Measurements from the Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS), both on board the Aura spacecraft, have been used to produce daily global maps of column and profile ozone since August 2004. Here we compare and evaluate three strategies to obtain daily maps of tropospheric and stratospheric ozone from OMI and MLS measurements: trajectory mapping, direct profile retrieval, and data assimilation. Evaluation is based on an assessment that includes validation using ozonesondes and comparisons with the Global Modeling Initiative (GMI) chemical transport model. We investigate applications of the three ozone data products from near-decadal and interannual time scales to day-to-day case studies. Interannual changes in zonal mean tropospheric ozone from all of the products in any latitude range are of the order 1-2 Dobson units while changes (increases) over the 8 year Aura record investigated vary by 2-4 Dobson units. It is demonstrated that all of the ozone products can measure and monitor exceptional tropospheric ozone events including major forest fire and pollution transport events. Stratospheric ozone during the Aura record has several anomalous interannual events including split stratospheric warmings in the Northern Hemisphere extratropics that are well captured using the data assimilation ozone profile product. Data assimilation with continuous daily global coverage and vertical ozone profile information is the best of the three strategies at generating a global tropospheric and stratospheric ozone product for science applications.
[1] The extratropical stratosphere-troposphere exchange (STE) of ozone from 2005 to 2010 is estimated by combining Microwave Limb Sounder ozone observations and MERRA reanalysis meteorological fields in an established direct diagnostic framework. The multiyear mean ozone STE is 275 Tg yr À1 and 214 Tg yr À1 in the Northern and Southern Hemispheres, respectively. The year-to-year variability is greater in the Northern Hemisphere, where the difference between the highest and the lowest annual flux is 15% of the multiyear mean compared with 6% in the Southern Hemisphere. Variability of lower stratospheric ozone and variability of the net mass flux both contribute to interannual variability in the Northern Hemisphere ozone flux. The flux across the extratropical 380 K surface determines the amount of flux across the extratropical tropopause, and the greatest seasonal variability of the 380 K ozone flux occurs in the late winter/early spring, around the time of greatest flux. Both the mass flux and the ozone mixing ratios on the 380 K surface show recurring spatial patterns, but interannual variability of these quantities and their alignment contribute to the ozone flux variability. The spatial and temporal variability are not well represented when zonal and/or monthly mean fields are used to calculate the ozone STE, although this results in a small high bias of the seasonal amplitude and annual magnitude. If the climatological variability over these 6 years is representative, the estimated number of years required to detect a 2 À 3% decade À1 trend in ozone STE using this diagnostic is 35 À 39 years.Citation: Olsen, M. A., A. R. Douglass, and T. B. Kaplan (2013), Variability of extratropical ozone stratosphere-troposphere exchange using microwave limb sounder observations,
Atmospheric aerosols have been profiled using a simple, imaging, bistatic lidar system. A vertical laser beam is imaged onto a charge-coupled-device camera from the ground to the zenith with a wide-angle lens (CLidar). The altitudes are derived geometrically from the position of the camera and laser with submeter resolution near the ground. The system requires no overlap correction needed in monostatic lidar systems and needs a much smaller dynamic range. Nighttime measurements of both molecular and aerosol scattering were made at Mauna Loa Observatory. The CLidar aerosol total scatter compares very well with a nephelometer measuring at 10 m above the ground. The results build on earlier work that compared purely molecular scattered light to theory, and detail instrument improvements.
[1] The NASA/Aura/Microwave Limb Sounder (MLS) instrument has been compared to the Mauna Loa Observatory Raman water vapor lidar. Calibration of the lidar used Vaisala RS80-H radiosondes launched from the observatory. The average standard deviation between the sondes and the lidar, in the range 6 km to 11.5 km, is 11.9%. The sondes indicate no overlap correction for the lidar at low altitudes is necessary. A comparison was made between the lidar total column water and a GPS total column water measurement as a check on the calibration, resulting in a correlation slope of 1.026 ± 0.058 and R 2 = 0.84. The MLS measurements are significantly better in the stratosphere where the lidar has poor sensitivity. The MLS measurement in the troposphere has much lower altitude resolution than the lidar so the validation overlap altitudes are limited. A comparison is made with version 1.5 MLS data for 32 overpasses at the three MLS altitudes in the troposphere. The GPS total column water measurement was used to screen the overpasses by eliminating ones where the water varied by more than 50% during the lidar integration period. At 147 hPa the MLS data show a dry bias of 44.8% ± 36%. At 215 hPa the MLS measurement also shows a dry bias of 22.3% ± 22%, and at 316 hPa there is a dry bias of 19.9% ± 46%. The dry bias seen is consistent with the cryogenic frost point hygrometer (CFH) measurements at many latitudes (23% ± 37% at 215 hPa and 4% ± 62% at 316 hPa).
A bistatic lidar configuration of a wide-angle camera (1008) and vertically pointed laser (532 nm) was used to profile aerosols at a coastal site. Aerosol profiles were measured on two evenings from the surface through the boundary layer. The site, on the eastern tip of the Big Island of Hawaii, is influenced by both marine boundary layer aerosols and breaking waves. Two nephelometers, located at 7 and 25 m above sea level, were compared directly with the 0.5-m-altitude resolution of the camera lidar (clidar). At 7 m, changes in aerosol were tracked quite well by the clidar. At 25 m the aerosol was fairly constant and a useful comparison could only be made with averaged values. The clidar results showed a steep gradient (decreasing with altitude) in the aerosol extinction from 7 to about 35 m. The gradient continued to 200 m at a lower rate. This demonstrated the use of the clidar in characterizing the environment for the in situ aerosol sampling. Both a measured and a NASA Aerosol Robotic Network (AERONET)-derived aerosol phase function, representing similar marine conditions but from different locations, were used to convert the single-angle clidar scatter to extinction. The measured function gave the best fit to the near-surface nephelometer data. The extinction/ backscatter ratio, derived by comparing the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth to the integrated clidar profile, was higher than the long-term average value from the AERONET aerosol phase function.
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