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The authors apply principal component analysis (PCA) to the extratropical total column ozone from the combined merged ozone data product and the European Centre for Medium-Range Weather Forecasts assimilated ozone from January 1979 to August 2002. The interannual variability (IAV) of extratropical [O.sub.3] in the Northern Hemisphere (NH) is characterized by four main modes. Attributable to dominant dynamical effects, these four modes account for nearly 60% of the total ozone variance in the NH. The patterns of variability are distinctly different from those derived for total [O.sub.3] in the tropics. To relate the derived patterns of [O.sub.3] to atmospheric dynamics, similar decompositions are performed for the 30-100-hPa geopotential thickness. The results reveal intimate connections between the IAV of total ozone and the atmospheric circulation. The first two leading modes are nearly zonally symmetric and represent the connections to the annular modes and the quasi-biennial oscillation. The other two modes exhibit in-quadrature, wavenumber-1 structures that, when combined, describe the displacement of the polar vortices in response to planetary waves. In the NH, the extrema of these combined modes have preferred locations that suggest fixed topographical and land-sea thermal forcing of the involved planetary waves. Similar spatial patterns and trends in extra-tropical column ozone are simulated by the Goddard Earth Observation System chemistry-climate model (GEOS-CCM). The decreasing [O.sub.3] trend is captured in the first mode. The largest trend occurs at the North Pole, with values ~-1 Dobson Unit (DU) [yr.sup.-1] There is almost no trend in tropical [O.sub.3]. The trends derived from PCA are confirmed using a completely independent method, empirical mode decomposition, for zonally averaged [O.sub.3] data. The [O.sub.3] trend is also captured by mode 1 in the GEOS-CCM, but the decrease is substantially larger than that in the real atmosphere.

A principal component analysis (PCA) is applied to the Southern Hemisphere (SH) total column ozone following the method established for analyzing the data in the Northern Hemisphere (NH) in a companion paper. The interannual variability (IAV) of extratropical [O.sub.3] in the SH is characterized by four main modes, which account for 75% of the total variance. The first two leading modes are approximately zonally symmetric and relate to the Southern Hemisphere annular mode and the quasi-biennial oscillation. The third and fourth modes exhibit wavenumber-1 structures. Contrary to the Northern Hemisphere, the third and fourth modes are not related to stationary waves. Similar results are obtained for the 30-100-hPa geopotential thickness. The decreasing [O.sub.3] trend in the SH is captured in the first mode. The largest trend is at the South Pole, with value ~-2 Dobson Units (DU) [yr.sup.-1]. Both the spatial pattern and trends in the column ozone are captured by the Goddard Earth Observation System chemistry--climate model (GEOS-CCM) in the SH.

Hydrogen chloride (HCl) is the most abundant (more than 95%) among inorganic chlorine compounds Cly in the stratosphere. The HCl molecule has been observed to obtain long-term quantitative estimations of total budget of the stratospheric anthropogenic chlorine compounds. In this study, we provided HCl vertical profiles at altitudes of 16-100km using the superconducting submillimeter-wave limb-emission sounder (SMILES) from space. We used the SMILES Level-2 research product version 3.0.0. The period of the SMILES HCl observation was from October 12, 2009 to April 21, 2010, and the latitude coverage was 40S-65N. The average HCl vertical profile showed an increase with altitude up to the stratopause (~45km), approximately constant values between the stratopause and the upper mesosphere (~80km), and a decrease from the mesopause to the lower thermosphere (~100km). This behavior was observed in the all latitude regions, and reproduced by the SD-WACCM model. We compared the SMILES HCl vertical profiles in the stratosphere and lower mesosphere with HCl profiles from MLS on the Aura satellite, as well as from ACE-FTS on SCISAT and from TELIS (balloon-borne). The TELIS observations were performed using the superconductive limb emission technique, as used by SMILES. The globally averaged vertical HCl profiles of SMILES well agreed with those of MLS and ACE-FTS within 0.25 and 0.2ppbv between 20 and 40km, respectively. The SMILES HCl concentration was smaller than those of MLS and ACE/FTS as the altitude increased from 40km, and the difference was approximately 0.4-0.5ppbv at 50-60km. The difference between SMILES and TELIS HCl observations was about 0.3ppbv in the polar winter region between 20 and 34km, except near 26km. SMILES HCl error sources that may cause discrepancies with the other observations are investigated by a theoretical error analysis. We calculated errors caused by the uncertainties of spectroscopic parameters, instrument functions, and atmospheric temperature profiles. The jacobian for the temperature explains the negative bias of the SMILES HCl concentration at 50-60km. The HCl vertical profile from the middle troposphere to the lower thermosphere is reported for the first time from SMILES observations; the data quality is quantified by comparisons with other measurements and via theoretical error analysis. [ABSTRACT FROM AUTHOR]

