1. SBUV/2 Observations of Atmospheric Response to Solar Variations Matthew DeLand Science Systems and Applications, Inc. (SSAI) Background -SBUV/2 instruments measure stratospheric profile, total column ozone, solar UV irradiance between 160-400 nm. -Continuous measurement record available since 1978. Future data expected through ~2015. Impulsive Events Solar proton events can inject large quantities of charged particles into the upper atmosphere. Increased ionization leads to rapid ozone loss in upper stratosphere (> 40%). Short chemical time constants  typical recovery time of 1-2 days. Solar cycle 23 shows logarithmic relationship between peak proton flux [>10 MeV] and maximum ozone depletion [0.5 hPa]. Ionization also increases production of odd nitrogen (NO x ), which has chemical lifetime of several months. Transport + chemistry predicts sustained ozone depletion in middle stratosphere. Observations support this prediction, but dynamical variations complicate interpretation. Rotational Timescales Solar irradiance shows clear rotational modulation for < 265 nm. Amplitude reaches 6-7% at 205 nm. Ozone response depends on chemical time constants, peaks at ~2 hPa. Solar Cycle Timescales Ozone Ozone responses to solar cycle variations observed in stratospheric layers and integrated total column. Model predictions of  O 3 response to  F UV are consistent with data for total ozone, disagree on altitude dependence. Polar Mesospheric Clouds Polar mesospheric clouds (PMCs) are composed of water ice, form at 80-85 km in summer polar regions. SBUV/2 instrument detects PMCs as albedo enhancement at short wavelengths. Occurrence frequency shows consistent seasonal pattern, variations in amplitude. Variations in cumulative seasonal frequency are anti- correlated with solar Lyman alpha variations. This is consistent with photochemical model predictions. Conclusions SBUV/2 instruments observe both solar UV forcing and atmospheric response. Solar UV irradiance data from NOAA-9 and NOAA-11 SBUV/2 are available on-line. Mg II index data are also available. Reprocessed Version 8 profile ozone data from all instruments (available June 2004) will have improved accuracy for trends. Continuation of SBUV/2 measurements provides invaluable multi- decade data sets for long-term studies. - Spectral range of solar irradiance observed by SBUV/2 directly affects stratosphere. Solar variability increases significantly at shorter wavelengths. DeLand et al. [2004] Jackman et al. [2000] DeLand et al. [2004]Chandra and McPeters [1994] McCormack and Hood [1996] Hood [1997] McCormack and Hood [1996] DeLand et al. [2003] References Chandra, S., and R. D. McPeters, The solar cycle variation of ozone in the stratosphere inferred from Nimbus 7 and NOAA 11 satellites, J. Geophys. Res. 99, 20,665-20,671, 1994. DeLand, M. T., E. P. Shettle, G. E. Thomas, and J. J. Olivero, Solar backscattered ultraviolet (SBUV) observations of polar mesospheric clouds (PMCs) over two solar cycles, J. Geophys. Res. 108(D8), 8445, doi:10.1029/2002JD002398, 2003. DeLand, M. T., R. P. Cebula, and E. Hilsenrath, Observations of solar spectral irradiance change during cycle 22 from NOAA-9 Solar Backscattered Ultraviolet Model 2 (SBUV/2), J. Geophys. Res. 109, D06304, doi:10.1029/2003JD004074, 2004. Hood, L. L., The solar cycle variation of total ozone: Dynamical forcing in the lower stratosphere, J. Geophys. Res. 102, 1355-1370, 1997. Jackman, C. H., E. L. Fleming, and F. M. Vitt, Influence of extremely large solar proton events in a changing stratosphere, J. Geophys. Res. 105, 11,659-11,670, 2000. McCormack, J. P., and L. L. Hood, Apparent solar cycle variations of upper stratospheric ozone and temperature: Latitude and seasonal dependences, J. Geophys. Res. 101, 20,933-20,944, 1996.