Ground‐based measurements of stratospheric constituents were carried out from Thule Air Base, Greenland (76.5°N, 68.7°W), during the winters of 2001–2002 and 2002–2003, involving operation of a millimeter‐wave spectrometer (GBMS) and a lidar system. This work focuses on the GBMS retrievals of stratospheric O3, CO, N2O, and HNO3, and on lidar stratospheric temperature data obtained during the first of the two winter campaigns, from mid‐January to early March 2002. For the Arctic lower stratosphere, the winter 2001–2002 is one of the warmest winters on record. During a large fraction of the winter, the vortex was weakened by the influence of the Aleutian high, with low ozone concentrations and high temperatures observed by GBMS and lidar above ∼27 km during the second half of February and in early March. At 900 K (∼32 km altitude), the low ozone concentrations observed by GBMS in the Aleutian high are shown to be well correlated to low solar exposure. Throughout the winter, PSCs were rarely observed by POAM III, and the last detection was recorded on 17 January. During the lidar and GBMS observing period that followed, stratospheric temperatures remained above the threshold for PSCs formation throughout the vortex. Nonetheless, using correlations between GBMS O3 and N2O mixing ratios, in early February a large ozone deficiency owing to local ozone loss is noted inside the vortex. GBMS O3‐N2O correlations suggest that isentropic transport brought a O3 deficit also to regions near the vortex edge, where transport most likely mimicked local ozone loss.

Abstract. We compare differences and similarities in the annual stratospheric HNO3 cycle derived from ground-based measurements at the South Pole during 1993 and 1995, after correcting an error in earlier published profile retrievals for 1993 which led to under estimation of mixing ratios. The data series presented here provide profiling over the range •16-48 km, and cover the fall-winter-spring cycle in the behavior of HNO3 in the extreme Antarctic with a large degree of temporal overlap. With the exception of one gap of 20 days, the combined data sets cover a full annual cycle. The record shows an increase in HNO3 above 30 km occ•g about 20 days before stmset, which aPlyaxrs to be the result of higher altitude heterogeneous conversion of NO• as photolysis diminishes. Both years show a strong incrinse in HNO3 beginning about polar stmset, in a layer peaking at about 25 km, as additional NO• is heterogeneously converted to nitric acid. When temperatures drop to the polar stmtospheric cloud (PSC) formation range near the end of May, gas phase HNO3 is rapidly reduce• in the lower stratosphere, although at least 2-3 weeks of temperatures <192 K appear to be required to complete most of the gas-phase removal at the upper end of the depletion range (22-25 km). Despite a significant difference in residual sulfate loading from the explosion of Mount Pinambo, there appem• to be little gross difference in the timing and effects of PSC fonnation in removing gas phase HNO3 in these 2 years, though removal may be more rapid in 1995. Incorporation of gas phase HNO3 into PSCs aplyaxrs to be nearly complete up to -•25 km by midwinter. We also see a repeat of the formation of gas phase HNO3 in the middle stratosphere in early midwinter of 1995 with about the same timing as in 1993, suggesting that this phenomenon is driven by a repetition of dynmnical transport and appropriate temperatures and pressures in the polar night, and not (as has been suggested) by ion-based heterogeneous chemistry that requires triggering by large relativistic electron fluxes. High-altitude HNO3 production peaks during a period of •20 days, but appears to persist for up to •40 days in the 40-45 km range, ceding well before stmrise. This HNO3 descends rapidly throughout the production period, at a rate in good agreement with theoretically determined midwinter subsidence rates. As noted in earlier studies, later warming of this region above PSC evaporation temperatures does not cause reap•ce of large amounts of HNO3, indicating that most PSCs gravitationally sink out of the stratosphere before early spring. We present evidence that smaller PSCs do evaporate to -1 to 3.5 ppbv of HNO3 in the lower stratosphere, however, working downward from •25 km as temperatures rise during the late winter. There is a delay of•15 days after stmrise before photolysis causes significant depletion in the altitude range below •30 km, where subsidence has carded virtually all higher-altitude HNO3 by polar sunrise. Some continued subsidence and photolysis combine to keep mixi...

