Aleksey V. Nevzorov

Lidar Observations of Aerosol Disturbances of the Stratosphere over Tomsk (N; E) in Volcanic Activity Period 2006–2011

The lidar measurements (Tomsk: N; E) of the optical characteristics of the stratospheric aerosol layer (SAL) in the volcanic activity period 2006–2011 are summarized and analyzed. The background SAL state with minimum aerosol content, observed since 1997 under the conditions of long-term volcanically quiet period, was interrupted in October 2006 by series of explosive eruptions of volcanoes of Pacific Ring of Fire: Rabaul (October 2006, New Guinea); Okmok and Kasatochi (July-August 2008, Aleutian Islands); Redoubt (March-April 2009, Alaska); Sarychev Peak (June 2009, Kuril Islands); Grimsvotn (May 2011, Iceland). A short-term and minor disturbance of the lower stratosphere was also observed in April 2010 after eruption of the Icelandic volcano Eyjafjallajokull. The developed regional empirical model of the vertical distribution of background SAL optical characteristics was used to identify the periods of elevated stratospheric aerosol content after each of the volcanic eruptions. Trends of variations in the total ozone content are also considered.

Results of joint observations of aerosol perturbations of the stratosphere at the CIS-LiNet network in 2008

The results of lidar observations of stratospheric aerosol perturbations for the period of July–November 2008 at three lidar stations of the CIS-LiNet network in Tomsk, Minsk, and Vladivostok are presented along with the results obtained in the Gobi Desert during a research expedition. The behavior of stratospheric profiles of the scattering ratio R(H) (ratio of the total aerosol and molecular backscattering coefficient to the molecular backscattering coefficient) is analyzed at different wavelengths characterizing the aerosol stratification in the stratosphere. The transport of air masses in the stratosphere is studied by the method of direct and backward trajectories using the NOAA HYSPLIT model. It is shown that stratospheric aerosol perturbations are connected with explosive eruptions of volcanoes of the Aleutian islands Okmok (53.4° N, 168.1° W; July 12, 2008) and Kasatochi (52.2° N, 175.5° W; August 6–8, 2008).

Optical monitoring of characteristics of the stratospheric aerosol layer and total ozone content at the Siberian Lidar Station Tomsk: 56° 30′ N; 85° E

We consider the results of long-term remote optical monitoring obtained at the Siberian Lidar Station of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk (56° 30′ N, 85° E). The scattering characteristics of stratospheric aerosol layer, obtained according to data of lidar measurements recorded since 1986, are presented. We analyse the trends of changes in the total ozone (TO) content over Tomsk for the period 1996–2013 according to data of spectrophotometric measurements employing Total Ozone Mapping Spectrometer (TOMS) data for the period 1979–1994. We determined the periods of elevated content of stratospheric aerosol over Tomsk after a series of explosive eruptions of volcanoes in the Pacific Ring of Fire and Iceland in 2006–2011. Since the second half of the 1990s we have recorded an increasing TO trend, equalling 0.65 DU/year for the period 1996–2013.

Aerosol disturbances of the stratosphere after eruption of Grimsvötn volcano (Iceland, May 21, 2011) according to observations at lidar network stations of CIS countries CIS-LiNet in Minsk, Tomsk, and Vladivostok

In 2010 and first half of 2011, a background aerosol content was observed in the atmosphere of the Northern Hemisphere midlatitudes. The report presents the observations of aerosol disturbances of the stratosphere in the second half of 2011, which were performed at lidar network stations of CIS countries CIS-LiNet in Minsk (53.9°N; 27.6°E), Tomsk (56.5°N; 85.0°E), and Vladivostok (43.0°N; 131.9°E). Data of lidar measurements at the sensing wavelengths of 353, 355, and 532 nm indicate that increased aerosol content was observed since June – July almost until the end of 2011 in the lower stratosphere up to the altitudes ~ 18 km. A well-defined, temporally stable aerosol layer was observed until October 2011 in the altitude interval ~ (13-17) km. The trajectory analysis of air mass transport in the stratosphere according to NOAA HYSPLIT MODEL with employment of CALIPSO satellite data shows that the increased aerosol content observed was most likely due to transport of eruption products of Grimsvötn volcano (May 21, 2011, Iceland: 64.4°N; 17.3°W).

Effect of ozone anomaly during spring of 2011 on long-term (1996-2011) trends of the total ozone content according to ground-based (Tomsk: 56.48°N, 85.05°E) and satellite spectrophotometric measurements

Anomalous decreases in the total ozone (TO) content were observed in March 2011 at Arctic latitudes and in April at midlatitudes of the Northern Hemisphere. In Arctic this was a consequence of extended stratospheric coolings, while at midlatitudes the TO decreases were due to export of ozone depleted air from Arctic regions. Total ozone largely returned to its seasonal behavior in May 2011, however remaining deficient throughout 2011 and being recovered only in the period of resumed wintertime meridional ozone transport from equatorial reservoir. All this led to a decrease in the multiyear (1996-2011) positive TO trend, most appreciably at the Northern Hemisphere Arctic and high latitudes. The M-124 ozonometer measurements indicate that the positive ozone trend decreased from 1.09 DU/yr for the period 1996- 2010 to 0.26 DU/yr for the period 1996-2011 due to the springtime TO decrease over Tomsk in 2011.

