SBUV/2 Observations of Atmospheric Response

to Solar VariationsMatthew 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 (NOx), 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 O3 response to FUV 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.