Abstract
In this study, an air mass (containing a cirrus cloud) was detected by light detection and ranging (lidar) above São Paulo (Brazil) in June 2007 and tracked around the globe, thanks to Lagrangian calculations as well as ground-based and satellite observations. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data were also used to provide locations of occurrence of cirrus around the globe and extract their respective macro physical parameters (altitude and temperature). An analysis of the air mass history based on Lagrangian trajectories reveals that water coming from the Equator is channelized through the southern subtropical jet for weeks. In this case, the back-trajectories showed that the cirrus cloud detected at São Paulo was a mixture of air masses from two different locations: (1) the active convective area located around the Equator, with transport into the upper troposphere that promotes cirrus cloud formation; and (2) the South Pacific Ocean, with transport that follows the subtropical jet stream (STJ). Air masses coming from equatorial convective regions are trapped by the jet, which contributes to maintaining the lifetime of the cirrus cloud for a few days. The cloud disappears near the African continent, due to a southern excursion and warmer temperatures, then reappears and is detected again by the lidar system in São Paulo after 12 days. The observed cloud is located at a similar altitude, revealing that sedimentation is small or compensated by radiative uplift.
Highlights
In the lower stratosphere, water vapor plays a key role in the radiation budget [1]
Cirrus clouds have been frequently observed at São Paulo (23◦ 330 S, 46◦ 440 W), by MSP-lidar measurements since 2004 [13]
On 4–5 June 2007, trajectories returned to the Equator as they remained on the same isentropic level, temperatures cooled back to the same level, and cirrus clouds were detected again, mainly for the trajectory corresponding to the mean altitude of the initial cloud observed above São Paulo
Summary
Water vapor plays a key role in the radiation budget [1]. upper tropospheric cirrus clouds are highly dependent on local temperature and water vapor. Global climate models (GCM) have difficulties simulating water vapor density and cirrus cloud occurrence in the TTL and the lower stratosphere, revealing large differences between themselves depending on the parametrization used [10,11,12]. Even a mixture of both types of cloud origins [13] These observations suggest some potential preferred routes and the existence of permanent moist air over the sub-tropical jet. While a Lagrangian approach appears to be well-adapted to study the evolution and maintenance of cirrus in the upper troposphere [9], another approach consists in sampling air masses by several ground-based instruments, as well as by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