[1] We present new ground-based measurements of polar stratospheric and mesospheric CO, made with a millimeter-wave spectrometer at Thule, Greenland (76.5°N, 68.7°W). Almost daily measurements were made between 17 January and 4 March 2002 and again between 5 January and 22 February 2003. We stress here the retrieval and analysis of CO mixing ratios in the 50-80 km altitude range, though it can be monitored at lower altitudes as well. Since CO exhibits a strong positive latitude gradient from the summer to the winter pole, it is an excellent tracer for poleward transport from lower latitudes. Moreover, the mixing ratio of CO increases rapidly from $40 km to at least 100 km at midlatitudes, providing a good tracer for high-altitude vertical transport as well. Our profiles indicate that in winter near the poles the CO mixing ratio decreases above $70 km because of subsidence of air and minimal high-altitude photoproduction at high latitudes. Our data also show large variations in mixing ratio and vertical distribution, yielding a good picture of stratospheric and mesospheric dynamics-induced changes on a scale of hours to days. These observations verify that CO serves as an excellent tracer of vortex-related dynamics in the 30-80 km altitude range, where other information, particularly above $40 km, may be sparse, unreliable, or nonexistent. Our results are in general agreement with analyses of 1991-1992 Improved Stratospheric and Mesospheric Sounder (ISAMS) satellite data by Lopez-Valverde et al. [1993, 1996] and by Allen et al. [1999, 2000]. We show the contrast between CO over the summer pole and CO over the winter pole with the aid of trial observations made at the South Pole during the austral summer of 1999-2000. Our Thule data indicate that large concentrations of CO generally exist in winter just outside the vortex boundary. The large rapid variations in vertical profile that are found in our data in 2002 appear to be well correlated with vortex position in the lower stratosphere. In 2003 this correlation appeared to be much weaker, but early 2003 was also a period of vortex splitting in the Arctic on three occasions during our observation period, accompanied by generally more complex vortex dynamics.

Abstract. We present data from a 9-month series of ground-based measurements of stratospheric nitric acid, made over the South Pole from mid-April 1993 to mid-January 1994. Observations were typically made at 3-to 6-day intervals. Both profiles and column densities have been retrieved from pressure-broadened millimeter-wave emission spectra. These measurements provide the first quasi-continuous series of vertical mixing ratio profiles for this species in the heart of the south polar votex. Conversion of NOz to nitric acid by heterogeneous reactions, and its incorporation into polar stratospheric cloud (PSC) particles, along with subsequent gravitational settling, is considered to be the main denitrifying mechanism in the Antarctic stratosphere, setting up conditions for ozone destruction at the end of winter. In our observations, a small increase in HNO3 was seen between April and the end of May, after which a rapid loss took place below 25 km. Column density above ~15 km decreased to _<1/4 its maximum within 30 days, and depletion continued until middle to late July, by which time the nitric acid column above 15 km had diminished by more than a factor of 10. The initial depletion was coincident with the onset of a rapid increase in lidar backscatter from polar stratospheric cloud formation at the same altitude range. Gas-phase depletion was tracked as a function of altitude and temperature and found to be consistent with the temperature and partial pressure relationship for formation of ternary mixtures of HNOa, H2SO4, and H20. Depletion occurred •3 weeks earlier in 1993 than was seen in 1992 column density measurements by Van Allen et al. [1995]. In late June a new layer of HNO3 was generated in the vicinity of 40-km altitude and, subsequently, appeared to be carried downward with general vertical transport of air within the vortex. In spring, as temperatures increased, no rapid increase of gas-phase HNO3 was seen, indicating that gravitational settling had carried PSC-accreted nitric acid to low altitudes. By the end of observations in January 1994, mixing ratios and column densities above •15 km had not yet reached more than about half the values seen the previous April, indicating that a rather large increase in stratospheric HNO3 occurs in the early austral fall over the south polar region.