**4. Stratosphere**

#### **4.1 Historical overview**

The first lidar measurements concerning stratospheric aerosols in Latin America were performed in Kingston, Jamaica, between 1964 and 1979 [46]. The lidar system held for these measurements was managed by the University of the West Indies and supported by the US Air Force [47]. Its primary purpose was to investigate the atmospheric profile, measuring molecular scattering. Moreover, the system proved valuable for measurements of stratospheric aerosol layers at wavelength 694 nm [48]. These lidar measurements from Jamaica represented a pioneering role, concomitantly with different research teams, developing lidars' capacities to measure aerosols in the lower stratosphere [49]. Those measurements were also an essential contribution to the stratosphere's early studies in the tropics [50].

In 1969, a new lidar instrument was designed and developed at INPE by Prof. Barclay Clemesha (see Section 3 for details). This equipment's primary objective was to investigate the mesosphere dynamics; besides, stratospheric aerosol measurements were also performed. The first measurements were carried in 1970 at wavelength 694 nm [16], and regular measurements began in 1972 [51]. This project was responsible for collecting the longest stratospheric aerosol profile measurements in Latin America and the Southern Hemisphere's tropical zone, extending from 1971 to 2016. It includes stratospheric aerosols profiles from the two more significant volcanic eruptions of the XX century second half: the first happened in Mexico on 04 April 1982 (El Chichón), and the second in the Philippines on 14 June 1991 (Mount Pinatubo) [51, 52]. Measurements conducted at INPE between 1972 and 2016 proved the value and the importance of the stratospheric aerosols' longterm monitoring. They have rendered information to understand the stratospheric aerosols layer evolution in the Southern Hemisphere's tropics since the '50s [53].

A Cuban-Soviet scientific cooperation agreement supported the deployment in 1988 of a lidar system designed for stratospheric aerosols measurements at the Camagüey Meteorologic Center in Cuba [54]. The instrument operated intermittently between 1988 and 1997, providing stratospheric aerosols measurements from the Mount Pinatubo eruption in 1991. The 1988–1990 lidar aerosol profiles, at 532 nm, combined with satellite measurements, have been used to study background stratospheric aerosols in the Caribbean [55]. Camagüey Lidar Station (CLS) stratospheric aerosols profiles from Mount Pinatubo also contributed to the study of the radiative impacts of the eruption at regional [56] and global [57] scales. Moreover, the Camagüey lidar database was also used to validate the stratospheric aerosol SAGE II satellite measurements from Mount Pinatubo eruption [58, 59]. Furthermore, it was used to generate an extinction climatology in the UV for correcting Brewer ozone measurements [60].

By 1994 the Laser and Applications Research Center (CEILAP - UNIDEF) in Buenos Aires, Argentina, developed various lidar systems for atmospheric research [7]. One of these devices was designed to measure the atmospheric boundary layer, cirrus clouds, and tropospheric aerosols, operating at wavelength 532 nm [61]. A collaborative study between CEILAP and CLS evaluated how this lidar system could also be used for the higher troposphere and lower stratospheric aerosols research. Upon analyzing two tropospheric aerosols profiles extending into the lower stratosphere, encouraging results were found [62]. In June 2005, another lidar system was designed and installed by CEILAP in Río Gallegos, Patagonia. This instrument's primary goal was performing measurements of stratospheric ozone, tropospheric and stratospheric aerosols, and water vapor. In particular, stratospheric aerosol profiles are used to correct the stratospheric ozone [63].

Western South America is bordered by the Andes, which divides the continent into two distinct regions. In South America, the vast majority of active volcanoes are located in the eastern part of the continent, and ash eruptions are routinely reported throughout the region. The volcanic activity includes periods of ash eruptions and cycling eruptions that spread out over months or even years [64, 65]. Great active volcanoes in South America are Nevado del Ruíz, in Colombia; Cotopaxi, Tungurahua, and Reventador, in Ecuador; Villarrica, Llaima, Nilahue, Lascar, Chaitén, and Calbuco, in Chile; El Misti, Ubinas and Sabancaya, in Peru; Aracar, Copahue, and Planchón-Peteroa in Argentina. There are no reported active volcanoes in Paraguay, Uruguay, Venezuela, Guyana, Suriname, and Brazil [64, 65].

On 22 April 2015, in Chile, the Calbuco volcano erupted and injected a significant amount of ashes and aerosols into the atmosphere [66].

The volcanic aerosol profiles in both the upper troposphere and the lower stratosphere, which originated from the Calbuco volcano eruption in Chile on 22 April 2015, were measured by different lidar stations in South America [7]. It was the first time that LALINET lidar stations, distributed across the continent, could analyze aerosol profiles together during an event. Lidar stations located in Buenos Aires, Comodoro Rivadavia, San Carlos de Bariloche, Neuquén, and Rio Gallegos (all five in Argentina), Concepción (Chile), and São Paulo (Brazil) observed the

#### *Lidar Observations in South America. Part I - Mesosphere and Stratosphere DOI: http://dx.doi.org/10.5772/intechopen.95038*

aerosols profiles [7, 67]. LALINET stations' capabilities to operate in a coordinated way in case of a volcanic eruption were challenged, highlighting the coordination among LALINET teams.

On 23 April 2015 (one day after the eruption), the lidar system at the University of Concepción measured the aerosols profiles between 5 and 9 km, showing a multilayer structure. Both layers merged at around 7 km, decreasing its intensity and narrowing. The following day 24 April 2015, the two layers registered in the day before at Concepción were detected in the nighttime by the lidar system placed in Buenos Aires, Argentina, in heights varying between 5 and 7 km showing a drowning leaning. The aerosol's multilayer formation was present at both lidar sites when identified for the first time. Lidar measurements conducted at IPEN in São Paulo on 27 April 2015 (five days after the eruption) exhibited aerosols found at an altitude of about 19 km in the stratosphere (**Figure 7**) [66]. Those lidar extinction profiles were confronted with those measured by the Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP) instrument, revealing promising results [7].
