Jacobo Salvador

New differential absorption lidar for stratospheric ozone monitoring in Patagonia, South Argentina

As part of environmental studies concerned with measurements of the stratospheric ozone layer, CEILAP has developed a new differential absorption lidar (DIAL) instrument. Since the initial construction of the first DIAL instrument, the Lidar Division of CEILAP has made important financial and scientific investments to upgrade this initial prototype. The new version has a bigger reception system formed by four Newtonian telescopes, each of 50 cm diameter, and a larger number of detection channels: four different wavelengths are detected simultaneously and six digital channels record the Rayleigh and Raman backscattered photons emitted by a ClXe excimer laser at 308 nm and the third harmonic of a Nd–YAG laser at 355 nm. A number of different changes have been made to increase the dynamic range of this lidar: a mechanical chopper was installed together with a gated photomultiplier in the high-energy detection channels to avoid the detector being overloaded by strong signals from lower atmospheric layers. This new version was installed inside a shelter, giving the possibility to make field campaigns outside CEILAP laboratories, for example the SOLAR campaign made in the Argentine Patagonian region during 2005 and 2006 spring periods. In this paper a full description of the instrument update is given. Intercomparisons with the ozone sonde and satellite platform instrument are presented. The results show agreement better than 10% in 16–38 km altitude range when the same airmasses are sampled. The comparison with five quasi-coincident sondes launched in Punta Arenas during spring 2005 shows good agreement between both types of measurement, with relative differences inside 1σ deviation of the lidar measurement. The comparison of the integral of height integrated lidar profiles with total ozone column measured with a Brewer photometer shows good agreement, with relative differences less than 10%.

UV ground based measurements in Río Gallegos, Argentina

CEILAP’s Lidar Division has established an atmospheric remote sensing site in Rio Gallegos (51°55′ S, 69°14′ W) in the southern region of Argentina. SOLAR Campaign was held during 2005–2006. The main objectives of this experiment were to measure stratospheric ozone profiles and surface UV radiation in a subpolar region, where the influence of polar vortex and the Antarctic ozone hole are remarkable. This remote sensing site has lidar instruments and passive sensors to measure solar UV irradiance. In this paper we focused on passive remote sensing sensors and the Rio Gallegos erythemal irradiances reported during 2005–2006. Time evolution of UV index was derived from these measurements and the influence of ozone depleted air masses passing over over Rio Gallegos is highlighted in this paper. This Patagonian region is characterized by high cloud cover during the day that strongly changes the distribution of UV radiation that reaches the ground surface. For that reason some overpasses of ozone hole are maske...

Measurement and subtraction of Schumann resonances at gravitational-wave interferometers

Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible.

Aerosol monitoring with a lidar observation network in southern South America

In the southern South America, various types of aerosols have been observed including biomass burning aerosols from the Amazon region, flying ashes from the volcanic eruptions coming from the Andean Volcanic Belt, mineral dust from the Patagonian Desert, and air pollution aerosols from urban areas. To monitor such aerosols continuously, we developed a lidar observation network in Argentina and Chile. Eight lidars were installed in Argentina and one in Punta Arenas, Chile. Backscattering signals are measured at three wavelengths: 355, 532, and 1064 nm. Eight of those instruments are measuring depolarization ratio at 355 and 532 nm to detect non-spherical aerosols. In addition, four lidars are equipped Ramans channels and two high-spectral-resolution channels to measure backscattering and extinction coefficients quantitatively. Lidar operation, data analysis, and products release are implemented within the South American Environmental Risk Management Network (SAVER-Net) system, which was developed by a trinational project among Japan, Argentina, and Chile. Using lidar data, hazard information on the aerosol type and extinction coefficient at low altitude is provided for public in a near real time. In addition, plume height and qualitatively concentration for volcanic ashes are estimated. The information on volcanic ashes may be effectively used for advising aircraft landing and departing when volcanic eruptions occurs.

Attenuation by clouds of UV radiation for low stratospheric ozone conditions

Stratospheric poor ozone air masses related to the polar ozone hole overpass subpolar regions in the Southern Hemisphere during spring and summer seasons, resulting in increases of surface Ultraviolet Index (UVI). The impact of these abnormal increases in the ultraviolet radiation could be overestimated if clouds are not taking into account. The aim of this work is to determine the percentage of cases in which cloudiness attenuates the high UV radiation that would reach the surface in low total ozone column situations and in clear sky hypothetical condition for Rio Gallegos, Argentina. For this purpose, we analysed UVI data obtained from a multiband filter radiometer GUV-541 (Biospherical Inc.) installed in the Observatorio Atmosferico de la Patagonia Austral (OAPA-UNIDEF (MINDEF – CONICET)) (51 ° 33’ S, 69 ° 19’ W), Rio Gallegos, since 2005. The database used covers the period 2005-2012 for spring seasons. Measured UVI values are compared with UVI calculated using a parametric UV model proposed by Madron...