The middle atmosphere version of the National Center for Atmospheric Research Community Climate Model 2 (MACCM2) mechanistic model is used to simulate several aspects of the observed two-day wave near the stratopause and its possible connection with inertial instability. Model experiments show that, for a prescribed initial wind condition with strong horizontal wind variation in the Tropics, inertial instability can trigger the two-day wave. An increase in horizontal wind curvature fostered by inertial instability circulation barotropically destabilizes the easterly jet in low summer latitudes and allows first the growth of the wavenumber-4 and then the wavenumber-3 component of the two-day wave. Near the stratopause, the two-day wave Eliassen--Palm flux is directed equatorward away from the wave's critical line source and westerly momentum is transported into the easterly jet core by the wave. While much of the wavenumber-4 energy is confined near the stratopause, the wavenumber-3 energy can propagate upward well into the mesosphere where strong Rayleigh damping is imposed. The model results suggest that the observed disparity in the wavenumber-3 amplitude between the austral and boreal summers is a consequence of the difference in summer easterly jet strength.

The two-day wave is observed in the Upper Atmosphere Research Satellite Microwave Limb Sounder temperature data around 40-58 km. Between December 1991 and September 1994, the two-day wave temperature signature is most significant after each solstice when the derived easterly winds near the stratopause extend across the equator to at least 20 [degrees] latitude in the winter hemisphere, and the zonal mean winds near the equator are inertially unstable with observed inertial instability disturbances. The observed two-day wave consists of a 2.0-day period zonal wavenumber-3 and a 1.8-day period zonal wavenumber-4 component, named (3, 2.0) and (4, 1.8), respectively. The (3, 2.0) component is dominant during two of the three available austral summers, but its amplitude is much weaker than the (4, 1.8) component during the two observed boreal summers. During the austral summers, correspondence between amplification of the two-day wave temperature signatures, regions of reversed potential vorticity gradient due to meridional curvature of the zonal mean flow, and the critical lines for the (3, 2.0) and (4, 1.8) modes suggest barotropic instability as a source of both wave components. Momentum redistribution by observed inertial instability appears to barotropically destabilize the equatorward flank of the easterly jet where the wave components subsequently grow. During the boreal summers, the (4, 1.8) component appears to be excited by instability that is associated with vertical shear and curvature of the flow seated above the observational domain. The boreal (3, 2.0) mode appears unrelated to the zonal flow instability within the observational domain and may reflect a normal-mode-like response during these periods.

The 'Arctic Oscillation' (AO) is the dominant mode of Northern hemisphere wintertime climate variability. Characterized by the irregular shifting of atmospheric mass across the Arctic Circle, the Arctic Oscillation corresponds [...]

A westward propagating wavenumber 1 disturbance with a period of 5-15 days in the summer hemisphere is observed using temperature data measured by the Microwave Limb Sounder (MLS) aboard the [...]

A Sudden Stratospheric Warming (SSW) affects the chemistry and dynamics of the middle atmosphere. The major warmings occur roughly every second year in the Northern Hemispheric (NH) winter, but has only been observed once in the Southern Hemisphere (SH), during the Antarctic winter of 2002. Using the National Center for Atmospheric Research's (NCAR) Whole Atmosphere Community Climate Model with specified dynamics (WACCM-SD), this study investigates the effects of this rare warming event on the ozone layer located around the SH mesopause. This secondary ozone layer changes with respect to hydrogen, oxygen, temperature, and the altered SH polar circulation during the major SSW. The 2002 SH winter was characterized by three zonal-mean zonal wind reductions in the upper stratosphere before a fourth wind reversal reaches the lower stratosphere, marking the onset of the major SSW. At the time of these four wind reversals, a corresponding episodic increase can be seen in the modeled nighttime ozone concentration in the secondary ozone layer. Observations by the Global Ozone Monitoring by Occultation of Stars (GOMOS, an instrument on board the satellite Envisat) demonstrate similar ozone enhancement as in the model. This ozone increase is attributable largely to enhanced upwelling and the associated cooling of the altitude region in conjunction with the wind reversal. Unlike its NH counterpart, the secondary ozone layer during the SH major SSW appeared to be impacted more by the effects of atomic oxygen than hydrogen. [ABSTRACT FROM AUTHOR]