[1] The current study provides a comparison of the photochemical environments for two NASA field studies focused on the western North Pacific (PEM-West-B (PWB) and TRACE-P (TP)). These two studies were separated in calendar time by approximately 7 years. Both studies were carried out under springtime conditions, with PWB being launched in 1994 and TP being deployed in 2001 (i.e., 23 February-15 March 1994 and 10 March-15 April 2001. Because of the 7-year time separation, these two studies presented a unique scientific opportunity to assess whether evidence could be found to support the Department of Energy's projections in 1997 that increases in anthropogenic emissions from East Asia could reach 5%/yr. Such projections would lead one to the conclusion that a significant shift in the atmospheric photochemical properties of the western North Pacific would occur. To the contrary, the findings from this study support the most recent emission inventory data [Streets et al., 2003] in that they show no significant systematic trend involving increases in any O 3 precursor species and no evidence for a significant shift in the level of photochemical activity over the western North Pacific. This conclusion was reached in spite of there being real differences in the concentration levels of some species as well as differences in photochemical activity between PWB and TP. However, nearly all of these differences were shown to be a result of a near 3-week shift in TP's sampling window relative to PWB, thus placing it later in the spring season. The photochemical enhancements seen during TP were most noticeable for latitudes in the range of 25-45°N. Most important among these were increases in J(O 1 D), OH, and HO 2 and values for photochemical ozone formation and destruction, all of which were typically two times larger than those calculated for PWB. A comparison of these airborne results with ozonesonde data from four Japanese stations provided further evidence showing that the 3-week shift in the respective sampling windows of PWB and TP was a likely cause for the differences seen in O 3 levels and in photochemical activity between the two airborne studies.

This paper investigates isentropic ozone exchange between the extratropical lower stratosphere and the subtropical upper troposphere in the Northern Hemisphere. The quantification method is based on the potential vorticity (PV) mapping of Stratospheric Aerosol and Gas Experiment (SAGE)-II ozone measurements and contour advection calculations using the NASA Goddard Space Center Data Assimilation Office (DAO) analysis for the year 1990. The magnitude of the annual isentropic stratosphere-to-troposphere ozone flux is calculated to be approximately twice the flux that is directed from the troposphere into the stratosphere. The net effect is that 46 10 9 kg yr 1 of ozone are transferred quasi horizontally from the extratropical lower stratosphere into the subtropical upper troposphere between the isentropic surfaces of 330 and 370 K. The estimated monthly ozone fluxes show that the isentropic cross-tropopause ozone transport is stronger in summer/fall than in winter/ spring, and this seasonality is more obvious at the upper three levels (i.e., 345, 355, and 365 K) than at 335 K. The distributions of the estimated monthly ozone fluxes indicate that the isentropic stratosphere-to-troposphere ozone exchange is associated with wave breaking and occurs preferentially over the eastern Atlantic Ocean and northwest Africa in winter and over the Atlantic and Pacific Oceans in summer.

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[1] A midlatitude (25°-65°) monthly zonal median ozone climatology in the upper troposphere and lower stratosphere (UTLS), from 8 to 20 km with a 0.5-km vertical resolution and a 5°latitudinal resolution, is developed on the basis of version 6.2 (V6.2) ozone profile retrievals from the Stratospheric Aerosol and Gas Experiment (SAGE) II measurements from October 1984 to August 2005. To avoid mixing of the tropospheric ozone data with stratospheric values, the thermal tropopause height is used as a base altitude for developing the climatology (the monthly mean tropopause height has been added back to the climatological profile). This feature of the developed ozone climatology, together with the near global SAGE II data coverage, complements the existing ozone climatologies in the midlatitude UTLS. In addition to using this climatology to describe hemispheric differences in the UTLS ozone (the primary purpose of this paper), the database can also be used to initialize atmospheric chemistry-transport models or for satellite data retrieval. The specific new findings include (1) the differences in the vertical structure of monthly ozone evolution across the tropopause between the NH and the SH, (2) all year bimodal probability distribution functions (PDFs) of the tropopause ozone, and (3) the annual cycle of the tropopause ozone PDF with increasing (decreasing) presence of ozone-rich air leading to tropopause ozone enhancements (reductions) during spring and early summer (fall and winter). The derived climatology is shown to be consistent with the ozonesonde climatologies of Logan (1985Logan ( , 1999a in many respects, including ozone seasonal cycle at the tropopause and in the UT, the broad summer ozone maximum in the northern UT, and non-Gaussian ozone PDFs at the tropopause. This consistency strengthens the confidence in SAGE II satellite ozone remote sensing in the UTLS. The derived SAGE II midlatitude ozone climatology is compared to ozonesonde measurements at Hohenpeissenberg (47.4°N, 11°E), Germany, and Lauder (45°S, 169.7°E), New Zealand. The monthly ozone climatology data are provided as auxiliary material to this report.

Ozone columns below 147 hPa are derived over the United States from September 2004 to August 2005 from the differences between clear‐sky Aura OMI columns and coincident MLS columns. The mean difference from coincident ozonesonde measurements at four USA sites is 0.3 DU with an rms difference of 10.1 DU and a correlation coefficient of 0.67. Semimonthly patterns of the columns over the USA for the summer of 2005 have been produced. The observed columns, as well as Regional Air Quality Forecast (RAQAST) model columns, show high values over the southeastern USA and its surrounding oceans. Changes of these columns exceeding 6 DU in many places were observed between June 17–30 and July 1–16 and the changes reversed in the following two‐week period. Comparisons against calculations from the RAQAST model, as well as correlations with geopotential height changes at 147 hPa, indicate that these changes were primarily related to dynamics.