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A 22 year, high‐latitude, stratospheric aerosol and cloud database has been formed in a “unified” manner by combining the Stratospheric Aerosol Measurement (SAM) II, Stratospheric Aerosol and Gas Measurement (SAGE) II, Polar Ozone and Aerosol Measurement (POAM) II, and POAM III 1 μm aerosol extinction profiles. The database is “unified” in that it embodies similar aerosol extinction measurements, uses a single meteorological data set, and employs a single algorithm for calculating background extinction and cloud detection thresholds. Latitude is constrained to poleward of 45° in each hemisphere. The Unified cloud detection algorithm and database are designed for the straightforward addition of new data when other compatible data sets (e.g., SAGE III) become available. “Unified” cloud detection is similar to, but a refinement of, earlier attempts to identify polar stratospheric clouds (PSCs) with SAM II and POAM II data. The Unified algorithm is instrument‐independent and circumvents fundamental cloud detection pitfalls. The database contains over 73,000 (36,000) polar vortex‐region profiles in the Antarctic (Arctic) and over 21,000 (2000) PSC observations. An introductory climatology of Unified “background” extinction is presented. It is seen that volcanic effects dominate the evolution of outside‐vortex background extinctions, but perturbations apparently not related to volcanoes are seen as well. Interannual variations of background extinction inside the austral vortex are seen to be nearly decoupled from volcanic effects, while in the Arctic, inside‐vortex extinctions show a considerable volcanic influence. An analysis of long‐term PSC sighting is presented. Midwinter (July and January) PSC and clear‐sky measurements at 20 km, in a fixed temperature range, are used for computing PSC probability. The grand average PSC probability calculated this way is nearly identical between hemispheres. In the Antarctic the interannual PSC probability pattern is distinctly cyclic but is convoluted by volcanic perturbations in background aerosol. In the Arctic the PSC probability has much less temporal coherence than in the Antarctic but is similarly impacted by volcanic background increases. An explanation for the variation in PSC probabilities, in terms of interannual differences in denitrification, is discussed. Finally, a statistical analysis of tropopause height in relation to PSC formation is also presented. PSC observations are seen to be strongly associated with elevated tropopause heights, indicating that tropospheric, synoptic‐scale flow perturbations are the primary forcing mechanism for Arctic PSC formation, as evidenced in this long‐term satellite record.

We present an overview of polar stratospheric cloud (PSC) measurements obtained by POAM III in the 1999/2000 Northern Hemisphere winter. PSCs were observed at POAM latitudes from mid‐November to 15 March. PSCs in the early season generally occurred between 17 and 25 km. The central altitude of the PSC observations, roughly 21 km, is unchanged between November and late January. PSCs were not observed between 7 and 27 February. When they reappeared, they formed at distinctly lower altitudes, centered roughly at 16 km. We also present both qualitative and quantitative comparisons with airborne lidar and in situ balloon measurements of PSCs obtained over the Norwegian Sea and Scandinavia over the 25–27 January time period. We find that the large‐scale PSC altitude features and morphology are well reproduced in the POAM measurements. Finally, we use PSC occurrence probabilities, analyzed as a function of ambient temperature relative to the NAT saturation point, to infer irreversible denitrification. This denitrification is observed to maximize in late February at levels of at least 75% in the 19–21 km region, with similar values in the 16–18 km region. No denitrification was inferred above 21 km or below 16 km.

[1] The top edge (20 -22 km) of the Antarctic ozone hole has been identified as a good place to detect ozone recovery (D.

Abstract. The Polar Ozone and Aerosol Measurement and Stratospheric Aerosol and Gas Experiment instruments both observed high numbers of polar stratospheric clouds (PSCs) in the polar region during the second SAGE Ozone Loss and Validation (SOLVE II) and Validation of INTERnational Satellites and Study of Ozone Loss (VINTERSOL) campaign, conducted during the 2002/2003 Northern Hemisphere winter. Between 15 November 2002 (14 November 2002) and 18 March 2003 (21 March 2003) SAGE (POAM) observed 122 (151) aerosol extinction profiles containing PSCs. PSCs were observed on an almost daily basis, from early December through 15 January, in both instruments. No PSCs were observed from either instrument from 15 January until 4 February, and from then only sparingly in three periods in mid- and late February and mid-March. In early December, PSCs were observed in the potential temperature range from roughly 375 K to 750 K. Throughout December the top of this range decreases to near 600 K. In February and March, PSC observations were primarily constrained to potential temperatures below 500 K. The PSC observation frequency as a function of ambient temperature relative to the nitric acid-trihydrate saturation point (using a nitric acid profile prior to denitrification) was used to infer irreversible denitrification. By late December 38% denitrification was inferred at both the 400–475 K and 475–550 K potential temperature ranges. By early January extensive levels of denitrification near 80% were inferred at both potential temperature ranges, and the air remained denitrified at least through early March.