intrigued scientists studying climate and precipitation patterns in the Amazon for two decades: the place of origin of the microscopic particles that contribute to the formation of rain clouds in the world\u2019s largest tropical forest. Years ago, a piece of the answer came to light. The seeds of clouds in the Amazon are suspended particles, or aerosols, of organic origin\u2014formed in particular through chemical conversion of the isoprene gas emitted by plants\u2014around which water vapor condenses and cloud droplets form (see <\/em>Pesquisa FAPESP\u00a0issue n\u00ba 97<\/em><\/a>). But measurements taken by aircraft from four kilometers (km) above the ground have detected only a fraction of the aerosols released by the forest.<\/p>\n

Now the rest of the answer has been found. The aerosol particles are present in the clouds, but not at their bases, as scientists had thought. In August and September 2014, a German jet aircraft measured the chemical composition and physical characteristics of clouds in 14 flights over the Amazon. The measurements are being used in a joint campaign for two projects: Green Ocean Amazon (GoAmazon) and Acridicon-Chuva, funded by FAPESP, the Amazonas Research Foundation, the Max Planck Institute and the U.S. government (see <\/em>Pesquisa FAPESP issue n\u00ba 217<\/em><\/a>).<\/p>\n

The jet, able to fly at an altitude of 15 km, confirmed that most of the new aerosol particles are found above 8 km\u2014concentrated at the tops of the clouds, which in the Amazon can reach 16 km high\u2014in regions where there is preserved forest. \u201cWe have looked for the mechanisms that form these particles for 20 years,\u201d says physicist Paulo Artaxo of the University of S\u00e3o Paulo (USP). \u201cNow we\u2019ve seen that most of them are formed in clouds and brought to the forest surface by descending air currents,\u201d explains the researcher, who heads a project linked to GoAmazon.<\/p>\n

The mechanisms by which these aerosols are generated in clouds are still being studied, and the extent to which they explain the rains in the Amazon is not yet known. Scientists conjecture that the organic gases emitted by the forest enter into deep clouds and, as they get pushed upwards by ascending air currents, they freeze at -20 or -30 degrees Celsius and form the aerosols. \u201cThis strong interaction of the clouds with forest emissions feeds back into the most intense water cycle on the planet,\u201d Artaxo says. \u201cIn Rond\u00f4nia, a state that has cut down 60% of its forests, the composition and properties of the aerosols change and rain is produced through other mechanisms.\u201d<\/p>\n

On some of the flights, the German aircraft was accompanied by an American plane that collected data at lower altitudes, having already flown over the forest months earlier during the rainy season. Aggregated with the data from radar, satellites and radiosondes, this information revealed two cloud patterns in the Amazon. Over the areas of forest that had undergone little change and were nearly pollution-free, clouds have fewer aerosols. \u201cTheir droplets are concentrated at the base of the clouds, are larger and grow more rapidly, so they generate abundant rainfall,\u201d says meteorologist Luiz Augusto Machado, a researcher at the National Institute for Space Research (INPE) and the coordinator of Projeto Chuva [the Rain Project], who investigated the types and distribution of rain clouds in Brazil.<\/p>\n

\"056-058_Chuvas<\/a>This was the profile found in the area of Boa Vista, in the state of Roraima. The clean-atmosphere region at the base of clouds contained nearly 200 droplets per cubic centimeter (cm3<\/sup>), each measuring 100 to 1,000 micrometers in diameter. In the area of forest that receives pollutants from Manaus or from fires, the clouds have more aerosols. With more nuclei around which to condense, the water is distributed in more droplets (400 per cm3<\/sup>) of smaller size (60 micrometers). The droplets take longer to grow in volume, and they can evaporate instead of raining. These clouds are higher, have more ice crystals and generate frequent lightning.<\/p>\n

Meteorologist Rachel Albrecht of the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG) at USP also observed that in polluted regions, storm clouds generate unusual positive lightning, in which the discharge is more intense and occurs only once. These lightning strikes are more frequent at the end of the dry season, when there are more fires.<\/p>\n

\u201cKnowing these mechanisms is essential for feeding into models with high spatial resolution and better capability to reproduce local rainfall and prevent disasters,\u201d says Machado, who will discuss the data from Acridicon-Chuva this month at a workshop in Ilhabela, on the coast of S\u00e3o Paulo State.<\/p>\n

\u201cWhat we are observing in the region affected by the Manaus pollution plume could signal the future of an urbanized tropical forest,\u201d Artaxo says. \u201cAnd it is representative of the present-day mechanism of rain formation in Africa or Indonesia, where there are many cities surrounded by forest, or in a more urban Amazon.\u201d Maria Assun\u00e7\u00e3o da Silva Dias, a meteorologist at IAG and researcher with GoAmazon, cautions that what is happening in the Amazon could have global impact. \u201cChanges in the clouds in Amazonia,\u201d she says, \u201caffect climate throughout the planet.\u201d<\/p>\n

Projects<\/strong>
\n1.<\/strong> GoAmazon: interactions of the urban plume of Manaus with biogenic forest emissions in Amazonia (n\u00ba 2013\/05014-0<\/a>); Grant Mechanism <\/strong>Research Program on Global Climate Change; Principal Investigators <\/strong>Paulo Artaxo Netto (IF-USP) and Maria Assun\u00e7\u00e3o da Silva Dias (IAG-USP); Investment\u00a0<\/strong>R$ 3,246,351.45.
\n2.<\/strong> Cloud processes of the main precipitation systems in Brazil: a contribution to cloud-resolving modeling and to the GPM (Global Precipitation Measurement) (n\u00ba 2009\/15235-8<\/a>);\u00a0Grant Mechanism <\/strong>Thematic Project;\u00a0Principal Investigator\u00a0<\/strong>Luiz Augusto Toledo Machado (INPE);\u00a0Investment\u00a0<\/strong>R$ 2,362,708.53.<\/p>\n","protected":false},"excerpt":{"rendered":"Missing particles explain how clouds form in the Amazon","protected":false},"author":16,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[159],"tags":[217,224,200],"coauthors":[105],"class_list":["post-219848","post","type-post","status-publish","format-standard","hentry","category-science","tag-climate","tag-ecology","tag-environment"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/219848","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/16"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=219848"}],"version-history":[{"count":0,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/219848\/revisions"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=219848"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=219848"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=219848"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=219848"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}