Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology 1Institute of Interplanetary Space Physics, INAF, Rome, Italy
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
*now at: Physics Department, University of Santiago de Chile, Santiago, Chile
Received: 28 April 2010 – Published in Atmos. Chem. Phys. Discuss.: 11 June 2010 Abstract. Analyses of OH zonal means, recorded at boreal high latitudes by the Aura
Microwave Limb Sounder (MLS) in winters of
2005–2009, have shown medium- (weeks)
and short- (days) term variability of the nighttime OH layer.
Revised: 23 September 2010 – Accepted: 15 October 2010 – Published: 04 November 2010
Because of the exceptional descent of air from the mesosphere-lower
thermosphere (MLT) region, medium-term variability occurred during February 2006
and February/March 2009. The layer normally situated at about 82 km
descended by about 5–7 km, and its density increased to more than twice
January values. In these periods and location the abundance of the lowered OH
layer is comparable to the OH values induced by Solar Energetic Particle
(SEP) forcing (e.g., SEP events of January 2005) at the same altitudes. In
both years, the descent of the OH layer was coupled with
increased mesospheric temperatures, elevated carbon monoxide and an almost
complete disappearance of ozone at the altitude of the descended layer
(which was not observed in other years). Moreover, under these exceptional
atmospheric conditions, the third ozone peak, normally
at about 72 km, is shown to descend about 5 km to lower altitude
and increase in magnitude, with maximum values recorded during February 2009.
Short-term variability occurred during Sudden Stratospheric Warming
(SSW) events, in particular in January 2006, February 2008 and January
2009, when dynamics led to a smaller abundance of the OH layer at its
typical altitude. During these periods, there was
an upward displacement of the OH layer coupled to changes in ozone and carbon
monoxide. These perturbations were the strongest during the SSW of January 2009;
coincident upper mesospheric temperatures were the lowest recorded over the
late winters of 2005–2009. Finally, the series of SSW events that occurred
in late January/February 2008 induced noticeable short-term variability in
ozone at altitudes of both the ozone minimum and the third ozone peak.
These phenomena, confined inside the polar vortex, are an additional
tool that can be used to investigate mesospheric vortex dynamics.
Citation: Damiani, A., Storini, M., Santee, M. L., and Wang, S.: Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology, Atmos. Chem. Phys., 10, 10291-10303, doi:10.5194/acp-10-10291-2010, 2010.