Observing Odd Hydrogen Species from Space- and Ground-based Instruments - 5-year Aura/MLS HOx Measurements and 12-year FTUVS OH Column Measurements (Invited)

The Microwave Limb Sounder (MLS) on board Aura provides the first global measurements of OH and HO2 on a daily basis, starting in August 2004. The diurnal variation of OH column abundance has been measured regularly by a ground-based Fourier Transform Ultraviolet Spectrometer (FTUVS) at the Table Mountain Facility (TMF) of Jet Propulsion Laboratory (JPL) since 1997. The combination of the two data sets provides a unique opportunity for studying variability of odd hydrogen species. The five-year time series of zonal mean MLS data (OH and HO2) and a 3-D climatology data versus time of year, pressure, and latitude derived from the MLS observations will be presented. Inter-annual and intra-annual variability will be discussed. The general decrease in OH from 2004 to 2009 hints at the impact of solar 11-year cycle. The 12-year record of OH column data at TMF covers an entire solar 11-year cycle. The corresponding OH column variability will be discussed and compared to the observed changes in MLS OH data. For long-term validation, MLS OH measurements are compared with ground-based FTUVS OH column measurements at TMF during 2004 - 2009. MLS OH densities over TMF are integrated vertically to derive partial OH columns for comparison with TMF OH columns. The residual OH in the lower atmosphere that MLS measurements do not cover is estimated using GMI (Global Modeling Initiative) OH products. The agreement between FTUVS total columns and the combined total columns of MLS+GMI will be discussed. The results are also compared with a previous validation study using GEOS-Chem OH data to assist the total column comparison. The advantages of using GMI over GEOS-Chem include: 1) GMI directly covers both the troposphere and the lower stratosphere while GEOS-Chem covers only the troposphere and a 2-D model implemented in GEOS-Chem has to be used for the lower stratospheric calculation; 2) the GMI model runs are real-time and offer Aura overpass time products. Possible causes of the observed differences will be discussed.