Oleg Bazhenov

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.

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.

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.

Elevated Humidity in the Stratosphere as a Gain Factor of Ozone Depletion in the Arctic According to Aura MLS Observations

The analysis of Aura MLS data showed that the temperature in the Arctic stratosphere was much lower than normal throughout the period from January to March 2011 in the altitude range 20–35 km. That led to a considerable spread of polar stratospheric clouds (PSCs), which were formed most intensely in periods and at altitudes of minimal temperatures (maximal temperature drop below PSC formation threshold). The main ozone losses were observed in March. They were due to a photochemical release of chlorine that avoided deactivation in view of the nitrogen deficit caused by denitrification in the course of frequent dehydration events indicated by oscillations of the altitude of maximal humidity distortion. Elevated humidity in the stratosphere had raised the threshold temperature of formation of PSCs that persisted until late March; this promoted the chlorine activation and, thereby, delayed the chlorine deactivation, resulting in an even higher level of overall ozone losses during March 2011.

On the role of the eruption of the Merapi volcano in an anomalous total ozone decrease over Tomsk in April 2011

In April 2011, at Northern Hemisphere midlatitudes, a long-term anomalous decrease in the total ozone content was recorded over a number of regions, attributed to echoes of a large-scale Arctic ozone anomaly, observed in March. We showed that stratospheric ozone destruction over Tomsk during that period was caused by an eruption of Indonesian volcano Merapi in November, 2010. The NOAA HYSPLIT model was used to analyze air mass transport in the lower stratosphere starting from coordinates of volcanic emission from the date of eruption until late April. It was found that air masses, containing volcanic aerosol, came to the Northern Hemisphere midlatitudes in late March, 2011, in agreement with high aerosol content recorded in the stratosphere over Tomsk during that period. Based on analysis of temperature and ozone anomalies in the stratosphere over Tomsk, these anomalies were shown to be due to the presence of volcanic soot in aerosol composition.

Quasi-biennial oscillation of the total ozone and ozone concentrations at separate altitude levels over Arctic and Tomsk according to TOMS, OMI, and MLS observations

We analysed the quasi-biennial oscillation of the total ozone (TO) and ozone concentrations at separate altitudinal levels in the stratosphere over Arctic territory and Tomsk according to data from the Total Ozone Mapping Spectrometer (TOMS), the Ozone Monitoring Instrument (OMI), and the Microwave Limb Sounder (MLS), flown on different satellite platforms. The correlation coefficient between TO and equatorial zonal wind for the period of 1996–2013 is statistically insignificant. The spring (March–April) average ozone concentrations and zonal wind mostly show the correlation in the interval from −0.23 to −0.26. The mixing ratio time series, composed for separate altitudinal levels over the period of 2005–2013, exhibit quasi-biennial oscillation, which is weakly manifested at lowest heights, takes shape at heights of ~30 km, and weakens in overlying regions. The correlation between the ozone mixing ratio and the equatorial zonal wind index is most distinct at Western Hemisphere sites and more complex in the Eastern Hemisphere.

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.

Study of vertical NO 2 and 0 3 distributions in the stratosphere at Siberian Lidar Station (56.5°N, 85.1°E) in the period from 1996 to 2004

The paper presents the results of analysis of regular spectrophotometric and lidar measurements of vertical distribution ozone and nitrogen dioxide content obtained at Siberian Lidar Station of Institute of Atmospheric Optics SB RAS (56.48N/85.05E) from January 1996 to December 2004. The profiles obtained from the results of lidar atmospheric sensing in the altitude range from 25 to 35 km were the initial data for analysis of the vertical ozone distribution. The data on vertical distribution content of nitrogen dioxide in the altitude range from 30 to 35 km were calculated using twilight measurements of the spectral sky brightness along the zenith in the wavelength range from 430 to 450nm.

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.