Measuring the characteristics of stratospheric aerosol layer and total ozone concentration at Siberian Lidar Station in Tomsk

We consider the results of long-term remote optical monitoring, obtained at the Siberian Lidar Station of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences in Tomsk (56.5 °N, 85.0 °E). The scattering characteristics of stratospheric aerosol layer, obtained according to data of lidar measurements since 1986, are presented. We analyze the trends of changes in the total ozone (TO) content over Tomsk for the period 1996-2013 according to data of spectrophotometric measurements with employment of TOMS satellite data for the period 1979- 1994. We determined the periods of elevated content of stratospheric aerosol over Tomsk after a series of explosive eruptions of volcanoes of Pacific Ring of Fire and Iceland in 2006-2011. Since the second half of 1990s, researchers record an increasing TO trend, equaling 0.65 DU/yr for the period 1996-2013.

Aerosol disturbances of the stratosphere over Tomsk according to data of lidar observations in volcanic activity period 2006–2011

We summarize and analyze the lidar measurements (Tomsk: 56.5°N; 85.0°E) of the optical characteristics of the stratospheric aerosol layer (SAL) in the volcanic activity period 2006-2011. The background SAL state with minimal aerosol content, which was observed since 1997 under the conditions of long-term volcanically quiescent period, was interrupted in October 2006 by a series of explosive eruptions of volcanoes of the Pacific Ring of Fire: Rabaul (October 2006, New Guinea); Okmok and Kasatochi (July-August 2008, Aleutian Islands); Redoubt (March-April 2009, Alaska); Sarychev Peak (June 2009, Kuril Islands), and Grimsvötn (May 2011, Iceland). A short-term and minor disturbance of the lower stratosphere was also observed in April 2010 after eruption of the Icelandic volcano Eyjafjallajokull. The developed regional empirical model of the vertical distribution of background SAL optical characteristics was used to identify the periods of elevated stratospheric aerosol content after each of the volcanic eruptions.

Anomalous behavior of the total nitrogen dioxide content in the stratosphere over Tomsk in 2011

In January, February, and April 2011, observations over Tomsk recorded anomalous decreases in the total contents of nitrogen dioxide and ozone. The total nitrogen dioxide and ozone contents decreased by ~30% relative to multiyear averages. The observed decreases in the total nitrogen dioxide and ozone contents over Tomsk are associated with ozone destruction in the polar stratosphere due to low temperatures at altitudes of 15-30 km and transport of Arctic air masses to midlatitudes.

Lidar observation of midlatitude stratospheric aerosols in long-term volcanically quiet period

We analyze the data of measurements of the optical characteristics of stratospheric aerosol layer (SAL), obtained at the Siberian Lidar Station of lAO SB RAS in Tomsk (56°N, 85°E). The data are considered in comparison with results of previous years of observations in Tomsk and at other midlatitude stations of the Northern Hemisphere. The results characterize SAL state in extended volcanically quiet period. The last explosive volcanic eruption was observed in June 1991 (volcano Pinatubo). For the first time such a SAL state is studied using modem ground-based and satellite measurement facilities. The results of observations show that the background levels of the natural aerosols in the stratosphere may be lower than was considered earlier. The anthropogenic growth of background stratospheric aerosol content is not observed. The presence of seasonality and quasi-biennial oscillation (QBO), with a characteristic increase of aerosol content at midlatitudes in periods of intensification of winter-spring meridional transport from tropical belt to midlatitudes and in westerly QBO phases, is an evidence in favor of hypothesis about the presence of tropical reservoir of not only volcanic but also background stratospheric aerosol.

Quasi-biennial oscillation in variations of vertical distribution of midlatitude stratospheric ozone and aerosol

Based on analysis of data of lidar, spectrophotometric, and satellite measurements of integrated content of stratospheric ozone and aerosol for period 1986-2002 for observation site in Tomsk (56.48°N, 85.05°E), earlier we showed the presence of quasibiennial oscillation (QBO) of variations of their integrated content. The report analyzes data of lidar measurements of ozone and aerosol vertical distributions for background stratospheric state under conditions of extended volcanically quiet period 1996-2005. For analysis, we averaged profiles corresponding to easterly and westerly QBO phases, which were determined from monthly mean zonal wind components in the equatorial stratosphere. Larger aerosol content is observed in westerly QBO phases, and larger ozone content in easterly phases, in correspondence with views on general stratospheric circulation. Differences are most marked in the lower stratosphere, up to heights about 22 km. In the lower stratosphere, we also observe insignificantly larger aerosol content in winter-spring than summer-fall period. The presence of seasonality and quasibiennial oscillation, with increase of aerosol content at midlatitudes in periods of intensification of winter-spring meridional transport from tropical belt to midlatitudes and in westerly QBO phases, is an evidence in favor of hypothesis on the presence of tropical reservoir of background stratospheric aerosol.