Study of UV cloud modification factors in Southern Patagonia

Anthropogenic perturbation of the ozone layer has induced change in the amount of UV radiation that reaches the Earth’s surface, mainly through the Antarctic ozone hole, making the ozone and ultraviolet (UV) radiation two important issues in the study of Earth atmosphere in the scientific community. Also the clouds have been identified as the main modulator of UV amount in short time scales and produce the main source of uncertainty in the projection of surface UV level as consequence of projected ozone recovery. While clouds can decrease direct radiation, they can produce an increase in the diffuse component, and as consequence the surface UV radiation may be higher than an equivalent clear sky scenario for several minutes. In particular this situation can be important when low ozone column and partially cloud cover skies happen simultaneously. These situations happen frequently in southern Patagonia, where the CEILAP Lidar Division has established the Atmospheric Observatory of Southern Patagonia, an at...

Comparison of ozone profiles from DIAL, MLS, and chemical transport model simulations over Río Gallegos, Argentina during the spring Antarctic vortex breakup, 2009

This study evaluates the agreement between ozone profiles derived from the ground-based differential absorption lidar (DIAL), satellite-borne Aura Microwave Limb Sounder (MLS), and 3-D chemical transport model (CTM) simulations such as the Model for Interdisciplinary Research on Climate (MIROC-CTM) over the Atmospheric Observatory of Southern Patagonia (Observatorio Atmosférico de la Patagonia Austral, OAPA; 51.6 S, 69.3W) in Río Gallegos, Argentina, from September to November 2009. In this austral spring, measurements were performed in the vicinity of the polar vortex and inside it on some occasions; they revealed the variability in the potential vorticity (PV) of measured air masses. Comparisons between DIAL and MLS were performed between 6 and 100 hPa with 500 km and 24 h coincidence criteria. The results show a good agreement between DIAL and MLS with mean differences of ±0.1 ppmv (MLS−DIAL, n= 180) between 6 and 56 hPa. MIROC-CTM also agrees with DIAL, with mean differences of ±0.3 ppmv (MIROC-CTM−DIAL, n= 23) between 10 and 56 hPa. Both comparisons provide mean differences of 0.5 ppmv (MLS) to 0.8–0.9 ppmv (MIROC-CTM) at the 83– 100 hPa levels. DIAL tends to underestimate ozone values at this lower altitude region. Between 6 and 8 hPa, the MIROCCTM ozone value is 0.4–0.6 ppmv (5–8 %) smaller than those from DIAL. Applying the scaled PV (sPV) criterion for matching pairs in the DIAL–MLS comparison, the variability in the difference decreases 21–47 % between 10 and 56 hPa. However, the mean differences are small for all pressure levels, except 6 hPa. Because ground measurement sites in the Southern Hemisphere (SH) are very sparse at midto high latitudes, i.e., 35–60 S, the OAPA site is important for evaluating the bias and long-term stability of satellite instruments. The good performance of this DIAL system will be useful for such purposes in the future.

Study of cloud enhanced surface UV radiation at the atmospheric observatory of Southern Patagonia, Río Gallegos, Argentina

Ozone and ultraviolet (UV) radiation are two important issues in the study of Earth’s atmosphere. The anthropogenic perturbation of the ozone layer has induced change in the amount of UV radiation that reaches the Earth’s surface, mainly through the Antarctic ozone hole. Also clouds have been identified as the main modulator of UV amount over short time scales. While clouds can decrease direct radiation, they can produce an increase in the diffuse component, and as a consequence the surface UV radiation may be higher than during an equivalent clear sky scenario. In particular this situation can be important when a low ozone column and partially cloud coverered skies occur simultaneously. These situations happen frequently in southern Patagonia, where the CEILAP Lidar Division has established the Atmospheric Observatory of Southern Patagonia, an atmospheric remote sensing site near the city of Rio Gallegos (51°55’S, 69°14’W). In this paper, the impact of clouds on UV radiation is investigated by the use of...

New Differential Absorption Lidar for Stratospheric Ozone Monitoring in Argentina

As part of environmental studies concerning with measurements of the stratospheric ozone layer, the CEILAP developed a new Differential Absorption Lidar (DIAL) instrument. Since the early construction of the first DIAL instrument, Lidar Division has been made important financial and scientific investments to improve this initial prototype. The new version has a bigger reception system formed by 4 newtonian telescopes of 50 cm diameter each one and a higher number of detection channels: four different wavelengths are detected simultaneously and six digital channels record the Rayleigh and Raman backscattered photons emitted by an ClXe Excimer laser at 308 nm and third harmonic of Nd‐YAG laser at 355 nm. A number of different changes have been made to increase the dynamical range of this lidar: a mechanical chopper was installed together with gated photomultiplier in the high energy detection channels to avoid strong signals from lower atmospheric layers. This new version was installed inside a shelter give...

Using Lidar to Measure the Ozone Layer

South American scientists are using lidar technology to measure stratospheric ozone, water vapor and aerosols in Argentine Patagonia. Their work is helping to monitor global climate change, and has led to the development of a method for alerting local populations to the presence of the ozone hole.