SIMA

Finished ProjectsSIMA

Überblick

Einer der Hauptfaktoren, die Ozon und die mittlere Atmosphäre beeinflussen, sind Änderungen der spektralen Sonneneinstrahlung. Im SIMA-Projekt (Study to Determine Spectral Solar Irradiance and its Impact on the Middle Atmosphere) wurden gleichzeitig die spektrale Sonnenbestrahlung (SSI) und die Variabilität der Sonneneinstrahlung in der Atmosphäre bestimmt. In Zeiträumen, die länger als ein paar Monate dauern, ist SSI immer noch eine sehr unsichere Größe und damit auch seine Auswirkung auf Chemie, Temperatur und Dynamik in der mittleren Atmosphäre.

Overview

One of the major factors influencing ozone and the middle atmosphere are changes in spectral solar irradiance. In the SIMA (Study to Determine Spectral Solar Irradiance and its Impact on the Middle Atmosphere) project, we simultaneously determined solar spectral irradiance (SSI) and the range of variability the Sun can induce in the atmosphere. On timescales longer than a few months, SSI is still a highly uncertain quantity and, therefore, so is its impact on chemistry, temperature and dynamics in the middle atmosphere.

Results and Discussion

Success of the project requires an accurate estimate of the solar cycle (SC) response in ozone observations, from which estimates of ozone changes from models allows (within a Bayesian framework) an extraction of the solar cycle changes that induce the ozone change seen in the observations (Work package 1, WP1). Our original aim was to use a set of recent ozone composites from which to extract the SC ozone changes.

However, we found that the use of multiple linear regression to estimate the SC ozone response led to very different SC changes estimated from four ozone composites that we considered (colours, Figure 1), and indeed, in decadal ozone trends. Thus, in order to determine a reliable SC response, we developed a procedure to correct the ozone composites and remove artefacts that were the cause of the different multiple linear regresion SC estimates. The approach uses a Gaussian mixture model, singular value decomposition uncertainty estimates, and Hamiltonian Monte Carlo sampling, resulting in a procedure that can account for jumps and drifts. A major result is improved decadal trend estimates, as well as other additional results that are currently being prepared for publication. The major step forward for SIMA is a new ozone composite, free from artefacts that interfere with multiple linear regresion estimates of the SC (black line, Figure 1; see Ball et al., 2017).

Figure 1. Equatorial (25°S – 25°N) solar cycle change in ozone from four composites and the particle filter ozone composite using multiple linear regression to extract the signal. Error bars are uncertainties at the 95% level.

 

Our work has also determined that multiple linear regresion does not robustly estimate SC changes, due to the large unaccounted for variance, and the short observation period available. We find that the use of dynamical linear modelling (DLM) improves the robustness of estimates, but the lack of a SC signal in the tropical upper stratosphere is not fully understood. Further additional considerations are therefore required. Despite the additional work to correct the ozone composites and understand the lack of a solar signal in the tropics, the next step to integrate the temperature solar cycle signal with ozone is nearly complete: the temperature response has been extracted, the Bayesian method expanded to include temperature with ozone, and all required 2D modelling runs completed. Upon finalising the ozone signal, this milestone will be completed (Ball et al., in prep.).

Following a meeting in Brussels between collaborators at PMOD/WRC, BIRA and CNRS to progress simultaneous work needed to complete the remainder of the project, by constraining coherent SC changes at different wavelengths, a clear methodology has been determined of how to estimate wavelength dependent priors that will constrain SSI changes. The implementation is currently ongoing. In addition, work on integrating these spectral variation constraints with H2O and OH in a 2D model has commenced. A 3D model will later be used that also includes realistic dynamics, whereupon all information can then be combined to reconstruct solar irradiance variations from atmospheric observations, which is the ultimate goal of the project.

SIMA Final Scientific Report 2018

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SIMA Literature Publications

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References

Ball W. T., Alsing J., Mortlock D. J., Rozanov E. V., Tummon F., Haigh J. D., (2017), Reconciling differences in stratospheric ozone composites, Atmos. Chem. Phys., 17, 12269-12302, doi: 10.5194/acp-17-12269-2017
Ball W. T. et al., in prep., Estimate of ultraviolet solar cycle changes from stratospheric ozone and temperature observations.
For further information please contact: Dr. T. Sukhodolov