Optical and geometrical properties of cirrus clouds in Amazonia derived from 1 year of ground-based lidar measurements

Optical and geometrical properties of cirrus clouds in Amazonia derived from 1 year of ground-based lidar measurements

Author Gouveia, Diego A. Google Scholar
Barja, Boris Google Scholar
Barbosa, Henrique M. J. Google Scholar
Seifert, Patric Google Scholar
Baars, Holger Google Scholar
Pauliquevis, Theotonio Autor UNIFESP Google Scholar
Artaxo, Paulo Google Scholar
Abstract Cirrus clouds cover a large fraction of tropical latitudes and play an important role in Earth's radiation budget. Their optical properties, altitude, vertical and horizontal coverage control their radiative forcing, and hence detailed cirrus measurements at different geographical locations are of utmost importance. Studies reporting cirrus properties over tropical rain forests like the Amazon, however, are scarce. Studies with satellite profilers do not give information on the diurnal cycle, and the satellite imagers do not report on the cloud vertical structure. At the same time, ground-based lidar studies are restricted to a few case studies. In this paper, we derive the first comprehensive statistics of optical and geometrical properties of upper-tropospheric cirrus clouds in Amazonia. We used 1 year (July 2011 to June 2012) of ground-based lidar atmospheric observations north of Manaus, Brazil. This dataset was processed by an automatic cloud detection and optical properties retrieval algorithm. Uppertropospheric cirrus clouds were observed more frequently than reported previously for tropical regions. The frequency of occurrence was found to be as high as 88% during the wet season and not lower than 50% during the dry season. The diurnal cycle shows a minimum around local noon and maximum during late afternoon, associated with the diurnal cycle of precipitation. The mean values of cirrus cloud top and base heights, cloud thickness, and cloud optical depth were 14.3 +/- 1.9 (SD) km, 12.9 +/- 2.2 km, 1.4 +/- 1.1 km, and 0.25 +/- 0.46, respectively. Cirrus clouds were found at tem-peratures down to 90 degrees C. Frequently cirrus were observed within the tropical tropopause layer (TTL), which are likely associated to slow mesoscale uplifting or to the remnants of overshooting convection. The vertical distribution was not uniform, and thin and subvisible cirrus occurred more frequently closer to the tropopause. The mean lidar ratio was 23.3 +/- 8.0 sr. However, for subvisible cirrus clouds a bimodal distribution with a secondary peak at about 44 sr was found suggesting a mixed composition. A dependence of the lidar ratio with cloud temperature (altitude) was not found, indicating that the clouds are vertically well mixed. The frequency of occurrence of cirrus clouds classified as subvisible (tau < 0 : 03) were 41.6 %, whilst 37.8% were thin cirrus (0 : 03 < tau < 0 : 3) and 20.5% opaque cirrus (tau > 0 : 3). Hence, in central Amazonia not only a high frequency of cirrus clouds occurs, but also a large fraction of subvisible cirrus clouds. This high frequency of subvisible cirrus clouds may contaminate aerosol optical depth measured by sun photometers and satellite sensors to an unknown extent.
xmlui.dri2xhtml.METS-1.0.item-coverage Gottingen
Language English
Sponsor CNPq fellowship program
CAPES project on the program Science without Frontiers
SAVERNET project
FAPESP Research Program on Global Climate Change
Grant number CAPES: A016_2013
FAPESP Research Program on Global Climate Change: 2008/58100-1
FAPESP Research Program on Global Climate Change: 2009/15235-8
FAPESP Research Program on Global Climate Change: 2012/16100-1
FAPESP Research Program on Global Climate Change: 2013/50510-5
FAPESP Research Program on Global Climate Change: 2013/05014-0
Date 2017
Published in Atmospheric Chemistry And Physics. Gottingen, v. 17, n. 5, p. 3619-3636, 2017.
ISSN 1680-7316 (Sherpa/Romeo, impact factor)
Publisher Copernicus Gesellschaft Mbh
Extent 3619-3636
Origin http://dx.doi.org/10.5194/acp-17-3619-2017
Access rights Open access Open Access
Type Article
Web of Science ID WOS:000397928200001
URI https://repositorio.unifesp.br/handle/11600/54924

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