Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

OBSERVATIONS OF POLAR STRATOSPHERIC CLOUDS OVER MURMANSK IN JANUARY-FEBRUARY 2010 V.D. Tereshchenko, V .A . Tereshchenko, S.M. Chem yakov (Polar Geophysical Institute, Murmansk, 183010, Russia; E-mail: vladter@pgi.ru) Abstract. The results of photographic observations o f polar stratospheric (nacreous or mother-of-pearl) clouds over Murmansk in January-February 2010 are presented. Heights of the stratospheric clouds are estimated, conditions of their formation and the impact on the total ozone content in the atmosphere are discussed. Introduction On January 11 and 19, February 8 and 10 2010 in Murmansk, from 6:30 to 12:30 UT in the angular sector of ± 20 degrees from the south at altitudes of 15-25 km polar stratospheric (nacreous or mother-of-pearl) clouds were observed. The similar beautiful and rare phenomenon was recorded over Murmansk on 29 January 2008 [Tereshchenko and Tereshchenko, 2009], and in January 1997 and December 2003. Over the entire history of Atmospheric Physics nacreous clouds were observed slightly more than 100 times. By virtue of the rarity of this phenomenon, these clouds are poorly understood. They are highly reflective capacity thanks to it they shine, shimmering, as sea shells. Observations o f stratospheric clouds began with the end of the 19th century. As it turned out, these beautiful clouds play the significant role in the destruction of the stratospheric ozone layer. For the first time they were found under the ozone holes in the Antarctic and therefore received the name o f the polar stratospheric clouds [McCormick et a l, 1982]. Since they formed in the stratosphere at altitudes of 20-30 km, they are often simply called stratospheric clouds. The appearance of the observed cloud has some similarities with the cumulus, stratocumulus, cirri and cirrocumulus clouds with a very strong iridescence, i.e. with iridescent plays. They are formed and exist in the polar stratosphere in both hemispheres during the polar winter [Solomon, 1999]. In the Antarctic, they appear from June to September and in the Arctic they appear from December to mid-March [Saitoh et a l, 2002], when the temperature at the height o f 20 km drops to minus 80 °C and below. The clouds have many kilometers the thickness and length. They are composed of ice crystals of spherical shape with dimensions of less than 10 microns. The structure of these particles includes: water, nitrogen oxides, and sometimes small amounts of chloric and sulfuric acids, as well as solid particles o f other substances. According to their chemical composition, they are divided into three types: clouds, containing nitric acid and water, clouds, that include super cooled droplets o f sulfuric acid, and clouds, composed exclusively o f water crystals. In the conditions of the polar night air pollutants are not subjected to destruction by ultraviolet light and freeze. In spring, ultraviolet rays cause chemical reactions of substances accumulated in the clouds, converting harmless substances to highly active radicals, which react with ozone and cause reduction in its content in the atmosphere. However, until now it does not yet disclosed the nature o f the clouds of nitrogen-water ice, contributing to the chemical activation of these radicals. Some of scientists consider that the main sources of formation of nacreous clouds are deep degassing of the Earth [Marakushev, 1998] and emissions of industrial gases. In the work, the results o f photographic and visual observations of stratospheric clouds are presented and the lower boundary of the cloud field is estimated. Assumptions about the possible relationship between the appearance of nacreous clouds and some geophysical phenomena are made. Results o f observations In Figure 1 the polar stratospheric clouds which were observed above Murmansk on 11 January 2010 from 07:20 UT are shown. At 10:30 UT they have been closed by grey clouds of the lower level. This day the sun was under the line of horizon. The height of the lower border of the cloudy field, found based on the concept of the equivalent radius of the Earth [Tereshchenko and Tereshchenko, 2009], was 20-25 km. According to high-altitude sounding of the Murmansk management of the Hydrometeorological Service the temperature of air at these heights fell up to minus 85 °C. In the Figure, two types of nacreous clouds are shown. They are similar to stratocumulus (at the left) and cumulus (on the right). Clouds have very rich plying iridescent coloring. Such color spectrum is given by fine crystals of water and nitric acid about the identical size, which form the clouds and refract sunrays. By our estimations, the clouds of the second type were on the distance about 50 km from the place of observation (68.948° N, 33.063° E) in the southwest direction. Under the form and luminescence, they were similar to clouds, which were observed in Murmansk on 29 January 2008. “P hysics o f Auroral P h enom en a”, Proc. XXXIII A n n u a l Sem inar, A patity, pp. 190 - 193, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute 190